for National Geographic News
Due to global warming, glaciers on Greenland are slipping into the ocean twice as fast as they were just five years ago, scientists announced today.
Current estimates already suggest that Greenland (map) is contributing to rising seas. Now it seems that those estimates may have underestimated the melting island's effect, says Eric Rignot, a glaciologist with NASA's Jet Propulsion Laboratory at the California Institute of Technology in Pasadena.
Warming surface temperatures in Greenland are allowing more meltwater to trickle down to the glacier bed. There, where glacier meets earth, the water acts as a lubricant, allowing the ice to flow more quickly to the ocean.
When the increasing speed of the glacier ice is factored into sea level rise models, Greenland accounts for about 0.02 inch (0.5 millimeter) per year of the global rise, which currently stands at about 0.1 inch (3 millimeters) per year, he said.
The recent increases in glacier speed on Greenland are responsible for more than two-thirds of Greenland's contribution to sea level rise, he added.
Rignot presented the results today at the annual meeting of the American Association for the Advancement of Science in St. Louis, Missouri. The finding is also published in tomorrow's issue of the research journal Science.
"This paper is extremely important, because it shows the rapid response of this ice sheet to climate warming," said Jason Box, a climate researcher at Ohio State University in Columbus.
Richard Alley is an earth scientist at Pennsylvania State University in University Park. He said the study confirms what a lot of other studies of Greenland's ice sheets have already suggested: The island is melting.
According to Jay Zwally, a glaciologist with the NASA Goddard Space Flight Center in Greenbelt, Maryland, Rignot's research overestimates the total amount of mass annually lost from Greenland. Still, he said, it is a "significant study."
"Some of the glaciers are accelerating, and that has happened mostly in the last five, at most ten, years. There are significant changes going on," Zwally said.
Measuring the Ice
Over the last 20 years temperatures have increased by about 5.4 degrees Fahrenheit (3 degrees Celsius) along the southeast coast of Greenland, scientists say.
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