Part of East Antarctica is more vulnerable than expected to a thaw that could trigger an unstoppable slide of ice into the ocean and raise world sea levels for thousands of years, a study shows.
The Wilkes Basin in East Antarctica, stretching more than 1,000 inland, held enough ice to raise sea levels by between three and four metres if it were to melt as an effect of global warming, the report said.
The basin is vulnerable because it is held in place by a small rim of ice, resting on bedrock below sea level by the coast of the frozen continent. That "ice plug" might melt away in coming centuries if ocean waters warmed up.
"East Antarctica's Wilkes Basin is like a bottle on a slant. Once uncorked, it empties out," Matthias Mengel of the Potsdam Institute for Climate Impact Research, lead author of the study in the journal Nature Climate Change, said.
Co-author Anders Levermann, also at Potsdam in Germany, said the main finding was that the ice flow would be irreversible if set in motion. He said there was still time to limit warming to levels to keep the ice plug in place.
Almost 200 governments have promised to devise a UN deal by the end of next year to curb increasing emissions of man-made greenhouse gases that a UN panel said would cause more droughts, heatwaves, downpours and rising sea levels.
Worries about rising seas that could swamp low-lying areas from Shanghai to Florida focus most on ice in Greenland and West Antarctica, as well as ice in mountain ranges.
The study is among the first to gauge risks in East Antarctica, the biggest wedge of the continent and previously considered stable.
"I would not be surprised if this [basin] is more vulnerable than West Antarctica," Levermann said.
Antarctica holds enough ice to raise sea levels by nearly 60 metres if it all melted.
The study indicated that it could take 200 years or more to melt the ice plug if ocean temperatures rose. Once removed, it could take between 5,000 and 10,000 years for ice in the Wilkes Basin to empty as gravity pulled the ice seawards.
"It sounds plausible," Tony Payne, a professor of glaciology at Bristol University who was not involved in the study, said of the findings.