Changes in the speed that ice travels in more than 200 outlet glaciers indicates that Greenland’s contribution to rising sea level in the 21st century might be significantly less than the upper limits some scientists thought possible, a new study shows.
“So far, on average we’re seeing about a 30 percent speedup in 10 years,” said Twila Moon, a University of Washington doctoral student in Earth and space sciences and lead author of a paper documenting the observations published May 4 in Science.
The faster the glaciers move, the more ice and meltwater they release into the ocean. In a previous study, scientists trying to understand the contribution of melting ice to rising sea level in a warming world considered a scenario in which the Greenland glaciers would double their velocity between 2000 and 2010 and then stabilize at the higher speed, and another scenario in which the speeds would increase tenfold and then stabilize.
At the lower rate, Greenland ice would contribute about four inches to rising sea level by 2100 and at the higher rate the contribution would be nearly 19 inches by the end of this century. But the researchers who conducted that study had little precise data available for how major ice regions, primarily in Greenland and Antarctica, were behaving in the face of climate change.
In the new study, the scientists created a decadelong record of changes in Greenland outlet glaciers by producing velocity maps using data from the Canadian Space Agency’s Radarsat-1 satellite, Germany’s TerraSar-X satellite and Japan’s Advanced Land Observation Satellite. They started with the winter of 2000-01 and then repeated the process for each winter from 2005-06 through 2010-11, and found that the outlet glaciers had not increased in velocity as much as had been speculated.