Study: Greenland Ice Sheet Melting Faster Than Thought
RENEE MONTAGNE, host:
Greenland's massive icecap is shrinking faster than researchers had previously thought. That's according to a study published today in Science magazine. In the past few years, big glaciers that had been slowly flowing toward the sea have suddenly started to surge forward. A strong warming trend in Greenland may be to blame. NPR's Richard Harris reports.
RICHARD HARRIS reporting:
Glaciologists care a lot about Greenland because it holds more ice than anywhere on earth other than Antarctica. There's enough ice there to raise global sea levels by 20 feet. Eric Rignot at the Jet Propulsion Laboratory says it's been a challenge figuring out what that ice is doing in a warming world.
Mr. ERIC RIGNOT (Research Scientist, Jet Propulsion Laboratory, Pasadena, California): On one side you would expect the ice to melt faster and the glaciers to fill faster because of the warmer air temperatures. On the other side, you would expect more precipitation of snow in the interior, and the two processes work against each other and it was not clear which process might win.
HARRIS: Surveys by airplane have showed that Greenland, overall, is losing elevation; so, ice is melting faster than new snow is accumulating. Rignot has now improved on the early measurements using satellite-based radars to gauge how fast huge rivers of ice, glaciers, are flowing toward the sea.
Mr. RIGNOT: A lot of the glaciers in Greenland have been accelerating in recent years and this is not an isolated event. We found some rather strong evidence of widespread acceleration of glaciers.
HARRIS: Rignot says he wasn't surprised to see some of these glaciers picking up speed, after all, Greenland is warming rapidly at the moment.
Mr. RIGNOT: But I did not quite expect to see such abrupt changes and such a large acceleration.
HARRIS: The new results show that Greenland is now losing ice twice as fast as it did in the previous decade. Overall the island is currently dumping enough water into the Atlantic Ocean to raise sea levels around the world by a quarter of an inch per decade. That doesn't sound too dramatic, but Rignot says he's concerned that the pace is quickening.
Mr. RIGNOT: Current models predict that you would take of the order of a thousand years to really remove a large amount of ice from Greenland and I think from what we've seen, this number should be revised down more in the time scale of centuries than the time scale of millennias.
HARRIS: The rapid change in Greenland is due, at least in part to the warming trend there. Konrad Steffan at the University of Colorado in Boulder has been measuring actual conditions on the Greenland ice sheet on a daily basis since 1979.
Mr. KONRAD STEFFAN (Director of CIRES, Cooperative Institute for Research in Environmental Sciences; Professor of Geography, University of Colorado, Boulder): And we have seen an increase it melts; that means when the snow gets wet, it melts, the water percolates down and flows off the ice.
HARRIS: Some of that water trickles down to the bottom of the glaciers. There, it serves as a lubricant so that glaciers flow faster. The fastest glacier now flows toward the sea at a foot and a half a day during the summer, Steffan says. That's faster than any other glacier on earth. Steffan says the effect isn't only on sea level; Greenland's melting will make the nearby ocean water less salty.
Mr. STEFFAN: And that eventually could have an impact on ocean circulation.
HARRIS: Are you worried about this?
Mr. STEFFAN: Oh, I'm certainly worried, yes. After two, three years ago, we had no idea that glaciers in Greenland that large can react that fast.
HARRIS: And all the fresh water they're adding to the ocean can, in theory, disrupt the currents that keep Europe's climate moderate. Steffan cautions, though, not to make too much of the current trends that he and Eric Rignot have documented.
Mr. STEFFAN: This is only a data set of a few years, so we're looking at a very small window and we have very little insight how was the exchange in the past.
HARRIS: Maybe these glacial surges just happen from time to time, he says. Or, maybe it's another sign that the world is heading into a new climate regime. Richard Harris, NPR News.
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