It may be dropping huge chunks of iceberg that drift hundreds of miles while they slowly melt, but the West Antarctic Ice Sheet just may have stopped melting, scientists have reported.
Their study, published in Science, is sure to provoke controversy and will have to be confirmed by other experts.
The team at NASA's Jet Propulsion Laboratory and the California Institute of Technology say their measurements show the ice sheet is getting thicker. "We find strong evidence for ice-sheet growth,'' Ian Joughlin and Slawek Tulaczyk wrote in their report.
Joughlin and many others have been taking measurements that show the ice sheet, known to scientists as the WAIS, has been steadily melting since the end of the last Ice Age about 11,000 years ago. It currently covers about 360,000 square miles .
The sheet has enough ice to raise global sea levels by 5 to 18 feet if it all melted. Earlier predictions had said that it could melt in 4,000 years.
The United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC) predicts the average global temperature could be as much as 11 degrees Fahrenheit higher at the end of the century than it was in 1990. If this affected the Antarctic, it could melt enough ice to raise sea levels enough to swamp coastal areas. It would also greatly alter the planet's climate by changing ocean currents and temperatures.
However, experts have been saying there is little evidence that global warming is responsible for melting the ice sheet; they say currents and the way water washes underneath the floating portions seems to have more of an effect.
Joughlin and Tulaczyk used satellite radar to measure the thickness of the ice. They specifically looked at ice streams, which are similar to large, flowing rivers of ice.
While previous measurements had suggested ice was being steadily lost, they found that in fact there was slightly more ice in the areas feeding the streams than before. Overall, there were 26 billion tons more ice each year, they said not the loss of nearly 21 billion tons a year that other studies showed. These are extremely large amounts that can measurably affect world sea levels.
Richard Allen of Pennsylvania State University wrote in a commentary that the satellite radar tool could be useful in measuring a huge, complex ice system that has been extremely difficult to measure. "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,'' Allen said.