Papers on Indian Ocean Dipole (IOD) and climate change

This is a list of papers on Indian Ocean Dipole (IOD) and climate change. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Indo-Pacific Climate Modes in Warming Climate: Consensus and Uncertainty Across Model Projections – Zheng (2019)
“Purpose of Review: Understanding the changes in climate variability in a warming climate is crucial for reliable projections of future climate change. This article reviews the recent progress in studies of how climate modes in the Indo-Pacific respond to greenhouse warming, including the consensus and uncertainty across climate models. Recent Findings: Recent studies revealed a range of robust changes in the properties of climate modes, often associated with the mean state changes in the tropical Indo-Pacific. In particular, the intermodel diversity in the ocean warming pattern is a prominent source of uncertainty in mode changes. The internal variability also plays an important role in projected changes in climate modes. Summary: Model biases and intermodel variability remain major challenges for reducing uncertainty in projecting climate mode changes in warming climate. Improved models and research linking simulated present-day climate and future changes are essential for reliable projections of climate mode changes. In addition, large ensembles should be used for each model to reduce the uncertainty from internal variability and isolate the forced response to global warming.”
Zheng, X. Indo-Pacific Climate Modes in Warming Climate: Consensus and Uncertainty Across Model Projections. Curr Clim Change Rep 5, 308–321 (2019) doi:10.1007/s40641-019-00152-9. [FULL TEXT]

Disentangling the Changes in the Indian Ocean Dipole–Related SST and Rainfall Variability under Global Warming in CMIP5 Models – Huang et al. (2019)
“This study disentangles the changes in Indian Ocean (IO) dipole (IOD)-related SST and rainfall variability under global warming projected by the RCP8.5 runs in 29 CMIP5 models. The IOD rainfall changes consist of the thermodynamic component due to the surface moisture increase and the dynamic component due to the changes in IOD-related circulation. The IOD circulation changes are dominated by the IOD SST changes, which were further clarified using the amplitude and structural decomposition. The amplitudes of IOD SST and circulation are both decreased at rates of around 7.2% and 13.7% °C⁻¹, respectively. The structural changes in IOD SST and circulation show a pattern with increases from the eastern to the western coast of the equatorial IO, similar to the pattern of so-called extreme IOD events in previous studies. Disentangling previous mechanisms and projections, we conclude that the increased atmospheric stability suppresses the amplitudes in IOD SST and circulation, whereas the positive IOD (pIOD)-like mean-state SST changes, leading to greater warming in the west than the east, mainly alter the structure of IOD SST and circulation. Both the amplitude and structural changes in the IOD SST and circulation are robust among the CMIP5 models, but their distinct patterns and out-of-step changes lead to an uncertain projection of IOD changes defined by the dipole mode index or EOF analysis in previous studies. Furthermore, the structural changes, dominated by the pIOD-like mean-state SST changes, are significantly correlated with the historical IOD amplitude among the models. Considering the commonly overestimated IOD amplitude as an emergent constraint, the structural changes in IOD SST and circulation should not be as robust as the original multimodel projection.”
Huang, P., X. Zheng, and J. Ying, 2019: Disentangling the Changes in the Indian Ocean Dipole–Related SST and Rainfall Variability under Global Warming in CMIP5 Models. J. Climate, 32, 3803–3818, https://doi.org/10.1175/JCLI-D-18-0847.1. [FULL TEXT]

Influence of internal climate variability on Indian Ocean Dipole properties – Ng et al. (2018)
“The Indian Ocean Dipole (IOD) is the dominant mode of interannual variability over the tropical Indian Ocean (IO) and its future changes are projected to impact the climate and weather of Australia, East Africa, and Indonesia. Understanding the response of the IOD to a warmer climate has been largely limited to studies of individual coupled general circulation models or multi-model ensembles. This has provided valuable insight into the IOD’s projected response to increasing greenhouse gases but has limitations in accounting for the role of internal climate variability. Using the Community Earth System Model Large Ensemble (CESM-LE), the IOD is examined in thirty-five present-day and future simulations to determine how internal variability influences properties of the IOD and their response to a warmer climate. Despite small perturbations in the initial conditions as the only difference between ensemble members, significant relationships between the mean state of the IO and the IOD arise, leading to a spread in the projected IOD responses to increasing greenhouse gases. This is driven by the positive Bjerknes feedback, where small differences in mean thermocline depth, which are caused by internal climate variability, generate significant variations in IOD amplitude, skewness, and the climatological zonal sea surface temperature gradient.”
Ng, B., Cai, W., Cowan, T. et al. Influence of internal climate variability on Indian Ocean Dipole properties. Sci Rep 8, 13500 (2018) doi:10.1038/s41598-018-31842-3. [FULL TEXT]

Uncertainty in Indian Ocean Dipole response to global warming: the role of internal variability – Hui & Zheng (2018)
“The Indian Ocean Dipole (IOD) is one of the leading modes of interannual sea surface temperature (SST) variability in the tropical Indian Ocean (TIO). The response of IOD to global warming is quite uncertain in climate model projections. In this study, the uncertainty in IOD change under global warming, especially that resulting from internal variability, is investigated based on the community earth system model large ensemble (CESM-LE). For the IOD amplitude change, the inter-member uncertainty in CESM-LE is about 50% of the intermodel uncertainty in the phase 5 of the coupled model intercomparison project (CMIP5) multimodel ensemble, indicating the important role of internal variability in IOD future projection. In CESM-LE, both the ensemble mean and spread in mean SST warming show a zonal positive IOD-like (pIOD-like) pattern in the TIO. This pIOD-like mean warming regulates ocean-atmospheric feedbacks of the interannual IOD mode, and weakens the skewness of the interannual variability. However, as the changes in oceanic and atmospheric feedbacks counteract each other, the inter-member variability in IOD amplitude change is not correlated with that of the mean state change. Instead, the ensemble spread in IOD amplitude change is correlated with that in ENSO amplitude change in CESM-LE, reflecting the close inter-basin relationship between the tropical Pacific and Indian Ocean in this model.”
Hui, C., Zheng, X. Uncertainty in Indian Ocean Dipole response to global warming: the role of internal variability. Clim Dyn 51, 3597–3611 (2018) doi:10.1007/s00382-018-4098-2.

Assessing the Impact of Model Biases on the Projected Increase in Frequency of Extreme Positive Indian Ocean Dipole Events – Wang et al. (2017)
“For many generations, models simulate an Indian Ocean dipole (IOD) that is overly large in amplitude. The possible impact of this systematic bias on climate projections, including a projected frequency increase in extreme positive IOD (pIOD) using a rainfall-based definition, has attracted attention. In particular, a recent study suggests that the increased frequency is an artifact of the overly large IOD amplitude. In contrast, here the opposite is found. Through intermodel ensemble regressions, the present study shows that models producing a high frequency in the present-day climate generate a small future frequency increase. The frequency is associated with the mean equatorial west-minus-east sea surface temperature (SST) gradient: the greater the gradient, the greater the frequency because it is easier to shift convection to the west, which characterizes an extreme pIOD. A greater present-day gradient is associated with a present-day shallower thermocline, lower SSTs, and lower rainfall in the eastern equatorial Indian Ocean (EEIO). Because there is an inherent limit for a maximum rainfall reduction and for the impact on surface cooling by a shallowing of an already shallow mean EEIO thermocline, there is a smaller increase in frequency in models with a shallower present-day EEIO thermocline. Given that a bias of overly shallow EEIO thermocline and overly low EEIO SSTs and rainfall is common in models, the future frequency increase should be underestimated, opposite to an implied overestimation resulting from the overly large IOD amplitude bias. Therefore, correcting the projected frequency from a single bias, without considering other biases that are present, is not appropriate and should be avoided.”
Wang, G., W. Cai, and A. Santoso, 2017: Assessing the Impact of Model Biases on the Projected Increase in Frequency of Extreme Positive Indian Ocean Dipole Events. J. Climate, 30, 2757–2767, https://doi.org/10.1175/JCLI-D-16-0509.1. [FULL TEXT]

A Robust but Spurious Pattern of Climate Change in Model Projections over the Tropical Indian Ocean – Li et al. (2016)
“Climate models consistently project reduced surface warming over the eastern equatorial Indian Ocean (IO) under increased greenhouse gas (GHG) forcing. This IO dipole (IOD)-like warming pattern, regarded as robust based on consistency among models by the new Intergovernmental Panel on Climate Change (IPCC) report, results in a large increase in the frequency of extreme positive IOD (pIOD) events, elevating the risk of climate and weather disasters in the future over IO rim countries. These projections, however, do not consider large model biases in both the mean state and interannual IOD variance. In particular, a “present–future relationship” is identified between the historical simulations and representative concentration pathway (RCP) 8.5 experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel ensemble: models with an excessive IOD amplitude bias tend to project a strong IOD-like warming pattern in the mean and a large increase in extreme pIOD occurrences under increased GHG forcing. This relationship links the present simulation errors to future climate projections, and is also consistent with our understanding of Bjerknes ocean–atmosphere feedback. This study calibrates regional climate projections by using this present–future relationship and observed IOD amplitude. The results show that the projected IOD-like pattern of mean changes and frequency increase of extreme pIOD events are largely artifacts of model errors and unlikely to emerge in the future. These results illustrate that a robust projection may still be biased and it is important to consider the model bias effect.”
Li, G., S. Xie, and Y. Du, 2016: A Robust but Spurious Pattern of Climate Change in Model Projections over the Tropical Indian Ocean. J. Climate, 29, 5589–5608, https://doi.org/10.1175/JCLI-D-15-0565.1. [FULL TEXT]

Monsoon-Induced Biases of Climate Models over the Tropical Indian Ocean – Li et al. (2015)
“Long-standing biases of climate models limit the skills of climate prediction and projection. Overlooked are tropical Indian Ocean (IO) errors. Based on the phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel ensemble, the present study identifies a common error pattern in climate models that resembles the IO dipole (IOD) mode of interannual variability in nature, with a strong equatorial easterly wind bias during boreal autumn accompanied by physically consistent biases in precipitation, sea surface temperature (SST), and subsurface ocean temperature. The analyses show that such IOD-like biases can be traced back to errors in the South Asian summer monsoon. A southwest summer monsoon that is too weak over the Arabian Sea generates a warm SST bias over the western equatorial IO. In boreal autumn, Bjerknes feedback helps amplify the error into an IOD-like bias pattern in wind, precipitation, SST, and subsurface ocean temperature. Such mean state biases result in an interannual IOD variability that is too strong. Most models project an IOD-like future change for the boreal autumn mean state in the global warming scenario, which would result in more frequent occurrences of extreme positive IOD events in the future with important consequences to Indonesia and East Africa. The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) characterizes this future IOD-like projection in the mean state as robust based on consistency among models, but the authors’ results cast doubts on this conclusion since models with larger IOD amplitude biases tend to produce stronger IOD-like projected changes in the future.”
Li, G., S. Xie, and Y. Du, 2015: Monsoon-Induced Biases of Climate Models over the Tropical Indian Ocean. J. Climate, 28, 3058–3072, https://doi.org/10.1175/JCLI-D-14-00740.1. [FULL TEXT]

Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming – Cai et al. (2014)
“The Indian Ocean dipole is a prominent mode of coupled ocean–atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra–Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change—with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean—facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD.”
Wenju Cai, Agus Santoso, Guojian Wang, Evan Weller, Lixin Wu, Karumuri Ashok, Yukio Masumoto & Toshio Yamagata (2014). Nature volume 510:254–258. doi:10.1038/nature13327. [FULL TEXT]

Projected response of the Indian Ocean Dipole to greenhouse warming – Cai et al. (2013)
“Natural modes of variability centred in the tropics, such as the El Niño/Southern Oscillation and the Indian Ocean Dipole, are a significant source of interannual climate variability across the globe. Future climate warming could alter these modes of variability. For example, with the warming projected for the end of the twenty-first century, the mean climate of the tropical Indian Ocean is expected to change considerably. These changes have the potential to affect the Indian Ocean Dipole, currently characterized by an alternation of anomalous cooling in the eastern tropical Indian Ocean and warming in the west in a positive dipole event, and the reverse pattern for negative events. The amplitude of positive events is generally greater than that of negative events. Mean climate warming in austral spring is expected to lead to stronger easterly winds just south of the Equator, faster warming of sea surface temperatures in the western Indian Ocean compared with the eastern basin, and a shoaling equatorial thermocline. The mean climate conditions that result from these changes more closely resemble a positive dipole state. However, defined relative to the mean state at any given time, the overall frequency of events is not projected to change — but we expect a reduction in the difference in amplitude between positive and negative dipole events.”
Cai, W., Zheng, X., Weller, E. et al. Projected response of the Indian Ocean Dipole to greenhouse warming. Nature Geosci 6, 999–1007 (2013) doi:10.1038/ngeo2009. [FULL TEXT]

Indian Ocean Dipole Response to Global Warming in the CMIP5 Multimodel Ensemble – Zheng et al. (2013)
“The response of the Indian Ocean dipole (IOD) mode to global warming is investigated based on simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In response to increased greenhouse gases, an IOD-like warming pattern appears in the equatorial Indian Ocean, with reduced (enhanced) warming in the east (west), an easterly wind trend, and thermocline shoaling in the east. Despite a shoaling thermocline and strengthened thermocline feedback in the eastern equatorial Indian Ocean, the interannual variance of the IOD mode remains largely unchanged in sea surface temperature (SST) as atmospheric feedback and zonal wind variance weaken under global warming. The negative skewness in eastern Indian Ocean SST is reduced as a result of the shoaling thermocline. The change in interannual IOD variance exhibits some variability among models, and this intermodel variability is correlated with the change in thermocline feedback. The results herein illustrate that mean state changes modulate interannual modes, and suggest that recent changes in the IOD mode are likely due to natural variations.”
Zheng, X., S. Xie, Y. Du, L. Liu, G. Huang, and Q. Liu, 2013: Indian Ocean Dipole Response to Global Warming in the CMIP5 Multimodel Ensemble. J. Climate, 26, 6067–6080, https://doi.org/10.1175/JCLI-D-12-00638.1. [FULL TEXT]

Indian Ocean Dipole Response to Global Warming: Analysis of Ocean–Atmospheric Feedbacks in a Coupled Model – Zheng et al. (2010)
“Low-frequency modulation and change under global warming of the Indian Ocean dipole (IOD) mode are investigated with a pair of multicentury integrations of a coupled ocean–atmosphere general circulation model: one under constant climate forcing and one forced by increasing greenhouse gas concentrations. In the unforced simulation, there is significant decadal and multidecadal modulation of the IOD variance. The mean thermocline depth in the eastern equatorial Indian Ocean (EEIO) is important for the slow modulation, skewness, and ENSO correlation of the IOD. With a shoaling (deepening) of the EEIO thermocline, the thermocline feedback strengthens, and this leads to an increase in IOD variance, a reduction of the negative skewness of the IOD, and a weakening of the IOD–ENSO correlation. In response to increasing greenhouse gases, a weakening of the Walker circulation leads to easterly wind anomalies in the equatorial Indian Ocean; the oceanic response to weakened circulation is a thermocline shoaling in the EEIO. Under greenhouse forcing, the thermocline feedback intensifies, but surprisingly IOD variance does not. The zonal wind anomalies associated with IOD are found to weaken, likely due to increased static stability of the troposphere from global warming. Linear model experiments confirm this stability effect to reduce circulation response to a sea surface temperature dipole. The opposing changes in thermocline and atmospheric feedbacks result in little change in IOD variance, but the shoaling thermocline weakens IOD skewness. Little change under global warming in IOD variance in the model suggests that the apparent intensification of IOD activity during recent decades is likely part of natural, chaotic modulation of the ocean–atmosphere system or the response to nongreenhouse gas radiative changes.”
Zheng, X., S. Xie, G.A. Vecchi, Q. Liu, and J. Hafner, 2010: Indian Ocean Dipole Response to Global Warming: Analysis of Ocean–Atmospheric Feedbacks in a Coupled Model. J. Climate, 23, 1240–1253, https://doi.org/10.1175/2009JCLI3326.1. [FULL TEXT]

Recent unprecedented skewness towards positive Indian Ocean Dipole occurrences and its impact on Australian rainfall – Cai et al. (2009)
“Is the recent high frequency of positive Indian Ocean Dipole (pIOD) events a consequence of global warming? Using available observations and reanalyses, we show that the pIOD occurrences increase from about four per 30 years early in the 20th century to about 10 over the last 30 years; by contrast, the number of negative Indian Ocean Dipole (nIOD) events decreases from about 10 to two over the same periods, respectively. A skewness measure, defined as the difference in occurrences of pIODs and nIODs, illustrates a systematic trend in this parameter commencing early in the 20th century. After 1950, there are more pIODs than nIODs, with consistent mean circulation changes in the pIOD‐prevalent seasons. Over southeastern Australia (SEA), these changes potentially account for much of the observed austral winter and spring rainfall reduction since 1950. These features are consistent with projected future climate change and hence with what is expected from global warming.”
Cai, W., Cowan, T., and Sullivan, A. ( 2009), Recent unprecedented skewness towards positive Indian Ocean Dipole occurrences and its impact on Australian rainfall, Geophys. Res. Lett., 36, L11705, doi:10.1029/2009GL037604. [FULL TEXT]

Climate change contributes to more frequent consecutive positive Indian Ocean Dipole events – Cai et al. (2009)
“Are the 2006–2008 three‐consecutive positive Indian Ocean Dipole (pIOD) events linked to climate change? Using 20th century experiments submitted for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), we show that a 19‐model average IOD index over the 1950–1999 period yields an upward trend. The associated circulation trends provide a favourable environment for pIOD development, leading to a 17% increase in pIOD frequency compared with the case in which trends are removed. The majority of the increase manifests as a frequency increase in the two‐ and three‐consecutive events. The circulation trends are in turn consistent with wind changes associated with a weaker Walker circulation in the Pacific and an enhanced land‐sea temperature contrast in the Indian Ocean (IO) sector. Our results suggest that although it is difficult to attribute the trigger of the recent consecutive pIODs, climate change is increasing the occurrences of such events.”
Cai, W., Sullivan, A., and Cowan, T. ( 2009), Climate change contributes to more frequent consecutive positive Indian Ocean Dipole events, Geophys. Res. Lett., 36, L23704, doi:10.1029/2009GL040163. [FULL TEXT]

Recent intensification of tropical climate variability in the Indian Ocean – Abram et al. (2008)
“The interplay of the El Niño Southern Oscillation, Asian monsoon and Indian Ocean Dipole (IOD) drives climatic extremes in and around the Indian Ocean. Historical and proxy records reveal changes in the behaviour of the El Niño Southern Oscillation and the Asian monsoon over recent decades. However, reliable instrumental records of the IOD cover only the past 50 years, and there is no consensus on long-term variability of the IOD or its possible response to greenhouse gas forcing. Here we use a suite of coral oxygen-isotope records to reconstruct a basin-wide index of IOD behaviour since AD 1846. Our record reveals an increase in the frequency and strength of IOD events during the twentieth century, which is associated with enhanced seasonal upwelling in the eastern Indian Ocean. Although the El Niño Southern Oscillation has historically influenced the variability of both the IOD and the Asian monsoon, we find that the recent intensification of the IOD coincides with the development of direct, positive IOD–monsoon feedbacks. We suggest that projected greenhouse warming may lead to a redistribution of rainfall across the Indian Ocean and a growing interdependence between the IOD and Asian monsoon precipitation variability.”
Abram, N., Gagan, M., Cole, J. et al. Recent intensification of tropical climate variability in the Indian Ocean. Nature Geosci 1, 849–853 (2008) doi:10.1038/ngeo357. [FULL TEXT]

GCM simulations of the Indian Ocean dipole influence on East African rainfall: Present and future – Conway et al. (2007)
“Six coupled GCMs are assessed in terms of their ability to simulate observed characteristics of East African rainfall, the Indian Ocean dipole and their temporal correlation. Model results are then used to analyze the future behaviour of rainfall and the DMI. All models simulate reasonably well the spatial distribution and variability of annual and seasonal rainfall over the 1961–1990 period. Model simulation of observed DMI characteristics is less consistent with observations, however, five models reproduce similar correlations to those observed between the DMI and East African short rains (SON). In the future, there are no clear inter‐model patterns of rainfall or DMI behaviour. In this sample of models four (two) out of six simulate modest increases (decreases) in annual rainfall by the 2080s. For SON, three of the six models indicate a trend towards increasingly positive phase of the DMI, two indicate a decrease and one shows no substantial change.”
Conway, D., Hanson, C. E., Doherty, R., and Persechino, A. ( 2007), GCM simulations of the Indian Ocean dipole influence on East African rainfall: Present and future, Geophys. Res. Lett., 34, L03705, doi:10.1029/2006GL027597. [FULL TEXT]

Papers on Australia wildfires and climate change

This is a list of papers on Australia wildfires and climate change. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (January 10, 2020): Cai et al. (2009) added.

Climate change effects on the frequency, seasonality and interannual variability of suitable prescribed burning weather conditions in south-eastern Australia – Clarke et al. (2019)
“Despite the importance of prescribed burning in contemporary fire management, there is little understanding of how climate change will influence the weather conditions under which it is deployed. We provide quantitative estimates of potential changes in the number of prescribed burning days in coastal NSW in south-eastern Australia, a fire-prone area dominated by dry sclerophyll forests. Burning days are calculated from an objectively designed regional climate model ensemble using three definitions of suitable weather conditions based on: a literature search (Literature), actual weather observed during recorded prescribed burns (Observed) and operational guidelines (Operational). Contrary to some claims, evidence for a decrease in prescribed burning days under projected future climates is weak. We found a complex pattern of changes, with the potential for substantial and widespread increases in the current burning seasons of autumn (March-May) and spring (August-October). Projected changes were particularly uncertain in northern NSW, spanning substantial increases and decreases during autumn. The magnitude of projected changes in the frequency of burning days was highly sensitive to which definition of suitable weather conditions was used, with a relatively small change for the Operational definition (+0.3 to +1.9 days per year across the study area) and larger ranges for the Observed (+0.2 to +7.9 days) and Literature (+1.7 to +6.2 days) definitions. Interannual variability in the number of burning days is projected to increase slightly under projected climate change. Our study highlights the need for a better understanding of the weather conditions required for safe and effective prescribed burning. Our analysis provides practitioners with quantitative information to assess their exposure to a range of potential changes in the frequency, seasonality and variability of prescribed burning weather conditions.”
Hamish Clarke, Bruce Tran, Matthias M. Boer, Owen Price, Belinda Kenny, Ross Bradstock (2019). Agricultural and Forest Meteorology 271(15):148-157. doi:https://doi.org/10.1016/j.agrformet.2019.03.005.

Future changes in extreme weather and pyroconvection risk factors for Australian wildfires – Dowdy et al. (2019)
“Extreme wildfires have recently caused disastrous impacts in Australia and other regions of the world, including events with strong convective processes in their plumes (i.e., strong pyroconvection). Dangerous wildfire events such as these could potentially be influenced by anthropogenic climate change, however, there are large knowledge gaps on how these events might change in the future. The McArthur Forest Fire Danger Index (FFDI) is used to represent near-surface weather conditions and the Continuous Haines index (CH) is used here to represent lower to mid-tropospheric vertical atmospheric stability and humidity measures relevant to dangerous wildfires and pyroconvective processes. Projected changes in extreme measures of CH and FFDI are examined using a multi-method approach, including an ensemble of global climate models together with two ensembles of regional climate models. The projections show a clear trend towards more dangerous near-surface fire weather conditions for Australia based on the FFDI, as well as increased pyroconvection risk factors for some regions of southern Australia based on the CH. These results have implications for fields such as disaster risk reduction, climate adaptation, ecology, policy and planning, noting that improved knowledge on how climate change can influence extreme wildfires can help reduce future impacts of these events.”
Andrew J. Dowdy, Hua Ye, Acacia Pepler, Marcus Thatcher, Stacey L. Osbrough, Jason P. Evans, Giovanni Di Virgilio & Nicholas McCarthy (2019). Scientific Reports 9:10073. doi:10.1038/s41598-019-46362-x. [FULL TEXT]

Exploring the future change space for fire weather in southeast Australia – Clarke & Evans (2019)
“High-resolution projections of climate change impacts on fire weather conditions in southeast Australia out to 2080 are presented. Fire weather is represented by the McArthur Forest Fire Danger Index (FFDI), calculated from an objectively designed regional climate model ensemble. Changes in annual cumulative FFDI vary widely, from − 337 (− 21%) to + 657 (+ 24%) in coastal areas and − 237 (− 12%) to + 1143 (+ 26%) in inland areas. A similar spread is projected in extreme FFDI values. In coastal regions, the number of prescribed burning days is projected to change from − 11 to + 10 in autumn and − 10 to + 3 in spring. Across the ensemble, the most significant increases in fire weather and decreases in prescribed burn windows are projected to take place in spring. Partial bias correction of FFDI leads to similar projections but with a greater spread, particularly in extreme values. The partially bias-corrected FFDI performs similarly to uncorrected FFDI compared to the observed annual cumulative FFDI (ensemble root mean square error spans 540 to 1583 for uncorrected output and 695 to 1398 for corrected) but is generally worse for FFDI values above 50. This emphasizes the need to consider inter-variable relationships when bias-correcting for complex phenomena such as fire weather. There is considerable uncertainty in the future trajectory of fire weather in southeast Australia, including the potential for less prescribed burning days and substantially greater fire danger in spring. Selecting climate models on the basis of multiple criteria can lead to more informative projections and allow an explicit exploration of uncertainty.”
Clarke, H. & Evans, J.P. Theor Appl Climatol (2019) 136: 513. https://doi.org/10.1007/s00704-018-2507-4. [FULL TEXT]

On Determining the Impact of Increasing Atmospheric CO2 on the Record Fire Weather in Eastern Australia in February 2017 – Hope et al. (2019)
“February 2017 saw a broad region with record fire weather across central-eastern Australia. A hybrid attribution technique using modified observations and a seasonal forecast framework did not give a clear signal as to the influence of increasing atmospheric CO2 on the fire weather.”
Pandora Hope, Mitchell T. Black, Eun-Pa Lim, Andrew Dowdy, Guomin Wang, Acacia S. Pepler, and Robert J. B. Fawcett (2019). Bulletin of the American Meteorological Society, vol. 100, issue 1, pp. S111-S117. doi:10.1175/BAMS-D-18-0135.1. [FULL TEXT]

Climatological Variability of Fire Weather in Australia – Dowdy (2018)
“Long-term variations in fire weather conditions are examined throughout Australia from gridded daily data from 1950 to 2016. The McArthur forest fire danger index is used to represent fire weather conditions throughout this 67-yr period, calculated on the basis of a gridded analysis of observations over this time period. This is a complementary approach to previous studies (e.g., those based primarily on model output, reanalysis, or individual station locations), providing a spatially continuous and long-term observations-based dataset to expand on previous research and produce climatological guidance information for planning agencies. Long-term changes in fire weather conditions are apparent in many regions. In particular, there is a clear trend toward more dangerous conditions during spring and summer in southern Australia, including increased frequency and magnitude of extremes, as well as indicating an earlier start to the fire season. Changes in fire weather conditions are attributable at least in part to anthropogenic climate change, including in relation to increasing temperatures. The influence of El Niño–Southern Oscillation (ENSO) on fire weather conditions is found to be broadly consistent with previous studies (indicating more severe fire weather in general for El Niño conditions than for La Niña conditions), but it is demonstrated that this relationship is highly variable (depending on season and region) and that there is considerable potential in almost all regions of Australia for long-range prediction of fire weather (e.g., multiweek and seasonal forecasting). It is intended that improved understanding of the climatological variability of fire weather conditions will help lead to better preparedness for risks associated with dangerous wildfires in Australia.”
Dowdy, A.J., 2018: Climatological Variability of Fire Weather in Australia. J. Appl. Meteor. Climatol., 57, 221–234, https://doi.org/10.1175/JAMC-D-17-0167.1. [FULL TEXT]

Pyroconvection Risk in Australia: Climatological Changes in Atmospheric Stability and Surface Fire Weather Conditions – Dowdy & Pepler (2018)
“Extreme wildfires with strong convective processes in their plumes have recently led to disastrous impacts on various regions of the world. The Continuous Haines index (CH) is used in Australia to represent vertical atmospheric stability and humidity measures relating to pyroconvective processes. CH climatology is examined here using reanalysis data from 1979 to 2016, revealing large spatial and seasonal variations throughout Australia. Various measures of severity are investigated, including regionally specific thresholds. CH is combined with near‐surface fire weather conditions, as a type of compound event, and is examined in relation to environmental conditions associated with pyroconvection. Significant long‐term changes in CH are found for some regions and seasons, with these changes corresponding to changes in near‐surface conditions in some cases. In particular, an increased risk of pyroconvection is identified for southeast Australia during spring and summer, due to decreased vertical atmospheric stability and humidity combined with more severe near‐surface conditions.”
Dowdy, A. J., & Pepler, A. ( 2018). Pyroconvection risk in Australia: Climatological changes in atmospheric stability and surface fire weather conditions. Geophysical Research Letters, 45, 2005– 2013. https://doi.org/10.1002/2017GL076654. [FULL TEXT]

Fire frequency analysis for different climatic stations in Victoria, Australia – Khastagir (2018)
“Frequent occurrence of fire events will have severe impact on Victoria’s water supply catchments. Hence, it is important to perform fire frequency analysis to obtain fire frequency curves (FFC) on fire intensity using Forest Fire Danger Index (FFDI) at different parts of Victoria. FFDI is a measure of fire initiation, spreading speed and containment difficulty. FFC will guide water harvesting by providing information with regard to future fire events and the subsequent impact on catchment yield. Five probability distributions, namely normal, Log Pearson Type III (LPIII), gamma, log-normal and Weibull distributions were used for the development of FFCs at ten selected meteorological stations spread all over Victoria. LPIII distribution was identified as the best fit distribution for Victoria and subsequently applied for an additional 30 more stations to show spatial variability for the entire Victoria.”
Anirban Khastagir (2018). Natural Hazards volume 93, pages 787–802. doi:https://doi.org/10.1007/s11069-018-3324-x.

Fanning the Blame: Media Accountability, Climate and Crisis on the Australian “Fire Continent” – Anderson et al. (2018)
“This paper raises questions of media coverage of “compounded crises” related to extreme weather disaster, in the context of urgent calls to address the implications of a changing climate. Through media analysis, it examines the ways debate over bushfire protection policy was framed and made culturally meaningful, thereby politically consequential, in the wake of the worst bushfires in modern Australian history, Black Saturday (2009). The fires, in which 173 people died, led to a Royal Commission and fierce debate over the use of prescribed burning to reduce bushfire hazard. Longitudinal analysis of local, state and national mainstream media coverage (2009–2016) reveals blame games that targeted environmentalists and the government, which near-silenced meaningful discussion of the complexity of fire science, impacts of climate change on weather conditions, and calls for adaptation. By exploring the media’s constitutive role in crisis response, the paper highlights the legacy and potency of ideological conflict that shapes the media-policy nexus in Australia.”
Deb Anderson, Philip Chubb & Monika Djerf-Pierre (2018) Fanning the Blame: Media Accountability, Climate and Crisis on the Australian “Fire Continent”, Environmental Communication, 12:7, 928-941, DOI: 10.1080/17524032.2018.1424008. [FULL TEXT]

Big data integration shows Australian bush-fire frequency is increasing significantly – Dutta et al. (2016)
“Increasing Australian bush-fire frequencies over the last decade has indicated a major climatic change in coming future. Understanding such climatic change for Australian bush-fire is limited and there is an urgent need of scientific research, which is capable enough to contribute to Australian society. Frequency of bush-fire carries information on spatial, temporal and climatic aspects of bush-fire events and provides contextual information to model various climate data for accurately predicting future bush-fire hot spots. In this study, we develop an ensemble method based on a two-layered machine learning model to establish relationship between fire incidence and climatic data. In a 336 week data trial, we demonstrate that the model provides highly accurate bush-fire incidence hot-spot estimation (91% global accuracy) from the weekly climatic surfaces. Our analysis also indicates that Australian weekly bush-fire frequencies increased by 40% over the last 5 years, particularly during summer months, implicating a serious climatic shift.”
Ritaban Dutta, Aruneema Das and Jagannath Aryal (2016). Royal Society Open Science 3(2). doi:https://doi.org/10.1098/rsos.150241. [FULL TEXT]

Natural hazards in Australia: extreme bushfire – Sharples et al. (2016)
“Bushfires are one of the most frequent natural hazards experienced in Australia. Fires play an important role in shaping the landscape and its ecological dynamics, but may also have devastating effects that cause human injuries and fatalities, as well as broad-scale environmental damage. While there has been considerable effort to quantify changes in the occurrence of bushfire in Australia, a comprehensive assessment of the most extreme bushfire cases, which exact the greatest economic and environmental impacts, is lacking. In this paper we reflect upon recently developed understanding of bushfire dynamics to consider (i) historical changes in the occurrence of extreme bushfires, and (ii) the potential for increasing frequency in the future under climate change projections. The science of extreme bushfires is still a developing area, thus our conclusions about emerging patterns in their occurrence should be considered tentative. Nonetheless, historical information on noteworthy bushfire events suggests an increased occurrence in recent decades. Based on our best current understanding of how extreme bushfires develop, there is strong potential for them to increase in frequency in the future. As such there is a pressing need for a greater understanding of these powerful and often destructive phenomena.”
Sharples, J.J., Cary, G.J., Fox-Hughes, P. et al. Climatic Change (2016) 139: 85. https://doi.org/10.1007/s10584-016-1811-1. [FULL TEXT]

ENSO controls interannual fire activity in southeast Australia – Mariani et al. (2016)
“El Niño–Southern Oscillation (ENSO) is the main mode controlling the variability in the ocean‐atmosphere system in the South Pacific. While the ENSO influence on rainfall regimes in the South Pacific is well documented, its role in driving spatiotemporal trends in fire activity in this region has not been rigorously investigated. This is particularly the case for the highly flammable and densely populated southeast Australian sector, where ENSO is a major control over climatic variability. Here we conduct the first region‐wide analysis of how ENSO controls fire activity in southeast Australia. We identify a significant relationship between ENSO and both fire frequency and area burnt. Critically, wavelet analyses reveal that despite substantial temporal variability in the ENSO system, ENSO exerts a persistent and significant influence on southeast Australian fire activity. Our analysis has direct application for developing robust predictive capacity for the increasingly important efforts at fire management.”
Mariani, M., Fletcher, M.‐S., Holz, A., and Nyman, P. ( 2016), ENSO controls interannual fire activity in southeast Australia, Geophys. Res. Lett., 43, 10,891– 10,900, doi:10.1002/2016GL070572. [FULL TEXT]

People, El Niño southern oscillation and fire in Australia: fire regimes and climate controls in hummock grasslands – Bird et al. (2016)
“While evidence mounts that indigenous burning has a significant role in shaping pyrodiversity, the processes explaining its variation across local and external biophysical systems remain limited. This is especially the case with studies of climate–fire interactions, which only recognize an effect of humans on the fire regime when they act independently of climate. In this paper, we test the hypothesis that an anthropogenic fire regime (fire incidence, size and extent) does not covary with climate. In the lightning regime, positive El Niño southern oscillation (ENSO) values increase lightning fire incidence, whereas La Niña (and associated increases in prior rainfall) increase fire size. ENSO has the opposite effect in the Martu regime, decreasing ignitions in El Niño conditions without affecting fire size. Anthropogenic ignition rates covary positively with high antecedent rainfall, whereas fire size varies only with high temperatures and unpredictable winds, which may reduce control over fire spread. However, total area burned is similarly predicted by antecedent rainfall in both regimes, but is driven by increases in fire size in the lightning regime, and fire number in the anthropogenic regime. We conclude that anthropogenic regimes covary with climatic variation, but detecting the human–climate–fire interaction requires multiple measures of both fire regime and climate.”
Bliege Bird Rebecca, Bird Douglas W. and Codding Brian F. People, El Niño southern oscillation and fire in Australia: fire regimes and climate controls in hummock grasslands. Phil. Trans. R. Soc. B. 371(1696). doi:https://doi.org/10.1098/rstb.2015.0343. [FULL TEXT]

Responses of resilience traits to gradients of temperature, rainfall and fire frequency in fire-prone, Australian forests: potential consequences of climate change – Hammill et al. (2016)
“The composition of plant communities may be driven by responses of key plant resilience traits (resprouting R+, non-resprouting R−, persistent P+ and transient P− seedbanks) to either resource competition or disturbance regimes. We explored responses of overall species richness and the richness of herbs and shrubs within the three most common functional types (i.e. facultative resprouters R+P+, obligate resprouters R+P−, obligate seeders R−P+) to orthogonal combinations of temperature (MAT), rainfall (MAP) and fire frequency (FF) in Dry Sclerophyll Forest in the Sydney basin (south-eastern Australia). R+ and P+ species were predominant (>72 % of total species). Overall richness was a significant positive function of MAT, MAP and FF. Positive relationships between species richness and MAP, MAT and FF occurred across all trait and functional type groups, with MAP being the most influential and FF the least. Responses of proportions of species within trait- and functional-type groups were complex. Proportion of R+ species was negatively related to MAT and MAP, but species-rich herb and shrub R+P+ proportions were positively and negatively related to MAT, respectively. The herb R+P+ proportion was negatively related to FF. The results were inconsistent with the disturbance frequency and resource competition models of resilience variation. Rises in MAT under climate change have the potential not only to increase overall species plus richness across all trait groups but also to diminish shrubs relative to herbs in the key R+P+ functional types. Such a scenario is highly uncertain given the variability in future MAP projections for the region.”
Hammill, K., Penman, T. & Bradstock, R. Plant Ecol (2016) 217: 725. https://doi.org/10.1007/s11258-016-0578-9.

Divergent responses of fire to recent warming and drying across south‐eastern Australia – Bradstock et al. (2014)
“The response of fire to climate change may vary across fuel types characteristic of differing vegetation types (i.e. litter vs. grass). Models of fire under climatic change capture these differing potential responses to varying degrees. Across south‐eastern Australia, an elevation in the severity of weather conditions conducive to fire has been measured in recent decades. We examined trends in area burned (1975–2009) to determine if a corresponding increase in fire had occurred across the diverse range of ecosystems found in this part of the continent. We predicted that an increase in fire, due to climatic warming and drying, was more likely to have occurred in moist, temperate forests near the coast than in arid and semiarid woodlands of the interior, due to inherent contrasts in the respective dominant fuel types (woody litter vs. herbaceous fuels). Significant warming (i.e. increased temperature and number of hot days) and drying (i.e. negative precipitation anomaly, number of days with low humidity) occurred across most of the 32 Bioregions examined. The results were mostly consistent with predictions, with an increase in area burned in seven of eight forest Bioregions, whereas area burned either declined (two) or did not change significantly (nine) in drier woodland Bioregions. In 12 woodland Bioregions, data were insufficient for analysis of temporal trends in fire. Increases in fire attributable mostly to warming or drying were confined to three Bioregions. In the remainder, such increases were mostly unrelated to warming or drying trends and therefore may be due to other climate effects not explored (e.g. lightning ignitions) or possible anthropogenic influences. Projections of future fire must therefore not only account for responses of different fuel systems to climatic change but also the wider range of ecological and human effects on interactions between fire and vegetation.”
Bradstock, R., Penman, T., Boer, M., Price, O. and Clarke, H. (2014), Divergent responses of fire to recent warming and drying across south‐eastern Australia. Glob Change Biol, 20: 1412-1428. doi:10.1111/gcb.12449.

Changes in Australian fire weather between 1973 and 2010 – Clarke et al. (2013)
“A data set of observed fire weather in Australia from 1973–2010 is analysed for trends using the McArthur Forest Fire Danger Index (FFDI). Annual cumulative FFDI, which integrates daily fire weather across the year, increased significantly at 16 of 38 stations. Annual 90th percentile FFDI increased significantly at 24 stations over the same period. None of the stations examined recorded a significant decrease in FFDI. There is an overall bias in the number of significant increases towards the southeast of the continent, while the largest trends occur in the interior of the continent and the smallest occur near the coast. The largest increases in seasonal FFDI occurred during spring and autumn, although with different spatial patterns, while summer recorded the fewest significant trends. These trends suggest increased fire weather conditions at many locations across Australia, due to both increased magnitude of FFDI and a lengthened fire season. Although these trends are consistent with projected impacts of climate change on FFDI, this study cannot separate the influence of climate change, if any, with that of natural variability.”
Clarke, H., Lucas, C. and Smith, P. (2013), Changes in Australian fire weather between 1973 and 2010. Int. J. Climatol., 33: 931-944. doi:10.1002/joc.3480. [FULL TEXT]

Fire and carbon dynamics under climate change in south-eastern Australia: insights from FullCAM and FIRESCAPE modelling – King et al. (2011)
“This study used simulation modelling to investigate fire and carbon dynamics for projected warmer and drier climates in the south-eastern Australian high country. A carbon accounting model FullCAM and the landscape fire regime simulator FIRESCAPE were combined and used to simulate several fire management options under three climate scenarios – the recent climate (1975–2005); a moderate climate projected for 2070 (B1); and a more extreme climate projected for 2070 (A1FI). For warmer and drier climates, model simulations predicted (i) an increase in fire incidence; (ii) larger areas burned; (iii) higher mean fire intensities; (iv) shorter fire cycle lengths; (v) a greater proportion of fires burning earlier in the fire season; (vi) a reduction in carbon stores; (vii) a reduction in carbon sequestration rates; and (viii) an increase in the proportion of stored carbon emitted to the atmosphere. Prescribed burning at historical or twice historical levels had no effect on fire or carbon dynamics. In contrast, increasing the initial attack success (a surrogate for suppression) partially offset the adverse effects of warmer and drier climates on fire activity, but not on carbon dynamics. For the south-eastern Australian high country, simulations indicated that fire and carbon dynamics are sensitive to climate change, with simulated fire management only being able to partially offset the adverse effects of warmer and drier climate.”
King Karen J., de Ligt Robert M., Cary Geoffrey J. (2011) Fire and carbon dynamics under climate change in south-eastern Australia: insights from FullCAM and FIRESCAPE modelling. International Journal of Wildland Fire 20, 563-577. doi:https://doi.org/10.1071/WF09073.

Assessing the impact of climate change on extreme fire weather events over southeastern Australia – Hasson et al. (2009)
“Extreme fire weather events in southeastern Australia are frequently associated with strong cold fronts moving through the area. A recent study has shown that the 850 hPa temperature and the magnitude of its gradient over a small region of southeastern Australia provide a simple means of discriminating the most extreme cold frontal events during the last 40 yr from reanalysis data sets. Applying this technique to 10 general circulation models (GCMs) from the Coupled Model Intercomparison Project and calibrating the temperature gradient and temperature climatology of each model’s simulation of the climate of the 20th century against the reanalysis climates allows estimates of likely changes in frequency of this type of extreme cold front in the middle and end of the 21st century. Applying this analysis to the output of 10 GCM simulations of the 21st century, using low and high greenhouse gas emissions scenarios, suggests that the frequency of such events will increase from around 1 event every 2 yr during the late 20th century to around 1 event per year in the middle of the 21st century and 1 to 2 events per year by the end of the 21st century; however, there is a great degree of variation between models. In addition to a greater overall increase under the high emissions scenario, the rate at which the increase occurs amplifies during the second half of the century, whereas under the low emissions scenario the number of extreme cases stabilizes, although still at a higher rate than that experienced in the late 20th century.”
Hasson AEA, Mills GA, Timbal B, Walsh K (2009) Assessing the impact of climate change on extreme fire weather events over southeastern Australia. Clim Res 39:159-172. https://doi.org/10.3354/cr00817. [FULL TEXT]

Positive Indian Ocean Dipole events precondition southeast Australia bushfires – Cai et al. (2009)
“The devastating “Black Saturday” bushfire inferno in the southeast Australian state of Victoria in early February 2009 and the “Ash Wednesday” bushfires in February 1983 were both preceded by a positive Indian Ocean Dipole (pIOD) event. Is there a systematic pIOD linkage beyond these two natural disasters? We show that out of 21 significant bushfires seasons since 1950, 11 were preceded by a pIOD. During Victoria’s wet season, particularly spring, a pIOD contributes to lower rainfall and higher temperatures exacerbating the dry conditions and increasing the fuel load leading into summer. Consequently, pIODs are effective in preconditioning Victoria for bushfires, more so than El Niño events, as seen in the impact on soil moisture on interannual time scales and in multi‐decadal changes since the 1950s. Given that the recent increase in pIOD occurrences is consistent with what is expected from global warming, an increased bushfire risk in the future is likely across southeast Australia.”
Cai, W., Cowan, T., and Raupach, M. ( 2009), Positive Indian Ocean Dipole events precondition southeast Australia bushfires, Geophys. Res. Lett., 36, L19710, doi:10.1029/2009GL039902. [FULL TEXT]

The impact of climate change on the risk of forest and grassland fires in Australia – Pitman et al. (2007)
“We explore the impact of future climate change on the risk of forest and grassland fires over Australia in January using a high resolution regional climate model, driven at the boundaries by data from a transitory coupled climate model. Two future emission scenarios (relatively high and relatively low) are used for 2050 and 2100 and four realizations for each time period and each emission scenario are run. Results show a consistent increase in regional-scale fire risk over Australia driven principally by warming and reductions in relative humidity in all simulations, under all emission scenarios and at all time periods. We calculate the probability density function for the fire risk for a single point in New South Wales and show that the probability of extreme fire risk increases by around 25% compared to the present day in 2050 under both relatively low and relatively high emissions, and that this increases by a further 20% under the relatively low emission scenario by 2100. The increase in the probability of extreme fire risk increases dramatically under the high emission scenario by 2100. Our results are broadly in-line with earlier analyses despite our use of a significantly different methodology and we therefore conclude that the likelihood of a significant increase in fire risk over Australia resulting from climate change is very high. While there is already substantial investment in fire-related management in Australia, our results indicate that this investment is likely to have to increase to maintain the present fire-related losses in Australia.”
Pitman, A.J., Narisma, G.T. & McAneney, J. The impact of climate change on the risk of forest and grassland fires in Australia. Climatic Change 84, 383–401 (2007) doi:10.1007/s10584-007-9243-6. [FULL TEXT]

The Sensitivity of Australian Fire Danger to Climate Change – Williams et al. (2001)
“Global climate change, such as that due to the proposed enhanced greenhouse effect, is likely to have a significant effect on biosphere-atmosphere interactions, including bushfire regimes. This study quantifies the possible impact of climate change on fire regimes by estimating changes in fire weather and the McArthur Forest Fire Danger Index (FDI), an index that is used throughout Australia to estimate fire danger. The CSIRO 9-level general circulation model(CSIRO9 GCM)is used to simulate daily and seasonal fire danger for the present Australian climate and for a doubled-CO2 climate. The impact assessment includes validation of the GCMs daily control simulation and the derivation of ‘correction factors’ which improve the accuracy of the fire danger simulation. In summary, the general impact of doubled-CO2 is to increase fire danger at all sites by increasing the number of days of very high and extreme fire danger.Seasonal fire danger responds most to the large CO2-induced changes in maximum temperature.”
Williams, A.A.J., Karoly, D.J. & Tapper, N. Climatic Change (2001) 49: 171. https://doi.org/10.1023/A:1010706116176. [FULL TEXT]

Fire Regime Sensitivity to Global Climate Change: An Australian Perspective – Cary & Banks (2000)
“The Australian eucalypt forests are highly adapted to fire, and their component species possess well-developed response mechanisms that ensure post-fire recovery of these ecosystems. Fire regimes, which may alter forest floristics and structure, have changed since pre-European times because of management practices and may again change because of a changing climate. Two complimentary approaches are used to determine spatial and temporal patterns of fire regimes, a) dendrochronology to determine pre- and post-European fire histories for specific sites and b) fire-climate-landscape modelling to predict spatial patterns in fire regimes for topographically complex landscapes. This paper brings together these two approaches which have been applied independently to the same forest in the Southern Tablelands of New South Wales. The model predictions of spatial patterns in fire regimes under the present climate provide reasonable results when compared with observed site fire histories. Also, model results indicate that around half of the landscape is likely to experience a significant increase in fire frequency as a result of climate change. These findings, which have implications for fire-prone forest environments world-wide, are discussed in relation to the effects that anthropogenic ignition have had on the fire frequency in the study area over the last century.”
Cary G.J., Banks J.C.G. (2000) Fire Regime Sensitivity to Global Climate Change: An Australian Perspective. In: Innes J.L., Beniston M., Verstraete M.M. (eds) Biomass Burning and Its Inter-Relationships with the Climate System. Advances in Global Change Research, vol 3. Springer, Dordrecht.

Papers of Wally Broecker

A list of climate related papers where Wally Broecker (1931-2019) is the first author:

1957

Lamont Natural Radiocarbon Measurements IV https://www.jstor.org/stable/1752751

1958

The relation of deep sea sedimentation rates to variations in climate http://www.ajsonline.org/content/256/7/503.extract

Radiocarbon chronology of Lake Lahontan and Lake Bonneville https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/69/8/1009/5015

1959

Re-evaluation of the salt chronology of several Great Basin Lakes https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/70/5/601/5108

Lamont Radiocarbon Measurements VI https://www.cambridge.org/core/journals/radiocarbon/article/lamont-radiocarbon-measurements-vi/EE4DAF2397F34D5D7C1AEEE88CE750C1

1960

Evidence for an abrupt change in climate close to 11,000 years ago http://www.ajsonline.org/content/258/6/429.short

Natural radiocarbon in the Atlantic Ocean https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JZ065i009p02903

1965

Uranium-Series Dating of Corals and Oolites from Bahaman and Florida Key Limestones http://science.sciencemag.org/content/149/3679/58

Radiocarbon Chronology of Lake Lahontan and Lake Bonneville II, Great Basin https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/76/5/537/5914

1968

Milankovitch Hypothesis Supported by Precise Dating of Coral Reefs and Deep-Sea Sediments http://science.sciencemag.org/content/159/3812/297

In Defense of the Astronomical Theory of Glaciation https://link.springer.com/chapter/10.1007/978-1-935704-38-6_14

1970

Insolation changes, ice volumes, and the O18 record in deep‐sea cores https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/RG008i001p00169

1975

Climatic Change: Are We on the Brink of a Pronounced Global Warming? http://science.sciencemag.org/content/189/4201/460

1980

Modeling the Carbon System https://www.cambridge.org/core/journals/radiocarbon/article/modeling-the-carbon-system/5379951AF625C8A15696E4E52DE79BD6

1981

Glacial to Interglacial Changes in Ocean and Atmosphere Chemistry https://link.springer.com/chapter/10.1007/978-94-009-8514-8_5

1982

Ocean chemistry during glacial time https://www.sciencedirect.com/science/article/pii/0016703782901107

1984

Terminations https://link.springer.com/chapter/10.1007/978-94-017-4841-4_14

Is There A Tie Between Atmospheric CO2 Content and Ocean Circulation? https://www.cambridge.org/core/journals/annals-of-glaciology/article/is-there-a-tie-between-atmospheric-co2-content-and-ocean-circulation-abstract/4C4FE09E12D93C25A2003F1F3BE16EE3

Radiocarbon measurements on coexisting benthic and planktic foraminifera shells: potential for reconstructing ocean ventilation times over the past 20 000 years https://www.sciencedirect.com/science/article/pii/0168583X8490538X

1985

Does the ocean–atmosphere system have more than one stable mode of operation? https://www.nature.com/articles/315021a0

Sources and flow patterns of deep‐ocean waters as deduced from potential temperature, salinity, and initial phosphate concentration https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JC090iC04p06925

1986

Carbon Cycle: 1985 Glacial to Interglacial Changes in the Operation of the Global Carbon Cycle https://www.cambridge.org/core/journals/radiocarbon/article/carbon-cycle-1985-glacial-to-interglacial-changes-in-the-operation-of-the-global-carbon-cycle/453E35DB3657CEF83F8B9E247287FF38

Hydrography, chemistry, and radioisotopes in the Southeast Asian basins https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JC091iC12p14345

1987

Unpleasant surprises in the greenhouse? https://www.nature.com/articles/328123a0

1988

New evidence from the South China Sea for an abrupt termination of the last glacial period https://www.nature.com/articles/333156a0

Can the Greenland Climatic Jumps be Identified in Records from Ocean and Land? https://www.cambridge.org/core/journals/quaternary-research/article/can-the-greenland-climatic-jumps-be-identified-in-records-from-ocean-and-land/3717F76BA966C1A7E4B51E96891F6033

The chronology of the last Deglaciation: Implications to the cause of the Younger Dryas Event https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/PA003i001p00001

1989

The role of ocean-atmosphere reorganizations in glacial cycles https://www.sciencedirect.com/science/article/pii/0016703789901233

The salinity contrast between the Atlantic and Pacific oceans during glacial time https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/PA004i002p00207

Some thoughts about the radiocarbon budget for the glacial Atlantic https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/PA004i002p00213

1990

The role of ocean-atmosphere reorganizations in glacial cycles https://www.sciencedirect.com/science/article/abs/pii/0277379190900267

The magnitude of global fresh-water transports of importance to ocean circulation https://link.springer.com/article/10.1007/BF00208902

The magnitude of global fresh-water transports of importance to ocean circulation https://link.springer.com/article/10.1007/BF00208902

A salt oscillator in the glacial Atlantic? 1. The concept https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/PA005i004p00469

The distribution of radiocarbon in the glacial ocean https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/GB004i001p00103

Salinity history of the northern Atlantic during the last deglaciation https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/PA005i004p00459

1991

The Great Ocean Conveyor https://www.jstor.org/stable/43924572

Keeping global change honest https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/91GB01421

The Influence of CaCO3 Dissolution on Core Top Radiocarbon Ages for Deep‐Sea Sediments https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/91PA01768

Radiocarbon age of waters in the deep Atlantic revisited https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/90GL02707

1992

Origin of the northern Atlantic’s Heinrich events https://link.springer.com/article/10.1007/BF00193540

The influence of air and sea exchange on the carbon isotope distribution in the sea https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92GB01672

Defining the Boundaries of the Late-Glacial Isotope Episodes https://www.cambridge.org/core/journals/quaternary-research/article/defining-the-boundaries-of-the-lateglacial-isotope-episodes/ED0290CB6C9734A818CFE909CCEFB312

Interhemispheric transport of carbon dioxide by ocean circulation https://www.nature.com/articles/356587a0

1993

Heinrich Events: Triggers of Ocean Circulation Change? https://link.springer.com/chapter/10.1007/978-3-642-85016-5_10

A Search for an Early Holocene CACO3 Preservation Event https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/93PA00423

What Caused the Glacial to Interglacial CO2 Change? https://link.springer.com/chapter/10.1007/978-3-642-84608-3_4

Evaluation of the 13C constraint on the uptake of fossil fuel CO2 by the ocean https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/93GB01445

Interhemispheric Transport of Carbon Through the Ocean https://link.springer.com/chapter/10.1007/978-3-642-84608-3_22

1994

Massive iceberg discharges as triggers for global climate change https://www.nature.com/articles/372421a0

1996

Glacial Climate in the Tropics http://science.sciencemag.org/content/272/5270/1902

1997

Thermohaline Circulation, the Achilles Heel of Our Climate System: Will Man-Made CO2 Upset the Current Balance? http://science.sciencemag.org/content/278/5343/1582

Future directions of paleoclimate research https://www.sciencedirect.com/science/article/abs/pii/S0277379197000504

Will Our Ride into the Greenhouse Future be a Smooth One? http://oceanrep.geomar.de/33087/

Mountain glaciers: Recorders of atmospheric water vapor content? https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/97GB02267

Magnitude of the CaCO3 dissolution events marking the onset of times of glaciation https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/97PA01020

1998

The end of the present interglacial: How and when? https://www.sciencedirect.com/science/article/abs/pii/S0277379198000377

Does atmospheric CO2 police the rate of chemical weathering? https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/98GB01927

Paleocean circulation during the Last Deglaciation: A bipolar seesaw? https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/97PA03707

Antiphasing between Rainfall in Africa’s Rift Valley and North America’s Great Basin https://www.cambridge.org/core/journals/quaternary-research/article/antiphasing-between-rainfall-in-africas-rift-valley-and-north-americas-great-basin/9B1EE73D21721A2EEFD0F1897034E52E

The sequence of events surrounding Termination II and their implications for the cause of glacial‐interglacial CO2 changes https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/98PA00920

1999

Climate Change Prediction http://science.sciencemag.org/content/283/5399/175.6

A Possible 20th-Century Slowdown of Southern Ocean Deep Water Formation http://science.sciencemag.org/content/286/5442/1132

CaCO3 size distribution: A paleocarbonate ion proxy? https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999PA900016

How strong is the Harvardton‐Bear Constraint? https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999GB900050

What If the Conveyor Were to Shut Down? Reflections on a Possible Outcome of the Great Global Experiment ftp://rock.geosociety.org/pub/gsatoday/gt9901.pdf

Core Top 14C Ages as a Function of Latitude and Water Depth on the Ontong‐Java Plateau https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1998PA900009

2000

Abrupt climate change: causal constraints provided by the paleoclimate record https://www.sciencedirect.com/science/article/pii/S0012825200000192

Was a change in thermohaline circulation responsible for the Little Ice Age? https://www.pnas.org/content/97/4/1339.short

Converging Paths Leading to the Role of the Oceans in Climate Change https://www.annualreviews.org/doi/full/10.1146/annurev.energy.25.1.1

Late glacial diatom accumulation at 9°S in the Indian Ocean https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999PA000439

2001

Climate Swings Come into Focus http://science.sciencemag.org/content/294/5550/2308

Was the Medieval Warm Period Global? http://science.sciencemag.org/content/291/5508/1497

What caused the atmosphere’s CO2 content to rise during the last 8000 years? https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001GC000177

Rock varnish: recorder of desert wetness? https://www.geosociety.org/gsatoday/archive/11/8/pdf/i1052-5173-11-8-4.pdf

A dramatic Atlantic dissolution event at the onset of the last glaciation https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001GC000185

Reevaluation of the CaCO3 size index paleocarbonate ion proxy https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2001PA000660

Record of seafloor CaCO3 dissolution in the central equatorial Pacific https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2000GC000151

2002

Dust: Climate’s Rosetta Stone https://www.jstor.org/stable/1558157

Constraints on the glacial operation of the atlantic ocean’s conveyor circulation https://onlinelibrary.wiley.com/doi/abs/10.1560/8K19-VRHE-6F14-PFQQ

Carbonate ion concentration in glacial‐age deep waters of the Caribbean Sea https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001GC000231

2003

Does the Trigger for Abrupt Climate Change Reside in the Ocean or in the Atmosphere? http://science.sciencemag.org/content/300/5625/1519

Holocene atmospheric CO2 increase as viewed from the seafloor https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002GB001985

Shell weights from intermediate depths in the Caribbean Sea https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002GC000491

2004

Future Global Warming Scenarios http://science.sciencemag.org/content/304/5669/388.2

Glacial ventilation rates for the deep Pacific Ocean https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2003PA000974

Ventilation of the Glacial Deep Pacific Ocean http://science.sciencemag.org/content/306/5699/1169

2006

Abrupt climate change revisited https://www.sciencedirect.com/science/article/pii/S092181810600186X

The Holocene CO2 rise: Anthropogenic or natural? https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2006EO030002

Was the Younger Dryas Triggered by a Flood? http://science.sciencemag.org/content/312/5777/1146

Global warming: Take action or wait? https://link.springer.com/article/10.1007/s11434-006-1017-4

2007

CO2 Arithmetic http://science.sciencemag.org/content/315/5817/1371

Radiocarbon age of late glacial deep water from the equatorial Pacific https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2006PA001359

A 190‰ drop in atmosphere’s Δ14C during the “Mystery Interval” (17.5 to 14.5 kyr) https://www.sciencedirect.com/science/article/pii/S0012821X07000313

Is the magnitude of the carbonate ion decrease in the abyssal ocean over the last 8 kyr consistent with the 20 ppm rise in atmospheric CO2 content? https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2006PA001311

2008

Near constancy of the Pacific Ocean surface to mid-depth radiocarbon-age difference over the last 20 kyr https://www.sciencedirect.com/science/article/pii/S0012821X08004780

A need to improve reconstructions of the fluctuations in the calcite compensation depth over the course of the Cenozoic https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007PA001456

2009

A Great Basin-wide dry episode during the first half of the Mystery Interval? https://www.sciencedirect.com/science/article/abs/pii/S0277379109002509

The Mysterious 14C Decline https://www.cambridge.org/core/journals/radiocarbon/article/mysterious-14c-decline/61A16C59506B7D1B570A51A4EF3C05D3

Wally’s Quest to Understand the Ocean’s CaCO3 Cycle https://www.annualreviews.org/doi/full/10.1146/annurev.marine.010908.163936

2010

Putting the Younger Dryas cold event into context https://www.sciencedirect.com/science/article/abs/pii/S027737911000051X

Long-Term Water Prospects in the Western United States https://journals.ametsoc.org/doi/full/10.1175/2010JCLI3780.1

Search for a glacial‐age 14C‐depleted ocean reservoir https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010GL043969

2012

The Carbon Cycle and Climate Change: Memoirs of my 60 years in Science https://pubs.geoscienceworld.org/perspectives/article-abstract/1/2/221/138762

How did the hydrologic cycle respond to the two-phase mystery interval? https://www.sciencedirect.com/science/article/abs/pii/S0277379112003757

2013

Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO2 https://www.pnas.org/content/110/42/16710.short

2014

Delayed Holocene reappearance of G. menardii https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013PA002590

2015

Two contributors to the glacial CO2 decline https://www.sciencedirect.com/science/article/pii/S0012821X1500446X

2017

When climate change predictions are right for the wrong reasons https://link.springer.com/article/10.1007/s10584-017-1927-y

2018

CO2: Earth’s Climate Driver https://pubs.geoscienceworld.org/perspectives/article-abstract/7/2/117/567159

Global warming hiatus paper list, version 1.0 (224 papers), part 2

Continued from part 1.

