New Study Shows that Sea Level Rise Resulting From Collapse of West Antarctic Ice Sheet Would be Non-Uniform; Some Regions to See Levels Much Higher Than Previously Predicted
A new study by researchers at the University of Toronto and Oregon State University concludes that when physical and gravitational factors are applied to projections of sea level rise resulting from a catastrophic collapse of the West Antarctic Ice Sheet, the impact on coastal areas is dramatically worse in some parts of the world than predicted so far.
They found that the catastrophic increase in sea level, already projected to average between 16 and 17 feet around the world (~5m), would be almost 21 feet in such places as Washington, DC, putting it largely underwater. Many coastal areas would be devastated. Much of southern Florida would disappear.
Recent projections of sea-level rise after a future collapse of the West Antarctic Ice Sheet (for example, the Fourth Intergovernmental Panel on Climate Change Assessment Report) assume that meltwater will spread uniformly (eustatically) across the oceans once marine-based sectors of the West Antarctic are filled. (The WAIS is grounded below sea-level. Under a WAIS melt scenario, the underwater volume formerly filled by ice would be filled first.)
The new study, by Jerry Mitrovica and Natalya Gomez at the University of Toronto and Peter Clark at Oregon State University, shows that the sea-level rise in excess of the eustatic value will be ~30% higher than previously predicted for US coastal sites.
|“We aren’t suggesting that a collapse of the West Antarctic Ice Sheet is imminent. But these findings do suggest that if you are planning for sea level rise, you had better plan a little higher. ”|
—Prof. Peter Clark
The report is published in the 6 February issue of the journal Science. The research was funded by the National Science Foundation and other agencies from the US and Canada.
The Intergovernmental Panel on Climate Change has estimated that a collapse of the WAIS would raise sea levels around the world by about 16.5 feet, on average, and that figure is still widely used. However, that theoretical average does not consider several key forces, such as gravity, changes in the Earth’s rotation or a rebound of the land on which the massive glacier now rests, the authors say.
The ice sheet has a huge mass, towering more than 6,000 feet above sea level over a large section of Antarctica that’s about the size of Texas. This mass is sufficient to exert a substantial gravitational attraction, researchers say, pulling water toward it.
The rapid melting of ice sheets and glaciers leads to a sea-level change that departs dramatically from the assumption of a uniform redistribution of meltwater. An ice sheet exerts a gravitational attraction on the nearby ocean and thus draws water toward it. If the ice sheet melts, this attraction will be reduced, and water will migrate away from the ice sheet. The net effect, despite the increase in the total volume of the oceans after a melting event, is that sea level will actually fall within ~2000 km of the collapsing ice sheet and progressively increase as one moves further from this region.—Mitrovica et al. (2009)
|View an NSF video interview with University of Toronto professor of geophysics Jerry X. Mitrovica and graduate student Natalya Gomez; and Oregon State University glacial geologist Peter U. Clark.|
Aside from incorporating the gravitational effect, the new study adds further factors to the calculation—the weight of the ice forcing down the land mass on which it sits, and also affecting the orientation of the Earth’s spin. When the ice is removed, it appears the underlying land would rebound, and the Earth’s axis of rotation defined by the North and South Pole would actually shift about one-third of a mile, also affecting the sea level at various points.
If the West Antarctic Ice Sheet completely melted, the East Coast of North America would experience sea levels more than four feet higher than had been previously predicted—almost 21 feet—and the West Coast, as well as Miami, Fla., would be about a foot higher than that. Most of Europe would have seas about 18 feet higher.
It’s still unclear, Clark said, when or if a breakup of the West Antarctic Ice Sheet might occur, or how fast it could happen. It may not happen for hundreds of years, he said, and even then it may not melt in its entirety. Research should continue to better understand the forces at work, he said.
However, these same effects apply to any amount of melting that may occur from West Antarctica. So many coastal areas need to plan for greater sea level rise than they may have expected.—Peter CLark
Jerry X. Mitrovica, Natalya Gomez, Peter U. Clark (2009) The Sea-Level Fingerprint of West Antarctic Collapse. Science Vol. 323. no. 5915, p. 753 doi: 10.1126/science.1166510
Digital images and video of projected impact
Digital image of Antarctica if it consisted only of land actually above sea level