Jonathan Overpeck and others have a paper Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise in Science (24 March 2006) that suggests that sea level rise due to anthropogenic climate change could occur much faster than people have previously expected. Possibly an increase of 5 to 10 m of several centuries. (For news articles see BBC, NYTimes, & Toronto G&M).
To visualize the consquences of sea level rise:
WorldChanging points to Flood Maps. A site that mashes up NASA elevation data with Google Maps, and offers a visualization of the effects of a single meter increase all the way to a 14 meter rise. Some examples are: Vancouver with 6m sea rise, New Orleans, and the Netherlands.
Richard Kerr writes in a news article in Science, A Worrying Trend of Less Ice, Higher Seas:
The ice sheet problem today very much resembles the ozone problem of the early 1980s, before researchers recognized the Antarctic ozone hole, Oppenheimer and Alley have written. The stakes are high in both cases, and the uncertainties are large. Chemists had shown that chlorine gas would, in theory, destroy ozone, but no ozone destruction had yet been seen in the atmosphere. While the magnitude of the problem remained uncertain, only a few countries restricted the use of chlorofluorocarbons, mainly by banning their use in aerosol sprays.
But then the ozone hole showed up, and scientists soon realized a second, far more powerful loss mechanism was operating in the stratosphere; the solid surfaces of ice cloud particles were accelerating the destruction of ozone by chlorine. Far more drastic measures than banning aerosols would be required to handle the problem.
Now glaciologists have a second mechanism for the loss of ice: accelerated flow of the ice itself, not just its meltwater, to the sea. “In the end, ice dynamics is going to win out” over simple, slower melting, says Bindschadler. Is glacier acceleration the ozone hole of sea level rise? No one knows. No one knows whether the exceptionally strong warmings around the ice will continue apace, whether the ice accelerations of recent years will slow as the ice sheets adjust to the new warmth, or whether more glaciers will fall prey to the warmth. No one knows, yet.