A large part of the West Antarctic ice sheet appears to be in an "unstoppable" decline meaning global sea level rise predictions will have to be revised, scientists have found.
Glaciers in the Amundsen Sea that contain enough ice to raise sea levels by four feet (1.2 metres) are thawing faster than expected and there is nothing to stop them melting into the ocean, according to a study based on 40 years of observations by researchers from the Nasa space agency and the University of California, Irvine.
"The collapse of this sector of West Antarctica appears to be unstoppable," said glaciologist Eric Rignot, lead author of the study. "It's passed the point of no return."
The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers, he said. The changes were thought to be linked to climate change.
Some scientists have previously warned that increased concentrations of man-made greenhouse gases in the atmosphere may be affecting wind patterns around Antarctica and causing other changes that are pushing warmer waters towards the continent.
It could take several centuries for all the ice to flow into the sea, Professor Rignot said, adding that the sector would be a "major contributor to sea level rise in the decades and centuries to come".
Projections of global sea levels, which have already risen by nearly 20cm since 1900, will have to be revised as a result of the study's findings, he said.