The Earth's polar regions long have been considered canaries in the coal mine on climate change - the first places to look, many scientists said, to learn whether the planet's temperature is, in fact, rising. Indeed, climate models generally predict that the heating of the atmosphere - precipitated by global warming - will cause the vast layer of ice that covers Antarctica to melt, raising sea levels and changing regional climate patterns by altering ocean currents.
This week, that widely held presumption is being challenged.
Two studies of temperatures and ice-cap movements in Antarctica suggest that the Southern Hemisphere's "canary" isn't going down without a fight - key sections of the ice cap appear to be growing thicker, not thinner, as previously believed. And the continent's average temperature appears to have cooled slightly during the past 35 years, not warmed.
Even as scientists work to make their climate models more accurate in the light of the new data, political opponents of the proposed Kyoto Protocol - which would limit human activity thought to cause atmospheric warming - are likely to pounce upon the results. The studies will likely be seen as vindication of their argument that the Kyoto treaty shouldn't be ratified until more is known about the science of climate change.
"This shows we really don't understand the climate dynamics of Antarctica," says Peter Dornan, an assistant professor at the University of Illinois at Chicago. It was Dornan's team of scientists whose research highlighted the temperature trend as part of a broader study of cooling's effect on the microscopic plant and animal life in the McMurdo Dry Valleys of Antarctica.
Dr. Dornan's study points to an average cooling of 0.7 degrees per decade from 1986 to 2000 at the McMurdo Dry Valleys Long-Term Ecological Research Station. Using estimates from British data taken since 1966, the team calculates that the cooling trend has been under way since at least that date.
The report, published in the current issue of the journal Nature, appears to confirm a study published last year in the Journal of Climate by Josephino Comiso, an atmospheric scientist at the National Aeronautics and Space Administration's Goddard Space Flight Center in Greenbelt, Md. Using satellite data for the months of January and July from 1979 to 1999, he reported a drop in the continent's average temperature that amounted to 0.4 degrees per decade.
Yet Dr. Comiso cautions that his results were uncertain to within 0.6 degrees, a margin that swamps the result itself. That uncertainty, he says, may shrink with new data he's been analyzing.
Dornan holds that any cooling down south comes as cold comfort in the face of climate-change predictions because Antarctica's temperature record "is already included in the global averages that show the climate is warming."
Indeed, David Vaughn, a scientist with the British Antarctic Survey, notes that if it's real, the continental cooling trend may be a relatively brief departure from a longer-term warming trend. The average temperature trend for all Antarctic stations from 1959 to 1996 point to an average warming of 1.2 degrees C.
He adds that while early climate models pointed to broad-scale warming at both poles, improved models suggest the heating will be uneven at high latitudes and more pronounced in the north than in the south. That effect, he says, is evident in the greater-than-average warming that has occurred in Alaska, northern Siberia, and Greenland.
Modelers also will be poring over results from studies of the west Antarctica Ice Sheet, conducted by Ian Joughin of CalTech's Jet Propulsion Laboratory and Slawek Tulaczyk at the University of California at Santa Cruz.
Using satellite-borne radar and ice cores, the scientists calculate that the Ross ice streams are gaining ice, not losing it, as previous studies suggested. The new data, published in yesterday's edition of the journal Science, shift the region's crystalline balance sheet from losses of 20.9 billion tons of ice a year to gains averaging 26.8 billion tons a year.
The difference is due to the more comprehensive nature of satellite information. In the past, scientists have had to place a relatively small number of markers in the ice and traced their movements over time, first by shooting the stars with a sextant, and later using satellites.
Ironically, as the sheet thickens and slows its push to the sea, it could affect the region's climate by allowing the Ross Ice Shelf, which sits over water, to thin and break up. That breakup might not affect sea levels much, since the shelf ice is already in the water. But a breakup would expose some 400,000 square kilometers of the sea surface to solar warming, adding heat to the region's climate system and generating a pulse of fresh water to the oceans that could alter the flow of currents there.
"We're trying to understand the physical controls on an ice stream, which will place tighter constraints on models," says Robert Bindschadler, a glaciologist at the Goddard Space Flight Center who has spent a great deal of his career gathering west Antarctic ice-flow data the old-fashioned way. "It's wonderful to catch it when it's changing, because it helps us understand the physics more. No one expected us to be blessed with these kinds of results."