Antarctica's desert valleys getting colder

Antarctica's harsh desert valleys -- long considered a bellwether for global climate change -- have grown noticeably cooler since the mid-1980s, scientists report, even while the Earth as a whole is warming.

Air temperatures recorded continuously over a 14-year period ending in 1999 declined by about 1 degree Fahrenheit in the polar deserts and across the White Continent, according to prominent researchers from 11 American universities and government laboratories.

The cooler temperatures are triggering a cascade of ecological consequences in the sensitive and barren region known as the Dry Valleys. They include a 10 percent annual decline in tiny soil organisms and a 9 percent annual decline in the biological productivity of a handful of ice-covered freshwater lakes, the study shows.

The report appeared Sunday in an online edition of the journal Nature.

The cooler temperatures defy a trend spanning more than 100 years in which average land surface temperatures have increased worldwide by about 1 degree Fahrenheit.

Nearly all of the warmest years in the modern climate record have occurred in the past decade; 1998 was the warmest yet, with 2001 coming in second, according to the National Climatic Data Center.

According to the report, Antarctica is the only one of the Earth's seven continents that is cooling. Scientists concede they cannot explain the contradiction.

"This doesn't change the global warming scenario; the planet is still warming," said the study's lead author, limnologist Peter T. Doran of the University of Illinois-Chicago. "But this is an unexpected twist. This shows we don't understand Antarctica as well as we thought."

The Dry Valleys, ringed by jagged mountain peaks and glaciers, cover about 6,000 square miles. The area accounts for less than 2 percent of the continent, but represents nearly all the open terrain in an otherwise white expanse.

It is the driest place on Earth, with 2 inches of annual precipitation accompanied by subzero temperatures and howling winds. It's so bleak that NASA uses the Dry Valleys as a test track for Mars exploration.

Even small environmental changes there raise scientific eyebrows.

"The decline is alarming," said co-author Diana Wall of Colorado State University. The soil biologist studies the effect of climate change on microscopic soil worms that are the largest native life in the Dry Valleys.

These nematodes have rebounded before from environmental setbacks. The question is how long this cooling will continue.

Ice is growing thicker atop lakes, while freshwater flowing off the surrounding glaciers is diminishing and lake levels are dropping.

"These cooling repercussions may have a long-term effect," Wall said by e-mail from a scientific outpost on the shores of Lake Hoare in the Dry Valleys. "There is very little diversity here and the life cycles of these invertebrates is very slow."

Some scientists who were not involved in the study complained it was too limited to draw such broad conclusions.

Imre Friedmann, director of the Polar Desert Research Center at Florida State University, said the study excludes the surrounding mountains. Friedmann described them as a "totally different landscape" than the valley floors, but still considered to be within the Dry Valleys region.

"I have noticed a slight warming in the mountains," he said. "And there has been a heavier snow cover that is a result of the warming."

Nor is global warming necessarily a uniform trend.

"Some short-term reversals and regional variability should not be a surprise," said Benjamin Preston, a senior research fellow at the Pew Center for Climate Change in Arlington, Va. "And, 14 years is a relatively short period."

Doran, the study's lead author, said previous climate calculations that showed Antarctica was warming had been skewed by temperature data collected on the Antarctic Peninsula. Reaching northward toward South America, conditions on the narrow arm are heavily influenced by surrounding oceans

In the past 50 years, peninsula temperatures have been increasing five times faster than global average temperatures.

"Take away the peninsula temperatures and the vast majority of the continent is cooling," Doran said.

The next step is to determine why Antarctica is cooling. Calmer weather is one possible reason.

Said Doran, "It seems the Dry Valleys have been getting less wind, and you lose the warming effect of the winds coming down off the mountains."