BioEd Online

The exceptional warming of the Antarctic Peninsula is due mainly to stronger winds in the area, scientists have found. These warm winds probably caused the recent break-up of a massive Antarctic ice shelf, they say.

The Antarctic Peninsula, which reaches up towards South America, is the northernmost and mildest part of Antarctica. It is also known to be a hotspot of climate change: since the mid-1960s average temperatures there have increased by more than two degrees Celsius. That's a more rapid temperature rise than any other region on Earth.

Scientists from the British Antarctic Survey (BAS), University College London and the University of Munich, have now found the cause of this warming.

Westerly winds circling the pole have strengthened over the past 50 years, the team reports in the Journal of Climate¹. The stronger these westerlies, the more likely they are to cross the chain of mountains up to 2,800 m high that runs from north to south along the peninsula. As air masses move up the mountains, they lose moisture, and tip onto the lee side as dry, warm winds. The same effect produces the föhn wind in the Alps and the Chinook in the Rockies.

"On some days the effect can lead to quite dramatic warming, says meteorologist John King of the BAS in Cambridge, and co-author of the study. "We've seen temperatures climb five degrees higher than when the passage is blocked."

Summer melt

The stronger winds cause warming mostly in the summer. Warming on the Antarctic Peninsula has actually been most intense in winter, but in summer a large part of the extra heat goes into melting ice.

This has dramatic consequences. Percolating meltwater enlarges crevasses and leads ultimately to the disintegration of floating ice shelves.

The largest and most prominent such event happened in March 2002 when the Larsen ice shelf, with an area of 3,250 square kilometres, collapsed. Overall, more than 13,500 square kilometres, an area larger than Jamaica, of floating ice shelves have broken up in the past 30 years. This is expected to speed the flow of inland ice to the coast, accelerating global sea level rise.

The 2002 event can now be pinned down to a specific change in climate, which is in turn linked to human-induced global warming, the authors say. Some argue that this is the first single event proved to have been caused by manmade climate change. "It's close to being evidence," says Ted Scambos, lead scientist of the National Snow and Ice Data Center at the University of Colorado in Boulder.

Hot air

The wind strengths were calculated from data on air pressure, collected by a large number of research stations in the area.

Researchers have previously shown that Antarctic warming can be linked to increased greenhouse gas concentrations in the troposphere and ozone loss in the stratosphere²,³. It was thought that these changes might increase the strength of circumpolar winds.

"This has made the case definitive," says Scambos. "The results may not be entirely unexpected, but it is a great study to have it nailed in such a fashion."

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