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Global warming hiatus claims prebunked in 1980s and 1990s

Posted by Ari Jokimäki on January 17, 2017

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

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

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

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

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

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

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

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

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

And on the global warming moratorium:

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

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

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

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

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

Oceans and surface temperature studies in 1980s

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

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

Gaffin et al. (1986) got similar results:

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

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

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

The global warming moratorium discussion of early 1990s

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

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

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

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

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

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

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

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

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

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

And:

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

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

The significance for current hiatus discussion

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

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

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

References:

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

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

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

J. Hansen, D. Johnson, A. Lacis, S. Lebedeff, P. Lee, D. Rind, G. Russell (1981) Climate Impact of Increasing Atmospheric Carbon Dioxide, Science 28 Aug 1981: Vol. 213, Issue 4511, pp. 957-966, DOI: 10.1126/science.213.4511.957.
http://science.sciencemag.org/content/213/4511/957
http://people.oregonstate.edu/~schmita2/Teaching/ATS421-521/2015/papers/hansen81sci.pdf

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

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

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

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

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

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

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

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

Wigley, T.M.L., Angell, J.K. and Jones, P.D., 1985. Analysis of the temperature record. In: M.C. MacCracken and F.M. Luther (Eds.), Detecting the Climatic Effects of Increasing Carbon Dioxide, (DOE/ER-0235), U.S. Department of Energy, Carbon Dioxide Research Division, Washington, D.C., 55-90.
http://archives.aaas.org/docs/Detecting_Climate_Effects_Increasing_CO2.pdf

Posted in AGW evidence, Climate claims, Climate science | Leave a Comment »

New research – temperature (October 18, 2016)

Posted by Ari Jokimäki on October 18, 2016

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

Highlights

Comparing tropospheric warming in climate models and satellite data (Santer et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0333.1

Abstract: We use updated and improved satellite retrievals of the temperature of the mid- to upper troposphere (TMT) to address key questions about the size and significance of TMT trends, agreement with model-derived TMT values, and whether models and satellite data show similar vertical profiles of warming. A recent study claimed that TMT trends over 1979 and 2015 are three times larger in climate models than in satellite data, but did not correct for the contribution TMT trends receive from stratospheric cooling. Here we show that the average ratio of modeled and observed TMT trends is sensitive to both satellite data uncertainties and to model-data differences in stratospheric cooling. When the impact of lower stratospheric cooling on TMT is accounted for, and when the most recent versions of satellite datasets are used, the previously claimed ratio of three between simulated and observed near-global TMT trends is reduced to ≈ 1.7. Next, we assess the validity of the statement that satellite data show no significant tropospheric warming over the last 18 years. This claim is not supported by our analysis: in five out of six corrected satellite TMT records, significant global-scale tropospheric warming has occurred within the last 18 years. Finally, we address long-standing concerns regarding discrepancies in modeled and observed vertical profiles of warming in the tropical atmosphere. We show that amplification of tropical warming between the lower and mid- to upper troposphere is now in close agreement in the average of 37 climate models and in one updated satellite record.

Deep and Abyssal Ocean Warming from 35 years of Repeat Hydrography (Desbruyères et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070413/abstract

Abstract: Global and regional ocean warming deeper than 2000 m is investigated using 35 years of sustained repeat hydrographic survey data starting in 1981. The global long-term temperature trend below 2000 m, representing the time period 1991–2010, is equivalent to a mean heat flux of 0.065 ± 0.040 W m−2 applied over the Earth’s surface area. The strongest warming rates are found in the abyssal layer (4000–6000 m), which contributes to one third of the total heat uptake with the largest contribution from the Southern and Pacific Oceans. A similar regional pattern is found in the deep layer (2000–4000 m), which explains the remaining two thirds of the total heat uptake yet with larger uncertainties. The global average warming rate did not change within uncertainties pre-2000 versus post-2000, whereas ocean average warming rates decreased in the Pacific and Indian Oceans and increased in the Atlantic and Southern Oceans.

