West Antarctica is warming almost twice as fast as previously believed, adding to worries of a thaw that would add to sea level rise from San Francisco to Shanghai, a study showed on Sunday.
Annual average temperatures at the Byrd research station in West Antarctica had risen 2.4 degrees Celsius (4.3F) since the 1950s, one of the fastest gains on the planet and three times the global average in a changing climate, it said.
The unexpectedly big increase adds to fears the ice sheet is vulnerable to thawing. West Antarctica holds enough ice to raise world sea levels by at least 3.3 metres (11 feet) if it ever all melted, a process that would take centuries.
"The western part of the ice sheet is experiencing nearly twice as much warming as previously thought," Ohio State University said in a statement of the study led by its geography professor David Bromwich.
The warming "raises further concerns about the future contribution of Antarctica to sea level rise," it said. Higher summer temperatures raised risks of a surface melt of ice and snow even though most of Antarctica is in a year-round deep freeze.
Low-lying nations from Bangladesh to Tuvalu are especially vulnerable to sea level rise, as are coastal cities from London to Buenos Aires. Sea levels have risen by about 20 cms (8 inches) in the past century.
The United Nations panel of climate experts projects that sea levels will rise by between 18 and 59 cms (7-24 inches) this century, and by more if a thaw of Greenland and Antarctica accelerates, due to global warming caused by human activities.