OSLO A glacier in Greenland slides up to 220 percent faster toward the sea in summer than in winter and global warming could mean a wider acceleration that would raise sea levels, according to a study published Sunday.
A group of experts led by Ian Bartholomew at Edinburgh University in Scotland said the variability was much stronger than earlier observations of glacier movement in Greenland.
The study, published in the journal Nature Geoscience, is a new piece of a puzzle to understand the world's second biggest ice sheet behind Antarctica. Greenland has enough ice to raise world sea levels by about 7 meters (23 ft) if it all melted.
The study said GPS satellite measurements of the glacier in south-west Greenland, up to 35 km (22 miles) inland and at altitudes of up to 1,095 meters (3,592 ft), showed that the ice in some places slid at 300 meters per year at peak summer rates.
"Our measurements reveal substantial increases in ice velocity during summer, up to 220 percent above winter background values," it said.
The scientists said that the summer slide might be linked to melt water seeping under the ice. It did not speculate if the change in speed between summer and winter was part of natural shifts or was influenced by a changing climate.
But they wrote: "In a warming climate, with longer and more intense summer melt seasons, we would expect that water will reach the bed farther inland and a larger portion of the ice sheet will experience summer velocity changes."
The United Nations panel of climate experts said in 2007 that global warming was unequivocal and that it was more than 90 percent certain that most warming in the past half century was caused by human activities led by the burning of fossil fuels.
The U.N. panel has come under fire this year after officials said its latest report in 2007 exaggerated the pace of melt of Himalayan glaciers by saying they might all disappear by 2035.
More than 250 members of the U.S. National Academy of Sciences Thursday defended climate change research against "political assaults," and said that any delay in tackling global warming heightens the risk of a planet-wide catastrophe.
(Editing by Maria Golovnina)