The contribution of greenhouse gases to the recent slowdown in global-mean temperature trends (Checa-Garcia et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/9/094018/meta

Abstract: The recent slowdown in the rate of increase in global-mean surface temperature (GMST) has generated extensive discussion, but little attention has been given to the contribution of time-varying trends in greenhouse gas concentrations. We use a simple model approach to quantify this contribution. Between 1985 and 2003, greenhouse gases (including well-mixed greenhouse gases, tropospheric and stratospheric ozone, and stratospheric water vapour from methane oxidation) caused a reduction in GMST trend of around 0.03–0.05 K decade−1 which is around 18%–25% of the observed trend over that period. The main contributors to this reduction are the rapid change in the growth rates of ozone-depleting gases (with this contribution slightly opposed by stratospheric ozone depletion itself) and the weakening in growth rates of methane and tropospheric ozone radiative forcing. Although CO2 is the dominant greenhouse gas contributor to GMST trends, the continued increase in CO2 concentrations offsets only about 30% of the simulated trend reduction due to these other contributors. These results emphasize that trends in non-CO2 greenhouse gas concentrations can make significant positive and negative contributions to changes in the rate of warming, and that they need to be considered more closely in analyses of the causes of such variations.

The Stancari air thermometer and the 1715–1737 record in Bologna, Italy (Camuffo et al. 2016) http://rd.springer.com/article/10.1007%2Fs10584-016-1797-8

Abstract: This paper is focused on the closed-tube Stancari air thermometer that was developed at the beginning of the eighteenth century as an improvement of the Amontons thermometer, and used to record the temperature in Bologna, Italy, from 1715 to 1737. The problems met with this instrument, its calibration and the building technology in the eighteenth century are discussed in order to correct the record. The used methodological approach constitutes a useful example for other early series. The analysis of this record shows that the temperature in Bologna was not different from the 1961–1990 reference period. This result is in line with the contemporary record taken in Padua, Italy, confirming that this period of the Little Ice Age was not cold in the Mediterranean area.

Twenty-five winters of unexpected Eurasian cooling unlikely due to Arctic sea-ice loss (McCusker et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2820.html

Abstract: Surface air temperature over central Eurasia decreased over the past twenty-five winters at a time of strongly increasing anthropogenic forcing and Arctic amplification. It has been suggested that this cooling was related to an increase in cold winters due to sea-ice loss in the Barents–Kara Sea. Here we use over 600 years of atmosphere-only global climate model simulations to isolate the effect of Arctic sea-ice loss, complemented with a 50-member ensemble of atmosphere–ocean global climate model simulations allowing for external forcing changes (anthropogenic and natural) and internal variability. In our atmosphere-only simulations, we find no evidence of Arctic sea-ice loss having impacted Eurasian surface temperature. In our atmosphere–ocean simulations, we find just one simulation with Eurasian cooling of the observed magnitude but Arctic sea-ice loss was not involved, either directly or indirectly. Rather, in this simulation the cooling is due to a persistent circulation pattern combining high pressure over the Barents–Kara Sea and a downstream trough. We conclude that the observed cooling over central Eurasia was probably due to a sea-ice-independent internally generated circulation pattern ensconced over, and nearby, the Barents–Kara Sea since the 1980s. These results improve our knowledge of high-latitude climate variability and change, with implications for our understanding of impacts in high-northern-latitude systems.

Other papers

New method of estimating temperatures near the mesopause region using meteor radar observations (Lee et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL071082/abstract

Estimated influence of urbanization on surface warming in Eastern China using time-varying land use data (Liao et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4908/abstract

The influence of winter and summer atmospheric circulation on the variability of temperature and sea ice around Greenland (Ogi et al. 2016) http://www.tellusa.net/index.php/tellusa/article/view/31971

A cold and fresh ocean surface in the Nordic Seas during MIS 11: Significance for the future ocean (Kandiano et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070294/abstract

