Antarctic: Cooling or Warming?

An unexpectedly rapid warming of lakes on a desolate Antarctic island is evidence of global warming, according to a 20-year study by British and Canadian scientists. They say that dramatic changes have taken place in Signy Island?s lakes caused by a 1.8-degree Fahrenheit rise in air temperature.

This increase has triggered a series of changes in the lakes on the island, which is located 435 miles northeast of the Antarctic Peninsula. The scientists consider polar lakes to be early detectors of change due to global warming.

?This is almost a beacon going off saying, ?Look, we’ve gone through this threshold at this point on the planet, and it?s an indicator that the environment is changing rapidly,?? says Lloyd Peck of the British Antarctic Survey. ?The main finding of our work is that the ecology and the ecosystem in the lakes that we?ve looked at have changed really dramatically fast. …What we?re seeing is an amplification of the larger-scale environmental change signal.?

Peck and his team published their study just two weeks after other researchers reported in the journal Nature that temperatures in Antarctica had dropped since the mid-1980s, in the area?s arid desert valleys, making Antarctica an exception to the global warming taking place on the rest of the Earth. Peck says his team?s contradictory results show that regional variations exist in the midst of global warming.

Signy Island is about four miles long and three miles wide. There is permanent ice covering a large part of the island, but in summer, extensive areas of moss and some grasses are exposed, and there are numerous freshwater pools and lakes.

Peck and his team found that the increase in winter lake temperatures was three times higher than the increase in local air temperatures. The amount of time during a given year that the lakes were completely frozen over declined by more than four weeks. This decline allowed the lake water and sediments to absorb solar energy that normally would be reflected away by the ice. Nutrient levels in the lakes rose, most likely because streams ran over thawed ground rather than ice. Algae and phytoplankton in the lakes also increased.

The island?s isolated location allowed the researchers to come up with measurements that were not affected by local pollution or heating associated with cities. ?In the Northern Hemisphere, where they?re seeing fast changes in lakes, they?ve often been associated with large human centers of population,? Peck says. ?So it?s hard to say whether it?s a global change …or whether it?s something to do with extra heating and pollution from big cities, like Chicago and the Great Lakes. Whereas here, we?re in an island that is several thousand [miles] away from the nearest big city.?

He also noted that the Dry Valleys where cooler temperatures were found are about 4,000 miles away from Signy Island. ?You would not expect to get the same message from every point on the planet of warming, or whatever, during a changing environmental scenario. It just doesn?t work that way,? he says.

John Turner, also of the British Antarctic Survey, says a complex picture is emerging of temperature change over the whole Antarctic continent. While the Antarctic Peninsula region experienced one of the largest temperature increases on Earth over the last 50 years, the South Pole has experienced a modest cooling. He says, ?However, what we can say with certainty is that Antarctica is extremely sensitive to environmental change.?

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