slr-6m.jpg

The fate of Florida and Louisiana if we’re myopic and greedy enough to let the West Antarctic Ice Sheet collapse (click to see entire SE coast).

A new study in Science finds that sea-level rise from a collapse of the WAIS would likely be 25 percent higher for North America than previously estimated:

The catastrophic increase in sea level, already projected to average between 16 and 17 feet around the world, would be almost 21 feet in such places as Washington, D.C., scientists say, putting it largely underwater. Many coastal areas would be devastated. Much of Southern Florida would disappear.

This article has already started to make news around the globe (Reuters story here). But, frankly, divining the difference between a rise of 16.5 feet (an incalculably devastating catastrophe) and 21 feet (an incalculably devastating catastrophe) is like trying to count the number of devils on a pin.

Nonetheless, WAIS collapse is all but inevitable given business-as-usual warming of 5-7°C. As I explained in my book:

Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level.

For a longer discussion of WAIS and its unique instability, see “Antarctica has warmed significantly over past 50 years.”

So what is new in the Science article, “The Sea-Level Fingerprint of West Antarctic Collapse” ($ub. req’d)? Study coauthor and geophysicist Jerry X. Mitrovica, director of the Earth System Evolution Program at the Canadian Institute for Advanced Research, explains:

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. However, this estimate is far too simplified because it ignores three significant effects:

  • 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;
  • 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;
  • 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.

And this all means that if WAIS 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.”

A digital animation of various sea-level rise scenarios up to six metres is here.

The time to act is now.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.