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New research – climate sensitivity, forcings, and feedbacks (September 22, 2016)

Posted by Ari Jokimäki on September 22, 2016

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


The Effects of Ocean Heat Uptake on Transient Climate Sensitivity (Rose & Rayborn, 2016)

Abstract: Transient climate sensitivity tends to increase on multiple timescales in climate models subject to an abrupt CO2 increase. The interdependence of radiative and ocean heat uptake processes governing this increase are reviewed. Heat uptake tends to be spatially localized to the subpolar oceans, and this pattern emerges rapidly from an initially uniform distribution. Global climatic impact of heat uptake is studied through the lens of the efficacy concept and a linear systems perspective in which responses to individual climate forcing agents are additive. Heat uptake can be treated as a slowly varying forcing on the atmosphere and surface, whose efficacy is strongly determined by its geographical pattern. An illustrative linear model driven by simple prescribed uptake patterns demonstrates the emergence of increasing climate sensitivity as a consequence of the slow decay of high-efficacy subpolar heat uptake. Evidence is reviewed for the key role of shortwave cloud feedbacks in setting the high efficacy of ocean heat uptake and thus in increasing climate sensitivity. A causal physical mechanism is proposed, linking subpolar heat uptake to a global-scale increase in lower-tropospheric stability. It is shown that the rate of increase in estimated inversion strength systematically slows as heat uptake decays. Variations in heat uptake should therefore manifest themselves as differences in low cloud feedbacks.

Understanding Climate Feedbacks and Sensitivity Using Observations of Earth’s Energy Budget (Loeb et al. 2016)

Abstract: While climate models and observations generally agree that climate feedbacks collectively amplify the surface temperature response to radiative forcing, the strength of the feedback estimates varies greatly, resulting in appreciable uncertainty in equilibrium climate sensitivity. Because climate feedbacks respond differently to different spatial variations in temperature, short-term observational records have thus far only provided a weak constraint for climate feedbacks operating under global warming. Further complicating matters is the likelihood of considerable time variation in the effective global climate feedback parameter under transient warming. There is a need to continue to revisit the underlying assumptions used in the traditional forcing-feedback framework, with an emphasis on how climate models and observations can best be utilized to reduce the uncertainties. Model simulations can also guide observational requirements and provide insight on how the observational record can most effectively be analyzed in order to make progress in this critical area of climate research.

Insights from a Refined Decomposition of Cloud Feedbacks (Zelinka et al. 2016)

Abstract: Decomposing cloud feedback into components due to changes in several gross cloud properties provides valuable insights into its physical causes. Here we present a refined decomposition that separately considers changes in free tropospheric and low cloud properties, better connecting feedbacks to individual governing processes and avoiding ambiguities present in a commonly used decomposition. It reveals that three net cloud feedback components are robustly nonzero: positive feedbacks from increasing free tropospheric cloud altitude and decreasing low cloud cover and a negative feedback from increasing low cloud optical depth. Low cloud amount feedback is the dominant contributor to spread in net cloud feedback but its anticorrelation with other components damps overall spread. The ensemble mean free tropospheric cloud altitude feedback is roughly 60% as large as the standard cloud altitude feedback because it avoids aliasing in low cloud reductions. Implications for the “null hypothesis” climate sensitivity from well-understood and robustly simulated feedbacks are discussed.

Rapid systematic assessment of the detection and attribution of regional anthropogenic climate change (Stone & Hansen, 2016)

Abstract: Despite being a well-established research field, the detection and attribution of observed climate change to anthropogenic forcing is not yet provided as a climate service. One reason for this is the lack of a methodology for performing tailored detection and attribution assessments on a rapid time scale. Here we develop such an approach, based on the translation of quantitative analysis into the “confidence” language employed in recent Assessment Reports of the Intergovernmental Panel on Climate Change. While its systematic nature necessarily ignores some nuances examined in detailed expert assessments, the approach nevertheless goes beyond most detection and attribution studies in considering contributors to building confidence such as errors in observational data products arising from sparse monitoring networks. When compared against recent expert assessments, the results of this approach closely match those of the existing assessments. Where there are small discrepancies, these variously reflect ambiguities in the details of what is being assessed, reveal nuances or limitations of the expert assessments, or indicate limitations of the accuracy of the sort of systematic approach employed here. Deployment of the method on 116 regional assessments of recent temperature and precipitation changes indicates that existing rules of thumb concerning the detectability of climate change ignore the full range of sources of uncertainty, most particularly the importance of adequate observational monitoring.

One Year of Downwelling Spectral Radiance Measurements from 100 to 1400 cm−1 at Dome-Concordia: Results in Clear Conditions (Rizzi et al. 2016)

Abstract: The present work examines downwelling radiance spectra measured at the ground during 2013 by a Far Infrared Fourier Transform Spectrometer at Dome-C, Antarctica. A tropospheric backscatter and depolarization Lidar is also deployed at same site and a radiosonde system is routinely operative. The measurements allow characterization of the water vapor and clouds infrared properties in Antarctica under all sky conditions. In this paper we specifically discuss cloud detection and the analysis in clear sky condition, required for the discussion of the results obtained in cloudy conditions. Firstly, the paper discusses the procedures adopted for the quality control of spectra acquired automatically. Then it describes the classification procedure used to discriminate spectra measured in clear-sky from cloudy conditions. Finally a selection is performed and 66 clear cases, spanning the whole year, are compared to simulations. The computation of layer molecular optical depth is performed with line-by-line techniques and a convolution to simulate the REFIR-PAD measurements; the downwelling radiance for selected clear cases is computed with a state-of-the-art adding-doubling code. The mean difference over all selected cases between simulated and measured radiance is within experimental error for all the selected micro-windows except for the negative residuals found for all micro-windows in the range 200 to 400 cm−1, with largest values around 295.1 cm−1. The paper discusses possible reasons for the discrepancy and identifies the incorrect magnitude of the water vapor total absorption coefficient as the cause of such large negative radiance bias below 400 cm−1.

Other papers

Dependence of global radiative feedbacks on evolving patterns of surface heat fluxes (Rugenstein et al. 2016)

Understanding the varied influence of mid-latitude jet position on clouds and cloud-radiative effects in observations and global climate models (Grise & Medeiros, 2016)

Effect of land cover change on snow free surface albedo across the continental United States (Wickham et al. 2016)

Forced response and internal variability of summer climate over western North America (Kamae et al. 2016)

Detection and attribution of climate change at regional scale: case study of Karkheh river basin in the west of Iran (Zohrabi et al. 2016)

Atmospheric lifetimes, infrared absorption spectra, radiative forcings and global warming potentials of NF3 and CF3CF2Cl (CFC-115) (Totterdill et al. 2016)

A long-term study of aerosol–cloud interactions and their radiative effect at the Southern Great Plains using ground-based measurements (Sena et al. 2016)

Detection of dimming/brightening in Italy from homogenized all-sky and clear-sky surface solar radiation records and underlying causes (1959–2013) (Manara et al. 2016)

Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic (Leaitch et al. 2016)

Assessment of the first indirect radiative effect of ammonium-sulfate-nitrate aerosols in East Asia (Han et al. 2016)

Sensitivity of precipitation extremes to radiative forcing of greenhouse gases and aerosols (Lin et al. 2016)

Global climate forcing of aerosols embodied in international trade (Lin et al. 2016)

Reprocessing of HIRS Satellite Measurements from 1980-2015: Development Towards a Consistent Decadal Cloud Record (Menzel et al. 2016)

Radiative Forcing from Anthropogenic Sulfur and Organic Emissions Reaching the Stratosphere (Yu et al. 2016)

Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution (Archer, 2016)

Long-Term Variations of Noctilucent Clouds at ALOMAR (Fiedler et al. 2016)

Estimating Arctic sea-ice shortwave albedo from MODIS data (Qu et al. 2016)

Surface albedo raise in the South American Chaco: Combined effects of deforestation and agricultural changes (Houspanossian et al. 2016)

New Observational Evidence for a Positive Cloud Feedback that Amplifies the Atlantic Multidecadal Oscillation (Bellomo et al. 2016)

Surface water and heat exchange comparison between alpine meadow and bare land in a permafrost region of the Tibetan Plateau (You et al. 2016)

foF2 vs Solar Indices for the Rome station: looking for the best general relation which is able to describe the anomalous minimum between cycles 23 and 24 (Perna & Pezzopane, 2016)

Comparison of Methods: Attributing the 2014 record European temperatures to human influences (Uhe et al. 2016)

Relevance of long term time – series of atmospheric parameters at a mountain observatory to models for climate change (Kancírová et al. 2016)

An energy balance perspective on regional CO2-induced temperature changes in CMIP5 models (Räisänen, 2016)

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New research – temperature (September 5, 2016)

Posted by Ari Jokimäki on September 5, 2016

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


Observed and simulated full-depth ocean heat-content changes for 1970–2005 (Cheng et al. 2016)

Abstract: Greenhouse-gas emissions have created a planetary energy imbalance that is primarily manifested by increasing ocean heat content (OHC). Updated observational estimates of full-depth OHC change since 1970 are presented that account for recent advancements in reducing observation errors and biases. The full-depth OHC has increased by 0.74 [0.68, 0.80]  ×  1022 J yr-1 (0.46 Wm−2) and 1.22 [1.16–1.29]  ×  1022 J yr-1 (0.75 Wm-2) for 1970–2005 and 1992–2005, respectively, with a 5 to 95 % confidence interval of the median. The CMIP5 models show large spread in OHC changes, suggesting that some models are not state-of-the-art and require further improvements. However, the ensemble median has excellent agreement with our observational estimate: 0.68 [0.54–0.82]  ×  1022 J yr-1 (0.42 Wm-2) from 1970 to 2005 and 1.25 [1.10–1.41]  ×  1022 J yr-1 (0.77 Wm-2) from 1992 to 2005. These results increase confidence in both the observational and model estimates to quantify and study changes in Earth’s energy imbalance over the historical period. We suggest that OHC be a fundamental metric for climate model validation and evaluation, especially for forced changes (decadal timescales).

Pacific sea level rise patterns and global surface temperature variability (Peyser et al. 2016)

Abstract: During 1998–2012, climate change and sea level rise (SLR) exhibit two notable features: a slowdown of global surface warming (hiatus) and a rapid SLR in the tropical western Pacific. To quantify their relationship, we analyze the long-term control simulations of 38 climate models. We find a significant and robust correlation between the east-west contrast of dynamic sea level (DSL) in the Pacific and global mean surface temperature (GST) variability on both interannual and decadal time scales. Based on linear regression of the multimodel ensemble mean, the anomalously fast SLR in the western tropical Pacific observed during 1998–2012 indicates suppression of a potential global surface warming of 0.16° ± 0.06°C. In contrast, the Pacific contributed 0.29° ± 0.10°C to the significant interannual GST increase in 1997/1998. The Pacific DSL anomalies observed in 2015 suggest that the strong El Niño in 2015/2016 could lead to a 0.21° ± 0.07°C GST jump.

Contrasting effects of urbanization and agriculture on surface temperature in eastern China (Zhou et al. 2016)

Abstract: The combined effect of urbanization and agriculture, two most pervasive land use activities, on the surface climate remains poorly understood. Using Moderate Resolution Imaging Spectroradiometer data over 2010–2015 and forests as reference, we showed that urbanization warmed the land surface temperature (LST), especially during the daytime and in growing seasons (maximized at 5.0 ± 2.0°C in May), whereas agriculture (dominated by double-cropping system) cooled the LST in two growing seasons during the daytime and all the months but July during the nighttime in Jiangsu Province, eastern China. Collectively, they had insignificant effects on the LST during the day (−0.01°C) and cooled the LST by −0.6°C at night. We also found large geographic variations associated with their thermal effects, indicated by a warming tendency southward. These spatiotemporal patterns depend strongly on vegetation activity, evapotranspiration, surface albedo, and the background climate. Our results emphasize the great potential of agriculture in offsetting the heating effects caused by rapid urbanization in China.

A summer temperature bias in early alcohol thermometers (Camuffo & Valle, 2016)

Abstract: This paper analyses the response of alcohol thermometers in relation to the departure from linearity and the choice of the calibration points. The result is that alcohol thermometers are affected by large departures that reach a maximum (i.e. −6 °C) at 50 °C ambient temperature. This may have caused a severe bias in early records, when alcohol thermometers were popular, especially during the Little Ice Age. Choosing a lower temperature for the upper point, calibration may substantially reduce this bias. Examples are given with thermometers in use in the 17th and 18th centuries. A careful correction of long series is necessary to avoid misleading climate interpretations.

The phenology of Arctic Ocean Surface warming (Steele & Dickinson, 2016)

Abstract: In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near-term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season.