Papers 100 – 225

NR – 100
TY – JOUR
AU – Thorne, Peter
AU – Outten, Stephen
AU – Bethke, Ingo
AU – Seland, Øyvind
TI – Investigating the recent apparent hiatus in surface temperature increases: 2. Comparison of model ensembles to observational estimates
JO – Journal of Geophysical Research: Atmospheres
VL – 120
IS – 17
UR – http://dx.doi.org/10.1002/2014JD022805
DO – 10.1002/2014JD022805
SP – 8597
EP – 8620
PY – 2015
AB – To assess published hypotheses surrounding the recent slowdown in surface warming (hiatus), we compare five available global observational surface temperature estimates to two 30-member ensembles from the Norwegian Earth System Model (NorESM). Model ensembles are initialized in 1980 from the transient historical runs and driven with forcings used in the CMIP5 experiments and updated forcings based upon current observational understanding, described in Part 1. The ensembles’ surface temperature trends are statistically indistinguishable over 1998–2012 despite differences in the prescribed forcings. There is thus no evidence that forcing errors play a significant role in explaining the hiatus according to NorESM. The observations fall either toward the lower portion of the ensembles or, for some observational estimates and regions, outside. The exception is the Arctic where the observations fall toward the upper ensemble bounds. Observational data set choices can make a large difference to findings of consistency or otherwise. Those NorESM ensemble members that exhibit Nino3.4 Sea Surface Temperature (SST) trends similar to observed also exhibit comparable tropical and to some extent global mean trends, supporting a role for El Nino Southern Oscillation in explaining the hiatus. Several ensemble members capture the marked seasonality observed in Northern Hemisphere midlatitude trends, with cooling in the wintertime and warming in the remaining seasons. Overall, we find that we cannot falsify NorESM as being capable of explaining the observed hiatus behavior. Importantly, this is not equivalent to concluding NorESM could simultaneously capture all important facets of the hiatus. Similar experiments with further, distinct, Earth System Models are required to verify our findings.
ER –

NR – 101
TY – JOUR
AU – Fyfe, John C.
AU – Meehl, Gerald A.
AU – England, Matthew H.
AU – Mann, Michael E.
AU – Santer, Benjamin D.
AU – Flato, Gregory M.
AU – Hawkins, Ed
AU – Gillett, Nathan P.
AU – Xie, Shang-Ping
AU – Kosaka, Yu
AU – Swart, Neil C.
TI – Making sense of the early-2000s warming slowdown
JF – Nature Climate Change
PY – 2016
VL – 6
SP – 224
UR – http://dx.doi.org/10.1038/nclimate2938
DO – 10.1038/nclimate2938
AB – It has been claimed that the early-2000s global warming slowdown or hiatus, characterized by a reduced rate of global surface warming, has been overstated, lacks sound scientific basis, or is unsupported by observations. The evidence presented here contradicts these claims.
ER –

NR – 102
TY – JOUR
AU – Boykoff, Maxwell T.
TI – Media discourse on the climate slowdown
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 156
UR – http://dx.doi.org/10.1038/nclimate2156
DO – 10.1038/nclimate2156
AB – We must not fall victim to decontextualized and ahistorical media accounting of climate trends.
ER –

NR – 103
TY – JOUR
AU – Somavilla, R.
AU – González-Pola, C.
AU – Schauer, U.
AU – Budéus, G.
TI – Mid-2000s North Atlantic shift: Heat budget and circulation changes
JO – Geophysical Research Letters
VL – 43
IS – 5
UR – http://dx.doi.org/10.1002/2015GL067254
DO – 10.1002/2015GL067254
SP – 2059
EP – 2068
PY – 2016
AB – Prior to the 2000s, the North Atlantic was the basin showing the greatest warming. However, since the mid-2000s during the so-called global warming hiatus, large amounts of heat were transferred in this basin from upper to deeper levels while the dominance in terms of atmospheric heat capture moved into the Indo-Pacific. Here we show that a large transformation of modal waters in the eastern North Atlantic (ENA) played a crucial role in such contrasting behavior. First, strong winter mixing in 2005 transformed ENA modal waters into a much saltier, warmer, and denser variety, transferring upper ocean heat and salt gained slowly over time to deeper layers. The new denser waters also altered the zonal dynamic height gradient reversing the southward regional flow and enhancing the access of saltier southern waters to higher latitudes. Then, the excess salinity in northern regions favored additional heat injection through deep convection events in later years.
ER –

NR – 104
TY – JOUR
T1 – Periodicities in mean sea-level fluctuations and climate change proxies: Lessons from the modelling for coastal management
AU – Baker, R.G.V.
AU – McGowan, S.A.
JO – Ocean & Coastal Management
VL – 98
SP – 187
EP – 201
PY – 2014
DO – https://doi.org/10.1016/j.ocecoaman.2014.05.027
UR – http://www.sciencedirect.com/science/article/pii/S0964569114001781
AB – The question of whether sea levels and global temperatures are accelerating or decelerating is a major source of current debate. Single taper and multi-taper spectral analysis from seventeen globally distributed tidal stations and twenty climate proxies show aggregate significant common periodicities in mean sea level fluctuations and the climate proxies of approximately 7 yr, 13 yr, 23 yr, 32 yr, 41 yr, 53 yr, 66 yr, 88 yr, 105 yr and 132 yr, respectively. These periods are shown to strongly correlate with an harmonic sequence of n, m = n + n/4 and p = n + n/2n for n = 5.5 yr and this synchronicity allows for a climate state function to be defined by Lotka–Volterra limit cycles. Such a model can include both anthropogenic warming and complex natural cycles, based on past evidence, and these cycles can form or bifurcate into extreme events close to critical values. The model suggests that accelerating sea levels can be in-phase, but lag decelerating global temperatures or vice versa, so a ‘pause’ in global warming should not be surprising. Further, the model can simulate the uneven regional effect of climate responses and replicate the chaos apparent in monthly sea-level records. The approach poses ‘a planner’s dilemma’ whereby the likelihood of a present 1 in 100 yr positive extreme event can either be caused by anthropogenic warming within shorter cycles or by a stationary mean in a longer cycle. We simply show that for rising average temperatures in a double period cascading model, there would be a three-fold increase in the likelihood of an equivalent 1 in 100 yr positive extreme event relative to present over a 20 yr period. A consequence to the ‘planner’s dilemma’ is the ‘manager’s risk imperative’ where risk cycles can be quantified into strategic GIS maps of potential future inundations: identifying vulnerability, defining possible economic impacts and underpinning response strategies that are legally defensible and transparent to a range of stakeholders.
ER –

NR – 105
TY – JOUR
AU – Morrison, Kyle W.
AU – Battley, Phil F.
AU – Sagar, Paul M.
AU – Thompson, David R.
PY – 2015
TI – Population dynamics of Eastern Rockhopper Penguins on Campbell Island in relation to sea surface temperature 1942–2012: current warming hiatus pauses a long-term decline
JO – Polar Biology
SP – 163
EP – 177
VL – 38
IS – 2
AB – Major population changes of marine mega-fauna are ongoing as global warming, and other anthropogenic drivers affect prey availability. The historical stronghold of the Eastern Rockhopper Penguin (Eudyptes chrysocome filholi) was New Zealand’s sub-Antarctic Campbell Island, but the population declined by 94 % between 1942 and 1984. The apparent mechanism of collapse was warm ocean temperatures causing an inadequate food supply. Eudyptes penguin population declines are ongoing at some breeding sites, highlighting the need to investigate the population trend on Campbell Island since 1984. We estimated the Eastern Rockhopper Penguin breeding population size through physical and photo-counts of birds and nests in 2012, and changes in colony area relative to 1984 and 1996 photographs. We estimated the 2012 population size at 33,239 breeding pairs, a 21.8 % decrease from an (adjusted) estimate of 42,528 pairs in 1984. Although substantial, the recent 1984–2012 decline occurred at a much slower rate (? = 0.991) than the 1942–1984 decline (? = 0.940). Despite great variation in trends between colonies ostensibly linked to differences in predation rates, the recent decline occurred primarily between 1984 and 1996, and thereafter the overall population grew. A 100-year time series of extended reconstructed sea surface temperatures (ERSST) confirmed that the population declined during warm periods and increased during cool periods, but that the initial decline began before increases in regional ERSST. Population growth after 1996 appears related to the current global warming hiatus, lower ERSST, and increased abundance of a key prey species. We predict a continuation of the long-term population decline after warming resumes.
UR – https://doi.org/10.1007/s00300-014-1575-x
DO – 10.1007/s00300-014-1575-x
ER –

NR – 106
TY – JOUR
AU – An, Wenling
AU – Hou, Shugui
AU – Zhang, Wangbin
AU – Wu, Shuangye
AU – Xu, Hao
AU – Pang, Hongxi
AU – Wang, Yetang
AU – Liu, Yaping
T1 – Possible recent warming hiatus on the northwestern Tibetan Plateau derived from ice core records
PY – 2016
AB – Many studies have reported enhanced warming trend on the Tibetan Plateau (TP), even during the warming hiatus period. However, most of these studies are based on instrumental data largely collected from the eastern TP, whereas the temperature trend over the extensive northwestern TP remains uncertain due to few meteorological stations. Here we combined the stable isotopic d(18)O record of an ice core recovered in 2012 from the Chongce glacier with the d(18)O records of two other ice cores (i.e., Muztagata and Zangser Kangri) in the same region to establish a regional temperature series for the northwestern TP. The reconstruction shows a significant warming trend with a rate of 0.74?±?0.12?°C/decade for the period 1970–2000, but a decreasing trend from 2001 to 2012. This is consistent with the reduction of warming rates during the recent decade observed at the only two meteorological stations on the northwestern TP, even though most stations on the eastern TP have shown persistent warming during the same period. Our results suggest a possible recent warming hiatus on the northwestern TP. This could have contributed to the relatively stable status of glaciers in this region.
SP – 32813
VL – 6
DO – 10.1038/srep32813
UR – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017263/
JF – Scientific Reports
ER –

NR – 107
TY – JOUR
T1 – Present contributions to sea level rise by thermal expansion and ice melting and implication on coastal management
AU – Parker, Albert
JO – Ocean & Coastal Management
VL – 98
SP – 202
EP – 211
PY – 2014
DO – https://doi.org/10.1016/j.ocecoaman.2014.05.026
UR – http://www.sciencedirect.com/science/article/pii/S0964569114001744
AB – Increasing ocean heat content has been suggested on the basis of theories. Reconstructions (modelling results based on selected scattered measurements) and simulations (modelling results not based on observations) have both shown a significant warming since the year 1970 that increased at an ever faster rate over the 14 years this century. It is shown here that, contrary to this claim, the detailed measurements of the ocean temperature and salinity by the sampling buoys of the ARGO project show only minor changes of temperature and salinity since the early 2000s. The ARGO results cover the ocean layers 0–2000m except for the North and South Poles. The satellite NSSTC surface air temperature measurements over the world oceans show a global cooling over the last 11 years, and the satellite NSDIC sea ice extent measurements show globally increasing ice coverage over the North and South Poles. The North Pole sea ice is certainly reducing, but over the last 11 years the growth of the South Pole sea ice has more than compensated that loss. The true measurements are in marked contrast to theoretical reconstructions and simulations. This result has a huge implication on coastal management that should be based on observationally derived forecasts rather than “projections” of models lacking validation.
ER –

NR – 108
TY – JOUR
T1 – Recent hiatus caused by decadal shift in Indo-Pacific heating
JF – Science
SP – 532
LP – 535
DO – 10.1126/science.aaa4521
VL – 349
IS – 6247
AU – Nieves, Veronica
AU – Willis, Josh K.
AU – Patzert, William C.
UR – http://science.sciencemag.org/content/349/6247/532.abstract
AB – Global warming apparently slowed, or even stopped, during the first decade of the 21st century. This pause is commonly called the “hiatus.” We know, however, that Earth's climate system is accumulating excess solar energy owing to the build-up of greenhouse gases in the atmosphere. Where, then, has this energy gone if not into the air? Nieves et al. find that over this period, the surface Pacific Ocean has cooled but the upper Indian and Southern Oceans have warmed. Thus, the decade-long hiatus that began in 2003 would appear to be the result of a redistribution of heat within the ocean, rather than a change in the whole-Earth warming rate.Science, this issue p. 532Recent modeling studies have proposed different scenarios to explain the slowdown in surface temperature warming in the most recent decade. Some of these studies seem to support the idea of internal variability and/or rearrangement of heat between the surface and the ocean interior. Others suggest that radiative forcing might also play a role. Our examination of observational data over the past two decades shows some significant differences when compared to model results from reanalyses and provides the most definitive explanation of how the heat was redistributed. We find that cooling in the top 100-meter layer of the Pacific Ocean was mainly compensated for by warming in the 100- to 300-meter layer of the Indian and Pacific Oceans in the past decade since 2003.
ER –

NR – 109
TY – JOUR
AU – Gonzalez-Hidalgo, José Carlos
AU – Peña-Angulo, Dhais
AU – Brunetti, Michele
AU – Cortesi, Nicola
TI – Recent trend in temperature evolution in Spanish mainland (1951–2010): from warming to hiatus
JO – International Journal of Climatology
VL – 36
IS – 6
UR – http://dx.doi.org/10.1002/joc.4519
DO – 10.1002/joc.4519
SP – 2405
EP – 2416
PY – 2016
AB – The most recent debate on global warming focuses on the hiatus in global temperature, for which several explanations have been proposed. On the other hand, spatial variability and nonlinearity in temperature evolution has been recognized as a key point in global change analyses. In this study, we analyse the evolution of the warming rate in the Spanish mainland using the MOTEDAS data set for the last 60 years (1951–2010). Our special emphasis is on the last decades to detect and identify a possible hiatus, and to determine the effects of daytime (Tmax) and night-time (Tmin) records at annual and seasonal scale on the hiatus. Moving windows running trend analyses were applied to calculate temperature trend and significance for any temporal window from the beginning to the end of the series, ranging from 20 years to the whole series length (60 years) The results suggest that the warming rate in the Spanish mainland reached a maximum between 1970 and 1990, followed by a decrease in intensity in both Tmax and Tmin until the present. Furthermore, the decrease in the warming rate in Tmax has been higher than in Tmin for the last three decades; therefore, recent annual warming rates appears to depend more on Tmin than on Tmax. Significant trends disappear from the middle of the 1980s at any temporal window length in both Tmax and Tmin at annual and seasonal scales except in spring Tmin. Some differences among seasons are evident and, during the last few decades, the highest rates of warming are found in spring and summer, with Tmax and Tmin behaving in different ways. This study highlights how the warming rate is highly dependent on the length of the period analysed.
ER –

NR – 110
TY – JOUR
AU – Zhang, Yuanjie
AU – Gao, Zhiqiu
AU – Pan, Zaitao
AU – Li, Dan
AU – Wan, Bingcheng
TI – Record-breaking temperatures in China during the warming and recent hiatus periods
JO – Journal of Geophysical Research: Atmospheres
VL – 121
IS – 1
UR – http://dx.doi.org/10.1002/2015JD023886
DO – 10.1002/2015JD023886
SP – 241
EP – 258
PY – 2016
AB – The observed and modeled record-breaking temperature (RBT) frequency in China is analyzed for different segments of the period 1961–2050 including the hiatus period. It is found that significant changes in the RBT frequency occurred earlier, with greater amplitude, for daily minimum temperatures (TN) compared to maximum temperatures (TX) during the past five decades. Changes in the RBT frequency can be mostly explained by the mean warming trend, especially for TN, while in summer also slightly by variance. Moreover, mean climate change affects more the multiday mean RBT than the single-day counterpart as RBT occurrence is inversely proportional to variance that is smaller for multiday means. In the hiatus period (1998–2013), the ratios of record highs to lows in summer continue to increase in southern China primarily due to the lower frequency of record lows, since the decreasing temperature variance suppressed the increase in record highs under the summer warming. While the winter ratios decreased significantly across most of the country due to the winter cooling. Model simulations show a much smaller asymmetry of the RBT frequency between TX and TN as compared to the observations. The 28-model median overestimates the ratios for TX owning to missing the relative cooling in the “warming hole” region and is unable to reproduce the RBT characteristics in the hiatus period. Under a high-emission scenario, increasing rates of future temperature extremes are projected to accelerate with almost doubling ratio trends in the first half of 21st century compared to the historical results.
ER –

NR – 111
TY – JOUR
T1 – Revisiting the Relationship between Observed Warming and Surface Pressure in the Tibetan Plateau
AU – You, Qinglong
AU – Jiang, Zhihong
AU – Moore, G. W. K.
AU – Bao, Yuntao
AU – Kong, Lei
AU – Kang, Shichang
PY – 2016
DO – 10.1175/JCLI-D-15-0834.1
JF – Journal of Climate
SP – 1721
EP – 1737
VL – 30
IS – 5
AB – The Tibetan Plateau (TP) has an average elevation of over 4000 m and with its surrounding mountains is regarded as Earth?s ?third pole.? As a result of its size and height, climate change in the TP has its own unique characteristics that include a proposed positive correlation between the surface temperature and pressure. This study examines the trends and relationships between the surface pressure and temperature in the TP through the examination of monthly mean data from 71 stations during 1961?2013. On annual, seasonal, and monthly time scales, the TP exhibits a statistically significant warming trend that attains a rate of 0.30°C decade?1 for annual means over the period 1961?2013. The most pronounced warming occurs in winter, in agreement with previous studies, with evidence of acceleration in the rate after the mid-1980s and the global warming slowdown period. For the entire period of 1961?2013, the surface pressure in the TP has a positive trend of 0.08 hPa decade?1 on an annual basis, again with the largest trends occurring in winter. However, unlike what occurred with the surface temperature, the trend in surface pressure, in most cases, reversed sign after the mid-1980s. The trend in the geopotential height at 500 hPa from the National Centers for Environmental Prediction?National Center for Atmospheric Research (NCEP?NCAR) reanalysis is consistent with the observed surface pressure trends. Over the period 1961?2013, there is a seasonal shift in the nature of the relationship between the surface temperature and pressure with a negative correlation during summer and autumn, and a positive correlation during winter. This suggests that the nature of the relationship between these two climate elements reflects the changing nature of the seasonal snow cover (land surface property) and cloud in the region.
UR – https://doi.org/10.1175/JCLI-D-15-0834.1
ER –

NR – 112
TY – JOUR
T1 – Revisiting Whether Recent Surface Temperature Trends Agree with the CMIP5 Ensemble
AU – Lin, Marena
AU – Huybers, Peter
PY – 2016
DO – 10.1175/JCLI-D-16-0123.1
JF – Journal of Climate
SP – 8673
EP – 8687
VL – 29
IS – 24
AB – In an earlier study, a weaker trend in global mean temperature over the past 15 years relative to the preceding decades was characterized as significantly lower than those contained within the phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensemble. In this study, divergence between model simulations and observations is estimated using a fixed-intercept linear trend with a slope estimator that has one-third the noise variance compared to simple linear regression. Following the approach of the earlier study, where intermodel spread is used to assess the distribution of trends, but using the fixed-intercept trend metric demonstrates that recently observed trends in global mean temperature are consistent with the CMIP5 ensemble for all 15-yr intervals of observation?model divergence since 1970. Significant clustering of global trends according to modeling center indicates that the spread in CMIP5 trends is better characterized using ensemble members drawn across models as opposed to using ensemble members from a single model. Despite model?observation consistency at the global level, substantial regional discrepancies in surface temperature trends remain.
UR – https://doi.org/10.1175/JCLI-D-16-0123.1
ER –

NR – 113
TY – JOUR
T1 – Role of Changes in Mean Temperatures versus Temperature Gradients in the Recent Widening of the Hadley Circulation
AU – Adam, Ori
AU – Schneider, Tapio
AU – Harnik, Nili
PY – 2014
DO – 10.1175/JCLI-D-14-00140.1
JF – Journal of Climate
SP – 7450
EP – 7461
VL – 27
IS – 19
AB – The Hadley circulation (HC) has widened in recent decades, and it widens as the climate warms in simulations. But the mechanisms responsible for the widening remain unclear, and the widening in simulations is generally smaller than observed.To identify mechanisms responsible for the HC widening and for model?observation discrepancies, this study analyzes how interannual variations of tropical-mean temperatures and meridional temperature gradients influence the HC width. Changes in mean temperatures are part of any global warming signal, whereas changes in temperature gradients are primarily associated with ENSO. Within this study, 6 reanalysis datasets, 22 Atmospheric Modeling Intercomparison Project (AMIP) simulations, and 11 historical simulations from phase 5 of the Climate Modeling Intercomparison Project (CMIP5) are analyzed, covering the years 1979?2012. It is found that the HC widens as mean temperatures increase or as temperature gradients weaken in most reanalyses and climate models. On average, climate models exhibit a smaller sensitivity of HC width to changes in mean temperatures and temperature gradients than do reanalyses. However, the sensitivities differ substantially among reanalyses, rendering the HC response to mean temperatures in climate models not statistically different from that in reanalyses.While global-mean temperatures did not increase substantially between 1997 and 2012, the HC continued to widen in most reanalyses. The analysis here suggests that the HC widening from 1979 to 1997 is primarily the result of global warming, whereas the widening of the HC from 1997 to 2012 is associated with increased midlatitude temperatures and hence reduced temperature gradients during this period.
UR – https://doi.org/10.1175/JCLI-D-14-00140.1
ER –

NR – 114
TY – JOUR
AU – Wei, Meng
AU – Qiao, FangLi
PY – 2017
TI – Attribution analysis for the failure of CMIP5 climate models to simulate the recent global warming hiatus
JO – Science China Earth Sciences
SP – 397
EP – 408
VL – 60
IS – 2
AB – The Coupled Model Inter-comparison Project Phase 5 (CMIP5) contains a group of state-of-the-art climate models and represents the highest level of climate simulation thus far. However, these models significantly overestimated global mean surface temperature (GMST) during 2006–2014. Based on the ensemble empirical mode decomposition (EEMD) method, the long term change of the observed GMST time series of HadCRUT4 records during 1850–2014 was analyzed, then the simulated GMST by 33 CMIP5 climate models was assessed. The possible reason that climate models failed to project the recent global warming hiatus was revealed. Results show that during 1850–2014 the GMST on a centennial timescale rose with fluctuation, dominated by the secular trend and the multi-decadal variability (MDV). The secular trend was relatively steady beginning in the early 20th century, with an average warming rate of 0.0883°C/decade over the last 50 years. While the MDV (with a ~65-year cycle) showed 2.5 multi-decadal waves during 1850–2014, which deepened and steepened with time, the alarming warming over the last quarter of the 20th century was a result of the concurrence of the secular warming trend and the warming phase of the MDV, both of which accounted one third of the temperature increase during 1975–1998. Recently the slowdown of global warming emerged as the MDV approached its third peak, leading to a reduction in the warming rate. A comparative analysis between the GMST time series derived from HadCRUT4 records and 33 CMIP5 model outputs reveals that the GMSTs during the historical simulation period of 1850–2005 can be reproduced well by models, especially on the accelerated global warming over the last quarter of 20th century. However, the projected GMSTs and their linear trends during 2006–2014 under the RCP4.5 scenario were significantly higher than observed. This is because the CMIP5 models confused the MDV with secular trend underlying the GMST time series, which results in a fast secular trend and an improper MDV with irregular phases and small amplitudes. This implies that the role of atmospheric CO2 in global warming may be overestimated, while the MDV which is an interior oscillation of the climate system may be underestimated, which should be related to insufficient understanding of key climatic internal dynamic processes. Our study puts forward an important criterion for the new generation of climate models: they should be able to simulate both the secular trend and the MDV of GMST.
UR – https://doi.org/10.1007/s11430-015-5465-y
DO – 10.1007/s11430-015-5465-y
ER –

NR – 115
TY – JOUR
AU – Zhou, Chunlüe
AU – Wang, Kaicun
T1 – Coldest Temperature Extreme Monotonically Increased and Hottest Extreme Oscillated over Northern Hemisphere Land during Last 114 Years
PY – 2016
AB – Most studies on global warming rely on global mean surface temperature, whose change is jointly determined by anthropogenic greenhouse gases (GHGs) and natural variability. This introduces a heated debate on whether there is a recent warming hiatus and what caused the hiatus. Here, we presented a novel method and applied it to a 5°?×?5° grid of Northern Hemisphere land for the period 1900 to 2013. Our results show that the coldest 5% of minimum temperature anomalies (the coldest deviation) have increased monotonically by 0.22?°C/decade, which reflects well the elevated anthropogenic GHG effect. The warmest 5% of maximum temperature anomalies (the warmest deviation), however, display a significant oscillation following the Atlantic Multidecadal Oscillation (AMO), with a warming rate of 0.07?°C/decade from 1900 to 2013. The warmest (0.34?°C/decade) and coldest deviations (0.25? °C/decade) increased at much higher rates over the most recent decade than last century mean values, indicating the hiatus should not be interpreted as a general slowing of climate change. The significant oscillation of the warmest deviation provides an extension of previous study reporting no pause in the hottest temperature extremes since 1979, and first uncovers its increase from 1900 to 1939 and decrease from 1940 to 1969.
SP – 25721
VL – 6
DO – 10.1038/srep25721
UR – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4865736/
JF – Scientific Reports
ER –

NR – 116
TY – JOUR
AU – Dai, Aiguo
AU – Fyfe, John C.
AU – Xie, Shang-Ping
AU – Dai, Xingang
TI – Decadal modulation of global surface temperature by internal climate variability
JF – Nature Climate Change
PY – 2015
VL – 5
SP – 555
UR – http://dx.doi.org/10.1038/nclimate2605
DO – 10.1038/nclimate2605
AB – Despite a steady increase in atmospheric greenhouse gases (GHGs), global-mean surface temperature (T) has shown no discernible warming since about 2000, in sharp contrast to model simulations, which on average project strong warming1,2,3. The recent slowdown in observed surface warming has been attributed to decadal cooling in the tropical Pacific1,4,5, intensifying trade winds5, changes in El Niño activity6,7, increasing volcanic activity8,9,10 and decreasing solar irradiance7. Earlier periods of arrested warming have been observed but received much less attention than the recent period, and their causes are poorly understood. Here we analyse observed and model-simulated global T fields to quantify the contributions of internal climate variability (ICV) to decadal changes in global-mean T since 1920. We show that the Interdecadal Pacific Oscillation (IPO) has been associated with large T anomalies over both ocean and land. Combined with another leading mode of ICV, the IPO explains most of the difference between observed and model-simulated rates of decadal change in global-mean T since 1920, and particularly over the so-called ‘hiatus’ period since about 2000. We conclude that ICV, mainly through the IPO, was largely responsible for the recent slowdown, as well as for earlier slowdowns and accelerations in global-mean T since 1920, with preferred spatial patterns different from those associated with GHG-induced warming or aerosol-induced cooling. Recent history suggests that the IPO could reverse course and lead to accelerated global warming in the coming decades.
ER –

NR – 117
TY – JOUR
AU – Lin, Yong
AU – Franzke, Christian L. E.
TI – Scale-dependency of the global mean surface temperature trend and its implication for the recent hiatus of global warming
JF – Scientific Reports
PY – 2015
VL – 5
SP – 12971
UR – http://dx.doi.org/10.1038/srep12971
DO – 10.1038/srep12971
AB – Studies of the global mean surface temperature trend are typically conducted at a single (usually annual or decadal) time scale. The used scale does not necessarily correspond to the intrinsic scales of the natural temperature variability. This scale mismatch complicates the separation of externally forced temperature trends from natural temperature fluctuations. The hiatus of global warming since 1999 has been claimed to show that human activities play only a minor role in global warming. Most likely this claim is wrong due to the inadequate consideration of the scale-dependency in the global surface temperature (GST) evolution. Here we show that the variability and trend of the global mean surface temperature anomalies (GSTA) from January 1850 to December 2013, which incorporate both land and sea surface data, is scale-dependent and that the recent hiatus of global warming is mainly related to natural long-term oscillations. These results provide a possible explanation of the recent hiatus of global warming and suggest that the hiatus is only temporary.
ER –

NR – 118
TY – JOUR
T1 – Does the NMME Capture a Recent Decadal Shift toward Increasing Drought Occurrence in the Southwestern United States?
AU – Barnston, Anthony G.
AU – Lyon, Bradfield
PY – 2015
DO – 10.1175/JCLI-D-15-0311.1
JF – Journal of Climate
SP – 561
EP – 581
VL – 29
IS – 2
AB – A global-scale decadal climate shift, beginning in 1998/99 and enduring through 2013, has been documented in recent studies, with associated precipitation shifts in key regions throughout the world. These precipitation shifts are most easily detected during March?May when ENSO effects are weak. Analyses have linked this climate shift to a shift in the Pacific decadal variability (PDV) pattern to its negative phase. Here the authors evaluate the predictive skill of the North American Multimodel Ensemble (NMME), and the CFSv2 model alone, in maintaining the observed precipitation shifts in seasonal forecasts, emphasizing the southwestern United States where deficient precipitation has tended to prevail since the late 1990s.The NMME hindcasts out to 6 months lead are found to maintain the observed decadal precipitation shifts in key locations qualitatively correctly, but with increasingly underestimated amplitude with increasing lead time. This finding holds in the separate CFSv2 model hindcasts. The decadal precipitation shift is relatively well reproduced in the southwestern United States. The general underestimation of the precipitation shift is suggested to be related to a muted reproduction of the observed shift in Pacific sea surface temperature (SST). This conclusion is supported by runs from a different (but overlapping) set of atmospheric models, which when forced with observed SST reproduce the decadal shifts quite well. Overall, the capability of the NMME model hindcasts to reflect the observed decadal rainfall pattern shift, but with weakened amplitude (especially at longer leads), underscores the broader challenge of retaining decadal signals in predictions of droughts and pluvials at seasonal-to-interannual time scales.
UR – https://doi.org/10.1175/JCLI-D-15-0311.1
ER –

NR – 119
TY – JOUR
AU – Knutson, Thomas R.
AU – Ploshay, Jeffrey J.
PY – 2016
TI – Detection of anthropogenic influence on a summertime heat stress index
JO – Climatic Change
SP – 25
EP – 39
VL – 138
IS – 1
AB – One of the most consequential impacts of anthropogenic warming on humans may be increased heat stress, combining temperature and humidity effects. Here we examine whether there are now detectable changes in summertime heat stress over land regions. As a heat stress metric we use a simplified wet bulb globe temperature (WBGT) index. Observed trends in WBGT (1973–2012) are compared to trends from CMIP5 historical simulations (eight-model ensemble) using either anthropogenic and natural forcing agents combined or natural forcings alone. Our analysis suggests that there has been a detectable anthropogenic increase in mean summertime heat stress since 1973, both globally and in most land regions analyzed. A detectable increase is found over a larger fraction of land for WBGT than for temperature, as WBGT summertime means have lower interannual variability than surface temperature at gridbox scales. Notably, summertime WBGT over land has continued increasing in recent years–consistent with climate models–despite the apparent ‘hiatus’ in global warming and despite a decreasing tendency in observed relative humidity over land since the late 1990s.
UR – https://doi.org/10.1007/s10584-016-1708-z
DO – 10.1007/s10584-016-1708-z
ER –

NR – 120
TY – JOUR
AU – Dong, Lu
AU – Zhou, Tianjun
AU – Dai, Aiguo
AU – Song, Fengfei
AU – Wu, Bo
AU – Chen, Xiaolong
TI – The Footprint of the Inter-decadal Pacific Oscillation in Indian Ocean Sea Surface Temperatures
JO – Scientific Reports
PY – 2016
VL – 6
SP – 21251
UR – http://dx.doi.org/10.1038/srep21251
DO – 10.1038/srep21251
AB – Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871–2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcings account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. The decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.
ER –

NR – 121
TY – JOUR
AU – Blanchette, Jeanne
AU – Huang, Yi
TI – Earth Infrared Radiation Spectra During Global Warming Hiatus
JO – McGill Science Undergraduate Research Journal
PY – 2015
VL – 10
IS – 1
SP – 14
EP – 17
UR – http://msurj.mcgill.ca/vol10/iss1/MSURJ2015.pdf#page=14
AB – Background: Since 1997-98, observations of annual mean surface temperature have shown a slowdown of global temperature increases, suggesting a hiatus in global warming. Given this finding, we are interested in diagnosing trends in the Earth’s outgoing longwave radiation (OLR) spectrum throughout the last decade. Methods: We calculated the trend in OLR measured by the Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite between 2003 and 2013, and compared these results with the trend in atmospheric and surface temperature and tropospheric absolute humidity, obtained from AIRS retrieval product and from the ECMWF (European Center for Medium range Weather Forecasting) Re-Analysis (ERA) interim product. We also isolated the greenhouse effect from the OLR trend by subtracting the amount of surface radiation emitted from the total radiation received by the sounder. Results: The OLR trend is negative in the CO2 absorption band, negative in the window spectral region, and positive in the water vapor band. The trend in surface and tropospheric temperature is negative, as is the trend in tropospheric absolute humidity. The greenhouse effect is increasing in the CO2 band, generally slightly increasing in the window region, and decreasing in the H2O band. Conclusion: Our results show that the CO2 forcing was still present globally through the last decade, with steadily increasing effects. Contributors to the negative trend in OLR in the window region are a small decrease in surface temperature and a strong decrease in tropospheric temperature, where tropospheric H2O emit radiation to space. The decreasing effect of water vapor in the H2O band is due to decreasing tropospheric humidity. This analysis will allow us to detect the changes in greenhouse gas forcing, to examine the correlated surface temperature response, and to study changes and effects in tropospheric water vapor concentration.
ER –

NR – 122
TY – JOUR
AU – Zhou, Chunlüe
AU – Wang, Kaicun
TI – Spatiotemporal Divergence of the Warming Hiatus over Land Based on Different Definitions of Mean Temperature
JO – Scientific Reports
PY – 2016
VL – 6
SP – 31789
UR – http://dx.doi.org/10.1038/srep31789
DO – 10.1038/srep31789
AB – Existing studies of the recent warming hiatus over land are primarily based on the average of daily minimum and maximum temperatures (T2). This study compared regional warming rates of mean temperature based on T2 and T24 calculated from hourly observations available from 1998 to 2013. Both T2 and T24 show that the warming hiatus over land is apparent in the mid-latitudes of North America and Eurasia, especially in cold seasons, which is closely associated with the negative North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) and cold air propagation by the Arctic-original northerly wind anomaly into mid-latitudes. However, the warming rates of T2 and T24 are significantly different at regional and seasonal scales because T2 only samples air temperature twice daily and cannot accurately reflect land-atmosphere and incoming radiation variations in the temperature diurnal cycle. The trend has a standard deviation of 0.43?°C/decade for T2 and 0.41?°C/decade for T24, and 0.38?°C/decade for their trend difference in 5°?×?5° grids. The use of T2 amplifies the regional contrasts of the warming rate, i.e., the trend underestimation in the US and overestimation at high latitudes by T2.
ER –

NR – 123
TY – JOUR
AU – Urabe, Yusuke
AU – Maeda, Shuhei
TI – The Relationship between Japans Recent Temperature and Decadal Variability
JO – SOLA
PY – 2014
DA – 2014
VL – 10
SP – 176-179
UR – https://ci.nii.ac.jp/naid/130004704543/en/
DO – 10.2151/sola.2014-037
AB – Since the late 1990s, surface temperature has been higher than (near or lower than) normal for summer/autumn (winter/spring) over Japan, indicating that the seasonal temperature contrast has become enhanced. In order to relate this to global-scale variability on decadal timescale, atmospheric re-analysis and ocean assimilation datasets were analyzed. It is suggested that the La Niña-like conditions which have been frequently observed in the tropical Pacific oceanic and atmospheric fields in the last decade have contributed to these temperature tendencies observed in Japan. These global characteristics are consistent with the global warming hiatus. The results presented here indicate that not only interannual variability and century-scale long-term trends but also decadal variability in global oceanic and atmospheric fields significantly affect Japans temperature.
ER –

NR – 124
TY – JOUR
AU – He, Haozhe
AU – Yang, Jing
AU – Wu, Liguang
AU – Gong, Daoyi
AU – Wang, Bin
AU – Gao, Miaoni
PY – 2017
TI – Unusual growth in intense typhoon occurrences over the Philippine Sea in September after the mid-2000s
JO – Climate Dynamics
SP – 1893
EP – 1910
VL – 48
IS – 5
AB – During the global warming hiatus period (1998–present), a pronounced increase in the number of intense typhoon occurrences was identified over the Philippine Sea (PS: 5°–25°N, 125°–140°E) in September after the mid-2000s. Comparing two periods before and after the mid-2000s indicates that intense typhoons rarely occurred over the PS in September before the mid-2000s, with a frequency of fewer than 0.4 per year, but reached up to nearly 1.5 per year after the mid-2000s. The abrupt increase in intense typhoon occurrences over the PS was primarily attributed to increased tropical cyclone (TC) genesis and favorable large-scale conditions for TC intensification. The increase in TC genesis number over the PS was caused by contributory dynamical conditions, including positive low-level relative vorticity anomalies and anomalous ascents, which corresponded to a southwestward shift and strengthening of the monsoon trough. In addition, among the favorable large-scale conditions, the increased relative humidity that resulted from intensified moisture flux convergence exerted essential effect on the TC intensification. These changes in atmospheric environmental conditions favoring intense typhoon occurrences over the PS were primarily associated with the change in the tropical Indo-Pacific sea surface temperature (SST) around the mid-2000s. Besides that, the positive feedback TCs exerted on the circulation was also conducive to the unusual growth in intense typhoon occurrences over the PS. And note that the role of SST anomalies in the air–sea interaction is the key to interpret why the unique phenomenon only occurred in September.
UR – https://doi.org/10.1007/s00382-016-3181-9
DO – 10.1007/s00382-016-3181-9
ER –

NR – 125
TY – JOUR
AU – Lovejoy, S.
TI – Using scaling for macroweather forecasting including the pause
JO – Geophysical Research Letters
VL – 42
IS – 17
UR – http://dx.doi.org/10.1002/2015GL065665
DO – 10.1002/2015GL065665
SP – 7148
EP – 7155
PY – 2015
AB – The ScaLIng Macroweather model (SLIMM) is a new class of stochastic atmospheric model. It exploits the large system memory to overcome the biases of conventional numerical climate models, it makes hindcasts and forecasts over macroweather forecast horizons (˜10?days to decades). Using the simplest (scalar), SLIMM model with only two parameters, we present various twentieth century hindcasts including several of the slowdown (“pause”) in the warming since 1998. The 1999–2013 hindcast is accurate to within ±0.11?K, with all the 2002–2013 anomalies hindcast to within ±0.02?K. In comparison, the Climate Model Intercomparison Project Phase 3 hindcasts were on average about 0.2?K too warm.
ER –

NR – 126
TY – JOUR
AU – Guan, Xiaodan
AU – Huang, Jianping
AU – Guo, Ruixia
AU – Lin, Pu
TI – The role of dynamically induced variability in the recent warming trend slowdown over the Northern Hemisphere
JO – Scientific Reports
PY – 2015
VL – 5
SP – 12669
UR – http://dx.doi.org/10.1038/srep12669
DO – 10.1038/srep12669
AB – Since the slowing of the trend of increasing surface air temperature (SAT) in the late 1990?s, intense interest and debate have arisen concerning the contribution of human activities to the warming observed in previous decades. Although several explanations have been proposed for the warming-trend slowdown (WTS), none has been generally accepted. We investigate the WTS using a recently developed methodology that can successfully identify and separate the dynamically induced and radiatively forced SAT changes from raw SAT data. The dynamically induced SAT changes exhibited an obvious cooling effect relative to the warming effect of the adjusted SAT in the hiatus process. A correlation analysis suggests that the changes are dominated primarily by the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). Our results confirm that dynamically induced variability caused the WTS. The radiatively forced SAT changes are determined mainly by anthropogenic forcing, indicating the warming influence of greenhouse gases (GHGs), which reached levels of 400?ppm during the hiatus period. Therefore, the global SAT will not remain permanently neutral. The increased radiatively forced SAT will be amplified by increased dynamically induced SAT when the natural mode returns to a warming phase in the next period.
ER –

NR – 127
TY – JOUR
AU – Pasini, Antonello
AU – Triacca, Umberto
AU – Attanasio, Alessandro
PY – 2017
TI – Evidence for the role of the Atlantic multidecadal oscillation and the ocean heat uptake in hiatus prediction
JO – Theoretical and Applied Climatology
SP – 873
EP – 880
VL – 129
IS – 3
AB – The recent hiatus in global temperature at the surface has been analysed by several studies, mainly using global climate models. The common accepted picture is that since the late 1990s, the increase in anthropogenic radiative forcings has been counterbalanced by other factors, e.g., a decrease in natural forcings, augmented ocean heat storage and negative phases of ocean–atmosphere-coupled oscillation patterns. Here, simple vector autoregressive models are used for forecasting the temperature hiatus in the period 2001–2014. This gives new insight into the problem of understanding the ocean contribution (in terms of heat uptake and atmosphere–ocean-coupled oscillations) to the appearance of this recent hiatus. In particular, considering data about the ocean heat content until a depth of 700 m and the Atlantic multidecadal oscillation is necessary for correctly forecasting the hiatus, so catching both trend and interannual variability. Our models also show that the ocean heat uptake is substantially driven by the natural component of the total radiative forcing at a decadal time scale, confining the importance of the anthropogenic influences to a longer range warming of the ocean.
UR – https://doi.org/10.1007/s00704-016-1818-6
DO – 10.1007/s00704-016-1818-6
ER –

NR – 128
TY – JOUR
T1 – Extreme North America Winter Storm Season of 2013/14: Roles of Radiative Forcing and the Global Warming Hiatus
AU – Yang, Xiaosong
AU – Vecchi, G. A.
AU – Delworth, T. L.
AU – Paffendorf, K.
AU – Jia, L.
AU – Gudgel, R.
AU – Zeng, F.
AU – Underwood, Seth D.
PY – 2015
DO – 10.1175/BAMS-D-15-00133.1
JF – Bulletin of the American Meteorological Society
SP – S25
EP – S28
VL – 96
IS – 12
UR – https://doi.org/10.1175/BAMS-D-15-00133.1
AB – The extreme 2013/14 winter storm season over much of North America was made more likely by the multiyear anomalous tropical Pacific winds associated with the recent global warming hiatus.
ER –

NR – 129
TY – JOUR
AU – Huang, Rui Xin
PY – 2015
TI – Heaving modes in the world oceans
JO – Climate Dynamics
SP – 3563
EP – 3591
VL – 45
IS – 11
AB – Part of climate changes on decadal time scales can be interpreted as the result of adiabatic motions associated with the adjustment of wind-driven circulation, i.e., the heaving of the isopycnal surfaces. Heat content changes in the ocean, including hiatus of global surface temperature and other phenomena, can be interpreted in terms of heaving associated with adjustment of wind-driven circulation induced by decadal variability of wind. A simple reduced gravity model is used to examine the consequence of adiabatic adjustment of the wind-driven circulation. Decadal changes in wind stress forcing can induce three-dimensional redistribution of warm water in the upper ocean. In particular, wind stress change can generate baroclinic modes of heat content anomaly in the vertical direction; in fact, changes in stratification observed in the ocean may be induced by wind stress change at local or in the remote parts of the world oceans. Intensification of the equatorial easterly can induce cooling in the upper layer and warming in the subsurface layer. The combination of this kind of heat content anomaly with the general trend of warming of the whole water column under the increasing greenhouse effect may offer an explanation for the hiatus of global surface temperature and the accelerating subsurface warming over the past 10–15 years. Furthermore, the meridional transport of warm water in the upper ocean can lead to sizeable transient meridional overturning circulation, poleward heat flux and vertical heat flux. Thus, heaving plays a key role in the oceanic circulation and climate.
UR – https://doi.org/10.1007/s00382-015-2557-6
DO – 10.1007/s00382-015-2557-6
ER –

NR – 130
TY – JOUR
AU – Zhou, Chen
AU – Zelinka, Mark D.
AU – Klein, Stephen A.
TI – Impact of decadal cloud variations on the Earth’s energy budget
JO – Nature Geoscience
PY – 2016
VL – 9
SP – 871
UR – http://dx.doi.org/10.1038/ngeo2828
DO – 10.1038/ngeo2828
AB – Feedbacks of clouds on climate change strongly influence the magnitude of global warming1,2,3. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming4,5,6,7,8,9, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback4. Here we present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. We find that cloud anomalies associated with these patterns significantly modify the Earth’s energy budget. Specifically, the decadal cloud feedback between the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. These results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and offer a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low4.
ER –

NR – 131
TY – JOUR
AU – Wang, Linying
AU – Yuan, Xing
AU – Xie, Zhenghui
AU – Wu, Peili
AU – Li, Yaohui
TI – Increasing flash droughts over China during the recent global warming hiatus
JO – Scientific Reports
PY – 2016
VL – 6
SP – 30571
UR – http://dx.doi.org/10.1038/srep30571
DO – 10.1038/srep30571
AB – The recent global warming slowdown or hiatus after the big El Niño event in 1997/98 raises the questions of whether terrestrial hydrological cycle is being decelerated and how do the hydrological extremes respond to the hiatus. However, the rapidly developing drought events that are termed as “flash droughts” accompanied by extreme heat, low soil moisture and high evapotranspiration (ET), occurred frequently around the world, and caused devastating impacts on crop yields and water supply. Here, we investigate the long-term trend and variability of flash droughts over China. Flash droughts are most likely to occur over humid and semi-humid regions, such as southern and northeastern China. Flash drought averaged over China increased by 109% from 1979 to 2010, and the increase was mainly due to a long term warming of temperature (50%), followed by the contributions from decreasing soil moisture and increasing ET. There was a slight drop in temperature after 1997, but the increasing trend of flash droughts was tripled. Further results indicate that the decreasing temperature was compensated by the accelerated drying trends of soil moisture and enhanced ET, leading to an acceleration of flash droughts during the warming hiatus. The anthropogenic warming in the next few decades may exacerbate future flash drought conditions in China.
ER –

NR – 132
TY – JOUR
TI – Investigation on the Tendencies of the Land–Ocean Warming Contrast in the Recent Decades
SP – 1522
EP – 1526
AU – L. Zhao
AU – J. Xu
AU – A. Powell
AU – D. Guo
AU – C. Shi
AU – M. Shao
AU – D. Wang
PY – 2016
DO – 10.1109/LGRS.2016.2594954
JO – IEEE Geoscience and Remote Sensing Letters
IS – 10
VL – 13
AB – In this letter, the surface climate temperature trends for the land and the oceans (land-ocean warming contrast) have been examined and compared based on five data sets. The five data sets included three reconstructed data sets of surface temperature observations and two data sets derived using the satellite microwave sounding unit retrieval products in the lower troposphere (LT) for the period from January 1980 to December 2014. Unlike previous studies, the current study shows that the warming trends significantly decreased over both the land and ocean since 1992 and reached their minimum (near zero) in the early 2000s, which is consistent with the occurrence of the warming hiatus. However, due to the sharp decrease in the surface warming trend over the land (1992 to 2007) in conjunction with an increase in the ocean surface warming trend after 2002, the combined trend carries an overall positive sign (between 2005 and 2007) due to the greater ocean warming trend. The rate of warming increase in the ocean, which began in 2002, is surprisingly fast and is approaching the highest warming trends observed over the land since 1980. These basic land and ocean trend results are confirmed by all five data sets with slightly different values due to the various techniques used in compiling the data sets. However, there is consistency in the overall trend pattern results.
ER –

NR – 133
TY – JOUR
AU – Santer, Benjamin D.
AU – Solomon, Susan
AU – Bonfils, Céline
AU – Zelinka, Mark D.
AU – Painter, Jeffrey F.
AU – Beltran, Francisco
AU – Fyfe, John C.
AU – Johannesson, Gardar
AU – Mears, Carl
AU – Ridley, David A.
AU – Vernier, Jean-Paul
AU – Wentz, Frank J.
TI – Observed multivariable signals of late 20th and early 21st century volcanic activity
JO – Geophysical Research Letters
VL – 42
IS – 2
UR – http://dx.doi.org/10.1002/2014GL062366
DO – 10.1002/2014GL062366
SP – 500
EP – 509
PY – 2015
AB – The relatively muted warming of the surface and lower troposphere since 1998 has attracted considerable attention. One contributory factor to this “warming hiatus” is an increase in volcanically induced cooling over the early 21st century. Here we identify the signals of late 20th and early 21st century volcanic activity in multiple observed climate variables. Volcanic signals are statistically discernible in spatial averages of tropical and near-global SST, tropospheric temperature, net clear-sky short-wave radiation, and atmospheric water vapor. Signals of late 20th and early 21st century volcanic eruptions are also detectable in near-global averages of rainfall. In tropical average rainfall, however, only a Pinatubo-caused drying signal is identifiable. Successful volcanic signal detection is critically dependent on removal of variability induced by the El Niño–Southern Oscillation.
ER –

NR – 134
TY – JOUR
AU – Peyser, Cheryl E.
AU – Yin, Jianjun
AU – Landerer, Felix W.
AU – Cole, Julia E.
TI – Pacific sea level rise patterns and global surface temperature variability
JO – Geophysical Research Letters
VL – 43
IS – 16
UR – http://dx.doi.org/10.1002/2016GL069401
DO – 10.1002/2016GL069401
SP – 8662
EP – 8669
PY – 2016
AB – During 1998–2012, climate change and sea level rise (SLR) exhibit two notable features: a slowdown of global surface warming (hiatus) and a rapid SLR in the tropical western Pacific. To quantify their relationship, we analyze the long-term control simulations of 38 climate models. We find a significant and robust correlation between the east-west contrast of dynamic sea level (DSL) in the Pacific and global mean surface temperature (GST) variability on both interannual and decadal time scales. Based on linear regression of the multimodel ensemble mean, the anomalously fast SLR in the western tropical Pacific observed during 1998–2012 indicates suppression of a potential global surface warming of 0.16°?±?0.06°C. In contrast, the Pacific contributed 0.29°?±?0.10°C to the significant interannual GST increase in 1997/1998. The Pacific DSL anomalies observed in 2015 suggest that the strong El Niño in 2015/2016 could lead to a 0.21°?±?0.07°C GST jump.
ER –

NR – 135
TY – JOUR
AU – Chikamoto, Y.
AU – Mochizuki, T.
AU – Timmermann, A.
AU – Kimoto, M.
AU – Watanabe, M.
TI – Potential tropical Atlantic impacts on Pacific decadal climate trends
JO – Geophysical Research Letters
VL – 43
IS – 13
UR – http://dx.doi.org/10.1002/2016GL069544
DO – 10.1002/2016GL069544
SP – 7143
EP – 7151
PY – 2016
AB – The tropical Pacific cooling from the early 1990s to 2013 has contributed to the slowdown of globally averaged sea surface temperatures (SSTs). The origin of this regional cooling trend still remains elusive. Here we demonstrate that the remote impact of Atlantic SST anomalies, as well as local atmosphere-ocean interactions, contributed to the eastern Pacific cooling during this period. By assimilating observed three-dimensional Atlantic temperature and salinity anomalies into a coupled general circulation model, we are able to qualitatively reproduce the observed Pacific decadal trends of SST and sea level pressure (SLP), albeit with reduced amplitude. Although a major part of the Pacific SLP trend can be explained by equatorial Pacific SST forcing only, the origin of this low-frequency variability can be traced back further to the remote impacts of equatorial Atlantic and South Atlantic SST trends. Atlantic SST impacts on the atmospheric circulation can also be detected for the Northeastern Pacific, thus providing a linkage between Atlantic climate and Western North American drought conditions.
ER –

