You might think that if/when the huge ice sheet in West Antarctica melts, sea levels around the world will rise by roughly the same amount everywhere. You’d be wrong.

You’d be in good company though. Some predictions – including the influential Intergovernmental Panel on Climate Change Assessment Reports – have also assumed that meltwater will spread uniformly.

In this week’s issue of Science researchers report that some parts of the world – such as the United States – would see much more of a rise than others. Their paper – which draws on an apparently much overlooked work in Nature from 1977 – says US coastal states will see a sea level rise 30% higher than the uniform rise – called the effective eustatic value – estimates.

“When an ice sheet melts, sea level does not change uniformly,” says Jerry Mitrovica, a geophysicist at the University of Toronto (Globe and Mail). “You get this whopping amplification of sea-level rise in North America.”

The problem, say the authors, is that the West Antarctic Ice Sheet is so big is actually has a gravitational attraction large enough to pull water towards it. “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,” write the authors.

In addition the sheer weight of ice is forcing down the land underneath it and having an impact on the Earth’s spin. When the ice is removed up bounces the land and the Earth moves.

“Consider Washington, DC, and the case where we adopt the conventional value of 5 m for the EEV,” they say. “We predict a sea-level rise 1.3 m higher than the EEV (or 6.3 m total) at this site, an increase above the EEV that is three times greater than predicted using the standard sea-level theory.”

On the plus side DC-ites: this scenario is a ways away: “It’s a time scale of hundreds of years”, says Mitrovica (Reuters).

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Photo: by shioshvili via Flickr under creative commons

Graphic: Jerry Mitrovica & Natalya Gomez, University of Toronto