Climate Research News

Nothing to do with President Obama’s first full day in office, I’m sure, but it just happens to coincide with a new paper in the journal Nature entitled, ‘Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year,’ by Eric J. Steig, David P. Schneider, Scott D. Rutherford, Michael E. Mann, Josefino C. Comiso & Drew T. Shindell.

Some names to conjure with there, including Rutherford and Mann who are part of the ‘Hockey Team’ involved in the infamous ‘Hockey Stick’ graph saga. So who better to call on when much of Antarctica isn’t playing ball with global warming. But wait! There is more fun to be had here – Real Climate, which includes Michael Mann, have previously said, “A cold Antarctica and Southern Ocean do not contradict our models of global warming.” You just can’t lose when playing the ‘consistent with climate models’ game can you!? Presumably, the findings of this new paper don’t contradict climate models either.

Moving on to the new Nature paper, the first paragraph states:

Assessments of Antarctic temperature change have emphasized the contrast between strong warming of the Antarctic Peninsula and slight cooling of the Antarctic continental interior in recent decades. This pattern of temperature change has been attributed to the increased strength of the circumpolar westerlies, largely in response to changes in stratospheric ozone. This picture, however, is substantially incomplete owing to the sparseness and short duration of the observations. Here we show that significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, an area of warming much larger than previously reported. West Antarctic warming exceeds 0.1 6C per decade over the past 50 years, and is strongest in winter and spring. Although this is partly offset by autumn cooling in East Antarctica, the continent-wide average near-surface temperature trend is positive. Simulations using a general circulation model reproduce the essential features of the spatial pattern and the long-term trend, and we suggest that neither can be attributed directly to increases in the strength of the westerlies. Instead, regional changes in atmospheric circulation and associated changes in sea surface temperature and sea ice are required to explain the enhanced warming in West Antarctica.

The paper concludes:

Mean surface temperature trends in both West and East Antarctica are positive for 1957–2006, and the mean continental warming is comparable to that for the Southern Hemisphere as a whole. This warming trend is difficult to explain without the radiative forcing associated with increasing greenhouse-gas concentrations. However, the future trajectory of Antarctic temperature change also depends on the extent to which changes in atmospheric composition (whether from greenhouse gases or stratospheric ozone) affect Southern Hemisphere sea ice and regional atmospheric circulation patterns. Improved representation in models of coupled atmosphere/sea-ice dynamics will be critical for forecasting Antarctic temperature change.

There is also an accompanying press release from Eric Steig:

New data show much of Antarctica is warming more than previously thought

Scientists studying climate change have long believed that while most of the rest of the globe has been getting steadily warmer, a large part of Antarctica – the East Antarctic Ice Sheet – has actually been getting colder.

But new research shows that for the last 50 years, much of Antarctica has been warming at a rate comparable to the rest of the world. In fact, the warming in West Antarctica is greater than the cooling in East Antarctica, meaning that on average the continent has gotten warmer, said Eric Steig, a University of Washington professor of Earth and space sciences and director of the Quaternary Research Center at the UW.

“West Antarctica is a very different place than East Antarctica, and there is a physical barrier, the Transantarctic Mountains, that separates the two,” said Steig, lead author of a paper documenting the warming published in the Jan. 22 edition of Nature.

For years it was believed that a relatively small area known as the Antarctic Peninsula was getting warmer, but that the rest of the continent – including West Antarctica, the ice sheet most susceptible to potential future collapse – was cooling.

Steig noted that the West Antarctic Ice Sheet, with an average elevation of about 6,000 feet above sea level, is substantially lower than East Antarctica, which has an average elevation of more than 10,000 feet. While the entire continent is essentially a desert, West Antarctica is subject to relatively warm, moist storms and receives much greater snowfall than East Antarctica.

The study found that warming in West Antarctica exceeded one-tenth of a degree Celsius per decade for the last 50 years and more than offset the cooling in East Antarctica.

Co-authors of the paper are David Schneider of the National Center for Atmospheric Research in Boulder, Colo., a former student of Steig’s; Scott Rutherford of Roger Williams University in Bristol, R.I.; Michael Mann of Pennsylvania State University; Josefino Comiso of NASA’s Goddard Space Flight Center in Greenbelt, Md.; and Drew Shindell of NASA’s Goddard Institute for Space Studies in New York City. The work was supported by grants from the National Science Foundation.

The researchers devised a statistical technique that uses data from satellites and from Antarctic weather stations to make a new estimate of temperature trends.

“People were calculating with their heads instead of actually doing the math,” Steig said. “What we did is interpolate carefully instead of just using the back of an envelope. While other interpolations had been done previously, no one had really taken advantage of the satellite data, which provide crucial information about spatial patterns of temperature change.”

Satellites calculate the surface temperature by measuring the intensity of infrared light radiated by the snowpack, and they have the advantage of covering the entire continent. However, they have only been in operation for 25 years. On the other hand, a number of Antarctic weather stations have been in place since 1957, the International Geophysical Year, but virtually all of them are within a short distance of the coast and so provide no direct information about conditions in the continent’s interior.

The scientists found temperature measurements from weather stations corresponded closely with satellite data for overlapping time periods. That allowed them to use the satellite data as a guide to deduce temperatures in areas of the continent without weather stations.

“Simple explanations don’t capture the complexity of climate,” Steig said. “The thing you hear all the time is that Antarctica is cooling and that’s not the case. If anything it’s the reverse, but it’s more complex than that. Antarctica isn’t warming at the same rate everywhere, and while some areas have been cooling for a long time the evidence shows the continent as a whole is getting warmer.”

A major reason most of Antarctica was thought to be cooling is because of a hole in the Earth’s protective ozone layer that appears during the spring months in the Southern Hemisphere’s polar region. Steig noted that it is well established that the ozone hole has contributed to cooling in East Antarctica.

“However, it seems to have been assumed that the ozone hole was affecting the entire continent when there wasn’t any evidence to support that idea, or even any theory to support it,” he said.

“In any case, efforts to repair the ozone layer eventually will begin taking effect and the hole could be eliminated by the middle of this century. If that happens, all of Antarctica could begin warming on a par with the rest of the world.”

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For more information, contact Steig at (206) 685-3715, (206) 543-6327 or steig@ess.washington.edu .

Climate Research News has previously mentioned an article that helps to confirm the divergent climate histrories for the East and West Antarctic ice sheets – a phenomenon that persists from 14 million years ago to modern times.

How do the authors of the new Nature paper find evidence for Antarctic warming? Using “statistical climate-field-reconstruction techniques to obtain a 50-year-long, spatially complete estimate of monthly Antarctic temperature anomalies.”

So there you have it Mr President – you apparently have 4 years to save the world and Antarctica from ‘global warming.’

January 22nd, 2009 | Tags: Antarctic, Climate Reconstructions | Category: News | Subscribe to comments | Leave a comment | Trackback URL