Eric J. Steig & Drew T. Shindell: Antarctica is warming

Warming in Antarctica Looks Certain

by KENNETH CHANG, New York Times, January 21, 2009

NASA. An illustration that depicts the warming that scientists have determined has occurred in West Antarctica during the last 50 years. The dark red shows the area that has warmed the most.

Antarctica is warming.

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.

While some regions of Antarctica, particularly the peninsula the stretches toward South America, have warmed rapidly in recent decades, weather stations 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 space sciences at the University of Washington in Seattle and the lead author of a paper appearing Thursday in the journal Nature.

“We’re highly confident our calculation is very good,” Dr. Steig said.

Because of 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.

He and another author, Drew T. Shindell of the NASA Goddard Institute for Space Studies in New York, presented the findings at a news conference on Wednesday.

From 1957 through 2006, temperatures across Antarctica rose an average of 0.18 °F 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 °F. In East Antarctica, where temperatures had been believed 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 any cooling.

The average temperature for Antarctica is about -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 reported in Nature.

As with earlier studies, the scientists found that temperatures had cooled in East Antarctica since the late 1970s, a phenomenon that many atmospheric scientists attribute to emissions of chloroflurocarbons, a family of chemicals used as coolants that destroyed high-altitude ozone. 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 much higher elevation and extends farther north than West Antarctica. The Transantarctic Mountains separate the two.

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.

Andrew C. Revkin contributed reporting.

Link to article: http://www.nytimes.com/2009/01/22/science/earth/22climate.html