Using satellites to monitor most of Antarctica's coastline, the scientists estimate that West Antarctica lost 132 billion tonnes of ice in 2006, compared to about 83 billion tonnes in 1996. The Antarctic Peninsula, which stretches toward South America, lost about 60 billion tonnes in 2006.

To put this in perspective, 4 billion tonnes of ice would be enough to provide drinking water to the more than 60 million people of the United Kingdom for a year, fellow author Jonathan Bamber of the University of Bristol said in a statement.

This ice loss is not from the so-called ice sheets that cover the water around the continent. This melting occurred in the glaciers that cover much of the Antarctic land mass, and when that melts, it contributes to sea level rise in a way that sea ice does not.

"One immediate consequence (of the melting Antarctic ice) is to raise sea level," Rignot, of the Jet Propulsion Laboratory, said in an e-mail interview. Antarctica's contribution to global sea level rise was about 0.02 inch (0.5 mm) in 2006, compared to about 0.01 inch (0.3 mm) in 1996.

Rignot noted that the UN Intergovernmental Panel on Climate Change figured Antarctica would not contribute at all to sea level rise, and in fact predicted a growth of the big ice sheet the covers much of the continent from enhanced precipitation.

This prediction was supposed to come from increased evaporation from the oceans as the planet warmed up, but this has not been observed so far in Antarctica, Rignot said.

"In some regions the ice sheet is close to warm sources of water. ... The parts of Antarctica we are seeing change right now are closest to these heat sources," he said.

These findings are in line with what is happening to the Greenland ice sheet, which melted at a record rate last year, and with studies of Arctic sea ice, which ebbed to its lowest level ever measured in 2007.