www.nature.com/news/2005/050516/full/050516-10.html
Mark Peplow Increased snowfall could slow sea-level rise. East Antarctica may be piling on the pounds, but glaciers in the west are accelerating into the ocean. British Antarctic Survey Increased snowfall over a large area of Antarctica is thickening the ice sheet and slowing the rise in sea level caused by melting ice. A satellite survey shows that between 1992 and 2003, the East Antarctic i ce sheet gained about 45 billion tonnes of ice - enough to reduce the oc eans' rise by 012 millimetres per year. The ice sheets that cover Antar ctica's bedrock are several kilometres thick in places, and contain abou t 90% of the world's ice. But scientists fear that if they melt in subst antial quantities, this will swell the oceans and cause devastation on i slands and coastal lands. The Intergovernmental Panel on Climate Change (IPCC) has reported that se a level is currently rising at about 18 millimetres per year, largely t hrough melting of the Greenland and Antarctic ice sheets as a result of global warming. But the panel also expected that climate change would tr igger an increase in snowfall over the Antarctic continent, as increased evaporation from the oceans puts more moisture into the air. It is the only large terrestrial ice body that is gaining mass rather th an losing it. Curt Davis University of Missouri, Columbia "This is a phenomenal piece of research, but it is what we expected, " co mments David Vaughan, a glaciologist at the British Antarctic Survey in Cambridge, UK. "These effects have been predicted for a long time, it's just that no one has measured them before." Although the results of the satellite survey are in line with the predict ions of global-warming models, the thickening of the ice sheet could sti ll be explained by natural weather variability, warns Curt Davis of the University of Missouri, Columbia, a member of the research team.
This map shows which areas of Antarctica are thickening. Science The team used data from the European Space Agency's radar satellites ERS- 1 and ERS-2, which measured changes in altitude over about 70% of Antarc tica's interior - more than 85 million square kilometres, roughly the s ame size as the United States. East Antarctica thickened at an average rate of about 18 centimetres per year over the time period studied, the researchers discovered. The regi on comprises about 75% of Antarctica's total land area - but as its ice is thicker, it carries about 85% of the total ice volume. "It is the onl y large terrestrial ice body that is gaining mass rather than losing it, " says Davis. In contrast, smaller West Antarctica showed an overall thinning of 09 ce ntimetres per year. "It's amazing that they can measure such small chang es," says Vaughan. Thick skin The thickening of the eastern ice sheet should not be seen as a long-term protection against a rise in sea level, warns Vaughan. Glaciers in West Antarctica are accelerating, releasing more and more icebergs into the sea. And the Antarctic Peninsula, which stretches towards South America, now regularly hits temperatures above 0 C in the summer, leading to di rect melting of the ice there. What's more, snowfall over East Antarctica will not continue to increase indefinitely in a warming world, Vaughan adds. Conversely, every extra d egree of temperature rise will continue to accelerate glaciers and cause more melting on the western side of Antarctica, swelling the world's oc eans further.
Scientists have already estimated that Antarctic melting may be responsib le for up to a third of the overall sea-level rise. But the instruments on ERS-1 and 2 only work over very flat areas, and tend to lose track of the radar echo over steeper areas around the continent's coast, so a vi tal piece of the puzzle is still missing, says Vaughan. And because Anta rctica is so vast, it is also impossible to measure snowfall comprehensi vely on the ground, he adds. However, the European Space Agency satellite CryoSat, due to be launched later this year, should be able to make very accurate altitude measureme nts around the coast, providing evidence of exactly how much ice is bein g lost there. Only when scientists put all these measurements together w ill the full truth about Antarctica's ice become clear, says Vaughan.
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