Melting Ice in the Western Antarctic "unstoppable"

Ice is melting in the western Antarctic at an "unstoppable" pace, scientists said Monday, warning that the finding holds major consequences for global sea level rise in the coming decades.

The speedy melting means that prior calculations about how much the sea level will rise worldwide made by the Intergovernmental Panel on Climate Change will have to be adjusted upwards, scientists told reporters.

"A large sector of the West Antarctic ice sheet has gone into a state of irreversible retreat. It has passed the point of no return," said Eric Rignot, professor of Earth system science at the University of California Irvine.

"The retreat of ice is unstoppable," he said, noting that surveys have shown there is no large hill at the back of these glaciers that could hold back the melting ice.

Scientists have been warning about this so-called weak underbelly of western Antarctic for decades, but only since the 1990s have they been able to gather detailed information on this remote area.
The results are included in pair of published studies that document observational changes in the Antarctic in recent years, and predict the future behaviour of the melting ice through computer models.

"This retreat will have major consequences for sea level rise worldwide," Rignot added, anticipating the melting will take place largely in the next two centuries.

"It will raise sea level by 1.2 meters or four feet," said Rignot, whose paper appears in the peer-reviewed Geophysical Research Letters, a journal of the American Geophysical Union.
Rignot, a glaciologist at NASA's Jet Propulsion Laboratory, said his study compiled data from satellites, airplanes, ships and ground surveys in the West Antarctic ice sheet.

Retreat of the area's Pine Island glacier has slowed in recent years, but scientists said that was likely to due to the very rapid retreat it went through early on.

The nearby Thwaites glacier has been melting faster since 2006, and the long term trend toward faster melting is clear.

A separate study published in the journal Science on Monday found that Thwaites glacier is melting fast and that its collapse could raise global sea level nearly 60 centimetres.

That study was based largely on computer modelling to predict future conditions, along with airborne radar measurements of the West Antarctic ice sheet that allowed scientists to map the underlying bedrock.

Study author Ian Joughin, a glaciologist at the University of Washington, said the process is now expected to take between 200 and 1000 years.