Sea level rise may be worse than expected

WASHINGTON -- Melting ice from global warming may raise sea levels even more than had been expected, an analysis suggests. Long-term melting of ice in Antarctica and other areas could raise sea levels by 16 feet to 17 feet, previous studies have indicated. But a report in Friday's edition of the journal Science warns that factors not previously considered could boost that increase to up to 21 feet in some areas.

Earlier research has focused on melting ice adding water to the oceans and on thermal expansion of sea water in a warmer climate.

In the new report geophysicist Jerry X. Mitrovica and physics graduate student Natalya Gomez of the University of Toronto, Canada, and Oregon State University geoscientist Peter Clark, say other factors need to be considered.

•When an ice sheet melts, its gravitational pull on the ocean is reduced and water moves away from it. That means sea levels could fall near Antarctica and rise more than expected in the northern hemisphere.

•Antarctic bedrock that currently sits under the weight of the ice sheet will rebound from the weight, pushing some water out into the ocean.

•The melting of the West Antarctic ice sheet will cause the Earth's rotation axis to shift, potentially moving water northward.

"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," Mitrovica said in a statement.