Why do climatologists predict rising sea levels from melting polar ice caps since ice is less dense than water?

Dear Tom,

Why do climatologists predict rising sea levels from melting polar ice caps since ice is less dense than water?

Jim Doty,
Clayton, Missouri

Dear Jim,
The relative density of ice versus water has nothing to do with the predicted rise of the world’s oceans. Ice floating in the Arctic Ocean (in the north polar region) has no effect on the level of the ocean because, when it melts, water displaced by the ice occupies the same volume as water from the melted ice. At the South Pole, however, ice (most of it, at least) is on land (Antarctica) and consequently above sea level. Upon melting or plunging into the sea at the periphery of the continent, there is a net rise in the sea level. This is true of the ice cap on Greenland, as well. Antarctic ice, if completely melted, would account for about a 200-foot rise in sea levels; Greenland, about another 20 feet.