Science: Uneven Sea Level Rise from Antarctic Melting May Affect Some Regions More Than Previously Estimated

The melting of the West Antarctic Ice Sheet may cause sea level to rise more than previously predicted for some regions, including the U.S. coastline, researchers estimate.

In their Brevium article in the 6 February issue of Science, Jerry Mitrovica of the University of Toronto and coauthors note that most projections of future sea-level change, including the Intergovernmental Panel on Climate Change's fourth assessment report, assume that upon a collapse of the West Antarctic Ice Sheet, meltwater would spread uniformly across the oceans.

In their study, the authors use computer simulations to show that sea-level rise would actually be higher in the oceans bordering North America and in the Indian Ocean than it would be in the rest of the world.

Taking Washington D.C. as an example, they predict an additional sea-level rise of 1.3 meters, on top of the previously estimated 5 meters, if the entire West Antarctic Ice Sheet melted.

These regional differences would arise in part because an ice sheet exerts a gravitational attraction on the nearby ocean and thus draws water toward it. If the ice sheet melts and the attraction subsides, sea level will actually fall within 2,000 kilometers of the collapsing ice sheet and will progressively increase with distance from this region.

Other important processes include the uplift of inundated regions exposed when the marine-based ice sheet collapses, and water redistribution associated with a shift in the Earth's rotation axis.

Each of the world's ice reservoirs will therefore produce a distinct "fingerprint" of sea level change, according to the authors.

"There is still some important debate as to how much ice would actually disappear if the West Antarctic Ice sheet collapses—some fraction of the ice sheet may remain quite stable," Mitrovica said.

"But, whatever happens, our work shows that the sea-level rise that would occur at many populated coastal sites would be much larger than one would estimate by simply distributing the meltwater evenly. Any careful assessment of the sea-level hazard associated with the loss of major ice reservoirs must, of course, account for the sea-level fingerprint of other sources of meltwater, namely Greenland, the East Antarctic and mountain glaciers. The most important lesson is that scientists and policy makers should focus on projections that avoid simplistic assumptions."

Kathleen Wren

5 February 2009