Scientists report rapid Antarctic melting, predict ice shelves could be gone ‘within 100 years’

Source: Gayathri Vaidyanathan, E&E reporter • Posted: Monday, March 30, 2015

Ice shelves in Antarctica have been melting more rapidly in recent years, generating enough water each year since 1994 to fill 66 million Olympic-sized swimming pools.

The ice melt has become especially pronounced since 2003.

Some shelves have thinned by 18 percent over a two-decade span, a remarkable development given that they had existed unchanged for thousands of years, said Fernando Paolo, a graduate student at the Scripps Institution of Oceanography at the University of California, San Diego, and lead author of the study.

At the present rate of melt, “these ice shelves might disappear within 100 years,” Paolo said.

The findings were published yesterday in Science. The study is the latest to document the rapid changes at the bottom of the world. Antarctica is a continent few spare a thought for, and at first glance, it appears more resilient than the Arctic to a rapidly warming world.

Recent events have proved this untrue. In 2002, an ice shelf the size of Rhode Island, called Larsen B, disintegrated on the western coast of Antarctica (ClimateWire, Sept. 15, 2014).

The collapse was a natural experiment that confirmed scientists’ worst fears. Ice shelves, which are tongues of ice that float on the ocean and get fed by continental glaciers, are key stabilizers. They act as plugs and stop the glaciers from sliding into the sea.

“The glaciers that were behind the Larsen Ice Shelf are now flowing eight times as fast as they were [before the ice shelf collapse],” said Andrew Shepherd, a professor of earth observation at the University of Leeds, who was not affiliated with the study, “which means [they are] putting eight times as much ice into the ocean and causing sea levels to rise.”

At least six glaciers have already sped up, and they could eventually raise sea levels locally by 4 feet. The Intergovernmental Panel on Climate Change predicts that sea levels globally will rise by between 0.85 and 3.18 feet by the end of the 21st century. Some Antarctica experts say this could be an underestimate.

‘The melting can’t carry on forever’

Antarctica lost 40 cubic miles of ice every year between 1994 and 2012, the Science study finds.

Much of the loss happened after 2003 and on the west coast. The Getz Ice Shelf by itself was responsible for 30 percent of the ice volume loss from the West Antarctic. The melt from the shelf each year could fill up 21 million Olympic-sized swimming pools.

At this rate of thinning, “it doesn’t take a genius to work out that the melting can’t carry on forever,” Shepherd said. Some shelves, such as the Venable Ice Shelf, could disintegrate before the century is out, the study finds.

Getting such granular long-term data about Antarctica has been a challenge for scientists. Satellite records exist on ice thickness, but the records stretch just five to 10 years. That is hardly long enough to tell a comprehensive story about a continent where individual seasons can last five years.

To get around this limitation, Paolo and his colleagues employed a clever approach. They downloaded and combined data from three separate satellites to get a cumulative 18 years of data.

Ice in East Antarctica may face trouble

The results confirm what scientists have long suspected: West Antarctic ice shelves are particularly vulnerable to melting. A portion of the shelves lie below sea level, which is not an issue when the surrounding ocean is cold. Due to a quirk of nature, the warmest waters in the region occur at depths of hundreds of feet, while the coldest waters are at the ocean surface.

But in recent years, wind patterns have shifted and caused warm waters to rise to the surface and lap at the undersides of the shelves, triggering melting (ClimateWire, Dec. 5, 2014).

The picture is not as dire in eastern Antarctica, where the ocean is not in close contact with the ice. Or, at least, that is what scientists thought until a study published last week in Nature Geoscience revealed that the Totten Ice Shelf, located on the east coast, is directly accessible to the ocean.

That is concerning in itself. Scientists are now measuring the temperature of the water below the Totten to see if it is warm enough to trigger melting from below, said Eric Rignot, a professor of earth system science at the University of California, Irvine, who was not involved with the study.

The Science study finds that East Antarctic ice shelves have been thinning since 2003. Other studies have shown that shelves in the vicinity of Totten are particularly unhealthy, Rignot said.

“It is just not a small part of Antarctica affected by this,” he said. “There are many parts of Antarctica where you see this thinning ice shelves, and we should be concerned by that.”