US coastal cities at risk if Antarctic ice sheet collapses

Washington, May 15 (IANS) If the West Antarctic Ice Sheet collapses due to global warming, it would directly threaten New York, Washington and San Francisco as sea levels near US coasts would rise by 25 percent more than the global average, according to a new study.

Antarctica holds about nine times the volume of ice of Greenland. The West Antarctic Ice Sheet (WAIS) is of particular interest to scientists due to its inherent instability, thanks to a parts of the continent's bedrock lying below sea level.

'There's a vast body of research that has looked at the likelihood of a WAIS collapse and what implications such a catastrophic event would have for the globe,' said Jonathan Bamber, the study co-author.

'But all of these studies have assumed a five to six metre contribution to sea level rise. Our calculations show those estimates are much too large, even on a thousand-year timescale,' he added.

Bamber and his colleagues found a WAIS collapse would only raise sea levels by 3.3 meters or about 11 feet.

Bamber, professor at the University of Bristol in England, currently is a visiting fellow at the University of Colorado at Boulder's Cooperative Institute for Research in Environmental Science (CIRES).

The study authors used models based on glaciological theory to simulate how the massive ice sheet would likely respond if the floating ice shelves fringing the continent broke free. Vast ice shelves currently block WAIS from spilling into the Weddell and Ross seas, limiting total ice loss to the ocean.

According to the theory, if these floating ice shelves were removed, it would free sizeable areas of WAIS presently dammed up, triggering an acceleration of the ice sheet toward the ocean and a rapid inland migration of the grounding line (the point where the ice sheet's margins meet the ocean and begin to float), said a CIRES release.

The most unstable areas of WAIS are those sections sitting in enormous inland basins on bedrock entirely below sea level. If the ice filling these basins gets free from being dammed up by the disappearance of floating ice shelves, it quickly would become buoyant and form new floating ice shelves further inland, in time precipitating further breakup and collapse, according to existing theories.

'Unlike the world's other major ice sheets - the East Antarctic Ice Sheet and Greenland - WAIS is the only one with such an unstable configuration,' said Bamber.

These findings were published in the Friday issue of Science.