Greenland glaciers may melt slower than thought

A decade-long study of Greenland's glaciers suggests they may not be melting as quickly as thought, leading to a slower sea-level rise than worst-case predictions, said a study on Thursday. How fast glaciers melt depends in large part on how fast they move, and the research in the journal Science shows the glaciers may lead to a sea level rise of 0.8 meters (2.6 feet) by 2100, not two meters (6.5 feet) as some have estimated previously. Scientists pored over satellite data from Canada, Germany and Japan spanning from 2000 to 2011, and found that Greenland's largest glaciers, which end on land, move rather slowly, between 30 and 325 feet (nine to 100 meters) per year. Glaciers that end in ice shelves move more quickly, from 1,000 feet (305 meters) to a mile (1.6 kilometers) per year. "So far, on average we're seeing about a 30 percent speedup in 10 years," said lead author Twila Moon, a University of Washington doctoral student in earth and space sciences. Fast-moving glaciers release more ice and meltwater into the ocean than slow-moving ones. Since previous estimates of Greenland's glacier melt speed varied widely -- from adding four to 19 inches (10 to 48 centimeters) to the rising sea level by 2100 -- Moon said she embarked on the research get a better grasp on what was actually happening. "We don't have a really good handle on it and we need to have that if we're going to understand the effects of climate change," she said. However, while the study gave researchers a clearer picture of how glaciers currently move and melt at varying speeds, many questions still remain about how that may impact sea-level rise in the decades to come. "There's the caveat that this 10-year time series is too short to really understand long-term behavior," said co-author Ian Howat, an assistant professor of earth sciences at Ohio State University. "So there still may be future events -- tipping points -- that could cause large increases in glacier speed to continue," he added. "Or perhaps some of the big glaciers in the north of Greenland that haven't yet exhibited any changes may begin to speed up, which would greatly increase the rate of sea level rise." The research was funded by the US space agency NASA and the National Science Foundation.