NR – 136
TY – JOUR
AU – Ramesh, Nandini
AU – Cane, Mark A.
AU – Seager, Richard
AU – Lee, Dong Eun
PY – 2017
TI – Predictability and prediction of persistent cool states of the Tropical Pacific Ocean
JO – Climate Dynamics
SP – 2291
EP – 2307
VL – 49
IS – 7
AB – The Tropical Pacific Ocean displays persistently cool sea surface temperature (SST) anomalies that last several years to a decade, with either no El Niño events or a few weak El Niño events. These cause large-scale droughts in the extratropics, including major North American droughts such as the 1930s Dust Bowl, and also modulate the global mean surface temperature. Here we show that two models with different levels of complexity—the Zebiak–Cane intermediate model and the Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1—are able to produce such periods in a realistic manner. We then test the predictability of these periods in the Zebiak–Cane model using an ensemble of experiments with perturbed initial states. Our results show that in most cases the cool mean state is predictable. We then apply this method to make retrospective forecasts of shifts in the decadal mean state and to forecast the mean state of the Tropical Pacific Ocean for the upcoming decade. Our results suggest that the Pacific will undergo a shift to a warmer mean state after the 2015–2016 El Niño. This could imply the cessation of the drier than normal conditions that have generally afflicted southwest North America since the 1997–1998 El Niño, as well as the twenty-first-century pause in global warming. Implications for our understanding of the origins of such persistent cool states and the possibility of improving predictions of large-scale droughts are discussed.
UR – https://doi.org/10.1007/s00382-016-3446-3
DO – 10.1007/s00382-016-3446-3
ER –

NR – 137
TY – JOUR
AU – Knutson, Thomas R.
AU – Zhang, Rong
AU – Horowitz, Larry W.
TI – Prospects for a prolonged slowdown in global warming in the early 21st century
JO – Nature Communications
PY – 2016
VL – 7
SP – 13676
UR – http://dx.doi.org/10.1038/ncomms13676
DO – 10.1038/ncomms13676
AB – Global mean temperature over 1998 to 2015 increased at a slower rate (0.1?K decade-1) compared with the ensemble mean (forced) warming rate projected by Coupled Model Intercomparison Project 5 (CMIP5) models (0.2?K decade-1). Here we investigate the prospects for this slower rate to persist for a decade or more. The slower rate could persist if the transient climate response is overestimated by CMIP5 models by a factor of two, as suggested by recent low-end estimates. Alternatively, using CMIP5 models’ warming rate, the slower rate could still persist due to strong multidecadal internal variability cooling. Combining the CMIP5 ensemble warming rate with internal variability episodes from a single climate model—having the strongest multidecadal variability among CMIP5 models—we estimate that the warming slowdown (<0.1?K decade-1 trend beginning in 1998) could persist, due to internal variability cooling, through 2020, 2025 or 2030 with probabilities 16%, 11% and 6%, respectively.
ER –

NR – 138
TY – JOUR
AU – Gleisner, Hans
AU – Thejll, Peter
AU – Christiansen, Bo
AU – Nielsen, Johannes K.
TI – Recent global warming hiatus dominated by low-latitude temperature trends in surface and troposphere data
JO – Geophysical Research Letters
VL – 42
IS – 2
UR – http://dx.doi.org/10.1002/2014GL062596
DO – 10.1002/2014GL062596
SP – 510
EP – 517
PY – 2015
AB – Over the last 15 years, global mean surface temperatures exhibit only weak trends. Recent studies have attempted to attribute this so called temperature hiatus to several causes, amongst them incomplete sampling of the rapidly warming Arctic region. We here examine zonal mean temperature trends in satellite-based tropospheric data sets (based on data from (Advanced) Microwave Sounding Unit and Global Navigation Satellite System Radio Occultation instruments) and in global surface temperatures (HadCRUT4). Omission of successively larger polar regions from the global mean temperature calculations, in both tropospheric and surface data sets, shows that data gaps at high latitudes cannot explain the observed differences between the hiatus and the prehiatus period. Instead, the dominating causes of the global temperature hiatus are found at low latitudes. The combined use of several independent data sets, representing completely different measurement techniques and sampling characteristics, strengthens the conclusions.
ER –

NR – 139
TY – JOUR
AU – England, Matthew H.
AU – Kajtar, Jules B.
AU – Maher, Nicola
TI – Robust warming projections despite the recent hiatus
JO – Nature Climate Change
PY – 2015
VL – 5
SP – 394
UR – http://dx.doi.org/10.1038/nclimate2575
DO – 10.1038/nclimate2575
AB – The hiatus in warming has led to questions about the reliability of long-term projections, yet here we show they are statistically unchanged when considering only ensemble members that capture the recent hiatus. This demonstrates the robust nature of twenty-first century warming projections.
ER –

NR – 140
TY – JOUR
T1 – Role of Indian Ocean SST variability on the recent global warming hiatus
AU – Arora, Anika
AU – Rao, Suryachandra A.
AU – Chattopadhyay, R.
AU – Goswami, Tanmoy
AU – George, Gibies
AU – Sabeerali, C.T.
JO – Global and Planetary Change
VL – 143
SP – 21
EP – 30
PY – 2016
DO – https://doi.org/10.1016/j.gloplacha.2016.05.009
UR – http://www.sciencedirect.com/science/article/pii/S0921818115300412
AB – Previous studies have shown a slowdown in the warming rate of the annual mean global surface temperature in the recent decade and it is referred to as the hiatus in global warming. Some recent studies have suggested that the hiatus in global warming is possibly due to strong cooling in the tropical Pacific. This study investigates the possible role of the Indian Ocean warming on the tropical Pacific cooling. Despite the continued rise in sea surface temperature (SST) over the tropical Indian Ocean, SST over the tropical Pacific has shown a cooling trend in the recent decade (2002 – 2012). It is well known fact that the Indian Ocean and the Pacific Ocean are strongly coupled to each other and the Indian Ocean basin wide warming is triggered by El Niño on interannual time scale. However, in the recent decade, this relationship is weakening. The recent Indian Ocean warming is triggering a Matsuno-Gill type response in the atmosphere by generating anomalous cyclonic circulations on either side of equator over the tropical Indian Ocean and anomalous easterlies along the tropical Pacific Ocean. These anomalous easterlies result in Ekman divergence in the equatorial Pacific and produce upwelling Kelvin waves, cools the tropical Pacific and therefore indirectly contributes to the hiatus in global warming.
ER –

NR – 141
TY – JOUR
T1 – A Significant Component of Unforced Multidecadal Variability in the Recent Acceleration of Global Warming
AU – DelSole, Timothy
AU – Tippett, Michael K.
AU – Shukla, Jagadish
PY – 2010
DO – 10.1175/2010JCLI3659.1
JF – Journal of Climate
SP – 909
EP – 926
VL – 24
IS – 3
AB – The problem of separating variations due to natural and anthropogenic forcing from those due to unforced internal dynamics during the twentieth century is addressed using state-of-the-art climate simulations and observations. An unforced internal component that varies on multidecadal time scales is identified by a new statistical method that maximizes integral time scale. This component, called the internal multidecadal pattern (IMP), is stochastic and hence does not contribute to trends on long time scales; however, it can contribute significantly to short-term trends. Observational estimates indicate that the trend in the spatially averaged ?well observed? sea surface temperature (SST) due to the forced component has an approximately constant value of 0.1 K decade?1, while the IMP can contribute about ±0.08 K decade?1 for a 30-yr trend. The warming and cooling of the IMP matches that of the Atlantic multidecadal oscillation and is of sufficient amplitude to explain the acceleration in warming during 1977?2008 as compared to 1946?77, despite the forced component increasing at the same rate during these two periods. The amplitude and time scale of the IMP are such that its contribution to the trend dominates that of the forced component on time scales shorter than 16 yr, implying that the lack of warming trend during the past 10 yr is not statistically significant. Furthermore, since the IMP varies naturally on multidecadal time scales, it is potentially predictable on decadal time scales, providing a scientific rationale for decadal predictions. While the IMP can contribute significantly to trends for periods of 30 yr or shorter, it cannot account for the 0.8°C warming that has been observed in the twentieth-century spatially averaged SST.
UR – https://doi.org/10.1175/2010JCLI3659.1
ER –

NR – 142
TY – JOUR
T1 – Changes in Aridity in Response to Warming Hiatus
AU – Guan, Xiaodan
AU – Huang, Jianping
AU – Guo, Ruixia
PY – 2016
JF – Journal of Meteorological Research
VL – 31
SP – 117
EP – 125
DO – 10.1007/s13351-017-6038-1
AB – The global warming trend slowdown or warming hiatus began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation underlying this temperature change. In this study, changes in the global aridity index (AI) were analyzed using a newly developed dynamical adjustment method that can successfully identify and separate dynamically induced and radiatively-forced aridity changes in the raw data. The AI and Palmer Drought Severity Index (PDSI) appeared a wetting zone over the mid-to-high latitudes of the Northern Hemisphere in recent decades. The dynamical adjustment analysis suggests that this wetting zone occurred in response to the global warming hiatus. The dynamically-induced AI (DAI) played a major role in the AI changes during the hiatus period, and its relationships with the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO) also indicate that different phases of the NAO, PDO, and AMO contributed to different performance of the DAI over the Northern Hemisphere. Although the aridity wetting over the mid-to-high latitudes may relieve long-term drying in certain regions, the hiatus is temporary, and so is the relief. Accelerated global warming will return when the NAO, PDO, and AMO revert to their opposite phases in the future, and the wetting zone is likely to disappear.
ER –

NR – 143
TY – JOUR
AU – Tan, Ming
PY – 2016
TI – Circulation background of climate patterns in the past millennium: Uncertainty analysis and re-reconstruction of ENSO-like state
JO – Science China Earth Sciences
SP – 1225
EP – 1241
VL – 59
IS – 6
AB – The question of whether or not global warming has paused since more than ten years ago, namely “warming hiatus”, has attracted the attention of climate science community including the IPCC. Some authors have attributed the “warming hiatus” to the internal changes in the climate system, i.e., the recombination of ocean-atmosphere circulations. Therefore, it is necessary to propose higher requirements on reconstructing circulation background of climate change for the past millennium. However, the analyses of changes in atmospheric circulation over the last millennium as well as the conclusions of related regional climate patterns are so widely different and contradictory, bringing uncertainties to our understanding of regional even global climate change to a great extent. On the other hand, in the last 10 years the high-precision U/Th-dated stalagmite oxygen isotope ratio (d18O) sequences provided an accurate chronological frame for the paleoclimate study of the middle and late Pleistocene, in which all authors from China took the Chinese stalagmite d18O as the summer monsoon index without exception. However, this point of view misleads the climate scientists into thinking that the stalagmite d18O can be as the proxy of precipitation amount. Nevertheless, it is well known that all of these records have a lot in common in the low frequency trend. However, most sequences cannot be calibrated by instrumental precipitation records, and thus the uncertainty of the climate research framework of China and even of the world has increased. Therefore, it is imperative for climatology to clarify the origin of contradiction and to reduce the uncertainty as early as possible. On the basis of analyzing the significance of stalagmite d18O in the monsoon regions of China, the author tries to propose a new circulation proxy in this paper: integrating the Chinese stalagmite oxygen isotope sequence to reconstruct the tropical Pacific sea surface temperature gradient, i.e., the large-scale ENSO-like state over the past millennium. Furthermore, the author speculates that it was warm in the modern times and the Medieval Period, but the circulation recombination was different in both periods. And this inference could be supported by the longer record since Last Glacial Maximum. In other words, the attribution analysis of the identical low-frequency trends of Chinese stalagmite d18O on a large scale shows that the ENSO-like state controls the climate change in the monsoon regions of China at different time scales (from interannual to century or even longer time scales). Wherein the important connection of circulations is the western Pacific subtropical high (WPSH), that is to say, besides the interannual and decadal time scales, the WPSH would possess the circulation mode on longer timescales. For example, we may discuss the change of the WPSH in the whole Holocene epoch, i.e., the half precession period. These discussions could make sense to the study of not only the paleoclimate but also the modern climate.
UR – https://doi.org/10.1007/s11430-015-5256-6
DO – 10.1007/s11430-015-5256-6
ER –

NR – 144
TY – JOUR
AU – Cheng, Lijing
AU – Zheng, Fei
AU – Zhu, Jiang
T1 – Distinctive ocean interior changes during the recent warming slowdown
PY – 2015
AB – The earth system experiences continuous heat input, but a “climate hiatus” of upper ocean waters has been observed in this century. This leads to a question: where is the extra heat going? Using four in situ observation datasets, we explore the ocean subsurface temperature changes from 2004 to 2013. The observations all show that the ocean has continued to gain heat in this century, which is indicative of anthropogenic global warming. However, a distinctive pattern of change in the interior ocean is observed. The sea surface (1–100?m) temperature has decreased in this century, accompanied by warming in the 101–300?m layer. This pattern is due to the changes in the frequency of El Niño and La Niña events (ENSO characteristics), according to both observations and CMIP5 model simulations. In addition, we show for the first time that the ocean subsurface within 301–700?m experienced a net cooling, indicative of another instance of variability in the natural ocean. Furthermore, the ocean layer of 701–1500?m has experienced significant warming.
SP – 14346
VL – 5
DO – 10.1038/srep14346
UR – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4585812/
JF – Scientific Reports
ER –

NR – 145
TY – JOUR
AU – Jochner, Susanne
AU – Menzel, Annette
TI – Does flower phenology mirror the slowdown of global warming?
JO – Ecology and Evolution
VL – 5
IS – 11
UR – http://dx.doi.org/10.1002/ece3.1503
DO – 10.1002/ece3.1503
SP – 2284
EP – 2295
PY – 2015
AB – Although recent global warming trends in air temperature are not as pronounced as those observed only one decade ago, global mean temperature is still at a very high level. Does plant phenology – which is believed to be a suitable indicator of climate change – respond in a similar way, that is, does it still mirror recent temperature variations? We explored in detail long-term flowering onset dates of snowdrop, cherry, and lime tree and relevant spring temperatures at three sites in Germany (1901–2012) using the Bayesian multiple change-point approach. We investigated whether mean spring temperature changes were amplified or slowed down in the past decade and how plant phenology responded to the most recent temperature changes. Incorporating records with different end points (i.e., 2002 and 2012), we compared differences in trends and inferred possible differences caused by extrapolating phenological and meteorological data. The new multiple-change point approach is characterized by an enhanced structure and greater flexibility compared to the one change point model. However, the highest model probabilities for phenological (meteorological) records were still obtained for the one change point (linear) model. Marked warming trends in the recent decade were only revealed for mean temperatures of March to May, here better described with one or two change point models. In the majority of cases analyzed, changes in temperatures were well mirrored by phenological changes. However, temperatures in March to May were linked to less strongly advancing onset dates for lime tree flowering during the period 1901-2012, pointing to the likely influence of photoperiodic constraints or unfulfilled chilling requirements. Due to the slowdown of temperature increase, analyses conducted on records ending in 2002 demonstrated distinct differences when compared with records ending in 2012. Extrapolation of trends could therefore (along with the choice of the statistical method) lead to distinctly different results and most recent data should be integrated in order not to over- or underestimate future phenological changes.
ER –

NR – 146
TY – JOUR
AU – Dieng, Habib B.
AU – Palanisamy, Hindumathi
AU – Cazenave, Anny
AU – Meyssignac, Benoit
AU – von Schuckmann, Karina
PY – 2015
TI – The Sea Level Budget Since 2003: Inference on the Deep Ocean Heat Content
JO – Surveys in Geophysics
SP – 209
EP – 229
VL – 36
IS – 2
AB – This study provides an overview of the various components of the global mean sea level evolution over two time spans: (1) 2005–2012 (corresponding to the full deployment of the Argo program) and (2) 2003–2012. Using a sea level budget approach, we compare altimetry-based global mean sea level, global ocean mass from GRACE space gravimetry and steric sea level from Argo and other in situ measurements. One goal of this study is to investigate whether it is possible to constrain the deep ocean contribution to the global mean sea level rise over the last decade. This question is particularly relevant, considering the current debate about the ‘hiatus,’ i.e., the observed recent pause of the global mean air and sea surface temperature evolution while the planet is still in thermal imbalance. We consider a total of 16 different data sets. Differences are noticed between data sets related to each variable (sea level, ocean mass and steric sea level), mostly due to data processing issues. Therefore, we perform the analysis using averages of the available data sets. For each period, we find that, when removing from the global mean sea level, the contributions of the global mean ocean mass and steric sea level (estimated for the 0–1,500 m ocean layer), there remains a residual signal displaying a positive slope of 0.3 ± 0.6 and 0.55 ± 0.6 mm/year over 2005–2012 and 2003–2012, respectively. Comparing with an ocean reanalysis and according to direct (but sparse) ocean temperature measurements below 1,500 m, it seems unlikely that the observed residual signal can be attributed to deep (below 1,500 m) ocean warming, in agreement with other recently published results. We estimate that it possibly reflects, at least partly, the signature of a missing upper ocean steric signal in regions uncovered by current observing systems. Our study also shows a steady warming increase since 2003 of the 700–1,500 m ocean layer (amounting ~0.2 mm/year in steric sea level equivalent), confirming previous findings, but seen in our study in each of the eight different steric data sets considered.
UR – https://doi.org/10.1007/s10712-015-9314-6
DO – 10.1007/s10712-015-9314-6
ER –

NR – 147
TY – JOUR
AU – Ying, Lingxiao
AU – Shen, Zehao
AU – Piao, Shilong
TI – The recent hiatus in global warming of the land surface: Scale-dependent breakpoint occurrences in space and time
JO – Geophysical Research Letters
VL – 42
IS – 15
UR – http://dx.doi.org/10.1002/2015GL064884
DO – 10.1002/2015GL064884
SP – 6471
EP – 6478
PY – 2015
AB – The spatial and temporal variability of the recent land warming hiatus have seldom been explored, despite their importance for understanding the mechanisms underlying the phenomenon. In this study, we applied piecewise linear regression to investigate the spatiotemporal patterns of the breakpoint time of warming over 40?years (1974–2013). Our results showed that at the global scale, mean annual temperature (MAT) over the land increased significantly until 2005 and that the warming trend then stalled. However, the breakpoint time of the warming varied greatly among different seasons and continents. We found no statistically significant breakpoint in MAT over the Northern Hemisphere, but MAT over the Southern Hemisphere showed a significant breakpoint (P? 0.5), with root mean squared error 1500m. The Hilbert spectrum from the OHC in the Labrador Sea interior reveals two important components at frequencies of 0.8-1.2cycleyr-1 (T=0.8–1.25 years) and 0.1-0.3cycleyr-1 (T=3.3–10 years), respectively, superimposed on the warming trends. The former corresponds to the dominant seasonal cycle due to surface heating, while the latter is concomitant with the timing of the reoccurrence of convective events. We also found that the cumulative North Atlantic Oscillation (NAO) index significantly correlates to the low-frequency OHC variations. Therefore, the interannual signals in the Labrador Sea at especially the intermediate layers are attributed to changes in the deep convective processes and the atmospheric conditions. By comparing with an extended OHC record (1945–2010), it was further shown that the warming trends obtained from the 10-year Argo record are part of multi-decadal variations that presumably reflect the Atlantic Multi-decadal Oscillation (AMO). In addition, the recent OHC changes in the Labrador Sea (i.e., increased heat in the deeper layers) may be related to the current global warming hiatus, suggesting the potential contributions from the Atlantic Meridional Overturning Circulation (AMOC) to the low-frequency OHC in the Labrador Sea.
ER –

NR – 148
TY – JOUR
AU – Regayre, L. A.
AU – Pringle, K. J.
AU – Booth, B. B. B.
AU – Lee, L. A.
AU – Mann, G. W.
AU – Browse, J.
AU – Woodhouse, M. T.
AU – Rap, A.
AU – Reddington, C. L.
AU – Carslaw, K. S.
TI – Uncertainty in the magnitude of aerosol-cloud radiative forcing over recent decades
JO – Geophysical Research Letters
VL – 41
IS – 24
UR – http://dx.doi.org/10.1002/2014GL062029
DO – 10.1002/2014GL062029
SP – 9040
EP – 9049
PY – 2014
AB – Aerosols and their effect on the radiative properties of clouds are one of the largest sources of uncertainty in calculations of the Earth’s energy budget. Here the sensitivity of aerosol-cloud albedo effect forcing to 31 aerosol parameters is quantified. Sensitivities are compared over three periods; 1850–2008, 1978–2008, and 1998–2008. Despite declining global anthropogenic SO2 emissions during 1978–2008, a cancelation of regional positive and negative forcings leads to a near-zero global mean cloud albedo effect forcing. In contrast to existing negative estimates, our results suggest that the aerosol-cloud albedo effect was likely positive (0.006 to 0.028Wm-2) in the recent decade, making it harder to explain the temperature hiatus as a forced response. Proportional contributions to forcing variance from aerosol processes and natural and anthropogenic emissions are found to be period dependent. To better constrain forcing estimates, the processes that dominate uncertainty on the timescale of interest must be better understood.
ER –

NR – 149
TY – JOUR
AU – Sévellec, F.
AU – Sinha, B.
AU – Skliris, N.
TI – The rogue nature of hiatuses in a global warming climate
JO – Geophysical Research Letters
VL – 43
IS – 15
UR – http://dx.doi.org/10.1002/2016GL068950
DO – 10.1002/2016GL068950
SP – 8169
EP – 8177
PY – 2016
AB – The nature of rogue events is their unlikelihood and the recent unpredicted decade-long slowdown in surface warming, the so-called hiatus, may be such an event. However, given decadal variability in climate, global surface temperatures were never expected to increase monotonically with increasing radiative forcing. Here surface air temperature from 20 climate models is analyzed to estimate the historical and future likelihood of hiatuses and “surges” (faster than expected warming), showing that the global hiatus of the early 21st century was extremely unlikely. A novel analysis of future climate scenarios suggests that hiatuses will almost vanish and surges will strongly intensify by 2100 under a “business as usual” scenario. For “CO2 stabilisation” scenarios, hiatus, and surge characteristics revert to typical 1940s values. These results suggest to study the hiatus of the early 21st century and future reoccurrences as rogue events, at the limit of the variability of current climate modelling capability.
ER –

NR – 150
TY – JOUR
T1 – Variations of the Global Net Air–Sea Heat Flux during the “Hiatus” Period (2001–10)
AU – Liang, Xinfeng
AU – Yu, Lisan
PY – 2016
DO – 10.1175/JCLI-D-15-0626.1
JF – Journal of Climate
SP – 3647
EP – 3660
VL – 29
IS – 10
AB – An assessment is made of the mean and variability of the net air?sea heat flux, Qnet, from four products (ECCO, OAFlux?CERES, ERA-Interim, and NCEP1) over the global ice-free ocean from January 2001 to December 2010. For the 10-yr ?hiatus? period, all products agree on an overall net heat gain over the global ice-free ocean, but the magnitude varies from 1.7 to 9.5 W m?2. The differences among products are particularly large in the Southern Ocean, where they cannot even agree on whether the region gains or loses heat on the annual mean basis. Decadal trends of Qnet differ significantly between products. ECCO and OAFlux?CERES show almost no trend, whereas ERA-Interim suggests a downward trend and NCEP1 shows an upward trend. Therefore, numerical simulations utilizing different surface flux forcing products will likely produce diverged trends of the ocean heat content during this period. The downward trend in ERA-Interim started from 2006, driven by a peculiar pattern change in the tropical regions. ECCO, which used ERA-Interim as initial surface forcings and is constrained by ocean dynamics and ocean observations, corrected the pattern. Among the four products, ECCO and OAFlux?CERES show great similarities in the examined spatial and temporal patterns. Given that the two estimates were obtained using different approaches and based on largely independent observations, these similarities are encouraging and instructive. It is more likely that the global net air?sea heat flux does not change much during the so-called hiatus period.
UR – https://doi.org/10.1175/JCLI-D-15-0626.1
ER –

NR – 151
TY – JOUR
AU – Wang, You-Lin
AU – Wu, Chau-Ron
AU – Chao, Shenn-Yu
TI – Warming and weakening trends of the Kuroshio during 1993–2013
JO – Geophysical Research Letters
VL – 43
IS – 17
UR – http://dx.doi.org/10.1002/2016GL069432
DO – 10.1002/2016GL069432
SP – 9200
EP – 9207
PY – 2016
AB – Global warming seems leveling off somewhat during 1993–2013 despite increasing atmospheric greenhouse gases. What has happened to the Kuroshio Current system concurrently? Available independent data sets from 1993 to 2013 point to a single answer. Here we show a systemwide weakened Kuroshio during the period despite enhanced warming along its path. The Pacific warm pool upstream of the Kuroshio is still becoming warmer during the period. It injects more heat into the Current despite the weakened Kuroshio, which is associated with weakened westerlies and cyclonic trends of basin-scale wind stress curl. The weakened Kuroshio will modulate heat and mass exchanges between the tropics and extratropics, impacting the energy balance of climate system. It will also significantly influence mass, heat, salinity, and nutrient exchanges between the Pacific and adjacent marginal seas, which in turn impacts the regional weather, fisheries, and environments.
ER –

NR – 152
TY – JOUR
AU – Pretis, Felix
AU – Mann, Michael L.
AU – Kaufmann, Robert K.
PY – 2015
TI – Testing competing models of the temperature hiatus: assessing the effects of conditioning variables and temporal uncertainties through sample-wide break detection
JO – Climatic Change
SP – 705
EP – 718
VL – 131
IS – 4
AB – Explaining the recent slowdown in the rise of global mean surface temperature (the hiatus in warming) has become a major focus of climate research. Efforts to identify the causes of the hiatus that compare simulations from experiments run by climate models raise several statistical issues. Specifically, it is necessary to identify whether an experiment’s inability to simulate the hiatus is unique to this period or reflects a more systematic failure throughout the sample period. Furthermore, efforts to attribute the hiatus to a particular factor by including that mechanism in an experimental treatment must improve the model’s performance in a statistically significant manner at the time of the hiatus. Sample-wide assessments of simulation errors can provide an accurate assessment of whether or not the control experiment uniquely fails at the hiatus, and can identify its causes using experimental treatments. We use this approach to determine if the hiatus constitutes a unique failure in simulated climate models and to re- examine the conclusion that the hiatus is uniquely linked to episodes of La Niña-like cooling (Kosaka and Xie 2013). Using statistical techniques that do not define the hiatus a priori, we find no evidence that the slowdown in temperature increases are uniquely tied to episodes of La Niña-like cooling.
UR – https://doi.org/10.1007/s10584-015-1391-5
DO – 10.1007/s10584-015-1391-5
ER –

NR – 153
TY – JOUR
TI – Weakening of the Kuroshio Intrusion Into the South China Sea Under the Global Warming Hiatus
SP – 5064
EP – 5070
AU – C. R. Wu
AU – Y. L. Wang
AU – Y. F. Lin
AU – T. L. Chiang
AU – C. C. Wu
PY – 2016
DO – 10.1109/JSTARS.2016.2574941
JO – IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
IS – 11
VL – 9
AB – We analyze a 22-year (1993-2014) record of the Kuroshio intrusion (KI) index defined from maps of mean absolute dynamic topography west of Luzon Island in the Philippines to investigate the long-term trend of the KI into the South China Sea (SCS). The monotonically increasing trend of the KI index extracted by empirical mode decomposition implies a slight decreasing trend of the meridional pressure gradient across the Luzon Strait, suggesting a weakening of the KI into the SCS based on the geostrophy. This weakening is largely due to an intensification of the upstream Kuroshio east of Luzon, which is closely correlated with the latitude of the North Equatorial Current (NEC) bifurcation off the Philippines. We also find that the latitude of the NEC bifurcation has tended to migrate southward in recent years, coincident with the strengthening of the Kuroshio east of Luzon. The forcing of the trends of low-latitude circulation is attributable to changing surface wind fields in the tropical Pacific. The trade winds have intensified in response to the recent global warming hiatus, and an anomalous cyclonic wind field has appeared over the Philippine Sea. Both of these phenomena have contributed to the southward migration of the NEC bifurcation latitude in recent years. This has led to enhance the Kuroshio transport east of Luzon, and the Kuroshio has tended to bypass the Luzon Strait without significant westward encroachment.
ER –

NR – 154
TY – JOUR
AU – Vuille, Mathias
AU – Franquist, Eric
AU – Garreaud, René
AU – Lavado Casimiro, Waldo Sven
AU – Cáceres, Bolivar
TI – Impact of the global warming hiatus on Andean temperature
JO – Journal of Geophysical Research: Atmospheres
VL – 120
IS – 9
UR – http://dx.doi.org/10.1002/2015JD023126
DO – 10.1002/2015JD023126
SP – 3745
EP – 3757
PY – 2015
AB – The recent hiatus in global warming is likely to be reflected in Andean temperature, given its close dependence on tropical Pacific sea surface temperature (SST). While recent work in the subtropical Andes has indeed documented a cooling along coastal areas, trends in the tropical Andes show continued warming. Here we analyze spatiotemporal temperature variability along the western side of the Andes with a dense station network updated to 2010 and investigate its linkages to tropical Pacific modes of variability. Results indicate that the warming in tropical latitudes has come to a halt and that the subtropical regions continue to experience cooling. Trends, however, are highly dependent on elevation. While coastal regions experience cooling, higher elevations continue to warm. The coastal cooling is consistent with the observed Pacific Decadal Oscillation (PDO) fingerprint and can be accurately simulated using a simple PDO-analog model. Much of the PDO imprint is modulated and transmitted through adjustments in coastal SST off western South America. At inland and higher-elevation locations, however, temperature trends start to diverge from this PDO-analog model in the late 1980s and have by now emerged above the 1s model spread. Future warming at higher elevation is likely and will contribute to further vertical stratification of atmospheric temperature trends. In coastal locations, future warming or cooling will depend on the potential future intensification of the South Pacific anticyclone but also on continued temperature dependence on the state of the PDO.
ER –

NR – 155
TY – JOUR
AU – Gu, Guojun
AU – Adler, Robert F.
AU – Huffman, George J.
PY – 2016
TI – Long-term changes/trends in surface temperature and precipitation during the satellite era (1979–2012)
JO – Climate Dynamics
SP – 1091
EP – 1105
VL – 46
IS – 3
AB – During the post-1979 period in which the satellite-based precipitation measurements with global coverage are available, global mean surface temperature rapidly increased up to late 1990s, followed by a period of temperature hiatus after about 1998/1999. Comparing observed surface temperature trends against the simulated ones by the CMIP5 historical experiments especially in the zonal mean context suggests that although the anthropogenic greenhouse-gases (GHG) forcing has played a major role, in addition to the anthropogenic aerosols and various natural forcings, the effects from decadal-to-interdecadal-scale internal modes specifically the Pacific Decadal Oscillation (PDO) are also very strong. Evident temperature changes associated with the PDO’s phase shift are seen in the Pacific basin, with decadal-scale cooling in the tropical central-eastern Pacific and most of the east basin and concurrent warming in the subtropics of both hemispheres, even though the PDO’s net effect on global mean temperature is relatively weak. The Atlantic Multidecadal Oscillation (AMO) also changed its phase in the mid-1990s, and hence its possible impact is estimated and assessed as well. However, comparisons with CMIP5 simulations suggest that the AMO may have not contributed as significantly as the PDO in terms of the changes/trends in global surface temperature, even though the data analysis technique used here suggests otherwise. Long-term precipitation changes or trends during the post-1979 period are further shown to have been modulated by the two major factors: anthropogenic GHG and PDO, in addition to the relatively weak effects from aerosols and natural forcings. The spatial patterns of observed precipitation trends in the Pacific, including reductions in the tropical central-eastern Pacific and increases in the tropical western Pacific and along the South Pacific Convergence Zone, manifest the PDO’s contributions. Removing the PDO effect from the total precipitation trends makes the spatial structures of precipitation trends more similar to those simulated by CMIP5 historical full forcing experiments particularly in the context of zonal-mean results. This also confirms that in spite of the PDO effect specifically on regional scales, the anthropogenic GHG signals are still discernible in observed precipitation during the time period. Following the increase of GHG, precipitation tends to increase roughly along the climatological ITCZ and decrease south of the equator and in the subtropics of both hemispheres.
UR – https://doi.org/10.1007/s00382-015-2634-x
DO – 10.1007/s00382-015-2634-x
ER –

NR – 156
TY – JOUR
AU – Lee, Sang-Ki
AU – Park, Wonsun
AU – Baringer, Molly O.
AU – Gordon, Arnold L.
AU – Huber, Bruce
AU – Liu, Yanyun
TI – Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus
JA – Nature Geoscience
PY – 2015
VL – 8
SP – 445
UR – http://dx.doi.org/10.1038/ngeo2438
DO – 10.1038/ngeo2438
AB – Global mean surface warming has stalled since the end of the twentieth century1,2, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. This apparent contradiction has been reconciled by an anomalous heat flux into the ocean3,4,5,6,7,8, induced by a shift towards a La Niña-like state with cold sea surface temperatures in the eastern tropical Pacific over the past decade or so. A significant portion of the heat missing from the atmosphere is therefore expected to be stored in the Pacific Ocean. However, in situ hydrographic records indicate that Pacific Ocean heat content has been decreasing9. Here, we analyse observations along with simulations from a global ocean–sea ice model to track the pathway of heat. We find that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. As a result, Indian Ocean heat content has increased abruptly, which accounts for more than 70% of the global ocean heat gain in the upper 700 m during the past decade. We conclude that the Indian Ocean has become increasingly important in modulating global climate variability.
ER –

NR – 157
TY – JOUR
AU – Roberts, C. D.
AU – Palmer, M. D.
AU – McNeall, D.
AU – Collins, M.
TI – Quantifying the likelihood of a continued hiatus in global warming
JF – Nature Climate Change
PY – 2015
VL – 5
SP – 337
UR – http://dx.doi.org/10.1038/nclimate2531
DO – 10.1038/nclimate2531
AB – Since the end of the twentieth century, global mean surface temperature has not risen as rapidly as predicted by global climate models1,2,3 (GCMs). This discrepancy has become known as the global warming ‘hiatus’ and a variety of mechanisms1,4,5,6,7,8,9,10,11,12,13,14,15,16,17 have been proposed to explain the observed slowdown in warming. Focusing on internally generated variability, we use pre-industrial control simulations from an observationally constrained ensemble of GCMs and a statistical approach to evaluate the expected frequency and characteristics of variability-driven hiatus periods and their likelihood of future continuation. Given an expected forced warming trend of ~0.2 K per decade, our constrained ensemble of GCMs implies that the probability of a variability-driven 10-year hiatus is ~10%, but less than 1% for a 20-year hiatus. Although the absolute probability of a 20-year hiatus is small, the probability that an existing 15-year hiatus will continue another five years is much higher (up to 25%). Therefore, given the recognized contribution of internal climate variability to the reduced rate of global warming during the past 15 years, we should not be surprised if the current hiatus continues until the end of the decade. Following the termination of a variability-driven hiatus, we also show that there is an increased likelihood of accelerated global warming associated with release of heat from the sub-surface ocean and a reversal of the phase of decadal variability in the Pacific Ocean.
ER –

NR – 158
TY – JOUR
AU – Notaro, Michael
AU – Yu, Yan
AU – Kalashnikova, Olga V.
TI – Regime shift in Arabian dust activity, triggered by persistent Fertile Crescent drought
JO – Journal of Geophysical Research: Atmospheres
VL – 120
IS – 19
UR – http://dx.doi.org/10.1002/2015JD023855
DO – 10.1002/2015JD023855
SP – 10,229
EP – 10,249
PY – 2015
AB – The Arabian Peninsula has experienced pronounced interannual to decadal variability in dust activity, including an abrupt regime shift around 2006 from an inactive dust period during 1998–2005 to an active period during 2007–2013. Corresponding in time to the onset of this regime shift, the climate state transitioned into a combined La Niña and negative phase of the Pacific Decadal Oscillation, which incited a hiatus in global warming in the 2000s. Superimposed upon a long-term regional drying trend, synergistic interactions between these teleconnection modes triggered the establishment of a devastating and prolonged drought, which engulfed the Fertile Crescent, namely, Iraq and Syria, and led to crop failure and civil unrest. Dried soils and diminished vegetation cover in the Fertile Crescent, as evident through remotely sensed enhanced vegetation indices, supported greater dust generation and transport to the Arabian Peninsula in 2007–2013, as identified both in increased dust days observed at weather stations and enhanced remotely sensed aerosol optical depth. According to backward trajectory analysis of dust days on the Arabian Peninsula, increased dust lifting and atmospheric dust concentration in the Fertile Crescent during this recent, prolonged drought episode supported a greater frequency of dust events across the peninsula with associated northerly trajectories and led to the dust regime shift. These findings are particularly concerning, considering projections of warming and drying for the eastern Mediterranean region and potential collapse of the Fertile Crescent during this century.
ER –

NR – 159
TY – JOUR
AU – Meehl, Gerald A.
AU – Teng, Haiyan
TI – Regional precipitation simulations for the mid-1970s shift and early-2000s hiatus
JO – Geophysical Research Letters
VL – 41
IS – 21
UR – http://dx.doi.org/10.1002/2014GL061778
DO – 10.1002/2014GL061778
SP – 7658
EP – 7665
PY – 2014
AB – It has been demonstrated that climate models initialized with observations produce better simulations of Pacific sea surface temperature (SST) patterns than uninitialized simulations for the two major climate regime changes of the last 40?years, the mid-1970s climate shift and early-2000s hiatus. A fundamental feature of these hindcasts is the simulation of the SST anomalies associated with the phase of the Interdecadal Pacific Oscillation (IPO). Since regional precipitation patterns over selected land areas in south Asia, Australia, and North America are known to be affected by SST patterns over the Pacific, it is shown that the initialized climate model simulations produce qualitatively better agreement with observations for regional precipitation anomalies in those regions compared to uninitialized climate models. Though the signals are small, the anomalies are consistent with our physical process-based understanding of precipitation responses over certain land areas during different IPO phases.
ER –

NR – 160
TY – JOUR
AU – Zhu, Yali
AU – Wang, Tao
AU – Wang, Huijun
PY – 2016
TI – Relative contribution of the anthropogenic forcing and natural variability to the interdecadal shift of climate during the late 1970s and 1990s
JO – Science Bulletin
SP – 416
EP – 424
VL – 61
IS – 5
AB – Global warming accelerated after the late 1970s and slowed down after the late 1990s, accompanying the significant interdecadal changes in the regional climate. We hypothesized that the interdecadal changes linearly consisted of two independent components, anthropogenic forcing and natural decadal variability, which can be represented simply by the radiative forcing effect of carbon dioxide (RF CO 2 ) (RFCO2) and the Pacific Decadal Oscillation (PDO), respectively. The combined effect of the RF CO 2 RFCO2 and PDO could explain the majority of the surface temperature changes during the late 1970s and 1990s, but the magnitudes of the relative contribution of the RF CO 2 RFCO2 and the PDO are inconsistent in different regions. For both the surface temperature and geopotential height, the RF CO 2 RFCO2 could induce significantly positive anomalies over almost the entire globe for these two shifts, exhibiting a larger magnitude in the mid–high latitudes and in the late 1990s shift. The PDO could induce opposite anomalies for the two interdecadal shifts due to its phase transitions (negative-positive–negative). Furthermore, for the shift in the late 1970s, both the RF CO 2 RFCO2 (53.7 %–66.7 %) and the PDO (33.3 %–46.3 %) were important in regulating the tropical geopotential height, whereas the RF CO 2 RFCO2 dominated the changes in the mid-latitudes. For the western Pacific subtropical high, the RF CO 2 RFCO2 (PDO) could explain 52.3 %–62.1 % (37.9 %–47.7 %) of the change. The negative effect of the PDO counteracted most of the RF CO 2 RFCO2 effects for the late 1990s shift.
UR – https://doi.org/10.1007/s11434-016-1012-3
DO – 10.1007/s11434-016-1012-3
ER –

NR – 161
TY – JOUR
AU – Song, Jinjie
AU – Wang, Yuan
AU – Tang, Jianping
TI – A Hiatus of the Greenhouse Effect
JF – Scientific Reports
PY – 2016
VL – 6
SP – 33315
UR – http://dx.doi.org/10.1038/srep33315
DO – 10.1038/srep33315
AB – The rate at which the global average surface temperature is increasing has slowed down since the end of the last century. This study investigates whether this warming hiatus results from a change in the well-known greenhouse effect. Using long-term, reliable, and consistent observational data from the Earth’s surface and the top of the atmosphere (TOA), two monthly gridded atmospheric and surface greenhouse effect parameters (Ga and Gs) are estimated to represent the radiative warming effects of the atmosphere and the surface in the infrared range from 1979 to 2014. The atmospheric and surface greenhouse effect over the tropical monsoon-prone regions is found to contribute substantially to the global total. Furthermore, the downward tendency of cloud activity leads to a greenhouse effect hiatus after the early 1990?s, prior to the warming pause. Additionally, this pause in the greenhouse effect is mostly caused by the high number of La Niña events between 1991 and 2014. A strong La Niña indicates suppressed convection in the tropical central Pacific that reduces atmospheric water vapor content and cloud volume. This significantly weakened regional greenhouse effect offsets the enhanced warming influence in other places and decelerates the rising global greenhouse effect. This work suggests that the greenhouse effect hiatus can be served as an additional factor to cause the recent global warming slowdown.
ER –

NR – 162
TY – JOUR
AU – Meehl, Gerald A.
AU – Arblaster, Julie M.
AU – Bitz, Cecilia M.
AU – Chung, Christine T. Y.
AU – Teng, Haiyan
TI – Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability
JA – Nature Geoscience
PY – 2016
VL – 9
SP – 590
UR – http://dx.doi.org/10.1038/ngeo2751
DO – 10.1038/ngeo2751
AB – Antarctic sea-ice extent has been slowly increasing in the satellite record that began in 19791,2. Since the late 1990s, the increase has accelerated, but the average of all climate models shows a decline3. Meanwhile, the Interdecadal Pacific Oscillation, an internally generated mode of climate variability4, transitioned from positive to negative5, with an average cooling of tropical Pacific sea surface temperatures5, a slowdown of the global warming trend6,7,8 and a deepening of the Amundsen Sea Low near Antarctica1,9,10,11,12 that has contributed to regional circulation changes in the Ross Sea region and expansion of sea ice10. Here we show that the negative phase of the Interdecadal Pacific Oscillation in global coupled climate models is characterized by anomalies similar to the observed sea-level pressure and near-surface 850?hPa wind changes near Antarctica since 2000 that are conducive to expanding Antarctic sea-ice extent, particularly in the Ross Sea region in all seasons, involving a deepening of the Amundsen Sea Low. These atmospheric circulation changes are shown to be mainly driven by precipitation and convective heating anomalies related to the Interdecadal Pacific Oscillation in the equatorial eastern Pacific, with additional contributions from convective heating anomalies in the South Pacific convergence zone and tropical Atlantic regions.
ER –

NR – 163
TY – JOUR
T1 – Atlantic and Pacific multidecadal oscillations and Northern Hemisphere temperatures
JF – Science
SP – 988
LP – 991
DO – 10.1126/science.1257856
VL – 347
IS – 6225
AU – Steinman, Byron A.
AU – Mann, Michael E.
AU – Miller, Sonya K.
PY – 2015
UR – http://science.sciencemag.org/content/347/6225/988.abstract
AB – Which recent climate changes have been forced by greenhouse gas emissions, and which have been natural fluctuations of the climate system? Steinman et al. combined observational data and a large collection of climate models to assess the Northern Hemisphere climate over the past 150 years (see the Perspective by Booth). At various points in time, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation have played particularly large roles in producing temperature trends. Their effects have combined to cause the apparent pause in warming at the beginning of the 21st century, known as the warming “hiatus.” This pause is projected to end in the near future as temperatures resume their upward climb.Science, this issue p. 988; see also p. 952 The recent slowdown in global warming has brought into question the reliability of climate model projections of future temperature change and has led to a vigorous debate over whether this slowdown is the result of naturally occurring, internal variability or forcing external to Earth’s climate system. To address these issues, we applied a semi-empirical approach that combines climate observations and model simulations to estimate Atlantic- and Pacific-based internal multidecadal variability (termed “AMO” and “PMO,” respectively). Using this method, the AMO and PMO are found to explain a large proportion of internal variability in Northern Hemisphere mean temperatures. Competition between a modest positive peak in the AMO and a substantially negative-trending PMO are seen to produce a slowdown or “false pause” in warming of the past decade.
ER –

NR – 164
TY – JOUR
AU – Visbeck, Martin
TI – Bumpy path to a warmer world
JA – Nature Geoscience
PY – 2014
VL – 7
SP – 160
UR – http://dx.doi.org/10.1038/ngeo2104
DO – 10.1038/ngeo2104
AB – Decadal climate variability has long received limited attention. With the slow-down in surface warming since the late 1990s, the decadal scale has rightly become a focus of attention: for assessing climate change and its impacts, it is of critical importance.
ER –

NR – 165
TY – JOUR
AU – Meehl, Gerald A.
AU – Hu, Aixue
AU – Santer, Benjamin D.
AU – Xie, Shang-Ping
TI – Contribution of the Interdecadal Pacific Oscillation to twentieth-century global surface temperature trends
JF – Nature Climate Change
PY – 2016
VL – 6
SP – 1005
UR – http://dx.doi.org/10.1038/nclimate3107
DO – 10.1038/nclimate3107
AB – Longer-term externally forced trends in global mean surface temperatures (GMSTs) are embedded in the background noise of internally generated multidecadal variability1. A key mode of internal variability is the Interdecadal Pacific Oscillation (IPO), which contributed to a reduced GMST trend during the early 2000s1,2,3. We use a novel, physical phenomenon-based approach to quantify the contribution from a source of internally generated multidecadal variability—the IPO—to multidecadal GMST trends. Here we show that the largest IPO contributions occurred in its positive phase during the rapid warming periods from 1910–1941 and 1971–1995, with the IPO contributing 71% and 75%, respectively, to the difference between the median values of the externally forced trends and observed trends. The IPO transition from positive to negative in the late-1990s contributed 27% of the discrepancy between model median estimates of the forced part of the GMST trend and the observed trend from 1995 to 2013, with additional contributions that are probably due to internal variability outside of the Pacific4 and an externally forced response from small volcanic eruptions5. Understanding and quantifying the contribution of a specific source of internally generated variability—the IPO—to GMST trends is necessary to improve decadal climate prediction skill.
ER –

NR – 166
TY – JOUR
AU – Balmaseda, Magdalena A.
AU – Trenberth, Kevin E.
AU – Källén, Erland
TI – Distinctive climate signals in reanalysis of global ocean heat content
JO – Geophysical Research Letters
VL – 40
IS – 9
UR – http://dx.doi.org/10.1002/grl.50382
DO – 10.1002/grl.50382
SP – 1754
EP – 1759
PY – 2013
AB – The elusive nature of the post-2004 upper ocean warming has exposed uncertainties in the ocean’s role in the Earth’s energy budget and transient climate sensitivity. Here we present the time evolution of the global ocean heat content for 1958 through 2009 from a new observation-based reanalysis of the ocean. Volcanic eruptions and El Niño events are identified as sharp cooling events punctuating a long-term ocean warming trend, while heating continues during the recent upper-ocean-warming hiatus, but the heat is absorbed in the deeper ocean. In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend. The warming below 700 m remains even when the Argo observing system is withdrawn although the trends are reduced. Sensitivity experiments illustrate that surface wind variability is largely responsible for the changing ocean heat vertical distribution.
ER –

NR – 167
TY – JOUR
AU – Johansson, Daniel J. A.
AU – O’Neill, Brian C.
AU – Tebaldi, Claudia
AU – Häggström, Olle
TI – Equilibrium climate sensitivity in light of observations over the warming hiatus
JF – Nature Climate Change
PY – 2015
VL – 5
SP – 449
UR – http://dx.doi.org/10.1038/nclimate2573
DO – 10.1038/nclimate2573
AB – A key uncertainty in projecting future climate change is the magnitude of equilibrium climate sensitivity (ECS), that is, the eventual increase in global annual average surface temperature in response to a doubling of atmospheric CO2 concentration. The lower bound of the likely range for ECS given in the IPCC Fifth Assessment Report (AR5; refs 1, 2) was revised downwards to 1.5 °C, from 2 °C in its previous report3, mainly as an effect of considering observations over the warming hiatus—the period of slowdown of global average temperature increase since the early 2000s. Here we analyse how estimates of ECS change as observations accumulate over time and estimate the contribution of potential causes to the hiatus. We find that including observations over the hiatus reduces the most likely value for ECS from 2.8 °C to 2.5 °C, but that the lower bound of the 90% range remains stable around 2 °C. We also find that the hiatus is primarily attributable to El Niño/Southern Oscillation-related variability and reduced solar forcing.
ER –

NR – 168
TY – JOUR
A1 – Schleussner, C. F.
A1 – Runge, J.
A1 – Lehmann, J.
A1 – Levermann, A.
T1 – The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability
JA – Earth Syst. Dynam.
VL – 5
IS – 1
SP – 103
EP – 115
PY – 2014
UR – https://www.earth-syst-dynam.net/5/103/2014/
DO – 10.5194/esd-5-103-2014
AB – Earth’s climate exhibits internal modes of variability on various timescales. Here we investigate multi-decadal variability of the Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions. We report an inter-annual GMT variability of about ±0.1° C originating solely from natural variability in the model ensemble. By decomposing the GMT variance into contributions of the AMOC and Northern Hemisphere sea-ice extent using a graph-theoretical statistical approach, we find the AMOC to contribute 8% to GMT variability in the ensemble mean. Our results highlight the importance of AMOC sea-ice feedbacks that explain 5% of the GMT variance, while the contribution solely related to the AMOC is found to be about 3%. As a consequence of multi-decadal AMOC variability, we report substantial variations in North Atlantic deep-ocean heat content with trends of up to 0.7 × 1022 J decade-1 that are of the order of observed changes over the last decade and consistent with the reduced GMT warming trend over this period. Although these temperature anomalies are largely density-compensated by salinity changes, we find a robust negative correlation between the AMOC and North Atlantic deep-ocean density with density lagging the AMOC by 5 to 11 yr in most models. While this would in principle allow for a self-sustained oscillatory behavior of the coupled AMOC–deep- ocean system, our results are inconclusive about the role of this feedback in the model ensemble.
ER –

NR – 169
TY – JOUR
T1 – Extratropical Ocean Warming and Winter Arctic Sea Ice Cover since the 1990s
AU – Li, Fei
AU – Wang, Huijun
AU – Gao, Yongqi
PY – 2015
DO – 10.1175/JCLI-D-14-00629.1
JF – Journal of Climate
SP – 5510
EP – 5522
VL – 28
IS – 14
AB – Despite the fact that the Arctic Oscillation (AO) has reached a more neutral state and a global-warming hiatus has occurred in winter since the late 1990s, the Arctic sea ice cover (ASIC) still shows a pronounced decrease. This study reveals a close connection (R = 0.5) between the extratropical sea surface temperature (ET-SST) and ASIC in winter from 1994 to 2013. In response to one positive (negative) unit of deviation in the ET-SST pattern, the ASIC decreases (increases) in the Barents?Kara Seas and Hudson Bay (the Baffin Bay and Bering Sea) by 100?400 km2. This relationship might be maintained because of the impact of warming extratropical oceans on the polar vortex. Positive SST anomalies in the midlatitudes of the North Pacific and Atlantic (around 40°N) strengthen the equatorward planetary wave propagation, whereas negative SST anomalies in the high latitudes weaken the upward planetary wave propagation from the lower troposphere to the stratosphere. The former indicates a strengthening of the poleward meridional eddy momentum flux, and the latter implies a weakening of the poleward eddy heat flux, which favors an intensified upper-level polar night jet and a colder polar vortex, implying a stronger-than-normal polar vortex. Consequently, an anomalous cyclone emerges over the eastern Arctic, limiting or encouraging the ASIC by modulating the mean meridional heat flux. A possible reason for the long-term changes in the relationship between the ET-SST and ASIC is also discussed.
M3 – doi: 10.1175/JCLI-D-14-00629.1
UR – https://doi.org/10.1175/JCLI-D-14-00629.1
ER –

NR – 170
TY – JOUR
AU – Zhou, Yu
AU – Luo, Ming
AU – Leung, Yee
TI – On the detection of precipitation dependence on temperature
JO – Geophysical Research Letters
VL – 43
IS – 9
UR – http://dx.doi.org/10.1002/2016GL068811
DO – 10.1002/2016GL068811
SP – 4555
EP – 4565
PY – 2016
AB – Employing their newly proposed interannual difference method (IADM), Liu et al. (2009) and Shiu et al. (2012) reported a shocking increase of around 100% K-1 in heavy precipitation with warming global temperature in 1979–2007. Such increase is alarming and prompts us to probe into the IADM. In this study, both analytical derivations and numerical analyses demonstrate that IADM provides no additional information to that of the conventional linear regression, and also, it may give a false indication of dependence. For clarity and simplicity, we therefore recommend linear regression analysis over the IADM for the detection of dependence. We also find that heavy precipitation decreased during the global warming hiatus, and the precipitation dependence on temperature drops by almost 50% when the study period is extended to 1979–2014 and it may keep dropping in the near future. The risk of having heavy precipitation under warming global temperature may have been overestimated.
ER –

NR – 171
TY – JOUR
AU – Mann, Michael E.
AU – Steinman, Byron A.
AU – Miller, Sonya K.
AU – Frankcombe, Leela M.
AU – England, Matthew H.
AU – Cheung, Anson H.
TI – Predictability of the recent slowdown and subsequent recovery of large-scale surface warming using statistical methods
JO – Geophysical Research Letters
VL – 43
IS – 7
UR – http://dx.doi.org/10.1002/2016GL068159
DO – 10.1002/2016GL068159
SP – 3459
EP – 3467
PY – 2016
AB – The temporary slowdown in large-scale surface warming during the early 2000s has been attributed to both external and internal sources of climate variability. Using semiempirical estimates of the internal low-frequency variability component in Northern Hemisphere, Atlantic, and Pacific surface temperatures in concert with statistical hindcast experiments, we investigate whether the slowdown and its recent recovery were predictable. We conclude that the internal variability of the North Pacific, which played a critical role in the slowdown, does not appear to have been predictable using statistical forecast methods. An additional minor contribution from the North Atlantic, by contrast, appears to exhibit some predictability. While our analyses focus on combining semiempirical estimates of internal climatic variability with statistical hindcast experiments, possible implications for initialized model predictions are also discussed.
ER –

NR – 172
TY – JOUR
AU – You, Qinglong
AU – Min, Jinzhong
AU – Kang, Shichang
TI – Rapid warming in the Tibetan Plateau from observations and CMIP5 models in recent decades
JO – International Journal of Climatology
VL – 36
IS – 6
UR – http://dx.doi.org/10.1002/joc.4520
DO – 10.1002/joc.4520
SP – 2660
EP – 2670
PY – 2016
AB – On the basis of mean temperature, maximum temperature and minimum temperature from the updated China Homogenized Historical Temperature Data Sets, the recent warming in the Tibetan Plateau (TP) during 1961–2005 and global warming hiatus period are examined. During 1961–2005, the mean temperature, maximum temperature and minimum temperature in the whole TP show a statistically increasing trend especially after the 1980s, with the annual rates of 0.27, 0.19 and 0.36 °C decade-1, respectively. The performance of 26 general circulation models (GCMs) available in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) is evaluated in the TP by comparison with the observations during 1961–2005. Most CMIP5 GCMs can capture the decadal variations of the observed mean temperature, maximum temperature and minimum temperature, and have significant positive correlations with observations (R > 0.5), with root mean squared error 1500m. The Hilbert spectrum from the OHC in the Labrador Sea interior reveals two important components at frequencies of 0.8-1.2cycleyr-1 (T=0.8–1.25 years) and 0.1-0.3cycleyr-1 (T=3.3–10 years), respectively, superimposed on the warming trends. The former corresponds to the dominant seasonal cycle due to surface heating, while the latter is concomitant with the timing of the reoccurrence of convective events. We also found that the cumulative North Atlantic Oscillation (NAO) index significantly correlates to the low-frequency OHC variations. Therefore, the interannual signals in the Labrador Sea at especially the intermediate layers are attributed to changes in the deep convective processes and the atmospheric conditions. By comparing with an extended OHC record (1945–2010), it was further shown that the warming trends obtained from the 10-year Argo record are part of multi-decadal variations that presumably reflect the Atlantic Multi-decadal Oscillation (AMO). In addition, the recent OHC changes in the Labrador Sea (i.e., increased heat in the deeper layers) may be related to the current global warming hiatus, suggesting the potential contributions from the Atlantic Meridional Overturning Circulation (AMOC) to the low-frequency OHC in the Labrador Sea.
ER –

NR – 173
TY – JOUR
AU – Beniston, Martin
PY – 2015
TI – Ratios of record high to record low temperatures in Europe exhibit sharp increases since 2000 despite a slowdown in the rise of mean temperatures
JO – Climatic Change
SP – 225
EP – 237
VL – 129
IS – 1
AB – A study has been undertaken to analyze the behavior of record high and low values of temperature since the early 1950s for 30 locations spread across Europe. When establishing the ratios of the number of record Tmax to record Tmin values in each year, it is seen that there is a sharp increase in these ratios in the most recent decade. This seems to be an apparent paradox in view of the slow-down in atmospheric temperatures that has been observed since the early 2000s at both the hemispheric and European scales, but closer analysis suggests that the relationship between the record high:low ratios and mean annual temperatures is not linear but rather a square relationship. It is suggested that the record high to record low ratios in both the Mediterranean region and beyond 60° latitude north, observed in the most recent decade, may be related to an amplification of low-level atmospheric temperatures resulting from shorter snow seasons in the north and enhanced summer dryness in the south.
UR – https://doi.org/10.1007/s10584-015-1325-2
DO – 10.1007/s10584-015-1325-2
ER –