Observed and projected sea surface temperature seasonal changes in the Western English Channel from satellite data and CMIP5 multi-model ensemble (L’Hévéder et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4882/abstract

Historical ocean reanalyses (1900–2010) using different data assimilation strategies (Yang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/qj.2936/abstract

Analysis of the warmest Arctic winter, 2015-2016 (Cullather et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL071228/abstract

The influence of synoptic circulations and local processes on temperature anomalies at three French observatories (Dione et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JAMC-D-16-0113.1

Ocean atmosphere thermal decoupling in the eastern equatorial Indian ocean (Joseph et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3359-1

Changes of the time-varying percentiles of daily extreme temperature in China (Li et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1938-z

High atmospheric horizontal resolution eliminates the wind-driven coastal warm bias in the southeastern tropical Atlantic (Milinski et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070530/abstract

Effects of Natural Variability of Seawater Temperature, Time Series Length, Decadal Trend and Instrument Precision on the Ability to Detect Temperature Trends (Schlegel & Smit, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0014.1

Interhemispheric SST gradient trends in the Indian Ocean prior to and during the recent global warming hiatus (Dong & McPhaden, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0130.1

Temperature and precipitation extremes in century-long gridded observations, reanalyses, and atmospheric model simulations (Donat et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025480/abstract

Atmospheric structure favoring high sea surface temperatures in the western equatorial Pacific (Wirasatriya et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025268/abstract

Spatial and temporal changes in daily temperature extremes in China during 1960–2011 (Shen et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1934-3

Disaggregation of Remotely Sensed Land Surface Temperature: A New Dynamic Methodology (Zhan et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD024891/abstract

Impact of high-resolution sea surface temperature and urban data on estimations of surface air temperature in a regional climate (Adachi et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD024961/abstract

Trends of urban surface temperature and heat island characteristics in the Mediterranean (Benas et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1905-8

Impacts of urbanization on summer climate in China: An assessment with coupled land-atmospheric modeling (Cao et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025210/abstract

The impact of climatic and non-climatic factors on land surface temperature in southwestern Romania (Roşca et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1923-6

Posted in Climate claims, Climate science | Leave a Comment »

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.

Highlights

The Effects of Ocean Heat Uptake on Transient Climate Sensitivity (Rose & Rayborn, 2016) http://rd.springer.com/article/10.1007%2Fs40641-016-0048-4

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) http://rd.springer.com/article/10.1007%2Fs40641-016-0047-5

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069917/abstract

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) http://link.springer.com/article/10.1007%2Fs00382-015-2909-2

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025341/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070907/abstract

Understanding the varied influence of mid-latitude jet position on clouds and cloud-radiative effects in observations and global climate models (Grise & Medeiros, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0295.1

Effect of land cover change on snow free surface albedo across the continental United States (Wickham et al. 2016) http://www.sciencedirect.com/science/article/pii/S0921818116302892

Forced response and internal variability of summer climate over western North America (Kamae et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3350-x

Detection and attribution of climate change at regional scale: case study of Karkheh river basin in the west of Iran (Zohrabi et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1896-5

Atmospheric lifetimes, infrared absorption spectra, radiative forcings and global warming potentials of NF3 and CF3CF2Cl (CFC-115) (Totterdill et al. 2016) http://www.atmos-chem-phys.net/16/11451/2016/

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) http://www.atmos-chem-phys.net/16/11301/2016/

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) http://www.atmos-chem-phys.net/16/11145/2016/

Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic (Leaitch et al. 2016) http://www.atmos-chem-phys.net/16/11107/2016/

Assessment of the first indirect radiative effect of ammonium-sulfate-nitrate aerosols in East Asia (Han et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1913-8

Sensitivity of precipitation extremes to radiative forcing of greenhouse gases and aerosols (Lin et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070869/abstract

Global climate forcing of aerosols embodied in international trade (Lin et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2798.html

Reprocessing of HIRS Satellite Measurements from 1980-2015: Development Towards a Consistent Decadal Cloud Record (Menzel et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JAMC-D-16-0129.1

