North America at greater risk from Antarctic ice sheet melt: study

The rising of sea levels as a result of the melting of the West Antarctic ice sheet might hit coastal regions in Canada, the U.S. and the southern Indian Ocean harder than other regions of the world, according to a new study.

The Antarctic ice sheet is enormous, with a volume of water about 100 times that of the Great Lakes combined and a height that reaches 1,800 metres above sea level. Its collapse is one of the more dire potential consequences of rising global temperatures, though scientists look at it as a long-term problem, one that might take centuries or even millenniums to occur.

It's important enough, however, that the Intergovernmental Panel on Climate Change included it in their most recent assessment, predicting the collapse of the ice sheet would lead annual sea levels to rise about five metres.

But University of Toronto geophysicists Jerry Mitrovica and Natalya Gomez, writing in the Friday issue of the journal Science, propose a new model that suggests some regions, including Canada, could see sea levels rise about 30 per cent higher than the five metre average currently predicted.

"If the West Antarctic ice sheet completely collapses, the U.S. and Canadian coasts will be inundated by six to seven metres of additional water, not five metres as people previously thought," said Mitrovica.

That difference of a metre or two could be the difference between regions like southern Florida surviving or submerging and would also inundate low-lying regions in New Brunswick, Nova Scotia, P.E.I. and British Columbia with water.

Some of the factors they included in their assessment that they say were ignored in the IPCC's predictions are:

• The impact of the gravitational pull the ice sheet exerts today on the surrounding water.
• The shift that would occur in the Earth's rotation axis should the ice sheet melt. 
• The changes in depressions of the Antarctic continent once the ice disappeared, which generally speaking would push more water out into the oceans.

Taking these and other considerations into account, the researchers predict much higher sea levels for North American coastlines, as well as for a southern region of the Indian Ocean, than most models predict.

At the same time, the adjusted predictions suggest sea levels won't rise quite as high around the southern portion of South America and around Europe and Asia.

The researchers acknowledge their findings are far from complete: for example, they don't take into account the impact of sea ice melt in Greenland, the East Antarctic and mountain glaciers, which would provide a better picture of the total impact on sea ice levels.

Peter Clark, a professor of geosciences at Oregon State University, also contributed to the study.