NR – 174
TY – JOUR
T1 – Decadal Climate Prediction: An Update from the Trenches
AU – Meehl, Gerald A.
AU – Goddard, Lisa
AU – Boer, George
AU – Burgman, Robert
AU – Branstator, Grant
AU – Cassou, Christophe
AU – Corti, Susanna
AU – Danabasoglu, Gokhan
AU – Doblas-Reyes, Francisco
AU – Hawkins, Ed
AU – Karspeck, Alicia
AU – Kimoto, Masahide
AU – Kumar, Arun
AU – Matei, Daniela
AU – Mignot, Juliette
AU – Msadek, Rym
AU – Navarra, Antonio
AU – Pohlmann, Holger
AU – Rienecker, Michele
AU – Rosati, Tony
AU – Schneider, Edwin
AU – Smith, Doug
AU – Sutton, Rowan
AU – Teng, Haiyan
AU – van Oldenborgh, Geert Jan
AU – Vecchi, Gabriel
AU – Yeager, Stephen
PY – 2013
DO – 10.1175/BAMS-D-12-00241.1
JF – Bulletin of the American Meteorological Society
SP – 243
EP – 267
VL – 95
IS – 2
AB – This paper provides an update on research in the relatively new and fast-moving field of decadal climate prediction, and addresses the use of decadal climate predictions not only for potential users of such information but also for improving our understanding of processes in the climate system. External forcing influences the predictions throughout, but their contributions to predictive skill become dominant after most of the improved skill from initialization with observations vanishes after about 6?9 years. Recent multimodel results suggest that there is relatively more decadal predictive skill in the North Atlantic, western Pacific, and Indian Oceans than in other regions of the world oceans. Aspects of decadal variability of SSTs, like the mid-1970s shift in the Pacific, the mid-1990s shift in the northern North Atlantic and western Pacific, and the early-2000s hiatus, are better represented in initialized hindcasts compared to uninitialized simulations. There is evidence of higher skill in initialized multimodel ensemble decadal hindcasts than in single model results, with multimodel initialized predictions for near-term climate showing somewhat less global warming than uninitialized simulations. Some decadal hindcasts have shown statistically reliable predictions of surface temperature over various land and ocean regions for lead times of up to 6?9 years, but this needs to be investigated in a wider set of models. As in the early days of El Niño?Southern Oscillation (ENSO) prediction, improvements to models will reduce the need for bias adjustment, and increase the reliability, and thus usefulness, of decadal climate predictions in the future.
M3 – doi: 10.1175/BAMS-D-12-00241.1
UR – https://doi.org/10.1175/BAMS-D-12-00241.1
ER –

NR – 175
TY – JOUR
AU – Thoma, Malte
AU – Greatbatch, Richard J.
AU – Kadow, Christopher
AU – Gerdes, Ruediger
TI – Decadal hindcasts initialized using observed surface wind stress: Evaluation and prediction out to 2024
JO – Geophysical Research Letters
VL – 42
IS – 15
UR – http://dx.doi.org/10.1002/2015GL064833
DO – 10.1002/2015GL064833
SP – 6454
EP – 6461
PY – 2015
AB – We use surface air temperature to evaluate the decadal forecast skill of the fully coupled Max Planck Institut Earth System Model (MPI-ESM) initialized using only surface wind stress applied to the ocean component of the model (Modini: Model initialization by partially coupled spin-up). Our analysis shows that the greenhouse gas forcing alone results in a significant forecast skill on the 2–5 and 6–9 year range even for uninitialized hindcasts. For the first forecast year, the forecast skill of Modini is generally comparable with previous initialization procedures applied to MPI-ESM. But only Modini is able to generate a significant skill (correlation) in the tropical Pacific for a 2–5 year (and to a lesser extent for a 6–9 year) hindcast. Modini is also better able to capture the observed hiatus in global warming in hindcast mode than the other methods. Finally, we present forecasts for 2015 and the average of years 2016–2019 and 2020–2024, predicting an end to the hiatus.
ER –

NR – 176
TY – JOUR
A1 – Boer, G. J.
A1 – Smith, D. M.
A1 – Cassou, C.
A1 – Doblas-Reyes, F.
A1 – Danabasoglu, G.
A1 – Kirtman, B.
A1 – Kushnir, Y.
A1 – Kimoto, M.
A1 – Meehl, G. A.
A1 – Msadek, R.
A1 – Mueller, W. A.
A1 – Taylor, K. E.
A1 – Zwiers, F.
A1 – Rixen, M.
A1 – Ruprich-Robert, Y.
A1 – Eade, R.
T1 – The Decadal Climate Prediction Project (DCPP) contribution to CMIP6
JA – Geosci. Model Dev.
VL – 9
IS – 10
SP – 3751
EP – 3777
PY – 2016
UR – https://www.geosci-model-dev.net/9/3751/2016/
DO – 10.5194/gmd-9-3751-2016
AB – The Decadal Climate Prediction Project (DCPP) is a coordinated multi-model investigation into decadal climate prediction, predictability, and variability. The DCPP makes use of past experience in simulating and predicting decadal variability and forced climate change gained from the fifth Coupled Model Intercomparison Project (CMIP5) and elsewhere. It builds on recent improvements in models, in the reanalysis of climate data, in methods of initialization and ensemble generation, and in data treatment and analysis to propose an extended comprehensive decadal prediction investigation as a contribution to CMIP6 (Eyring et al., 2016) and to the WCRP Grand Challenge on Near Term Climate Prediction (Kushnir et al., 2016). The DCPP consists of three components. Component A comprises the production and analysis of an extensive archive of retrospective forecasts to be used to assess and understand historical decadal prediction skill, as a basis for improvements in all aspects of end-to-end decadal prediction, and as a basis for forecasting on annual to decadal timescales. Component B undertakes ongoing production, analysis and dissemination of experimental quasi-real-time multi-model forecasts as a basis for potential operational forecast production. Component C involves the organization and coordination of case studies of particular climate shifts and variations, both natural and naturally forced (e.g. the “hiatus”, volcanoes), including the study of the mechanisms that determine these behaviours. Groups are invited to participate in as many or as few of the components of the DCPP, each of which are separately prioritized, as are of interest to them. The Decadal Climate Prediction Project addresses a range of scientific issues involving the ability of the climate system to be predicted on annual to decadal timescales, the skill that is currently and potentially available, the mechanisms involved in long timescale variability, and the production of forecasts of benefit to both science and society.
ER –

NR – 177
TY – JOUR
AU – Smith, Doug M.
AU – Allan, Richard P.
AU – Coward, Andrew C.
AU – Eade, Rosie
AU – Hyder, Patrick
AU – Liu, Chunlei
AU – Loeb, Norman G.
AU – Palmer, Matthew D.
AU – Roberts, Chris D.
AU – Scaife, Adam A.
TI – Earth’s energy imbalance since 1960 in observations and CMIP5 models
JO – Geophysical Research Letters
VL – 42
IS – 4
UR – http://dx.doi.org/10.1002/2014GL062669
DO – 10.1002/2014GL062669
SP – 1205
EP – 1213
PY – 2015
AB – Observational analyses of running 5 year ocean heat content trends (Ht) and net downward top of atmosphere radiation (N) are significantly correlated (r?~?0.6) from 1960 to 1999, but a spike in Ht in the early 2000s is likely spurious since it is inconsistent with estimates of N from both satellite observations and climate model simulations. Variations in N between 1960 and 2000 were dominated by volcanic eruptions and are well simulated by the ensemble mean of coupled models from the Fifth Coupled Model Intercomparison Project (CMIP5). We find an observation-based reduction in N of -? 0.31?±?0.21?W?m-2 between 1999 and 2005 that potentially contributed to the recent warming slowdown, but the relative roles of external forcing and internal variability remain unclear. While present-day anomalies of N in the CMIP5 ensemble mean and observations agree, this may be due to a cancelation of errors in outgoing longwave and absorbed solar radiation.
ER –

NR – 178
TY – JOUR
A1 – Piecuch, C. G.
A1 – Quinn, K. J.
T1 – El Niño, La Niña, and the global sea level budget
JA – Ocean Sci.
VL – 12
IS – 6
SP – 1165
EP – 1177
PY – 2016
UR – https://www.ocean-sci.net/12/1165/2016/
DO – 10.5194/os-12-1165-2016
AB – Previous studies show that nonseasonal variations in global-mean sea level (GMSL) are significantly correlated with El Niño–Southern Oscillation (ENSO). However, it has remained unclear to what extent these ENSO-related GMSL fluctuations correspond to steric (i.e., density) or barystatic (mass) effects. Here we diagnose the GMSL budget for ENSO events observationally using data from profiling floats, satellite gravimetry, and radar altimetry during 2005–2015. Steric and barystatic effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize the barystatic component. The steric contributions reflect changes in global ocean heat content, centered on the Pacific. Distributions of ocean heat storage in the Pacific arise from a mix of diabatic and adiabatic effects. Results have implications for understanding the surface warming slowdown and demonstrate the usefulness of the Global Ocean Observing System for constraining Earth’s hydrological cycle and radiation imbalance.
ER –

NR – 179
TY – JOUR
T1 – Varying temperature and heat content signatures in the central Labrador Sea at different layers and timescales
AU – Li, Feili
AU – Jo, Young-Heon
AU – Yan, Xiao-Hai
AU – Timothy Liu, W.
JO – Deep Sea Research Part I: Oceanographic Research Papers
VL – 103
SP – 114
EP – 124
PY – 2015
DO – https://doi.org/10.1016/j.dsr.2015.04.012
UR – http://www.sciencedirect.com/science/article/pii/S0967063715000862
AB – The dominant modes of variability in the temperature and ocean heat content (OHC; 0–1000m) of the central Labrador Sea were investigated using the Hilbert–Huang Transform (HHT) based on Argo profiles collected during 2003–2012. Warming trends of approximately 0.03°Cyr-1 were observed in the upper 2000m of the water column. A strong annual temperature cycle exists and dominates at the 500m depth, while signals at the interannual timescales can explain most of the temperature variability at the 1000m and 1500m depths. These interannual signals are closely correlated to the variability of deep convection in the Labrador Sea, which has intermittent enhancement of mixed layer depth (MLD)>1500m. The Hilbert spectrum from the OHC in the Labrador Sea interior reveals two important components at frequencies of 0.8-1.2cycleyr-1 (T=0.8–1.25 years) and 0.1-0.3cycleyr-1 (T=3.3–10 years), respectively, superimposed on the warming trends. The former corresponds to the dominant seasonal cycle due to surface heating, while the latter is concomitant with the timing of the reoccurrence of convective events. We also found that the cumulative North Atlantic Oscillation (NAO) index significantly correlates to the low-frequency OHC variations. Therefore, the interannual signals in the Labrador Sea at especially the intermediate layers are attributed to changes in the deep convective processes and the atmospheric conditions. By comparing with an extended OHC record (1945–2010), it was further shown that the warming trends obtained from the 10-year Argo record are part of multi-decadal variations that presumably reflect the Atlantic Multi-decadal Oscillation (AMO). In addition, the recent OHC changes in the Labrador Sea (i.e., increased heat in the deeper layers) may be related to the current global warming hiatus, suggesting the potential contributions from the Atlantic Meridional Overturning Circulation (AMOC) to the low-frequency OHC in the Labrador Sea.
ER –

NR – 180
TY – JOUR
T1 – Very early warning of next El Niño
JF – Proceedings of the National Academy of Sciences
SP – 2064
LP – 2066
DO – 10.1073/pnas.1323058111
VL – 111
IS – 6
AU – Ludescher, Josef
AU – Gozolchiani, Avi
AU – Bogachev, Mikhail I.
AU – Bunde, Armin
AU – Havlin, Shlomo
AU – Schellnhuber, Hans Joachim
PY – 2014
UR – http://www.pnas.org/content/111/6/2064.abstract
AB – The most important driver of climate variability is the El Niño Southern Oscillation, which can trigger disasters in various parts of the globe. Despite its importance, conventional forecasting is still limited to 6 mo ahead. Recently, we developed an approach based on network analysis, which allows projection of an El Niño event about 1 y ahead. Here we show that our method correctly predicted the absence of El Niño events in 2012 and 2013 and now announce that our approach indicated (in September 2013 already) the return of El Niño in late 2014 with a 3-in-4 likelihood. We also discuss the relevance of the next El Niño to the question of global warming and the present hiatus in the global mean surface temperature.
ER –

NR – 181
TY – JOUR
AU – Laepple, T.
AU – Huybers, P.
TI – Global and regional variability in marine surface temperatures
JO – Geophysical Research Letters
VL – 41
IS – 7
UR – http://dx.doi.org/10.1002/2014GL059345
DO – 10.1002/2014GL059345
SP – 2528
EP – 2534
PY – 2014
AB – The temperature variability simulated by climate models is generally consistent with that observed in instrumental records at the scale of global averages, but further insight can also be obtained from regional analysis of the marine temperature record. A protocol is developed for comparing model simulations to observations that account for observational noise and missing data. General consistency between Coupled Model Intercomparison Project Phase 5 model simulations and regional sea surface temperature variability is demonstrated at interannual timescales. At interdecadal timescales, however, the variability diagnosed from observations is significantly greater. Discrepancies are greatest at low latitudes, with none of the 41 models showing equal or greater interdecadal variability. The pattern of suppressed variability at longer timescales and smaller spatial scales appears consistent with models generally being too diffusive. Suppressed variability of low-latitude marine temperatures points to underestimation of intrinsic variability and may help explain why few models reproduce the observed temperature trends during the last 15?years.
ER –

NR – 182
TY – JOUR
AU – de Boisséson, E.
AU – Balmaseda, M. A.
AU – Abdalla, S.
AU – Källén, E.
AU – Janssen, P. A. E. M.
TI – How robust is the recent strengthening of the Tropical Pacific trade winds?
JO – Geophysical Research Letters
VL – 41
IS – 12
UR – http://dx.doi.org/10.1002/2014GL060257
DO – 10.1002/2014GL060257
SP – 4398
EP – 4405
PY – 2014
AB – The persistent strengthening of the trade winds over the Pacific Ocean over the past 20 years has recently been proposed as a driver for the increase of ocean heat uptake linked to the hiatus in surface global warming. Crucial aspects in this argument are the reliability of the wind signal, usually derived from atmospheric reanalyses, and the ability of models to represent it. This study addresses these two aspects by comparing various observations with reanalyses and model integrations from the European Centre for Medium-Range Weather Forecasts system. We show that the strengthening of trades over the Pacific is a robust feature in several observational data sets as well as in the reanalyses based on full and limited sets of observations. The wind trend is also reproduced in an atmospheric model integration forced by sea surface temperature analysis, a result that opens the doors to further investigation on the nature of the changes.
ER –

NR – 183
TY – JOUR
AU – Gleckler, Peter J.
AU – Durack, Paul J.
AU – Stouffer, Ronald J.
AU – Johnson, Gregory C.
AU – Forest, Chris E.
TI – Industrial-era global ocean heat uptake doubles in recent decades
JF – Nature Climate Change
PY – 2016
VL – 6
SP – 394
UR – http://dx.doi.org/10.1038/nclimate2915
DO – 10.1038/nclimate2915
AB – Formal detection and attribution studies have used observations and climate models to identify an anthropogenic warming signature in the upper (0–700?m) ocean1,2,3,4. Recently, as a result of the so-called surface warming hiatus, there has been considerable interest in global ocean heat content (OHC) changes in the deeper ocean, including natural and anthropogenically forced changes identified in observational5,6,7, modelling8,9 and data re- analysis10,11 studies. Here, we examine OHC changes in the context of the Earth’s global energy budget since early in the industrial era (circa 1865– 2015) for a range of depths. We rely on OHC change estimates from a diverse collection of measurement systems including data from the nineteenth-century Challenger expedition12, a multi-decadal record of ship-based in situ mostly upper-ocean measurements, the more recent near-global Argo floats profiling to intermediate (2,000?m) depths13, and full-depth repeated transoceanic sections5. We show that the multi-model mean constructed from the current generation of historically forced climate models is consistent with the OHC changes from this diverse collection of observational systems. Our model- based analysis suggests that nearly half of the industrial-era increases in global OHC have occurred in recent decades, with over a third of the accumulated heat occurring below 700?m and steadily rising.
ER –

NR – 184
TY – JOUR
AU – Liu, Qin-Yan
AU – Feng, Ming
AU – Wang, Dongxiao
AU – Wijffels, Susan
TI – Interannual variability of the Indonesian Throughflow transport: A revisit based on 30 year expendable bathythermograph data
JO – Journal of Geophysical Research: Oceans
VL – 120
IS – 12
UR – http://dx.doi.org/10.1002/2015JC011351
DO – 10.1002/2015JC011351
SP – 8270
EP – 8282
PY – 2015
AB – Based on 30 year repeated expendable bathythermograph (XBT) deployments between Fremantle, Western Australia, and the Sunda Strait, Indonesia, from 1984 to 2013, interannual variability of geostrophic transport of the Indonesian Throughflow (ITF) and its relationships with El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are investigated. The IOD induced coastal Kelvin waves propagate along the Sumatra-Java coast of Indonesia, and ENSO induced coastal Kelvin waves propagate along the northwest coast of Australia, both influencing interannual variations of the ITF transport. The ITF geostrophic transport is stronger during La Niña phase and weaker during El Niño phase, with the Niño3.4 index leading the ITF variability by 7 months. The Indian Ocean wind variability associated with the IOD to a certain extent offset the Pacific ENSO influences on the ITF geostrophic transport during the developing and mature phases of El Niño and La Niña, due to the covarying IOD variability with ENSO. The ITF geostrophic transport experiences a strengthening trend of about 1 Sv every 10 years over the study period, which is mostly due to a response to the strengthening of the trade winds in the Pacific during the climate change hiatus period. Decadal variations of the temperature-salinity relationships need to be considered when estimating the geostrophic transport of the ITF using XBT data.
ER –

NR – 185
TY – JOUR
AU – Li, Jianping
AU – Sun, Cheng
AU – Jin, Fei-Fei
TI – NAO implicated as a predictor of Northern Hemisphere mean temperature multidecadal variability
JO – Geophysical Research Letters
VL – 40
IS – 20
UR – http://dx.doi.org/10.1002/2013GL057877
DO – 10.1002/2013GL057877
SP – 5497
EP – 5502
PY – 2013
AB – The twentieth century Northern Hemisphere mean surface temperature (NHT) is characterized by a multidecadal warming-cooling-warming pattern followed by a flat trend since about 2000 (recent warming hiatus). Here we demonstrate that the North Atlantic Oscillation (NAO) is implicated as a useful predictor of NHT multidecadal variability. Observational analysis shows that the NAO leads both the detrended NHT and oceanic Atlantic Multidecadal Oscillation (AMO) by 15–20?years. Theoretical analysis illuminates that the NAO precedes NHT multidecadal variability through its delayed effect on the AMO due to the large thermal inertia associated with slow oceanic processes. An NAO-based linear model is therefore established to predict the NHT, which gives an excellent hindcast for NHT in 1971–2011 with the recent flat trend well predicted. NHT in 2012–2027 is predicted to fall slightly over the next decades, due to the recent NAO decadal weakening that temporarily offsets the anthropogenically induced warming.
ER –

NR – 186
TY – JOUR
T1 – Northwestern Pacific typhoon intensity controlled by changes in ocean temperatures
JF – Science Advances
DO – 10.1126/sciadv.1500014
VL – 1
IS – 4
AU – Mei, Wei
AU – Xie, Shang-Ping
AU – Primeau, François
AU – McWilliams, James C.
AU – Pasquero, Claudia
PY – 2015
UR – http://advances.sciencemag.org/content/1/4/e1500014.abstract
AB – Dominant climatic factors controlling the lifetime peak intensity of typhoons are determined from six decades of Pacific typhoon data. We find that upper ocean temperatures in the low-latitude northwestern Pacific (LLNWP) and sea surface temperatures in the central equatorial Pacific control the seasonal average lifetime peak intensity by setting the rate and duration of typhoon intensification, respectively. An anomalously strong LLNWP upper ocean warming has favored increased intensification rates and led to unprecedentedly high average typhoon intensity during the recent global warming hiatus period, despite a reduction in intensification duration tied to the central equatorial Pacific surface cooling. Continued LLNWP upper ocean warming as predicted under a moderate [that is, Representative Concentration Pathway (RCP) 4.5] climate change scenario is expected to further increase the average typhoon intensity by an additional 14% by 2100.
ER –

NR – 187
TY – JOUR
AU – Takahashi, Chiharu
AU – Watanabe, Masahiro
TI – Pacific trade winds accelerated by aerosol forcing over the past two decades
JF – Nature Climate Change
PY – 2016
VL – 6
SP – 768
UR – http://dx.doi.org/10.1038/nclimate2996
DO – 10.1038/nclimate2996
AB – The Pacific trade winds, coupled with the zonal sea surface temperature gradient in the equatorial Pacific Ocean, control regional sea levels1, and therefore their trend is a great concern in the Pacific Rim. Over the past two decades, easterly winds have been accelerated in association with eastern tropical Pacific cooling2. They may represent natural interdecadal variability in the Pacific3 and possibly explain the recent global warming hiatus4,5,6,7. However, the intensification of the winds has been the strongest ever observed in the past century2,5,8, the reason for which is still unclear. Here we show, using multiple climate simulations for 1921–2014 by a global climate model, that approximately one-third of the trade-wind intensification for 1991–2010 can be attributed to changes in sulfate aerosols. The multidecadal sea surface temperature anomaly induced mostly by volcanic aerosols dominates in the western North Pacific, and its sign changed rapidly from negative to positive in the 1990s, coherently with Atlantic multidecadal variability9,10,11. The western North Pacific warming resulted in intensification of trade winds to the west of the dateline. These trends have not contributed much to the global warming hiatus, but have greatly impacted rainfall over the western Pacific islands.
ER –

NR – 188
TY – JOUR
AU – Li, Xichen
AU – Xie, Shang-Ping
AU – Gille, Sarah T.
AU – Yoo, Changhyun
TI – Atlantic-induced pan-tropical climate change over the past three decades
JF – Nature Climate Change
PY – 2015
VL – 6
SP – 275
UR – http://dx.doi.org/10.1038/nclimate2840
DO – 10.1038/nclimate2840
AB – During the past three decades, tropical sea surface temperature (SST) has shown dipole-like trends, with warming over the tropical Atlantic and Indo-western Pacific but cooling over the eastern Pacific. Competing hypotheses relate this cooling, identified as a driver of the global warming hiatus1,2, to the warming trends in either the Atlantic3,4 or Indian Ocean5. However, the mechanisms, the relative importance and the interactions between these teleconnections remain unclear. Using a state-of-the-art climate model, we show that the Atlantic plays a key role in initiating the tropical-wide teleconnection, and the Atlantic-induced anomalies contribute ~55–75% of the tropical SST and circulation changes during the satellite era. The Atlantic warming drives easterly wind anomalies over the Indo-western Pacific as Kelvin waves and westerly anomalies over the eastern Pacific as Rossby waves. The wind changes induce an Indo-western Pacific warming through the wind–evaporation–SST effect6,7, and this warming intensifies the La Niña-type response in the tropical Pacific by enhancing the easterly trade winds and through the Bjerknes ocean dynamical processes8. The teleconnection develops into a tropical-wide SST dipole pattern. This mechanism, supported by observations and a hierarchy of climate models, reveals that the tropical ocean basins are more tightly connected than previously thought.
ER –

NR – 189
TY – JOUR
T1 – Climate Signals in the Mid- to High-Latitude North Atlantic from Altimeter Observations
AU – Li, Feili
AU – Jo, Young-Heon
AU – Yan, Xiao-Hai
AU – Liu, W. Timothy
PY – 2015
DO – 10.1175/JCLI-D-12-00670.1
JF – Journal of Climate
SP – 4905
EP – 4925
VL – 29
IS – 13
AB – The variability of the sea surface height anomaly (SSHA) in the mid- to high-latitude North Atlantic for the period of 1993?2010 was investigated using the ensemble empirical mode decomposition to identify the dominant time scales. Sea level variations in the North Atlantic subpolar gyre (SPG) are dominated by the annual cycle and the long-term increasing trend. In comparison, the SSHA along the Gulf Stream (GS) is dominated by variability at intraseasonal and annual time scales. Moreover, the sea level rise in the SPG developed at a reduced rate in the 2000s compared to rates in the 1990s, which was accompanied by a rebound in SSHA variability following a period of lower variability in the system. These changes in both apparent trend and low-frequency SSHA oscillations reveal the importance of low-frequency variability in the SPG. To identify the possible contributing factors for these changes, the heat content balance (equivalent variations in the sea level) in the subpolar region was examined. The results indicate that horizontal circulations may primarily contribute to the interannual to decadal variations, while the air?sea heat flux is not negligible at annual time scale. Furthermore, the low-frequency variability in the SPG relates to the propagation of Atlantic meridional overturning circulation (AMOC) variations from the deep-water formation region to midlatitudes in the North Atlantic, which might have the implications for recent global surface warming hiatus.
UR – https://doi.org/10.1175/JCLI-D-12-00670.1
ER –

NR – 190
TY – JOUR
TI – How Long will the Pause of Global Warming Stay Again?
AU – Bin, Huang Jian
AU – Yong, Luo
AU – Wu, Wang Shao
AU – Yu, Wen Xin
AU – Ci, Zhao Zong
PY – 2014
JO – Progressus Inquisitiones De Mutatione Climatis
VL – 10
IS – 6
SP – 465
EP – 468
DO – 10.3969/j.issn.1673-1719.2014.06.011
ER –

NR – 191
TY – JOUR
AU – Veettil, Bijeesh Kozhikkodan
AU – Pereira, Sebastián Felipe Ruiz
AU – Wang, Shanshan
AU – Valente, Pedro Teixeira
AU – Grondona, Atilio Efrain Bica
AU – Rondón, Adriana Coromoto Becerra Rondón
AU – Rekowsky, Isabel Cristiane
AU – de Souza, Sergio Florêncio
AU – Bianchini, Nilceia
AU – Bremer, Ulisses Franz
AU – Simões, Jefferson Cardia
TI – Un análisis comparativo del comportamiento diferencial de los glaciares en los Andes Tropicales usando teledetección
T2 – A comparative analysis of glacier retreat in the Tropical Andes using remote sensing
PY – 2016
JO – Investigaciones Geográficas
VL – 51
SP – 3
EP – 36
DO – 10.5354/0719-5370.2016.41215
UR – https://investigacionesgeograficas.uchile.cl/index.php/IG/article/view/41215
AB – In this research paper, we analysed the behaviour of Tropical Andean glaciers in a changing climate. We used multi-source satellite images as well as meteorological datasets to achieve this objective. Representative glaciers in four different climatic zones, namely the inner tropics, northern wet outer tropics, southern wet outer tropics and dry outer tropics, were considered in this study. Changes in annual maximum snowline during 1985 – 2015 and also the decadal changes in the area between 1975 and 2015 of these glaciers were calculated. Furthermore, we analysed the rate of glacier retreat during the occurrence of El Niño–Southern Oscillation and Pacific Decadal Oscillation. It is observed that the glaciers in both the inner and outer tropics underwent retreat during the study period and most of this retreat occurred during 1975 – 1997 which is parallel with the so-called Pacific shift. Exceptional variations in snowline altitude were observed when an El Niño event occurs during the warm phase of the Pacific Decadal Oscillation. No significant signals of the recent hiatus in global warming were observed, except in the dry outer tropics which are situated near the subtropical region.
ER –

NR – 192
TY – JOUR
TI – The Global Warming Hiatus Simulated in HadGEM2-AO Based on RCP8.5
AU – Wie, Jieun
AU – Moon, Byung-Kwon
AU – Kim, Ki-Young
AU – Lee, Johan
PY – 2014
JO – Journal of the Korean earth science society
VL – 35
IS – 4
SP – 249
EP – 258
DO – 10.5467/JKESS.2014.35.4.249
UR – http://www.koreascience.or.kr/article/ArticleFullRecord.jsp?cn=JGGHBA_2014_v35n4_249
AB – Despite the greenhouse gases like carbon dioxide have steadily increased in atmosphere, the overall trend of the global average surface air temperature has stalled during the last decade (2002-present). This phenomenon is often called hiatus or warming pause, which is challenging the prevailing view that anthropogenic forcing causes warming environment. Our study characterized the hiatus by analyzing the HadGEM2-AO (95 yrs) simulation data based on RCP8.5 scenario. The PC2 time series from the EOF of the zonal mean vertical ocean temperature has been defined as the index that represents the warming pause. The relationship between the hiatus, ENSO and the changes in climate system are identified by utilizing the newly defined PC2. Since the La Nina index (defined as the negative of NINO3 index) leads PC2 by about 11 months, it may be possible that the La Nina causes the warming to be interrupted. We also show that the cooling of the climate system closed tied to the heat penetration into the deep ocean, indicating the weakening the warming rate is due to the oceanic heat uptake. Finally, the global warming hiatus is characterized by the anomalous warming in Arctic region as well as the intensification of the trade wind in the equatorial Pacific.
ER –

NR – 193
TY – JOUR
TI – Linear and Nonlinear Trends of Extreme Temperatures in Korea
AU – Kim, Sang-Wook
AU – Song, Kanghyun
AU – Kim, Seo-Yeon
AU – Son, Seok-Woo
AU – Franzke, C.
JO – Atmosphere
VL – 24
IS – 3
SP – 379
EP – 390
PY – 2014
UR – http://www.dbpia.co.kr/Article/NODE02486406
AB – This study explores the long-term trends of surface air temperatures in 11 KMA stations over the period of 1960~2012. Both linear and nonlinear trends are examined for the 95^th, 50^th, and 5^th percentiles of daily maximum (T_max) and minimum temperatures (T_min) by using quantile regression method. It is found that in most stations linear trends of T_max and T_min are generally stronger in winter than in summer, and warming trend of the 5^th percentile temperature (cold extreme) is stronger than that of the 95^th percentile temperature (warm extreme) in both seasons. The nonlinear trends, which are evaluated by the second order polynomial fitting, show a strong nonlinearity in winter. Specifically, winter temperatures have increased until 2000s but slightly decreased afterward in all percentiles. This contrasts with the 95^th and 50t^h percentiles of summer T_min that show a decreasing trend until 1980s then an increasing trend. While this result is consistent with a seasonal dependence of the recent global warming hiatus, most of the nonlinear trends are statistically insignificant, making a quantitative attribution of nonlinear temperature trends challenging.
ER –

NR – 194
TY – JOUR
TI – Enhanced Responses of Sea Surface Temperature over Offshore China to Global Warming and Hiatus
AU – Tan, Hongjian
AU – Cai, Rongshuo
AU – Huang, Ronghui
PY – 2016
JO – Advances in Climate Change Research
VL – 12
IS – 6
SP – 500
EP – 507
DO – 10.12006/j.issn.1673-1719.2016.038
UR – http://www.climatechange.cn/CN/abstract/abstract9266.shtml
AB – In this study, we assessed and compared the sea surface temperature (SST) trends between offshore China and other sea regions of interest as well as global mean surface temperature based on four SST datasets. The results revealed an enhanced SST response over offshore China during different periods. During the accelerated global warming periods (1980s and 1990s), SST over offshore China shows faster rising trend than the global mean. The most pronounced warming area is located over the East China Sea, with the rising rate up to 0.60? per decade, which is 5 times faster than that of the global mean. While during the hiatus period (1998-2014), SST over offshore China exhibits significant cooling trend. The decadal variability of offshore China SST is closely linked to the Pacific Decadal Oscillation (PDO). The periods with rapid warming (cooling) over offshore China are consistent with the positive (negative) phase of PDO. PDO may affect SST over offshore China through the East Asian Monsoon and Kuroshio Current.
ER –

NR – 195
TY – JOUR
TI – Research on the global warming Hiatus
AU – Lin, Xiaopei
AU – Xu, Lixiao
AU – Li, Jianping
AU – Luo, Dehai
AU – Liu, Hailong
PY – 2016
JO – Advances in Earth Science
VL – 31
IS – 10
SP – 995
EP – 1000
DO – 10.11867/j.issn.1001-8166.2016.10.0995
UR – http://www.adearth.ac.cn/article/2016/1001-8166-31-10-995.html
AB – A global warming “hiatus” has been observed since the beginning of the 21st century despite the increase in heat-trapping greenhouse gases, challenging the current global warming studies. Focusing on the phenomena and mechanisms of the global warming “hiatus”, the National Key Research Program of China launched a project in July, 2016. The main research themes of this project cover: ?Revealing the spatial and temporal variability of the global warming hiatus, and quantifying the contributions of external forcing and internal (natural) variability, respectively; ?Revealing the role of the atmosphere in the global heat and energy redistribution under global warming hiatus; ?Revealing the role of the ocean in the global heat and energy redistribution under global warming hiatus; ?Investigating the predictability of the global warming hiatus. The key scientific issues to be resolved include: ?Identifying characteristics of the global warming hiatus and discerning the roles of decadal, multi-decadal oscillations; ?Revealing the role of ocean-atmosphere dynamical processes in the global redistribution of heat and energy; ?Understanding the predictability of the global warming hiatus. The research aims to predict the future development of the global warming hiatus, and to point out the possible impacts on China and other important areas, including “The Belt and Road” core area and the Polar Regions.
ER –

NR – 196
TY – JOUR
TI – Research Progress on Hiatus in The Process of Global Warming
AU – Chen, Xingrong
AU – Cai Yi
AU – Tan Jing
AU – Wang Lei
PY – 2014
JO – Advances in Earth Science
VL – 29
IS – 8
SP – 947
EP – 955
UR – http://www.adearth.ac.cn/article/2014/1001-8166-29-8-0947.html
AB – In the 21st century, global warming hiatus has become a new hotspot in the research of climate change. This paper introduces the research progress on this phenomenon in detail, especially the validation studies of hiatus, research on the influence of the radiation forcing and the natural variability of the climate system due to air?sea interaction, and then puts forward several puzzles that still need to be solved on current research of hiatus. The paper particularly introduces the international major view, which think that the main reason of the hiatus in this century is that the strengthened trade wind on the background of the PDO negative phase leads to the warm water “accumulation”? in the equatorial western Pacific while the cooling in equatorial eastern Pacific causes the heat transferred down to the deep ocean. Therefore, hiatus phenomenon does not mean the stop of global warming, but just the heat transportation to the deep ocean, which is another manifestation of global warming.
ER –

NR – 197
TY – JOUR
TI – A review of recent studies on global warming hiatus
AU – Song, Bin
AU – Zhi, Xie-Fei
AU – Hu, Yao-Xing
PY – 2015
JO – Transactions of Atmospheric Sciences
VL – 38
IS – 2
SP – 145
EP – 154
DO – 10.13878/j.cnki.dqkxxb.20150105002
UR – http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=njqxxyxb201502001
AB – Since the industrial revolution, the content of anthropogenic greenhouse gas is increasing. As a result, the global surface air temperature grows rapidly. However, the global surface air temperature has stalled since 1998, despite the greenhouse gas steadily increases. This paper reviewed the latest research progress on this phenomenon, especially the mechanism of the global warming hiatus. There are two main viewpoints on the mechanism, namely, the external forcing and natural variability. The former includes the influence of solar activity, volcanic aerosol particles, man-made aerosol particles and stratospheric water vapor forcing. Scientists in the opinion of natural variability hold the idea that the missing heat produced by human activity has entered the deep ocean, especially the layer below 700 m. They believe that the oceans play a key role in the global warming hiatus. There are two main ideas for that: Pacific Decadal Oscillation (PDO), especially the cooling in the eastern tropical Pacific, and the Atlantic Meridional Overturning Circulation (AMOC). The widely accepted idea on the mechanism of recent global warming hiatus is natural variability. The missing heat has entered the deep ocean. But it still remains controversial which ocean basin gain the missing heat.
ER –

NR – 198
TY – JOUR
TI – Evolution of Surface Temperature during Global Warming Hiatus Based on Observations and CMIP5 Simulations
AU – He, Jinhai
AU – Zhan, Fengxing
AU – Qi, Li
AU – Wang, Di
PY – 2016
JO – Chinese Journal of Atmospheric Sciences
VL – 40
IS – 1
SP – 33
EP – 45
DO – 10.3878/j.issn.1006-9895.1409.14217
UR – http://www.dqkxqk.ac.cn/dqkx/dqkx/ch/html/20160105.htm
AB – The rise in global surface temperature has significantly declined after 2000. In this study, the evolution of the surface temperature of the global land-mean and Eurasia middle-high latitudes during the global warming hiatus was analyzed based on CRU observations. Simulations and projections were also evaluated using the Coupled Model Intercomparison Project 5 (CMIP5). The results indicate that, in the global warming hiatus period, the trend of the global land-mean surface temperature is only 0.14? (10 a)-1, which is half that during 1976-1999. The trend is less than that before 2000 in nine of the 13 global land regions, and four of them show a decreasing trend. The Eurasia middle-high latitude region is the most interesting among all the regions. For 1976-1999, the Eurasia middle-high latitude region shows the largest warming among all the land regions and reaches 0.50? (10 a)-1. After 2000, the trend significantly declines to -0.17? (10 a)-1, the greatest cooling trend over land, globally, contributing 49.13% of the remarkable change in global land surface temperatures before and after 2000. Furthermore, the surface temperature of the Eurasia middle-high latitude region shows an opposite change in autumn and winter after 2000; the temperature of the former rises by 0.86? (10 a)-1, while the that of the latter decreases by 2.68? (10 a)-1. In CMIP5, only the simulation and projects in BCC-CSM1.1 under the RCP2.6 scenario and MRI-ESM1 under the RCP8.5 scenario reproduce the evolution of the global land-mean and Eurasia middle-high latitude surface temperature, as well as the opposite change between autumn and winter of the Eurasia middle-high latitude region, during the global warming hiatus. The temperature projection of the BCC-CSM1.1 under the RCP2.6 scenario for the Eurasia middle-high latitude remains flat, near 1.2?, after 2012, and jumps to 2? after 2020. The change in the MRI-ESM1’s projected temperature under the RCP8.5 scenario is close to zero before 2030; the temperature then rises remarkably, to ? (10 a)-1.
ER –

NR – 199
TY – JOUR
TI – Hiatus of global warming: A review
AU – Su, Jingzhi
AU – Wen, Min
AU – Ding, Yihui
AU – Gao, Yongqi
AU – Song, Yafang
PY – 2016
JO – Chinese Journal of Atmospheric Sciences
VL – 40
IS – 6
SP – 1143
EP – 1153
DO – 10.3878/j.issn.1006-9895.1512.15242
UR – http://www.dqkxqk.ac.cn/dqkx/ch/reader/create_pdf.aspx?file_no=20160604&flag=1&journal_id=dqkx
ER –

NR – 200
TY – JOUR
TI – Debate on Global Warming “Hiatus”
AU – Zhao, Zongci
AU – Luo, Yong
AU – Huang, Jianbin
PY – 2016
JO – Climate Change Research
VL – 12
IS – 6
SP – 571
EP – 574
DO – 10.12006/j.issn.1673-1719.2016.055
UR – http://www.climatechange.cn/CN/10.12006/j.issn.1673-1719.2016.055
ER –

NR – 201
TY – JOUR
TI – Climate change science and sustainable development
AU – Qin, Dahe
PY – 2014
JO – Progress in Geography
VL – 33
IS – 7
SP – 874
EP – 883
DO – 10.11820/dlkxjz.2014.07.002
UR – http://www.progressingeography.com/CN/abstract/abstract14634.shtml
AB – Since the Fourth Assessment Report (AR4) was released by the Intergovernmental Panel on Climate Change (IPCC) in 2007, new observations have further proved that the warming of the global climate system is unequivocal. Each of the last three successive decades before 2012 has been successively warmer at global mean surface temperature than any preceding decade since 1850. 1983-2012 was likely the warmest 30-year period of the last 1400 years. From 1998 to 2012, the rate of warming of the global land surface slowed down, but it did not reflect the long-term trends in climate change. The ocean has warmed, and the upper 75 m of the ocean warmed by more than 0.11? per decade since 1970. Over the period of 1971 to 2010, 93% of the net energy increase in the Earth’s climate system was stored in the oceans. The rate of global mean sea level rise has accelerated, which was up to 3.2 mm yr-1 between 1993 and 2010. Anthropogenic global ocean carbon stocks were likely to have increased and caused acidification of the ocean surface water. Since 1971, the glaciers and the Greenland and Antarctic ice sheets have been losing mass. Since 1979, the Arctic sea ice extent deceased at 3.5% to 4.1% per decade, and the Antarctic sea ice extent in the same period increased by 1.2% to 1.8% per decade. The extent of the Northern Hemisphere snow cover has decreased. Since the early 1980s, the permafrost temperatures have increased in most regions. Human influence has been detected in the warming of the atmosphere and the ocean, changes in the water cycle, reductions in snow and ice, global mean sea level rise, and changes in climate extremes. The largest contribution to the increase in the anthropogenic radiative forcing was by the increase in the atmospheric concentration of CO2 since 1750. It led to more than half of global warming since the 1950s (with 95 % confidence). It is predicted using Coupled Model Intercomparison Project Phase 5 (CMIP5) and Representative Concentration Pathways (RCPs) that the global mean surface temperature will continue to rise for the end of this century, the frequency of extreme events such as heat waves and heavy precipitation will increase, and precipitation will present a trend of “the dry becomes drier, the wet becomes wetter”. The temperature of the upper ocean will increase by 0.6 to 2.0? compared to the period of 1986 to 2005, heat will penetrate from the surface to the deep ocean which will affect ocean circulation, and sea level will rise by 0.26 to 0.82 m in 2100. Cryosphere will continue to warm. To control global warming, humans need to reduce the greenhouse gas emissions. If the increase in temperature is higher than 2? than before industrialization, the mean annual economic losses worldwide will reach 0.2% to 2.0% of income, and cause large-scale irreversible effects, including death, disease, food insecurity, inland flooding and water logging, and rural drinking water and irrigation difficulties that affect human security. If taking prompt actions, however, it is still possible to limit the increase in temperature within 2?. To curb the gradually out-of-control global warming and achieve the goal of sustainable development of the human society, global efforts to reduce emissions are needed.
ER –

NR – 202
TY – JOUR
TI – Temperature mutation and globe warming stagnate study in typical area of Yellow River basin in recently 60years
AU – Huang, Xing
AU – Ma, Long
AU – Liu, Ting-xi
AU – Wang, Jing-ru
AU – Liu, Dan-hui
AU – Li, Hong-yu
PY – 2016
JO – China Environmental Science
VL – 36
IS – 11
SP – 3253
EP – 3262
UR – http://manu36.magtech.com.cn/Jweb_zghjkx/CN/abstract/abstract14853.shtml
AB – The part of Yellow River in Inner Mongolia was chosen as a typical area of Yellow River Basin. The regional annual average maximum temperature (AMaxT), annual average minimum temperature (AMinT) and annual average temperature (AvT) from 1951 to 2012 were selected and analyzed by Mann-Kendall method. The temperature variations before and after the mutation and the warming stagnate following the mutation were also discussed. Annual (or seasonal) AMinT mutation happened first on 1977 to 1987. Then the AvT and AMaxT mutation happened on 1978 to 1993 and 1978 to 1994, respectively. The mutation period of average autumn and winter temperature were same as AMaxT. The earliest intra-annual mutation was winter (1977 to 1978), and the latest was summer (1987 to 1994). The winter and AMaxT had more variations than summer and AMinT. The increase ratio or AMinT was 0.231~0.604?/10a which have the most contribution. All the annual (or seasonal) temperatures had a warming stagnate from 1997 to 2007 after the mutation, successively. The stagnate occurred in spring and not stagnate occurred in summer. Mostly annual and seasonal temperature stagnate happened later than the global period which winter firstly, then autumn, the AvT was the last one (on 2007). The AMaxT increase rate was lower in the period of after mutation and before stagnate. However, the decrease rate of AMaxT if faster after stagnate. The AMinT was on the contrary. This indicates that the AMinT was sensitive to temperature increase and the AMaxT was sensitive to the temperature decrease. In seasonal, the spring AMaxT increase rate is higher from mutation to stagnate, and the spring AMinT decrease rate was the fastest after the temperature stagnate which is -0.324?/a.
ER –

NR – 203
TY – JOUR
TI – Recent global-warming “hiatus” and its implications on the measures to be taken against global warming
AU – Junichi, Tsuitii
PY – 2014
JO – Energy and power
VL – 64
IS – 283
SP – 80
EP – 86
UR – http://ci.nii.ac.jp/naid/40020266117/
ER –

NR – 204
TY – JOUR
TI – Surface Temperature and Precipitation Variation of Pastoral Transitional Zone in Northern China during 1964-2013
AU – Zhao, Wei
AU – Wei, Zhigang
AU – Zheng, Zhiyuan
AU – Dong, Wenjie
PY – 2016
JO – Plateau Meteorology
VL – 35
IS – 4
SP – 979
EP – 988
DO – 10.7522/j.issn.1000-0534.2015.00079
UR – http://html.rhhz.net/gyqx/html/20160413.htm
AB – This study analyzed the spatial-temporal change of historical temperature and precipitation in pastoral transitional zone in Northern China, based on observational temperature and precipitation grid datasets during 1964-2013 from Chinese Meteorology Administration (CMA). The climate division was made using rotated empirical orthogonal function (REOF) in the meantime. The result shows that: (1) The whole pastoral transitional zone in Northern China can be divided into 4 regions which can be simply named the west region, the central region, the southern section of the east region, and the northern section of the east region, respectively. (2) In general, the pastoral transitional zone in Northern China had experienced a significant warming during 1964-2013 which was mainly attributed to the warming of winter and larger increase of minimum temperature rather than the increase of maximum temperature. The pastoral transitional zone in Northern China had also experienced a slightly decrease of precipitation (13 mm less during 1964 -2013), and it was largely because the summer precipitation had declined the most in this period. (3) Focused on sub-regions, the temperature of the central region in pastoral transitional zone increased the most in the period of 1964-2013 among 4 sub-regions. As for the precipitation, annual precipitation in western north region decreased in the last 50 years mostly because of the decrease of spring precipitation in local. Meanwhile, the annual precipitation in central region and the southern section of the east region had decreased as well, but differently, it can be mainly attributed to the summer precipitation’s decline. Moreover, the annual precipitation increased in the northern section of the east region, and the spring precipitation contributed it the most. (4) The pastoral transitional zone in Northern China has experienced a warming hiatus resembling to the global warming hiatus since late 1990s, only the temperature has declined more, meaning that the declining trend of temperature in pastoral transitional zone is more obvious.
ER –

NR – 205
TY – JOUR
TI – Characteristics of Climate Change over the Tibetan Plateau Under the Global Warming During 1979-2014
AU – Duan, Anmin
AU – Xiao, Zhixiang
AU – Wu, Guoxiong
PY – 2016
JO – Advances in Climate Change Research
VL – 12
IS – 5
SP – 374
EP – 381
DO – 10.12006/j.issn.1673-1719.2016.039
UR – http://www.climatechange.cn/CN/Y2016/V12/I5/374
AB – Global warming has been a hot issue during recent decades, while the global warming hiatus since 1998 was detected as documented by many papers, meanwhile the Tibetan Plateau (TP) experiencing a rapid warming process. Based on previous studies, this paper mainly reviews the TP climate change under the global warming in four aspects: temperature, snow cover, precipitation and atmospheric apparent heat source, and points out that the accelerated warming over the TP results in the retreat of snow cover accompanied by the increase of precipitation. Though the TP heat source has been declined in recent decades whether based on observation or reanalysis datasets, it shows large uncertainties.
ER –

NR – 206
TY – JOUR
TI – CMIP5 climate model simulates the empirical study of global temperature change from 1850 to 2014
AU – Meng, Wei
AU – Fangli, Qiao
PY – 2016
JO – SCIENTIA SINICA Terrae
VL – 46
IS – 12
SP – 1675
EP – 1688
DO – 10.1360/N072015-00465
UR – http://engine.scichina.com/publisher/scp/journal/SSTe/46/12/10.1360/N072015-00465
ER –

NR – 207
TY – JOUR
T1 – The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability
AU – Kay, J. E.
AU – Deser, C.
AU – Phillips, A.
AU – Mai, A.
AU – Hannay, C.
AU – Strand, G.
AU – Arblaster, J. M.
AU – Bates, S. C.
AU – Danabasoglu, G.
AU – Edwards, J.
AU – Holland, M.
AU – Kushner, P.
AU – Lamarque, J.-F.
AU – Lawrence, D.
AU – Lindsay, K.
AU – Middleton, A.
AU – Munoz, E.
AU – Neale, R.
AU – Oleson, K.
AU – Polvani, L.
AU – Vertenstein, M.
PY – 2014
DO – 10.1175/BAMS-D-13-00255.1
JF – Bulletin of the American Meteorological Society
SP – 1333
EP – 1349
VL – 96
IS – 8
AB – While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments [e.g., phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model, version 5). The core simulations replay the twenty to twenty-first century (1920?2100) 30 times under historical and representative concentration pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-yr-long preindustrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on twentieth- to twenty-first-century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.
UR – https://doi.org/10.1175/BAMS-D-13-00255.1
ER –

NR – 208
TY – JOUR
AU – Meehl, Gerald A.
AU – Teng, Haiyan
TI – Case studies for initialized decadal hindcasts and predictions for the Pacific region
JO – Geophysical Research Letters
VL – 39
IS – 22
UR – http://dx.doi.org/10.1029/2012GL053423
DO – 10.1029/2012GL053423
PY – 2012
AB – Case studies involving notable past decadal climate variability are analyzed for the mid-1970s climate shift, when the tropical Pacific warmed over a decade and globally averaged temperature rapidly increased, and the early 2000s hiatus when the tropical Pacific cooled over a decade and global temperatures warmed little. Ten year hindcasts following the CMIP5 decadal climate prediction experiment design are analyzed for those two periods using two different initialization techniques in a global coupled climate model, the CCSM4. There is additional skill in the initialized hindcasts for surface temperature patterns over the Pacific region for those two case studies over and above that in free-running historical simulations with the same model. A 30 year hindcast also shows added skill over the Pacific compared to the historical simulations. A 30 year prediction from the initialized model simulations shows less global warming for the 2016–2035 period than the free-running model projection for that same time period.
ER –

NR – 209
TY – JOUR
T1 – Anthropogenic CO2 warming challenged by 60-yearcycle
AU – Gervais, François
JO – Earth-Science Reviews
VL – 155
SP – 129
EP – 135
PY – 2016
DO – https://doi.org/10.1016/j.earscirev.2016.02.005
UR – http://www.sciencedirect.com/science/article/pii/S0012825216300277
AB – Time series of sea-level rise are fitted by a sinusoid of period ~60years, confirming the cycle reported for the global mean temperature of the earth. This cycle appears in phase with the Atlantic Multidecadal Oscillation (AMO). The last maximum of the sinusoid coincides with the temperature plateau observed since the end of the 20th century. The onset of declining phase of AMO, the recent excess of the global sea ice area anomaly and the negative slope of global mean temperature measured by satellite from 2002 to 2015, all these indicators sign for the onset of the declining phase of the 60-yearcycle. Once this cycle is subtracted from observations, the transient climate response is revised downwards consistent with latest observations, with latest evaluations based on atmospheric infrared absorption and with a general tendency of published climate sensitivity. The enhancement of the amplitude of the CO2 seasonal oscillations which is found up to 71% faster than the atmospheric CO2 increase, focus on earth greening and benefit for crops yields of the supplementary photosynthesis, further minimizing the consequences of the tiny anthropogenic contribution to warming.
ER –

NR – 210
TY – JOUR
AU – Lorentzen, Torbjørn
PY – 2015
TI – A statistical analysis of sea temperature data
JO – Theoretical and Applied Climatology
SP – 585
EP – 610
VL – 119
IS – 3
AB – The paper analyzes sea temperature series measured at two geographical locations along the coast of Norway. We address the question whether the series are stable over the sample period 1936–2012 and whether we can measure any signal of climate change in the regional data. We use nonstandard supF, OLS-based CUSUM, RE, and Chow tests in combination with the Bai-Perron’s structural break test to identify potential changes in the temperature. The augmented Dickey-Fuller, the KPSS, and the nonparametric Phillips-Perron tests are in addition applied in the evaluation of the stochastic properties of the series. The analysis indicates that both series undergo similar structural instabilities in the form of small shifts in the temperature level. The temperature at Lista (58° 06′ N, 06° 38′ E) shifts downward about 1962 while the Skrova series (68° 12′ N, 14° 10′ E) shifts to a lower level about 1977. Both series shift upward about 1987, and after a period of increasing temperature, both series start leveling off about the turn of the millennium. The series have no significant stochastic or deterministic trend. The analysis indicates that the mean temperature has moved upward in decadal, small steps since the 1980s. The result is in accordance with recent analyses of sea temperatures in the North Atlantic. The findings are also related to the so-called hiatus phenomenon where natural variation in climate can mask global warming processes. The paper contributes to the discussion of applying objective methods in measuring climate change.
UR – https://doi.org/10.1007/s00704-014-1119-x
DO – 10.1007/s00704-014-1119-x
ER –

NR – 211
TY – JOUR
AU – Li, Qingxiang
AU – Yang, Su
AU – Xu, Wenhui
AU – Wang, Xiaolan L.
AU – Jones, Phil
AU – Parker, David
AU – Zhou, Liming
AU – Feng, Yang
AU – Gao, Yun
TI – China experiencing the recent warming hiatus
JO – Geophysical Research Letters
VL – 42
IS – 3
UR – http://dx.doi.org/10.1002/2014GL062773
DO – 10.1002/2014GL062773
SP – 889
EP – 898
PY – 2015
AB – Based on the homogenized data set, we analyze changes in mean temperature and some extreme temperature indices over China since 1961 and especially during the recent warming hiatus period (1998–2012) in a global average context. The result shows that the decrease of annual mean maximum has contributed most to the decreases in overall mean temperature and in diurnal temperature range (DTR) during the warming hiatus period. In most parts of China except the southwest, the summer mean maximum temperature (TxS) shows the largest increase, while the winter mean minimum temperature (TnW) indicates slight cooling trends. These changes have augmented the seasonal cycle and increased the likelihood of extreme warm and cold events. Further analyses reveal that the increases in TxS are significantly correlated with concurrent increases in solar radiation. In southwest China, the annual mean temperature, TxS, TnW, and DTR increased during 1998–2012, possibly related to increased dryness in this region during the hiatus period.
ER –

NR – 212
TY – JOUR
AU – Ueda, Hiroaki
AU – Kamae, Youichi
AU – Hayasaki, Masamitsu
AU – Kitoh, Akio
AU – Watanabe, Shigeru
AU – Miki, Yurisa
AU – Kumai, Atsuki
TI – Combined effects of recent Pacific cooling and Indian Ocean warming on the Asian monsoon
JA – Nature Communications
PY – 2015
VL – 6
SP – 8854
UR – http://dx.doi.org/10.1038/ncomms9854
DO – 10.1038/ncomms9854
AB – Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase. During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase. This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale. Here, based on model experiments, we show that the SST pattern during the hiatus explains pronounced regional anomalies of rainfall in the Asian monsoon region and thermodynamic effects due to specific humidity change are secondary. Specifically, Indo-Pacific SST anomalies cause convection to intensify over the tropical western Pacific, which in turn suppresses rainfall in mid-latitude East Asia through atmospheric teleconnection. Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.
ER –

NR – 213
TY – JOUR
AU – Saffioti, Claudio
AU – Fischer, Erich M.
AU – Knutti, Reto
TI – Contributions of atmospheric circulation variability and data coverage bias to the warming hiatus
JO – Geophysical Research Letters
VL – 42
IS – 7
UR – http://dx.doi.org/10.1002/2015GL063091
DO – 10.1002/2015GL063091
SP – 2385
EP – 2391
PY – 2015
AB – The warming hiatus shows a strong seasonal and geographical asymmetry, with cooling in the Northern Hemisphere winter, especially over land, and warming elsewhere and in the other seasons. We show that the characteristics of the Northern Hemisphere winter cooling in 1998–2012 can mostly be explained by missing observations and by internal variability in the atmospheric circulation of the Northern Hemisphere extratropics. Estimates of the annual and seasonal temperature trends in 1998–2012 obtained by considering the concurrent effects of unforced natural variability and of coverage bias are much closer to the corresponding long-term trends. Reanalyses suggest that the coverage bias was exceptionally pronounced during recent years and that an area of strong warming was missed due to the incomplete observational coverage. Coupled Model Intercomparison Project Phase 5 climate models indicate that trends in atmospheric circulation during the hiatus period did not occur as a response to anthropogenic forcing.
ER –