Radiative Forcing from Anthropogenic Sulfur and Organic Emissions Reaching the Stratosphere (Yu et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070153/abstract

Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution (Archer, 2016) http://rd.springer.com/article/10.1007%2Fs10584-016-1725-y

Long-Term Variations of Noctilucent Clouds at ALOMAR (Fiedler et al. 2016) http://www.sciencedirect.com/science/article/pii/S1364682616302024

Estimating Arctic sea-ice shortwave albedo from MODIS data (Qu et al. 2016) http://www.sciencedirect.com/science/article/pii/S0034425716303182

Surface albedo raise in the South American Chaco: Combined effects of deforestation and agricultural changes (Houspanossian et al. 2016) http://www.sciencedirect.com/science/article/pii/S0168192316303707

New Observational Evidence for a Positive Cloud Feedback that Amplifies the Atlantic Multidecadal Oscillation (Bellomo et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069961/abstract

Surface water and heat exchange comparison between alpine meadow and bare land in a permafrost region of the Tibetan Plateau (You et al. 2016) http://www.sciencedirect.com/science/article/pii/S0168192316303598

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) http://www.sciencedirect.com/science/article/pii/S1364682616301894

Comparison of Methods: Attributing the 2014 record European temperatures to human influences (Uhe et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069568/abstract

Relevance of long term time – series of atmospheric parameters at a mountain observatory to models for climate change (Kancírová et al. 2016) http://www.sciencedirect.com/science/article/pii/S1364682616301882

An energy balance perspective on regional CO2-induced temperature changes in CMIP5 models (Räisänen, 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3277-2

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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.

Highlights

Observed and simulated full-depth ocean heat-content changes for 1970–2005 (Cheng et al. 2016) http://www.ocean-sci.net/12/925/2016/

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069401/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025359/abstract

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) http://rd.springer.com/article/10.1007%2Fs10584-016-1760-8

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JC012089/abstract

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) http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-16-0092.1

First ground-based observations of mesopause temperatures above the Eastern-Mediterranean Part I: Multi-day oscillations and tides (Silber et al. 2016) http://www.sciencedirect.com/science/article/pii/S1364682616302206

An enhanced single-channel algorithm for retrieving land surface temperature from Landsat series data (Wang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025270/abstract

Observed changes of temperature extremes in Serbia over the period 1961 − 2010 (Ruml et al. 2016) http://www.sciencedirect.com/science/article/pii/S016980951630254X

The inter-annual variations and the long-term trends of monthly air temperatures in Iraq over the period 1941–2013 (Muslih & Błażejczyk, 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1915-6

A multiregion model evaluation and attribution study of historical changes in the area affected by temperature and precipitation extremes (Dittus et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0164.1

Changes in wind speed under heat waves enhance urban heat islands in Beijing metropolitan area (Li et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JAMC-D-16-0102.1

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) http://www.sciencedirect.com/science/article/pii/S0169809516302319

Confidence intervals for time averages in the presence of long range correlations, a case study on earth surface temperature anomalies (Massah & Kantz, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069555/abstract

An ensemble of ocean reanalyses for 1815–2013 with sparse observational input (Giese et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JC012079/abstract

Arctic-North Pacific coupled impacts on the late autumn cold in North America (Sung et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/8/084016/meta

Wet-bulb, dew point, and air temperature trends in Spain (Moratiel et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1891-x

Insights into elevation-dependent warming in the Tibetan Plateau-Himalayas from CMIP5 model simulations (Palazzi et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3316-z

Spatial variations in temperature in a mountainous region of Jeju Island, South Korea (Um & Kim, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4854/abstract

Gap filling and homogenization of climatological datasets in the headwater region of the Upper Blue Nile Basin, Ethiopia (Woldesenbet et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4839/abstract

A homogenized long-term temperature record for the Western Cape Province in South Africa: 1916–2013 (Lakhraj-Govender et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4849/abstract

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) http://link.springer.com/article/10.1007%2Fs00382-016-3303-4

