East Antarctic Ice sheet more vulnerable than we thought.

The East Antarctic Ice sheet is more vulnerable than we thought.

Researchers in Germany have found the East Antarctic ice sheet may be less stable than anyone had realized.

Two scientists from the Potsdam Institute for Climate Impact Research say the melting of ice on the East Antarctic shore could ultimately trigger a discharge into the ocean which would result in unstoppable sea-level rise for thousands of years . The Wilkes Basin in East Antarctica, stretching more than 1,000 km (600 miles) inland, has enough ice to raise sea levels by 10-13 feet  if it were to melt. The Wilkes 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 warm up.

"East Antarctica's Wilkes Basin is like a bottle on a slant," said Matthias Mengel of the Potsdam Institute for Climate Impact Research. "Once uncorked, it empties out."

Co-author Anders Levermann, also at Potsdam in Germany, told Reuters 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 work out a U.N. deal by the end of 2015 to curb increasing emissions of man-made greenhouse gases that a U.N. panel says will 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 smaller amounts of ice in mountain ranges from the Himalayas to the Andes. Sunday's study is among the first to gauge risks in East Antarctica, the largest volume of ice of the continent and usually considered stable. "I would not be surprised if this is more vulnerable than West Antarctica. If half of that ice loss occurred in the ice-cork region, then the discharge would begin. We have probably overestimated the stability of East Antarctica so far," said co-author Anders Levermann.

A rim of ice currently holds back the largest region of marine ice on rocky ground in East Antarctica. 
Warming oceans could lead to loss of ice on the coast, while the air over Antarctica stays cold, the researchers say.  If this rim is lost it could trigger sea-level rise of 300-400 centimeters (about 10-13 feet) the researchers report. Sea level rise from Antarctica is projected to increase by 16 centimeters this century.

Computer simulations of the region show it would take 5,000-10,000 years for the basin to discharge completely.  But once started the basin would empty, even if global warming was halted. Their findings, which they say amount to the discovery of a hitherto overlooked source of sea level rise, appear unlikely to happen any time soon. They are based on computer simulations of the Antarctic ice flow using improved data of the ground profile beneath the ice sheet.