OSLO (Reuters) - Greenland's ice losses are accelerating and nudging up sea levels, according to a study showing that icebergs breaking away and meltwater runoff are equally to blame for the shrinking ice sheet.
The report, using computer models to confirm satellite readings, indicated that ice losses quickened in 2006-08 to the equivalent of 0.75 mm (0.03 inch) of world sea level rise per year from an average 0.46 mm a year for 2000-08.
"Mass loss has accelerated," said Michiel van den Broeke, of Utrecht University in the Netherlands, who led the study, in Friday's edition of the journal Science.
"The years 2006-08, with their warm summers, have seen a huge melting," he told Reuters of the study with colleagues in the United States, the Netherlands and Britain.
"The underlying causes suggest this trend is likely to continue in the near future," Jonathan Bamber, a co-author at the University of Bristol, said in a statement.
The computer models matched satellite data for ice losses -- raising confidence in the findings -- and showed that losses were due equally to meltwater, caused by rising temperatures, and icebergs breaking off from glaciers.
"This helps us to understand the processes that affect Greenland. This will also help us predict what will happen," van den Broeke said. Until now, the relative roles of snowfall, icebergs and thawing ice have been poorly understood.
Greenland locks up enough ice to raise world sea levels by 7 meters (23 ft) if it ever all thawed. At the other end of the globe, far-colder Antarctica contains ice equivalent to 58 meters of sea level rise, according to U.N. estimates.
About 190 governments will meet in Copenhagen from December 7-18 to try to agree a U.N. pact to slow global warming, fearing that rising temperatures will bring more powerful storms, heatwaves, mudslides and species extinctions as well as rising sea levels.
The study said losses of ice from Greenland would have been roughly double recent rates but were masked by more snowfall and a re-freezing of some meltwater before it reached the sea.
In total, Greenland lost about 1,500 billion tons of ice from 2000-08, split between icebergs cracking into the sea from glaciers and water runoff. "The mass loss would have been twice as great," without offsetting effects, Van den Broeke said.
The U.N.'s Intergovernmental Panel on Climate Change estimated in 2007 that world sea levels could rise by 18-59 cms by 2100. A natural expansion of water as it warms would account for most of the rise, rather than melting ice.
Greenland's current rate, of 0.75 mm a year, would be 7.5 cms if continued for 100 years. "This is...much more that previous estimates of the Greenland contribution," van den Broeke said.