Other papers

Comparisons of time series of annual mean surface air temperature for China since the 1900s: Observations, model simulations and extended reanalysis (Li et al. 2016)

First ground-based observations of mesopause temperatures above the Eastern-Mediterranean Part I: Multi-day oscillations and tides (Silber et al. 2016)

An enhanced single-channel algorithm for retrieving land surface temperature from Landsat series data (Wang et al. 2016)

Observed changes of temperature extremes in Serbia over the period 1961 − 2010 (Ruml et al. 2016)

The inter-annual variations and the long-term trends of monthly air temperatures in Iraq over the period 1941–2013 (Muslih & Błażejczyk, 2016)

A multiregion model evaluation and attribution study of historical changes in the area affected by temperature and precipitation extremes (Dittus et al. 2016)

Changes in wind speed under heat waves enhance urban heat islands in Beijing metropolitan area (Li et al. 2016)

Regional differential behaviour of maximum temperatures in the Iberian Peninsula regarding the Summer NAO in the second half of the twentieth century (Favà et al. 2016)

Confidence intervals for time averages in the presence of long range correlations, a case study on earth surface temperature anomalies (Massah & Kantz, 2016)

An ensemble of ocean reanalyses for 1815–2013 with sparse observational input (Giese et al. 2016)

Arctic-North Pacific coupled impacts on the late autumn cold in North America (Sung et al. 2016)

Wet-bulb, dew point, and air temperature trends in Spain (Moratiel et al. 2016)

Insights into elevation-dependent warming in the Tibetan Plateau-Himalayas from CMIP5 model simulations (Palazzi et al. 2016)

Spatial variations in temperature in a mountainous region of Jeju Island, South Korea (Um & Kim, 2016)

Gap filling and homogenization of climatological datasets in the headwater region of the Upper Blue Nile Basin, Ethiopia (Woldesenbet et al. 2016)

A homogenized long-term temperature record for the Western Cape Province in South Africa: 1916–2013 (Lakhraj-Govender et al. 2016)

Inter-model diversity of Arctic amplification caused by global warming and its relationship with the Inter-tropical Convergence Zone in CMIP5 climate models (Yim et al. 2016)

Urban–rural differences in near-surface air temperature as resolved by the Central Europe Refined analysis (CER): sensitivity to planetary boundary layer schemes and urban canopy models (Jänicke et al. 2016)

Monotonic Decrease of the Zonal SST Gradient of the Equatorial Pacific as a Function of CO2 Concentration in CCSM3 and CCSM4 (Yang et al. 2016)

Recent seasonal and long-term changes in southern Australian frost occurrence (Crimp et al. 2016)

Surface temperature trends from homogenized time series in South Africa: 1931–2015 (Kruger & Nxumalo, 2016)

Investigations of the middle atmospheric thermal structure and oscillations over sub-tropical regions in the Northern and Southern Hemispheres (Sharma et al. 2016)

Recent amplification of the North American winter temperature dipole (Singh et al. 2016)

Use of remotely-sensed land surface temperature as a proxy for air temperatures at high elevations: Findings from a 5000 metre elevational transect across Kilimanjaro (Pepin et al. 2016)

Spatial distribution of temperature trends and extremes over Maharashtra and Karnataka States of India (Dhorde et al. 2016)

Assessing atmospheric temperature data sets for climate studies (Cederlöf et al. 2016)

Ocean heat uptake and interbasin transport of passive and redistributive surface heating (Garuba & Klinger, 2016)

Temperature and precipitation regional climate series over the central Pyrenees during 1910–2013 (Pérez-Zanón et al. 2016)

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New research – climate models and projections (August 16, 2016)

Posted by Ari Jokimäki on August 16, 2016

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


CMIP5 scientific gaps and recommendations for CMIP6 (Stouffer et al. 2016)

Abstract: The Coupled Model Intercomparison Project (CMIP) is an ongoing coordinated international activity of numerical experimentation of unprecedented scope and impact on climate science. Its most recent fifth phase, CMIP5, has created nearly two petabytes of output from dozens of experiments performed by dozens of comprehensive climate models available to the climate science research community. In so doing, it has greatly advanced climate science. While CMIP5 has given answers to important science questions, with the help of a community survey we identify and motivate three broad topics here that guided the scientific framework of the next phase of CMIP, i.e. CMIP6:

1.How does the Earth System respond to changes in forcing?

2.What are the origins and consequences of systematic model biases?

3.How can we assess future climate changes given internal climate variability, predictability and uncertainties in scenarios?

CMIP has demonstrated the power of idealized experiments to better understand how the climate system works. We expect that these idealized approaches will continue to contribute to CMIP6. The quantification of radiative forcings and responses was poor and requires new methods and experiments to address this gap. There are a number of systematic model biases that appear in all phases of CMIP which remain a major climate modeling challenge. These biases need increased attention to better understand their origins and consequences through targeted experiments. Improving understanding of the mechanisms underlying internal climate variability for more skillful decadal climate predictions and long-term projections remains another challenge for CMIP6.

Climate change in the next 30 years: What can a convection-permitting model tell us that we did not already know? (Fosser et al. 2016)

Abstract: To investigate the climate change in the next 30 years over a complex terrain in southwestern Germany, simulations performed with the regional climate model COSMO-CLM at convection-permitting resolution are compared to simulations at 7 km resolution with parameterised convection. An earlier study has shown the main benefits of convection-permitting resolution in the hourly statistics and the diurnal cycle of precipitation intensities. Here, we investigate whether the improved simulation of precipitation in the convection-permitting model is affecting future climate projections in summer. Overall, the future scenario (ECHAM5 with A1B forcing) brings weak changes in mean precipitation, but stronger hourly intensities in the morning and less frequent but more intense daily precipitation. The two model simulations produce similar changes in climate, despite differences in their physical characteristics linked to the formation of convective precipitation. A significant increase in the morning precipitation probably due to large-scale forced convection is found when considering only the most extreme events (above 50 mm/day). In this case, even the diurnal cycles of precipitation and convection-related indices are similar between resolutions, leading to the conclusion that the 7 km model sufficiently resolves the most extreme convective events. In this region and time periods, the 7 km resolution is deemed sufficient for most assessments of near future precipitation change. However, conclusions could be dependent on the characteristics of the region of investigation.

Evaluating Arctic warming mechanisms in CMIP5 models (Franzke et al. 2016)

Abstract: Arctic warming is one of the most striking signals of global warming. The Arctic is one of the fastest warming regions on Earth and constitutes, thus, a good test bed to evaluate the ability of climate models to reproduce the physics and dynamics involved in Arctic warming. Different physical and dynamical mechanisms have been proposed to explain Arctic amplification. These mechanisms include the surface albedo feedback and poleward sensible and latent heat transport processes. During the winter season when Arctic amplification is most pronounced, the first mechanism relies on an enhancement in upward surface heat flux, while the second mechanism does not. In these mechanisms, it has been proposed that downward infrared radiation (IR) plays a role to a varying degree. Here, we show that the current generation of CMIP5 climate models all reproduce Arctic warming and there are high pattern correlations—typically greater than 0.9—between the surface air temperature (SAT) trend and the downward IR trend. However, we find that there are two groups of CMIP5 models: one with small pattern correlations between the Arctic SAT trend and the surface vertical heat flux trend (Group 1), and the other with large correlations (Group 2) between the same two variables. The Group 1 models exhibit higher pattern correlations between Arctic SAT and 500 hPa geopotential height trends, than do the Group 2 models. These findings suggest that Arctic warming in Group 1 models is more closely related to changes in the large-scale atmospheric circulation, whereas in Group 2, the albedo feedback effect plays a more important role. Interestingly, while Group 1 models have a warm or weak bias in their Arctic SAT, Group 2 models show large cold biases. This stark difference in model bias leads us to hypothesize that for a given model, the dominant Arctic warming mechanism and trend may be dependent on the bias of the model mean state.

The Impact of SST Biases on Projections of Anthropogenic Climate Change: A Greater Role for Atmosphere-only Models? (He & Soden, 2016)

Abstract: There is large uncertainty in the model simulation of regional climate change from anthropogenic forcing. Recent studies have tried to link such uncertainty to intermodel differences in the pattern of sea surface temperature (SST) change. On the other hand, coupled climate models also contain systematic biases in their climatology, largely due to drift in SSTs. To the extent that the projected changes depend on the mean state, biases in the present-day climatology also contribute to the intermodel spread in climate change projections. By comparing atmospheric general circulation model (AGCM) simulations using the climatological SSTs from different coupled models, we show that biases in the climatological SST generally have a larger impact on regional projections over land than do intermodel differences in the pattern of SST change. These results advocate for a greater application of AGCM simulations with observed SSTs or flux-adjusted coupled models to improve regional projections of anthropogenic climate change.

The art and science of climate model tuning (Hourdin et al. 2016)

Abstract: We survey the rationale and diversity of approaches for tuning, a fundamental aspect of climate modeling which should be more systematically documented and taken into account in multi-model analysis.

The process of parameter estimation targeting a chosen set of observations is an essential aspect of numerical modeling. This process is usually named tuning in the climate modeling community. In climate models, the variety and complexity of physical processes involved, and their interplay through a wide range of spatial and temporal scales, must be summarized in a series of approximate sub-models. Most sub-models depend on uncertain parameters. Tuning consists of adjusting the values of these parameters to bring the solution as a whole into line with aspects of the observed climate. Tuning is an essential aspect of climate modeling with its own scientific issues, which is probably not advertised enough outside the community of model developers. Optimization of climate models raises important questions about whether tuning methods a priori constrain the model results in unintended ways that would affect our confidence in climate projections. Here we present the definition and rationale behind model tuning, review specific methodological aspects, and survey the diversity of tuning approaches used in current climate models. We also discuss the challenges and opportunities in applying so-called ‘objective‘ methods in climate model tuning. We discuss how tuning methodologies may affect fundamental results of climate models, such as climate sensitivity. The article concludes with a series of recommendations to make the process of climate model tuning more transparent.

Other papers

High-resolution ensemble projections of near-term regional climate over the continental United States (Ashfaq et al. 2016)

Twentieth century temperature trends in CMIP3, CMIP5, and CESM-LE climate simulations – spatial-temporal uncertainties, differences and their potential sources (Kumar et al. 2016)

Assessing the robustness and uncertainties of projected changes in temperature and precipitation in AR4 Global Climate Models over the Arabian Peninsula (Almazroui et al. 2016)

The influence of model resolution on temperature variability (Klavans et al. 2016)

Evaluation of the skill of North-American Multi-Model Ensemble (NMME) Global Climate Models in predicting average and extreme precipitation and temperature over the continental USA (Slater et al. 2016)

Assessing uncertainties in land cover projections (Alexander et al. 2016)

Effects of southeastern Pacific sea surface temperature on the double-ITCZ bias in NCAR CESM1 (Song & Zhang, 2016)

Stochastic Parameterization: Towards a new view of Weather and Climate Models (Berner et al. 2016)

Do convection-permitting regional climate models improve projections of future precipitation change? (Kendon et al. 2016)

MiKlip – a National Research Project on Decadal Climate Prediction (Marotzke et al. 2016)

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New research – composition of atmosphere (August 15, 2016)

Posted by Ari Jokimäki on August 15, 2016

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


Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006 (McNorton et al. 2016)

Abstract: The growth in atmospheric methane (CH4) concentrations over the past 2 decades has shown large variability on a timescale of several years. Prior to 1999 the globally averaged CH4 concentration was increasing at a rate of 6.0 ppb yr−1, but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6 ppb yr−1. From 2007 to 2009 the growth rate again increased to 4.9 ppb yr−1. These changes in growth rate are usually ascribed to variations in CH4 emissions. We have used a 3-D global chemical transport model, driven by meteorological reanalyses and variations in global mean hydroxyl (OH) concentrations derived from CH3CCl3 observations from two independent networks, to investigate these CH4 growth variations. The model shows that between 1999 and 2006 changes in the CH4 atmospheric loss contributed significantly to the suppression in global CH4 concentrations relative to the pre-1999 trend. The largest factor in this is relatively small variations in global mean OH on a timescale of a few years, with minor contributions of atmospheric transport of CH4 to its sink region and of atmospheric temperature. Although changes in emissions may be important during the stagnation period, these results imply a smaller variation is required to explain the observed CH4 trends. The contribution of OH variations to the renewed CH4 growth after 2007 cannot be determined with data currently available.

Diverse policy implications for future ozone and surface UV in a changing climate (Butler et al. 2016)

Abstract: Due to the success of the Montreal Protocol in limiting emissions of ozone-depleting substances, concentrations of atmospheric carbon dioxide, nitrous oxide, and methane will control the evolution of total column and stratospheric ozone by the latter half of the 21st century. As the world proceeds down the path of reducing climate forcing set forth by the 2015 Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 21), a broad range of ozone changes are possible depending on future policies enacted. While decreases in tropical stratospheric ozone will likely persist regardless of the future emissions scenario, extratropical ozone could either remain weakly depleted or even increase well above historical levels, with diverse implication for ultraviolet (UV) radiation. The ozone layer’s dependence on future emissions of these gases creates a complex policy decision space for protecting humans and ecosystems, which includes unexpected options such as accepting nitrous oxide emissions in order to maintain historical column ozone and surface UV levels.

Changes in surface aerosol extinction trends over China during 1980–2013 inferred from quality-controlled visibility data (Li et al. 2016)

Abstract: Pollution in China has been attracting extensive attention both globally and regionally, especially due to the perceptually worsening “smog” condition in recent years. We use routine visibility measurements from 1980 to 2013 at 272 WMO stations in China to assess the temporal changes in the magnitude and the sign of pollution trends. A strict and comprehensive quality control procedure is enforced by considering several issues not typically addressed in previous studies. Two methods are used to independently estimate the trend and its significance level. Results show that in general, a strong increase in Aerosol Extinction Coefficient (AEC) over the majority of China is observed in the 1980s, followed by a moderate decrease in the 1990s, another increase in the 2000s, and a shift to decrease since around 2006 for some regions. Seasonally, winter and fall trends appear to be the strongest, while summer has the lowest trend.

