Satellite shows 'ominous' polar melting

A NASA satellite has revealed more accurately than ever that polar ice in Antarctica and Greenland is melting from glaciers and ice sheets far faster than scientists had previously thought, a discovery that one UC Berkeley climate expert calls "ominous and distressing."

Using a laser aboard an orbiting spacecraft that precisely measures minute changes in the thickness of glaciers and ice sheets, scientists with the British Antarctic Survey calculate that along the coast of West Antarctica's Amundsen Sea, for example, the massive Pine Island glacier and two others thinned by nearly 30 feet a year from 2003 to 2007, 50 percent faster than the glacier's thinning rate between 1995 and 2003.

In Greenland, the satellite's radar has shown that 111 fast-flowing glaciers are now thinning at an average rate of nearly three feet a year — much more rapidly than previous estimates based on less-precise instruments, according to the scientists tabulating the satellite's radar measurements.

A report on the survey's findings, published today in the journal Nature, also says glaciers on the coast of East Antarctica are thinning three times faster than scientists previously believed. Thick shelves of floating ice on the Antarctic coast, like the one named Larsen B, crumbled into the sea spectacularly in 2002 and more ice sheets are falling regularly.

Because the melting ice shelves float, they do not affect sea level any more than melting ice cubes would raise water in a glass. But as thinning glaciers flow down from dense ice caps covering the ground above, rising sea levels result.

In many areas, the report notes, glaciers are melting and thinning faster than even heavy snowfalls above would thicken them.

"Many glaciers along the margins of Greenland and Antarctic ice sheets are accelerating, and for this reason contribute increasingly to global sea-level rise," reported the team headed by polar physicist Hamish Pritchard. The report concedes that the rate of sea-level rise from melting glaciers in both land masses is still unpredictable, but its implication of faster-than-estimated global sea-level rise in this century brought dismay to some American experts.

"This report provides a much more ominous picture than we have had and a depressing prospect of the potential for sea-level rise," Inez Fung, a noted atmospheric scientist at UC Berkeley, said Wednesday. "It's very much a cause for worry."

The laser, carried aboard the spacecraft ICESat — for Ice, Cloud and land Elevation Satellite — is essentially a highly precise altimiteter that bounces its beam off the surface of ice with ultra-high resolution.