AGW Observer

Observations of anthropogenic global warming

New research from last week 50/2010

Posted by Ari Jokimäki on December 20, 2010

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Cloud cover over Australia changed very little since 1957

A high-quality monthly total cloud amount dataset for Australia – Jovanovic et al. (2010) “A high-quality monthly total cloud amount dataset for 165 stations has been developed for monitoring and assessing long-term trends in cloud cover over Australia. The dataset is based on visual 9 a.m. and 3 p.m. observations of total cloud amount, with most records starting around 1957. The quality control process involved examination of historical station metadata, together with an objective statistical test comparing candidate and reference cloud series. Individual cloud series were also compared against rainfall and diurnal temperature range series from the same site, and individual cloud series from neighboring sites. Adjustments for inhomogeneities caused by relocations and changes in observers were applied, as well as adjustments for biases caused by the shift to daylight saving time in the summer months. Analysis of these data reveals that the Australian mean annual total cloud amount is characterised by high year-to-year variability and shows a weak, statistically non-significant increase over the 1957–2007 period. A more pronounced, but also non-significant, decrease from 1977 to 2007 is evident. A strong positive correlation is found between all-Australian averages of cloud amount and rainfall, while a strong negative correlation is found between mean cloud amount and diurnal temperature range. Patterns of annual and seasonal trends in cloud amount are in general agreement with rainfall changes across Australia, however the high-quality cloud network is too coarse to fully capture topographic influences. Nevertheless, the broadscale consistency between patterns of cloud and rainfall variations indicates that the new total cloud amount dataset is able to adequately describe the broadscale patterns of change over Australia. Favourable simple comparisons between surface and satellite measures of cloudiness suggest that satellites may ultimately provide the means for monitoring long-term changes in cloud over Australia. However, due to the relative shortness and homogeneity problems of the satellite record, a robust network of surface cloud observations will be required for many years to come.” Branislava Jovanovic, Dean Collins, Karl Braganza, Doerte Jakob and David A. Jones, Climatic Change, DOI: 10.1007/s10584-010-9992-5. [full text]

Correlation between Arctic sea ice and NH snow cover

On the emergence of an Arctic amplification signal in terrestrial Arctic snow extent – Ghatak et al. (2010) “The impact of declining sea ice in amplifying surface air temperatures (SAT) over the Arctic Ocean is readily visible, and this “Arctic amplification” will become more pronounced as more sea ice is lost in the coming decades. The effect of sea ice loss on atmospheric temperatures and circulation patterns is of utmost significance as these changes will affect the terrestrial climate. Land-surface snow is vulnerable to these changes; hence, we search for any link between changes in Arctic sea ice and Northern Hemisphere snow cover. Analyses of observational data sets suggest that the increasing snow cover over Siberia during fall and early winter is correlated with the decreasing September Arctic sea ice over the Pacific sector. We also examine modeled covariance between sea ice and snow using historical and future simulations of the Community Climate System Model (CCSM3). Results indicate the emergence of a Siberian snow signal during the last half of the 21st century most strongly during late winter. Moreover, CCSM3 future simulations show diminishment of snow at a hemispheric scale outside of the Siberian region, which is correlated with the loss of Arctic sea ice. These results indicate that we may be seeing the first, albeit weak, signs of “Arctic amplification” on the terrestrial Arctic snowpack; that only a weak and therefore inconclusive signal would be expected at this time; and that the signal should strengthen over the coming decades.” Ghatak, D., A. Frei, G. Gong, J. Stroeve, and D. Robinson (2010), On the emergence of an Arctic amplification signal in terrestrial Arctic snow extent, J. Geophys. Res., 115, D24105, doi:10.1029/2010JD014007.

A 1000 year reconstruction of Norwegian sea temperatures

Response of Norwegian Sea temperature to solar forcing since 1000 A.D. – Sejrup et al. (2010) “We report on a 1000 year long oxygen isotope record in sediments of the eastern Norwegian Sea which, we argue, represents the temperature and transport of warm Atlantic waters entering the Nordic Sea basin via the North Atlantic Drift and the large-scale Meridional Overturning Circulation. The single-sample resolution of the record is 2.5–10 years and age control is provided by 210Pb and 137Cs dating, identification of historic tephra, and a 14C “wiggle-match” dating method in which the surface reservoir 14C age in the past is constrained rather than assumed, thereby eliminating a large source of chronological uncertainty. The oxygen isotope results indicate decade- to century-scale temperature variations of 1–2°C in the shallow (∼50 m deep) subsurface which we find to be strongly correlated with various proxies of past solar activity. The correlations are synchronous to within the timescale uncertainties of the ocean and solar proxy records, which vary among the records and in time with a range of about 5–30 years. The observed ocean temperature response is larger than expected based on simple thermodynamic considerations, indicating that there is dynamical response of the high-latitude ocean to the Sun. Correlations of our results with a gridded temperature reconstruction for Europe are greater in central Europe than in coastal regions, suggesting that the temperature and transport of warm Atlantic waters entering the Nordic Basin and the pattern of temperature variability over Europe are both the proximate responses to a change in the atmospheric circulation, consistent with a forced shift in the primary modes of high-latitude atmospheric variability.” Sejrup, H. P., S. J. Lehman, H. Haflidason, D. Noone, R. Muscheler, I. M. Berstad, and J. T. Andrews (2010), Response of Norwegian Sea temperature to solar forcing since 1000 A.D., J. Geophys. Res., 115, C12034, doi:10.1029/2010JC006264.

