The warm cap over Antarctica

By analysing 30 years of high-altitude weather balloon records, meteorologists at the British Antarctic Survey in Cambridge, England, concluded that temperatures in the polar troposphere8212;the dense layer of air reaching from the surface to an altitude of about 5 miles8212;have risen by 3.6 degrees Fahrenheit since the early 1970s. 8216;8216;We have the largest regional warming on Earth at the tropospheric level,8217;8217; said climate specialist John Turner, who led the research team.

As levels of carbon dioxide in the atmosphere worldwide rise to levels not seen for a million years, the ice sheets of Antarctica8212;the world8217;s largest reservoir of fresh water8212;are shrinking faster than new snow can fall. But no one knows whether the heat-trapping effects of human atmospheric pollution are at fault or nature8217;s own cycles of change.

For scientists trying to understand the impact of rising temperatures, Antarctica always has been a world unto itself8212;the highest, driest, windiest and coldest continent on Earth, isolated by the Southern Ocean8212;where extremes of weather routinely confound the computer models used to predict climate trends. The dramatic warming made public Thursday was nowhere evident in any of the climate models on which global warming forecasts are based, Turner said. The researchers checked their finding against 20 computer simulations used by the United Nations8217; Intergovernmental Panel on Climate Change to replicate past climate patterns and make predictions about the future.

In their study, Turner and his colleagues drew on daily temperature records from 1971 to 2003 kept by eight international research stations that rim the continent and the US Amundsen-Scott Station at the South Pole. It was the first time any one had been able to collate all the high-altitude atmosphere readings. When the researchers examined the data, they not only saw evidence of a winter season warming throughout the troposphere, but a cooling in the stratosphere above8212;a layering effect that researchers predict as a consequence of greenhouse warming. 8216;8216;We have the classic global warming signal,8217;8217; Turner said. 8216;8216;It is like the blanket on the bed: When we wrap the Earth with a blanket of greenhouse gases like carbon dioxide and methane, we trap heat under it at the expense of the atmosphere above, which then cools.8217;8217;

The new finding about Antarctic warming is particularly important, several experts said, because until now researchers had only partial8212;and often conflicting8212;temperature readings from a few surface stations on the icy continent. Even as one weather station has reported the fastest warming of anywhere on Earth, others simultaneously reported seasonal cooling.

Even so, the discovery has only deepened the mystery for those who study the climate at Earth8217;s polar extremes. Climate experts were especially surprised that the consistent warming trend detected in the upper atmosphere had no apparent effect on surface temperatures. Some wondered whether powerful polar winds, which have progressively strengthened during the past 40 years, might be partly responsible. The influence of the annual ozone hole over Antarctica also may be driving climate changes across the continent.

Los Angeles Times