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(Reuters) - U.S. scientists using satellite data have established a more accurate figure of the amount of annual sea level rise from melting glaciers and ice caps which should aid studies on how quickly coastal areas may flood as global warming gathers pace.
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John Wahr of the University of Colorado in Boulder and colleagues, in a study published on Thursday, found that thinning glaciers and icecaps were pushing up sea levels by 1.5 millimeters (0.06 inches) a year, in line with a 1.2 to 1.8 mm range from other studies, some of which forecast sea levels could rise as much as 2 meters (2.2 yards) by 2100.
Sea levels have already risen on average about 18 centimeters since 1900 and rapid global warming will accelerate the pace of the increase, scientists say, threatening coastlines from Vietnam to Florida and forcing low-lying megacities to build costly sea defenses.
To get a better picture of the pace of the melting, Wahr and colleagues used a satellite that measures variations in gravity fields to study changes in the mass of large ice-covered areas. The data covered 2003-2010.
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The glaciers and ice caps included those in the Arctic, South America, Asia as well as Greenland and Antarctica.
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Globally, the rate of sea level rise has accelerated in recent decades to reach about 3.5 millimeters a year, with more than half coming from thermal expansion of the oceans.
Water expands as it gets warmer.
While the creeping annual increase might seem small, the rate of sea level rise is expected to grow. Yet scientists have struggled to refine estimates given the uncertainty about the future pace of global warming, growth trajectory of greenhouse gas emissions and the rate at which ice caps will melt.
Using satellite data instead of more limited and time-consuming data from ground measurements was crucial, Wahr said in an email to Reuters.
The team found that loss ice from Greenland and Antarctica was pushing up sea levels by just over one millimeter a year, comprising most of the 1.5 mm annual rise.
Glaciers and mountain ice caps elsewhere comprised the rest, at 0.4 mm/yr between 2003-10.
"That's a large number, and represents a lot of melting ice," said Wahr. "But it's at least 30 percent smaller than previous global estimates, none of which have used GRACE," he said, referring to the name of the satellite.
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The United Nations' Climate Panel estimates sea global sea level rise of 18 to 59 centimeters from 1990 to the 2090s. But those numbers do not include melting from polar regions where the vast majority of the world's freshwater is locked away.