NR – 214
TY – JOUR
T1 – Clarifying the Roles of Greenhouse Gases and ENSO in Recent Global Warming through Their Prediction Performance
AU – Triacca, Umberto
AU – Pasini, Antonello
AU – Attanasio, Alessandro
AU – Giovannelli, Alessandro
AU – Lippi, Marco
PY – 2014
DO – 10.1175/JCLI-D-13-00784.1
JF – Journal of Climate
SP – 7903
EP – 7910
VL – 27
IS – 20
AB – It is well known that natural external forcings and decadal-to-millennial variability drove changes in the climate system throughout the Holocene. Regarding recent times, attribution studies have shown that greenhouse gases (GHGs) determined the trend of temperature (T) in the last half century, while circulation patterns contributed to modify its interannual, decadal, or multidecadal behavior over this period. Here temperature predictions based on vector autoregressive models (VARs) have been used to study the influence of GHGs and El Niño?Southern Oscillation (ENSO) on recent temperature behavior. It is found that in the last decades of steep temperature increase, ENSO shows just a very short-range influence on T, while GHGs are dominant for each forecast horizon. Conversely and quite surprisingly, in the previous quasi-stationary period the influences of GHGs and ENSO are comparable, even at longer range. Therefore, if the recent hiatus in global temperatures should persist into the near future, an enhancement of the role of ENSO can be expected. Finally, the predictive ability of GHGs is more evident in the Southern Hemisphere, where the temperature series is smoother.
UR – https://doi.org/10.1175/JCLI-D-13-00784.1
ER –

NR – 215
TY – JOUR
T1 – The global warming hiatus’s irrelevance
JO – Science
SP – 1482
LP – 1483
DO – 10.1126/science.350.6267.1482-d
VL – 350
IS – 6267
AU – Wehner, Michael F.
AU – Easterling, David R.
PY – 2015
UR – http://science.sciencemag.org/content/350/6267/1482.4.abstract
ER –

NR – 216
TY – JOUR
AU – Quirk, Tom
PY – 2012
TI – Did the global temperature trend change at the end of the 1990s?
JO – Asia-Pacific Journal of Atmospheric Sciences
SP – 339
EP – 344
VL – 48
IS – 4
AB – The apparent leveling of the global temperature time series at the end of the 1990s may represent a break in the upward trend. A study of the time series measurements for temperature, carbon dioxide, humidity and methane shows changes coincident with phase changes of the Atlantic and Pacific Decadal Oscillations. There are changes in carbon dioxide, humidity and methane measurement series in 2000. If these changes mark a phase change of the Pacific Decadal Oscillation then it might explain the global temperature behavior.
UR – https://doi.org/10.1007/s13143-012-0032-4
DO – 10.1007/s13143-012-0032-4
ER –

NR – 217
TY – JOUR
TI – Discussion of the case of the missing heat
AU – Parker, Albert
PY – 2014
JO – Nonlinear Engineering
VL – 3
IS – 4
SP – 247
EP – 253
DO – 10.1515/nleng-2014-0011
UR – http://www.degruyter.com/view/j/nleng.ahead-of-print/nleng-2014-0011/nleng-2014-0011.xml
AB – The sea level projection of a 1 meter rise for the 21st century depends on climate models that have projected a given amount of anthropogenic warming during the same period. However, these same climate models predicted a warming also from 2000 to 2014, which has not been seen in the global surface temperature. Researchers have proposed several solutions such as the fact that the “missing heat” was accumulated in the deep ocean. However, no evidences of a sufficient warming of the deep oceans have been observed. Other arguments has been proposed as well and found unsatisfactory. There is the opportunity that the “heat” is not “real” but “missing” or “hiding” somewhere. If the climate model projected “heat” that simply does not exist in reality in the first place, consequently the models overestimate the anthropogenicwarming and also the sea level projections for the 21st century are overestimated.
ER –

NR – 218
TY – JOUR
T1 – Expected halt in the current global warming trend?
AU – Njau, Ernest C.
JO – Renewable Energy
VL – 30
IS – 5
SP – 743
EP – 752
PY – 2005
DO – https://doi.org/10.1016/j.renene.2004.07.011
UR – http://www.sciencedirect.com/science/article/pii/S0960148104002939
AB – The variation patterns of global temperature were considerably turbulent from about 1870 up to 1940. Then just after 1940 these patterns underwent a sunspot-related change and adopted to relatively less turbulent variability. It is established here that these global temperature patterns are currently in the process of undergoing a sunspot-related change from the post-1940 relatively less turbulent variability back into relatively more turbulent variability. This apparently imminent state of more turbulent variability is expected to stop and at least slightly reverse the global warming trend, which has been going on since about 1965. Besides, it is shown separately that the mean of ‘global mean temperature variations’ reaches the next peak at about the year 2005 after which it will expectedly be on a decreasing trend. Finally, it is shown that, contrary to projections made in the Third IPCC Assessment Report, Greenland is currently in an ongoing cooling trend which is expected to last up to at least the year 2035.
ER –

NR – 219
TY – JOUR
TI – Why global warming went missing since the year 2000
AU – Parker, Albert
PY – 2013
JO – Nonlinear Engineering
VL – 2
IS – 3-4
SP – 129
EP – 135
DO – 10.1515/nleng-2013-0017
UR – http://www.degruyter.com/view/j/nleng.2013.2.issue-3-4/nleng-2013-0017/nleng-2013-0017.xml
AB – Over the period January 2004 to present, the seas have experienced the lack of any warming, as finally properly measured in the ARGO project where a global array of more than 3,600 free-drifting profiling floats has measured the temperature of the upper 2000 m of the sea as it was not possible before. The warming of the seas has been a negligible 1.1*10-3 °C/year on average over the layer 0 – 2000 dbar below the accuracy of the measure. Over the period January 2000 to present, the measured land and sea temperatures of the less reliable GISS, NCDC and HADCRUT4 data sets have shown a small warming of 4.2*10-3 °C/year on average. Same period, the climate models propose for the land and sea temperatures an unrealistic warming of 20.5*10-3 °C/year (average of CMIP3) and 18.2*10-3 °C/year (average of the CMIP5). The “inconvenient truth” is that climate models are predicting a warming when there is no warming rather than simply overestimating the warming as discussed so far. The paper presents the failed validation of the climate models since their introduction and suggests the reasons of their failure in the overrated effect of the changed composition of the atmosphere and the neglected natural oscillations.
ER –

NR – 220
TY – JOUR
TI – Key Issues on Debating about the Global Warming
AU – Wang, Shaowu
AU – Ge, Quansheng
AU – Wang, Fang
AU – Wen, Xinyu
AU – Huang, Jianbin
PY – 2010
JO – Advances in Earth Science
VL – 6
UR – http://en.cnki.com.cn/Article_en/CJFDTOTAL-DXJZ201006015.htm
AB – Key issues on debating about global warming are reviewed:?Does the global warming pause? The answer is not sure.The HadCRUT3 data show that the temperature during 1999-2008 increased only a little(0.07?/10a),but this decade is still the most warmest one among the last 30 years.However,the data from NASA GISS indicate that the temperature increased in the same period is higher(0.19?/10a).Thus,global surface temperature in recent years oscillates on a warm level.However,natural variability needs to be taken into consideration.?Does the global warming be caused fully by anthropogenic factors? The answer is no.ENSO,solar activity,volcanism,and thermohaline circulation can also exert impact in some extent on climate change,though the morden global warming may be mostly attributed to the increasing of greenhouse effect.However,the natural factors may sometimes overwhelm the anthropogenic effect in the interannual to interdecadal time scale.Specially,the solar activity factor should be given more attention.?Does the impact of global warming become more evident recently? The answer is yes.New observational datas indicate that the melting speed of glaciers and ice caps and rising speed of sea level in recent years have exceeded the related projections by IPCC 4th Assessment Report.Accordingly,the updated projection of the future sea level also increases.
ER –

NR – 221
TY – JOUR
TI – Mechanisms for the hiatus in global warming
AU – Tung, Ka-Kit
AU – Zhang, Rong
AU – Trenberth, Kevin E.
PY – 2014
JO – Engineering Sciences
VL – 2
DO – 10.3969/j.issn.1672-4178.2014.02.007
UR – http://d.wanfangdata.com.cn/periodical_zggckx-e201402007.aspx
AB – The observed global mean temperature is the highest on record for the past decade but has plateaued to form an apparent“hiatus”in global temperature rise,with an almost zero short-term trend. Several speakers presented results on the hiatus and suggested possible mechanisms.
ER –

NR – 222
TY – JOUR
TI – On the definition and identifiability of the alleged “hiatus” in global warming
AU – Lewandowsky, Stephan
AU – Risbey, James S.
AU – Oreskes, Naomi
JF – Scientific Reports
PY – 2015
VL – 5
SP – 16784
UR – http://dx.doi.org/10.1038/srep16784
DO – 10.1038/srep16784
AB – Recent public debate and the scientific literature have frequently cited a “pause” or “hiatus” in global warming. Yet, multiple sources of evidence show that climate change continues unabated, raising questions about the status of the “hiatus”. To examine whether the notion of a “hiatus” is justified by the available data, we first document that there are multiple definitions of the “hiatus” in the literature, with its presumed onset spanning a decade. For each of these definitions we compare the associated temperature trend against trends of equivalent length in the entire record of modern global warming. The analysis shows that the “hiatus” trends are encompassed within the overall distribution of observed trends. We next assess the magnitude and significance of all possible trends up to 25 years duration looking backwards from each year over the past 30 years. At every year during the past 30 years, the immediately preceding warming trend was always significant when 17 years (or more) were included in the calculation, alleged “hiatus” periods notwithstanding. If current definitions of the “pause” used in the literature are applied to the historical record, then the climate system “paused” for more than 1/3 of the period during which temperatures rose 0.6?K.
ER –

NR – 223
TY – JOUR
AU – Lempereur, Morine
AU – Limousin, Jean-Marc
AU – Guibal, Frédéric
AU – Ourcival, Jean-Marc
AU – Rambal, Serge
AU – Ruffault, Julien
AU – Mouillot, Florent
TI – Recent climate hiatus revealed dual control by temperature and drought on the stem growth of Mediterranean Quercus ilex
JO – Global Change Biology
JA – Glob Change Biol
VL – 23
IS – 1
UR – http://dx.doi.org/10.1111/gcb.13495
DO – 10.1111/gcb.13495
SP – 42
EP – 55
PY – 2017
AB – A better understanding of stem growth phenology and its climate drivers would improve projections of the impact of climate change on forest productivity. Under a Mediterranean climate, tree growth is primarily limited by soil water availability during summer, but cold temperatures in winter also prevent tree growth in evergreen forests. In the widespread Mediterranean evergreen tree species Quercus ilex, the duration of stem growth has been shown to predict annual stem increment, and to be limited by winter temperatures on the one hand, and by the summer drought onset on the other hand. We tested how these climatic controls of Q. ilex growth varied with recent climate change by correlating a 40-year tree ring record and a 30-year annual diameter inventory against winter temperature, spring precipitation, and simulated growth duration. Our results showed that growth duration was the best predictor of annual tree growth. We predicted that recent climate changes have resulted in earlier growth onset (-10 days) due to winter warming and earlier growth cessation (-26 days) due to earlier drought onset. These climatic trends partly offset one another, as we observed no significant trend of change in tree growth between 1968 and 2008. A moving-window correlation analysis revealed that in the past, Q. ilex growth was only correlated with water availability, but that since the 2000s, growth suddenly became correlated with winter temperature in addition to spring drought. This change in the climate–growth correlations matches the start of the recent atmospheric warming pause also known as the ‘climate hiatus’. The duration of growth of Q. ilex is thus shortened because winter warming has stopped compensating for increasing drought in the last decade. Decoupled trends in precipitation and temperature, a neglected aspect of climate change, might reduce forest productivity through phenological constraints and have more consequences than climate warming alone.
ER –

NR – 224
TY – JOUR
T1 – Briefing: How do we know the globe has warmed? What do we know about why?
AU – Thorne, Peter
PY – 2015
JF – Proceedings of the Institution of Civil Engineers – Forensic Engineering
VL – 168
IS – 2
SP – 58
EP – 64
DO – 10.1680/feng.15.00003
UR – https://www.icevirtuallibrary.com/doi/abs/10.1680/feng.15.00003
AB – This briefing outlines the evidence from instrumental records that leads to an unequivocal finding that the world has warmed. It then goes on to address the underlying causes, showing that only through invoking the effects of humans can the last 50 years be adequately explained. Finally, it addresses the recent hiatus/pause in warming of global surface temperatures and the implications thereof.
UR – https://doi.org/10.1680/feng.15.00003
ER –

NR – 225
TY – JOUR
TI – Characteristics of the Trends in the Global Tropopause Estimated From COSMIC Radio Occultation Data
AU – P. Gao
AU – X. Xu
AU – X. Zhang
PY – 2015
JO – IEEE Transactions on Geoscience and Remote Sensing
VL – 53
IS – 12
SP – 6813
EP – 6822
DO – 10.1109/TGRS.2015.2449338
UR – https://ieeexplore.ieee.org/abstract/document/7156128/
AB – This paper discusses the variabilities and trends in the global tropopause based on the gridded monthly mean Global Positioning System radio occultation data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission during July 2006-February 2014. We find that the tropopause height can reflect El Niño-Southern Oscillation (ENSO) events. The correlation coefficient between global tropopause height anomalies and the Niño 3.4 sea surface temperature index is 0.53, with a maximum correlation coefficient of 0.8 at a lag of three months. We present first the detailed investigations about the spatial distribution of trends in tropopause parameters in each 10° × 5° longitude-latitude grid cell over the globe and find that the rates of change in the tropopause parameters during this time period are high in some particular regions such as the Southern Indian Ocean, Antarctica, Western Europe, North Pacific, and the east coast of North America. An analysis of global monthly means of the tropopause parameters indicates a global tropopause height increase of 0.03 ± 2.36 m/year during 2006-2014, with a corresponding temperature increase of 0.020 ± 0.008°C/year, and a pressure increase of 0.11 ± 0.059 hPa/year. The upward trend of tropopause height is significantly weaker than that in the past years, which might be attributed to the expected stratospheric ozone recovery associated with the Montreal Protocol, the global warming slowdown, and the abnormal global climate change in recent years. The trends of the tropopause parameters are the most significant over the Southern Indian Ocean and Antarctica during September/October/November, which could be due to the stratospheric ozone recovery.
ER –

Global warming hiatus paper list, version 1.0 (224 papers), part 1

For quite some time now I have been gathering papers relating to the global warming hiatus (GWH). GWH was a period in climate where Earth’s global surface temperature apparently warmed less than during the previous years. I have written about this before (here, here, and here), so I’m not going to make an in-depth explanation of the issue here.

Due to some problems in publishing the whole list at once, I have divided the list in two parts. This is part 1 and the list is continued in part 2.

Hiatus paper list methods

I have used Google Scholar with certain search phrases. Google Scholar is not best possible search engine for scientific literature searches but it seems to yield most extensive search results and is freely accessible. The problems with Google Scholar for these searches are mainly related to Google Scholar returning lots of results that are not peer-reviewed. Problems of Google Scholar shouldn’t matter much here, because I have gone through all the results from these searches by systematically inspecting each search result.

Search phrases used: “global warming hiatus”, “global warming slowdown”, “global warming slow-down”, “global warming pause”, “pause in global warming”, “global warming plateau”, “global warming stagnation”, “global warming has stopped”, “climate change hiatus”, “climate warming hiatus”, “global warming halted”, “global warming slowed”.

Additionally there are a few papers not captured by these searches, but which I have picked up from here and there. I know that there still are some relevant papers missing from the list that these searches have not captured but I will be adding more papers in the future.

Following papers are included to the list:
– Only peer reviewed papers are included. Book chapters, reports, editorials, or perspective/opinion/news articles are not included even if they have been published in peer-reviewed journals. It is not always straight-forward to identify peer-reviewed papers. For example, Nature has a habit of not indicating properly which of their papers are real research articles and which ones are just opinion or news articles. There are also plenty of journals which are not real scientific journals but pretend to be, and of course Google Scholar includes them in their database. As a result, the list below probably contains a few papers that are published in questionable journals.
– Abstract or title has to contain clear mention of GWH. Only papers mentioning the early 2000s hiatus are included, not the ones that discuss hiatus periods generally or discuss some other hiatus period if they don’t mention the early 2000s hiatus (I had to draw the line somewhere).

The list

The global warming hiatus paper list is given below in RIS format (which is one of commonly offered citation formats by journals). I have numbered the papers and the number is the first field for each paper (marked as “NR”, which is not in the official RIS format – I was going to use “M1” first, which is said to be “number” but decided to use NR instead because it is more descriptive). It should be noted that different publishers unfortunately seem to have their own ideas of how to use the RIS format. For example, the first entry is from Nature and they use “L3” for additional URL and for DOI, even if DOI has its own “DO” tag. They also have a creative way to give publication year. Whoever designed the RIS format export in Nature, didn’t consider much of the possibility that someone might want to read these entries automatically. I have made some editing on the RIS entries but there still might be some curiosities.

The list contains 224 papers, but the numbering goes to 225 because I removed number 48 at some point because it turned out to be a non-peer-reviewed paper. The list is fairly complete to the end of 2016 (there are a few papers marked as 2017 papers but they have been published already in 2016 online which is why they have been included to this version).

There are a few papers that I suspect might not be peer-reviewed (mostly from Nature, see above), but the list will be polished in the future. I’m currently working on 2017 GWH papers and already there are over 300 papers in the list!

Papers 1 – 100

NR – 1
TY – JOUR
AU – Xie, Shang-Ping
AU – Kosaka, Yu
AU – Okumura, Yuko M.
TI – Distinct energy budgets for anthropogenic and natural changes during global warming hiatus
JA – Nature Geosci
PY – 2016
VL – 9
IS – 1
SP – 29
EP – 33
UR – http://dx.doi.org/10.1038/ngeo2581
DO – 10.1038/ngeo2581
AB – The Earth’s energy budget for the past four decades can now be closed1, and it supports anthropogenic greenhouse forcing as the cause for climate warming. However, closure depends on invoking an unrealistically large increase in aerosol cooling2 during the so-called global warming hiatus since the late 1990s (refs 3,4) that was due partly to tropical Pacific Ocean cooling5, 6, 7. The difficulty with this closure lies in the assumption that the same climate feedback applies to both anthropogenic warming and natural cooling. Here we analyse climate model simulations with and without anthropogenic increases in greenhouse gas concentrations, and show that top-of-the-atmosphere radiation and global mean surface temperature are much less tightly coupled for natural decadal variability than for the greenhouse-gas-induced response, implying distinct climate feedback between anthropogenic warming and natural variability. In addition, we identify a phase difference between top-of-the-atmosphere radiation and global mean surface temperature such that ocean heat uptake tends to slow down during the surface warming hiatus. This result deviates from existing energy theory but we find that it is broadly consistent with observations. Our study highlights the importance of developing metrics that distinguish anthropogenic change from natural variations to attribute climate variability and to estimate climate sensitivity from observations.
ER –

NR – 2
TY – JOUR
AU – Yao, Shuai-Lei
AU – Huang, Gang
AU – Wu, Ren-Guang
AU – Qu, Xia
PY – 2016
TI – The global warming hiatus—a natural product of interactions of a secular warming trend and a multi-decadal oscillation
JO – Theoretical and Applied Climatology
SP – 349
EP – 360
VL – 123
IS – 1
AB – The globally-averaged annual combined land and ocean surface temperature (GST) anomaly change features a slowdown in the rate of global warming in the mid-twentieth century and the beginning of the twenty-first century. Here, it is shown that the hiatus in the rate of global warming typically occurs when the internally generated cooling associated with the cool phase of the multi-decadal variability overcomes the secular warming from human- induced forcing. We provide compelling evidence that the global warming hiatus is a natural product of the interplays between a secular warming tendency due in a large part to the buildup of anthropogenic greenhouse gas concentrations, in particular CO2 concentration, and internally generated cooling by a cool phase of a quasi-60-year oscillatory variability that is closely associated with the Atlantic multi-decadal oscillation (AMO) and the Pacific decadal oscillation (PDO). We further illuminate that the AMO can be considered as a useful indicator and the PDO can be implicated as a harbinger of variations in global annual average surface temperature on multi-decadal timescales. Our results suggest that the recent observed hiatus in the rate of global warming will very likely extend for several more years due to the cooling phase of the quasi-60-year oscillatory variability superimposed on the secular warming trend.
UR – https://doi.org/10.1007/s00704-014-1358-x
DO – 10.1007/s00704-014-1358-x
ER –

NR – 3
TY – JOUR
T1 – The “Pause” in Global Warming: Turning a Routine Fluctuation into a Problem for Science
AU – Lewandowsky, Stephan
AU – Risbey, James S.
AU – Oreskes, Naomi
PY – 2015
DO – 10.1175/BAMS-D-14-00106.1
JF – Bulletin of the American Meteorological Society
SP – 723
EP – 733
VL – 97
IS – 5
AB – There has been much recent published research about a putative ?pause? or ?hiatus? in global warming. We show that there are frequent fluctuations in the rate of warming around a longer-term warming trend, and that there is no evidence that identifies the recent period as unique or particularly unusual. In confirmation, we show that the notion of a pause in warming is considered to be misleading in a blind expert test. Nonetheless, the most recent fluctuation about the longer-term trend has been regarded by many as an explanatory challenge that climate science must resolve. This departs from long-standing practice, insofar as scientists have long recognized that the climate fluctuates, that linear increases in CO2 do not produce linear trends in global warming, and that 15-yr (or shorter) periods are not diagnostic of long-term trends. We suggest that the repetition of the ?warming has paused? message by contrarians was adopted by the scientific community in its problem-solving and answer-seeking role and has led to undue focus on, and mislabeling of, a recent fluctuation. We present an alternative framing that could have avoided inadvertently reinforcing a misleading claim.
UR – https://doi.org/10.1175/BAMS-D-14-00106.1
ER –

NR – 4
TY – JOUR
AU – Liu, Wei
AU – Xie, Shang-Ping
AU – Lu, Jian
TI – Tracking ocean heat uptake during the surface warming hiatus
JA – Nature Communications
PY – 2016
VL – 7
SP – 10926
UR – http://dx.doi.org/10.1038/ncomms10926
DO – 10.1038/ncomms10926
AB – Ocean heat uptake is observed to penetrate deep into the Atlantic and Southern Oceans during the recent hiatus of global warming. Here we show that the deep heat penetration in these two basins is not unique to the hiatus but is characteristic of anthropogenic warming and merely reflects the depth of the mean meridional overturning circulation in the basin. We find, however, that heat redistribution in the upper 350?m between the Pacific and Indian Oceans is closely tied to the surface warming hiatus. The Indian Ocean shows an anomalous warming below 50?m during hiatus events due to an enhanced heat transport by the Indonesian throughflow in response to the intensified trade winds in the equatorial Pacific. Thus, the Pacific and Indian Oceans are the key regions to track ocean heat uptake during the surface warming hiatus.
ER –

NR – 5
TY – JOUR
AU – Smith, Doug M.
AU – Booth, Ben B. B.
AU – Dunstone, Nick J.
AU – Eade, Rosie
AU – Hermanson, Leon
AU – Jones, Gareth S.
AU – Scaife, Adam A.
AU – Sheen, Katy L.
AU – Thompson, Vikki
TI – Role of volcanic and anthropogenic aerosols in the recent global surface warming slowdown
JA – Nature Clim. Change
PY – 2016
VL – 6
IS – 10
SP – 936
EP – 940
UR – http://dx.doi.org/10.1038/nclimate3058
DO – 10.1038/nclimate3058
AB – The rate of global mean surface temperature (GMST) warming has slowed this century despite the increasing concentrations of greenhouse gases. Climate model experiments1, 2, 3, 4 show that this slowdown was largely driven by a negative phase of the Pacific Decadal Oscillation (PDO), with a smaller external contribution from solar variability, and volcanic and anthropogenic aerosols5, 6. The prevailing view is that this negative PDO occurred through internal variability7, 8, 9, 10, 11. However, here we show that coupled models from the Fifth Coupled Model Intercomparison Project robustly simulate a negative PDO in response to anthropogenic aerosols implying a potentially important role for external human influences. The recovery from the eruption of Mount Pinatubo in 1991 also contributed to the slowdown in GMST trends. Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years. Furthermore, the overestimation of the magnitude of recent warming by models is substantially reduced by using detection and attribution analysis to rescale their response to external factors, especially cooling following volcanic eruptions. Improved understanding of external influences on climate is therefore crucial to constrain near-term climate predictions.
ER –

NR – 6
TY – JOUR
AU – Wu, Huey-Tzu Jenny
AU – Lau, William K.-M.
TI – Detecting climate signals in precipitation extremes from TRMM (1998–2013)—Increasing contrast between wet and dry extremes during the “global warming hiatus”
JO – Geophysical Research Letters
VL – 43
IS – 3
UR – http://dx.doi.org/10.1002/2015GL067371
DO – 10.1002/2015GL067371
SP – 1340
EP – 1348
PY – 2016
AB – We investigate changes in daily precipitation extremes using Tropical Rainfall Measuring Mission (TRMM) data (1998–2013), which coincides with the “global warming hiatus.” Results show a change in probability distribution functions of local precipitation events (LPEs) during this period consistent with previous global warming studies, indicating increasing contrast between wet and dry extremes, with more intense LPE, less moderate LPE, and more dry (no rain) days globally. Analyses for land and ocean separately reveal more complex and nuanced changes over land, characterized by a strong positive trend (+12.0% per decade, 99% confidence level (c.l.)) in frequency of extreme LPEs over the Northern Hemisphere extratropics during the wet season but a negative global trend (-6.6% per decade, 95% c.l.) during the dry season. A significant global drying trend (3.2% per decade, 99% c.l.) over land is also found during the dry season. Regions of pronounced increased dry events include western and central U.S., northeastern Asia, and Southern Europe/Mediterranean.
ER –

NR – 7
TY – JOUR
AU – Zhang, Lei
PY – 2016
TI – The roles of external forcing and natural variability in global warming hiatuses
JO – Climate Dynamics
SP – 3157
EP – 3169
VL – 47
IS – 9
AB – Global mean surface temperature (GMST) rising has slowed down since late 1990s, which is referred to as the global warming hiatus. There was another global warming hiatus event during 1940s–1960s. The roles of the external forcing and the natural variability in both global warming hiatuses are explored, using EOF analysis. The first two leading EOF modes of the 5-year running mean global sea surface temperature (SST) reflect the global warming scenario (EOF1) and the interdecadal Pacific oscillation (IPO)-like natural variability (EOF2), respectively. In observation, PC2 was in its positive phase (eastern Pacific cooling) during 1940s–1960s, which contributed to the previous warming hiatus. In addition, GMST trends are found to be negative during late 1950s and 1960s in most of the CMIP5 historical runs, which implies that the external forcing also contributed to the pause in the GMST rising. It is further demonstrated that it is the natural radiative forcing (volcanic forcing) that caused the drop-down of GMST in 1960s. The current global warming hiatus has been attributed to the eastern Pacific cooling/enhanced Pacific trade winds. It is shown that the PC2 switched to its positive phase in late 1990s, and hence the IPO-like natural variability made a contribution to the slowdown of GMST rising in the past decade. It is also found that the EOF1 mode (global warming mode) of the observed SST features a smaller warming in tropical Pacific compared to the Indian Ocean and the tropical Atlantic. Such inter-basin warming contrast, which is attributed to the “ocean thermostat” mechanism, has been suggested to contribute to the intensification of Pacific trade winds since late 1990s as well. Global warming hiatuses are also found in the future projections from CMIP5 models, and the spatial pattern of the SST trends during the warming-hiatus periods exhibits an IPO-like pattern, which resembles the observed SST trends since late 1990s.
UR – https://doi.org/10.1007/s00382-016-3018-6
DO – 10.1007/s00382-016-3018-6
ER –

NR – 8
TY – JOUR
UR – http://stacks.iop.org/1748-9326/9/i=6/a=064023
T1 – Observed and simulated temperature extremes during the recent warming hiatus
A1 – Jana Sillmann and Markus G Donat and John C Fyfe and Francis W Zwiers
PY – 2014
SP – 064023
JF – Environmental Research Letters
VL – 9
IS – 6
DO – 10.1088/1748-9326/9/6/064023
AB – The discrepancy between recent observed and simulated trends in global mean surface temperature has provoked a debate about possible causes and implications for future climate change projections. However, little has been said in this discussion about observed and simulated trends in global temperature extremes. Here we assess trend patterns in temperature extremes and evaluate the consistency between observed and simulated temperature extremes over the past four decades (1971–2010) in comparison to the recent 15 years (1996–2010). We consider the coldest night and warmest day in a year in the observational dataset HadEX2 and in the current generation of global climate models (CMIP5). In general, the observed trends fall within the simulated range of trends, with better consistency for the longer period. Spatial trend patterns differ for the warm and cold extremes, with the warm extremes showing continuous positive trends across the globe and the cold extremes exhibiting a coherent cooling pattern across the Northern Hemisphere mid-latitudes that has emerged in the recent 15 years and is not reproduced by the models. This regional inconsistency between models and observations might be a key to understanding the recent hiatus in global mean temperature warming.
ER –

NR – 9
TY – JOUR
AU – Seneviratne, Sonia I.
AU – Donat, Markus G.
AU – Mueller, Brigitte
AU – Alexander, Lisa V.
TI – No pause in the increase of hot temperature extremes
JO – Nature Climate Change
PY – 2014
VL – 4
SP – 161
UR – http://dx.doi.org/10.1038/nclimate2145
DO – 10.1038/nclimate2145
AB – Observational data show a continued increase of hot extremes over land during the so-called global warming hiatus. This tendency is greater for the most extreme events and thus more relevant for impacts than changes in global mean temperature.
ER –

NR – 10
TY – JOUR
AU – Schmidt, Gavin A.
AU – Shindell, Drew T.
AU – Tsigaridis, Kostas
TI – Reconciling warming trends
JO – Nature Geoscience
PY – 2014
VL – 7
SP – 158
UR – http://dx.doi.org/10.1038/ngeo2105
DO – 10.1038/ngeo2105
AB – Climate models projected stronger warming over the past 15 years than has been seen in observations. Conspiring factors of errors in volcanic and solar inputs, representations of aerosols, and El Niño evolution, may explain most of the discrepancy.
ER –

NR – 11
TY – JOUR
AU – Santer, Benjamin D.
AU – Bonfils, Céline
AU – Painter, Jeffrey F.
AU – Zelinka, Mark D.
AU – Mears, Carl
AU – Solomon, Susan
AU – Schmidt, Gavin A.
AU – Fyfe, John C.
AU – Cole, Jason N. S.
AU – Nazarenko, Larissa
AU – Taylor, Karl E.
AU – Wentz, Frank J.
TI – Volcanic contribution to decadal changes in tropospheric temperature
JO – Nature Geoscience
PY – 2014
VL – 7
SP – 185
UR – http://dx.doi.org/10.1038/ngeo2098
DO – 10.1038/ngeo2098
AB – Despite continued growth in atmospheric levels of greenhouse gases, global mean surface and tropospheric temperatures have shown slower warming since 1998 than previously1,2,3,4,5. Possible explanations for the slow-down include internal climate variability3,4,6,7, external cooling influences1,2,4,8,9,10,11 and observational errors12,13. Several recent modelling studies have examined the contribution of early twenty-first-century volcanic eruptions1,2,4,8 to the muted surface warming. Here we present a detailed analysis of the impact of recent volcanic forcing on tropospheric temperature, based on observations as well as climate model simulations. We identify statistically significant correlations between observations of stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without the effects of early twenty-first-century volcanic eruptions overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic influences following the 1991 Pinatubo eruption, differences between simulated and observed tropospheric temperature trends over the period 1998 to 2012 are up to 15% smaller, with large uncertainties in the magnitude of the effect. To reduce these uncertainties, better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these eruption-specific properties in climate model simulations.
ER –

NR – 12
TY – JOUR
AU – Easterling, David R.
AU – Wehner, Michael F.
TI – Is the climate warming or cooling?
JO – Geophysical Research Letters
VL – 36
IS – 8
UR – http://dx.doi.org/10.1029/2009GL037810
DO – 10.1029/2009GL037810
PY – 2009
AB – Numerous websites, blogs and articles in the media have claimed that the climate is no longer warming, and is now cooling. Here we show that periods of no trend or even cooling of the globally averaged surface air temperature are found in the last 34 years of the observed record, and in climate model simulations of the 20th and 21st century forced with increasing greenhouse gases. We show that the climate over the 21st century can and likely will produce periods of a decade or two where the globally averaged surface air temperature shows no trend or even slight cooling in the presence of longer-term warming.
ER –

NR – 13
TY – JOUR
AU – Huber, Markus
AU – Knutti, Reto
TI – Natural variability, radiative forcing and climate response in the recent hiatus reconciled
JA – Nature Geoscience
PY – 2014
VL – 7
SP – 651
UR – http://dx.doi.org/10.1038/ngeo2228
DO – 10.1038/ngeo2228
AB – Global mean surface warming over the past 15 years or so has been less than in earlier decades and than simulated by most climate models1. Natural variability2,3,4, a reduced radiative forcing5,6,7, a smaller warming response to atmospheric carbon dioxide concentrations8,9 and coverage bias in the observations10 have been identified as potential causes. However, the explanations of the so-called ‘warming hiatus’ remain fragmented and the implications for long-term temperature projections are unclear. Here we estimate the contribution of internal variability associated with the El Niño/Southern Oscillation (ENSO) using segments of unforced climate model control simulations that match the observed climate variability. We find that ENSO variability analogous to that between 1997 or 1998 and 2012 leads to a cooling trend of about -0.06 °C. In addition, updated solar and stratospheric aerosol forcings from observations explain a cooling trend of similar magnitude (-0.07 °C). Accounting for these adjusted trends we show that a climate model of reduced complexity with a transient climate response of about 1.8 °C is consistent with the temperature record of the past 15 years, as is the ensemble mean of the models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). We conclude that there is little evidence for a systematic overestimation of the temperature response to increasing atmospheric CO2 concentrations in the CMIP5 ensemble.
ER –

NR – 14
TY – JOUR
AU – Hawkins, Ed
AU – Edwards, Tamsin
AU – McNeall, Doug
TI – Pause for thought
JF – Nature Climate Change
PY – 2014/02/26/online
VL – 4
SP – 154
UR – http://dx.doi.org/10.1038/nclimate2150
DO – 10.1038/nclimate2150
AB – The recent slowdown (or ‘pause’) in global surface temperature rise is a hot topic for climate scientists and the wider public. We discuss how climate scientists have tried to communicate the pause and suggest that ‘many-to-many’ communication offers a key opportunity to directly engage with the public.
ER –

NR – 15
TY – JOUR
A1 – Kaufmann, Robert K.
A1 – Kauppi, Heikki
A1 – Mann, Michael L.
A1 – Stock, James H.
T1 – Reconciling anthropogenic climate change with observed temperature 1998–2008
PY – 2011
JO – Proceedings of the National Academy of Sciences
SP – 11790
EP – 11793
DO – 10.1073/pnas.1102467108
VL – 108
IS – 29
UR – http://www.pnas.org/content/108/29/11790.abstract
AB – Given the widely noted increase in the warming effects of rising greenhouse gas concentrations, it has been unclear why global surface temperatures did not rise between 1998 and 2008. We find that this hiatus in warming coincides with a period of little increase in the sum of anthropogenic and natural forcings. Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations. As such, we find that recent global temperature records are consistent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects.
ER –

NR – 16
TY – JOUR
AU – Kamae, Youichi
AU – Shiogama, Hideo
AU – Watanabe, Masahiro
AU – Kimoto, Masahide
TI – Attributing the increase in Northern Hemisphere hot summers since the late 20th?century
JO – Geophysical Research Letters
VL – 41
IS – 14
UR – http://dx.doi.org/10.1002/2014GL061062
DO – 10.1002/2014GL061062
SP – 5192
EP – 5199
PY – 2014
AB – Anomalously high summertime temperatures have occurred with increasing frequency since the late 20th?century. It is not clear why hot summers are becoming more frequent despite the recent slowdown in the rise in global surface air temperature. To examine factors affecting the historical variation in the frequency of hot summers over the Northern Hemisphere (NH), we conducted three sets of ensemble simulations with an atmospheric general circulation model. The model accurately reproduced interannual variation and long-term increase in the occurrence of hot summers. Decadal variabilities in the Pacific and Atlantic Oceans accounted for 43?±?27% of the recent increase over the NH middle latitudes. In addition, direct influence of anthropogenic forcing also contributes to increasing the frequency since the late 20th?century. The results suggest that the heat extremes can become more frequent in the coming decade even with the persistent slowdown in the global-mean surface warming.
ER –

NR – 17
TY – JOUR
AU – Hunt, B. G.
PY – 2011
TI – The role of natural climatic variation in perturbing the observed global mean temperature trend
JO – Climate Dynamics
SP – 509
EP – 521
VL – 36
IS – 3
AB – Controversy continues to prevail concerning the reality of anthropogenically-induced climatic warming. One of the principal issues is the cause of the hiatus in the current global warming trend. There appears to be a widely held view that climatic change warming should exhibit an inexorable upwards trend, a view that implies there is no longer any input by climatic variability in the existing climatic system. The relative roles of climatic change and climatic variability are examined here using the same coupled global climatic model. For the former, the model is run using a specified CO2 growth scenario, while the latter consisted of a multi-millennial simulation where any climatic variability was attributable solely to internal processes within the climatic system. It is shown that internal climatic variability can produce global mean surface temperature anomalies of ±0.25 K and sustained positive and negative anomalies sufficient to account for the anomalous warming of the 1940s as well as the present hiatus in the observed global warming. The characteristics of the internally-induced negative temperature anomalies are such that if this internal natural variability is the cause of the observed hiatus, then a resumption of the observed global warming trend is to be expected within the next few years.
UR – https://doi.org/10.1007/s00382-010-0799-x
DO – 10.1007/s00382-010-0799-x
ER –

NR – 18
TY – JOUR
AU – Risbey, James S.
AU – Lewandowsky, Stephan
AU – Langlais, Clothilde
AU – Monselesan, Didier P.
AU – O’Kane, Terence J.
AU – Oreskes, Naomi
TI – Well-estimated global surface warming in climate projections selected for ENSO phase
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 835
UR – http://dx.doi.org/10.1038/nclimate2310
DO – 10.1038/nclimate2310
AB – The question of how climate model projections have tracked the actual evolution of global mean surface air temperature is important in establishing the credibility of their projections. Some studies and the IPCC Fifth Assessment Report suggest that the recent 15-year period (1998–2012) provides evidence that models are overestimating current temperature evolution. Such comparisons are not evidence against model trends because they represent only one realization where the decadal natural variability component of the model climate is generally not in phase with observations. We present a more appropriate test of models where only those models with natural variability (represented by El Niño/Southern Oscillation) largely in phase with observations are selected from multi-model ensembles for comparison with observations. These tests show that climate models have provided good estimates of 15-year trends, including for recent periods and for Pacific spatial trend patterns.
ER –

NR – 19
TY – JOUR
AU – Lovejoy, S.
TI – Return periods of global climate fluctuations and the pause
JO – Geophysical Research Letters
VL – 41
IS – 13
UR – http://dx.doi.org/10.1002/2014GL060478
DO – 10.1002/2014GL060478
SP – 4704
EP – 4710
PY – 2014
AB – An approach complementary to General Circulation Models (GCMs), using the anthropogenic CO2 radiative forcing as a linear surrogate for all anthropogenic forcings [Lovejoy, ], was recently developed for quantifying human impacts. Using preindustrial multiproxy series and scaling arguments, the probabilities of natural fluctuations at time lags up to 125?years were determined. The hypothesis that the industrial epoch warming was a giant natural fluctuation was rejected with 99.9% confidence. In this paper, this method is extended to the determination of event return times. Over the period 1880–2013, the largest 32?year event is expected to be 0.47?K, effectively explaining the postwar cooling (amplitude 0.42–0.47?K). Similarly, the “pause” since 1998 (0.28–0.37?K) has a return period of 20–50?years (not so unusual). It is nearly cancelled by the pre-pause warming event (1992–1998, return period 30–40?years); the pause is no more than natural variability.
ER –

NR – 20
TY – JOUR
AU – Guemas, Virginie
AU – Doblas-Reyes, Francisco J.
AU – Andreu-Burillo, Isabel
AU – Asif, Muhammad
TI – Retrospective prediction of the global warming slowdown in the past decade
JF – Nature Climate Change
PY – 2013
VL – 3
SP – 649
UR – http://dx.doi.org/10.1038/nclimate1863
DO – 10.1038/nclimate1863
AB – Despite a sustained production of anthropogenic greenhouse gases, the Earth’s mean near-surface temperature paused its rise during the 2000–2010 period1. To explain such a pause, an increase in ocean heat uptake below the superficial ocean layer2,3 has been proposed to overcompensate for the Earth’s heat storage. Contributions have also been suggested from the deep prolonged solar minimum4, the stratospheric water vapour5, the stratospheric6 and tropospheric aerosols7. However, a robust attribution of this warming slowdown has not been achievable up to now. Here we show successful retrospective predictions of this warming slowdown up to 5 years ahead, the analysis of which allows us to attribute the onset of this slowdown to an increase in ocean heat uptake. Sensitivity experiments accounting only for the external radiative forcings do not reproduce the slowdown. The top-of- atmosphere net energy input remained in the [0.5–1]?W?m-2 interval during the past decade, which is successfully captured by our predictions. Most of this excess energy was absorbed in the top 700?m of the ocean at the onset of the warming pause, 65% of it in the tropical Pacific and Atlantic oceans. Our results hence point at the key role of the ocean heat uptake in the recent warming slowdown. The ability to predict retrospectively this slowdown not only strengthens our confidence in the robustness of our climate models, but also enhances the socio-economic relevance of operational decadal climate predictions.
ER –

NR – 21
TY – JOUR
AU – Trenberth, Kevin E.
AU – Fasullo, John T.
TI – An apparent hiatus in global warming?
JO – Earth’s Future
VL – 1
IS – 1
UR – http://dx.doi.org/10.1002/2013EF000165
DO – 10.1002/2013EF000165
SP – 19
EP – 32
PY – 2013
AB – Global warming first became evident beyond the bounds of natural variability in the 1970s, but increases in global mean surface temperatures have stalled in the 2000s. Increases in atmospheric greenhouse gases, notably carbon dioxide, create an energy imbalance at the top-of-atmosphere (TOA) even as the planet warms to adjust to this imbalance, which is estimated to be 0.5–1?W?m-2 over the 2000s. Annual global fluctuations in TOA energy of up to 0.2?W?m-2 occur from natural variations in clouds, aerosols, and changes in the Sun. At times of major volcanic eruptions the effects can be much larger. Yet global mean surface temperatures fluctuate much more than these can account for. An energy imbalance is manifested not just as surface atmospheric or ground warming but also as melting sea and land ice, and heating of the oceans. More than 90% of the heat goes into the oceans and, with melting land ice, causes sea level to rise. For the past decade, more than 30% of the heat has apparently penetrated below 700?m depth that is traceable to changes in surface winds mainly over the Pacific in association with a switch to a negative phase of the Pacific Decadal Oscillation (PDO) in 1999. Surface warming was much more in evidence during the 1976–1998 positive phase of the PDO, suggesting that natural decadal variability modulates the rate of change of global surface temperatures while sea-level rise is more relentless. Global warming has not stopped; it is merely manifested in different ways.
ER –

NR – 22
TY – JOUR
AU – Meehl, Gerald A.
AU – Teng, Haiyan
AU – Arblaster, Julie M.
TI – Climate model simulations of the observed early-2000s hiatus of global warming
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 898
UR – http://dx.doi.org/10.1038/nclimate2357
DO – 10.1038/nclimate2357
AB – The slowdown in the rate of global warming in the early 2000s is not evident in the multi-model ensemble average of traditional climate change projection simulations1. However, a number of individual ensemble members from that set of models successfully simulate the early-2000s hiatus when naturally-occurring climate variability involving the Interdecadal Pacific Oscillation (IPO) coincided, by chance, with the observed negative phase of the IPO that contributed to the early-2000s hiatus. If the recent methodology of initialized decadal climate prediction could have been applied in the mid-1990s using the Coupled Model Intercomparison Project Phase 5 multi-models, both the negative phase of the IPO in the early 2000s as well as the hiatus could have been simulated, with the multi-model average performing better than most of the individual models. The loss of predictive skill for six initial years before the mid-1990s points to the need for consistent hindcast skill to establish reliability of an operational decadal climate prediction system.
ER –

NR – 23
TY – JOUR
AU – Allan, Richard P.
AU – Liu, Chunlei
AU – Loeb, Norman G.
AU – Palmer, Matthew D.
AU – Roberts, Malcolm
AU – Smith, Doug
AU – Vidale, Pier-Luigi
TI – Changes in global net radiative imbalance 1985–2012
JO – Geophysical Research Letters
VL – 41
IS – 15
UR – http://dx.doi.org/10.1002/2014GL060962
DO – 10.1002/2014GL060962
SP – 5588
EP – 5597
PY – 2014
AB – Combining satellite data, atmospheric reanalyses, and climate model simulations, variability in the net downward radiative flux imbalance at the top of Earth’s atmosphere (N) is reconstructed and linked to recent climate change. Over the 1985–1999 period mean N (0.34 ± 0.67?Wm-2) is lower than for the 2000–2012 period (0.62 ± 0.43?Wm-2, uncertainties at 90% confidence level) despite the slower rate of surface temperature rise since 2000. While the precise magnitude of N remains uncertain, the reconstruction captures interannual variability which is dominated by the eruption of Mount Pinatubo in 1991 and the El Niño Southern Oscillation. Monthly deseasonalized interannual variability in N generated by an ensemble of nine climate model simulations using prescribed sea surface temperature and radiative forcings and from the satellite-based reconstruction is significantly correlated (r~0.6) over the 1985–2012 period.
ER –

NR – 24
TY – JOUR
AU – Watanabe, Masahiro
AU – Shiogama, Hideo
AU – Tatebe, Hiroaki
AU – Hayashi, Michiya
AU – Ishii, Masayoshi
AU – Kimoto, Masahide
TI – Contribution of natural decadal variability to global warming acceleration and hiatus
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 893
UR – http://dx.doi.org/10.1038/nclimate2355
DO – 10.1038/nclimate2355
AB – Reasons for the apparent pause in the rise of global-mean surface air temperature (SAT) after the turn of the century has been a mystery, undermining confidence in climate projections1,2,3. Recent climate model simulations indicate this warming hiatus originated from eastern equatorial Pacific cooling4 associated with strengthening of trade winds5. Using a climate model that overrides tropical wind stress anomalies with observations for 1958–2012, we show that decadal-mean anomalies of global SAT referenced to the period 1961–1990 are changed by 0.11, 0.13 and -0.11 °C in the 1980s, 1990s and 2000s, respectively, without variation in human-induced radiative forcing. They account for about 47%, 38% and 27% of the respective temperature change. The dominant wind stress variability consistent with this warming/cooling represents the deceleration/acceleration of the Pacific trade winds, which can be robustly reproduced by atmospheric model simulations forced by observed sea surface temperature excluding anthropogenic warming components. Results indicate that inherent decadal climate variability contributes considerably to the observed global-mean SAT time series, but that its influence on decadal-mean SAT has gradually decreased relative to the rising anthropogenic warming signal.
ER –

NR – 25
TY – JOUR
AU – Meehl, Gerald A.
AU – Teng, Haiyan
TI – CMIP5 multi-model hindcasts for the mid-1970s shift and early 2000s hiatus and predictions for 2016–2035
JO – Geophysical Research Letters
VL – 41
IS – 5
UR – http://dx.doi.org/10.1002/2014GL059256
DO – 10.1002/2014GL059256
SP – 1711
EP – 1716
PY – 2014
AB – Compared to uninitialized climate change projections, a multi-model ensemble from the CMIP5 10?year decadal prediction experiments produces more warming during the mid-1970s climate shift and less warming in the early 2000s hiatus in both the tropical Indo-Pacific region and globally averaged surface air temperature (TAS) in closer agreement with observations. Assuming bias in TAS has stabilized in the 10?year predictions, after bias adjustment, TAS anomalies for the 2016–2035 period in the 30?year predictions initialized in 2006 are about 16% less than the uninitialized projections. One contributing factor for the improved climate simulation is the bias adjustment, which corrects the models’ systematic errors and higher-than- observed decadal warming trend. Another important factor is the initialization with observations which constrains the ocean such that the starting points of the initialized simulations are close to the observed initial states.
ER –

NR – 26
TY – JOUR
AU – Watanabe, Masahiro
AU – Kamae, Youichi
AU – Yoshimori, Masakazu
AU – Oka, Akira
AU – Sato, Makiko
AU – Ishii, Masayoshi
AU – Mochizuki, Takashi
AU – Kimoto, Masahide
TI – Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus
JO – Geophysical Research Letters
VL – 40
IS – 12
UR – http://dx.doi.org/10.1002/grl.50541
DO – 10.1002/grl.50541
SP – 3175
EP – 3179
PY – 2013
AB – The rate of increase of global-mean surface air temperature (SATg) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SATg linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (?), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SATg trend. The weakening of ? commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades.
ER –

NR – 27
TY – JOUR
T1 – Externally Forced and Internally Generated Decadal Climate Variability Associated with the Interdecadal Pacific Oscillation
AU – Meehl, Gerald A.
AU – Hu, Aixue
AU – Arblaster, Julie M.
AU – Fasullo, John
AU – Trenberth, Kevin E.
PY – 2013
DO – 10.1175/JCLI-D-12-00548.1
JF – Journal of Climate
SP – 7298
EP – 7310
VL – 26
IS – 18
AB – Globally averaged surface air temperatures in some decades show rapid increases (accelerated warming decades), and in other decades there is no warming trend (hiatus decades). A previous study showed that the net energy imbalance at the top of the atmosphere of about 1 W m?2 is associated with greater increases of deep ocean heat content below 750 m during the hiatus decades, while there is little globally averaged surface temperature increase or warming in the upper ocean layers. Here the authors examine processes involved with accelerated warming decades and address the relative roles of external forcing from increasing greenhouse gases and internally generated decadal climate variability associated with interdecadal Pacific oscillation (IPO). Model results from the Community Climate System Model, version 4 (CCSM4), show that accelerated warming decades are characterized by rapid warming of globally averaged surface air temperature, greater increases of heat content in the upper ocean layers, and less heat content increase in the deep ocean, opposite to the hiatus decades. In addition to contributions from processes potentially linked to Antarctic Bottom Water (AABW) formation and the Atlantic meridional overturning circulation (AMOC), the positive phase of the IPO, adding to the response to external forcing, is usually associated with accelerated warming decades. Conversely, hiatus decades typically occur with the negative phase of the IPO, when warming from the external forcing is overwhelmed by internally generated cooling in the tropical Pacific. Internally generated hiatus periods of up to 15 years with zero global warming trend are present in the future climate simulations. This suggests that there is a chance that the current observed hiatus could extend for several more years.
UR – https://doi.org/10.1175/JCLI-D-12-00548.1
ER –

NR – 28
TY – JOUR
AU – Meehl, Gerald A.
AU – Arblaster, Julie M.
AU – Fasullo, John T.
AU – Hu, Aixue
AU – Trenberth, Kevin E.
TI – Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods
JF – Nature Climate Change
PY – 2011
VL – 1
SP – 360
UR – http://dx.doi.org/10.1038/nclimate1229
DO – 10.1038/nclimate1229
AB – There have been decades, such as 2000–2009, when the observed globally averaged surface-temperature time series shows little increase or even a slightly negative trend1 (a hiatus period). However, the observed energy imbalance at the top-of-atmosphere for this recent decade indicates that a net energy flux into the climate system of about 1?W?m-2 (refs 2, 3) should be producing warming somewhere in the system4,5. Here we analyse twenty-first- century climate-model simulations that maintain a consistent radiative imbalance at the top-of-atmosphere of about 1?W?m-2 as observed for the past decade. Eight decades with a slightly negative global mean surface-temperature trend show that the ocean above 300?m takes up significantly less heat whereas the ocean below 300?m takes up significantly more, compared with non-hiatus decades. The model provides a plausible depiction of processes in the climate system causing the hiatus periods, and indicates that a hiatus period is a relatively common climate phenomenon and may be linked to La Niña-like conditions.
ER –

NR – 29
TY – JOUR
T1 – Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming
JF – Science
SP – 1219
LP – 1223
DO – 10.1126/science.1182488
VL – 327
IS – 5970
AU – Solomon, Susan
AU – Rosenlof, Karen H.
AU – Portmann, Robert W.
AU – Daniel, John S.
AU – Davis, Sean M.
AU – Sanford, Todd J.
AU – Plattner, Gian-Kasper
UR – http://science.sciencemag.org/content/327/5970/1219.abstract
AB – Stratospheric water vapor concentrations decreased by about 10% after the year 2000. Here we show that this acted to slow the rate of increase in global surface temperature over 2000–2009 by about 25% compared to that which would have occurred due only to carbon dioxide and other greenhouse gases. More limited data suggest that stratospheric water vapor probably increased between 1980 and 2000, which would have enhanced the decadal rate of surface warming during the 1990s by about 30% as compared to estimates neglecting this change. These findings show that stratospheric water vapor is an important driver of decadal global surface climate change.
ER –

NR – 30
TY – JOUR
AU – England, Matthew H.
AU – McGregor, Shayne
AU – Spence, Paul
AU – Meehl, Gerald A.
AU – Timmermann, Axel
AU – Cai, Wenju
AU – Gupta, Alex Sen
AU – McPhaden, Michael J.
AU – Purich, Ariaan
AU – Santoso, Agus
TI – Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 222
UR – http://dx.doi.org/10.1038/nclimate2106
DO – 10.1038/nclimate2106
AB – Despite ongoing increases in atmospheric greenhouse gases, the Earth’s global average surface air temperature has remained more or less steady since 2001. A variety of mechanisms have been proposed to account for this slowdown in surface warming. A key component of the global hiatus that has been identified is cool eastern Pacific sea surface temperature, but it is unclear how the ocean has remained relatively cool there in spite of ongoing increases in radiative forcing. Here we show that a pronounced strengthening in Pacific trade winds over the past two decades—unprecedented in observations/reanalysis data and not captured by climate models—is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake. The extra uptake has come about through increased subduction in the Pacific shallow overturning cells, enhancing heat convergence in the equatorial thermocline. At the same time, the accelerated trade winds have increased equatorial upwelling in the central and eastern Pacific, lowering sea surface temperature there, which drives further cooling in other regions. The net effect of these anomalous winds is a cooling in the 2012 global average surface air temperature of 0.1–0.2 °C, which can account for much of the hiatus in surface warming observed since 2001. This hiatus could persist for much of the present decade if the trade wind trends continue, however rapid warming is expected to resume once the anomalous wind trends abate.
ER –

NR – 31
TY – JOUR
AU – Drijfhout, S. S.
AU – Blaker, A. T.
AU – Josey, S. A.
AU – Nurser, A. J. G.
AU – Sinha, B.
AU – Balmaseda, M. A.
TI – Surface warming hiatus caused by increased heat uptake across multiple ocean basins
JO – Geophysical Research Letters
VL – 41
IS – 22
UR – http://dx.doi.org/10.1002/2014GL061456
DO – 10.1002/2014GL061456
SP – 7868
EP – 7874
PY – 2014
AB – The first decade of the 21st century was characterized by a hiatus in global surface warming. Using ocean model hindcasts and reanalyses we show that heat uptake between the 1990s and 2000s increased by 0.7 ± 0.3W?m-2. Approximately 30% of the increase is associated with colder sea surface temperatures in the eastern Pacific. Other basins contribute via reduced heat loss to the atmosphere, in particular, the Southern and subtropical Indian Oceans (30%) and the subpolar North Atlantic (40%). A different mechanism is important at longer timescales (1960s–present) over which the Southern Annular Mode trended upward. In this period, increased ocean heat uptake has largely arisen from reduced heat loss associated with reduced winds over the Agulhas Return Current and southward displacement of Southern Ocean westerlies.
ER –

NR – 32
TY – JOUR
T1 – Varying planetary heat sink led to global-warming slowdown and acceleration
JF – Science
SP – 897
LP – 903
DO – 10.1126/science.1254937
VL – 345
IS – 6199
AU – Chen, Xianyao
AU – Tung, Ka-Kit
UR – http://science.sciencemag.org/content/345/6199/897.abstract
AB – Global warming seems to have paused over the past 15 years while the deep ocean takes the heat instead. The thermal capacity of the oceans far exceeds that of the atmosphere, so the oceans can store up to 90% of the heat buildup caused by increased concentrations of greenhouse gases such as carbon dioxide. Chen and Tung used observational data to trace the pathways of recent ocean heating. They conclude that the deep Atlantic and Southern Oceans, but not the Pacific, have absorbed the excess heat that would otherwise have fueled continued warming.Science, this issue p. 897 A vacillating global heat sink at intermediate ocean depths is associated with different climate regimes of surface warming under anthropogenic forcing: The latter part of the 20th century saw rapid global warming as more heat stayed near the surface. In the 21st century, surface warming slowed as more heat moved into deeper oceans. In situ and reanalyzed data are used to trace the pathways of ocean heat uptake. In addition to the shallow La Niña–like patterns in the Pacific that were the previous focus, we found that the slowdown is mainly caused by heat transported to deeper layers in the Atlantic and the Southern oceans, initiated by a recurrent salinity anomaly in the subpolar North Atlantic. Cooling periods associated with the latter deeper heat- sequestration mechanism historically lasted 20 to 35 years.
ER –

