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Polar ice sheets becoming largest contributor to sea level rise

New figures upend conservative UN estimates

Expected, not-so great finding. Ocean waters are rising faster. A new NASA study says Greenland and Antartica’s ice sheets are melting at far higher rates than expected, and the melting rate is accelerating every year.

The new estimate of ice sheet melting, calculated by scientists at NASA’s Jet Propulsion Laboratory and the University of California, Irvine, predicts that if left unchecked, this will raise average sea level across the globe by 6 inches by 2050.

photo of an icefield at water's edgeEric Rignot, JPLStore Glacier, West Greenland.

Added to the predicted extra water coming in from glacial ice – 3.1 inches, and thermal expansion of oceans – 3.5 inches, and the total sea level rise by 2050 could be as high as 12.6 inches, the study says. By 2100, the sea level rise caused by just these two ice sheets (at current melting rates) would be about 22 inches.

This upends more conservative figures calculated by the UN’s Intergovernmental Panel on Climate Change in 2007, which estimated sea levels could rise from anything between 7 to 24 inches by 2100.

The nearly two–decade long study suggests these ice sheets are becoming the dominant contributor of global sea level rise, overtaking ice loss from glaciers and ice caps. For instance, in 2006, the Greenland and Antarctic ice sheets lost a combined mass of 475 gigatonnes a year on average – enough to raise global sea level by an average of 1.3 millimeters a year (1 gigatonne = 1 billion metric tons). And each year over the course of the study, the two ice sheets lost a combined average of 36.3 gigatonnes more than they did the year before (Ice sheets are usually larger than 20,000 square miles, and only exist in Greenland and Antarctica, while ice caps are areas smaller than 50,000 square km)

“That ice sheets will dominate future sea level rise is not surprising – they hold a lot more ice mass than mountain glaciers,” Eirc Rignot, the report’s lead author said in a statement emailed by NASA yesterday. “What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007. Our study helps reduce uncertainties in near-term projections of sea level rise.”

The results of the study will be published this month in Geophysical Research Letters, a journal of the American Geophysical Union.

The new figures are definitely going to cause much concern in coastal regions in the US and across the world, where governments and local inhabitants are struggling to figure out ways to protect themselves against rising waters.

Just last month scientists at the University of Arizona came out with a report that said by 2100, rising seas would severely affect 180 US coastal cities, with Miami, New Orleans and Virginia Beach among the most at risk. But despite mounting scientific evidence, few costal regions in this country are in any way prepared to face the challenges posed by climate change.

Maureen Nandini Mitra, Editor, Earth Island Journal.Maureen Nandini Mitra photo
In addition to her work at the Journal, Maureen writes for several other magazines and online publications in the US and India. A journalism graduate from Columbia University, her work has appeared in the San Francisco Public Press, The New Internationalist, Sueddeutsche Zeitung, The Caravan and Down to Earth.

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