The millennium water vapour drop in chemistry–climate model simulations (Brinkop et al. 2016)

Abstract: This study investigates the abrupt and severe water vapour decline in the stratosphere beginning in the year 2000 (the “millennium water vapour drop”) and other similarly strong stratospheric water vapour reductions by means of various simulations with the state-of-the-art Chemistry-Climate Model (CCM) EMAC (ECHAM/MESSy Atmospheric Chemistry Model). The model simulations differ with respect to the prescribed sea surface temperatures (SSTs) and whether nudging is applied or not. The CCM EMAC is able to most closely reproduce the signature and pattern of the water vapour drop in agreement with those derived from satellite observations if the model is nudged. Model results confirm that this extraordinary water vapour decline is particularly obvious in the tropical lower stratosphere and is related to a large decrease in cold point temperature. The drop signal propagates under dilution to the higher stratosphere and to the poles via the Brewer–Dobson circulation (BDC). We found that the driving forces for this significant decline in water vapour mixing ratios are tropical sea surface temperature (SST) changes due to a coincidence with a preceding strong El Niño–Southern Oscillation event (1997/1998) followed by a strong La Niña event (1999/2000) and supported by the change of the westerly to the easterly phase of the equatorial stratospheric quasi-biennial oscillation (QBO) in 2000. Correct (observed) SSTs are important for triggering the strong decline in water vapour. There are indications that, at least partly, SSTs contribute to the long period of low water vapour values from 2001 to 2006. For this period, the specific dynamical state of the atmosphere (overall atmospheric large-scale wind and temperature distribution) is important as well, as it causes the observed persistent low cold point temperatures. These are induced by a period of increased upwelling, which, however, has no corresponding pronounced signature in SSTs anomalies in the tropics. Our free-running simulations do not capture the drop as observed, because a) the cold point temperature has a low bias and thus the water vapour variability is reduced and b) because they do not simulate the appropriate dynamical state. Large negative water vapour declines are also found in other years and seem to be a feature which can be found after strong combined El Niño/La Niña events if the QBO west phase during La Niña changes to the east phase.

Evaluation of 4 years of continuous δ13C(CO2) data using a moving Keeling plot method (Vardag, Hammer & Levin, 2016)

Abstract: Different carbon dioxide (CO2) emitters can be distinguished by their carbon isotope ratios. Therefore measurements of atmospheric δ13C(CO2) and CO2 concentration contain information on the CO2 source mix in the catchment area of an atmospheric measurement site. This information may be illustratively presented as the mean isotopic source signature. Recently an increasing number of continuous measurements of δ13C(CO2) and CO2 have become available, opening the door to the quantification of CO2 shares from different sources at high temporal resolution. Here, we present a method to compute the CO2 source signature (δS) continuously and evaluate our result using model data from the Stochastic Time-Inverted Lagrangian Transport model. Only when we restrict the analysis to situations which fulfill the basic assumptions of the Keeling plot method does our approach provide correct results with minimal biases in δS. On average, this bias is 0.2 ‰ with an interquartile range of about 1.2 ‰ for hourly model data. As a consequence of applying the required strict filter criteria, 85 % of the data points – mainly daytime values – need to be discarded. Applying the method to a 4-year dataset of CO2 and δ13C(CO2) measured in Heidelberg, Germany, yields a distinct seasonal cycle of δS. Disentangling this seasonal source signature into shares of source components is, however, only possible if the isotopic end members of these sources – i.e., the biosphere, δbio, and the fuel mix, δF – are known. From the mean source signature record in 2012, δbio could be reliably estimated only for summer to (−25.0 ± 1.0) ‰ and δF only for winter to (−32.5 ± 2.5) ‰. As the isotopic end members δbio and δF were shown to change over the season, no year-round estimation of the fossil fuel or biosphere share is possible from the measured mean source signature record without additional information from emission inventories or other tracer measurements.

Other papers

Intercomparison of in situ NDIR and column FTIR measurements of CO2 at Jungfraujoch (Schibig et al. 2016)

Evaluation of 4 years of continuous δ13C(CO2) data using a moving Keeling plot method (Vardag, Hammer & Levin, 2016)

Intra-seasonal variability of atmospheric CO2 concentrations over India during summer monsoons (Kumar et al. 2016)

Impact of ENSO on variability of AIRS retrieved CO2 over India (Kumar et al. 2016)

Large XCH4 anomaly in summer 2013 over northeast Asia observed by GOSAT (Ishizawa et al. 2016)

Can we detect regional methane anomalies? A comparison between three observing systems (Cressot et al. 2016)

Non-homogeneous vertical distribution of methane over Indian region using surface, aircraft and satellite based data (Kavitha & Nair, 2016)

A probabilistic study of the return of stratospheric ozone to 1960 levels (Södergren et al. 2016)

The representation of solar cycle signals in stratospheric ozone – Part 1: A comparison of recently updated satellite observations (Maycock et al. 2016)

Summer ozone concentrations in the vicinity of the Great Salt Lake (Horel et al. 2016)

Impact of emissions and +2 °C climate change upon future ozone and nitrogen dioxide over Europe (Watson et al. 2016)

Natural and Anthropogenic Aerosol Trends from Satellite and Surface Observations and Model Simulations over the North Atlantic Ocean from 2002 to 2012 (Jongeward et al. 2016)

Aerosol Lidar Observations of Atmospheric Mixing in Los Angeles: Climatology and Implications for Greenhouse Gas Observations (Ware et al. 2016)

Future aerosol emissions: a multi-model comparison (Smith et al. 2016)

Multi-Year Study of the Dependence of Sea Salt Aerosol on Wind Speed and Sea Ice Conditions in the Coastal Arctic (May et al. 2016)

Effects of climate changes on dust aerosol over East Asia from RegCM3 (Zhang et al. 2016)

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New research – atmospheric and oceanic circulation (August 10, 2016)

Posted by Ari Jokimäki on August 10, 2016

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


The North Atlantic Oscillation as a driver of rapid climate change in the Northern Hemisphere (Delworth et al. 2016)

Abstract: Pronounced climate changes have occurred since the 1970s, including rapid loss of Arctic sea ice, large-scale warming and increased tropical storm activity in the Atlantic. Anthropogenic radiative forcing is likely to have played a major role in these changes, but the relative influence of anthropogenic forcing and natural variability is not well established. The above changes have also occurred during a period in which the North Atlantic Oscillation has shown marked multidecadal variations. Here we investigate the role of the North Atlantic Oscillation in these rapid changes through its influence on the Atlantic meridional overturning circulation and ocean heat transport. We use climate models to show that observed multidecadal variations of the North Atlantic Oscillation can induce multidecadal variations in the Atlantic meridional overturning circulation and poleward ocean heat transport in the Atlantic, extending to the Arctic. Our results suggest that these variations have contributed to the rapid loss of Arctic sea ice, Northern Hemisphere warming, and changing Atlantic tropical storm activity, especially in the late 1990s and early 2000s. These multidecadal variations are superimposed on long-term anthropogenic forcing trends that are the dominant factor in long-term Arctic sea ice loss and hemispheric warming.

Evidence of global warming impact on the evolution of the Hadley Circulation in ECMWF centennial reanalyses (D’Agostino & Lionello, 2016)

Abstract: This study analyzes the evolution of the Hadley Circulation (HC) during the twentieth century in ERA-20CM (AMIP-experiment) and ERA-20C (reanalysis). These two recent ECMWF products provide the opportunity for a new analysis of the HC trends and of their uncertainties. Further, the effect of sea surface temperature forcing (including its uncertainty) and data assimilation are investigated. Also the ECMWF reanalysis ERA-Interim, for the period 1979–2010, is considered for a complementary analysis. Datasets present important differences in characteristics and trends of the HC. In ERA-20C HC is weaker (especially the Southern Hemisphere HC) and the whole Northern Hemisphere HC is located more southward than in ERA-20CM (especially in the boreal summer). In ERA-Interim HC is stronger and wider than both other simulations. In general, the magnitude of trends is larger and more statistically significant in ERA-20C than in ERA-20CM. The presence of large multidecadal variability across twentieth century raises doubts on the interpretation of recent behavior, such as the onset of sustained long term trends, particularly for the HC strength. In spite of this, the southward shift of the Southern Edge and widening of the Southern Hemisphere HC appear robust features in all datasets, and their trends have accelerated in the last three decades, but actual expansion rates remain affected by considerable uncertainty. Inconsistencies between datasets are attributed to the different reproduction of the links between the HC width and factors affecting it (such as mean global temperature, tropopause height, meridional temperature contrast and planetary waves), which appear more robust in ERA-20CM than in ERA-20C, particularly for the two latter factors. Further, in ERA-Interim these correlations are not statistically significant. These outcomes suggest that data assimilation degrades the links between the HC and features influencing its dynamics.

Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports (Kelly et al. 2016)

Abstract: Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate.

The response of high-impact blocking weather systems to climate change (Kennedy et al. 2016)

Abstract: Midlatitude weather and climate are dominated by the jet streams and associated eastward moving storm systems. Occasionally, however, these are blocked by persistent anticyclonic regimes known as blocking. Climate models generally predict a small decline in blocking frequency under anthropogenic climate change. However, confidence in these predictions is undermined by, among other things, a lack of understanding of the physical mechanisms underlying the change. Here we analyze blocking (mostly in the Euro-Atlantic sector) in a set of sensitivity experiments to determine the effect of different parts of the surface global warming pattern. We also analyze projected changes in the impacts of blocking such as temperature extremes. The results show that enhanced warming both in the tropics and over the Arctic act to strengthen the projected decline in blocking. The tropical changes are more important for the uncertainty in projected blocking changes, though the Arctic also affects the temperature anomalies during blocking.

The anomalous change in the QBO in 2015-16 (Newman et al. 2016)

Abstract: The quasi-biennial oscillation (QBO) is a tropical lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months. The QBO has been constantly documented since 1953. Here we describe the evolution of the QBO during the Northern Hemisphere winter of 2015-16 using radiosonde observations and meteorological reanalyses. Normally, the QBO would show a steady downward propagation of the westerly phase. In 2015-16, there was an anomalous upward displacement of this westerly phase from ~30 hPa to 15 hPa. These westerlies impinge on, or “cut-off” the normal downward propagation of the easterly phase. In addition, easterly winds develop at 40 hPa. Comparisons to tropical wind statistics for the 1953-present record demonstrate that this 2015-16 QBO disruption is unprecedented.

Other papers

Impact of observed North Atlantic multidecadal variations to European summer climate: a linear baroclinic response to surface heating (Ghosh et al. 2016)

Gridded, monthly rainfall and temperature climatology for El Niño Southern Oscillation impacts in the United States (Dourte et al. 2016)

Southern European rainfall reshapes the early-summer circumglobal teleconnection after the late 1970s (Lin et al. 2016)

Moisture and heat budgets of the south American monsoon system: climatological aspects (Garcia et al. 2016)

The Relative Influence of ENSO and SAM on Antarctic Peninsula Climate (Clem et al. 2016)

Sinuosity of mid-latitude atmospheric flow in a warming world (Cattiaux et al. 2016)

ENSO response to high-latitude volcanic eruptions in the Northern Hemisphere: The role of the initial conditions (Pausata et al. 2016)

Remote influence of Interdecadal Pacific Oscillation on the South Atlantic Meridional Overturning Circulation variability (Lopez et al. 2016)

Robust response of the Amundsen Sea Low to stratospheric ozone depletion (England et al. 2016)

The response of winter Pacific North American pattern to strong volcanic eruptions (Liu et al. 2016)

Atlantic Multidecadal Variability in a model with an improved North Atlantic Current (Drews & Greatbatch, 2016)

Sub-decadal North Atlantic Oscillation variability in observations and the Kiel Climate Model (Reintges, Latif & Park, 2016)

Is there a robust effect of anthropogenic aerosols on the Southern Annular Mode? (Steptoe et al. 2016)

Climate Signals in the Mid- to High-Latitude North Atlantic from Altimeter Observations (Li et al. 2016)

Intensification and poleward shift of subtropical western boundary currents in a warming climate (Yang et al. 2016)

Inter-basin effects of the Indian Ocean on Pacific decadal climate change (Mochizuki et al. 2016)

The influence of boreal spring Arctic Oscillation on the subsequent winter ENSO in CMIP5 models (Chen et al. 2016)

Relationship between North American winter temperature and large-scale atmospheric circulation anomalies and its decadal variation (Yu et al. 2016)

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New research – Climate sensitivity, forcings, and feedbacks (August 8, 2016)

Posted by Ari Jokimäki on August 8, 2016

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


The Spectral Signature of Recent Climate Change (Brindley & Bantges, 2016)

Abstract: Spectrally resolved measurements of the Earth’s reflected shortwave (RSW) and outgoing longwave radiation (OLR) at the top of the atmosphere intrinsically contain the imprints of a multitude of climate relevant parameters. Here, we review the progress made in directly using such observations to diagnose and attribute change within the Earth system over the past four decades. We show how changes associated with perturbations such as increasing greenhouse gases are expected to be manifested across the spectrum and illustrate the enhanced discriminatory power that spectral resolution provides over broadband radiation measurements. Advances in formal detection and attribution techniques and in the design of climate model evaluation exercises employing spectrally resolved data are highlighted. We illustrate how spectral observations have been used to provide insight into key climate feedback processes and quantify multi-year variability but also indicate potential barriers to further progress. Suggestions for future research priorities in this area are provided.