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) http://onlinelibrary.wiley.com/doi/10.1002/joc.4835/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025231/abstract

Recent seasonal and long-term changes in southern Australian frost occurrence (Crimp et al. 2016) http://rd.springer.com/article/10.1007%2Fs10584-016-1763-5

Surface temperature trends from homogenized time series in South Africa: 1931–2015 (Kruger & Nxumalo, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4851/abstract

Investigations of the middle atmospheric thermal structure and oscillations over sub-tropical regions in the Northern and Southern Hemispheres (Sharma et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3293-2

Recent amplification of the North American winter temperature dipole (Singh et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025116/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025497/abstract

Spatial distribution of temperature trends and extremes over Maharashtra and Karnataka States of India (Dhorde et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1876-9

Assessing atmospheric temperature data sets for climate studies (Cederlöf et al. 2016) http://www.tellusa.net/index.php/tellusa/article/view/31503

Ocean heat uptake and interbasin transport of passive and redistributive surface heating (Garuba & Klinger, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0138.1

Temperature and precipitation regional climate series over the central Pyrenees during 1910–2013 (Pérez-Zanón et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4823/abstract

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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.

Highlights

CMIP5 scientific gaps and recommendations for CMIP6 (Stouffer et al. 2016)http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-15-00013.1

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) http://rd.springer.com/article/10.1007%2Fs00382-016-3186-4

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) http://link.springer.com/article/10.1007%2Fs00382-016-3262-9

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069803/abstract

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) http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-15-00135.1

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025285/abstract

Twentieth century temperature trends in CMIP3, CMIP5, and CESM-LE climate simulations – spatial-temporal uncertainties, differences and their potential sources (Kumar et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JD024382/abstract

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) http://www.sciencedirect.com/science/article/pii/S0169809516302058

The influence of model resolution on temperature variability (Klavans et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3249-6

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) http://link.springer.com/article/10.1007%2Fs00382-016-3286-1

Assessing uncertainties in land cover projections (Alexander et al. 2016) http://onlinelibrary.wiley.com/doi/10.1111/gcb.13447/abstract

Effects of southeastern Pacific sea surface temperature on the double-ITCZ bias in NCAR CESM1 (Song & Zhang, 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0852.1

Stochastic Parameterization: Towards a new view of Weather and Climate Models (Berner et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-15-00268.1

Do convection-permitting regional climate models improve projections of future precipitation change? (Kendon et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-15-0004.1

MiKlip – a National Research Project on Decadal Climate Prediction (Marotzke et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-15-00184.1

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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.

Highlights

Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006 (McNorton et al. 2016) http://www.atmos-chem-phys.net/16/7943/2016/

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) http://iopscience.iop.org/article/10.1088/1748-9326/11/6/064017/meta

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070201/abstract

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) http://www.atmos-chem-phys.net/16/8125/2016/

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)
http://www.biogeosciences.net/13/4237/2016/

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) http://www.atmos-chem-phys.net/16/9935/2016/

Evaluation of 4 years of continuous δ13C(CO2) data using a moving Keeling plot method (Vardag, Hammer & Levin, 2016) http://www.biogeosciences.net/13/4237/2016/

Intra-seasonal variability of atmospheric CO2 concentrations over India during summer monsoons (Kumar et al. 2016) http://www.sciencedirect.com/science/article/pii/S1352231016305428

Impact of ENSO on variability of AIRS retrieved CO2 over India (Kumar et al. 2016) http://www.sciencedirect.com/science/article/pii/S1352231016305209

Large XCH4 anomaly in summer 2013 over northeast Asia observed by GOSAT (Ishizawa et al. 2016) http://www.atmos-chem-phys.net/16/9149/2016/

Can we detect regional methane anomalies? A comparison between three observing systems (Cressot et al. 2016) http://www.atmos-chem-phys.net/16/9089/2016/

