No stopping rise in seas as Antarctic ice melts: Scientists

Human-driven release of greenhouse gases helping to destabilise ice sheet
The Straits Times, 14 May 2014

NEW YORK - A large section of the mighty West Antarctica ice sheet has begun falling apart and its continued melting now appears to be unstoppable, two groups of scientists have warned.

If the findings hold up, they suggest that the melting could destabilise neighbouring parts of the ice sheet and a rise in sea level of 3m or more may be unavoidable in coming centuries.

Global warming caused by the human-driven release of greenhouse gases has helped to destabilise the ice sheet, though other factors may also be involved, the scientists said in a report on Monday.

The rise of the sea is likely to continue to be relatively slow for the rest of the 21st century, the scientists added, but may accelerate markedly in the distant future, potentially throwing society into crisis.

"This is really happening," Mr Thomas Wagner, who runs NASA's programmes on polar ice and helped oversee some of the research, said in an interview. "There's nothing to stop it now."

Two scientific papers released on Monday by the journals Science and Geophysical Research Letters came to similar conclusions by different means.

Both groups of scientists found that West Antarctic glaciers had retreated far enough to set off an inherent instability in the ice sheet, one that experts have feared for decades.

NASA called a telephone news conference on Monday to highlight the urgency of the findings.

The West Antarctic ice sheet sits in a bowl-shaped depression in the earth, with the base of the ice below sea level. Warm ocean water is causing the ice along the rim of the bowl to thin and retreat. As the front edge of the ice pulls away from the rim and enters deeper water, it can retreat much faster.

In one of the new papers, a team led by Mr Eric Rignot, a glaciologist at the University of California, Irvine, used satellite and air measurements to document an accelerating retreat over the past several decades of six glaciers draining into the Amundsen Sea region.

And with updated mapping of the terrain beneath the ice sheet, the team was able to rule out the presence of any mountains or hills significant enough to slow the retreat.

"Today we present observational evidence that a large sector of the West Antarctic ice sheet has gone into irreversible retreat," Mr Rignot said at the NASA news conference. "It has passed the point of no return."

Those six glaciers alone could cause the ocean to rise 1.2m as they disappear, possibly within a couple of centuries. He added that their disappearance will most likely destabilise other sectors of the ice sheet, so the ultimate rise could be triple that.

A separate team led by Mr Ian Joughin of the University of Washington studied one of the most important glaciers, Thwaites, using sophisticated computer modelling, coupled with recent measurements of the ice flow. That team also found that a slow-motion collapse had become inevitable. Even if the warm water now eating away at the ice were to dissipate, it would be "too little, too late to stabilise the ice sheet", Mr Joughin said.

The two teams worked independently, preparing papers that were to be published within days of each other. After it was learnt that their results were similar, the teams and their journals agreed to release the findings on the same day.

NEW YORK TIMES