Deep time evidence for climate sensitivity increase with warming (Shaffer et al. 2016)

Abstract: Future global warming from anthropogenic greenhouse gas emissions will depend on climate feedbacks, the effect of which is expressed by climate sensitivity, the warming for a doubling of atmospheric CO2 content. It is not clear how feedbacks, sensitivity, and temperature will evolve in our warming world, but past warming events may provide insight. Here we employ paleoreconstructions and new climate-carbon model simulations in a novel framework to explore a wide scenario range for the Paleocene-Eocene Thermal Maximum (PETM) carbon release and global warming event 55.8 Ma ago, a possible future warming analogue. We obtain constrained estimates of CO2 and climate sensitivity before and during the PETM and of the PETM carbon input amount and nature. Sensitivity increased from 3.3–5.6 to 3.7–6.5 K (Kelvin) into the PETM. When taken together with Last Glacial Maximum and modern estimates, this result indicates climate sensitivity increase with global warming.

Insights into Earth’s energy imbalance from multiple sources (Trenberth et al. 2016)

Abstract: The current Earth’s energy imbalance (EEI) can best be estimated from changes in ocean heat content (OHC), complemented by top-of-atmosphere (TOA) radiation measurements and an assessment of the small non-ocean components. Sustained observations from the Argo array of autonomous profiling floats enable near-global estimates of OHC since 2005, which reveal considerable cancellation of variations in the upper 300 m. An analysis of the monthly contributions to EEI from non-ocean (land and ice) using the CESM Large Ensemble reveals standard deviations of 0.3 to 0.4 W m-2 (global); largest values occur in August, but values are below 0.75 W m-2 >95% of the time. Global standard deviations of EEI of 0.64 W m-2 based on top-of-atmosphere observations therefore substantially constrain ocean contributions, given by the tendencies of OHC. Instead, monthly standard deviations of many Argo-based OHC tendencies are 6 to 13 W m-2 and non-physical fluctuations are clearly evident. We show that an ocean reanalysis with multi-variate dynamical data assimilation features much better agreement with TOA radiation, and 44% of the vertically-integrated short-term OHC trend for 2005-14 of 0.8±0.2 W m-2 (globally) occurs below 700 m depth. Largest warming occurs from 20 to 50°S, especially over the Southern Oceans, and near 40°N, in all ocean analyses. The EEI is estimated to be 0.9±0.3 W m-2 for 2005-2014.

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016)

Abstract: Although it is well-established that cirrus warms the Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in the Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m-2) induced by ice clouds due to trapping longwave radiation exceeds their cooling effect (~-16.7 ± 1.7 W m-2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m-2) globally on the earth-atmosphere system. The net warming is over 15 W m-2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m-2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year round in the tropics. Ice cloud optical depth (τ) is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ~ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.

Giant natural fluctuation models and anthropogenic warming (Lovejoy et al. 2016)

Abstract: Explanations for the industrial epoch warming are polarized around the hypotheses of anthropogenic warming (AW) and Giant Natural Fluctuations (GNF’s). While climate sceptics have systematically attacked AW, up until now they have only invoked GNF’s. This has now changed with the publication by D. Keenan of a sample of 1000 series from stochastic processes purporting to emulate the global annual temperature since 1880. While Keenan’s objective was to criticize the IPCC’s trend uncertainty analysis (their assumption that residuals are only weakly correlated), for the first time it is possible to compare a stochastic GNF model with real data. Using Haar fluctuations, probability distributions and other techniques of time series analysis, we show that his model has unrealistically strong low frequency variability so that even mild extrapolations imply ice ages every ≈ 1000 years. The GNF model can easily be scientifically rejected.

Other papers

Constraining the low-cloud optical depth feedback at middle and high latitudes using satellite observations (Terai et al. 2016)

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016)

Which way will the circulation shift in a changing climate? Possible nonlinearity of extratropical cloud feedbacks (Tandon & Cane, 2016)

Regional and global temperature response to anthropogenic SO2 emissions from China in three climate models (Kasoar et al. 2016)

Effective radiative forcing from historical land use change (Andrews et al. 2016)

Reassessing properties and radiative forcing of contrail cirrus using a climate model (Bock & Burkhardt, 2016)

Could the Pliocene constrain the equilibrium climate sensitivity? (Hargreaves & Annan, 2016)

Influence of snow cover changes on surface radiation and heat balance based on the WRF model (Yu et al. 2016)

A sensitivity study of the impact of dynamic vegetation on simulated future climate change over Southern Europe and the Mediterranean (Alo & Anagnostou, 2016)

A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region (Saud et al. 2016)

Separating climate change signals into thermodynamic, lapse-rate and circulation effects: theory and application to the European summer climate (Kröner et al. 2016)

Early global radiation measurements: a review (Stanhill & Archiman, 2016)

Aerosol types and radiative forcing estimates over East Asia (Bhawar et al. 2016)

Solar irradiance observed at Summit, Greenland: Possible links to magnetic activity on short timescales (Frederick, 2016)

Limits to global and Australian temperature change this century based on expert judgment of climate sensitivity (Grose et al. 2016)

Indirect Forcing of Black carbon on Clouds over North East India (Panicker et al. 2016)

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra (Juszak et al. 2016)

Aerosol radiative effects under clear skies over Europe and their changes in the period of 2001–2012 (Bartók, 2016)

Review of Aerosol-Cloud Interactions: Mechanisms, Significance and Challenges (Fan et al. 2016)

Inference of Climate Sensitivity from Analysis of Earth’s Energy Budget (Forster, 2016)

Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations (Lee et al. 2016)

Spatiotemporal characteristics of ultraviolet radiation in recent 54 years from measurements and reconstructions over the Tibetan Plateau (Liu et al. 2016)

The whole-atmosphere response to changes in the Earth’s magnetic field from 1900 to 2000: an example of “top-down” vertical coupling (Cnossen et al. 2016)

Strong modification of stratospheric ozone forcing by cloud and sea-ice adjustments (Xia et al. 2016)

Evaluation of the Arctic surface radiation budget in CMIP5 models (Boeke & Taylor, 2016)

Climate Feedback Variance and the Interaction of Aerosol Forcing and Feedbacks (Gettelman et al. 2016)

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New research – temperature (July 26, 2016)

Posted by Ari Jokimäki on July 26, 2016

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


The rogue nature of hiatuses in a global warming climate (Sévellec, Sinha & Skliris, 2016)

Abstract: The nature of rogue events is their unlikelihood and the recent unpredicted decade-long slowdown in surface warming, the so-called hiatus, may be such an event. However, given decadal variability in climate, global surface temperatures were never expected to increase monotonically with increasing radiative forcing. Here, surface air temperature from twenty climate models is analysed to estimate the historical and future likelihood of hiatuses and “surges” (faster than expected warming), showing that the global hiatus of the early 21st Century was extremely unlikely. A novel analysis of future climate scenarios suggests that hiatuses will almost vanish and surges will strongly intensify by 2100 under a “business as usual” scenario. For “CO2 stabilisation” scenarios, hiatus and surge characteristics revert to typical 1940s values. These results suggest to study the hiatus of the early 21st Century and future re-occurrences as rogue events, at the limit of the variability of current climate modelling capability.

Underestimated warming of northern Canada in the Berkeley Earth temperature product (Way, Oliva & Viau, 2016)

Abstract: The Berkeley Earth surface temperature (BERK) project provides gridded global temperature anomaly products using an automated geostatistical approach to adjust station data for systematic biases. Despite its widespread usage, the BERK data set has not been evaluated at the national-scale, especially in data-sparse high latitude environments. This study provides an evaluation of the BERK product across all of Canada using 333 climate stations made available from the homogenized Environment Canada station network (HTcan). Comparison between co-located monthly air temperature anomalies for the two data sets suggests small differences between the two products for mean surface (∼2 m) air temperature. However, the relatively minimal bias in mean temperature is a consequence of contrasting cold and warm biases in minimum and maximum air temperatures, respectively, that are larger but effectively even out when averaged together. The BERK product is shown to exhibit systematic underestimation of recent regional warming in northern Canada which when combined with an overestimation of warmth earlier in the record results in an observable reduction in warming rates for minimum and mean temperature anomalies since 1950. The temporal evolution and spatial pattern of the observed biases suggest that the BERK-automated adjustments to station data in northern Canada miss some inhomogeneities in the raw station data. These results highlight the need for enhanced data recovery and homogenization efforts in data-sparse high latitude regions and emphasize the importance of national-scale climate data sets for evaluating global gridded products. We also recommend caution when using the BERK minimum and maximum monthly air temperature products for long-term trend analyses.

Revisiting whether recent surface temperature trends agree with the CMIP5 ensemble (Lin & Huybers, 2016)

Abstract: A weaker trend in global mean temperature over the past 15 years relative to the preceding decades has been characterized as significantly lower than those contained within the CMIP5 ensemble. In this study, divergence between model simulations and observations is estimated using a fixed-intercept linear trend with a slope estimator that has one-third the noise variance compared to simple linear regression. Following the approach of Fyfe et al. (2013) where inter-model spread is used to assess the distribution of trends, but using the fixed-intercept trend metric, demonstrates that recently observed trends in global-mean temperature are consistent (p > 0.1) with the CMIP5 ensemble for all 15-year intervals of observation-model divergence since 1970. Significant clustering of global trends according to modeling center indicates that the spread in CMIP5 trends is better characterized using ensemble members drawn across models, as opposed to using ensemble members from a single model. Despite model-observation consistency at the global level, substantial regional discrepancies in surface temperature trends remain.

Climate change in the Kola Peninsula, Arctic Russia, during the last 50 years from meteorological observations (Marshall, Vignols & Rees, 2016)

Abstract: We provide a detailed climatology and evaluation of recent climate change in the Kola Peninsula, Arctic Russia, a region influenced by both the North Atlantic and Arctic Oceans. The analysis is based on 50 years of monthly surface air temperature (SAT), precipitation (PPN) and sea level pressure (SLP) data from ten meteorological stations for 1966-2015. Regional mean annual SAT is ~0°C: the moderating effect of the ocean is such that coastal (inland) stations have a positive (negative) value. Examined mean annual PPN totals rise from ~430 mm in the north-east of the region to ~600 mm in the west.

Annual SAT in the Kola Peninsula has increased by 2.3 ± 1.0 °C over the past 50 years. Seasonally, statistically significant warming has taken place in spring and fall, although the largest trend has occurred in winter. While there has been no significant change in annual PPN, spring has become significantly wetter and fall drier. The former is associated with the only significant seasonal SLP trend (decrease). A positive winter North Atlantic Oscillation (NAO) index is generally associated with a warmer and wetter Kola Peninsula while a positive Siberian High (SH) index has the opposite impact. The relationship between both the NAO and SH and SAT is broadly coherent across the region whereas their relationship with PPN varies markedly, although none of the relationships are temporally invariant. Reduced sea ice in the Barents and White Seas and associated circulation changes are likely to be the principal drivers behind the observed changes.

Water temperature increases in the river Rhine in response to climate change (Hardenbicker et al. 2016)

Abstract: The present study analyzes climate change effects on the water temperature of the Rhine, one of the largest rivers in Central Europe. Simulation calculations were performed based on a range of climate and river flow projections for the near (2021–2050) and for the far future (2071–2100) compared to a reference period (1961–1990). Changes in mean annual water temperature in the near future range between +0.6 and +1.4 °C and between +1.9 and +2.2 °C in the far future (average of nine stations). Monthly mean values of the far future change in a more differentiated way by +0.4 to +1.3 °C in spring and +2.7 to +3.4 °C in late summer. The length of periods of high water temperature, expressed as successive days with water temperatures over 27 °C, increases by a factor of four until 2100. These prolonged durations of periods with unusually high water temperatures may provoke changes in the food web and in the rates of biological processes in the Rhine.

Other papers

Assessing the uncertainty of CESM-LE in simulating the trends of mean and extreme temperature and precipitation over China (Li, Zhu & Dong, 2016)

Reconciling Observed and Modelled Temperature and Precipitation Trends over Europe by Adjusting for Circulation Variability (Saffioti et al. 2016)

Geo-spatial analysis of temporal trends of temperature and its extremes over India using daily gridded (1°×1°) temperature data of 1969–2005 (Chakraborty et al. 2016)

Sudden stratospheric warmings observed in the last decade by satellite measurements (Kishore et al. 2016)

Longitudinal Asymmetric Trends of Tropical Cold-point Tropopause Temperature and Their Link to Strengthened Walker Circulation (Hu et al. 2016)

An in situ-based analysis of the relationship between land surface ‘skin’ and screen-level air temperatures (Good, 2016)

Spatiotemporal rainfall and temperature trends throughout the Brazilian Legal Amazon, 1973–2013 (Almeida et al. 2016)

Spatial variation of deterministic chaos in mean daily temperature and rainfall over Nigeria (Fuwape et al. 2016)

Homogenisation of temperature and precipitation time series with ACMANT3: method description and efficiency tests (Domonkos & Coll, 2016)

The tropical Pacific as a key pacemaker of the variable rates of global warming (Kosaka & Xie, 2016)

The changing shape of Northern Hemisphere summer temperature distributions (McKinnon et al. 2016)

Future Decreases in Freezing Days Across North America (Rawlins et al. 2016)

Arctic warming, moisture increase and circulation changes observed in the Ny-Ålesund homogenized radiosonde record (Maturilli & Kayser, 2016)

Trend analysis of air temperature time series in Greece and their relationship with circulation using surface and satellite data: recent trends and an update to 2013 (Feidas, 2016)

Urban Heat Island traverses in the City of Adelaide, South Australia (Clay et al. 2016)

Recent Extreme Arctic Temperatures are due to a Split Polar Vortex (Overland & Wang, 2016)

Potential tropical Atlantic impacts on Pacific decadal climate trends (Chikamoto et al. 2016)

Consistent land surface temperature data generation from irregularly spaced Landsat imagery (Fu & Weng, 2016)

Spatial and temporal variation in daily temperature indices in summer and winter seasons over India (1969–2012) (Kumar et al. 2016)

Spatial patterns of recent Antarctic surface temperature trends and the importance of natural variability: lessons from multiple reconstructions and the CMIP5 models (Smith & Polvani, 2016)

From Urban to National Heat Island: the effect of anthropogenic heat output on climate change in high population industrial countries (Murray & Heggie, 2016)

From accelerated warming to warming hiatus in China (Xie, Huang & Liu, 2016)

Weekly cycles in peak time temperatures and urban heat island intensity (Earl, Simmonds & Tapper, 2016)

Radiative and Dynamical Influences on Polar Stratospheric Temperature Trends (Ivy, Solomon & Rieder, 2016)

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Papers on ice sheet collapse

Posted by Ari Jokimäki on February 3, 2016

This is a list of papers on ice sheet collapse. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations – Ritz et al. (2015)
Abstract: Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.
Citation: Catherine Ritz, Tamsin L. Edwards, Gaël Durand, Antony J. Payne, Vincent Peyaud, Richard C. A. Hindmarsh, Nature 528, 115–118 (03 December 2015) doi:10.1038/nature16147.

Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica – Joughin et al. (2014)
Abstract: Resting atop a deep marine basin, the West Antarctic Ice Sheet has long been considered prone to instability. Using a numerical model, we investigated the sensitivity of Thwaites Glacier to ocean melt and whether its unstable retreat is already under way. Our model reproduces observed losses when forced with ocean melt comparable to estimates. Simulated losses are moderate (1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.
Citation: Ian Joughin, Benjamin E. Smith, Brooke Medley, Science 16 May 2014: Vol. 344, Issue 6185, pp. 735-738, DOI: 10.1126/science.1249055.

Where might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records? – Bradley et al. (2012) [FULL TEXT]
Abstract: Abundant indirect evidence suggests that the West Antarctic Ice Sheet (WAIS) reduced in size during the Last Interglacial (LIG) compared to the Holocene. This study explores this possibility by comparing, for the first time, ice core stable isotope records for the LIG with output from a glacio-isostatic adjustment (GIA) model. The results show that ice core records from East Antarctica are remarkably insensitive to vertical movement of the solid land motion driven by a simulated hypothetical collapse of the WAIS. However, new and so far unexplored sites are identified which are sensitive to the isostatic signal associated with WAIS collapse and so ice core proxy data from these sites would be effective in testing this hypothesis further.
Citation: S.L. Bradley, M. Siddall, G.A. Milne, V. Masson-Delmotte, E. Wolff, Global and Planetary Change, Volumes 88–89, May 2012, Pages 64–75, doi: 10.1016/j.gloplacha.2012.03.004.

Stability of the West Antarctic ice sheet in a warming world – Joughin & Alley (2011) [FULL TEXT]
Abstract: Ice sheets are expected to shrink in size as the world warms, which in turn will raise sea level. The West Antarctic ice sheet is of particular concern, because it was probably much smaller at times during the past million years when temperatures were comparable to levels that might be reached or exceeded within the next few centuries. Much of the grounded ice in West Antarctica lies on a bed that deepens inland and extends well below sea level. Oceanic and atmospheric warming threaten to reduce or eliminate the floating ice shelves that buttress the ice sheet at present. Loss of the ice shelves would accelerate the flow of non-floating ice near the coast. Because of the slope of the sea bed, the consequent thinning could ultimately float much of the ice sheet’s interior. In this scenario, global sea level would rise by more than three metres, at an unknown rate. Simplified analyses suggest that much of the ice sheet will survive beyond this century. We do not know how likely or inevitable eventual collapse of the West Antarctic ice sheet is at this stage, but the possibility cannot be discarded. For confident projections of the fate of the ice sheet and the rate of any collapse, further work including the development of well-validated physical models will be required.
Citation: Ian Joughin, Richard B. Alley, Nature Geoscience 4, 506–513 (2011) doi:10.1038/ngeo1194.

A new projection of sea level change in response to collapse of marine sectors of the Antarctic Ice Sheet – Gomez et al. (2010) [FULL TEXT]
Abstract: We present gravitationally self-consistent predictions of sea level change that would follow the disappearance of either the West Antarctic Ice Sheet (WAIS) or marine sectors of the East Antarctic Ice Sheet (EAIS). Our predictions are based on a state-of-the-art pseudo-spectral sea level algorithm that incorporates deformational, gravitational and rotational effects on sea level, as well as the migration of shorelines due to both local sea-level variations and changes in the extent of marine-based ice cover. If we define the effective eustatic value (EEV) as the geographically uniform rise in sea level once all marine-based sectors have been filled with water, then we find that some locations can experience a sea level rise that is ∼40 per cent higher than the EEV. This enhancement is due to the migration of water away from the zone of melting in response to the loss of gravitational attraction towards the ice sheet (load self-attraction), the expulsion of water from marine areas as these regions rebound due to the unloading, and the feedback into sea level of a contemporaneous perturbation in Earth rotation. In the WAIS case, this peak enhancement is twice the value predicted in a previous projection that did not include expulsion of water from exposed marine-sectors of the West Antarctic or rotational feedback. The peak enhancements occur over the coasts of the United States and in the Indian Ocean in the WAIS melt scenario, and over the south Atlantic and northwest Pacific in the EAIS scenario. We conclude that accurate projections of the sea level hazard associated with ongoing global warming should be based on a theory that includes the complete suite of physical processes described above.
Citation: Natalya Gomez, Jerry X. Mitrovica, Mark E. Tamisiea, Peter U. Clark, Geophys. J. Int. (2010) 180(2):623-634. doi: 10.1111/j.1365-246X.2009.04419.x.

Record of a Mid-Pleistocene depositional anomaly in West Antarctic continental margin sediments: an indicator for ice-sheet collapse? – Hillenbrand & Frederichs (2009)
Abstract: Modern global warming is likely to cause future melting of Earth’s polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5–6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial–interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424–374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial–interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15–MIS 13 (621–478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15–MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15–MIS 13. Some of these anomalies are observed in the pelagic Southern Ocean and the South Atlantic and might originate in major ice-sheet drawdown in Antarctica, but further research is required to test this hypothesis.
Citation: C.-D. Hillenbrand, G. Kuhn, T. Frederichs, Quaternary Science Reviews, Volume 28, Issues 13–14, June 2009, Pages 1147–1159, doi: 10.1016/j.quascirev.2008.12.010.

Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet – Bamber et al. (2009) [FULL TEXT]
Abstract: Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. We reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution. We obtain a value for the global, eustatic sea-level rise contribution of about 3.3 meters, with important regional variations. The maximum increase is concentrated along the Pacific and Atlantic seaboard of the United States, where the value is about 25% greater than the global mean, even for the case of a partial collapse.
Citation: Jonathan L. Bamber, Riccardo E. M. Riva, Bert L. A. Vermeersen, Anne M. LeBrocq, Science 15 May 2009: Vol. 324, Issue 5929, pp. 901-903, DOI: 10.1126/science.1169335.

The Sea-Level Fingerprint of West Antarctic Collapse – Mitrovica et al. (2009) [FULL TEXT]
Abstract: Recent projections of sea-level rise after a future collapse of theWest Antarctic Ice Sheet (for example, the Fourth Intergovernmental Panel on Climate Change Assessment Report) assume that meltwater will spread uniformly (that is, eustatically) across the oceans once marine-based sectors of the West Antarctic are filled. A largely neglected 1977 study predicted that peak values would be 20% higher than the eustatic in the North Pacific and 5 to 10% higher along the U.S. coastline. We show, with use of a state-of-the-art theory, that the sea-level rise in excess of the eustatic value will be two to three times higher than previously predicted for U.S. coastal sites.
Citation: Jerry X. Mitrovica, Natalya Gomez, Peter U. Clark, Science 06 Feb 2009: Vol. 323, Issue 5915, pp. 753, DOI: 10.1126/science.1166510.

Modelling West Antarctic ice sheet growth and collapse through the past five million years – Pollard & DeConto (2009) [FULL TEXT]
Abstract: The West Antarctic ice sheet (WAIS), with ice volume equivalent to ~5 m of sea level, has long been considered capable of past and future catastrophic collapse. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around ~15 kyr ago before retreating to near-modern locations by ~3 kyr ago. Prior collapses during the warmth of the early Pliocene epoch9 and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments. Until now, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31 (approx1.07 Myr ago) and other super-interglacials.
Citation: David Pollard, Robert M. DeConto, Nature 458, 329-332 (19 March 2009) | doi:10.1038/nature07809.

West Antarctic Ice Sheet collapse – the fall and rise of a paradigm – Vaughan (2008) [FULL TEXT]
Abstract: It is now almost 30 years since John Mercer (1978) first presented the idea that climate change could eventually cause a rapid deglaciation, or “collapse,” of a large part of the West Antarctic ice sheet (WAIS), raising world sea levels by 5 m and causing untold economic and social impacts. This idea, apparently simple and scientifically plausible, created a vision of the future, sufficiently alarming that it became a paradigm for a generation of researchers and provided an icon for the green movement. Through the 1990s, however, a lack of observational evidence for ongoing retreat in WAIS and improved understanding of the complex dynamics of ice streams meant that estimates of likelihood of collapse seemed to be diminishing. In the last few years, however, satellite studies over the relatively inaccessible Amundsen Sea sector of West Antarctica have shown clear evidence of ice sheet retreat showing all the features that might have been predicted for emergent collapse. These studies are re-invigorating the paradigm, albeit in a modified form, and debate about the future stability of WAIS. Since much of WAIS appears to be unchanging, it may, no longer be reasonable to suggest there is an imminent threat of a 5-m rise in sea level resulting from complete collapse of the West Antarctic ice sheet, but there is strong evidence that the Amundsen Sea embayment is changing rapidly. This area alone, contains the potential to raise sea level by around ~1.5 m, but more importantly it seems likely that it could, alter rapidly enough, to make a significant addition to the rate of sea-level rise over coming two centuries. Furthermore, a plausible connection between contemporary climate change and the fate of the ice sheet appears to be developing. The return of the paradigm presents a dilemma for policy-makers, and establishes a renewed set of priorities for the glaciological community. In particular, we must establish whether the hypothesized instability in WAIS is real, or simply an oversimplification resulting from inadequate understanding of the feedbacks that allow ice sheets to achieve equilibrium: and whether there is any likelihood that contemporary climate change could initiate collapse.
Citation: David G. Vaughan, Climatic Change, November 2008, Volume 91, Issue 1, pp 65-79, DOI: 10.1007/s10584-008-9448-3.

Glacier Surge After Ice Shelf Collapse – De Angelis & Skvarca (2003) [FULL TEXT]
Abstract: The possibility that the West Antarctic Ice Sheet will collapse as a consequence of ice shelf disintegration has been debated for many years. This matter is of concern because such an event would imply a sudden increase in sea level. Evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the Larsen Ice Shelf on the Antarctic Peninsula before its collapse in 1995. Satellite images and airborne surveys allowed unambiguous identification of active surging phases of Boydell, Sjögren, Edgeworth, Bombardier, and Drygalski glaciers. This discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves.
Citation: Hernán De Angelis, Pedro Skvarca, Science 07 Mar 2003: Vol. 299, Issue 5612, pp. 1560-1562, DOI: 10.1126/science.1077987.

Risk Estimation of Collapse of the West Antarctic Ice Sheet – Vaughan & Spouge (2002) [FULL TEXT]
Abstract: Complete collapse of the West Antarctic Ice Sheet (WAIS) would raise global sea level by around 5 m, but whether collapse is likely, or even possible, has been `glaciology’s grand unsolved problem’ for more than two decades. Collapse of WAIS may result from readjustments continuing since the last glacial maximum, or more recent climate change, but it is also possible that collapse will result from internal flow instabilities, or not occur at all in the present inter-glacial. Such complexity led the Intergovernmental Panel on Climate Change to conclude in its Second Assessment Report that `estimating the likelihood of a collapse during the next century is not yet possible’. However, a refusal by scientists to estimate the risk leaves policy-makers with no sound scientific basis on which to respond to legitimate public concerns. Here we present a discussion of the likelihood of WAIS-collapse, drawing input from an interdisciplinary panel of experts. The results help to summarise the state of scientific knowledge and uncertainty. While the overall opinion of the panel was that WAIS most likely will not collapse in the next few centuries, their uncertainty retains a 5% probability of WAIS causing sea level rise at least 10 mm/year within 200 years. Since this uncertainty reflects both the unpredictability of the physical system and the scientific uncertainty, it will undoubtedly change as a better understanding is established.
Citation: David G. Vaughan, John R. Spouge, Climatic Change, January 2002, Volume 52, Issue 1, pp 65-91, DOI: 10.1023/A:1013038920600.

