Antarctica is warming, not cooling, according to research published today in the journal Nature.
That's the conclusion of researchers at NASA and the University of Washington who used satellite records and weather station data to reconstruct Antarctica's climate over the past 50 years, challenging the popular notion that the icy continent's climate has escaped most global warming.
For years, Antarctica has been an enigma for climate scientists and an exception to global climate trends often cited by skeptics. Researchers had documented dramatic warming on the Antarctic Peninsula, a small arm of land that juts toward South America. But weather stations on the rest of the continent had shown temperatures holding steady or, near the South Pole, cooling slightly.
Part of the problem was the scarcity of data. At 5.4 million square miles, Antarctica is home to just 42 weather stations -- two located in its interior and the balance along its coastline. But the new study filled that gap by meshing a half-century of weather station data with 25 years of satellite measurements that cover the whole continent and climate models.
"What we found, in a nutshell, is that Antarctica is not cooling," said Eric Steig, one of the paper's two authors and a geochemist at the University of Washington. "We see warming is taking place on all seven continents in accord with what we predict from greenhouse gases."
That's a major leap from the Intergovernmental Panel on Climate Change's 2007 report, which concluded that Antarctica was the only continent where it was unclear whether human activities were influencing the climate.
'Last piece of a puzzle'
Gareth Marshall, a climatologist at the British Antarctic Survey, said the new study "can be considered as providing the last piece of a puzzle that enables us to examine temperature change across the Antarctic continent as a whole."
The new study shows that Antarctic temperature trends vary by season and location, but that overall, the continent has warmed at a rate comparable to that of the rest of the world, Steig said. Over the last 50 years, that has translated to about 0.18 degrees of warming per decade.
West Antarctica has warmed faster, about 0.3 degrees Celsius per decade.
The picture is more complicated in East Antarctica, which scientists believed was cooling. The region actually warmed slightly over the past century, though a cooling trend began in the late 1970s, as the ozone hole over Antarctica enlarged.
Drew Shindell, co-author of the paper and a climatologist at NASA's Goddard Institute for Space Studies, said he and Steig did not attempt to identify the cause of the Antarctic warming. It appears likely that greenhouse gas emissions "are almost certainly contributing to warming trends, but we can't say how much," Shindell said.
But a previous study, published in Nature Geoscience last fall by Nathan Gillett of Environment Canada, did make that connection, finding a small but statistically significant warming trend tied to human activities (ClimateWire, Oct. 31, 2008).
Shindell also said that part of the cooling over East Antarctica appears to be the result of ozone depletion, which has helped strengthen westerly winds that isolate much of the continent from warmer air that lies further north.