NR – 33
TY – JOUR
AU – Kosaka, Yu
AU – Xie, Shang-Ping
TI – Recent global-warming hiatus tied to equatorial Pacific surface cooling
JA – Nature
PY – 2013
VL – 501
SP – 403
UR – http://dx.doi.org/10.1038/nature12534
DO – 10.1038/nature12534
AB – Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century1,2, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming3,4,5,6, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970–2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase.
ER –

NR – 34
TY – JOUR
T1 – Application of the Singular Spectrum Analysis Technique to Study the Recent Hiatus on the Global Surface Temperature Record
A1 – Macias, Diego
A1 – Stips, Adolf
A1 – Garcia-Gorriz, Elisa
PY – 2014
AB – Global surface temperature has been increasing since the beginning of the 20th century but with a highly variable warming rate, and the alternation of rapid warming periods with ‘hiatus’ decades is a constant throughout the series. The superimposition of a secular warming trend with natural multidecadal variability is the most accepted explanation for such a pattern. Since the start of the 21st century, the surface global mean temperature has not risen at the same rate as the top-of-atmosphere radiative energy input or greenhouse gas emissions, provoking scientific and social interest in determining the causes of this apparent discrepancy. Multidecadal natural variability is the most commonly proposed cause for the present hiatus period. Here, we analyze the HadCRUT4 surface temperature database with spectral techniques to separate a multidecadal oscillation (MDV) from a secular trend (ST). Both signals combined account for nearly 88% of the total variability of the temperature series showing the main acceleration/deceleration periods already described elsewhere. Three stalling periods with very little warming could be found within the series, from 1878 to 1907, from 1945 to 1969 and from 2001 to the end of the series, all of them coincided with a cooling phase of the MDV. Henceforth, MDV seems to be the main cause of the different hiatus periods shown by the global surface temperature records. However, and contrary to the two previous events, during the current hiatus period, the ST shows a strong fluctuation on the warming rate, with a large acceleration (0.0085°C year-1 to 0.017°C year-1) during 1992–2001 and a sharp deceleration (0.017°C year-1 to 0.003°C year-1) from 2002 onwards. This is the first time in the observational record that the ST shows such variability, so determining the causes and consequences of this change of behavior needs to be addressed by the scientific community.
JF – PLOS ONE
VL – 9
IS – 9
UR – https://doi.org/10.1371/journal.pone.0107222
SP – e107222
DO – 10.1371/journal.pone.0107222
ER –

NR – 35
TY – JOUR
AU – Haywood, Jim M.
AU – Jones, Andy
AU – Jones, Gareth S.
TI – The impact of volcanic eruptions in the period 2000–2013 on global mean temperature trends evaluated in the HadGEM2-ES climate model
JO – Atmospheric Science Letters
VL – 15
IS – 2
UR – http://dx.doi.org/10.1002/asl2.471
DO – 10.1002/asl2.471
SP – 92
EP – 96
PY – 2014
AB – The slow-down in global warming over the last decade has lead to significant debate about whether the causes are of natural or anthropogenic origin. Using an ensemble of HadGEM2-ES coupled climate model simulations we investigate the impact of overlooked modest volcanic eruptions. We deduce a global mean cooling of around -0.02 to -0.03?K over the period 2008–2012. Thus while these eruptions do cause a cooling of the Earth and may therefore contribute to the slow-down in global warming, they do not appear to be the sole or primary cause.
ER –

NR – 36
TY – JOUR
AU – Goddard, Lisa
TI – Heat hide and seek
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 158
UR – http://dx.doi.org/10.1038/nclimate2155
DO – 10.1038/nclimate2155
AB – Natural variability can explain fluctuations in surface temperatures but can it account for the current slowdown in warming?
ER –

NR – 37
TY – JOUR
AU – Lin, I.-I.
AU – Pun, Iam-Fei
AU – Lien, Chun-Chi
TI – “Category-6” supertyphoon Haiyan in global warming hiatus: Contribution from subsurface ocean warming
JO – Geophysical Research Letters
VL – 41
IS – 23
UR – http://dx.doi.org/10.1002/2014GL061281
DO – 10.1002/2014GL061281
SP – 8547
EP – 8553
PY – 2014
AB – With the extra-ordinary intensity of 170 kts, supertyphoon Haiyan devastated the Philippines in November 2013. This intensity is among the highest ever observed for tropical cyclones (TCs) globally, 35 kts well above the threshold (135kts) of the existing highest category of 5. Though there is speculation to associate global warming with such intensity, existing research indicate that we have been in a warming hiatus period, with the hiatus attributed to the La Niña-like multi-decadal phenomenon. It is thus intriguing to understand why Haiyan can occur during hiatus. It is suggested that as the western Pacific manifestation of the La Niña-like phenomenon is to pile up warm subsurface water to the west, the western North Pacific experienced evident subsurface warming and created a very favorable ocean pre-condition for Haiyan. Together with its fast traveling speed, the air-sea flux supply was 158% as compared to normal for intensification.
ER –

NR – 38
TY – JOUR
AU – Fyfe, John C.
AU – Gillett, Nathan P.
AU – Zwiers, Francis W.
TI – Overestimated global warming over the past 20 years
JF – Nature Climate Change
PY – 2013
VL – 3
SP – 767
UR – http://dx.doi.org/10.1038/nclimate1972
DO – 10.1038/nclimate1972
AB – Recent observed global warming is significantly less than that simulated by climate models. This difference might be explained by some combination of errors in external forcing, model response and internal climate variability.
ER –

NR – 39
TY – JOUR
AU – Crowley, Thomas J.
AU – Obrochta, Stephen P.
AU – Liu, Junhua
TI – Recent global temperature “plateau” in the context of a new proxy reconstruction
JO – Earth’s Future
VL – 2
IS – 5
UR – http://dx.doi.org/10.1002/2013EF000216
DO – 10.1002/2013EF000216
SP – 281
EP – 294
PY – 2014
AB – Stable global temperatures of the last 10–15 years have been a topic of considerable discussion. A new proxy extension of the global temperature record enables better placement of this feature in a longer historical perspective. The fixed-grid composite covers the interval 1801–1984, with an extension to 1782, and anchors the global temperature record in the last major cold interval of the Little Ice Age, when carbon dioxide concentration was at preanthropogenic levels. Except for greater and longer cooling (approximately twice the length of Pinatubo) associated with the Tambora eruption, the proxy agrees with the most widely cited previous assessment of global temperature over this interval, lending more confidence to a centennial extension of the global temperature record. The proxy correlation is as high as 0.83 for the interval 1907–1984 (df?=?8, p?=?0.001), with the 21st century 1.0°C?±?0.2°C warmer than the nonvolcanic base state. This remarkable linearity requires a clear theoretical understanding as to how an exceedingly complex system can, on the global average, behave in such a simple way. Removal of the linear radiatively forced component from the global temperature record yields an estimate of natural variability for the last 230 years and indicates no unusual natural variability during the recent 10–15 years. Based on the estimate of unforced variability over the last 170 years, there is about a 40% chance of continued “natural cooling” over the next few years, with about a 10% chance of cooling persisting into the next decade.
ER –

NR – 40
TY – JOUR
AU – Trenberth, Kevin E.
AU – Fasullo, John T.
AU – Branstator, Grant
AU – Phillips, Adam S.
TI – Seasonal aspects of the recent pause in surface warming
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 911
UR – http://dx.doi.org/10.1038/nclimate2341
DO – 10.1038/nclimate2341
AB – Factors involved in the recent pause in the rise of global mean temperatures are examined seasonally. For 1999 to 2012, the hiatus in surface warming is mainly evident in the central and eastern Pacific. It is manifested as strong anomalous easterly trade winds, distinctive sea-level pressure patterns, and large rainfall anomalies in the Pacific, which resemble the Pacific Decadal Oscillation (PDO). These features are accompanied by upper tropospheric teleconnection wave patterns that extend throughout the Pacific, to polar regions, and into the Atlantic. The extratropical features are particularly strong during winter. By using an idealized heating to force a comprehensive atmospheric model, the large negative anomalous latent heating associated with the observed deficit in central tropical Pacific rainfall is shown to be mainly responsible for the global quasi-stationary waves in the upper troposphere. The wave patterns in turn created persistent regional climate anomalies, increasing the odds of cold winters in Europe. Hence, tropical Pacific forcing of the atmosphere such as that associated with a negative phase of the PDO produces many of the pronounced atmospheric circulation anomalies observed globally during the hiatus.
ER –

NR – 41
TY – JOUR
AU – Estrada, Francisco
AU – Perron, Pierre
AU – Martínez-López, Benjamín
TI – Statistically derived contributions of diverse human influences to twentieth-century temperature changes
JA – Nature Geoscience
PY – 2013
VL – 6
SP – 1050
UR – http://dx.doi.org/10.1038/ngeo1999
DO – 10.1038/ngeo1999
AB – The warming of the climate system is unequivocal as evidenced by an increase in global temperatures by 0.8?°C over the past century. However, the attribution of the observed warming to human activities remains less clear, particularly because of the apparent slow-down in warming since the late 1990s. Here we analyse radiative forcing and temperature time series with state-of-the-art statistical methods to address this question without climate model simulations. We show that long-term trends in total radiative forcing and temperatures have largely been determined by atmospheric greenhouse gas concentrations, and modulated by other radiative factors. We identify a pronounced increase in the growth rates of both temperatures and radiative forcing around 1960, which marks the onset of sustained global warming. Our analyses also reveal a contribution of human interventions to two periods when global warming slowed down. Our statistical analysis suggests that the reduction in the emissions of ozone-depleting substances under the Montreal Protocol, as well as a reduction in methane emissions, contributed to the lower rate of warming since the 1990s. Furthermore, we identify a contribution from the two world wars and the Great Depression to the documented cooling in the mid-twentieth century, through lower carbon dioxide emissions. We conclude that reductions in greenhouse gas emissions are effective in slowing the rate of warming in the short term.
ER –

NR – 42
TY – JOUR
AU – Ridley, D. A.
AU – Solomon, S.
AU – Barnes, J. E.
AU – Burlakov, V. D.
AU – Deshler, T.
AU – Dolgii, S. I.
AU – Herber, A. B.
AU – Nagai, T.
AU – Neely, R. R.
AU – Nevzorov, A. V.
AU – Ritter, C.
AU – Sakai, T.
AU – Santer, B. D.
AU – Sato, M.
AU – Schmidt, A.
AU – Uchino, O.
AU – Vernier, J. P.
TI – Total volcanic stratospheric aerosol optical depths and implications for global climate change
JO – Geophysical Research Letters
VL – 41
IS – 22
UR – http://dx.doi.org/10.1002/2014GL061541
DO – 10.1002/2014GL061541
SP – 7763
EP – 7769
PY – 2014
AB – Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth above 15?km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, Aerosol Robotic Network, and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15?km at middle to high latitudes and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be -0.19?±?0.09?Wm-2. This translates into an estimated global cooling of 0.05 to 0.12°C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15?km.
ER –

NR – 43
TY – JOUR
UR – http://stacks.iop.org/1748-9326/9/i=3/a=034016
T1 – Internal variability of Earth’s energy budget simulated by CMIP5 climate models
A1 – M D Palmer and D J McNeall
Y1 – 2014
SP – 034016
JF – Environmental Research Letters
VL – 9
IS – 3
DO – https://doi.org/10.1088/1748-9326/9/3/034016
AB – We analyse a large number of multi-century pre-industrial control simulations from the fifth phase
of the Coupled Model Intercomparison Project (CMIP5) to investigate relationships between: net
top-of-atmosphere radiation (TOA), globally averaged surface temperature (GST), and globally
integrated ocean heat content (OHC) on decadal timescales. Consistent with previous studies, we find
that large trends (~0.3 K dec -1 ) in GST can arise from internal climate variability and that these
trends are generally an unreliable indicator of TOA over the same period. In contrast, trends in
total OHC explain 95% or more of the variance in TOA for two-thirds of the models analysed;
emphasizing the oceans’ role as Earth’s primary energy store. Correlation of trends in total system
energy (TE = time integrated TOA) against trends in OHC suggests that for most models the ocean
becomes the dominant term in the planetary energy budget on a timescale of about 12 months. In the
context of the recent pause in global surface temperature rise, we investigate the potential
importance of internal climate variability in both TOA and ocean heat rearrangement. The model
simulations suggest that both factors can account for O (0.1 W m -2 ) on decadal timescales and may
play an important role in the recently observed trends in GST and 0–700 m (and 0–1800 m) ocean heat
uptake.
ER –

NR – 44
TY – JOUR
AU – Lu, Jianhua
AU – Hu, Aixue
AU – Zeng, Zhen
TI – On the possible interaction between internal climate variability and forced climate change
JO – Geophysical Research Letters
VL – 41
IS – 8
UR – http://dx.doi.org/10.1002/2014GL059908
DO – 10.1002/2014GL059908
SP – 2962
EP – 2970
PY – 2014
AB – The global warming hiatus does not necessarily mean a hiatus in anthropogenic greenhouse gas forcing and forced climate change (FCC). Here we show that both Atlantic Multidecadal Variability (AMV) and Pacific Decadal Oscillation (PDO) may cause fluctuations of the global mean surface air temperature (SAT) and hence alternately positive and negative trends on (inter)decadal time scales. However, the forced SAT change under a mean state due to greenhouse gas forcing does not depend on different phases of AMV and PDO, implying the effect of the FCC and internally generated climate variability can be linearly added up to the observed transient global mean SAT. On the other hand, the regional patterns of transient FCC do depend on the phases of the internal variability since the atmospheric and oceanic circulations can be affected by the different phases of the internal variability. Our results suggest a two-way interaction between internal variability and spatial patterns of FCC.
ER –

NR – 45
TY – JOUR
AU – McGregor, Shayne
AU – Timmermann, Axel
AU – Stuecker, Malte F.
AU – England, Matthew H.
AU – Merrifield, Mark
AU – Jin, Fei-Fei
AU – Chikamoto, Yoshimitsu
TI – Recent Walker circulation strengthening and Pacific cooling amplified by Atlantic warming
JF – Nature Climate Change
PY – 2014
VL – 4
SP – 888
UR – http://dx.doi.org/10.1038/nclimate2330
DO – 10.1038/nclimate2330
AB – An unprecedented strengthening of Pacific trade winds since the late 1990s (ref. 1) has caused widespread climate perturbations, including rapid sea-level rise in the western tropical Pacific2,3,4,5, strengthening of Indo-Pacific ocean currents6,7, and an increased uptake of heat in the equatorial Pacific thermocline1. The corresponding intensification of the atmospheric Walker circulation is also associated with sea surface cooling in the eastern Pacific, which has been identified as one of the contributors to the current pause in global surface warming1,8,9. In spite of recent progress in determining the climatic impacts of the Pacific trade wind acceleration, the cause of this pronounced trend in atmospheric circulation remains unknown. Here we analyse a series of climate model experiments along with observational data to show that the recent warming trend in Atlantic sea surface temperature and the corresponding trans-basin displacements of the main atmospheric pressure centres were key drivers of the observed Walker circulation intensification, eastern Pacific cooling, North American rainfall trends and western Pacific sea-level rise. Our study suggests that global surface warming has been partly offset by the Pacific climate response to enhanced Atlantic warming since the early 1990s.
ER –

NR – 46
TY – JOUR
T1 – An econometric analysis of global warming hiatus
AU – Furuoka, Fumitaka
PY – 2017
DO – 10.1080/13504851.2016.1270400
JF – Applied Economics Letters
SP – 1241
EP – 1246
VL – 24
IS – 17
AB – There is an avid debate concerning the presence of a hiatus in global warming. Recognizing that this phenomenon has considerable economic implications, this study aims to make a threefold contribution to the climate econometrics literature. Firstly, it formulates a testable hypothesis; secondly, it proposes a systematic empirical procedure; thirdly, it performs the Bai?Perron test to detect the starting point of the global warming hiatus. The findings supported the existence of the global warming hiatus.
UR – https://doi.org/10.1080/13504851.2016.1270400
ER –

NR – 47
TY – JOUR
UR – http://stacks.iop.org/1748-9326/10/i=8/a=084002
T1 – Change points of global temperature
A1 – Niamh Cahill and Stefan Rahmstorf and Andrew C Parnell
Y1 – 2015
SP – 084002
JF – Environmental Research Letters
VL – 10
IS – 8
DO – https://doi.org/10.1088/1748-9326/10/8/084002
AB – We aim to address the question of whether or not there is a significant recent ‘hiatus’, ‘pause’ or
‘slowdown’ of global temperature rise. Using a statistical technique known as change point (CP)
analysis we identify the changes in four global temperature records and estimate the rates of
temperature rise before and after these changes occur. For each record the results indicate that
three CPs are enough to accurately capture the variability in the data with no evidence of any
detectable change in the global warming trend since ~1970. We conclude that the term ‘hiatus’ or
‘pause’ cannot be statistically justified.
ER –

NR – 49
TY – JOUR
TI – Detecting Warming Hiatus Periods in CMIP5 Climate Model Projections
JO – International Journal of Atmospheric Sciences
VL – 2016
PY – 2016
AU – Li, Tony W.
AU – Baker, Noel C.
DO – 10.1155/2016/9657659
UR – http://dx.doi.org/10.1155/2016/9657659
AB – The observed slow-down in the global-mean surface temperature (GST) warming from 1998 to 2012 has been called a “warming hiatus.” Certain climate models, operating under experiments which simulate warming by increasing radiative forcing, have been shown to reproduce periods which resemble the observed hiatus. The present study provides a comprehensive analysis of 38 CMIP5 climate models to provide further evidence that models produce warming hiatus periods during warming experiments. GST rates are simulated in each model for the 21st century using two experiments: a moderate warming scenario (RCP4.5) and high-end scenario (RCP8.5). Warming hiatus periods are identified in model simulations by detecting (1) =15-year periods lacking a statistically meaningful trend and (2) rapid changes in the GST rate which resemble the observed 1998–2012 hiatus. Under the RCP4.5 experiment, all tested models produce warming hiatus periods. However, once radiative forcing exceeds 5?W/m2—about 2°C GST increase—as simulated in the RCP8.5 experiment after 2050, nearly all models produce only positive warming trends. All models show evidence of rapid changes in the GST rate resembling the observed hiatus, showing that the climate variations associated with warming hiatus periods are still evident in the models, even under accelerated warming conditions.
ER –

NR – 50
TY – JOUR
AU – Cazenave, Anny
AU – Dieng, Habib-Boubacar
AU – Meyssignac, Benoit
AU – von Schuckmann, Karina
AU – Decharme, Bertrand
AU – Berthier, Etienne
TI – The rate of sea-level rise
JO – Nature Climate Change
VL – 4
IS – 5
SP – 358
EP – 361
PY – 2014
DO – 10.1038/nclimate2159
UR – http://dx.doi.org/10.1038/nclimate2159
AB – Present-day sea-level rise is a major indicator of climate change. Since the early 1990s, sea level rose at a mean rate of ~3.1 mm yr-1 (refs 2, 3). However, over the last decade a slowdown of this rate, of about 30%, has been recorded. It coincides with a plateau in Earth’s mean surface temperature evolution, known as the recent pause in warming. Here we present an analysis based on sea-level data from the altimetry record of the past ~20 years that separates interannual natural variability in sea level from the longer-term change probably related to anthropogenic global warming. The most prominent signature in the global mean sea level interannual variability is caused by El Niño–Southern Oscillation, through its impact on the global water cycle. We find that when correcting for interannual variability, the past decade’s slowdown of the global mean sea level disappears, leading to a similar rate of sea-level rise (of 3.3 ± 0.4 mm yr-1) during the first and second decade of the altimetry era. Our results confirm the need for quantifying and further removing from the climate records the short-term natural climate variability if one wants to extract the global warming signal.
ER –

NR – 51
TY – JOUR
AU – Lian, Tao
PY – 2017
TI – Uncertainty in detecting trend: a new criterion and its applications to global SST
JO – Climate Dynamics
SP – 2881
EP – 2893
VL – 49
IS – 7
AB – In most parts of the global ocean, the magnitude of the long-term linear trend in sea surface temperature (SST) is much smaller than the amplitude of multi-scale internal variation. One can thus use a specific period in a much longer record to arbitrarily determine the sign of long-term trend, which is statistically significant, in regional SST. This could lead to a controversial conclusion on how global SST responded to the anthropogenic forcing in the recent history. In this study, the uncertainty in the linear trend due to multi-scale internal variation is theoretically investigated. It is found that the “estimated” trend will not change its sign only when its magnitude is greater than a theoretical threshold that scales the influence from the multi-scale internal variation. Otherwise, the sign of the “estimated” trend may depend on the period used. The new criterion is found to be superior over the existing methods when the de-trended time series is dominated by the oscillatory term. Applying this new criterion to a global SST reconstruction from 1881 to 2013 reveals that the influences from multi-scale internal variation on the sign of “estimated” linear trend cannot be excluded in most parts of the Pacific, the southern Indian Ocean and the northern Atlantic; therefore, the warming or/and cooling trends found in these regions cannot be interpreted as the consequences of anthropogenic forcing. It’s also suggested that the recent hiatus can be explained by combined uncertainty from internal variations at the interannual and decadal time scales.
UR – https://doi.org/10.1007/s00382-016-3483-y
DO – 10.1007/s00382-016-3483-y
ER –

NR – 52
TY – JOUR
AU – Marotzke, Jochem
AU – Forster, Piers M.
TI – Forcing, feedback and internal variability in global temperature trends
JA – Nature
PY – 2015
VL – 517
SP – 565
UR – http://dx.doi.org/10.1038/nature14117
DO – 10.1038/nature14117
AB – Most present-generation climate models simulate an increase in global-mean surface temperature (GMST) since 1998, whereas observations suggest a warming hiatus. It is unclear to what extent this mismatch is caused by incorrect model forcing, by incorrect model response to forcing or by random factors. Here we analyse simulations and observations of GMST from 1900 to 2012, and show that the distribution of simulated 15-year trends shows no systematic bias against the observations. Using a multiple regression approach that is physically motivated by surface energy balance, we isolate the impact of radiative forcing, climate feedback and ocean heat uptake on GMST—with the regression residual interpreted as internal variability—and assess all possible 15- and 62-year trends. The differences between simulated and observed trends are dominated by random internal variability over the shorter timescale and by variations in the radiative forcings used to drive models over the longer timescale. For either trend length, spread in simulated climate feedback leaves no traceable imprint on GMST trends or, consequently, on the difference between simulations and observations. The claim that climate models systematically overestimate the response to radiative forcing from increasing greenhouse gas concentrations therefore seems to be unfounded.
ER –

NR – 53
TY – JOUR
AU – Swanson, Kyle L.
AU – Tsonis, Anastasios A.
TI – Has the climate recently shifted?
JO – Geophysical Research Letters
VL – 36
IS – 6
UR – http://dx.doi.org/10.1029/2008GL037022
DO – 10.1029/2008GL037022
PY – 2009
AB – This paper provides an update to an earlier work that showed specific changes in the aggregate time evolution of major Northern Hemispheric atmospheric and oceanic modes of variability serve as a harbinger of climate shifts. Specifically, when the major modes of Northern Hemisphere climate variability are synchronized, or resonate, and the coupling between those modes simultaneously increases, the climate system appears to be thrown into a new state, marked by a break in the global mean temperature trend and in the character of El Niño/Southern Oscillation variability. Here, a new and improved means to quantify the coupling between climate modes confirms that another synchronization of these modes, followed by an increase in coupling occurred in 2001/02. This suggests that a break in the global mean temperature trend from the consistent warming over the 1976/77–2001/02 period may have occurred.
ER –

NR – 54
TY – JOUR
AU – Shi, Yan
AU – Zhai, Panmao
AU – Jiang, Zhihong
PY – 2016
TI – Multi-sliding time windows based changing trend of mean temperature and its association with the global-warming hiatus
JO – Journal of Meteorological Research
SP – 232
EP – 241
VL – 30
IS – 2
AB – Based on three global annual mean surface temperature time series and three Chinese annual mean surface air temperature time series, climate change trends on multiple timescales are analyzed by using the trend estimation method of multi-sliding time windows. The results are used to discuss the so-called global-warming hiatus during 1998–2012. It is demonstrated that different beginning and end times have an obvious effect on the results of the trend estimation, and the implications are particularly large when using a short window. The global-warming hiatus during 1998–2012 is the result of viewing temperature series on short timescales; and the events similar to it, or the events with even cold tendencies, have actually occurred many times in history. Therefore, the global-warming hiatus is likely to be a periodical feature of the long-term temperature change. It mainly reflects the decadal variability of temperature, and such a phenomenon in the short term does not alter the overall warming trend in the long term.
UR – https://doi.org/10.1007/s13351-016-5093-3
DO – 10.1007/s13351-016-5093-3
ER –

NR – 55
TY – JOUR
T1 – Possible artifacts of data biases in the recent global surface warming hiatus
JF – Science
SP – 1469
LP – 1472
DO – 10.1126/science.aaa5632
VL – 348
IS – 6242
AU – Karl, Thomas R.
AU – Arguez, Anthony
AU – Huang, Boyin
AU – Lawrimore, Jay H.
AU – McMahon, James R.
AU – Menne, Matthew J.
AU – Peterson, Thomas C.
AU – Vose, Russell S.
AU – Zhang, Huai-Min
UR – http://science.sciencemag.org/content/348/6242/1469.abstract
AB – Previous analyses of global temperature trends during the first decade of the 21st century seemed to indicate that warming had stalled. This allowed critics of the idea of global warming to claim that concern about climate change was misplaced. Karl et al. now show that temperatures did not plateau as thought and that the supposed warming “hiatus” is just an artifact of earlier analyses. Warming has continued at a pace similar to that of the last half of the 20th century, and the slowdown was just an illusion.Science, this issue p. 1469Much study has been devoted to the possible causes of an apparent decrease in the upward trend of global surface temperatures since 1998, a phenomenon that has been dubbed the global warming “hiatus.” Here, we present an updated global surface temperature analysis that reveals that global trends are higher than those reported by the Intergovernmental Panel on Climate Change, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a “slowdown” in the increase of global surface temperature.
ER –

NR – 56
TY – JOUR
T1 – Relationship between the Arctic oscillation and surface air temperature in multi-decadal time-scale
AU – Tanaka, Hiroshi L.
AU – Tamura, Mina
JO – Polar Science
VL – 10
IS – 3
SP – 199
EP – 209
PY – 2016
DO – 10.1016/j.polar.2016.03.002
UR – http://www.sciencedirect.com/science/article/pii/S1873965216300093
AB – In this study, a simple energy balance model (EBM) was integrated in time, considering a hypothetical long-term variability in ice-albedo feedback mimicking the observed multi-decadal temperature variability. A natural variability was superimposed on a linear warming trend due to the increasing radiative forcing of CO2. The result demonstrates that the superposition of the natural variability and the background linear trend can offset with each other to show the warming hiatus for some period. It is also stressed that the rapid warming during 1970–2000 can be explained by the superposition of the natural variability and the background linear trend at least within the simple model. The key process of the fluctuating planetary albedo in multi- decadal time scale is investigated using the JRA-55 reanalysis data. It is found that the planetary albedo increased for 1958–1970, decreased for 1970– 2000, and increased for 2000–2012, as expected by the simple EBM experiments. The multi-decadal variability in the planetary albedo is compared with the time series of the AO mode and Barents Sea mode of surface air temperature. It is shown that the recent AO negative pattern showing warm Arctic and cold mid-latitudes is in good agreement with planetary albedo change indicating negative anomaly in high latitudes and positive anomaly in mid-latitudes. Moreover, the Barents Sea mode with the warm Barents Sea and cold mid-latitudes shows long-term variability similar to planetary albedo change. Although further studies are needed, the natural variabilities of both the AO mode and Barents Sea mode indicate some possible link to the planetary albedo as suggested by the simple EBM to cause the warming hiatus in recent years.
ER –

NR – 57
TY – JOUR
T1 – A Quantitative Definition of Global Warming Hiatus and 50-Year Prediction of Global-Mean Surface Temperature
AU – Wei, Meng
AU – Qiao, Fangli
AU – Deng, Jia
PY – 2015
DO – 10.1175/JAS-D-14-0296.1
JF – Journal of the Atmospheric Sciences
SP – 3281
EP – 3289
VL – 72
IS – 8
AB – Recent global warming hiatus has received much attention; however, a robust and quantitative definition for the hiatus is still lacking. Recent studies by Scafetta, Wu et al., and Tung and Zhou showed that multidecadal variability (MDV) is responsible for the multidecadal accelerated warming and hiatuses in historical global-mean surface temperature (GMST) records, though MDV itself has not received sufficient attention thus far. Here, the authors introduce four key episodes in GMST evolution, according to different phases of the MDV extracted by the ensemble empirical-mode decomposition method from the ensemble HadCRUT4 monthly GMST time series. The ?warming (cooling) hiatus? and ?typical warming (cooling)? periods are defined as the 95% confidence intervals for the locations of local MDV maxima (minima) and of their derivatives, respectively. Since 1850, the warming hiatuses, cooling hiatuses, and typical warming have already occurred three times and the typical cooling has occurred twice. At present, the MDV is in its third warming-hiatus period, which started in 2012 and would last until 2017, followed by a 30-yr cooling episode, while the trend will sustain the current steady growth in the next 50 years. Their superposition presents steplike rising since 1850. It is currently ascending a new height and will stay there until the next warming phase of the MDV carries it higher.
AB – Recent global warming hiatus has received much attention; however, a robust and quantitative definition for the hiatus is still lacking. Recent studies by Scafetta, Wu et al., and Tung and Zhou showed that multidecadal variability (MDV) is responsible for the multidecadal accelerated warming and hiatuses in historical global-mean surface temperature (GMST) records, though MDV itself has not received sufficient attention thus far. Here, the authors introduce four key episodes in GMST evolution, according to different phases of the MDV extracted by the ensemble empirical-mode decomposition method from the ensemble HadCRUT4 monthly GMST time series. The ?warming (cooling) hiatus? and ?typical warming (cooling)? periods are defined as the 95% confidence intervals for the locations of local MDV maxima (minima) and of their derivatives, respectively. Since 1850, the warming hiatuses, cooling hiatuses, and typical warming have already occurred three times and the typical cooling has occurred twice. At present, the MDV is in its third warming-hiatus period, which started in 2012 and would last until 2017, followed by a 30-yr cooling episode, while the trend will sustain the current steady growth in the next 50 years. Their superposition presents steplike rising since 1850. It is currently ascending a new height and will stay there until the next warming phase of the MDV carries it higher.
UR – https://doi.org/10.1175/JAS-D-14-0296.1
ER –

NR – 58
TY – JOUR
AU – Cohen, Judah L.
AU – Furtado, Jason C.
AU – Barlow, Mathew
AU – Alexeev, Vladimir A.
AU – Cherry, Jessica E.
TI – Asymmetric seasonal temperature trends
JO – Geophysical Research Letters
VL – 39
IS – 4
UR – http://dx.doi.org/10.1029/2011GL050582
DO – 10.1029/2011GL050582
PY – 2012
AB – Current consensus on global climate change predicts warming trends driven by anthropogenic forcing, with maximum temperature changes projected in the Northern Hemisphere (NH) high latitudes during winter. Yet, global temperature trends show little warming over the most recent decade or so. For longer time periods appropriate to the assessment of trends, however, global temperatures have experienced significant warming trends for all seasons except winter, when cooling trends exist instead across large stretches of eastern North America and northern Eurasia. Hence, the most recent lapse in global warming is a seasonal phenomenon, prevalent only in boreal winter. Additionally, we show that the largest regional contributor to global temperature trends over the past two decades is land surface temperatures in the NH extratropics. Therefore, proposed mechanisms explaining the fluctuations in global annual temperatures should address this apparent seasonal asymmetry.
ER –

NR – 59
TY – JOUR
AU – Brown, Patrick T.
AU – Li, Wenhong
AU – Cordero, Eugene C.
AU – Mauget, Steven A.
TI – Comparing the model-simulated global warming signal to observations using empirical estimates of unforced noise
JF – Scientific Reports
PY – 2015
VL – 5
SP – 9957
UR – http://dx.doi.org/10.1038/srep09957
DO – 10.1038/srep09957
AB – The comparison of observed global mean surface air temperature (GMT) change to the mean change simulated by climate models has received much public and scientific attention. For a given global warming signal produced by a climate model ensemble, there exists an envelope of GMT values representing the range of possible unforced states of the climate system (the Envelope of Unforced Noise; EUN). Typically, the EUN is derived from climate models themselves, but climate models might not accurately simulate the correct characteristics of unforced GMT variability. Here, we simulate a new, empirical, EUN that is based on instrumental and reconstructed surface temperature records. We compare the forced GMT signal produced by climate models to observations while noting the range of GMT values provided by the empirical EUN. We find that the empirical EUN is wide enough so that the interdecadal variability in the rate of global warming over the 20th century does not necessarily require corresponding variability in the rate-of- increase of the forced signal. The empirical EUN also indicates that the reduced GMT warming over the past decade or so is still consistent with a middle emission scenario’s forced signal, but is likely inconsistent with the steepest emission scenario’s forced signal.
ER –

NR – 60
TY – JOUR
AU – Rajaratnam, Bala
AU – Romano, Joseph
AU – Tsiang, Michael
AU – Diffenbaugh, Noah S.
PY – 2015
TI – Debunking the climate hiatus
JO – Climatic Change
SP – 129
EP – 140
VL – 133
IS – 2
AB – The reported “hiatus” in the warming of the global climate system during this century has been the subject of intense scientific and public debate, with implications ranging from scientific understanding of the global climate sensitivity to the rate in which greenhouse gas emissions would need to be curbed in order to meet the United Nations global warming target. A number of scientific hypotheses have been put forward to explain the hiatus, including both physical climate processes and data artifacts. However, despite the intense focus on the hiatus in both the scientific and public arenas, rigorous statistical assessment of the uniqueness of the recent temperature time-series within the context of the long-term record has been limited. We apply a rigorous, comprehensive statistical analysis of global temperature data that goes beyond simple linear models to account for temporal dependence and selection effects. We use this framework to test whether the recent period has demonstrated i) a hiatus in the trend in global temperatures, ii) a temperature trend that is statistically distinct from trends prior to the hiatus period, iii) a “stalling” of the global mean temperature, and iv) a change in the distribution of the year-to-year temperature increases. We find compelling evidence that recent claims of a “hiatus” in global warming lack sound scientific basis. Our analysis reveals that there is no hiatus in the increase in the global mean temperature, no statistically significant difference in trends, no stalling of the global mean temperature, and no change in year-to-year temperature increases.
UR – https://doi.org/10.1007/s10584-015-1495-y
DO – 10.1007/s10584-015-1495-y
ER –

NR – 61
TY – JOUR
AU – Wang, Yuan
AU – Su, Hui
AU – Jiang, Jonathan H.
AU – Livesey, Nathaniel J.
AU – Santee, Michelle L.
AU – Froidevaux, Lucien
AU – Read, William G.
AU – Anderson, John
PY – 2017
TI – The linkage between stratospheric water vapor and surface temperature in an observation-constrained coupled general circulation model
JO – Climate Dynamics
SP – 2671
EP – 2683
VL – 48
IS – 7
AB – We assess the interactions between stratospheric water vapor (SWV) and surface temperature during the past two decades using satellite observations and the Community Earth System Model (CESM). From 1992 to 2013, to first order, the observed SWV exhibited three distinct piece-wise trends: a steady increase from 1992 to 2000, an abrupt drop from 2000 to 2004, and a gradual recovery after 2004, while the global-mean surface temperature experienced a strong increase until 2000 and a warming hiatus after 2000. The atmosphere-only CESM shows that the seasonal variation of tropical-mean (30°S–30°N) SWV is anticorrelated with that of the tropical-mean sea surface temperature (SST), while the correlation between the tropical SWV and SST anomalies on the interannual time scale is rather weak. By nudging the modeled SWV to prescribed profiles in coupled atmosphere-slab ocean experiments, we investigate the impact of SWV variations on surface temperature change. We find that a uniform 1 ppmv (0.5 ppmv) SWV increase (decrease) leads to an equilibrium global mean surface warming (cooling) of 0.12 ± 0.05 °C (-0.07 ± 0.05 °C). Sensitivity experiments show that the equilibrium response of global mean surface temperature to SWV perturbations over the extratropics is larger than that over the tropics. The observed sudden drop of SWV from 2000 to 2004 produces a global mean surface cooling of about -0.048 ± 0.041 °C, which suggests that a persistent change in SWV would make an imprint on long-term variations of global-mean surface temperature. A constant linear increase in SWV based on the satellite-observed rate of SWV change yields a global mean surface warming of 0.03 ± 0.01 °C/decade over a 50-year period, which accounts for about 19 % of the observed surface temperature increase prior to the warming hiatus. In the same experiment, trend analyses during different periods reveal a multi-year adjustment of surface temperature before the response to SWV forcing becomes strong relative to the internal variability in the model.
UR – https://doi.org/10.1007/s00382-016-3231-3
DO – 10.1007/s00382-016-3231-3
ER –

NR – 62
TY – JOUR
AU – Amaya, Dillon J.
AU – Xie, Shang-Ping
AU – Miller, Arthur J.
AU – McPhaden, Michael J.
TI – Seasonality of tropical Pacific decadal trends associated with the 21st century global warming hiatus
JO – Journal of Geophysical Research: Oceans
JA – J. Geophys. Res. Oceans
VL – 120
IS – 10
UR – http://dx.doi.org/10.1002/2015JC010906
DO – 10.1002/2015JC010906
SP – 6782
EP – 6798
PY – 2015
AB – Equatorial Pacific changes during the transition from a nonhiatus period (pre-1999) to the present global warming hiatus period (post-1999) are identified using a combination of reanalysis and observed data sets. Results show increased surface wind forcing has excited significant changes in wind-driven circulation. Over the last two decades, the core of the Equatorial Undercurrent intensified at a rate of 6.9 cm s-1 decade-1. Similarly, equatorial upwelling associated with the shallow meridional overturning circulation increased at a rate of 2.0 × 10-4 cm s-1 decade-1 in the central Pacific. Further, a seasonal dependence is identified in the sea surface temperature trends and in subsurface dynamics. Seasonal variations are evident in reversals of equatorial surface flow trends, changes in subsurface circulation, and seasonal deepening/shoaling of the thermocline. Anomalous westward surface flow drives cold-water zonal advection from November to February, leading to surface cooling from December through May. Conversely, eastward surface current anomalies in June–July drive warm-water zonal advection producing surface warming from July to November. An improved dynamical understanding of how the tropical Pacific Ocean responds during transitions into hiatus events, including its seasonal structure, may help to improve future predictability of decadal climate variations.
ER –

NR – 63
TY – JOUR
TI – The “Artefacts” of Data Biases in Surface Temperatures are Hiding the Hiatus
AU – Parker, A.
PY – 2015
JO – American Journal of Geophysics, Geochemistry and Geosystems
VL – 1
IS – 3
UR – http://files.aiscience.org/journal/article/pdf/70170008.pdf
SP – 66
EP – 70
AB – As almost any trend can be built by continuous tampering of past information rather than simply keeping the computational procedure unaltered and updating the data sets with freshly measured data, the latest paper published by NOAA in Science that negates the “hiatus” in global warming since 1998 also admitted by the IPCC is not a surprise. However, this prompts serious questions about the political bias of high impact factor journals. My contribution shows the information from conflicting data sets of measured lower troposphere temperatures and reconstructed surface air temperatures continuously corrected.
ER –

NR – 64
TY – JOUR
AU – Lean, Judith L.
AU – Rind, David H.
TI – How will Earth’s surface temperature change in future decades?
JO – Geophysical Research Letters
VL – 36
IS – 15
UR – http://dx.doi.org/10.1029/2009GL038932
DO – 10.1029/2009GL038932
PY – 2009
AB – Reliable forecasts of climate change in the immediate future are difficult, especially on regional scales, where natural climate variations may amplify or mitigate anthropogenic warming in ways that numerical models capture poorly. By decomposing recent observed surface temperatures into components associated with ENSO, volcanic and solar activity, and anthropogenic influences, we anticipate global and regional changes in the next two decades. From 2009 to 2014, projected rises in anthropogenic influences and solar irradiance will increase global surface temperature 0.15 ± 0.03°C, at a rate 50% greater than predicted by IPCC. But as a result of declining solar activity in the subsequent five years, average temperature in 2019 is only 0.03 ± 0.01°C warmer than in 2014. This lack of overall warming is analogous to the period from 2002 to 2008 when decreasing solar irradiance also countered much of the anthropogenic warming. We further illustrate how a major volcanic eruption and a super ENSO would modify our global and regional temperature projections.
ER –

NR – 65
TY – JOUR
AU – Saenko, Oleg A.
AU – Fyfe, John C.
AU – Swart, Neil C.
AU – Lee, Warren G.
AU – England, Matthew H.
PY – 2016
TI – Influence of tropical wind on global temperature from months to decades
JO – Climate Dynamics
SP – 2193
EP – 2203
VL – 47
IS – 7
AB – Using an Earth System Model and observations we analyze the sequence of events connecting episodes of trade wind strengthening (or weakening) to global mean surface temperature (GMST) cooling (or warming), with tropical ocean wave dynamics partially setting the time scale. In this sequence tropical west Pacific wind stress signals lead equatorial east Pacific thermocline depth signals which lead tropical east Pacific sea surface temperature (SST) signals which lead GMST signals. Using the anthropogenic, natural and tropical wind signals extracted from our simulations in a multivariate linear regression with observed GMST makes clear the balance that exists between anthropogenic warming and tropical wind-induced cooling during the recent warming slowdown, and between volcanic cooling and tropical wind-induced warming during the El Chichón and Pinatubo eruptions. Finally, we find an anticorrelation between global-mean temperatures in the near-surface (upper ~100 m) and subsurface (~100–300 m) ocean layers, linked to wind-driven interannual to decadal variations in the strength of the subtropical cell overturning in the upper Pacific Ocean.
UR – https://doi.org/10.1007/s00382-015-2958-6
DO – 10.1007/s00382-015-2958-6
ER –

NR – 66
TY – JOUR
T1 – A Link between the Hiatus in Global Warming and North American Drought
AU – Delworth, Thomas L.
AU – Zeng, Fanrong
AU – Rosati, Anthony
AU – Vecchi, Gabriel A.
AU – Wittenberg, Andrew T.
PY – 2015
DO – 10.1175/JCLI-D-14-00616.1
JF – Journal of Climate
SP – 3834
EP – 3845
VL – 28
IS – 9
AB – Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus?a decadal period with little increase in global mean surface temperature. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the anomalous tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.
AB – Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus?a decadal period with little increase in global mean surface temperature. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought. When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes. This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the anomalous tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.
UR – https://doi.org/10.1175/JCLI-D-14-00616.1
ER –

NR – 67
TY – JOUR
T1 – A perspective on sustained marine observations for climate modelling and prediction
JF – Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
DO – 10.1098/rsta.2013.0340
VL – 372
IS – 2025
AU – Dunstone, Nick J.
PY – 2014
UR – http://rsta.royalsocietypublishing.org/content/372/2025/20130340.abstract
AB – Here, I examine some of the many varied ways in which sustained global ocean observations are used in numerical modelling activities. In particular, I focus on the use of ocean observations to initialize predictions in ocean and climate models. Examples are also shown of how models can be used to assess the impact of both current ocean observations and to simulate that of potential new ocean observing platforms. The ocean has never been better observed than it is today and similarly ocean models have never been as capable at representing the real ocean as they are now. However, there remain important unanswered questions that can likely only be addressed via future improvements in ocean observations. In particular, ocean observing systems need to respond to the needs of the burgeoning field of near-term climate predictions. Although new ocean observing platforms promise exciting new discoveries, there is a delicate balance to be made between their funding and that of the current ocean observing system. Here, I identify the need to secure long-term funding for ocean observing platforms as they mature, from a mainly research exercise to an operational system for sustained observation over climate change time scales. At the same time, considerable progress continues to be made via ship-based observing campaigns and I highlight some that are dedicated to addressing uncertainties in key ocean model parametrizations. The use of ocean observations to understand the prominent long time scale changes observed in the North Atlantic is another focus of this paper. The exciting first decade of monitoring of the Atlantic meridional overturning circulation by the RAPID-MOCHA array is highlighted. The use of ocean and climate models as tools to further probe the drivers of variability seen in such time series is another exciting development. I also discuss the need for a concerted combined effort from climate models and ocean observations in order to understand the current slow-down in surface global warming.
ER –

NR – 68
TY – JOUR
AU – Power, Scott
AU – Delage, François
AU – Wang, Guomin
AU – Smith, Ian
AU – Kociuba, Greg
PY – 2017
TI – Apparent limitations in the ability of CMIP5 climate models to simulate recent multi-decadal change in surface temperature: implications for global temperature projections
JO – Climate Dynamics
SP – 53
EP – 69
VL – 49
IS – 1
AB – Observed surface temperature trends over the period 1998–2012/2014 have attracted a great deal of interest because of an apparent slowdown in the rate of global warming, and contrasts between climate model simulations and observations of such trends. Many studies have addressed the statistical significance of these relatively short-trends, whether they indicate a possible bias in the model values and the implications for global warming generally. Here we re-examine these issues, but as they relate to changes over much longer-term changes. We find that on multi-decadal time scales there is little evidence for any change in the observed global warming rate, but some evidence for a recent temporary slowdown in the warming rate in the Pacific. This multi-decadal slowdown can be partly explained by a cool phase of the Interdecadal Pacific Oscillation and a short-term excess of La Niña events. We also analyse historical and projected changes in 38 CMIP climate models. All of the model simulations examined simulate multi-decadal warming in the Pacific over the past half-century that exceeds observed values. This difference cannot be fully explained by observed internal multi-decadal climate variability, even if allowance is made for an apparent tendency for models to underestimate internal multi-decadal variability in the Pacific. Models which simulate the greatest global warming over the past half-century also project warming that is among the highest of all models by the end of the twenty-first century, under both low and high greenhouse gas emission scenarios. Given that the same models are poorest in representing observed multi-decadal temperature change, confidence in the highest projections is reduced.
UR – https://doi.org/10.1007/s00382-016-3326-x
DO – 10.1007/s00382-016-3326-x
ER –

NR – 69
TY – JOUR
AU – Liao, Enhui
AU – Lu, Wenfang
AU – Yan, Xiao-Hai
AU – Jiang, Yuwu
AU – Kidwell, Autumn
TI – The coastal ocean response to the global warming acceleration and hiatus
JF – Scientific Reports
PY – 2015
VL – 5
SP – 16630
UR – http://dx.doi.org/10.1038/srep16630
DO – 10.1038/srep16630
AB – Coastlines are fundamental to humans for habitation, commerce, and natural resources. Many coastal ecosystem disasters, caused by extreme sea surface temperature (SST), were reported when the global climate shifted from global warming to global surface warming hiatus after 1998. The task of understanding the coastal SST variations within the global context is an urgent matter. Our study on the global coastal SST from 1982 to 2013 revealed a significant cooling trend in the low and mid latitudes (31.4% of the global coastlines) after 1998, while 17.9% of the global coastlines changed from a cooling trend to a warming trend concurrently. The trend reversals in the Northern Pacific and Atlantic coincided with the phase shift of Pacific Decadal Oscillation and North Atlantic Oscillation, respectively. These coastal SST changes are larger than the changes of the global mean and open ocean, resulting in a fast increase of extremely hot/cold days, and thus extremely hot/cold events. Meanwhile, a continuous increase of SST was detected for a considerable portion of coastlines (46.7%) with a strengthened warming along the coastlines in the high northern latitudes. This suggests the warming still continued and strengthened in some regions after 1998, but with a weaker pattern in the low and mid latitudes.
ER –

NR – 70
TY – JOUR
AU – Duan, Anmin
AU – Xiao, Zhixiang
TI – Does the climate warming hiatus exist over the Tibetan Plateau?
JF – Scientific Reports
PY – 2015
VL – 5
SP – 13711
UR – http://dx.doi.org/10.1038/srep13711
DO – 10.1038/srep13711
AB – The surface air temperature change over the Tibetan Plateau is determined based on historical observations from 1980 to 2013. In contrast to the cooling trend in the rest of China, and the global warming hiatus post-1990s, an accelerated warming trend has appeared over the Tibetan Plateau during 1998–2013 (0.25?°C decade-1), compared with that during 1980–1997 (0.21?°C decade-1). Further results indicate that, to some degree, such an accelerated warming trend might be attributable to cloud–radiation feedback. The increased nocturnal cloud over the northern Tibetan Plateau would warm the nighttime temperature via enhanced atmospheric back-radiation, while the decreased daytime cloud over the southern Tibetan Plateau would induce the daytime sunshine duration to increase, resulting in surface air temperature warming. Meanwhile, the in situ surface wind speed has recovered gradually since 1998, and thus the energy concentration cannot explain the accelerated warming trend over the Tibetan Plateau after the 1990s. It is suggested that cloud–radiation feedback may play an important role in modulating the recent accelerated warming trend over the Tibetan Plateau.
ER –

NR – 71
TY – JOUR
AU – Ducic, Vladan D.
AU – Milovanovic, Boško M.
AU – Stanojevic, Gorica B.
AU – Milenkovic, Milan Ð.
AU – Curcic, Nina B.
TI – Tropical temperature altitude amplification in the hiatus period (1998-2012)
JF – Thermal Science
PY – 2015
VL – 19
IS – 2
SP – 371
EP – 379
UR – http://dx.doi.org/10.2298/TSCI150410103D
DO – 10.2298/TSCI150410103D
AB – In the period 1998-2012 there was a stagnation in temperature rise, despite the GHGs radiation forcing is increased (hiatus period). According to Global Circulation Models simulations, expected response on the rise of GHGs forcing is tropical temperature altitude amplification – temperature increases faster in higher troposphere than in lower troposphere. In this paper, two satellite data sets, UAH MSU and RSS, were used to test altitude temperature amplification in tropic (20°N-20°S) in the hiatus period. We compared data from satellite data sets from lower troposphere (TLT) and middle troposphere (TMT) in general and particularly for land and ocean (for UAH MSU). The results from both satellite measurements showed the presence of hiatus, i.e. slowdown of the temperature rise in the period 1998-2012 compared to period 1979-2012 (UAH MSU) and temperature fall for RSS data. Smaller increase, i.e. temperature fall over ocean showed that hiatus is an ocean phenomenon above all. Data for UAH MSU showed that temperature altitude amplification in tropic was not present either for period 1979-2012, or 1998-2012. RSS data set also do not show temperature altitude amplification either for longer (1979-2012), or for shorter period (1998-2012). RSS data for successive 15-year periods from 1979-1993 till 1998-2012 does not show tropical temperature altitude amplification and in one case negative trend is registered in TLT and in two cases in TMT. In general, our results do not show presence of temperature altitude amplification in tropic in the hiatus period.
ER –

NR – 72
TY – JOUR
T1 – Does the Global Warming Pause in the Last Decade: 1999–2008?
AU – Wang, Shaowu
AU – Wen, Xinyu
AU – Luo, Yong
AU – Tang, Guoli
AU – Zhao, Zongci
AU – Huang, Jianbin
JO – Advances in Climate Change Research
VL – 1
IS – 1
SP – 49
EP – 54
PY – 2010
DO – https://doi.org/10.3724/SP.J.1248.2010.00049
UR – http://www.sciencedirect.com/science/article/pii/S167492781050008X
AB – Issues related to the pause of global warming in the last decade are reviewed. It is indicated that: (1) The decade of 1999–2008 is still the warmest of the last 30 years, though the global temperature increment is near zero; (2) Natural factors such as volcanism, solar radiation, ENSO, and thermohaline circulation can have impact on the inter-annual and inter-decadal variability of global mean temperatures. However, it will not mask the global warming trend for a long time; (3) Temperatures of China continue to increase in 1999–2008 with an increment of 0.4–0.5°C per 10 years.
ER –

NR – 73
TY – JOUR
AU – Kumar, Sanjiv
AU – Kinter, James L.
AU – Pan, Zaitao
AU – Sheffield, Justin
TI – Twentieth century temperature trends in CMIP3, CMIP5, and CESM-LE climate simulations: Spatial-temporal uncertainties, differences, and their potential sources
JO – Journal of Geophysical Research: Atmospheres
VL – 121
IS – 16
UR – http://dx.doi.org/10.1002/2015JD024382
DO – 10.1002/2015JD024382
SP – 9561
EP – 9575
PY – 2016
AB – The twentieth century climate simulations from the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Phase 5 (CMIP5) are compared to assess the models’ ability to capture observed near-surface air temperature trends at global, continental, and regional scales. We computed trends by using a nonparametric method and considering long-term persistence in the time series. The role of internal variability is examined by using large ensemble climate simulations from the National Center for Atmospheric Research model Community Earth System Model (CESM). We computed temperature trends for three periods: the twentieth century, the second half of the twentieth century, and (3) the recent hiatus period to contrast the roles of external forcing and internal variability at various spatial and temporal scales. Both CMIP ensembles show statistically significant warming at global and continental scales during the twentieth century. We found a small but statistically significant difference between CMIP3 (0.57?±?0.07?°C/century) and CMIP5 (0.47?±?0.06?°C/century) twentieth century temperature trends, with the CMIP3 estimate being closer to the observations. The spatial structure of long-term temperature trends, and top-of-the atmosphere net radiation trends, suggests that differences in model parameterizations and feedback processes that lead to a smaller net radiative forcing are likely contributing to the differences between CMIP3 and CMIP5. The estimate of internal variability based on the CESM large ensemble spans 24% of the uncertainty in CMIP5 for the twentieth century temperature trends, and 76% for the recent hiatus period, both at global scales, and 43% and almost 100% during the corresponding time periods at regional scales.
ER –

NR – 74
TY – JOUR
AU – Huang, Jianping
AU – Xie, Yongkun
AU – Guan, Xiaodan
AU – Li, Dongdong
AU – Ji, Fei
PY – 2017
TI – The dynamics of the warming hiatus over the Northern Hemisphere
JO – Climate Dynamics
SP – 429
EP – 446
VL – 48
IS – 1
AB – A warming hiatus is a period of relatively little change in global mean surface air temperatures (SAT). Many studies have attributed the current warming hiatus to internal climate variability (ICV). But there is less work on discussion of the dynamics about how these ICV modes influence cooling over land in the Northern Hemisphere (NH). Here we demonstrate the warming hiatus was more significant over the continental NH. We explored the dynamics of the warming hiatus from a global perspective and investigated the mechanisms of the reversing from accelerated warming to hiatus, and how ICV modes influence SAT change throughout the NH land. It was found that these ICV modes and Arctic amplification can excite a decadal modulated oscillation (DMO), which enhances or suppresses the long-term trend on decadal to multi-decadal timescales. When the DMO is in an upward (warming) phase, it contributes to an accelerated warming trend, as in last 20 years of twentieth-century. It appears that there is a downward swing in the DMO occurring at present, which has balanced or reduced the radiative forced warming and resulted in the recent global warming hiatus. The DMO modulates the SAT, in particular, the SAT of boreal cold months, through changes in the asymmetric meridional and zonal thermal forcing (MTF and ZTF). The MTF represents the meridional temperature gradients between the mid- and high-latitudes, and the ZTF represents the asymmetry in temperatures between the extratropical large-scale warm and cold zones in the zonal direction. Via the different performance of combined MTF and ZTF, we found that the DMO’s modulation effect on SAT was strongest when both weaker (stronger) MTF and stronger (weaker) ZTF occurred simultaneously. And the current hiatus is a result of a downward DMO combined with a weaker MTF and stronger ZTF, which stimulate both a weaker polar vortex and westerly winds, along with the amplified planetary waves, thereby facilitating southward invasion of cold Arctic-air and promoting the blocking formation. The results conclude that the DMO can not only be used to interpret the current warming hiatus, it also suggests that global warming will accelerate again when it swings upward.
UR – https://doi.org/10.1007/s00382-016-3085-8
DO – 10.1007/s00382-016-3085-8
ER –

NR – 75
TY – JOUR
AU – Ma, Ying
AU – Mao, Rui
AU – Feng, Sheng-Hui
AU – Gong, Dao-Yi
AU – Kim, Seong-Joong
TI – Does the recent warming hiatus exist over Northern Asia for winter wind chill temperature?
JO – International Journal of Climatology
VL – 37
IS – 7
UR – http://dx.doi.org/10.1002/joc.4905
DO – 10.1002/joc.4905
SP – 3138
EP – 3144
PY – 2017
AB – Wind chill temperature (WCT) describes the joint effect of wind velocity and air temperature on exposed body skin and could support policymakers in designing plans to reduce the risks of notably cold and windy weather. This study examined winter WCT over Northern Asia during 1973–2013 by analysing in situ station data. The winter WCT warming rate over the Tibetan Plateau (TP) slowed during 1999–2013 (-0.04?°C?decade-1) compared with that of during 1973–1998 (0.67?°C?decade-1). The winter WCT warming hiatus has also been observed in the remainder of Northern Asia with trends of 1.11?°C? decade-1 during 1973–1998 but -1.02?°C?decade-1 during 1999–2013, except for the Far East (FE) of Russia, where the winter WCT has continued to heat up during both the earlier period of 1973–1998 (0.54?°C?decade-1) and the recent period of 1999–2013 (0.75?°C?decade-1). The results indicate that the influence of temperature on winter WCT is greater than that of wind speed over Northern Asia. Atmospheric circulation changes associated with air temperature and wind speed were analysed to identify the causes for the warming hiatus of winter WCT over Northern Asia. The distributions of sea-level pressure and 500-hPa height anomalies during 1999–2013 transported cold air from the high latitudes to middle latitudes, resulting in low air temperature over Northern Asia except for the FE of Russia. Over the TP, the increase in wind speed offset the increase in air temperature during 1999– 2013. For the FE, the southerly wind from the Western Pacific drove the temperature up during the 1999–2013 period through warm advection.
ER –

