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Melting glaciers raise sea level more than polar ice sheets

By AFP (Agence France Press) - July 20, 2007

Contrary to common belief, melting glaciers due to global warming contribute more to the rising sea level than the Antarctic and Greenland ice sheets, researchers said Thursday in a study.

Scientists found that the ebb and flow of glaciers where they meet the water causes them to speed up and deliver more ice into the world’s oceans than previously estimated, said the study published in Science’s latest issue.

Glaciers and ice caps account for 60 percent of the meltwater that flows into the oceans, which has been speeding up over the past 10 years from global warming, said the study’s chief author, emeritus professor Mark Meier of University of Colorado’s Boulder’s Institute of Arctic and Alpine Research.

Together, glaciers and ice caps drop into the oceans 417 cubic kilometers (100 cubic miles) of ice each year, equal to the volume of Lake Erie, one of the five Great Lakes of the United States.

And the volume of ice grows by 12.5 cubic kilometers (three cubic miles) each year.

By comparison, the study said, ice breaking off and melting from Greenland’s ice sheet contributes 28 percent of the world’s ice to the oceans, and the Antarctic ice sheet another 12 percent.

The accelerating contribution of glaciers and ice caps is due in part to rapid changes in the flow of tidewater glaciers that discharge icebergs directly into the ocean, the researchers said.

When the glacier with its “toe in the water” thins, they said, a larger fraction of its weight is supported by water and it slides faster and sends more ice into the ocean.

Alaska’s Columbia Glacier which drops three cubic kilometers (0.7 cubic miles) into Prince William sound is a good example, said geologist and co-author of the study Robert Anderson.

The glacier has thinned up to 400 meters (1,300 feet) in a few places, has shrunk about 14.5 kilometers (nine miles) since 1980 and is expected to shrink the same amount in the next two decades, he said.

The melting of the ice sheets of Greenland and the Antarctic is not expected to catch up with that of glaciers and ice caps until the end of the century, the scientists said.

They estimated the accelerated melting of glaciers and ice caps will add from 10.2 to 24.1 centimeters (4.0-9.5 inches) to the sea level rise globally by 2100.

The figures do not include the expansion of the oceans as they get warmer which could potentially double the levels, the researchers said.

A 30-centimeter (one foot) rise in the sea level causes a shoreline retreat of 30 meters (100 feet) or more, they said, adding that currently some 100 million people live within about one meter (three feet) of sea level.