Antarctic ice melting fast, study reports

WASHINGTON – The Antarctic ice sheet is losing as much as 36 cubic miles of ice a year in a trend that scientists link to global warming, according to a new paper that provides the first evidence that the sheet’s total mass is shrinking significantly.

The new findings, which are being published today in the journal Science, suggest global sea level could rise substantially over the next several centuries.

It is one of a slew of scientific papers in recent weeks that have sought to gauge the impact of climate change on the world’s oceans and lakes. Just last month two researchers reported that Greenland’s glaciers are melting into the sea twice as fast as previously believed, and a separate paper in Science today predicts that by the end of this century lakes and streams on one-fourth of the African continent could be drying up because of warmer temperatures.

The new Antarctic measurements, using data from two NASA satellites called the Gravity Recovery and Climate Experiment (GRACE), found that the amount of water pouring annually from the ice sheet into the ocean – equivalent to the amount of water the United States uses in three months – is causing global sea level to rise by 0.4 millimeters a year. The continent holds 90 percent of the world’s ice, and the disappearance of even its smaller, West Antarctic ice sheet could raise worldwide sea levels by an estimated 20 feet.

“The ice sheet is losing mass at a significant rate,” said Isabella Velicogna, the study’s lead author and a research scientist at Colorado University-Boulder’s Cooperative Institute for Research in Environmental Sciences. “It’s a good indicator of how the climate is changing. It tells us we have to pay attention.”

Richard Alley, a Penn State glaciologist who has studied the Antarctic ice sheet but was not involved in the new research, said more research is needed to determine if the shrinkage is a long-term trend, because the new report is based on just three years of data. “One person’s trend is another person’s fluctuation,” he said.

But Alley called the study significant and “a bit surprising” because a major international scientific panel predicted five years ago the Antarctic ice sheet would gain mass this century as higher temperatures led to increased snowfall.

“It looks like the ice sheets are ahead of schedule” in terms of melting, Alley said.

Scientists have been debating whether the Antarctic ice sheet was expanding or shrinking overall, because the center of the sheet tends to gain mass through snowfall while the coastal regions are more vulnerable to melting.

Velicogna and her co-author, University of Colorado-Boulder physics professor John Wahr, based their measurements on data from the two GRACE satellites that circle the world more than a dozen times a day at an altitude of 310 miles. The satellites measure variations in the Earth’s mass and gravitational pull – increases or decreases in the Antarctic ice sheet’s mass change the distance between the satellites as they fly over the region.

But some scientists remain unconvinced. Oregon state climatologist George Taylor noted that sea ice in some areas of Antarctica is expanding and part of the region is getting colder.

“The Antarctic is really a puzzle,” said Taylor, who writes for the Web site TSC Daily, which is partly financed by fossil fuel companies that oppose curbs on greenhouse gases. “A lot more research is needed to understand the degree of climate and ice trends in and around the Antarctic.”