Non-homogeneous vertical distribution of methane over Indian region using surface, aircraft and satellite based data (Kavitha & Nair, 2016) http://www.sciencedirect.com/science/article/pii/S1352231016305015

A probabilistic study of the return of stratospheric ozone to 1960 levels (Södergren et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069700/abstract

The representation of solar cycle signals in stratospheric ozone – Part 1: A comparison of recently updated satellite observations (Maycock et al. 2016) http://www.atmos-chem-phys.net/16/10021/2016/

Summer ozone concentrations in the vicinity of the Great Salt Lake (Horel et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/asl.680/abstract

Impact of emissions and +2 °C climate change upon future ozone and nitrogen dioxide over Europe (Watson et al. 2016) http://www.sciencedirect.com/science/article/pii/S1352231016305714

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) http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-15-0308.1

Aerosol Lidar Observations of Atmospheric Mixing in Los Angeles: Climatology and Implications for Greenhouse Gas Observations (Ware et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD024953/abstract

Future aerosol emissions: a multi-model comparison (Smith et al. 2016) http://rd.springer.com/article/10.1007%2Fs10584-016-1733-y

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025273/abstract

Effects of climate changes on dust aerosol over East Asia from RegCM3 (Zhang et al. 2016) http://www.sciencedirect.com/science/article/pii/S1674927816300053

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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.

Highlights

The North Atlantic Oscillation as a driver of rapid climate change in the Northern Hemisphere (Delworth et al. 2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2738.html

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) http://link.springer.com/article/10.1007%2Fs00382-016-3250-0

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069789/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069725/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070373/abstract

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) http://rd.springer.com/article/10.1007%2Fs00382-016-3283-4

Gridded, monthly rainfall and temperature climatology for El Niño Southern Oscillation impacts in the United States (Dourte et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4820/abstract

Southern European rainfall reshapes the early-summer circumglobal teleconnection after the late 1970s (Lin et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3306-1

Moisture and heat budgets of the south American monsoon system: climatological aspects (Garcia et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1882-y

The Relative Influence of ENSO and SAM on Antarctic Peninsula Climate (Clem et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025305/abstract

Sinuosity of mid-latitude atmospheric flow in a warming world (Cattiaux et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070309/abstract

ENSO response to high-latitude volcanic eruptions in the Northern Hemisphere: The role of the initial conditions (Pausata et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069575/abstract

Remote influence of Interdecadal Pacific Oscillation on the South Atlantic Meridional Overturning Circulation variability (Lopez et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069067/abstract

Robust response of the Amundsen Sea Low to stratospheric ozone depletion (England et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070055/abstract

The response of winter Pacific North American pattern to strong volcanic eruptions (Liu et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3287-0

Atlantic Multidecadal Variability in a model with an improved North Atlantic Current (Drews & Greatbatch, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069815/abstract

Sub-decadal North Atlantic Oscillation variability in observations and the Kiel Climate Model (Reintges, Latif & Park, 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3279-0

Is there a robust effect of anthropogenic aerosols on the Southern Annular Mode? (Steptoe et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JD024218/abstract

Climate Signals in the Mid- to High-Latitude North Atlantic from Altimeter Observations (Li et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00670.1

Intensification and poleward shift of subtropical western boundary currents in a warming climate (Yang et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JC011513/abstract

Inter-basin effects of the Indian Ocean on Pacific decadal climate change (Mochizuki et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069940/abstract

The influence of boreal spring Arctic Oscillation on the subsequent winter ENSO in CMIP5 models (Chen et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3243-z

Relationship between North American winter temperature and large-scale atmospheric circulation anomalies and its decadal variation (Yu et al. 2016) http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074001/meta

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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.

