WASHINGTON (AP) _ New measurements show the ice in West Antarctica is thickening, reversing earlier estimates that the sheet was melting.
Scientists concerned about global warming had worried that higher temperatures could melt the massive ice sheet, causing a rise in sea levels worldwide.
But new flow measurements for the Ross ice streams, using special satellite-based radars, indicate that movement of some of the ice streams has slowed or halted, allowing the ice to thicken, according to a paper in Friday's issue of the journal Science.
If the thickening is not merely part of some short-term fluctuation, it represents a reversal of the long retreat of the ice, say researchers Ian Joughin of the California Institute of Technology and Slawek Tulaczyk of the University of California, Santa Cruz.
Their finding comes less than a week after a separate paper in Nature reported that Antarctica's harsh desert valleys _ long considered a bellwether for global climate change _ have grown noticeably cooler since the mid-1980s.
Air temperatures recorded continuously over a 14-year period ending in 1999 declined by about 1 degree Fahrenheit in the polar deserts and across the White Continent, that paper said.
The cooling defies a trend spanning more than 100 years in which average land surface temperatures have increased worldwide by about 1 degree Fahrenheit. The scientists said Antarctica is the only continent that is cooling. They could not say why.
In their paper, Joughin and Tulaczyk suggest the West Antarctic ice streams may be undergoing the same transition from shrinking to growing that appears to have occurred on a neighboring stream 150 years ago.
The results, they add, suggest a reduced possibility of the feared massive collapse of the ice field.
``Perhaps, after 10,000 years of retreat from the ice-age maximum, researchers turned on their instruments just in time to catch the stabilization or re-advance of the ice sheet,'' Richard B. Alley of Pennsylvania State University, wrote in a commentary accompanying the Science paper.
But he warned that coastal property owners should not become too optimistic about the findings, since the instrumental record is short and coastal ice streams have changed periodically over the centuries.