Monday, December 24, 2012

977. Scientists Report Faster Warming in Antarctica

Warming map of Antarctica
By Justin Gillis, The New York Times, December 23, 2012

West Antarctica has warmed much more than scientists had thought over the last half century, new research suggests, an ominous finding given that the huge ice sheet there may be vulnerable to long-term collapse, with potentially drastic effects on sea levels.

A paper released Sunday by the journal Nature Geoscience reports that the temperature at a research station in the middle of West Antarctica has warmed by 4.4 degrees Fahrenheit since 1958. That is roughly twice as much as scientists previously thought and three times the overall rate of global warming, making central West Antarctica one of the fastest-warming regions on earth.
“The surprises keep coming,” said Andrew J. Monaghan, a scientist at the National Center for Atmospheric Research in Boulder, Colo., who took part in the study. “When you see this type of warming, I think it’s alarming.”
Of course, warming in Antarctica is a relative concept. West Antarctica remains an exceedingly cold place, with average annual temperatures in the center of the ice sheet that are nearly 50 degrees Fahrenheit below freezing.
But the temperature there does sometimes rise above freezing in the summer, and the new research raises the possibility that it might begin to happen more often, potentially weakening the ice sheet through surface melting. The ice sheet is already under attack at the edges by warmer ocean water, and scientists are on alert for any new threat.
A potential collapse of the West Antarctic ice sheet is one of the long-term hazards that have led experts to worry about global warming. The base of the ice sheet sits below sea level, in a configuration that makes it especially vulnerable. Scientists say a breakup of the ice sheet, over a period that would presumably last at least several hundred years, could raise global sea levels by 10 feet, possibly more.
The new research is an attempt to resolve a scientific controversy that erupted several years ago about exactly how fast West Antarctica is warming. With few automated weather stations and even fewer human observers in the region, scientists have had to use statistical techniques to infer long-term climate trends from sparse data.
A nearby area called the Antarctic Peninsula, which juts north from West Antarctica and for which fairly good records are available, was already known to be warming rapidly. A 2009 paper found extensive warming in the main part of West Antarctica, but those results were challenged by a group that included climate change contrarians.
To try to get to the bottom of the question, David H. Bromwich of Ohio State University pulled together a team that focused on a single temperature record. At a lonely outpost called Byrd Station, in central West Antarctica, people and automated equipment have been keeping track of temperature and other weather variables since the late 1950s.
It is by far the longest weather record in that region, but it had intermittent gaps and other problems that had made many researchers wary of it. The Bromwich group decided to try to salvage the Byrd record.
They retrieved one of the sensors and recalibrated it at the University of Wisconsin. They discovered a software error that had introduced mistakes into the record and then used computerized analyses of the atmosphere to fill the gaps.
The reconstruction will most likely undergo intensive scientific scrutiny, which Dr. Bromwich said he would welcome. “We’ve tested everything we could think of,” he said.
Assuming the research holds up, it suggests that the 2009 paper, far from overestimating warming in West Antarctica, had probably underestimated it, especially in summer.
Eric J. Steig, a University of Washington researcher who led the 2009 work, said in an interview that he considered his paper to have been supplanted by the new research. “I think their results are better than ours, and should be adopted as the best estimate,” he said. He noted that the new Byrd record matches a recent temperature reconstruction from a nearby borehole in the ice sheet, adding confidence in the findings.
Much of the warming discovered in the new paper happened in the 1980s, around the same time the planet was beginning to warm briskly. More recently, Dr. Bromwich said, the weather in West Antarctica seems to have become somewhat erratic. In the summer of 2005, the interior of West Antarctica warmed enough for the ice to undergo several days of surface melting.
Dr. Bromwich is worried that this could eventually become routine, perhaps accelerating the decay of the West Antarctic ice sheet, but the warming is not fast enough for that to happen right away. “We’re talking decades into the future, I think,” Dr. Bromwich said.

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