Scientists say the collapse of the West Antarctic Ice Sheet would have such profound effects it would shift the planet's rotation, sending a bulge of water into the Northern Hemisphere.

The enormous ice sheet, which many experts believe could collapse as the climate warms, is so heavy that as it melts it "will actually cause the Earth's rotation axis to shift rather dramatically," reports a team led by geophysicist Jerry Mitrovica, at the University of Toronto. The scientists say the North and South poles would move about half a kilometre if the entire ice sheet collapses and shifts more water north.

Coastal regions from Washington to Vancouver could expect sea levels to rise at least six metres, Mitrovica and his colleagues report Friday in the journal Science. Much of Florida would be drowned as would low-lying areas in Maritime Canada, the Arctic and along the Pacific coast.

There is nowhere on the coast of Canada or the U.S. that the sea level won't rise to at least six metres, Mitrovica said in an interview.

He and his colleagues stress that the collapse of the West Antarctic Ice Sheet, while a big concern, is not imminent and may not occur for centuries. "But these findings do suggest that if you are planning for sea level rise, you had better plan a little higher," says co-author Peter Clark at Oregon State University.