Alaskan glacier melt accelerates sea level rise

Johns Hopkins Glacier in Glacier Bay, southeast Alaska, melts into the sea.
© Commander John Bortniak/NOAA

The resulting meltwater is also contributing much more to the rise in sea level than previous estimates, according to the study by a team of University of Alaska researchers in Fairbanks, who found that both trends are accelerating.

"The rate of thinning has doubled in the past five years, compared to the 40 years before," said Anthony Arendt, of the university's Geophysical Institute, the study's main author.

Sea rise

As a result, the Alaskan contribution to sea-level rise has also doubled, to about 0.27 millimeters a year during the past decade, or about twice the amount assumed by an international panel of scientists that last year predicted sea level would rise up to 11 centimetres (4.3 inches) by the end of this century due to global warming.

"It's a big deal if those rates have been underestimated," said Tom Janetos, an expert at the Heinz Center for Science, Economics and the Environment. "If these results are correct, the rate of sea level rise has probably been underestimated in all international assessments."

More than 100 million people live on land within one metre (three feet) of sea level, and storm surges can devastate coral reefs and low-lying islands and coastlines around the world.

"Although some degree of sea level rise is anticipated in the coming decades, the greater the rise and the faster it occurs, the greater the impact will be on human population," said Benjamin Preston, a researcher at the Washington DC based Pew Center on Global Climate Change.

Despite their relatively small land mass - about 13 per cent of the world's total mountain glacier area - Alaska's glaciers contribute about half of all sea level rise caused by glacial melt and about twice as much as the amount of water lost from the entire Greenland Ice Sheet, according to the Arendt team.

Warmer temperatures

A second study published in Science will also add to concerns about the impact on oceans of faster ice melt. Using records compiled over the last 40 years, researchers at Columbia University have found a sharp decline in the salinity of waters in the Ross Sea near Antarctica, as well as warmer air and water temperatures in the area.

The warmer atmosphere appears to have caused more rain and snowfall, less sea ice, and faster melting of the West Antarctic ice sheet, the Columbia scientists say.

Previously, low salinity found in masses of seawater flowing from the Antarctic to the South Pacific was attributed to more precipitation, but the new study confirms that increased melting of the ice cap itself is also a major factor.

Declining salinity could affect major ocean currents, such as the Gulf Stream which warms the waters and climate of the North Atlantic region, according to oceanographers. One prominent theory suggests that a large flow of fresh water into the North Atlantic could reverse the Gulf Stream, as it has in the past, causing an abrupt plunge in water and air temperatures in northeastern North America and northwestern Europe.

Preston said, "If scientists have underestimated the amount of fresh water likely to enter the oceans in coming decades, they may have also underestimated the risk of such a phenomenon occurring."

© Copyright Environment News Service (ENS) 2002. All Rights Reserved. Republished with kind permission from ENS. This article was also published in co-operation with the OneWorld Network.

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Earth ice melting fast

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