Scientists Measure Cooling of Antarctica

BOULDER, Colorado, January 14, 2002 (ENS) - A cold desert region of Antarctica is getting even colder, and researchers measuring temperatures there say the entire continent is now colder than it was 35 years ago.

The unique cooling climate pattern is puzzling a team of researchers from many universities who would have expected a warming trend on the southernmost continent in concert with the rest of the Earth.

Antarctica

Lake Hoare research camp (Photo courtesy Thomas Nylen)
A global average increase in air temperature of 0.06 degrees Celsius has been recorded during the 20th century, yet the team of researchers with the National Science Foundation Longterm Ecological Research (LTER) site in Antarctica's Dry Valleys say temperatures there are dropping by 0.7 degrees Celsius per decade.

All life is microscopic in Antarctica's Dry Valleys which are always free of snow. The mountainous area is near the U.S. Antarctic research base on the western coast of McMurdo Sound. The Dry Valleys form the largest relatively ice free area, 4,800 square kilometers, on the Antarctic continent.

The perennially ice covered lakes, transitory streams and extensive areas of exposed soil within the McMurdo Dry Valleys are subject to low temperatures, limited precipitation and salt accumulation.

In a paper published Sunday in the online version of the scientific journal "Nature," the LTER researchers explain that long term data from weather stations across the Antarctic continent, coupled with a separate set of measurements from the Dry Valleys, confirm each other and detail the continental cooling trend.

"Our 14 year continuous weather station record from the shore of Lake Hoare reveals that seasonally averaged surface air temperature has decreased by 0.7 degrees Celsius per decade," they write. "The temperature decrease is most pronounced in summer and autumn."

The findings are puzzling because many climate models indicate that the polar regions should serve as bellwethers for any global warming trend, responding first and most rapidly to an increase in temperatures. An ice sheet many miles thick in places covers almost all of Antarctica.

Doran

Peter Doran specializes in hydrological and biogeochemical processes in polar lake systems, and the use of this modern calibration in paleoenvironmental reconstruction. (Photo courtesy University of Illinois)
Peter Doran, of the University of Illinois at Chicago, the lead author of the paper, and his co-authors, acknowledge that other studies conducted in Antarctica have shown a warming trend elsewhere in the continent. But they note that the data indicate that the warming occurred between 1958 and 1978.

The LTER researchers note that the previous claims that Antarctic is warming may have been "skewed" because the measurements were taken largely on the Antarctic Peninsula, which extends northwards toward South America. The peninsula itself is "warming dramatically" the authors note, and there are many more weather stations on the peninsula than elsewhere on the continent.

Averaging the temperature readings from the more numerous stations on the peninsula has led to the misleading conclusion that there is a net warming continent wide. "Our approach shows that if you remove the peninsula from the dataset, and look at the spatial trend the majority of the continent is cooling," said Doran.

Temperature irregularities also exist in Greenland, the largest ice sheet in the Northern Hemisphere, with cooling in the interior happening at the same time as warming at the coast.

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LTER scientists study soil ecology in the McMurdo Dry Valleys (Photo courtesy LTER)
Doran acknowledged that documentation of Antarctic continental cooling presents a challenge to climate modelers. "Although some do predict areas of cooling, widespread cooling is a bit of a conundrum that the models need to start to account for," he said."

The team says the cooling trend could adversely affect the unique ecosystems in the Dry Valleys region, which live in a niche where a delicate balance between freezing and warmer temperatures allows them to survive and where liquid water is only available during the very brief summer.

"We present data from the Dry Valleys representing the first evidence of rapid terrestrial ecosystem response to climate cooling in Antarctica, including decreased lake primary productivity and declining soil invertebrates," they write.

While the Antarctic ice sheets respond to climate change on the order of thousands of years, the glaciers, streams and ice covered lakes in the McMurdo Dry Valleys respond to change almost immediately, the scientists have observed.

The LTER researchers say their data are "the first to highlight the cascade of ecological consequences that result from the recent summer cooling."

Since 1993, the McMurdo Dry Valleys LTER project, based out of an office in Boulder, Colorado, has completed eight field seasons during the southern hemisphere summers, October to February.

During the 1993-94 season 18 scientists were deployed to McMurdo Station and Taylor Valley to conduct research associated with the LTER project. These scientists initiated core measurement programs to obtain baseline ecologically-relevant data from the atmosphere, glaciers, streams, soils, and lakes. Since then, about 25 scientists have participated each season.

This year's team includes scientists from Dartmouth, Ohio State, Portland State, University of Colorado, Colorado State, University of Toledo, and Montana State.