|Warming in Antarctica|
|Written by Marjorie Holt|
|Thursday, January 22 2009|
January 22, 2009
That is the conclusion of scientists analyzing half a century of temperatures on the continent, and the findings may help resolve a climate enigma at the bottom of the planet.
Some regions of Antarctica, particularly the peninsula that stretches toward South America, have warmed rapidly in recent years, contributing to the disintegration of ice shelves and accelerating the sliding of glaciers. But weather stations in other locations, including the one at the South Pole, have recorded a cooling trend. That ran counter to the forecasts of computer climate models, and global warming skeptics have pointed to Antarctica in questioning the reliability of the models.
In the new study, scientists took into account satellite measurements to interpolate temperatures in the vast areas between the sparse weather stations.
“We now see warming is taking place on all seven of the earth’s continents in accord with what models predict as a response to greenhouse gases,” said Eric J. Steig, a professor of earth and space sciences at the University of Washington in Seattle, who is the lead author of a paper to be published Thursday in the journal Nature.
Because the climate record is still short, more work needs to be done to determine how much of the warming results from natural climate swings and how much from the warming effects of carbon dioxide released by the burning of fossil fuels, Dr. Steig said.
But Drew T. Shindell of the NASA Goddard Institute for Space Studies in New York, who is another author of the paper, said, “It’s extremely difficult to think of any physical way that you could have increasing greenhouse gases not lead to warming at the Antarctic continent.”
Dr. Steig and Dr. Shindell presented the findings at a news conference on Wednesday. They found that from 1957 through 2006, temperatures across Antarctica rose an average of 0.2 degrees Fahrenheit per decade, comparable to the warming that has been measured globally.
In West Antarctica, where the base of some large ice sheets lies below sea level, the warming was even more pronounced, at 0.3 degrees Fahrenheit, though temperatures in this area are still well below freezing and the warming will not have an immediate effect on sea level.
In East Antarctica, where temperatures had been thought to be falling, the researchers found a slight warming over the 50-year period. With the uncertainties, East Antarctica may have indeed been cooling, but the rise in temperatures in the west more than offset the cooling. The average temperature for Antarctica is about minus 58 degrees.
“There is very convincing evidence in this work of warming over West Antarctica,” said Andrew Monaghan, a scientist at the National Center for Atmospheric Research in Boulder, Colo., who was not involved with the research.
As with earlier studies, the scientists found that more recently, since the late 1970s, temperatures had actually cooled in East Antarctica, a phenomenon that many atmospheric scientists attribute to emissions of chlorofluorocarbons, a family of chemicals used as coolants that destroyed high-altitude ozone. Because those chemicals have since been phased out, the ozone hole is expected to heal, and the cooling trend may reverse.
The region of East Antarctica, which includes the South Pole, is at a much higher elevation and extends farther north than West Antarctica. While the scientists said the ozone hole most likely had a significant influence on Antarctic temperatures, other factors, including sea ice and greenhouse gases, may play a larger role.
“Obviously the situation is complex, resulting from a combination of man-made factors and natural variability,” said Michael Oppenheimer, a professor of geosciences at Princeton, who was not involved in the research. “But the idea of a long-term cooling is pretty clearly debunked.”
Dr. Monaghan, who had not detected the rapid warming of West Antarctica in an earlier study, said the new study had “spurred me to take another look at ours — I’ve since gone back and included additional records.”
That reanalysis, which used somewhat different techniques and assumptions, has not yet been published, but he presented his revised findings last month at a meeting of the American Geophysical Union.
“The results I get are very similar to his,” Dr. Monaghan said.
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