No evidence for a Pleistocene collapse of the West Antarctic Ice Sheet from continental margin sediments recovered in the Amundsen Sea – Hillenbrand et al. (2002)
Abstract: Records of glaciomarine deposition recovered from the West Antarctic continental margin in the Amundsen Sea allow the reconstruction of the behaviour of the West Antarctic Ice Sheet (WAIS) in response to the natural climatic changes of the last 1.8 million years. Contents of gravel-sized and lithogenic components represent the input and redeposition of glaciogenic debris, whereas variations in the proportions of the calcareous sediment fraction reflect palaeoproductivity changes. All proxies, which are regarded as sensitive to a WAIS collapse, changed markedly during the global climatic cycles, but do not confirm a complete disintegration of the WAIS during the Pleistocene.
Citation: Claus-Dieter Hillenbrand, Dieter K. Fütterer, Hannes Grobe, Thomas Frederichs, Geo-Marine Letters, July 2002, Volume 22, Issue 2, pp 51-59, DOI: 10.1007/s00367-002-0097-7.

Pleistocene Collapse of the West Antarctic Ice Sheet – Scherer et al. (1998)
Abstract: Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 108 atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 106 atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.
Citation: Reed P. Scherer, Ala Aldahan, Slawek Tulaczyk, Göran Possnert, Hermann Engelhardt, Barclay Kamb, Science 03 Jul 1998: Vol. 281, Issue 5373, pp. 82-85, DOI: 10.1126/science.281.5373.82.

Active volcanism beneath the West Antarctic ice sheet and implications for ice-sheet stability – Blankenship et al. (1993)
Abstract: IT is widely understood that the collapse of the West Antarctic ice sheet (WAIS) would cause a global sea level rise of 6 m, yet there continues to be considerable debate about the detailed response of this ice sheet to climate changel–3. Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the ice sheet could increase basal melting and thereby trigger ice streaming, by providing the water for a lubricating basal layer of till on which ice streams are thought to slide4,5. Ice streams act to protect the reservoir of slowly moving inland ice from exposure to oceanic degradation, thus enhancing ice-sheet stability. Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where ice streaming begins. If this heat flow is indeed controlling ice-stream formation, then penetration of ocean waters inland of the thin hot crust of the active portion of the West Antarctic rift system could lead to the disappearance of ice streams, and possibly trigger a collapse of the inland ice reservoir.
Citation: Donald D. Blankenship, Robin E. Bell, Steven M. Hodge, John M. Brozena, John C. Behrendt, Carol A. Finn, Nature 361, 526 – 529 (11 February 1993); doi:10.1038/361526a0.

Irregular oscillations of the West Antarctic ice sheet – Macayeal (1992) [FULL TEXT]
Abstract: Model simulations of the West Antarctic ice sheet suggest that sporadic, perhaps chaotic, collapse (complete mobilization) of the ice sheet occurred throughout the past one million years. The irregular behaviour is due to the slow equilibration time of the distribution of basal till, which lubricates ice-sheet motion. This nonlinear response means that predictions of future collapse of the ice sheet in response to global warming must take into account its past history, and in particular whether the present basal till distribution predisposes the ice sheet towards rapid change.
Citation: Douglas R. MacAyeal, Nature 359, 29 – 32 (03 September 1992); doi:10.1038/359029a0.

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Papers on early 20th century warming

Posted by Ari Jokimäki on August 29, 2013

This is a list of papers on early 20th century warming. List contains both observational and theoretical studies. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (April 15, 2015): Thompson et al. (2015) added.
UPDATE (April 8, 2014): Suo et al. (2013), Kelly et al. (1980), Petterssen (1949), Ahlmann (1948) added.

Early twentieth-century warming linked to tropical Pacific wind strength – Thompson et al. (2015)
“Of the rise in global atmospheric temperature over the past century, nearly 30% occurred between 1910 and 1940 when anthropogenic forcings were relatively weak. This early warming has been attributed to internal factors, such as natural climate variability in the Atlantic region, and external factors, such as solar variability and greenhouse gas emissions. However, the warming is too large to be explained by external factors alone and it precedes Atlantic warming by over a decade. For the late twentieth century, observations and climate model simulations suggest that Pacific trade winds can modulate global temperatures, but instrumental data are scarce in the early twentieth century. Here we present a westerly wind reconstruction (1894–1982) from seasonally resolved measurements of Mn/Ca ratios in a western Pacific coral that tracks interannual to multidecadal Pacific climate variability. We then reconstruct central Pacific temperatures using Sr/Ca ratios in a coral from Jarvis Island, and find that weak trade winds and warm temperatures coincide with rapid global warming from 1910 to 1940. In contrast, winds are stronger and temperatures cooler between 1940 and 1970, when global temperature rise slowed down. We suggest that variations in Pacific wind strength at decadal timescales significantly influence the rate of surface air temperature change.”
Diane M. Thompson, Julia E. Cole, Glen T. Shen, Alexander W. Tudhope & Gerald A. Meehl, Nature Geoscience 8, 117–121 (2015) doi:10.1038/ngeo2321.

External forcing of the early 20th century Arctic warming – Suo et al. (2013) “The observed Arctic warming during the early 20th century was comparable to present-day warming in terms of magnitude. The causes and mechanisms for the early 20th century Arctic warming are less clear and need to be better understood when considering projections of future climate change in the Arctic. The simulations using the Bergen Climate Model (BCM) can reproduce the surface air temperature (SAT) fluctuations in the Arctic during the 20th century reasonably well. The results presented here, based on the model simulations and observations, indicate that intensified solar radiation and a lull in volcanic activity during the 1920s–1950s can explain much of the early 20th century Arctic warming. The anthropogenic forcing could play a role in getting the timing of the peak warming correct. According to the model the local solar irradiation changes play a crucial role in driving the Arctic early 20th century warming. The SAT co-varied closely with local solar irradiation changes when natural external forcings are included in the model either alone or in combination with anthropogenic external forcings. The increased Barents Sea warm inflow and the anomalous atmosphere circulation patterns in the northern Europe and north Atlantic can also contribute to the warming. In summary, the early 20th century warming was largely externally forced.” Lingling Suo, Odd Helge Otterå, Mats Bentsen, Yongqi Gao, Ola M. Johannessen, Tellus A 2013, 65, 20578, [Full text]

Early 20th century warming in the Arctic: A review – Yamanouchi (2011) “From the 1920s to the 1940s, the Artic experienced significant warming that is comparable to the recent 30-year warming. The former warming was concentrated mostly in high latitudes, in contrast to the recent 30-year warming, which has occurred in all latitudes. Several explanations have been proposed; however, one of these proposed explanations, single external forcing, which could once explain the global average, failed to explain the early 20th century scenario. A second possible explanation was internal atmospheric variability with low frequency. Another candidate for the explanation was still forcing by black carbon deposited on snow and ice surfaces. The answer is most likely to be a combination of intrinsic internal natural climate variability and positive feedbacks that amplified the radiative and atmospheric forcing. We must continue our study by discovering historical data, analyzing ice cores, reanalyzing the Arctic system together with long-term reanalysis dating back to the 1880s, and also determine the contributions of each factor.” Takashi Yamanouchi, Polar Science, Volume 5, Issue 1, April 2011, Pages 53–71,

Early 20th century Arctic warming in retrospect – Wood & Overland (2010) “The major early 20th century climatic fluctuation (∼1920–1940) has been the subject of scientific enquiry from the time it was detected in the 1920s. The papers of scientists who studied the event first-hand have faded into obscurity but their insights are relevant today. We review this event through a rediscovery of early research and new assessments of the instrumental record. Much of the inter-annual to decadal scale variability in surface air temperature (SAT) anomaly patterns and related ecosystem effects in the Arctic and elsewhere can be attributed to the superposition of leading modes of variability in the atmospheric circulation. Meridional circulation patterns were an important factor in the high latitudes of the North Atlantic during the early climatic fluctuation. Sea surface temperature (SST) anomalies that appeared during this period were congruent with low-frequency variability in the climate system but were themselves most likely the result of anomalous forcing by the atmosphere. The high-resolution data necessary to verify this hypothesis are lacking, but the consistency of multiple lines of evidence provides strong support. Our findings indicate that early climatic fluctuation is best interpreted as a large but random climate excursion imposed on top of the steadily rising global mean temperature associated with anthropogenic forcing.” Kevin R. Wood, James E. Overland, International Journal of Climatology, Volume 30, Issue 9, pages 1269–1279, July 2010, DOI: 10.1002/joc.1973.

Influence of volcanic activity and changes in solar irradiance on surface air temperatures in the early twentieth century – Shiogama et al. (2006) “Causes of the global surface air temperature warming in the early half of the 20th century are examined using a climate model and an optimal detection/attribution methodology. While the anthropogenic response seems to be underestimated in our model, our previous study detected the influence due to natural external forcing, including the combined effects of solar irradiance changes and the recovery from large volcanic activity. We further partition the responses between these two natural external factors, detecting both the solar and the volcanic signal in the observed early warming. A diagnosis of the sensitivity to solar forcing and a volcanic super-eruption simulation suggest that our model possesses larger climate sensitivities to solar forcing and longer relaxation times to volcanic forcing than HadCM3, enabling us to detect both the solar and volcanic forcing responses.” Hideo Shiogama, Tatsuya Nagashima, Tokuta Yokohata, Simon A. Crooks, Toru Nozawa, Geophysical Research Letters, Volume 33, Issue 9, May 2006, DOI: 10.1029/2005GL025622.

Detecting natural influence on surface air temperature change in the early twentieth century – Nozawa et al. (2005) “We analyze surface air temperature datasets simulated by a coupled climate model forced with different external forcings, to diagnose the relative importance of these forcings to the observed warming in the early 20th century. The geographical distribution of linear temperature trends in the simulations forced only by natural contributions (volcanic eruptions and solar variability) shows better agreement with observed trends than that does the simulations forced only by well-mixed greenhouse gases. Using an optimal fingerprinting technique we robustly detect a significant natural contribution to the early 20th century warming. In addition, the amplitude of our simulated natural signal is consistent with the observations. Over the same period, however, we could not detect a greenhouse gas signal in the observed surface temperature in the presence of the external natural forcings. Hence our analysis suggests that external natural factors caused more warming in the early 20th century than anthropogenic factors.” Toru Nozawa, Tatsuya Nagashima, Hideo Shiogama, Simon A. Crooks, Geophysical Research Letters, Volume 32, Issue 20, October 2005, DOI: 10.1029/2005GL023540. [Full text]

The Early Twentieth-Century Warming in the Arctic—A Possible Mechanism – Bengtsson et al. (2004) “The huge warming of the Arctic that started in the early 1920s and lasted for almost two decades is one of the most spectacular climate events of the twentieth century. During the peak period 1930–40, the annually averaged temperature anomaly for the area 60°–90°N amounted to some 1.7°C. Whether this event is an example of an internal climate mode or is externally forced, such as by enhanced solar effects, is presently under debate. This study suggests that natural variability is a likely cause, with reduced sea ice cover being crucial for the warming. A robust sea ice–air temperature relationship was demonstrated by a set of four simulations with the atmospheric ECHAM model forced with observed SST and sea ice concentrations. An analysis of the spatial characteristics of the observed early twentieth-century surface air temperature anomaly revealed that it was associated with similar sea ice variations. Further investigation of the variability of Arctic surface temperature and sea ice cover was performed by analyzing data from a coupled ocean–atmosphere model. By analyzing climate anomalies in the model that are similar to those that occurred in the early twentieth century, it was found that the simulated temperature increase in the Arctic was related to enhanced wind-driven oceanic inflow into the Barents Sea with an associated sea ice retreat. The magnitude of the inflow is linked to the strength of westerlies into the Barents Sea. This study proposes a mechanism sustaining the enhanced westerly winds by a cyclonic atmospheric circulation in the Barents Sea region created by a strong surface heat flux over the ice-free areas. Observational data suggest a similar series of events during the early twentieth-century Arctic warming, including increasing westerly winds between Spitsbergen and Norway, reduced sea ice, and enhanced cyclonic circulation over the Barents Sea. At the same time, the North Atlantic Oscillation was weakening.” Bengtsson, Lennart, Vladimir A. Semenov, Ola M. Johannessen, 2004: The Early Twentieth-Century Warming in the Arctic—A Possible Mechanism. J. Climate, 17, 4045–4057. doi:;2. [Full text]

Solar and Greenhouse Gas Forcing and Climate Response in the Twentieth Century – Meehl et al. (2003) “Ensemble experiments with a global coupled climate model are performed for the twentieth century with time-evolving solar, greenhouse gas, sulfate aerosol (direct effect), and ozone (tropospheric and stratospheric) forcing. Observed global warming in the twentieth century occurred in two periods, one in the early twentieth century from about the early 1900s to the 1940s, and one later in the century from, roughly, the late 1960s to the end of the century. The model’s response requires the combination of solar and anthropogenic forcing to approximate the early twentieth-century warming, while the radiative forcing from increasing greenhouse gases is dominant for the response in the late twentieth century, confirming previous studies. Of particular interest here is the model’s amplification of solar forcing when this acts in combination with anthropogenic forcing. This difference is traced to the fact that solar forcing is more spatially heterogeneous (i.e., acting most strongly in areas where sunlight reaches the surface) while greenhouse gas forcing is more spatially uniform. Consequently, solar forcing is subject to coupled regional feedbacks involving the combination of temperature gradients, circulation regimes, and clouds. The magnitude of these feedbacks depends on the climate’s base state. Over relatively cloud-free oceanic regions in the subtropics, the enhanced solar forcing produces greater evaporation. More moisture then converges into the precipitation convergence zones, intensifying the regional monsoon and Hadley and Walker circulations, causing cloud reductions over the subtropical ocean regions, and, hence, more solar input. An additional response to solar forcing in northern summer is an enhancement of the meridional temperature gradients due to greater solar forcing over land regions that contribute to stronger West African and South Asian monsoons. Since the greenhouse gases are more spatially uniform, such regional circulation feedbacks are not as strong. These regional responses are most evident when the solar forcing occurs in concert with increased greenhouse gas forcing. The net effect of enhanced solar forcing in the early twentieth century is to produce larger solar-induced increases of tropical precipitation when calculated as a residual than for early century solar-only forcing, even though the size of the imposed solar forcing is the same. As a consequence, overall precipitation increases in the early twentieth century in the Asian monsoon regions are greater than late century increases, qualitatively consistent with observed trends in all-India rainfall. Similar effects occur in West Africa, the tropical Pacific, and the Southern Ocean tropical convergence zones.” Meehl, Gerald A., Warren M. Washington, T. M. L. Wigley, Julie M. Arblaster, Aiguo Dai, 2003: Solar and Greenhouse Gas Forcing and Climate Response in the Twentieth Century. J. Climate, 16, 426–444. doi:;2. [Full text]

