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Observations of anthropogenic global warming

Archive for April, 2018

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

Posted by Ari Jokimäki on April 24, 2018

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problems with Google Scholar for these searches are mainly related to Google Scholar returning lots of results that are not peer-reviewed.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 –

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Papers on changes in Atlantic Meridional Overturning Circulation

Posted by Ari Jokimäki on April 12, 2018

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.

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.

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.

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.

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