New interesting article from Lonnie Thompson

Climate Change: The Evidence and Our Options – Thompson (2010) “Glaciers serve as early indicators of climate change. Over the last 35 years, our research team has recovered ice-core records of climatic and environmental variations from the polar regions and from low-latitude high-elevation ice fields from 16 countries. The ongoing widespread melting of high-elevation glaciers and ice caps, particularly in low to middle latitudes, provides some of the strongest evidence to date that a large-scale, pervasive, and, in some cases, rapid change in Earth’s climate system is underway. This paper highlights observations of 20th and 21st century glacier shrinkage in the Andes, the Himalayas, and on Mount Kilimanjaro. Ice cores retrieved from shrinking glaciers around the world confirm their continuous existence for periods ranging from hundreds of years to multiple millennia, suggesting that climatological conditions that dominate those regions today are different from those under which these ice fields originally accumulated and have been sustained. The current warming is therefore unusual when viewed from the millennial perspective provided by multiple lines of proxy evidence and the 160-year record of direct temperature measurements. Despite all this evidence, plus the well-documented continual increase in atmospheric greenhouse gas concentrations, societies have taken little action to address this global-scale problem. Hence, the rate of global carbon dioxide emissions continues to accelerate. As a result of our inaction, we have three options: mitigation, adaptation, and suffering.” Lonnie G. Thompson, The Behavior Analyst, 2010, 33, 153-170, No. 2 (Fall). [full text]

Update of GISS surface temperature analysis

Global surface temperature change – Hansen et al. (2010) “We update the Goddard Institute for Space Studies (GISS) analysis of global surface temperature change, compare alternative analyses, and address questions about perception and reality of global warming. Satellite-observed night lights are used to identify measurement stations located in extreme darkness and adjust temperature trends of urban and periurban stations for nonclimatic factors, verifying that urban effects on analyzed global change are small. Because the GISS analysis combines available sea surface temperature records with meteorological station measurements, we test alternative choices for the ocean data, showing that global temperature change is sensitive to estimated temperature change in polar regions where observations are limited. We use simple 12 month (and n × 12) running means to improve the information content in our temperature graphs. Contrary to a popular misconception, the rate of warming has not declined. Global temperature is rising as fast in the past decade as in the prior 2 decades, despite year-to-year fluctuations associated with the El Niño-La Niña cycle of tropical ocean temperature. Record high global 12 month running mean temperature for the period with instrumental data was reached in 2010.” Hansen, J., R. Ruedy, M. Sato, and K. Lo (2010), GLOBAL SURFACE TEMPERATURE CHANGE, Rev. Geophys., 48, RG4004, doi:10.1029/2010RG000345. [full text]

McShane & Wyner thoroughly debunked

Annals of Applied Statistics made a discussion paper out of recently published McShane & Wyner (2010). Many scientists commented on the paper which got quite thoroughly debunked. Among commenters – for some strange reason – were also McIntyre & McKitrick who, not surprisingly, were completely in agreement with McShane & Wyner. Full papers here (see the bottom of the page).

Global warming effects on southern oscillation

The impact of global warming on the Southern Oscillation Index – Power & Kociuba (2010) “The Southern Oscillation Index (SOI)—a measure of air pressure difference across the Pacific Ocean, from Tahiti in the south-east to Darwin in the west—is one of the world’s most important climatic indices. The SOI is used to track and predict changes in both the El Niño-Southern Oscillation phenomenon, and the Walker Circulation (WC). During El Niño, for example, the WC weakens and the SOI tends to be negative. Climatic variations linked to changes in the WC have a profound influence on climate, ecosystems, agriculture, and societies in many parts of the world. Previous research has shown that (1) the WC and the SOI weakened in recent decades and that (2) the WC in climate models tends to weaken in response to elevated atmospheric greenhouse gas concentrations. Here we examine changes in the SOI and air pressure across the Pacific in the observations and in numerous WCRP/CMIP3 climate model integrations for both the 20th and 21st centuries. The difference in mean-sea level air pressure (MSLP) between the eastern and western equatorial Pacific tends to weaken during the 21st century, consistent with previous research. Here we show that this primarily arises because of an increase in MSLP in the west Pacific and not a decline in the east. We also show, in stark contrast to expectations, that the SOI actually tends to increase during the 21st century, not decrease. Under global warming MSLP tends to increase at both Darwin and Tahiti, but tends to rise more at Tahiti than at Darwin. Tahiti lies in an extensive region where MSLP tends to rise in response to global warming. So while the SOI is an excellent indicator of interannual variability in both the equatorial MSLP gradient and the WC, it is a highly misleading indicator of long-term equatorial changes linked to global warming. Our results also indicate that the observed decline in the SOI in recent decades has been driven by natural, internally generated variability. The externally forced signal in the June–December SOI during 2010 is estimated to be approximately 5% of the standard deviation of variability in the SOI during the 20th century. This figure is projected to increase to 40% by the end of the 21st century under the A2 SRES scenario. The 2010 global warming signal is already a major contributor to interdecadal variability in the SOI, equal to 45% of the standard deviation of 30-year running averages of the SOI. This figure is projected to increase to nearly 340% by the end of the 21st century. Implications that these discoveries have for understanding recent climatic change and for seasonal prediction are discussed.” Scott B. Power and Greg Kociuba, Climate Dynamics, DOI: 10.1007/s00382-010-0951-7. [full text]

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