NR – 76
TY – JOUR
AU – Douville, H.
AU – Voldoire, A.
AU – Geoffroy, O.
TI – The recent global warming hiatus: What is the role of Pacific variability?
JO – Geophysical Research Letters
VL – 42
IS – 3
UR – http://dx.doi.org/10.1002/2014GL062775
DO – 10.1002/2014GL062775
SP – 880
EP – 888
PY – 2015
AB – The observed global mean surface air temperature (GMST) has not risen over the last 15?years, spurring outbreaks of skepticism regarding the nature of global warming and challenging the upper range transient response of the current-generation global climate models. Recent numerical studies have, however, tempered the relevance of the observed pause in global warming by highlighting the key role of tropical Pacific internal variability. Here we first show that many climate models overestimate the influence of the El Niño–Southern Oscillation on GMST, thereby shedding doubt on their ability to capture the tropical Pacific contribution to the hiatus. Moreover, we highlight that model results can be quite sensitive to the experimental design. We argue that overriding the surface wind stress is more suitable than nudging the sea surface temperature for controlling the tropical Pacific ocean heat uptake and, thereby, the multidecadal variability of GMST. Using the former technique, our model captures several aspects of the recent climate evolution, including the weaker slowdown of global warming over land and the transition toward a negative phase of the Pacific Decadal Oscillation. Yet the observed global warming is still overestimated not only over the recent 1998–2012 hiatus period but also over former decades, thereby suggesting that the model might be too sensitive to the prescribed radiative forcings.
ER –

NR – 77
TY – JOUR
AU – Schurer, Andrew P.
AU – Hegerl, Gabriele C.
AU – Obrochta, Stephen P.
TI – Determining the likelihood of pauses and surges in global warming
JO – Geophysical Research Letters
VL – 42
IS – 14
UR – http://dx.doi.org/10.1002/2015GL064458
DO – 10.1002/2015GL064458
SP – 5974
EP – 5982
PY – 2015
AB – The recent warming “hiatus” is subject to intense interest, with proposed causes including natural forcing and internal variability. Here we derive samples of all natural and internal variability from observations and a recent proxy reconstruction to investigate the likelihood that these two sources of variability could produce a hiatus or rapid warming in surface temperature. The likelihood is found to be consistent with that calculated previously for models and exhibits a similar spatial pattern, with an Interdecadal Pacific Oscillation-like structure, although with more signal in the Atlantic than in model patterns. The number and length of events increases if natural forcing is also considered, particularly in the models. From the reconstruction it can be seen that large eruptions, such as Mount Tambora in 1815, or clusters of eruptions, may result in a hiatus of over 20?years, a finding supported by model results.
ER –

NR – 78
TY – JOUR
AU – Ou, Nian-Sen
AU – Lin, Yi-Hua
AU – Bi, Xun-Qiang
PY – 2015
TI – Simulated Heat Sink in the Southern Ocean and Its Contribution to the Recent Hiatus Decade
JO – Atmospheric and Oceanic Science Letters
VL – 8
IS – 3
SP – 174
EP – 178
UR – http://dx.doi.org/10.3878/AOSL20150008
DO – 10.3878/AOSL20150008
AB – A set of numerical experiments is designed and carried out to understand a heat sink in the Southern Ocean in the recent hiatus decade. By using an oceanic general circulation model, the authors focus on the contributions from two types of forcing: wind stress and thermohaline forcing. The simulated results show that the heat sink in the upper Southern Ocean comes mainly from thermohaline forcing; while in the deeper layers, wind stress forcing also plays an important role. These different contributions may be due to different physical processes for the heat budget. The combination of these two types of forcing shows a significant heat sink in the Southern Ocean in the recent hiatus decade, and this is consistent with the observations and conclusions of a similar recently published study.
ER –

NR – 79
TY – JOUR
AU – Kosaka, Yu
AU – Xie, Shang-Ping
TI – The tropical Pacific as a key pacemaker of the variable rates of global warming
JO – Nature Geoscience
PY – 2016
VL – 9
SP – 669
UR – http://dx.doi.org/10.1038/ngeo2770
DO – 10.1038/ngeo2770
AB – Global mean surface temperature change over the past 120 years resembles a rising staircase1,2: the overall warming trend was interrupted by the mid-twentieth-century big hiatus and the warming slowdown2,3,4,5,6,7,8 since about 1998. The Interdecadal Pacific Oscillation9,10 has been implicated in modulations of global mean surface temperatures6,11, but which part of the mode drives the variability in warming rates is unclear. Here we present a successful simulation of the global warming staircase since 1900 with a global ocean–atmosphere coupled model where tropical Pacific sea surface temperatures are forced to follow the observed evolution. Without prescribed tropical Pacific variability, the same model, on average, produces a continual warming trend that accelerates after the 1960s. We identify four events where the tropical Pacific decadal cooling markedly slowed down the warming trend. Matching the observed spatial and seasonal fingerprints we identify the tropical Pacific as a key pacemaker of the warming staircase, with radiative forcing driving the overall warming trend. Specifically, tropical Pacific variability amplifies the first warming epoch of the 1910s– 1940s and determines the timing when the big hiatus starts and ends. Our method of removing internal variability from the observed record can be used for real-time monitoring of anthropogenic warming.
ER –

NR – 80
TY – JOUR
AU – Yan, Xiao-Hai
AU – Boyer, Tim
AU – Trenberth, Kevin
AU – Karl, Thomas R.
AU – Xie, Shang-Ping
AU – Nieves, Veronica
AU – Tung, Ka-Kit
AU – Roemmich, Dean
TI – The global warming hiatus: Slowdown or redistribution?
JO – Earth’s Future
VL – 4
IS – 11
UR – http://dx.doi.org/10.1002/2016EF000417
DO – 10.1002/2016EF000417
SP – 472
EP – 482
PY – 2016
AB – Global mean surface temperatures (GMST) exhibited a smaller rate of warming during 1998–2013, compared to the warming in the latter half of the 20th Century. Although, not a “true” hiatus in the strict definition of the word, this has been termed the “global warming hiatus” by IPCC (2013). There have been other periods that have also been defined as the “hiatus” depending on the analysis. There are a number of uncertainties and knowledge gaps regarding the “hiatus.” This report reviews these issues and also posits insights from a collective set of diverse information that helps us understand what we do and do not know. One salient insight is that the GMST phenomenon is a surface characteristic that does not represent a slowdown in warming of the climate system but rather is an energy redistribution within the oceans. Improved understanding of the ocean distribution and redistribution of heat will help better monitor Earth’s energy budget and its consequences. A review of recent scientific publications on the “hiatus” shows the difficulty and complexities in pinpointing the oceanic sink of the “missing heat” from the atmosphere and the upper layer of the oceans, which defines the “hiatus.” Advances in “hiatus” research and outlooks (recommendations) are given in this report.
ER –

NR – 81
TY – JOUR
T1 – Spatiotemporal Temperature Variability over the Tibetan Plateau: Altitudinal Dependence Associated with the Global Warming Hiatus
AU – Cai, Danlu
AU – You, Qinglong
AU – Fraedrich, Klaus
AU – Guan, Yanning
PY – 2016
DO – 10.1175/JCLI-D-16-0343.1
JF – Journal of Climate
SP – 969
EP – 984
VL – 30
IS – 3
AB – The recent slowdown in global warming has initiated a reanalysis of temperature data in some mountainous regions for understanding the consequences and impact that a hiatus has on the climate system. Spatiotemporal temperature variability is analyzed over the Tibetan Plateau because of its sensitivity to climate change with a station network updated to 2014, and its linkages to remote sensing?based variability of MODIS daytime and nighttime temperature are investigated. Results indicate the following: 1) Almost all stations have experienced a notable warming in the time interval 1961?2014, with most obvious warming in winter, which depends on the selected time intervals. 2) There is no clear shift from a predominant warming to a near stagnation during the most recent period (2001?present). 3) Uniform altitudinal dependence of temperature change trends could not be confirmed for all regions, time intervals, and seasons, but sometimes an altitude threshold around 3 km is apparent. 4) Most of the meteorological stations are associated with MODIS temperature warming pixels, and thus regional cooling is missing when considering only the locations of meteorological stations. In summarizing, previous studies based on station observations do not provide a complete picture for the temperature change over the Tibetan Plateau. Remote sensing?based analyses have the potential to find early signals of regional climate changes and assess the impact of global climate changes in complex regional, seasonal, and altitudinal environments.
UR – https://doi.org/10.1175/JCLI-D-16-0343.1
ER –

NR – 82
TY – JOUR
AU – Rackow, T.
AU – Goessling, H. F.
AU – Jung, T.
AU – Sidorenko, D.
AU – Semmler, T.
AU – Barbi, D.
AU – Handorf, D.
PY – 2016
TI – Towards multi-resolution global climate modeling with ECHAM6-FESOM. Part II: climate variability
JO – Climate Dynamics
AB – This study forms part II of two papers describing ECHAM6-FESOM, a newly established global climate model with a unique multi-resolution sea ice- ocean component. While part I deals with the model description and the mean climate state, here we examine the internal climate variability of the model under constant present-day (1990) conditions. We (1) assess the internal variations in the model in terms of objective variability performance indices, (2) analyze variations in global mean surface temperature and put them in context to variations in the observed record, with particular emphasis on the recent warming slowdown, (3) analyze and validate the most common atmospheric and oceanic variability patterns, (4) diagnose the potential predictability of various climate indices, and (5) put the multi-resolution approach to the test by comparing two setups that differ only in oceanic resolution in the equatorial belt, where one ocean mesh keeps the coarse ~1° resolution applied in the adjacent open-ocean regions and the other mesh is gradually refined to ~0.25°. Objective variability performance indices show that, in the considered setups, ECHAM6-FESOM performs overall favourably compared to five well-established climate models. Internal variations of the global mean surface temperature in the model are consistent with observed fluctuations and suggest that the recent warming slowdown can be explained as a once-in-one-hundred-years event caused by internal climate variability; periods of strong cooling in the model (‘hiatus’ analogs) are mainly associated with ENSO-related variability and to a lesser degree also to PDO shifts, with the AMO playing a minor role. Common atmospheric and oceanic variability patterns are simulated largely consistent with their real counterparts. Typical deficits also found in other models at similar resolutions remain, in particular too weak non-seasonal variability of SSTs over large parts of the ocean and episodic periods of almost absent deep-water formation in the Labrador Sea, resulting in overestimated North Atlantic SST variability. Concerning the influence of locally (isotropically) increased resolution, the ENSO pattern and index statistics improve significantly with higher resolution around the equator, illustrating the potential of the novel unstructured-mesh method for global climate modeling.
UR – https://doi.org/10.1007/s00382-016-3192-6
DO – 10.1007/s00382-016-3192-6
ER –

NR – 83
TY – JOUR
AU – Chen, Xianyao
AU – Tung, Ka-Kit
TI – Correspondence: Variations in ocean heat uptake during the surface warming hiatus
JO – Nature Communications
PY – 2016
VL – 7
SP – 12541
UR – http://dx.doi.org/10.1038/ncomms12541
DO – 10.1038/ncomms12541
ER –

NR – 84
TY – JOUR
T1 – Estimation of subsurface temperature anomaly in the Indian Ocean during recent global surface warming hiatus from satellite measurements: A support vector machine approach
AU – Su, Hua
AU – Wu, Xiangbai
AU – Yan, Xiao-Hai
AU – Kidwell, Autumn
JO – Remote Sensing of Environment
VL – 160
SP – 63
EP – 71
PY – 2015
DO – https://doi.org/10.1016/j.rse.2015.01.001
UR – http://www.sciencedirect.com/science/article/pii/S0034425715000103
AB – Estimating the thermal information in the subsurface and deeper ocean from satellite measurements over large basin-wide scale is important but also challenging. This paper proposes a support vector machine (SVM) method to estimate subsurface temperature anomaly (STA) in the Indian Ocean from a suite of satellite remote sensing measurements including sea surface temperature anomaly (SSTA), sea surface height anomaly (SSHA), and sea surface salinity anomaly (SSSA). The SVM estimation of STA features the inclusion of in-situ Argo STA data for training and testing. SVM, one of the most popular machine learning methods, can well estimate the STA in the upper 1000m of the Indian Ocean from satellite measurements of sea surface parameters (SSTA, SSHA and SSSA as input attributes for SVM). The results, based on the common SVM application of Support Vector Regression (SVR), were validated for accuracy and reliability using the Argo STA data. Both MSE and r2 for performance measures are improved after including SSSA for SVR (MSE decreased by 12% and r2 increased by 11% on average). The results showed that SSSA, in addition to SSTA and SSHA, is a useful parameter that can help detect and describe the deeper ocean thermal structure, as well as improve the STA estimation accuracy. Moreover, our method can provide a useful technique for studying subsurface and deeper ocean thermal variability which has played an important role in recent global surface warming hiatus since 1998, from satellite measurements in large basin-wide scale.
ER –

NR – 85
TY – JOUR
AU – Yeo, Sae-Rim
AU – Yeh, Sang-Wook
AU – Kim, Kwang-Yul
AU – Kim, WonMoo
PY – 2017
TI – The role of low-frequency variation in the manifestation of warming trend and ENSO amplitude
JO – Climate Dynamics
SP – 1197
EP – 1213
VL – 49
IS – 4
AB – Despite the increase in greenhouse gas concentration, the sea surface temperature (SST) over the tropical eastern Pacific during the period of 1999–2014 exhibits less warming trend compared to the earlier decades. It has been noted that this warming hiatus is accompanied by a negative phase of the Pacific Decadal Oscillation (PDO), which represents low-frequency variability over the Pacific. On the other hand, the 2015/2016 El Niño is among the strongest comparable to the 1997/1998 event, which coincides with the recently altered PDO phase from negative to positive. These observational evidences have generated substantial interest in the role of low-frequency variations in modulating El Niño-Southern Oscillation amplitude as well as manifestation of warming signal in the tropical Pacific. Therefore, it is necessary to appropriately separate low-frequency variability and global warming signal from SST records. Here, we present three primary modes of global SST that include secular warming trend, low-frequency variability, and biennial oscillation. Based on the independent behavior of these three modes, global warming is clearly continuing but its manifestation is enhanced (depressed) when the low-frequency variation is in the positive (negative) phase. Further, possibility of strong El Niño increases under the positive phase of the low-frequency mode, which amplifies warming over the tropical eastern Pacific. Indeed, the strong 2015/2016 El Niño is largely attributed to the positive phase of the low-frequency mode. In order to examine the climate models’ ability to simulate the three SST modes as obtained in the observational record, the Coupled Model Intercomparison Project phase 5 (CMIP5) datasets are also analyzed. The spatial and temporal characteristics of the three modes have been replicated closely by the selected CMIP5 models forced by the historical condition, which provides an analogy of the interplay of three modes in the observed tropical Pacific SST.
UR – https://doi.org/10.1007/s00382-016-3376-0
DO – 10.1007/s00382-016-3376-0
ER –

NR – 86
TY – JOUR
AU – Li, Chao
AU – Stevens, Bjorn
AU – Marotzke, Jochem
TI – Eurasian winter cooling in the warming hiatus of 1998–2012
JO – Geophysical Research Letters
VL – 42
IS – 19
UR – http://dx.doi.org/10.1002/2015GL065327
DO – 10.1002/2015GL065327
SP – 8131
EP – 8139
PY – 2015
AB – We investigate the relative magnitudes of the contributions of surface temperature trends from different latitude bands to the recent warming hiatus. We confirm from five different global data sets that the global-mean surface temperature trend in the period 1998–2012 is strongly influenced by a pronounced Eurasian winter cooling trend. To understand the drivers of this winter cooling trend, we perform three 20-member ensembles of simulations with different prescribed sea surface temperature and sea ice in the atmospheric model ECHAM6. Our experimental results suggest that the Arctic sea ice loss does not drive systematic changes in the Northern Hemisphere large-scale circulation in the past decades. The observed Eurasian winter cooling trend over 1998–2012 arises essentially from atmospheric internal variability and constitutes an extreme climate event. However, the observed reduction in Arctic sea ice enhances the variability of Eurasian winter climate and thus increases the probability of an extreme Eurasian winter cooling trend.
ER –

NR – 87
TY – JOUR
AU – Parker, Albert
PY – 2014
TI – The “Present Global Warming Hiatus” Is Part Of A Quasi-60 Years Oscillation In The Worldwide Average Temperatures In The Downwards Phase
JO – Environmental Science : An Indian Journal
VL – 9
IS – 1
SP – 14
EP – 22
UR – http://www.tsijournals.com/abstract/the-present-global-warming-hiatus-is-part-of-a-quasi60-years-oscillation-in-the-worldwide-average- temperatures-in-the-do-2828.html
AB – Since the beginning of this century, the seas have not been warming over the surface as well as in the layers up to 2000mdepth, asmeasured in theARGO project. Over the same period, the reconstructed land and sea temperatures of the HADCRUT4, GISS and NCDCdata sets have been warming marginally, mostly because of the largest opportunities to introduce upward biases in a less accurate mixed computational and experimental result. Over the same period of time, the CMIP3 and CMIP5 have predicted huge warmings that have no support in themeasurements or reconstructions. It is shown here that the Â?present global warming hiatusÂ? is possibly a repetition of a dwelling period of not significant warming that the reconstructions locate from1945 to 1975.
ER –

NR – 88
TY – JOUR
AU – Xie, Yongkun
AU – Huang, Jianping
AU – Liu, Yuzhi
TI – From accelerated warming to warming hiatus in China
JO – International Journal of Climatology
VL – 37
IS – 4
UR – http://dx.doi.org/10.1002/joc.4809
DO – 10.1002/joc.4809
SP – 1758
EP – 1773
PY – 2017
AB – As the recent global warming hiatus has attracted worldwide attention, we examined the robustness of the warming hiatus in China and the related dynamical mechanisms in this study. Based on the results confirmed by the multiple data and trend analysis methods, we found that the annual mean temperature in China had a cooling trend during the recent global warming hiatus period, which suggested a robust warming hiatus in China. The warming hiatus in China was dominated by the cooling trend in the cold season, which was mainly induced by the more frequent and enhanced extreme-cold events. By examining the variability of the temperature over different time scales, we found the recent warming hiatus was mainly associated with a downward change of decadal variability, which counteracted the background warming trend. Decadal variability was also much greater in the cold season than in the warm season, and also contributed the most to the previous accelerated warming. We found that the previous accelerated warming and the recent warming hiatus, and the decadal variability of temperature in China were connected to changes in atmospheric circulation. There were opposite circulation changes during these two periods. The westerly winds from the low to the high troposphere over the north of China all enhanced during the previous accelerated warming period, while it weakened during the recent hiatus. The enhanced westerly winds suppressed the invasion of cold air from the Arctic and vice versa. Less frequent atmospheric blocking during the accelerated warming period and more frequent blocking during the recent warming hiatus confirmed this hypothesis. Furthermore, variation in the Siberian High and East Asian winter monsoon season supports the given conclusions.
ER –

NR – 89
TY – JOUR
T1 – Why Has the Relationship between Indian and Pacific Ocean Decadal Variability Changed in Recent Decades?
AU – Dong, Lu
AU – McPhaden, Michael J.
PY – 2016
DO – 10.1175/JCLI-D-16-0313.1
JF – Journal of Climate
SP – 1971
EP – 1983
VL – 30
IS – 6
AB – Both the Indian and Pacific Oceans exhibit prominent decadal time scale variations in sea surface temperature (SST), linked dynamically via atmospheric and oceanic processes. However, the relationship between SST in these two basins underwent a dramatic transformation beginning around 1985. Prior to that, SST variations associated with the Indian Ocean basin mode (IOB) and the interdecadal Pacific oscillation (IPO) were positively correlated, whereas afterward they were much less clearly synchronized. Evidence is presented from both observations and coupled state-of-the-art climate models that enhanced external forcing, particularly from increased anthropogenic greenhouse gases, was the principal cause of this changed relationship. Using coupled climate model experiments, it is shown that without external forcing, the evolution of the IOB would be strongly forced by variations in the IPO. However, with strong external forcing, the dynamical linkage between the IOB and the IPO weakens so that the negative phase IPO after 2000 is unable to force a negative phase IOB-induced cooling of the Indian Ocean. This changed relationship in the IOB and IPO led to unique SST patterns in the Indo-Pacific region after 2000, which favored exceptionally strong easterly trade winds over the tropical Pacific Ocean and a pronounced global warming hiatus in the first decade of the twenty-first century.
UR – https://doi.org/10.1175/JCLI-D-16-0313.1
ER –

NR – 90
TY – JOUR
AU – Desbruyères, D. G.
AU – McDonagh, E. L.
AU – King, B. A.
AU – Garry, F. K.
AU – Blaker, A. T.
AU – Moat, B. I.
AU – Mercier, H.
TI – Full-depth temperature trends in the northeastern Atlantic through the early 21st century
JO – Geophysical Research Letters
VL – 41
IS – 22
UR – http://dx.doi.org/10.1002/2014GL061844
DO – 10.1002/2014GL061844
SP – 7971
EP – 7979
PY – 2014
AB – The vertical structure of temperature trends in the northeastern Atlantic (NEA) is investigated using a blend of Argo and hydrography data. The representativeness of sparse hydrography sampling in the basin mean is assessed using a numerical model. Between 2003 and 2013, the NEA underwent a strong surface cooling (0–450 m) and a significant warming at intermediate and deep levels (1000 m to 3000 m) that followed a strong cooling trend observed between 1988 and 2003. During 2003–2013, gyre-specific changes are found in the upper 1000 m (warming and cooling of the subtropical and subpolar gyres, respectively), while the intermediate and deep warming primarily occurred in the subpolar gyre, with important contributions from isopycnal heave and water mass property changes. The full-depth temperature change requires a local downward heat flux of 0.53 ± 0.06 W m-2 through the sea surface, and its vertical distribution highlights the likely important role of the NEA in the recent global warming hiatus.
ER –

NR – 91
TY – JOUR
AU – Chakrabarty, D. K.
AU – Peshin, S. K.
PY – 2013
TI – Global warming and solar anomaly
JO – Indian Journal of Radio & Space Physics
VL – 42
IS – 6
UR – http://op.niscair.res.in/index.php/IJRSP/article/view/2251
AB – During 2002-2008, there was no increase in global temperature, though green house gas concentrations had increased. Sun is the ultimate source of energy. It has been, therefore, examined if there was any anomaly in the solar characteristics during this period. The sunspot number data has been used for this purpose. This parameter has an 11-year solar activity cycle and the same is found in the global temperature. But the trend in sun’s output, after removing solar activity effect, does not match with the long term trend of global temperature. Peculiarities in the duration and in the peak value of solar cycle 23 were identified which might have portended the increase of global temperature during 2002-2008. The possibility of the pause of increase in temperature could also be that the heat generated due to the increase in the greenhouse gas concentration was absorbed in deep ocean layer.
ER –

NR – 92
TY – JOUR
AU – Zeng, Xubin
AU – Geil, Kerrie
TI – Global warming projection in the 21st century based on an observational data-driven model
JO – Geophysical Research Letters
VL – 43
IS – 20
UR – http://dx.doi.org/10.1002/2016GL071035
DO – 10.1002/2016GL071035
SP – 10,947
EP – 10,954
PY – 2016
AB – Global warming has been projected primarily by Earth system models (ESMs). Complementary to this approach, here we provide the decadal and long- term global warming projections based on an observational data-driven model. This model combines natural multidecadal variability with anthropogenic warming that depends on the history of annual emissions. It shows good skill in decadal hindcasts with the recent warming slowdown well captured. While our ensemble mean temperature projections at the end of 21st century are consistent with those from ESMs, our decadal warming projection of 0.35 (0.30- 0.43)?K from 1986–2005 to 2016–2035 is within their projection range and only two-thirds of the ensemble mean from ESMs. Our predicted warming rate in the next few years is slower than in the 1980s and 1990s, followed by a greater warming rate. Our projection uncertainty range is just one-third of that from ESMs, and its implication is also discussed.
ER –

NR – 93
TY – JOUR
AU – Leggett, L. M. W.
AU – Ball, D. A.
PY – 2015
TI – Granger causality from changes in level of atmospheric CO2 to global surface temperature and the El Niño–Southern Oscillation, and a candidate mechanism in global photosynthesis
JO – Atmospheric Chemistry and Physics
VL – 15
SP – 11571
EP – 11592
UR – http://dx.doi.org/10.5194/acp-15-11571-2015
DO – 10.5194/acp-15-11571-2015
AB – A significant difference, now of some 16 years’ duration, has been shown to exist between the observed global surface temperature trend and that expected from the majority of climate simulations. For its own sake, and to enable better climate prediction for policy use, the reasons behind this mismatch need to be better understood. While an increasing number of possible causes have been proposed, the candidate causes have not yet converged. With this background, this paper reinvestigates the relationship between change in the level of CO2 and two of the major climate variables, atmospheric temperature and the El Niño–Southern Oscillation (ENSO). Using time-series analysis in the form of dynamic regression modelling with autocorrelation correction, it is shown that first-difference CO2 leads temperature and that there is a highly statistically significant correlation between first- difference CO2 and temperature. Further, a correlation is found for second-difference CO2 with the Southern Oscillation Index, the atmospheric-pressure component of ENSO. This paper also shows that both these correlations display Granger causality. It is shown that the first-difference CO2 and temperature model shows no trend mismatch in recent years. These results may contribute to the prediction of future trends for global temperature and ENSO. Interannual variability in the growth rate of atmospheric CO2 is standardly attributed to variability in the carbon sink capacity of the terrestrial biosphere. The terrestrial biosphere carbon sink is created by the difference between photosynthesis and respiration (net primary productivity): a major way of measuring global terrestrial photosynthesis is by means of satellite measurements of vegetation reflectance, such as the Normalized Difference Vegetation Index (NDVI). In a preliminary analysis, this study finds a close correlation between an increasing NDVI and the increasing climate model/temperature mismatch (as quantified by the difference between the trend in the level of CO2 and the trend in temperature).
ER –

NR – 94
TY – JOUR
AU – Ducic, Vladan
AU – Milenkovic, Milan
AU – Milijaševic, Dragana
AU – Vujacic, Duško
AU – Bjeljac, Željko
AU – Lovic, Suzana
AU – Gajic, Mirjana
AU – Andelkovic, Goran
AU – Djordjevic, Aleksandar
PY – 2015
TI – Hiatus in global warming – example of water temperature of the Danube River at Bogojevo gauge (Serbia)
JO – Thermal Science
VL – 19
IS – 2
SP – 467
EP – 476
DO – 10.2298/TSCI150430133D
UR – http://dx.doi.org/10.2298/TSCI150430133D
AB – The research included trends in water temperature of the Danube River at Bogojevo gauge and surface air temperature at the nearby meteorological station Sombor, as well as an analysis of the results obtained in relation to the claims of the existence of the hiatus in global air temperature increase in the period 1998-2012. In the period 1961-2013, there was a statistically significant increase in the mean annual water temperature (0.039°C/year), as well as all the average monthly values. However, with annual values for the period 1998-2013, there was a decrease. The longest periods of negative trend (27 years) were recorded for January and February. A high correlation was found between the surface air temperature and water temperature for all monthly and seasonal values. In the mean annual air temperature the presence of the hiatus is not observed, but a negative trend is recorded in March (32 years), December (43 years) and February (49 years). The highest correlations between water temperature and North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Atlantic Multidecadal Oscillation (AMO) were obtained for the NAO in January (0.60), the AMO in autumn (0.52) and the NAO in winter (0.51). For surface air temperature, the highest correlations were registered for the AMO in summer (0.49) and the NAO in winter (0.42). The results indicate the dominant role of natural factors in the decrease of winter air temperature and water temperature of the Danube.
ER –

NR – 95
TY – JOUR
AU – Gettelman, A.
AU – Shindell, D. T.
AU – Lamarque, J. F.
PY – 2015
TI – Impact of aerosol radiative effects on 2000–2010 surface temperatures
JO – Climate Dynamics
SP – 2165
EP – 2179
VL – 45
IS – 7
AB – Aerosol radiative forcing from direct and indirect effects of aerosols is examined over the recent past (last 10–15 years) using updated sulfate aerosol emissions in two Earth System Models with very different surface temperature responses to aerosol forcing. The hypothesis is that aerosol forcing and in particular, the impact of indirect effects of aerosols on clouds (Aerosol–Cloud Interactions, or ACI), explains the recent ‘hiatus’ in global mean surface temperature increases. Sulfate aerosol emissions increase globally from 2000 to 2005, and then decrease slightly to 2010. Thus the change in anthropogenic sulfate induced net global radiative forcing is small over the period. Regionally, there are statistically significant forcings that are similar in both models, and consistent with changes in simulated emissions and aerosol optical depth. Coupled model simulations are performed to look at impacts of the forcing on recent surface temperatures. Temperature response patterns in the models are similar, and reflect the regional radiative forcing. Pattern correlations indicate significant correlations between observed decadal surface temperature changes and simulated surface temperature changes from recent sulfate aerosol forcing in an equilibrium framework. Sulfate ACI might be a contributor to the spatial patterns of recent temperature forcing, but not to the global mean ‘hiatus’ itself.
UR – https://doi.org/10.1007/s00382-014-2464-2
DO – 10.1007/s00382-014-2464-2
ER –

NR – 96
TY – JOUR
AU – Kuntz, L. B.
AU – Schrag, D. P.
C8 – 2016JD025430
TI – Impact of Asian aerosol forcing on tropical Pacific circulation and the relationship to global temperature trends
JO – Journal of Geophysical Research: Atmospheres
VL – 121
IS – 24
UR – http://dx.doi.org/10.1002/2016JD025430
DO – 10.1002/2016JD025430
SP – 14,403
EP – 14,413
PY – 2016
AB – The recent slowdown in the warming of global surface temperatures has been linked to the enhancement of trade winds in the central equatorial Pacific. The possible role of Asian aerosol emissions in forcing these wind anomalies is investigated through a series of idealized model simulations. Circulation patterns in response to localized negative radiative perturbations, indicative of aerosol effects, are investigated for both a slab and an active ocean models. The results suggest that Asian aerosols cannot explain the recent intensification of trade wind anomalies in the equatorial Pacific.
ER –

NR – 97
TY – JOUR
AU – Meehl, Gerald A.
AU – Hu, Aixue
AU – Teng, Haiyan
TI – Initialized decadal prediction for transition to positive phase of the Interdecadal Pacific Oscillation
JO – Nature Communications
PY – 2016
VL – 7
SP – 11718
UR – http://dx.doi.org/10.1038/ncomms11718
DO – 10.1038/ncomms11718
AB – The negative phase of the Interdecadal Pacific Oscillation (IPO), a dominant mode of multi-decadal variability of sea surface temperatures (SSTs) in the Pacific, contributed to the reduced rate of global surface temperature warming in the early 2000s. A proposed mechanism for IPO multidecadal variability indicates that the presence of decadal timescale upper ocean heat content in the off-equatorial western tropical Pacific can provide conditions for an interannual El Niño/Southern Oscillation event to trigger a transition of tropical Pacific SSTs to the opposite IPO phase. Here we show that a decadal prediction initialized in 2013 simulates predicted Niño3.4 SSTs that have qualitatively tracked the observations through 2015. The year three to seven average prediction (2015–2019) from the 2013 initial state shows a transition to the positive phase of the IPO from the previous negative phase and a resumption of larger rates of global warming over the 2013–2022 period consistent with a positive IPO phase.
ER –

NR – 98
TY – JOUR
T1 – Interhemispheric SST Gradient Trends in the Indian Ocean prior to and during the Recent Global Warming Hiatus
AU – Dong, Lu
AU – McPhaden, Michael J.
PY – 2016
DO – 10.1175/JCLI-D-16-0130.1
JF – Journal of Climate
SP – 9077
EP – 9095
VL – 29
IS – 24
AB – Sea surface temperatures (SSTs) have been rising for decades in the Indian Ocean in response to greenhouse gas forcing. However, this study shows that during the recent hiatus in global warming, a striking interhemispheric gradient in Indian Ocean SST trends developed around 2000, with relatively weak or little warming to the north of 10°S and accelerated warming to the south of 10°S. Evidence is presented from a wide variety of data sources showing that this interhemispheric gradient in SST trends is forced primarily by an increase of Indonesian Throughflow (ITF) transport from the Pacific into the Indian Ocean induced by stronger Pacific trade winds. This increased transport led to a depression of the thermocline that facilitated SST warming, presumably through a reduction in the vertical turbulent transport of heat in the southern Indian Ocean. Surface wind changes in the Indian Ocean linked to the enhanced Walker circulation also may have contributed to thermocline depth variations and associated SST changes, with downwelling- favorable wind stress curls between 10° and 20°S and upwelling-favorable wind stress curls between the equator and 10°S. In addition, the anomalous southwesterly wind stresses off the coast of Somalia favored intensified coastal upwelling and offshore advection of upwelled water, which would have led to reduced warming of the northern Indian Ocean. Although highly uncertain, lateral heat advection associated with the ITF and surface heat fluxes may also have played a role in forming the interhemispheric SST gradient change.
UR – https://doi.org/10.1175/JCLI-D-16-0130.1
ER –

NR – 99
TY – JOUR
AU – Outten, Stephen
AU – Thorne, Peter
AU – Bethke, Ingo
AU – Seland, Øyvind
TI – Investigating the recent apparent hiatus in surface temperature increases: 1. Construction of two 30-member Earth System Model ensembles
JO – Journal of Geophysical Research: Atmospheres
VL – 120
IS – 17
UR – http://dx.doi.org/10.1002/2015JD023859
DO – 10.1002/2015JD023859
SP – 8575
EP – 8596
PY – 2015
AB – The recent Intergovernmental Panel on Climate Change report, along with numerous studies since, has suggested that the apparent global warming hiatus results from some combination of natural variability and changes to external forcings. Herein the external forcings for greenhouse gases (GHGs), long-lived trace gases, volcanic and tropospheric aerosols, and solar irradiance have been replaced in the Norwegian Earth System Model using recent observational estimates. The potential impact of these alternative forcings, and by residual the internally generated variability, is examined through two 30-member ensembles covering the period 1980 to 2012. The Reference ensemble uses the Coupled Model Intercomparison Project phase 5 historical forcings extended with the Representative Concentration Pathway 8.5 (RCP8.5) scenario, while the Sensitivity ensemble uses the alternative forcings. Over the hiatus period defined herein as 1998–2012, all of the forcings show some change between the Sensitivity and Reference experiments and have a combined net forcing change of -0.03?W?m-2. The GHG forcing is 0.012?W?m-2 higher in the Sensitivity forcings. The alternative solar forcing differs from the Reference forcing by -0.08?W?m-2, the same as the alternative volcanic forcing that was based on the latest estimates from NASA Goddard Institute for Space Studies. Anthropogenic aerosol emissions were replaced using the EU-EclipseV4a data set and produce a mean forcing change of 0.11? W?m-2 over the period. Part 1 details the creation of the two 30-member ensembles and their characterization for parameters of particular relevance to the explanation of the hiatus. A detailed investigation of the two resulting ensembles global surface temperature behavior is given in Part 2, along with comparisons to observational data sets.
ER –

Papers on changes in Atlantic Meridional Overturning Circulation

This is a list of papers on changes in Atlantic Meridional Overturning Circulation. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Current Atlantic Meridional Overturning Circulation weakest in last millennium – Caesar et al. (2021). [FULL TEXT]
Abstract: The Atlantic Meridional Overturning Circulation (AMOC)—one of Earth’s major ocean circulation systems—redistributes heat on our planet and has a major impact on climate. Here, we compare a variety of published proxy records to reconstruct the evolution of the AMOC since about AD 400. A fairly consistent picture of the AMOC emerges: after a long and relatively stable period, there was an initial weakening starting in the nineteenth century, followed by a second, more rapid, decline in the mid-twentieth century, leading to the weakest state of the AMOC occurring in recent decades.
Citation: Caesar, L., McCarthy, G.D., Thornalley, D.J.R. et al. Current Atlantic Meridional Overturning Circulation weakest in last millennium. Nat. Geosci. 14, 118–120 (2021). https://doi.org/10.1038/s41561-021-00699-z.

A stable Atlantic Meridional Overturning Circulation in a changing North Atlantic Ocean since the 1990s – Fu et al. (2020). [FULL TEXT]
Abstract: The Atlantic Meridional Overturning Circulation (AMOC) is crucially important to global climate. Model simulations suggest that the AMOC may have been weakening over decades. However, existing array-based AMOC observations are not long enough to capture multidecadal changes. Here, we use repeated hydrographic sections in the subtropical and subpolar North Atlantic, combined with an inverse model constrained using satellite altimetry, to jointly analyze AMOC and hydrographic changes over the past three decades. We show that the AMOC state in the past decade is not distinctly different from that in the 1990s in the North Atlantic, with a remarkably stable partition of the subpolar overturning occurring prominently in the eastern basins rather than in the Labrador Sea. In contrast, profound hydrographic and oxygen changes, particularly in the subpolar North Atlantic, are observed over the same period, suggesting a much higher decoupling between the AMOC and ocean interior property fields than previously thought.
Citation: Yao Fu, Feili Li, Johannes Karstensen, Chunzai Wang (2020). Science Advances 6(48):eabc7836. DOI: 10.1126/sciadv.abc7836.

Atlantic Meridional Overturning Circulation: Observed Transport and Variability – Frajka-Williams et al. (2019). [FULL TEXT]
Abstract: The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and coastal sea level. AMOC observing approaches vary between the different systems, ranging from trans-basin arrays (OSNAP, RAPID 26°N, 11°S, SAMBA 34.5°S) to arrays concentrating on western boundaries (e.g., RAPID WAVE, MOVE 16°N). In this paper, we outline the different approaches (aims, strengths and limitations) and summarize the key results to date. We also discuss alternate approaches for capturing AMOC variability including direct estimates (e.g., using sea level, bottom pressure, and hydrography from autonomous profiling floats), indirect estimates applying budgetary approaches, state estimates or ocean reanalyses, and proxies. Based on the existing observations and their results, and the potential of new observational and formal synthesis approaches, we make suggestions as to how to evaluate a comprehensive, future-proof observational network of the AMOC to deepen our understanding of the AMOC and its role in global climate.
Citation: Frajka-Williams Eleanor, Ansorge Isabelle J., Baehr Johanna, Bryden Harry L., Chidichimo Maria Paz, et al. (2019). Frontiers in Marine Science 6:260. DOI=10.3389/fmars.2019.00260.

Stability of the Atlantic Meridional Overturning Circulation: A Review and Synthesis – Weijer et al. (2019). [FULL TEXT]
Abstract: The notion that the Atlantic Meridional Overturning Circulation (AMOC) can have more than one stable equilibrium emerged in the 1980s as a powerful hypothesis to explain rapid climate variability during the Pleistocene. Ever since, the idea that a temporary perturbation of the AMOC—or a permanent change in its forcing—could trigger an irreversible collapse has remained a reason for concern. Here we review literature on the equilibrium stability of the AMOC and present a synthesis that puts our understanding of past and future AMOC behavior in a unifying framework. This framework is based on concepts from Dynamical Systems Theory, which has proven to be an important tool in interpreting a wide range of model behavior. We conclude that it cannot be ruled out that the AMOC in our current climate is in, or close to, a regime of multiple equilibria. But there is considerable uncertainty in the location of stability thresholds with respect to our current climate state, so we have no credible indications of where our present-day AMOC is located with respect to thresholds. We conclude by identifying gaps in our knowledge and proposing possible ways forward to address these gaps.
Citation: Weijer, W., Cheng, W., Drijfhout, S. S., Federov, A.V., Hu, A., Jackson, L. C., et al. (2019). Stability of the Atlantic Meridional Overturning Circulation: A review and synthesis. Journal of Geophysical Research: Oceans, 124, 5336– 5375. https://doi.org/10.1029/2019JC015083.

Observed fingerprint of a weakening Atlantic Ocean overturning circulation – Caesar et al. (2018) [FULL TEXT]
Abstract: The Atlantic meridional overturning circulation (AMOC)—a system of ocean currents in the North Atlantic—has a major impact on climate, yet its evolution during the industrial era is poorly known owing to a lack of direct current measurements. Here we provide evidence for a weakening of the AMOC by about 3 ± 1 sverdrups (around 15 per cent) since the mid-twentieth century. This weakening is revealed by a characteristic spatial and seasonal sea-surface temperature ‘fingerprint’—consisting of a pattern of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region—and is calibrated through an ensemble of model simulations from the CMIP5 project. We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport, as well as an associated northward shift of the Gulf Stream. Comparisons with recent direct measurements from the RAPID project and several other studies provide a consistent depiction of record-low AMOC values in recent years.
Citation: L. Caesar, S. Rahmstorf, A. Robinson, G. Feulner & V. Saba (2018) Naturevolume 556, pages191–196. doi:10.1038/s41586-018-0006-5.

Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years – Thornalley et al. (2018) [FULL TEXT]
Abstract: The Atlantic meridional overturning circulation (AMOC) is a system of ocean currents that has an essential role in Earth’s climate, redistributing heat and influencing the carbon cycle1, 2. The AMOC has been shown to be weakening in recent years1; this decline may reflect decadal-scale variability in convection in the Labrador Sea, but short observational datasets preclude a longer-term perspective on the modern state and variability of Labrador Sea convection and the AMOC1, 3,4,5. Here we provide several lines of palaeo-oceanographic evidence that Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years. Our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the LIA, or as a more gradual, continued decline over the past 150 years; this ambiguity probably arises from non-AMOC influences on the various proxies or from the different sensitivities of these proxies to individual components of the AMOC. We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA—sourced from melting glaciers and thickened sea ice that developed earlier in the LIA—weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet6. Our results suggest that recent decadal variability in Labrador Sea convection and the AMOC has occurred during an atypical, weak background state. Future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the AMOC weakening described here.
Citation: David J. R. Thornalley, Delia W. Oppo, Pablo Ortega, Jon I. Robson, Chris M. Brierley, Renee Davis, Ian R. Hall, Paola Moffa-Sanchez, Neil L. Rose, Peter T. Spooner, Igor Yashayaev & Lloyd D. Keigwin (2018) Nature, volume 556, pages 227–230. doi:10.1038/s41586-018-0007-4.

Multi-centennial variability of the AMOC over the Holocene: A new reconstruction based on multiple proxy-derived SST records – Ayache et al. (2018)
Abstract: The Meridional Overturning Circulation (AMOC) is believed to have played a key role in climate variability over the Holocene, but the reconstruction of its variations remains limited by inconsistencies among different proxy records used. To circumvent this issue, we propose a new statistical method to reconstruct the AMOC variations based on multiple sources of information, i.e. 22 proxy records of annual Sea Surface Temperature (SST) compiled in the North Atlantic and covering the Holocene (HAMOC database). Our approach consists of isolating the main variability modes hidden in the Atlantic Ocean through principal component analysis (PCA) and then evaluating their link with the AMOC. To estimate the skill of our method, we use a pseudo-proxy approach applied to observational SST data covering the period 1870–2010, as well as simulations from a comprehensive climate model (IPSL-CM5A-LR) where the AMOC variations are known. In instrumental observations and most of the model simulations, the first mode of SST variations from the PCA analysis over the North Atlantic can be related with the external radiative forcing, while the second mode is reminiscent of the AMOC variability and of its signature on SST. When computed over the Holocene period using the HAMOC database, the first mode is indeed well correlated with the insolation changes, marked by a general cooling of the Northern Atlantic from 9 thousand years ago (ka). The second mode, that we consider here as a reconstruction of standardized AMOC variations following the pseudo-proxy analysis in the model simulations and in the observations, is in general agreement with a few independent reconstructions of the deep branch of the AMOC recorded in the North Atlantic. Based on this new AMOC index reconstruction, we highlight that the Early Holocene may have been associated with an AMOC enhancement, followed by a general weakening trend from around 6–7 ka up to 2 ka, in line with the major hydro-dynamical re-organization which occurred in the North Atlantic from the mid-Holocene period. We find that the late Holocene period is marked by two fluctuations, with maxima at about 4.2 and 5 ka, in line with short-term variations identified in proxy records of the velocity of the Greenland-Iceland-Scotland overflow waters..
Citation: Mohamed Ayache, Didier Swingedouw, Yannick Mary, Frédérique Eynaud, Christophe Colin (2018). Global and Planetary Change 170(November 2018):172-189. https://doi.org/10.1016/j.gloplacha.2018.08.016.

Timescales of AMOC decline in response to fresh water forcing – Jackson & Wood (2017)
Abstract: The Atlantic meridional overturning circulation (AMOC) is predicted to weaken over the coming century due to warming from greenhouse gases and increased input of fresh water into the North Atlantic, however there is considerable uncertainty as to the amount and rate of AMOC weakening. Understanding what controls the rate and timescale of AMOC weakening may help to reduce this uncertainty and hence reduce the uncertainty surrounding associated impacts. As a first step towards this we consider the timescales associated with weakening in response to idealized freshening scenarios. Here we explore timescales of AMOC weakening in response to a freshening of the North Atlantic in a suite of experiments with an eddy-permitting global climate model (GCM). When the rate of fresh water added to the North Atlantic is small (0.1 Sv; 1 Sv =1×106 m 3 /s), the timescale of AMOC weakening depends mainly on the rate of fresh water input itself and can be longer than a century. When the rate of fresh water added is large ( ≥ 0.3 Sv) however, the timescale is a few decades and is insensitive to the actual rate of fresh water input. This insensitivity is because with a greater rate of fresh water input the advective feedbacks become more important at exporting fresh anomalies, so the rate of freshening is similar. We find advective feedbacks from: an export of fresh anomalies by the mean flow; less volume import through the Bering Strait; a weakening AMOC transporting less subtropical water northwards; and anomalous subtropical circulations which amplify export of the fresh anomalies. This latter circulation change is driven itself by the presence of fresh anomalies exported from the subpolar gyre through geostrophy. This feedback has not been identified in previous model studies and when the rate of freshening is strong it is found to dominate the total export of fresh anomalies, and hence the timescale of AMOC decline. Although results may be model dependent, qualitatively similar mechanisms are also found in a single experiment with a different GCM.
Citation: Laura C. Jackson, Richard A. Wood (2017). Climate Dynamics, https://doi.org/10.1007/s00382-017-3957-6.

Arctic sea-ice decline weakens the Atlantic Meridional Overturning Circulation – Sévellec et al. (2017)
Abstract: The ongoing decline of Arctic sea ice exposes the ocean to anomalous surface heat and freshwater fluxes, resulting in positive buoyancy anomalies that can affect ocean circulation. In this study, we use an optimal flux perturbation framework and comprehensive climate model simulations to estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to such buoyancy forcing over the Arctic and globally, and more generally to sea-ice decline. It is found that on decadal timescales, flux anomalies over the subpolar North Atlantic have the largest impact on the AMOC, while on multi-decadal timescales (longer than 20 years), flux anomalies in the Arctic become more important. These positive buoyancy anomalies spread to the North Atlantic, weakening the AMOC and its poleward heat transport. Therefore, the Arctic sea-ice decline may explain the suggested slow-down of the AMOC and the ‘Warming Hole’ persisting in the subpolar North Atlantic.
Citation: Florian Sévellec, Alexey V. Fedorov & Wei Liu (2017) Nature Climate Change, volume 7, pages 604–610 (2017). doi:10.1038/nclimate3353.

Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting – Bakker et al. (2016) [FULL TEXT]
Abstract: The most recent Intergovernmental Panel on Climate Change assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis, and was limited to the 21st century. Here in a community effort, improved estimates of GrIS mass loss are included in multicentennial projections using eight state‐of‐the‐science climate models, and an AMOC emulator is used to provide a probabilistic uncertainty assessment. We find that GrIS melting affects AMOC projections, even though it is of secondary importance. By years 2090–2100, the AMOC weakens by 18% [−3%, −34%; 90% probability] in an intermediate greenhouse‐gas mitigation scenario and by 37% [−15%, −65%] under continued high emissions. Afterward, it stabilizes in the former but continues to decline in the latter to −74% [+4%, −100%] by 2290–2300, with a 44% likelihood of an AMOC collapse. This result suggests that an AMOC collapse can be avoided by CO2 mitigation.
Citation: Bakker, P., et al. (2016), Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting, Geophys. Res. Lett., 43, 12,252–12,260, doi:10.1002/2016GL070457.

Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation – Rahmstorf et al. (2015) [FULL TEXT]
Abstract: Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.
Citation: Stefan Rahmstorf, Jason E. Box, Georg Feulner, Michael E. Mann, Alexander Robinson, Scott Rutherford & Erik J. Schaffernicht (2015). Nature Climate Change volume 5, pages 475–480 (2015) doi:10.1038/nclimate2554.

Detecting changes in the transport of the Gulf Stream and the Atlantic overturning circulation from coastal sea level data: The extreme decline in 2009–2010 and estimated variations for 1935–2012 – Ezer (2015) [FULL TEXT]
Abstract: “Recent studies reported weakening in the Atlantic Meridional Overturning Circulation (AMOC) and in the Gulf Stream (GS), using records of about a decade (RAPID project) or two (altimeter data). Coastal sea level records are much longer, so the possibility of detecting climatic changes in ocean circulation from sea level data is intriguing and thus been examined here. First, it is shown that variations in the AMOC transport from the RAPID project since 2004 are consistent with the flow between Bermuda and the U. S. coast derived from the Oleander measurements and from sea level difference (SLDIF). Despite apparent disagreement between recent studies on the ability of data to detect weakening in the GS flow, estimated transport changes from 3 different independent data sources agree quite well with each other on the extreme decline in transport in 2009–2010. Due to eddies and meandering, the flow representing the GS part of the Oleander line is not correlated with AMOC or with the Florida Current, only the flow across the entire Oleander line from the U.S. coast to Bermuda is correlated with climatic transport changes. Second, Empirical Mode Decomposition (EMD) analysis shows that SLDIF can detect (with lag) the portion of the variations in the AMOC transport that are associated with the Florida Current and the wind-driven Ekman transport (SLDIF-transport correlations of ~ 0.7–0.9). The SLDIF has thus been used to estimate variations in transport since 1935 and compared with AMOC obtained from reanalysis data. The significant weakening in AMOC after ~ 2000 (~ 4.5 Sv per decade) is comparable to weakening seen in the 1960s to early 1970s. Both periods of weakening AMOC, in the 1960s and 2000s, are characterized by faster than normal sea level rise along the northeastern U.S. coast, so monitoring changes in AMOC has practical implications for coastal protection.”
Citation: Tal Ezer, Detecting changes in the transport of the Gulf Stream and the Atlantic overturning circulation from coastal sea level data: The extreme decline in 2009–2010 and estimated variations for 1935–2012, Global and Planetary Change, 129, June 2015, 23–36.

Impact of Greenland orography on the Atlantic Meridional Overturning Circulation – Davini et al. (2015)
Abstract: “We show that the absence of the Greenland ice sheet would have important consequences on the North Atlantic Ocean circulation, even without taking into account the effect of the freshwater input to the ocean from ice melting. These effects are investigated in a 600year long coupled ocean-atmosphere simulation with the high-resolution global climate model EC-Earth 3.0.1. Once a new equilibrium is established, a cooling of Eurasia and of the North Atlantic and a poleward shift of the subtropical jet are observed. These hemispheric changes are ascribed to a weakening of the Atlantic Meridional Overturning Circulation (AMOC) by about 12%. We attribute this slowdown to a reduction in salinity of the Arctic basin and to the related change of the mass and salt transport through the Fram Strait—a consequence of the new surface wind pattern over the lower orography. This idealized experiment illustrates the sensitivity of the AMOC to local surface winds.”
Citation: Davini, P., vonHardenberg, J., Filippi, L. and Provenzale, A. (2015), Impact of Greenland orography on the Atlantic Meridional Overturning Circulation. Geophys. Res. Lett., 42: 871–879. doi: 10.1002/2014GL062668.

Impact of a 30% reduction in Atlantic meridional overturning during 2009–2010 – Bryden et al. (2014) [FULL TEXT]
Abstract: “The Atlantic meridional overturning circulation comprises warm upper waters flowing northward, becoming colder and denser until they form deep water in the Labrador and Nordic Seas that then returns southward through the North and South Atlantic. The ocean heat transport associated with this circulation is 1.3 PW, accounting for 25% of the maximum combined atmosphere–ocean heat transport necessary to balance the Earth’s radiation budget. We have been monitoring the circulation at 25° N since 2004. A 30% slowdown in the circulation for 14 months during 2009–2010 reduced northward ocean heat transport across 25° N by 0.4 PW and resulted in colder upper ocean waters north of 25° N and warmer waters south of 25° N. The spatial pattern of upper ocean temperature anomalies helped push the wintertime circulation 2010–2011 into record-low negative NAO (North Atlantic Oscillation) conditions with accompanying severe winter conditions over northwestern Europe. The warmer temperatures south of 25° N contributed to the high intensity hurricane season in summer 2010.”
Citation: Bryden, H. L., King, B. A., McCarthy, G. D., and McDonagh, E. L.: Impact of a 30% reduction in Atlantic meridional overturning during 2009–2010, Ocean Sci., 10, 683-691, doi:10.5194/os-10-683-2014, 2014.

On the long-term stability of Gulf Stream transport based on 20 years of direct measurements – Rossby et al. (2014)
Abstract: “In contrast to recent claims of a Gulf Stream slowdown, two decades of directly measured velocity across the current show no evidence of a decrease. Using a well-constrained definition of Gulf Stream width, the linear least square fit yields a mean surface layer transport of 1.35 × 105 m² s⁻¹ with a 0.13% negative trend per year. Assuming geostrophy, this corresponds to a mean cross-stream sea level difference of 1.17 m, with sea level decreasing 0.03 m over the 20 year period. This is not significant at the 95% confidence level, and it is a factor of 2–4 less than that alleged from accelerated sea level rise along the U.S. Coast north of Cape Hatteras. Part of the disparity can be traced to the spatial complexity of altimetric sea level trends over the same period.”
Citation: Rossby, T., C. N. Flagg, K. Donohue, A. Sanchez-Franks, and J. Lillibridge (2014), On the long-term stability of Gulf Stream transport based on 20 years of direct measurements, Geophys. Res. Lett., 41, 114–120, doi:10.1002/2013GL058636.

Two Modes of Gulf Stream Variability Revealed in the Last Two Decades of Satellite Altimeter Data – Pérez-Hernández & Joyce (2014) [FULL TEXT]
Abstract: “Monthly mapped sea level anomalies (MSLAs) of the NW Atlantic in the region immediately downstream of the Gulf Stream (GS) separation point reveal a leading mode in which the path shifts approximately 100 km meridionally about a nominal latitude of 39°N, producing coherent sea level anomaly (SLA) variability from 72° to 50°W. This mode can be captured by use of a simple 16-point index based on SLA data taken along the maximum of the observed variability in the region 33°–46°N and 45°–75°W. The GS shifts between 2010 and 2012 are the largest of the last decade and equal to the largest of the entire record. The second group of EOF modes of variability describes GS meanders, which propagate mainly westward interrupted by brief periods of eastward or stationary meanders. These meanders have wavelengths of approximately 400 km and can be seen in standard EOFs by spatial phase shifting of a standing meander pattern in the SLA data. The spectral properties of these modes indicate strong variability at interannual and longer periods for the first mode and periods of a few to several months for the meanders. While the former is quite similar to a previous use of the altimeter for GS path, the simple index is a useful measure of the large-scale shifts in the GS path that is quickly estimated and updated without changes in previous estimates. The time-scale separation allows a low-pass filtered 16-point index to be reflective of large-scale, coherent shifts in the GS path.”
Citation: M. Dolores Pérez-Hernández and Terrence M. Joyce, 2014: Two Modes of Gulf Stream Variability Revealed in the Last Two Decades of Satellite Altimeter Data. J. Phys. Oceanogr., 44, 149–163. doi: http://dx.doi.org/10.1175/JPO-D-13-0136.1.

Probabilistic projections of the Atlantic overturning – Schleussner et al. (2014) [FULL TEXT]
Abstract: Changes in the Atlantic overturning circulation have a strong influence on European temperatures, North American sea level and other climate phenomena worldwide. A meaningful assessment of associated societal impacts needs to be based on the full range of its possible future evolution. This requires capturing both the uncertainty in future warming pathways and the inherently long-term response of the ocean circulation. While probabilistic projections of the global mean and regional temperatures exist, process-based probabilistic assessments of large-scale dynamical systems such as the Atlantic overturning are still missing. Here we present such an assessment and find that a reduction of more than 50 % in Atlantic overturning strength by the end of the 21 s t century is within the likely range under an unmitigated climate change scenario (RCP8.5). By combining linear response functions derived from comprehensive climate simulations with the full range of possible future warming pathways, we provide probability estimates of overturning changes by the year 2100. A weakening of more than 25 % is found to be very unlikely under a climate protection scenario (RCP2.6), but likely for unmitigated climate change. The method is able to reproduce the modelled recovery caused by climatic equilibration under climate protection scenarios which provides confidence in the approach. Within this century, a reduction of the Atlantic overturning is a robust climatic phenomena that intensifies with global warming and needs to be accounted for in global adaptation strategies.
Citation: Schleussner, CF., Levermann, A. & Meinshausen, M. Climatic Change (2014) 127: 579. https://doi.org/10.1007/s10584-014-1265-2.

