Unexpected High-Speed Antarctic Warming

Parts of Antarctica have recently been warming much faster than the rest of the Earth, according to scientists in the U.K. They believe this degree of warming is greater than it has been for nearly two thousand years. The scientists, from the British Antarctic Survey, reported their findings in the magazine Science.

At Amundsen-Scott base at the South Pole annual air temperatures have actually cooled since 1958. On the Antarctic peninsula, though, they have warmed since reliable records began in the 1950s.

Trends in annual air temperature for 1950-98 show three areas of especially rapid regional warming: northwestern North America and the Beaufort Sea; an area around the Siberian plateau; and the Antarctic peninsula and the adjoining Bellingshausen Sea.

The BAS scientists say the longest records show a warming in the northwest of the peninsula ?considerably larger than the mean Antarctic trend,? with shorter records suggesting that the warming extends further south and east. The warming has caused flowering plants to extend their ranges, glaciers to retreat and seasonal snow cover to shrink.

Penguin distribution is also changing. Adelie penguins, which need access to winter pack ice, are declining around Faraday. But chinstrap penguins, which usually need open water, are increasing.

The authors say three of the four ice cores from the peninsula show a rise in temperature over the last half century. Rapid regional warming has also led to the loss of seven ice shelves during the last 50 years. One, the Prince Gustav Channel shelf, disappeared in 1995. It came into existence 1900 years ago, when sedimentary cores show the climate was as warm as it has been recently. The scientists say, ?The recent rapid regional warming in the Antarctic peninsula is thus exceptional over several centuries, and probably unmatched for 1900 years.?

They suggest three possible causes: changing ocean currents may have brought warmer deep water onto the continental shelf, reducing sea-ice; warmer air may have come into the region; or a unique sea-ice-atmosphere feedback may be at work. Not knowing which theory is the correct one, the authors say they cannot predict the future. But they describe what has happened as ?a profound climatic change, an order of magnitude greater than global mean warming.?

One of the authors, Dr. David Vaughan, says, ?The important thing is predicting whether this change will continue. What?s stopping us is that we can?t say which of these mechanisms is responsible. The climate modelers have done an astounding job in the last ten years. But we now need to develop more sophisticated tools to enable us to predict regional climate changes.?

Another group of scientists is embarking on a seven-year research program tracking the effect of global warming on Antarctica?s vast ice sheets, seeking clues to how much ice could melt if temperatures continue to rise. The United Nations Intergovernmental Panel on Climate Change has predicted the global average surface temperature will continue to rise, due to rising levels of carbon dioxide and other greenhouse gases in the atmosphere.

If Antarctica lost its ice, ocean levels would rise as much as 211 feet and scientists want to know what happened last time a similar bout of global warming occurred 20 million years ago, according to Tim Naish of the Antarctica Drilling Consortium (ANDRILL). Drilling to depths that will take scientists back as far as 40 million years will enable them to see what Antarctica was like when the world was last 3-4 degrees warmer.

Antarctica is the world?s fifth largest continent with an area of 5.4 million square miles– twice the size of Australia. Naish thinks the current ice sheet on Antarctica is the biggest ever, as the world has generally been cooling for 60 million years. He says, ?It may be that it takes a few hundred to a thousand or a few thousand years to completely de-glaciate Antarctica… But what we do know is that it will happen if we maintain those levels of carbon dioxide (gain) and temperatures.?

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