Estimation of natural and anthropogenic contributions to twentieth century temperature change – Tett et al. (2002) “Using a coupled atmosphere/ocean general circulation model, we have simulated the climatic response to natural and anthropogenic forcings from 1860 to 1997. The model, HadCM3, requires no flux adjustment and has an interactive sulphur cycle, a simple parameterization of the effect of aerosols on cloud albedo (first indirect effect), and a radiation scheme that allows explicit representation of well-mixed greenhouse gases. Simulations were carried out in which the model was forced with changes in natural forcings (solar irradiance and stratospheric aerosol due to explosive volcanic eruptions), well-mixed greenhouse gases alone, tropospheric anthropogenic forcings (tropospheric ozone, well-mixed greenhouse gases, and the direct and first indirect effects of sulphate aerosol), and anthropogenic forcings (tropospheric anthropogenic forcings and stratospheric ozone decline). Using an “optimal detection” methodology to examine temperature changes near the surface and throughout the free atmosphere, we find that we can detect the effects of changes in well-mixed greenhouse gases, other anthropogenic forcings (mainly the effects of sulphate aerosols on cloud albedo), and natural forcings. Thus these have all had a significant impact on temperature. We estimate the linear trend in global mean near-surface temperature from well-mixed greenhouse gases to be 0.9 ± 0.24 K/century, offset by cooling from other anthropogenic forcings of 0.4 ± 0.26 K/century, giving a total anthropogenic warming trend of 0.5 ± 0.15 K/century. Over the entire century, natural forcings give a linear trend close to zero. We found no evidence that simulated changes in near-surface temperature due to anthropogenic forcings were in error. However, the simulated tropospheric response, since the 1960s, is ∼50% too large. Our analysis suggests that the early twentieth century warming can best be explained by a combination of warming due to increases in greenhouse gases and natural forcing, some cooling due to other anthropogenic forcings, and a substantial, but not implausible, contribution from internal variability. In the second half of the century we find that the warming is largely caused by changes in greenhouse gases, with changes in sulphates and, perhaps, volcanic aerosol offsetting approximately one third of the warming. Warming in the troposphere, since the 1960s, is probably mainly due to anthropogenic forcings, with a negligible contribution from natural forcings.” Simon F. B. Tett, Gareth S. Jones, Peter A. Stott, David C. Hill, John F. B. Mitchell, Myles R. Allen, William J. Ingram, Tim C. Johns, Colin E. Johnson, Andy Jones, David L. Roberts, David M. H. Sexton, Margaret J. Woodage, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 107, Issue D16, pages ACL 10-1–ACL 10-24, 27 August 2002, DOI: 10.1029/2000JD000028. [Full text]

Simulation of Early 20th Century Global Warming – Delworth & Knutson (2000) “The observed global warming of the past century occurred primarily in two distinct 20-year periods, from 1925 to 1944 and from 1978 to the present. Although the latter warming is often attributed to a human-induced increase of greenhouse gases, causes of the earlier warming are less clear because this period precedes the time of strongest increases in human-induced greenhouse gas (radiative) forcing. Results from a set of six integrations of a coupled ocean-atmosphere climate model suggest that the warming of the early 20th century could have resulted from a combination of human-induced radiative forcing and an unusually large realization of internal multidecadal variability of the coupled ocean-atmosphere system. This conclusion is dependent on the model’s climate sensitivity, internal variability, and the specification of the time-varying human-induced radiative forcing.” Thomas L. Delworth, Thomas R. Knutson, Science 24 March 2000: Vol. 287 no. 5461 pp. 2246-2250, DOI: 10.1126/science.287.5461.2246.

Changes in atmospheric circulation over northern hemisphere oceans associated with the rapid warming of the 1920s – Fu et al. (1999)
Global mean surface temperature has increased since the late 19th century. The warming occurred largely during two periods: 1920–1940, and since the mid-1970s. Although most recent studies have focused on the latter period, it is of interest to analyse the earlier period and compare its major features to the recent warming episode. The warming during 1920–1940 occurred most rapidly during the 1920s. It was strongest at high northern latitudes in winter, a pattern now believed to be characteristic of ‘greenhouse warming’. This warming of the Arctic was much discussed during the 1930s and 1940s, but the data available at that time were mostly derived from land areas. In this paper, we use the COADS marine data set and recent compilations of land surface temperature data sets to examine the behaviour of the surface fields over the ocean during this event. Considering the thermal and atmospheric fields at the surface, the strongest signal occurs in the North Atlantic Ocean during winter, being distinct but more gradual in the other oceans and seasons. The Northern Hemisphere continental record shows that both middle and high latitudes experienced rapid warming in the early 20th century warming interval (the 1920s and 1930s, hereafter referred to as ETCW). Temperature data for northern tropics, while displaying similar general characteristics, exhibit some differences with regard to timing and rates of change. There is a suggestion of weakening of the westerlies and the trade wind system in the 1930s, following an intensification of the westerlies across the North Atlantic during the previous two decades. This weakening may be related to a lessening of atmospheric baroclinicity in association with the fact that the amplitude of warming at high latitudes was much greater than that in low latitudes, reducing the mean meridional thermal gradient, and therefore the geostrophic pressure gradient. There is some indication that the North Atlantic and North Pacific high-pressure systems shifted northward. Coincident with this northward shift of the subtropical highs, typhoons in the Northwest Pacific and hurricanes in the North Atlantic became more numerous in this period of rising temperature, which we suggest is linked to a northward shift of the respective near-equatorial convergence zones. Concomitant to the weakening of the westerlies and trade wind systems, the Asian monsoon troughs deepened substantially, a situation generally favourable to the development of active monsoons. It is thought that the combination of these two features—enhanced continental monsoons and implied lowered vertical wind shear over the oceans—would tend to enhance the release of latent heat in the tropics, representing strengthened Hadley and Walker circulations, which may have been at least partly responsible for greater aridity in subtropical land areas of both hemispheres during this period. The latter is also consistent with an expansion and/or strengthening of the subtropical high-pressure belt into the continents.” Congbin Fu, Henry F. Diaz, Dongfeng Dong, Joseph O. Fletcher, International Journal of Climatology, Volume 19, Issue 6, pages 581–606, May 1999, DOI: 10.1002/(SICI)1097-0088(199905)19:63.0.CO;2-P.

Solar Forcing of Global Climate Change Since The Mid-17th Century – Reid et al. (1997) “Spacecraft measurements of the sun’s total irradiance since 1980 have revealed a long-term variation that is roughly in phase with the 11-year solar cycle. Its origin is uncertain, but may be related to the overall level of solar magnetic activity as well as to the concurrent activity on the visible disk. A low-pass Gaussian filtered time series of the annual sunspot number has been developed as a suitable proxy for solar magnetic activity that contains a long-term component related to the average level of activity as well as a short-term component related to the current phase of the 11-year cycle. This time series is also assumed to be a proxy for solar total irradiance, and the irradiance is reconstructed for the period since 1617 based on the estimate from climatic evidence that global temperatures during the Maunder Minimum of solar activity, which coincided with one of the coldest periods of the Little Ice Age, were about 1 °C colder than modern temperatures. This irradiance variation is used as the variable radiative forcing function in a one-dimensional ocean–climate model, leading to a reconstruction of global temperatures over the same period, and to a suggestion that solar forcing and anthropogenic greenhouse-gas forcing made roughly equal contributions to the rise in global temperature that took place between 1900 and 1955. The importance of solar variability as a factor in climate change over the last few decades may have been underestimated in recent studies.” George C. Reid, Climatic Change, October 1997, Volume 37, Issue 2, pp 391-405, DOI: 10.1023/A:1005307009726.

Changes in Global Surface Temperature From 1880 to 1977 Derived From Historical Records of Sea Surface Temperature – Paltridge & Woodruff (1981) “A preliminary analysis based primarily on historical records of sea surface temperature (SST) gives estimates of the change since 1880 of global, hemispheric and zonal average surface temperatures. The global change with time is roughly similar in shape and magnitude to that derived by Mitchell from land station data alone, but lags the Mitchell curve by 10-20 years. That is, the present data show a minimumof temperature somewhere between 1900 and 1925 and a maximum somewhere between 1945 and 1970. Comparing the means of these 25-year periods, the rise from minimum to maximum was (roughly) 0.6 K for the Northern Hemisphere and 0.9 K for the Southern Hemisphere. Comparing the means of the 50 years before 1930 and the 48 years from 1930 to 1977, the rise was 0.3 K for the Northern Hemisphere and 0.6 K for the Southern Hemisphere. The figures do not take into account the polar regions which, on linear extrapolation from lower latitudes, may have risen in temperature by twice the hemispheric averages. The temperature of the tropical zone (l0°N-10°S) has not changed over the years, so that the meridionaltemperature gradient has decreased in both hemispheres. The detail of the various conclusions may be revised later in the light of further analysis of the errors associated with the SST data sets. This furtheranalysis is underway at the Environmental Research Laboratories of NOAA.” Paltridge, G., S. Woodruff, 1981: Changes in Global Surface Temperature From 1880 to 1977 Derived From Historical Records of Sea Surface Temperature. Mon. Wea. Rev., 109, 2427–2434. doi:;2. [Full text]

Variations in Surface Air Temperatures: Part 2. Arctic Regions, 1881–1980 – Kelly et al. (1980) “We describe annual and seasonal changes in air temperatures over high latitudes of the Northern Hemisphere during the period 1881–1980. Trends (that is, fluctuations on time scales greater than 20 years) in the average temperature of the Arctic are compared with those of the Northern Hemisphere. Seasonal and regional departures from the long-term trends in the average temperature of the Arctic are identified. Spatial patterns of variation in the Arctic temperature field are determined by principal component analysis and the major characteristics of the time series of the dominant patterns are summarized. Trends in Arctic temperatures have been broadly similar to those for the Northern Hemisphere during the study period. The Arctic variations were, however, greater in magnitude and more rapid. The spatial pattern of change associated with the trend in Arctic temperatures is clearly identified by principal component analysis. It shows that the trends have, in general, been Arctic-wide, but that certain regions are particularly sensitive to long-term variations, most notably northwest Greenland and around the Kara Sea. There is some evidence that the pattern of Arctic cooling that occurred after 1940 was more complex than the warming that affected the whole Arctic during the 1920’s and 1930’s. Warming of the Arctic has occurred during the 1970’s, but is not yet of sufficient duration to be considered long term, except, perhaps, in spring. The average temperature of the Arctic during the 1970’s was equal to that of the 1960’s, indicating a cessation of the long-term cooling trend but not, as yet, a shift to long-term warming. Short-term variations in temperature appear to be most pronounced close to major regions of sea-ice production and decay.” Kelly, P. M., P. D. Jones, C. B. Sear, B. S. G. Cherry, R. K. Tavakol, 1982: Variations in Surface Air Temperatures: Part 2. Arctic Regions, 1881–1980. Mon. Wea. Rev., 110, 71–83. doi:;2. [Full text]

Temperature fluctuations and trends over the earth – Callendar (1961) “The annual temperature deviations at over 400 meteorological stations are combined on a regional basis to give the integrated fluctuations over large areas and zones. These are shown in graphical form, and it is concluded that a solar or atmospheric dust hypothesis is necessary to explain the world-wide fluctuations of a few years duration. An important change in the relationships of the zonal fluctuations has occurred since 1920. The overall temperature trends found from the data are considered in relation to the homogeneity of recording, and also to the evidence of glacial recession in different zones. It is concluded that the rising trend, shown by the instruments during recent decades, is significant from the Arctic to about 45°S lat., but quite small in most regions below 35°N. and not yet apparent in some. It is thought that the regional and zonal distribution of recent climatic trends is incompatible with the hypothesis of increased solar heating as the cause. On the other hand, the major features of this distribution are not incompatible with the hypothesis of increased carbon dioxide radiation, if the rate of atmospheric mixing between the hemispheres is a matter of decades rather than years.” G. S. Callendar, Quarterly Journal of the Royal Meteorological Society, Volume 87, Issue 371, pages 1–12, January 1961, DOI: 10.1002/qj.49708737102.

Changes in the General Circulation Associated with the Recent Climatic Variation – Petterssen (1949) No abstract. S. Petterssen, Geografiska Annaler, Vol. 31, Glaciers and Climate: Geophysical and Geomorphological Essays (1949), pp. 212-221.