Highlights

The Spectral Signature of Recent Climate Change (Brindley & Bantges, 2016) http://link.springer.com/article/10.1007%2Fs40641-016-0039-5

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL069243/abstract

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) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0339.1

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) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0799.1

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) http://onlinelibrary.wiley.com/doi/10.1002/2016GL070428/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025233/abstract

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0799.1

Which way will the circulation shift in a changing climate? Possible nonlinearity of extratropical cloud feedbacks (Tandon & Cane, 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3301-6

Regional and global temperature response to anthropogenic SO2 emissions from China in three climate models (Kasoar et al. 2016) http://www.atmos-chem-phys.net/16/9785/2016/

Effective radiative forcing from historical land use change (Andrews et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3280-7

Reassessing properties and radiative forcing of contrail cirrus using a climate model (Bock & Burkhardt, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025112/abstract

Could the Pliocene constrain the equilibrium climate sensitivity? (Hargreaves & Annan, 2016) http://www.clim-past.net/12/1591/2016/

Influence of snow cover changes on surface radiation and heat balance based on the WRF model (Yu et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1856-0

A sensitivity study of the impact of dynamic vegetation on simulated future climate change over Southern Europe and the Mediterranean (Alo & Anagnostou, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4833/abstract

A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region (Saud et al. 2016) http://www.sciencedirect.com/science/article/pii/S0169809516301983

Separating climate change signals into thermodynamic, lapse-rate and circulation effects: theory and application to the European summer climate (Kröner et al. 2016) http://rd.springer.com/article/10.1007%2Fs00382-016-3276-3

Early global radiation measurements: a review (Stanhill & Archiman, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4826/abstract

Aerosol types and radiative forcing estimates over East Asia (Bhawar et al. 2016) http://www.sciencedirect.com/science/article/pii/S1352231016305489

Solar irradiance observed at Summit, Greenland: Possible links to magnetic activity on short timescales (Frederick, 2016) http://www.sciencedirect.com/science/article/pii/S1364682616301626

Limits to global and Australian temperature change this century based on expert judgment of climate sensitivity (Grose et al. 2016) http://link.springer.com/article/10.1007%2Fs00382-016-3269-2

Indirect Forcing of Black carbon on Clouds over North East India (Panicker et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/qj.2878/abstract

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra (Juszak et al. 2016) http://www.biogeosciences.net/13/4049/2016/

Aerosol radiative effects under clear skies over Europe and their changes in the period of 2001–2012 (Bartók, 2016) http://onlinelibrary.wiley.com/doi/10.1002/joc.4821/abstract

Review of Aerosol-Cloud Interactions: Mechanisms, Significance and Challenges (Fan et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-16-0037.1

Inference of Climate Sensitivity from Analysis of Earth’s Energy Budget (Forster, 2016) http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105156

Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations (Lee et al. 2016) http://rd.springer.com/article/10.1007%2Fs00704-016-1860-4

Spatiotemporal characteristics of ultraviolet radiation in recent 54 years from measurements and reconstructions over the Tibetan Plateau (Liu et al. 2016) http://onlinelibrary.wiley.com/doi/10.1002/2015JD024378/abstract

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) http://onlinelibrary.wiley.com/doi/10.1002/2016JD024890/abstract

Strong modification of stratospheric ozone forcing by cloud and sea-ice adjustments (Xia et al. 2016) http://www.atmos-chem-phys.net/16/7559/2016/

Evaluation of the Arctic surface radiation budget in CMIP5 models (Boeke & Taylor, 2016) http://onlinelibrary.wiley.com/doi/10.1002/2016JD025099/abstract

Climate Feedback Variance and the Interaction of Aerosol Forcing and Feedbacks (Gettelman et al. 2016) http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0151.1

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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.

Highlights

The rogue nature of hiatuses in a global warming climate (Sévellec, Sinha & Skliris, 2016)
http://onlinelibrary.wiley.com/doi/10.1002/2016GL068950/abstract

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)
http://onlinelibrary.wiley.com/doi/10.1002/joc.4808/abstract

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)
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0123.1

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)
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0179.1

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)
http://link.springer.com/article/10.1007%2Fs10113-016-1006-3

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)
http://onlinelibrary.wiley.com/doi/10.1002/joc.4837/abstract