Linear weakening of the AMOC in response to receding glacial ice sheets in CCSM3 – Zhu et al. (2014) [FULL TEXT]
Abstract: The transient response of the Atlantic Meridional Overturning Circulation (AMOC) to a deglacial ice sheet retreat is studied using the Community Climate System Model version 3 (CCSM3), with a focus on orographic effects rather than meltwater discharge. It is found that the AMOC weakens significantly (41%) in response to the deglacial ice sheet retreat. The AMOC weakening follows the decrease of the Northern Hemisphere ice sheet volume linearly, with no evidence of abrupt thresholds. A wind‐driven mechanism is proposed to explain the weakening of the AMOC: lowering the Northern Hemisphere ice sheets induces a northward shift of the westerlies, which causes a rapid eastward sea ice transport and expanded sea ice cover over the subpolar North Atlantic; this expanded sea ice insulates the ocean from heat loss and leads to suppressed deep convection and a weakened AMOC. A sea ice‐ocean positive feedback could be further established between the AMOC decrease and sea ice expansion.
Citation: Zhu, J., Z. Liu, X. Zhang, I. Eisenman, and W. Liu (2014), Linear weakening of the AMOC in response to receding glacial ice sheets in CCSM3, Geophys. Res. Lett., 41, 6252–6258, doi:10.1002/2014GL060891.

Atlantic Meridional Overturning Circulation (AMOC) in CMIP5 Models: RCP and Historical Simulations – Cheng et al. (2013) [FULL TEXT]
Abstract: The Atlantic meridional overturning circulation (AMOC) simulated by 10 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) for the historical (1850–2005) and future climate is examined. The historical simulations of the AMOC mean state are more closely matched to observations than those of phase 3 of the Coupled Model Intercomparison Project (CMIP3). Similarly to CMIP3, all models predict a weakening of the AMOC in the twenty-first century, though the degree of weakening varies considerably among the models. Under the representative concentration pathway 4.5 (RCP4.5) scenario, the weakening by year 2100 is 5%–40% of the individual model’s historical mean state; under RCP8.5, the weakening increases to 15%–60% over the same period. RCP4.5 leads to the stabilization of the AMOC in the second half of the twenty-first century and a slower (then weakening rate) but steady recovery thereafter, while RCP8.5 gives rise to a continuous weakening of the AMOC throughout the twenty-first century. In the CMIP5 historical simulations, all but one model exhibit a weak downward trend [ranging from −0.1 to −1.8 Sverdrup (Sv) century−1; 1 Sv ≡ 106 m3 s−1] over the twentieth century. Additionally, the multimodel ensemble–mean AMOC exhibits multidecadal variability with a ~60-yr periodicity and a peak-to-peak amplitude of ~1 Sv; all individual models project consistently onto this multidecadal mode. This multidecadal variability is significantly correlated with similar variations in the net surface shortwave radiative flux in the North Atlantic and with surface freshwater flux variations in the subpolar latitudes. Potential drivers for the twentieth-century multimodel AMOC variability, including external climate forcing and the North Atlantic Oscillation (NAO), and the implication of these results on the North Atlantic SST variability are discussed.
Citation: Cheng, W., J.C. Chiang, and D. Zhang, 2013: Atlantic Meridional Overturning Circulation (AMOC) in CMIP5 Models: RCP and Historical Simulations. J. Climate, 26, 7187–7197, https://doi.org/10.1175/JCLI-D-12-00496.1.

Past, Present, and Future Changes in the Atlantic Meridional Overturning Circulation – Srokosz et al. (2012) [FULL TEXT]
Abstract: “Observations and numerical modeling experiments provide evidence for links between variability in the Atlantic meridional overturning circulation (AMOC) and global climate patterns. Reduction in the strength of the overturning circulation is thought to have played a key role in rapid climate change in the past and may have the potential to significantly influence climate change in the future, as noted in the last two Intergovernmental Panel on Climate Change (IPCC) assessment reports (Houghton et al.; Solomon et al.). Both IPCC reports also highlighted the significant uncertainties that exist regarding the future behavior of the AMOC under global warming. Model results suggest that changes in the AMOC can impact surface air temperature, precipitation patterns, and sea level, particularly in areas bordering the North Atlantic, thus affecting human populations. Here, the current understanding of past, present, and future changes in the AMOC and the effects of such changes on climate are reviewed. The focus is on observations of the AMOC, how the AMOC influences climate, and in what way the AMOC is likely to change over the next few decades and the twenty-first century. The potential for decadal prediction of the AMOC is also discussed. Finally, the outstanding challenges and possible future directions for AMOC research are outlined.”
Citation: M. Srokosz, M. Baringer, H. Bryden, S. Cunningham, T. Delworth, S. Lozier, J. Marotzke, and R. Sutton, 2012: Past, Present, and Future Changes in the Atlantic Meridional Overturning Circulation. Bull. Amer. Meteor. Soc., 93, 1663–1676. doi: http://dx.doi.org/10.1175/BAMS-D-11-00151.1.

Surface changes in the North Atlantic meridional overturning circulation during the last millennium – Wanamaker et al. (2012) [FULL TEXT]
Abstract: “Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector.”
Citation: Wanamaker, A., Butler, P., Scourse, J. et al. Surface changes in the North Atlantic meridional overturning circulation during the last millennium. Nat Commun 3, 899 (2012). https://doi.org/10.1038/ncomms1901.

Northward intensification of anthropogenically forced changes in the Atlantic meridional overturning circulation (AMOC) – Zhang (2010) [FULL TEXT]
Abstract: Extensive modeling studies show that changes in the anthropogenic forcing due to increasing greenhouse gases might lead to a slowdown of the Atlantic meridional overturning circulation (AMOC) in the 21st century, but the AMOC weakening estimated in most previous modeling studies is in depth space. Using a coupled ocean atmosphere model (GFDL CM2.1), this paper shows that in density space, the anthropogenically forced AMOC changes over the 21st century are intensified at northern high latitudes (nearly twice of those at lower latitudes) due to changes in the North Atlantic Deep Water (NADW) formation. In contrast, anthropogenically forced AMOC changes are much smaller in depth space at the same northern high latitudes. Hence projecting AMOC changes in depth space would lead to a significant underestimation of AMOC changes associated with changes in the NADW formation. The result suggests that monitoring AMOC changes at northern high latitudes in density space might reveal much larger signals than those at lower latitudes. The simulated AMOC changes in density space under anthropogenic forcing can not be distinguished from that induced by natural AMOC variability for at least the first 20 years of the 21st century, although the signal can be detected over a much longer period.
Citation: Zhang, R. (2010), Northward intensification of anthropogenically forced changes in the Atlantic meridional overturning circulation (AMOC), Geophys. Res. Lett., 37, L24603, doi:10.1029/2010GL045054.

Response of the Atlantic meridional overturning circulation to increasing atmospheric CO2: Sensitivity to mean climate state – Weaver et al. (2007) [FULL TEXT]
Abstract: The dependence on the mean climate state of the response of the Atlantic meridional overturning circulation (AMOC) is investigated in 17 increasing greenhouse gas experiments with different initial conditions. The AMOC declines in all experiments by 15% to 31%, with typically the largest declines in those experiments with the strongest initial AMOC. In all cases, changes in surface heat fluxes, rather than changes in surface freshwater fluxes, are the dominant cause for the transient AMOC decrease. Surface freshwater fluxes actually switch from reducing the transient AMOC decrease, for low values of atmospheric CO2, to reinforcing the transient AMOC decrease, for higher values of atmospheric CO2. In addition, we find that due to changes in the strengths of feedbacks associated with water vapour and snow/sea ice, the climate sensitivity and transient climate response of the UVic model strongly depends on the mean climate state.
Citation: Bryden, H. L., King, B. A., McCarthy, G. D., and McDonagh, E. L.: Impact of a 30% reduction in Atlantic meridional overturning during 2009–2010, Ocean Sci., 10, 683-691, doi:10.5194/os-10-683-2014, 2014.

Quantifying the AMOC feedbacks during a 2×CO2 stabilization experiment with land-ice melting – Swingedouw et al. (2007) [FULL TEXT]
Abstract: The response of the Atlantic Meridional Overturning Circulation (AMOC) to an increase in atmospheric CO2 concentration is analyzed using the IPSL-CM4 coupled ocean–atmosphere model. Two simulations are integrated for 70 years with 1%/year increase in CO2 concentration until 2×CO2, and are then stabilized for further 430 years. The first simulation takes land-ice melting into account, via a simple parameterization, which results in a strong freshwater input of about 0.13 Sv at high latitudes in a warmer climate. During this scenario, the AMOC shuts down. A second simulation does not include this land-ice melting and herein, the AMOC recovers after 200 years. This behavior shows that this model is close to an AMOC shutdown threshold under global warming conditions, due to continuous input of land-ice melting. The analysis of the origin of density changes in the Northern Hemisphere convection sites allows an identification as to the origin of the changes in the AMOC. The processes that decrease the AMOC are the reduction of surface cooling due to the reduction in the air–sea temperature gradient as the atmosphere warms and the local freshening of convection sites that results from the increase in local freshwater forcing. Two processes also control the recovery of the AMOC: the northward advection of positive salinity anomalies from the tropics and the decrease in sea-ice transport through the Fram Strait toward the convection sites. The quantification of the AMOC related feedbacks shows that the salinity related processes contribute to a strong positive feedback, while feedback related to temperature processes is negative but remains small as there is a compensation between heat transport and surface heat flux in ocean–atmosphere coupled model. We conclude that in our model, AMOC feedbacks amplify land-ice melting perturbation by 2.5.
Citation: D. Swingedouw, P. Braconnot, P. Delecluse, E. Guilyardi, O. Marti (2007). Climate Dynamics, Volume 29, Issue 5, pp 521–534. DOI: https://doi.org/10.1007/s00382-007-0250-0.

Will Greenland melting halt the thermohaline circulation? – Jungclaus et al. (2006) [FULL TEXT]
Abstract: Climate projections for the 21st century indicate a gradual decrease of the Atlantic Meridional Overturning Circulation (AMOC). The weakening could be accelerated substantially by meltwater input from the Greenland Ice Sheet (GIS). Here we repeat recent experiments conducted for the Intergovernmental Panel of Climate Change, providing an idealized additional source of freshwater along Greenland’s coast. For conservative and high melting estimates, the AMOC reduction is 35% and 42%, respectively, compared to a weakening of 30% for the original A1B scenario. Even for the high meltwater estimate the AMOC recovers in the 22nd century. The impact of the additional fresh water is limited to further enhancing the static stability in the Irminger and Labrador Seas, whereas the backbone of the overturning is maintained by the overflows across the Greenland‐Scotland Ridge. Our results suggest that abrupt climate change initiated by GIS melting is not a realistic scenario for the 21st century.
Citation: Jungclaus, J. H., H. Haak, M. Esch, E. Roeckner, and J. Marotzke (2006), Will Greenland melting halt the thermohaline circulation? Geophys. Res. Lett., 33, L17708, doi:10.1029/2006GL026815.

Papers on the warming hole of the United States

This is a list of papers on the warming hole of the United States. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

The United States “warming hole”: quantifying the forced aerosol response given large internal variability (Banerjee et al. 2017)
Abstract: “Twenty-five years of large summer cooling over the southeastern United States ending in the mid-1970s coincided with rapidly increasing anthropogenic aerosol emissions. Here, we assess the claim that the cooling in that period was predominantly due to such aerosols. We utilize two 50-member sets of coupled climate model simulations, one with only anthropogenic aerosol forcings and another with all known natural and anthropogenic forcings, together with a long control integration. We show that, in the absence of aerosol forcing, none of the model simulations capture the observed surface cooling rate (∼0.56∘C decade⁻¹), whereas with increasing aerosol emissions two (of fifty) of the simulations do. More importantly, however, we find that the cooling from aerosols (0.20° C decade−1) is insufficient to explain the observation. Our results therefore suggest that, while aerosols may have played a role, the observed cooling was a rare event that contained a large contribution from unforced internal variability.”
Citation: Banerjee A., L.M Polvani, and J.C. Fyfe (2017), The United States “warming hole’: quantifying the forced aerosol response given large internal variability, Geophys. Res. Lett., 44, doi:10.1002/2016GL071567.

Tracking regional temperature projections from the early 1990s in light of variations in regional warming, including ‘warming holes’ (Grose et al. 2017)
Abstract: “The perception of the accuracy of regional climate projections made in the early 1990s about climate change by 2030 may be influenced by how the temperature trend has changed in the 25 years since their publication. However, temperature trends over this period were influenced not only by external forcings such as greenhouse gases but also natural variations. The temperature of Southern Australia, the Sahel, South Asia and Southern Europe are currently within the warming estimates from statements in the early 1990s from the IPCC and CSIRO, assuming a linear trend between 1990 and 2030. However, northern Australia and central North America are currently at the lower limit or below these projections, having featured areas of multi-year regional cooling during global warming, sometimes called ‘warming holes’. Recent climate model simulations suggest that cooling can be expected in the recent past and near future in some regions, including in Australia and the US, and that cooling is less likely over 1990–2030 than in 1990–2015, bringing observations closer to the IPCC and CSIRO warming estimates by 2030. Cooling at the 25-year scale in some regions can be associated with cyclic variability such as the Inter-decadal Pacific Oscillation, or low trend such as in the Southern Ocean. Explicitly communicating the variability in regional warming rates in climate projections, including the possibility of regional warming ‘holes’ (or the opposite of ‘surges’ or ‘peaks’) would help to set more reliable expectations by users of those projections.”
Citation: Grose, M.R., Risbey, J.S. & Whetton, P.H. Climatic Change (2017) 140: 307. doi:10.1007/s10584-016-1840-9.

North Pacific SST Forcing on the Central United States “Warming Hole” as Simulated in CMIP5 Coupled Historical and Uncoupled AMIP Experiments (Pan et al. 2017)
Abstract: “The central United States experienced a cooling trend during the twentieth century, called the “warming hole,” most notably in the last quarter of the century when global warming accelerated. The coupled simulations of the models that participated in the Coupled Model Intercomparison Project, Phases 3 and 5 (CMIP3/5), have been unable to reproduce this abnormal cooling phenomenon satisfactorily. An unrealistic representation of the observed phasing of the Pacific Decadal Oscillation (PDO)—one of the proposed forcing mechanisms for the warming hole—in the models is considered to be one of the main causes of this effect. The CMIP5’s uncoupled Atmospheric Model Intercomparison Project (AMIP) experiment, whose duration approximately coincides with the peak warming hole cooling period, provides an opportunity, when compared with the coupled historical experiment, to examine the role of the variation in Pacific Ocean sea surface temperature (SST) in the warming hole’s formation and also to assess the skill of the models in simulating the teleconnection between Pacific SST and the continental climate in North America. Accordingly, this study compared AMIP and historical runs in the CMIP5 suite thereby isolating the role of SST forcing in the formation of the warming hole and its maintenance mechanisms. It was found that, even when SST forcing in the AMIP run was “perfectly” prescribed in the models, the skill of the models in simulating the warming hole cooling in the central United States showed little improvement over the historical run, in which SST is calculated interactively, even though the AMIP run overestimated the anti-correlation between temperature in the central United States and the PDO index. The fact that better simulation of the PDO phasing in the AMIP run did not translate into an improved summer cooling trend in the central United States suggests that the inability of the coupled CMIP5 models to reproduce the warming hole under the historical run is not mainly a result of the mismatch between simulated and observed PDO phasing, as believed.”
Citation: Zaitao Pan, Chunhua Shi, Sanjiv Kumar, and Zhiqiu Gao (2017) Atmosphere-Ocean, doi: 10.1080/07055900.2016.1261690.

Disappearance of the southeast U.S. “warming hole” with the late 1990s transition of the Interdecadal Pacific Oscillation (Meehl et al. 2015) [FULL TEXT]
Abstract: “Observed surface air temperatures over the contiguous U.S. for the second half of the twentieth century showed a slight cooling over the southeastern part of the country, the so-called “warming hole,” while temperatures over the rest of the country warmed. This pattern reversed after 2000. Climate model simulations show that the disappearance of the warming hole in the early 2000s is likely associated with the transition of the Interdecadal Pacific Oscillation (IPO) phase from positive to negative in the tropical Pacific in the late 1990s, coincident with the early 2000s slowdown of the warming trend in globally averaged surface air temperature. Analysis of a specified convective heating anomaly sensitivity experiment in an atmosphere-only model traces the disappearance of the warming hole to negative sea surface temperature anomalies and consequent negative precipitation and convective heating anomalies in the central equatorial Pacific Ocean associated with the negative phase of the IPO after 2000.”
Citation: Meehl, G. A., J. M. Arblaster, and C. T. Y. Chung (2015), Disappearance of the southeast U.S. “warming hole” with the late 1990s transition of the Interdecadal Pacific Oscillation, Geophys. Res. Lett., 42, 5564–5570, doi:10.1002/2015GL064586.

Sedimentary proxy evidence of a mid-Holocene hypsithermal event in the location of a current warming hole, North Carolina, USA (Tanner et al. 2015) [FULL TEXT]
Abstract: “A wetland deposit from the southern Appalachian mountains of North Carolina, USA, has been radiocarbon dated and shows continuous deposition from the early Holocene to the present. Non-coastal records of Holocene paleoenvironments are rare from the southeastern USA. Increased stable carbon isotope ratios (δ13C) of sedimentary organic matter and pollen percentages indicate warm, dry early- to mid-Holocene conditions. This interpretation is also supported by n-alkane biomarker data and bulk sedimentary C/N ratios. These warm, dry conditions coincide with a mid-Holocene hypsithermal, or altithermal, documented elsewhere in North America. Our data indicate that the southeastern USA warmed concurrently with much of the rest of the continent during the mid-Holocene. If the current “warming hole” in the southeastern USA persists, during a time of greenhouse gas-induced warming elsewhere, it will be anomalous both in space and time.”
Citation: Benjamin R. Tanner, Chad S. Lane, Elizabeth M. Martin, Robert Young, Beverly Collins (2015) Quaternary Research, Volume 83, Issue 2, March 2015, Pages 315–323, doi: 10.1016/j.yqres.2014.11.004.

Attribution of the United States “warming hole”: Aerosol indirect effect and precipitable water vapor (Yu et al. 2014) [FULL TEXT]
Abstract: “Aerosols can influence the climate indirectly by acting as cloud condensation nuclei and/or ice nuclei, thereby modifying cloud optical properties. In contrast to the widespread global warming, the central and south central United States display a noteworthy overall cooling trend during the 20th century, with an especially striking cooling trend in summertime daily maximum temperature (Tmax) (termed the U.S. “warming hole”). Here we used observations of temperature, shortwave cloud forcing (SWCF), longwave cloud forcing (LWCF), aerosol optical depth and precipitable water vapor as well as global coupled climate models to explore the attribution of the “warming hole”. We find that the observed cooling trend in summer Tmax can be attributed mainly to SWCF due to aerosols with offset from the greenhouse effect of precipitable water vapor. A global coupled climate model reveals that the observed “warming hole” can be produced only when the aerosol fields are simulated with a reasonable degree of accuracy as this is necessary for accurate simulation of SWCF over the region. These results provide compelling evidence of the role of the aerosol indirect effect in cooling regional climate on the Earth. Our results reaffirm that LWCF can warm both winter Tmax and Tmin.”
Citation: Shaocai Yu, Kiran Alapaty, Rohit Mathur, Jonathan Pleim, Yuanhang Zhang, Chris Nolte, Brian Eder, Kristen Foley & Tatsuya Nagashima (2014), Scientific Reports, 4, doi:10.1038/srep06929.

Multidecadal Climate Variability and the “Warming Hole” in North America: Results from CMIP5 Twentieth- and Twenty-First-Century Climate Simulations (Kumar et al. 2013) [FULL TEXT]
Abstract: “The ability of phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models to simulate the twentieth-century “warming hole” over North America is explored, along with the warming hole’s relationship with natural climate variability. Twenty-first-century warming hole projections are also examined for two future emission scenarios, the 8.5 and 4.5 W m−2 representative concentration pathways (RCP8.5 and RCP4.5). Simulations from 22 CMIP5 climate models were analyzed, including all their ensemble members, for a total of 192 climate realizations. A nonparametric trend detection method was employed, and an alternative perspective emphasizing trend variability. Observations show multidecadal variability in the sign and magnitude of the trend, where the twentieth-century temperature trend over the eastern United States appears to be associated with low-frequency (multidecadal) variability in the North Atlantic temperatures. Most CMIP5 climate models simulate significantly lower “relative power” in the North Atlantic multidecadal oscillations than observed. Models that have relatively higher skill in simulating the North Atlantic multidecadal oscillation also are more likely to reproduce the warming hole. It was also found that the trend variability envelope simulated by multiple CMIP5 climate models brackets the observed warming hole. Based on the multimodel analysis, it is found that in the twenty-first-century climate simulations the presence or absence of the warming hole depends on future emission scenarios; the RCP8.5 scenario indicates a disappearance of the warming hole, whereas the RCP4.5 scenario shows some chance (10%–20%) of the warming hole’s reappearance in the latter half of the twenty-first century, consistent with CO2 stabilization.”
Citation: Sanjiv Kumar, James Kinter, Paul A. Dirmeyer, Zaitao Pan, Jennifer Adams (2013), Journal of Climate, 26, 11, 3511-3527, doi: 10.1175/JCLI-D-12-00535.1.

Intermodel Variability and Mechanism Attribution of Central and Southeastern U.S. Anomalous Cooling in the Twentieth Century as Simulated by CMIP5 Models (Pan et al. 2013) [FULL TEXT]
Abstract: “Some parts of the United States, especially the southeastern and central portion, cooled by up to 2°C during the twentieth century, while the global mean temperature rose by 0.6°C (0.76°C from 1901 to 2006). Studies have suggested that the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) may be responsible for this cooling, termed the “warming hole” (WH), while other works reported that regional-scale processes such as the low-level jet and evapotranspiration contribute to the abnormity. In phase 3 of the Coupled Model Intercomparison Project (CMIP3), only a few of the 53 simulations could reproduce the cooling. This study analyzes newly available simulations in experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5) from 28 models, totaling 175 ensemble members. It was found that 1) only 19 out of 100 all-forcing historical ensemble members simulated negative temperature trend (cooling) over the southeast United States, with 99 members underpredicting the cooling rate in the region; 2) the missing of cooling in the models is likely due to the poor performance in simulating the spatial pattern of the cooling rather than the temporal variation, as indicated by a larger temporal correlation coefficient than spatial one between the observation and simulations; 3) the simulations with greenhouse gas (GHG) forcing only produced strong warming in the central United States that may have compensated the cooling; and 4) the all-forcing historical experiment compared with the natural-forcing-only experiment showed a well-defined WH in the central United States, suggesting that land surface processes, among others, could have contributed to the cooling in the twentieth century.”
Citation: Zaitao Pan, Xiaodong Liu, Sanjiv Kumar, Zhiqiu Gao, James Kinter (2013) Journal of Climate, 26, 17, 6215-6237, doi: 10.1175/JCLI-D-12-00559.1.

Mechanisms Contributing to the Warming Hole and the Consequent U.S. East–West Differential of Heat Extremes (Meehl et al. 2012) [FULL TEXT]
Abstract: “A linear trend calculated for observed annual mean surface air temperatures over the United States for the second-half of the twentieth century shows a slight cooling over the southeastern part of the country, the so-called warming hole, while temperatures over the rest of the country rose significantly. This east–west gradient of average temperature change has contributed to the observed pattern of changes of record temperatures as given by the ratio of daily record high temperatures to record low temperatures with a comparable east–west gradient. Ensemble averages of twentieth-century climate simulations in the Community Climate System Model, version 3 (CCSM3), show a slight west–east warming gradient but no warming hole. A warming hole appears in only several ensemble members in the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset and in one ensemble member of simulated twentieth-century climate in CCSM3. In this model the warming hole is produced mostly from internal decadal time-scale variability originating mainly from the equatorial central Pacific associated with the Interdecadal Pacific Oscillation (IPO). Analyses of a long control run of the coupled model, and specified convective heating anomaly experiments in the atmosphere-only version of the model, trace the forcing of the warming hole to positive convective heating anomalies in the central equatorial Pacific Ocean near the date line. Cold-air advection into the southeastern United States in winter, and low-level moisture convergence in that region in summer, contribute most to the warming hole in those seasons. Projections show a disappearance of the warming hole, but ongoing greater surface temperature increases in the western United States compared to the eastern United States.”
Citation: Gerald A. Meehl, Julie M. Arblaster, Grant Branstator (2012) Journal of Climate, 25, 18, 6394-6408, doi: 10.1175/JCLI-D-11-00655.1.

Can CGCMs Simulate the Twentieth-Century “Warming Hole” in the Central United States? (Kunkel et al. 2006) [FULL TEXT]
Abstract: “The observed lack of twentieth-century warming in the central United States (CUS), denoted here as the “warming hole,” was examined in 55 simulations driven by external historical forcings and in 19 preindustrial control (unforced) simulations from 18 coupled general circulation models (CGCMs). Twentieth-century CUS trends were positive for the great majority of simulations, but were negative, as observed, for seven simulations. Only a few simulations exhibited the observed rapid rate of warming (cooling) during 1901–40 (1940–79). Those models with multiple runs (identical forcing but different initial conditions) showed considerable intramodel variability with trends varying by up to 1.8°C century−1, suggesting that internal dynamic variability played a major role at the regional scale. The wide range of trend outcomes, particularly for those models with multiple runs, and the small number of simulations similar to observations in both the forced and unforced experiments suggest that the warming hole is not a robust response of contemporary CGCMs to the estimated external forcings. A more likely explanation based on these models is that the observed warming hole involves external forcings combined with internal dynamic variability that is much larger than typically simulated. The observed CUS temperature variations are positively correlated with North Atlantic (NA) sea surface temperatures (SSTs), and both NA SSTs and CUS temperature are negatively correlated with central equatorial Pacific (CEP) SSTs. Most models simulate rather well the connection between CUS temperature and NA SSTs. However, the teleconnections between NA and CEP SSTS and between CEP SSTs and CUS temperature are poorly simulated and the models produce substantially less NA SST variability than observed, perhaps hampering their ability to reproduce the warming hole.”
Citation: Kenneth E. Kunkel, Xin-Zhong Liang, Jinhong Zhu, and Yiruo Lin (2006) Journal of Climate, 19, 17, 4137-4153, doi: 10.1175/JCLI3848.1.

Altered hydrologic feedback in a warming climate introduces a “warming hole” (Pan et al. 2004) [FULL TEXT]
Abstract: “In the last 25 years of the 20th century most major land regions experienced a summer warming trend, but the central U.S. cooled by 0.2–0.8 K. In contrast most climate projections using GCMs show warming for all continental interiors including North America. We examined this discrepancy by using a regional climate model and found a circulation-precipitation coupling under enhanced greenhouse gas concentrations that occurs on scales too small for current GCMs to resolve well. Results show a local minimum of warming in the central U.S. (a “warming hole”) associated with changes in low-level circulations that lead to replenishment of seasonally depleted soil moisture, thereby increasing late-summer evapotranspiration and suppressing daytime maximum temperatures. These regional-scale feedback processes may partly explain the observed late 20th century temperature trend in the central U.S. and potentially could reduce the magnitude of future greenhouse warming in the region.”
Citation: Pan, Z., R. W. Arritt, E. S. Takle, W. J. Gutowski Jr., C. J. Anderson, and M. Segal (2004), Altered hydrologic feedback in a warming climate introduces a “warming hole”, Geophys. Res. Lett., 31, L17109, doi:10.1029/2004GL020528.

General circulation model simulations of recent cooling in the east-central United States (Robinson et al. 2002) [FULL TEXT]
Abstract: “In ensembles of retrospective general circulation model (GCM) simulations, surface temperatures in the east-central United States cool between 1951 and 1997. This cooling, which is broadly consistent with observed surface temperatures, is present in GCM experiments driven by observed time varying sea-surface temperatures (SSTs) in the tropical Pacific, whether or not increasing greenhouse gases and other time varying climate forcings are included. Here we focus on ensembles with fixed radiative forcing and with observed varying SST in different regions. In these experiments the trend and variability in east-central U.S. surface temperatures are tied to tropical Pacific SSTs. Warm tropical Pacific SSTs cool U.S. temperatures by diminishing solar heating through an increase in cloud cover. These associations are embedded within a year-round response to warm tropical Pacific SST that features tropospheric warming throughout the tropics and regions of tropospheric cooling in midlatitudes. Precipitable water vapor over the Gulf of Mexico and the Caribbean and the tropospheric thermal gradient across the Gulf Coast of the United States increase when the tropical Pacific is warm. In observations, recent warming in the tropical Pacific is also associated with increased precipitable water over the southeast United States. The observed cooling in the east-central United States, relative to the rest of the globe, is accompanied by increased cloud cover, though year-to-year variations in cloud cover, U.S. surface temperatures, and tropical Pacific SST are less tightly coupled in observations than in the GCM.”
Citation: Robinson, W. A., R. Reudy, and J. E. Hansen, General circulation model simulations of recent cooling in the east-central United States, J. Geophys. Res., 107(D24), 4748, doi:10.1029/2001JD001577, 2002.

Global warming hiatus claims prebunked in 1980s and 1990s

Recent global warming hiatus has been a subject of intensive studies during the last ten years. But it seems that there already was some research on global warming hiatus during 1980s and 1990s (earliest studies on the issue were actually back in 1940s-1970s). This seems to have gone largely unnoticed in the scientific literature of current global warming hiatus, and it certainly seems to have gone unnoticed by climate mitigation opponents who have made claims on global warming hiatus since at least 2006 and still continue to do so.

Some time ago I stumbled on a few old papers which discussed the temperature evolution of 1940s to 1970s. In the early 20th century there had been warming which seemed to have stopped around 1940 until it continued again in the turn of 1970s and 1980s. Here I will use “global warming moratorium” to describe this early hiatus (reason for this can be found below). Below I’ll go through some of the papers in question.

Early studies on the 1940s-1970s global warming moratorium

Global surface temperature increased during the first half of the 20th century. In 1940s, this warming apparently stopped. Possibly the first to notice this was Kincer (1946):

Up to the end of 1945, records for 13 subsequent years have become available, and these are here presented, supplementary to the original data, to determine tendencies since 1932. They show that the general upward temperature trend continued for several years but that the more recent records indicate a leveling off, and even contain currently a suggestion of an impending reversal.

This was confirmed by Mitchell (1961, 1963), as described by Wigley et al. (1985):

Mitchell (1961, 1963) extended Willett’s analysis beyond 1940, improved the method of area averaging, and found that the warming prior to 1940 had subsequently become a cooling trend (as suggested earlier by Kincer [1946]).

Later, Mitchell (1970) studied the effect of anthropogenic forcings (carbon dioxide and aerosols) on the temperature evolution of 20th century. Mitchell noted on the carbon dioxide forcing:

Changes of mean atmospheric temperature due to CO2, calculated by Manabe et al. as 0.3°C per 10% change in CO2, are sufficient to account for only about one third of the observed 0.6°C warming of the earth between 1880 and 1940, but will probably have become a dominant influence on the course of planetary average temperature changes by the end of this century.

And on the global warming moratorium:

Although changes of total atmospheric dust loading may possibly be sufficient to account for the observed 0.3°C-cooling of the earth since 1940, the human-derived contribution to these loading changes is inferred to have played a very minor role in the temperature decline.

Reitan (1974) extended the temperature analysis to 1968 and reported that the global warming moratorium had continued. Brinkmann (1976) extended the analysis to 1973 and saw the first signs of global warming moratorium ending and warming resuming.

Wigley et al. (1985) mention one further point worth mentioning about the global warming moratorium:

All seasons show the same long-term trends, trends that are also common to all other land-based data sets: a warming from the 1880s to around 1940, cooling to the mid-1960s/early-1970s (less obvious in winter), and subsequent warming, beginning later in summer and autumn than in spring and winter.

According to Wigley et al. (1985), the global warming moratorium remained largely unexplained, although there had been some relatively successful attempts to explain the short-term variability in the surface temperature by volcanic aerosols and solar variations, see for example the discussion and analysis in Hansen et al. (1981) and in Gilliland (1982).

Oceans and surface temperature studies in 1980s

Watts (1985) used a simple model to suggest that changes in the rate of the deep water formation can have an effect to surface temperature:

…variations in the rate of formation of deep water can lead to fluctuations in the globally averaged surface temperature similar in magnitude to variations in the earth’s surface-air temperature that have occurred during the last several hundred years.

Gaffin et al. (1986) got similar results:

The largest features of the northern hemispheric surface land temperature record can be simulated with our climate and deep ocean feedback formulation and CO₂ forcing alone.

Jones et al. (1987) studied the rapidity of carbon dioxide induced climate change. Within this study, they also looked at how changes in deep water formation affected warming caused by carbon dioxide. They created a simulation, where there was a global warming caused by carbon dioxide, and then they turned off the deep water formation in the Northern Hemisphere (because the global warming moratorium was strongest in Northern Hemisphere). This resulted in surface cooling right after the deep water formation was stopped, and later warming continued again.

In the late 1980s and early 1990s there were some other similar studies also.

The global warming moratorium discussion of early 1990s

So, it seems that at the turn of 1980s and 1990s there had been several studies suggesting that oceans could have considerable effect on the surface temperature. At this point, there was a discussion in the scientific literature on the global warming moratorium, and this discussion has some interesting resemblance to the current global warming hiatus discussion.

Watts and Morantine (1991), in an editorial of Springer’s journal Climatic Change, reviewed the research which I already have discussed above. They noted the possibility of energy transfer between the surface and the deep ocean and concluded:

It is entirely possible that the greenhouse gas climate change signal is alive and well and hiding in the ocean intermediate waters, having reached there because of increased upwelling, or by some other mechanism that could effectively transport heat from the upper layers of the ocean into the huge thermal reservoir of the intermediate and deep ocean.

Kellogg (1993) revisited the issue, also in the same journal, with a letter named as “An Apparent Moratorium on the Greenhouse Warming Due to the Deep Ocean”. Kellogg described some new observational evidence for the ocean’s role in the issue. Based on this he suggested:

…oceans could sequester a significant part of the incremental greenhouse-generated heat over a period of a few decades, a period during which the surface warming would be curtailed.

Kellogg also discussed some issues relating to timing of the global warming moratorium and what would have happened if oceans wouldn’t have had a role in the surface temperature. Relating to the current global warming hiatus discussion, Kellogg made an interesting note:

One of the arguments most frequently advanced by the skeptics is that the observed warming in this century should have been larger, based on climate models that do not take account of ocean circulations, and that there should theoretically have been no such ‘moratorium’ between 1940 and 1975.

Kellogg then notes that if the oceans played a role, there wouldn’t be such a problem.

Watts and Morantine (1993) also revisited the issue (perhaps the journal sent them Kellogg’s letter and asked for their response). There were couple of additional interesting points in their response relating to current discussion on global warming hiatus. They noted on the significance of the moratorium:

In a recent article by Galbraith and Green (1992), a series of statistical tests were performed on the global average temperature time series from 1880 to 1988 (Hansen and Lebedeff, 1987). A statistically significant trend that can be approximated by a linear term was found, and the deviation from this trend during the period between 1940 and 1970 was found to fall within the range of sample fluctuation.

And:

Even though the surface temperature of the Earth is an important piece of information, the distribution of thermal energy is a three-dimensional problem.

What I have shown here is just a sample of all papers that were studying the issue. The research on the issue also continued after the papers presented here.

The significance for current hiatus discussion

It is clear that before 2000s there had been lot of research on the subject of short-term variability of surface temperature in a presence of long-term warming trend. The research back then also pointed to probable causes of the short-term variability.

Apparently, the first claims of global warming hiatus after 1998 were made in 2006 by well-known climate change mitigation opponents. This was obviously far too soon statistically to make those claims, and there was no indication that the claims were made with knowledge of the earlier discussion and research on the subject. It also should be noted, that the claims in question were not made in scientific literature but in popular media (a situation that has continued after that and largely continues even today).

However, lots and lots of papers have been published on the recent global warming hiatus. I have sampled the reference lists of some of them and it seems that also scientific community has largely forgot that the issue has already been studied. This seems a bit unfortunate and makes one wonder if we will have forgotten the current research when the next moratorium or pause or hiatus or whatever happens.

References:

Waltraud A.R. Brinkmann (1976), Surface temperature trend for the Northern Hemisphere-updated, Quaternary Research, Volume 6, Issue 3, September 1976, Pages 355-358, doi:10.1016/0033-5894(67)90002-6.
http://www.sciencedirect.com/science/article/pii/0033589467900026

Gaffin, S. R., M. I. Hoffert, and T. Volk (1986), Nonlinear coupling between surface temperature and ocean upwelling as an agent in historical climate variations, J. Geophys. Res., 91(C3), 3944–3950, doi:10.1029/JC091iC03p03944.
http://onlinelibrary.wiley.com/doi/10.1029/JC091iC03p03944/full

Gilliland, R.L. (1982), Solar, volcanic, and CO2 forcing of recent climatic changes, Climatic Change, 4: 111. doi:10.1007/BF00140585.
http://rd.springer.com/article/10.1007/BF00140585

J. Hansen, D. Johnson, A. Lacis, S. Lebedeff, P. Lee, D. Rind, G. Russell (1981) Climate Impact of Increasing Atmospheric Carbon Dioxide, Science 28 Aug 1981: Vol. 213, Issue 4511, pp. 957-966, DOI: 10.1126/science.213.4511.957.
http://science.sciencemag.org/content/213/4511/957

Click to access hansen81sci.pdf

P. D. Jones, T. M. L. Wigley, , S. C. B. Raper (1986), The Rapidity of CO2-Induced Climatic Change: Observations, Model Results and Palaeoclimatic Implications, in Abrupt Climatic Change, Volume 216 of the series NATO ASI Series pp 47-55.
http://rd.springer.com/chapter/10.1007/978-94-009-3993-6_4

Kellogg, W.W. (1993), An apparent moratorium on the greenhouse warming due to the deep ocean, Climatic Change 25: 85. doi:10.1007/BF01094085.
http://rd.springer.com/article/10.1007%2FBF01094085

Kincer, J. B. (1946), Our changing climate, Eos Trans. AGU, 27(3), 342–347, doi:10.1029/TR027i003p00342.
http://onlinelibrary.wiley.com/doi/10.1029/TR027i003p00342/abstract

Mitchell, J. M. (1961), RECENT SECULAR CHANGES OF GLOBAL TEMPERATURE. Annals of the New York Academy of Sciences, 95: 235–250. doi:10.1111/j.1749-6632.1961.tb50036.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.1961.tb50036.x/abstract

J. Murray Mitchell Jr. (1970), A Preliminary Evaluation of Atmospheric Pollution as a Cause of the Global Temperature Fluctuation of the Past Century, 139-155. In, S.F. Singer (ed.), Global Effects of Environmental Pollution. Springer Verlag, New York, New York.
http://rd.springer.com/chapter/10.1007/978-94-010-3290-2_15

Clayton H. Reitan (1974), A climatic model of solar radiation and temperature change, Quaternary Research, Volume 4, Issue 1, March 1974, Pages 25–38, http://dx.doi.org/10.1016/0033-5894(74)90061-1.
http://www.sciencedirect.com/science/article/pii/0033589474900611

Watts, R. G. (1985), Global climate variation due to fluctuations in the rate of deep water formation, J. Geophys. Res., 90(D5), 8067–8070, doi:10.1029/JD090iD05p08067.
http://onlinelibrary.wiley.com/doi/10.1029/JD090iD05p08067/full

Watts, R.G. & Morantine, M.C. (1991), Is the greenhouse gas-climate signal hiding in the deep ocean?, Climatic Change 18: iii. doi:10.1007/BF00142966.
http://rd.springer.com/article/10.1007%2FBF00142966

Wigley, T.M.L., Angell, J.K. and Jones, P.D., 1985. Analysis of the temperature record. In: M.C. MacCracken and F.M. Luther (Eds.), Detecting the Climatic Effects of Increasing Carbon Dioxide, (DOE/ER-0235), U.S. Department of Energy, Carbon Dioxide Research Division, Washington, D.C., 55-90.

Click to access Detecting_Climate_Effects_Increasing_CO2.pdf

Carbon dioxide – a medical view from 1866

I noticed a paper, “Transactions Of Branches” by Charles Trustram (1866), in The British Medical Journal. It contains an interesting passage, which I give below in its entirety. I have highlighted especially interesting parts:

“Medicine. I propose, on the present occasion, to depart from the course pursued by my predecessors, and instead of confining myself to that stale subject, medical reform, and that everyday recurring matter of medical ethics, to take a cursory glance of the progress that medicine has made since our last meeting.

With the exception of those improvements that the treatment of diseases of the nervous centres has derived from the researches of Brown-Séquard and Lockhart Clarke, and the introduction of that new instrument for testing the character of the circulation (which, by the kindness of one of our members, Dr. Clapton, is now on the table, and which I have no doubt he will kindly explain to us), medicine proper seems to have made no very important advance. Pathology, physiology, and vital chemistry, have been pursuing the usual course of verifying, correcting, or rejecting the discoveries of past days. Chemistry, in its more extended sense, has been investigating the condition of the atmosphere, and trying to determine how far its constitution, as to that condition of its oxygen called ozone, determines the spread of epidemics and the character of disease; but as yet with no great practical result. But the question must some day arise, if it have not already done so, whether there is not another constituent which is exerting an influence on the animal economy; I mean an increase, at present inappreciable, of its carbonic acid gas. You are all aware that the subject of the possible exhaustion of our coal-fields, and its relation to the future of our country, which has often been hinted at by the philosopher, has just now seriously engaged the attention of our senate, not as a matter of public health, but as one of political economy. A new senator, but an old philosopher, feeling that the consideration of the subject of the taxation of his country was one, and not the least important one, of his duties, and yet too honest to regard taxes as one of the many means of spending without regard to repaying, suggested that we should try to repay some portion at least of our national debt before we had exhausted that mine of wealth which our coal-beds give us. A new feature most certainly in politics, but one that speaks well for the coming times of legislation, and one from which I hope medicine may soon derive some advantage. “Sufficient for the day is the evil thereof,” and “After us the Deluge,” has been too long the ruling creed of Governments, at all events in matters of finance.

But, I think, had he consulted the two sciences of physiology and chemistry, he need hardly have troubled himself about the matter. They would, I think, have told him that, when our coal-beds (at all events, if there be the quantity presumed) were gone, there would be nobody left to claim or to pay; for, before even the half of the coal of the world is consumed (and I do not suppose our national energy will before that time have exhausted the stock of our own country), the atmosphere will have again assumed a condition fatal to animal life – nearly that condition which a Book, in which I trust we all believe, describes it to have had, when its density, nearly three times that of the present atmosphere, held up and divided the firmament of water that was above it from that which was below it; when the very matter of these coal-beds floated in a gaseous form round earth’s surface, waiting to be fixed and solidified by the action of a gigantic flora, and stored for the use of coming man.

From the sublime to the ridiculous is said to be but one step; and from our gigantic national debt to our own fireside, and domestic expenditure in this matter, is but a short one, and to us an equally interesting and important one. What would be our feelings, if told one snowy morning in December that we had come to our last bushel of coal? We who live near the woods of Sussex might hope to get through the winter with their aid; but we should certainly feel a strong disposition to move off to a warmer climate ere the next winter began, and leave our houses and lands to settle our debt; for, in this free country, whilst coal does last, the manufacturer will take care to have his wants supplied in spite of all forebodings.

To return to that medical point at which I hinted. Let me ask this question, Is the atmosphere suffering from the extraordinary evolution of carbonic acid gas which is now going on? Is the pigmy and stunted flora of the present age equal to its decomposition, to the absorption of the carbon which combustion is now daily producing? and if so, will it continue to be so, seeing that the spread of the human family is daily diminishing the forest growths? Must there not some day be a perceptible increase of the present proportion of carbon in the atmosphere? and may not some already inappreciable increase be the cause of the present type of disease, as distinguished from that which prevailed at the beginning of this century, and which I myself have lived long enough to witness?

May not the altered type of disease have been produced rather from the presence of a depressing agent in the shape of carbonic acid gas, than from a less vivifying condition of the oxygen or its compounds of ozone?

We all, I am sure, regret to find that that dire and fatal malady, the cholera, has again reached our shores. Though it is now nearly fifty yers since this malady first skewed itself in our dependencies, where it has pretty constantly been under the eyes of our professional brethren, and more than thirty years since it came among us, it must be confessed that, beyond treating the symptoms and succouring the powers of life, we have learned but little about it. Various plans of cure have been tried, and each has had its advocates; but as yet there has not been one that has been admitted to be the best by the general voice of the profession. I have ventured to bring this subject to your notice, because I hold that it will, should this malady again spread in this country as it did in 1832, be the duty of every one of us to try to add his mite to the elucidation of the disease or verification of any plan of treatment that may come before him. The last plan of treatment propounded, which its author calls the eliminative one, is founded on the assumption, undoubtedly a true one, that the disease is a blood-poison, and that, therefore, it is desirable to assist Nature in the efforts she makes to rid herself of the poison by mild purgatives, and not by the opiates and stimulants that have been hitherto used. It is asserted that the one rids the system of the poison, which the other locks up. Before we place implicit confidence in this view, it must, I think, be shown that the diarrhoea that generally prevails at the same time as the cholera is not choleraic, or connected with that disease, but only an accompaniment, under the influence of which the poison of cholera has a better chance of exerting its power; for most assuredly hitherto it has been set down as a fact, that the cholera has generally attacked those in whom this condition has been neglected. Now, if elimination is to be the plan, it surely ought to be applied before that storm of symptoms begins, which, however curative they may be, so frequently prove fatal by their own severity. There is unquestionably a stage of incubation, even in those cases which die ere Nature sets up this eliminative action. The poison cannot well begin its action the moment it is taken into the system. Is there, then, no symptom by which this period can be distinguished? and is there no mode by which the poison can be neutralised, ere it makes itself an integral part of the blood? Can inhalation and hypodermic injection offer us no ready means of making a quick impression on the system? Certainly, if we are to look upon spasm of the smaller pulmonary arteries as the chief of the pathological conditions, inhalation would seem to offer us the readiest mode of reaching it. There is another plan of treatment which has been suggested in our JOURNAL; namely, that of transfusion of defibrinated blood. But I think the proposers of this would have done well to have taken a leaf out of the book of that sagacious cook who advised her readers to catch the hare before deciding how it was to be dressed; for, however good this plan, it would be only the rich who could hope to get it in any extensive epidemic.

Whilst doing all we can to treat this disease, we surely should not neglect to ask why and whence it comes, and what are the conditions that favour its spread? However convinced we might have been that the first epidemic was an imported one, we have lately had unmistakable evidence that it can arise in our own country. Then whence comes the poison, and what is it? Is it gaseous or molecular? Abounding, as the sunbeam shews us our atmosphere does, with matter, we can hardly regard it, however much it may assist the propagation of the disease by the deportation of its poisonous molecules, as the source of the poison. The mode of the progress of the disease forbids that. Dirt and bad water seem its almost invariable associates; but we had these for years without cholera. May we come to a conclusion that Nature occasionally loses her power of re-combining the poisonous results of decomposition? or do some intensified electro-magnetic currents occasionally revivify some dormant changes and so evolve this poison? or does this agent occasionally act electrically on some older source which was locked up in the earth’s crust ages past. The fitfulness of the disease favours the idea, either that the poison is not always present, or not liable to be evoked by every day recurring agency. On the other hand, if we are to believe what we bear of its origin among the Arabian Pilgrims, and look at what has lately occurred on board some emigrant ships, it would almost seem, that this poison, like that of typhus, may be produced by overcrowding and bad diet. What if in the end we should find it to be a modified typhus, which, instead of attacking the brain, tries conclusions with the sympathetic? If so, spasm of artery and engorgement of veins may be more dependent on the sympathetic than the direct action of a morbid agent.”

New research – atmospheric and oceanic circulation (October 27, 2016)

Some of the latest papers on atmospheric and oceanic circulation are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.

Highlights

On the atmospheric response experiment to a Blue Arctic Ocean (Nakamura et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070526/abstract

Abstract: We demonstrated atmospheric responses to a reduction in Arctic sea ice via simulations in which Arctic sea ice decreased stepwise from the present-day range to an ice-free range. In all cases, the tropospheric response exhibited a negative Arctic Oscillation (AO)-like pattern. An intensification of the climatological planetary-scale wave due to the present-day sea ice reduction on the Atlantic side of the Arctic Ocean induced stratospheric polar vortex weakening and the subsequent negative AO. Conversely, strong Arctic warming due to ice-free conditions across the entire Arctic Ocean induced a weakening of the tropospheric westerlies corresponding to a negative AO without troposphere-stratosphere coupling, for which the planetary-scale wave response to a surface heat source extending to the Pacific side of the Arctic Ocean was responsible. Because the resultant negative AO-like response was accompanied by secondary circulation in the meridional plane, atmospheric heat transport into the Arctic increased, accelerating the Arctic amplification.

Atlantic multi-decadal oscillation influence on weather regimes over Europe and the Mediterranean in spring and summer (Zampieri et al. 2016) http://www.sciencedirect.com/science/article/pii/S092181811630371X

Abstract: We analyze the influence of the Atlantic sea surface temperature multi-decadal variability on the day-by-day sequence of large-scale atmospheric circulation patterns (i.e. the “weather regimes”) over the Euro-Atlantic region. In particular, we examine of occurrence of weather regimes from 1871 to present. This analysis is conducted by applying a clustering technique on the daily mean sea level pressure field provided by the 20th Century Reanalysis project, which was successfully applied in other studies focused on the Atlantic Multi-decadal Oscillation (AMO). In spring and summer, results show significant changes in the frequencies of certain weather regimes associated with the phase shifts of the AMO. These changes are consistent with the seasonal surface pressure, precipitation, and temperature anomalies associated with the AMO shifts in Europe.

Ocean and atmosphere feedbacks affecting AMOC hysteresis in a GCM (Jackson et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3336-8

Abstract: Theories suggest that the Atlantic Meridional Overturning Circulation (AMOC) can exhibit a hysteresis where, for a given input of fresh water into the north Atlantic, there are two possible states: one with a strong overturning in the north Atlantic (on) and the other with a reverse Atlantic cell (off). A previous study showed hysteresis of the AMOC for the first time in a coupled general circulation model (Hawkins et al. in Geophys Res Lett. doi:10.1029/2011GL047208, 2011). In this study we show that the hysteresis found by Hawkins et al. (2011) is sensitive to the method with which the fresh water input is compensated. If this compensation is applied throughout the volume of the global ocean, rather than at the surface, the region of hysteresis is narrower and the off states are very different: when the compensation is applied at the surface, a strong Pacific overturning cell and a strong Atlantic reverse cell develops; when the compensation is applied throughout the volume there is little change in the Pacific and only a weak Atlantic reverse cell develops. We investigate the mechanisms behind the transitions between the on and off states in the two experiments, and find that the difference in hysteresis is due to the different off states. We find that the development of the Pacific overturning cell results in greater atmospheric moisture transport into the North Atlantic, and also is likely responsible for a stronger Atlantic reverse cell. These both act to stabilize the off state of the Atlantic overturning.

Arctic amplification: does it impact the polar jet stream? (Meleshko et al. 2016) http://www.tellusa.net/index.php/tellusa/article/view/32330

Abstract: It has been hypothesised that the Arctic amplification of temperature changes causes a decrease in the northward temperature gradient in the troposphere, thereby enhancing the oscillation of planetary waves leading to extreme weather in mid-latitudes. To test this hypothesis, we study the response of the atmosphere to Arctic amplification for a projected summer sea-ice-free period using an atmospheric model with prescribed surface boundary conditions from a state-of-the-art Earth system model. Besides a standard global warming simulation, we also conducted a sensitivity experiment with sea ice and sea surface temperature anomalies in the Arctic. We show that when global climate warms, enhancement of the northward heat transport provides the major contribution to decrease the northward temperature gradient in the polar troposphere in cold seasons, causing more oscillation of the planetary waves. However, while Arctic amplification significantly enhances near-surface air temperature in the polar region, it is not large enough to invoke an increased oscillation of the planetary waves.

Skilful predictions of the winter North Atlantic Oscillation one year ahead (Dunstone et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2824.html

Abstract: The winter North Atlantic Oscillation is the primary mode of atmospheric variability in the North Atlantic region and has a profound influence on European and North American winter climate. Until recently, seasonal variability of the North Atlantic Oscillation was thought to be largely driven by chaotic and inherently unpredictable processes. However, latest generation seasonal forecasting systems have demonstrated significant skill in predicting the North Atlantic Oscillation when initialized a month before the onset of winter. Here we extend skilful dynamical model predictions to more than a year ahead. The skill increases greatly with ensemble size due to a spuriously small signal-to-noise ratio in the model, and consequently larger ensembles are projected to further increase the skill in predicting the North Atlantic Oscillation. We identify two sources of skill for second-winter forecasts of the North Atlantic Oscillation: climate variability in the tropical Pacific region and predictable effects of solar forcing on the stratospheric polar vortex strength. We also identify model biases in Arctic sea ice that, if reduced, may further increase skill. Our results open possibilities for a range of new climate services, including for the transport, energy, water management and insurance sectors.

Other papers

Narrowing of the ITCZ in a warming climate: physical mechanisms (Byrne & Schneider, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070396/abstract

Observed and simulated fingerprints of multidecadal climate variability, and their contributions to periods of global SST stagnation (Barcikowska et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0443.1

Observed Changes in the Southern Hemispheric Circulation in May (Ivy et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0394.1

Annual Variations of the Tropopause Height over the Tibetan Plateau Compared with those over other regions (Yang et al. 2016) http://www.sciencedirect.com/science/article/pii/S0377026516300951

The influences of the Atlantic Multidecadal Oscillation on the Mean Strength of the North Pacific Subtropical High during Boreal Winter (Lyu et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0525.1

The Role of Tropical Inter-Basin SST Gradients in Forcing Walker Circulation Trends (Zhang & Karnauskas, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0349.1

The role of low-frequency variation in the manifestation of warming trend and ENSO amplitude (Yeo et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3376-0

Changes in meandering of the Northern Hemisphere circulation (Di Capua & Coumou, 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/9/094028/meta

Direct observations of the Antarctic Slope Current transport at 113°E (Peña-Molino et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JC011594/abstract

Accounting for Centennial Scale Variability when Detecting Changes in ENSO: a study of the Pliocene (Tindall et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016PA002951/abstract

The Quasi-Biennial Oscillation of 2015-16: Hiccup or Death Spiral? (Dunkerton, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070921/abstract

The weakening of the ENSO–Indian Ocean Dipole (IOD) coupling strength in recent decades (Ham et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3339-5

On the Recent Destabilization of the Gulf Stream Path downstream of Cape Hatteras (Andres, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069966/abstract

The relationship between the Madden Julian Oscillation and the North Atlantic Oscillation (Jiang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/qj.2917/abstract

Lessened response of boreal winter stratospheric polar vortex to El Niño in recent decades (Hu et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3340-z

Warming and weakening trends of the Kuroshio during 1993-2013 (Wang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069432/abstract

Prolonged El Niño conditions in 2014–15 and the rapid intensification of Hurricane Patricia in the eastern Pacific (Foltz et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070274/abstract

Connection between Anomalous Zonal Activities of the South Asian High and Eurasian Summer Climate Anomalies (Shi & Qian, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0823.1

Ranking the strongest ENSO events while incorporating SST uncertainty (Huang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070888/abstract

The influence of the Gulf Stream on wintertime European blocking (O’Reilly et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-015-2919-0

Projected changes in atmospheric rivers affecting Europe in CMIP5 models (Ramos et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070634/abstract

Hosed vs. unhosed: interruptions of the Atlantic Meridional Overturning Circulation in a global coupled model, with and without freshwater forcing (Brown & Galbraith, 2016) http://www.clim-past.net/12/1663/2016/

An Oceanic Heat Content Based Definition for the Pacific Decadal Oscillation (Kumar & Wen, 2016) http://journals.ametsoc.org/doi/abs/10.1175/MWR-D-16-0080.1

An investigation of the presence of atmospheric rivers over the North Pacific during planetary-scale wave life cycles and their role in Arctic warming (Baggett et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-16-0033.1

Alternative modelling approaches for the ENSO time series: persistence and seasonality (Gil-Alana, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4850/abstract

Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations (Davis et al. 2016) http://www.atmos-chem-phys.net/16/10083/2016/

Atmospheric River Landfall-Latitude Changes in Future Climate Simulations (Shields & Kiehl, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070470/abstract