The western portion of Antarctica is warming twice as fast as previously thought and triple the world's average temperature rise, U.S. scientists say.

The temperature in the center of western Antarctica, about 700 miles from the South Pole, has risen 4.3 degrees Fahrenheit since 1958, making that area one of the fastest-warming regions on Earth, the researchers wrote in the journal Nature Geoscience.

A 2009 measurement considered authoritative had indicated that part of the continent, which resembles a giant peninsula stretching roughly from the South Pole toward the southern tip of South America, had warmed just 2.2 degrees since 1957.

Eric J. Steig, a University of Washington researcher who led the 2009 work, told The New York Times the new research supersedes his efforts.

"I think their results are better than ours, and should be adopted as the best estimate," he said.

Surface temperatures at the middle of the West Antarctic Ice Sheet, which covers the land, remain well below freezing most of the year, but increasingly rise above freezing during the December-through-February summer months, said the researchers from Ohio State University, the University of Wisconsin-Madison and the National Center for Atmospheric Research.

"Our record suggests that continued summer warming in West Antarctica could upset the surface mass balance of the ice sheet, so that the region could make an even bigger contribution to sea level rise than it already does," Ohio State geography Professor David Bromwich said.

Some scientists fear the ice sheet could collapse like the Larsen B Ice Shelf did in February 2002.

"We've already seen enhanced surface melting contribute to the breakup of the Antarctic's Larsen B Ice Shelf, where glaciers at the edge discharged massive sections of ice into the ocean that contributed to sea level rise," study co-author and NCAR scientist Andrew Monaghan said.

"The stakes would be much higher if a similar event occurred to an ice shelf restraining one of the enormous WAIS glaciers," he said.

The ice-sheet breakup could take centuries, but could raise global sea levels 10 feet or more, the researchers said.

The base of the ice sheet sits below sea level in a configuration that makes it especially vulnerable, they said.

Their research was funded by the U.S. government's National Science Foundation