Reconciling Observed and Modelled Temperature and Precipitation Trends over Europe by Adjusting for Circulation Variability (Saffioti et al. 2016)
http://onlinelibrary.wiley.com/doi/10.1002/2016GL069802/abstract

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)
http://rd.springer.com/article/10.1007%2Fs00704-016-1869-8

Sudden stratospheric warmings observed in the last decade by satellite measurements (Kishore et al. 2016)
http://www.sciencedirect.com/science/article/pii/S0034425716302656

Longitudinal Asymmetric Trends of Tropical Cold-point Tropopause Temperature and Their Link to Strengthened Walker Circulation (Hu et al. 2016)
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0851.1

An in situ-based analysis of the relationship between land surface ‘skin’ and screen-level air temperatures (Good, 2016)
http://onlinelibrary.wiley.com/doi/10.1002/2016JD025318/abstract

Spatiotemporal rainfall and temperature trends throughout the Brazilian Legal Amazon, 1973–2013 (Almeida et al. 2016)
http://onlinelibrary.wiley.com/doi/10.1002/joc.4831/abstract

Spatial variation of deterministic chaos in mean daily temperature and rainfall over Nigeria (Fuwape et al. 2016)
http://rd.springer.com/article/10.1007%2Fs00704-016-1867-x

Homogenisation of temperature and precipitation time series with ACMANT3: method description and efficiency tests (Domonkos & Coll, 2016)
http://onlinelibrary.wiley.com/doi/10.1002/joc.4822/abstract

The tropical Pacific as a key pacemaker of the variable rates of global warming (Kosaka & Xie, 2016)
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2770.html

The changing shape of Northern Hemisphere summer temperature distributions (McKinnon et al. 2016)
http://onlinelibrary.wiley.com/doi/10.1002/2016JD025292/abstract

Future Decreases in Freezing Days Across North America (Rawlins et al. 2016)
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0802.1

Arctic warming, moisture increase and circulation changes observed in the Ny-Ålesund homogenized radiosonde record (Maturilli & Kayser, 2016)
http://rd.springer.com/article/10.1007%2Fs00704-016-1864-0

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)
http://rd.springer.com/article/10.1007%2Fs00704-016-1854-2

Urban Heat Island traverses in the City of Adelaide, South Australia (Clay et al. 2016)
http://www.sciencedirect.com/science/article/pii/S2212095516300293

Recent Extreme Arctic Temperatures are due to a Split Polar Vortex (Overland & Wang, 2016)
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0320.1

Potential tropical Atlantic impacts on Pacific decadal climate trends (Chikamoto et al. 2016)
http://onlinelibrary.wiley.com/doi/10.1002/2016GL069544/abstract

Consistent land surface temperature data generation from irregularly spaced Landsat imagery (Fu & Weng, 2016)
http://www.sciencedirect.com/science/article/pii/S0034425716302565

Spatial and temporal variation in daily temperature indices in summer and winter seasons over India (1969–2012) (Kumar et al. 2016)
http://rd.springer.com/article/10.1007%2Fs00704-016-1844-4

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)
http://rd.springer.com/article/10.1007%2Fs00382-016-3230-4

From Urban to National Heat Island: the effect of anthropogenic heat output on climate change in high population industrial countries (Murray & Heggie, 2016)
http://onlinelibrary.wiley.com/doi/10.1002/2016EF000352/abstract

From accelerated warming to warming hiatus in China (Xie, Huang & Liu, 2016)
http://onlinelibrary.wiley.com/doi/10.1002/joc.4809/abstract

Weekly cycles in peak time temperatures and urban heat island intensity (Earl, Simmonds & Tapper, 2016)
http://iopscience.iop.org/article/10.1088/1748-9326/11/7/074003/meta

Radiative and Dynamical Influences on Polar Stratospheric Temperature Trends (Ivy, Solomon & Rieder, 2016)
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0503.1

Posted in AGW evidence, Climate claims, Climate science | Leave a Comment »

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.

Posted in Climate claims, Climate science, Global warming effects | Leave a Comment »

 
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