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Researchers: After Collapse Of Antarctic Ice Sheet, Sea Level Rise Around North America Higher Than Expected

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TORONTO, Ontario -- University of Toronto geophysicists have shown that should the West Antarctic Ice Sheet collapse and melt in a warming world – as many scientists are concerned it will – it is the coastlines of North America and of nations in the southern Indian Ocean that will face the greatest threats from rising sea levels.

"There is widespread concern that the West Antarctic Ice Sheet may be prone to collapse, resulting in a rise in global sea levels," says geophysicist Jerry X. Mitrovica, who, along with physics graduate student Natalya Gomez and Oregon State University geoscientist Peter Clark, are the authors of a new study to be published in the February 6 issue of Science magazine. "We've been able to calculate that not only will the rise in sea levels at most coastal sites be significantly higher than previously expected, but that the sea-level change will be highly variable around the globe," adds Gomez.

"Scientists are particularly worried about the ice sheet because it is largely marine-based, which means that the bedrock underneath most of the ice sits under sea level," says Mitrovica, director of the Earth Systems Evolution Program at the Canadian Institute for Advanced Research. "The West Antarctic is fringed by ice shelves which act to stabilize the ice sheet – these shelves are sensitive to global warming, and if they break up, the ice sheet will have a lot less impediment to collapse." This concern was reinforced further in a recent study led by Eric Steig of the University of Washington that showed that the entire region is indeed warming.

"The typical estimate of the sea-level change is five metres, a value arrived at by taking the total volume of the West Antarctic Ice Sheet, converting it to water and spreading it evenly across the oceans, says Mitrovica. "However, this estimate is far too simplified because it ignores three significant effects:

  1. when an ice sheet melts, its gravitational pull on the ocean is reduced and water moves away from it. The net effect is that the sea level actually falls within 2,000 km of a melting ice sheet, and rises progressively further away from it. If the West Antarctic Ice Sheet collapses, sea level will fall close to the Antarctic and will rise much more than the expected estimate in the northern hemisphere because of this gravitational effect;

  2. the depression in the Antarctic bedrock that currently sits under the weight of the ice sheet will become filled with water if the ice sheet collapses. However, the size of this hole will shrink as the region rebounds after the ice disappears, pushing some of the water out into the ocean, and this effect will further contribute to the sea-level rise;

  3. the melting of the West Antarctic Ice Sheet will actually cause the Earth's rotation axis to shift rather dramatically – approximately 500 metres from its present position if the entire ice sheet melts. This shift will move water from the southern Atlantic and Pacific oceans northward toward North America and into the southern Indian Ocean.

"The net effect of all of these processes is that if the West Antarctic Ice Sheet collapses, the rise in sea levels around many coastal regions will be as much as 25 per cent more than expected, for a total of between six and seven metres if the whole ice sheet melts," says Mitrovica. "That's a lot of additional water, particularly around such highly populated areas as Washington, D.C., New York City, and the California coastline." Digital animation of what various sea-level rise scenarios might look like for up to six metres is at

"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," he says. "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."

Views expressed in this article do not necessarily reflect those of, its staff or its advertisers.

Reader Comments

3 people have commented so far. cloud add your comment

Call me suspicious but, if I float a block of ice in a filled glass and let it melt, the displacement does not change. Amazing how the Global Warmaholics ignore such simple stuff. Get real guys, ask yourself who is going to make the money out of carbon trading.
   comment# 1   - Dana Jennings · Cronulla, NSW Australia · May 1, 2009 @ 6:49am

If you honestly ask yourself who profits from carbon trade the only honest conclusion is...nobody. Carbon trade is expensive and make no mistake, that has always been the single underpinning argument against any attempt to lower carbon emissions...period. So lets get real, itís about profits and money and if nothing is done it doesnít take a scientist to know who will continue to make hundreds of billions in the oil and gas industries. Call me an individual thinker but, if my opinion came from a single global media group dedicated to perpetuating multinational profits over all else... I too would repeat an empty, although cleverly crafted slogan that equated to doing nothing.
   comment# 2   - Doug · Florida, United States · Feb 5, 2011 @ 4:10am

@comment #1, Dana, don't you realize that much of the ice in question is (was) part of a landmass? The article states that the ice is sitting on bedrock. This isn't like letting an ice cube melt into a drink. It is like dropping an ice cube into a full glass. What happens then? The water is displaced and the glass overflows. Moreover, salt doesn't freeze into the ice. Hence the higher salinity of the Polar regions. Adding that much fresh water to the sea most likely will alter the pattern of the 'ocean conveyer belt' currents. This has nothing to do with money. It has to do with the survival of life on the planet.
   comment# 3   - Jack Trevally · Columbia USA · Aug 30, 2011 @ 8:57pm
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