The Present Climatic Fluctuation – Ahlmann (1948) No abstract. Hans W:Son Ahlmann, The Geographical Journal, Vol. 112, No. 4/6 (Oct. – Dec., 1948), pp. 165-193.

The artificial production of carbon dioxide and its influence on temperature – Callendar (1938) “By fuel combustion man has added about 150,000 million tons of carbon dioxide to the air during the past half century. The author estimates from the best available data that approximately three quarters of this has remained in the atmosphere. The radiation absorption coefficients of carbon dioxide and water vapour are used to show the effect of carbon dioxide on “sky radiation.” From this the increase in mean temperature, due to the artificial production of carbon dioxide, is estimated to be at the rate of 0.003°C. per year at the present time. The temperature observations at 200 meteorological stations are used to show that world temperatures have actually increased at an average rate of 0.005°C. per year during the past half century.” G. S. Callendar, Quarterly Journal of the Royal Meteorological Society, Volume 64, Issue 275, pages 223–240, April 1938, DOI: 10.1002/qj.49706427503. [Full text]

Posted in AGW evidence, Climate claims, Climate science | 3 Comments »

Global warming has not stopped

Posted by Ari Jokimäki on August 19, 2013

The apparent lack of warming in Earth’s surface temperature measurements since 1998 is not yet significant from climatic perspective. Surface temperature also seems to be changing according to IPCC projections. Climate model simulations show similar warming breaks, and have done so even before current break started, even if they include the effect of carbon dioxide. Models also can re-create the current break and the cause for the break seems to be known: warming has gone to the oceans instead of warming the surface. The ocean warming has been observed. Also the continuing warming effect of greenhouse gases has been observed. Global warming as a whole seems to continue despite the apparent break in surface measurements.

Several decades of long-term warming is evident in recent surface temperature measurements. However, since 1998 surface temperature records don’t show clear warming. This is not very clear because the time period is not very long and the possible trends might not be statistically significant. Skeptical Science trend calculator shows warming trends since 1998 but they are not statistically significant. Santer and others (2011) estimated that it takes 17 years of satellite measurements, before effect of mankind to lower atmosphere can be detected. In some cases, 15 years has been mentioned for the limit of statistical significance, so the situation seems to be quite borderline. For example, from 1983 and 1998, which was time of rapid warming, SkS trend calculator still shows a trend that is not statistically significant. From 1982 to 1998 trend is significant. (Even if statistically enough time would pass without warming, it still wouldn’t mean that increases in greenhouse gases wouldn’t have a warming effect. This we will see below in more detail.)

Climate is usually considered as average weather over longer period of time. Standard length for the climatic time period is 30 years. Let us see what this means for the surface temperature. Following figure shows Earth’s surface temperature as a running 30 year mean (this means that the value of each point in the graph is the average of the surrounding 30 years of temperature values, for example, the running 30 year mean value for year 1990 is the average of temperatures of 30 years between 1975 and 2004):


As we can see from the graph, there are no signs of global warming stopping or even slowing down in this kind of inspection. From climatic perspective global warming still continues. Those with sharp eyes notice that the time shown in X axis stops in the graph before 2000. This is because in 30 year running mean the year 1998 is currently last one that can be shown. However, the temperature evolution after 1998 is included and is affecting the graph starting from 1983. The fact that graph stops at 1998 means that we have to wait 15 years before we know how climate has evolved since 1998.

Although global surface temperature evolution since 1998 is not yet climatically important, there has been quite a lot of research on the issue. One question appearing in public has been that does the temperature follow earlier projections. Rahmstorf and others (2012) have analyzed how IPCC projections match the surface temperature measurements. Here is a graph of their results:

The evolution of Earth’s surface temperature and IPCC projections. Surface temperature without corrections is shown in pink (one year running mean averaged from all surface temperature analyses) and corrected surface temperature is shown in red (corrections are explained in text). Blue area and blue lines are IPCC third assessment report projections. Green area and green lines are IPCC fourth assessment report (AR4) projections.

As we can see from the graph, surface temperature changes shown in pink sometimes go outside the projections. This is because some factors are not included in IPCC projections. Such factors are solar activity changes and eruptions of volcanoes. Additionally, the variation of El Niño/La Niña is random and therefore it doesn’t change in simulations at the same time it does in real life. IPCC projections are combined results from many simulations, so the El Niño/La Niña variations of different simulations tend to cancel out when simulation results are combined. This means that the projections don’t actually include El Niño/La Niña variation either. It should be noted that even if surface temperature shown in pink doesn’t stay within limits of projections, it does stay within limits of all individual simulations (not shown in the Figure above).

The effects of the Sun, volcanoes, and El Niño/La Niña variation have been corrected for in the temperature evolution shown in red. This graph stays quite well within limits of projections especially during last few years. It sometimes goes outside the projections in the beginning of the time period. There still might be some factors which would need to be corrected for. On the average it does seem to follow the projections even in the beginning of the time period (at least it doesn’t deviate permanently to one direction).

Already happened temperature evolution can be recreated with models also so that internal variability of climate system and changes in solar activity and in volcanoes are included (afterwards we have knowledge for example when a volcanic eruption has happened). Lean & Rind (2009) have done this and the following Figure shows their results:

a) The observed surface temperature (black) and simulation of surface temperature from a simple model (orange). b) The factors affecting surface temperature. Graphs are from Lean & Rind (2009).

The result of the simple model shown in the graph is so close to observed surface temperature evolution that we have good reason to suspect this study might be able to answer us why surface temperature has not apparently increased since 1998. Lower part of the Figure shows the factors affecting surface temperature, and from there we can see that ENSO (that is, the variation of El Niño and La Niña) seems to have varied in quite a similar manner than surface temperature in the period in question. Also the cause of the longer-term temperature rise seems to be clear: the effect of mankind is the only one of the factors, which shows long-term increase.

Also the future projections of climate models show periods where surface temperature doesn’t increase, even if models have the effect of greenhouse gases included. Here are some examples of such simulations:

Projections of climate models show periods of slowed/paused warming similar to that in the observations since 1998. On the left: simulations with three different emission scenarios from IPCC AR4. Upper right: simulation example from Easterling & Wehner (2009). Lower right: simulation example from Meehl and others (2011).

All shown simulation examples show periods where long-term warming trend is paused even for decades, and warming continues after that. The Figure also shows simulation examples from model runs for IPCC AR4 projections. These show similar pauses. AR4 discusses the expected temperature evolution rather carelessly. From the texts of the report one might get an impression that surface temperature should rise certain amount in each decade. They of course mean that on average certain rise in temperature is expected per decade, even if it doesn’t occur during each decade. Some people have used the carelessly worded texts in IPCC AR4 to distort the issue, even when the same report shows the simulations presented above, where the truth in the matter can be seen.

Simulation examples shown above are all quite recent. Model simulations have shown similar features also earlier. Here we see an example from IPCC second assessment report (SAR), which was published in 1995, before current warming pause apparently started:

Model simulations from IPCC second assessment report. Year 0 means year 1990.

One interesting detail in the SAR model simulations is that one of them shows strong spike around 1995. This is comparable to the 1998 peak in observed temperatures. Even if the post-1995 evolution is difficult to see in the graph, we can be sure that the simulation in question shows quite long pause in the warming after 1995. In principle, we could say that the simulation in question predicted the warming pause, albeit being off by few years. It’s not genuine prediction of course, but just a coincidence. Nevertheless, it’s a quite curious detail.

So, the simulations of climate models show clearly that while the increase of greenhouse gases in the atmosphere increases Earth’s surface temperature in the long run, other factors cause pauses to the warming every now and then. Similarly, those other factors also speed up the warming in other times. This has been explicitly stated in Easterling & Wehner (2009): “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”.

At the moment it seems that the factor causing the pause has been ENSO, which in practice means that the warming effect of greenhouse gases has gone deeper to the oceans instead of warming the surface. This has been the subject of some recent studies.

Already shown above were the results of Lean & Rind (2009) and Meehl and others (2011). Similar results have also been reported by Kaufmann and others (2011), Hunt (2011), Guemas and others (2013), and Watanabe and others (2013). According to all these studies, the primary cause for the apparent pause in the surface warming is that the warming has gone to the oceans. Solar activity has also been said to have played some role on the issue. Also, Solomon and others (2010) have suggested that changes in water vapor content in the atmosphere might have speeded up the warming during the 1990’s and slowed the warming during 2000’s.

The warming going into oceans has also been observed. Following Figure shows the ocean heat content in the top layer (0-700 m) of the oceans (from Lyman and others, 2010):


The graph shows that after 1998 the heat content in the oceans has increased substantially.

But when can we expect surface warming to continue? Surface warming continues when the sum of all factors affecting Earth’s surface temperature has a warming effect. It can take decades and decades, as long as there are other factors that have large enough cooling effect to mask the warming effect from greenhouse gases. However, our current knowledge suggests that there are no such factors that could have large enough cooling effect in order to make this pause much longer.

There are reasons to think that warming might continue soon. Earth’s surface temperature has been very high recently, close to record temperatures, while solar activity has been very low and La Niña has been the prevailing state of ENSO. Without the effect of greenhouse gases these factors would have cooled Earth’s surface substantially. We haven’t seen such cooling. When La Niña changes to El Niño, it is expected that warming will continue.

So it seems that the warming effect of greenhouse gases seems to be still there. Fortunately, we don’t need to guess this, as we also have observations of the effect of greenhouse gases, as we see next.

A group of researchers have studied spectral measurements of outgoing long-wave radiation taken from satellites (Chapman and others, 2013). They found out that the warming effect of carbon dioxide has continued to increase during the 2000’s. They calculated from the spectral measurements that between 2002 and 2012 the amount of outgoing long-wave radiation decreased in the characteristic absorption frequencies of greenhouse gases. This was the case at least for carbon dioxide, ozone, and methane. Largest warming effect was from carbon dioxide. Observed decreases in the outgoing long-wave radiation matched the expectation from the increased greenhouse gas concentrations during the study period. Here are their results in a graph:


It should be noted that the study of Chapman and others was presented in a conference in April 2013, and apparently official research paper has not been published yet. Information presented here is from the conference paper.


IPCC second assessment report (over 50 MB PDF file, the graph shown here is on the PDF page 314, page 300 of the report).

IPCC AR4 simulations: Figure 10.5 with caption.

D. Chapman, P. Nguyen, M. Halem, A decade of measured greenhouse forcings from AIRS, Proc. SPIE 8743, Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery XIX, 874313 (May 18, 2013); doi:10.1117/12.2017019. [abstract]

John A. Church, Neil J. White, Leonard F. Konikow, Catia M. Domingues, J. Graham Cogley, Eric Rignot, Jonathan M. Gregory, Michiel R. van den Broeke, Andrew J. Monaghan, Isabella Velicogna, Revisiting the Earth’s sea-level and energy budgets from 1961 to 2008, Geophysical Research Letters, Volume 38, Issue 18, 28 September 2011, DOI: 10.1029/2011GL048794. [abstract, full text]

David R. Easterling, Michael F. Wehner, 2009, Is the climate warming or cooling? Geophysical Research Letters, Volume 36, Issue 8, April 2009, DOI: 10.1029/2009GL037810. [abstract, full text]

Virginie Guemas, Francisco J. Doblas-Reyes, Isabel Andreu-Burillo & Muhammad Asif, Retrospective prediction of the global warming slowdown in the past decade, Nature Climate Change, 3, 649–653 (2013) doi:10.1038/nclimate1863. [abstract]

B. G. Hunt, The role of natural climatic variation in perturbing the observed global mean temperature trend, Climate Dynamics, February 2011, Volume 36, Issue 3-4, pp 509-521, DOI: 10.1007/s00382-010-0799-x. [abstract]

Robert K. Kaufmann, Heikki Kauppi, Michael L. Mann, and James H. Stock, Reconciling anthropogenic climate change with observed temperature 1998–2008, PNAS July 19, 2011 vol. 108 no. 29 11790-11793, doi: 10.1073/pnas.1102467108. [abstract, full text]

John M. Lyman, Simon A. Good, Viktor V. Gouretski, Masayoshi Ishii, Gregory C. Johnson, Matthew D. Palmer, Doug M. Smith, & Josh K. Willis, Robust warming of the global upper ocean, Nature 465, 334–337 (20 May 2010) doi:10.1038/nature09043. [abstract, full text]

Gerald A. Meehl, Julie M. Arblaster, John T. Fasullo, Aixue Hu & Kevin E. Trenberth, 2011, Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods, Nature Climate Change, 1, 360–364 (2011) doi:10.1038/nclimate1229. [abstract, full text]

Stefan Rahmstorf et al 2012, Comparing climate projections to observations up to 2011, Environ. Res. Lett. 7 044035 doi:10.1088/1748-9326/7/4/044035. [abstract, full text]

B. D. Santer, C. Mears, C. Doutriaux, P. Caldwell, P. J. Gleckler, T. M. L. Wigley, S. Solomon, N. P. Gillett, D. Ivanova, T. R. Karl, J. R. Lanzante, G. A. Meehl, P. A. Stott, K. E. Taylor, P. W. Thorne, M. F. Wehner, F. J. Wentz, 2011, Separating signal and noise in atmospheric temperature changes: The importance of timescale, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 116, Issue D22, November 2011, DOI: 10.1029/2011JD016263. [abstract, full text]

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