Lurking in the comments to this post was a discussion of how high and how fast sea levels could rise if the world keeps spewing out carbon unabated. Here's the latest research on the subject, which is still an area of some contention:
Melting glaciers, disappearing ice sheets and warming water could lift sea levels by as much as 1.5 meters (4.9 feet) by the end of this century, displacing tens of millions of people, new research showed on Tuesday.
Presented at a European Geosciences Union conference, the research forecasts a rise in sea levels three times higher than that predicted by the Intergovernmental Panel on Climate Change (IPCC) last year. ...
"The IPCC numbers are underestimates," said Simon Holgate, also of the Proudman Laboratory. The researchers said the IPCC had not accounted for ice dynamics -- the more rapid movement of ice sheets due to melt water which could markedly speed up their disappearance and boost sea levels. But this effect is set to generate around one-third of the future rise in sea levels, according to Steve Nerem from the University of Colorado in the United States.
"If (the sea level) rises by one meter, 72 million Chinese people will be displaced, and 10 percent of the Vietnamese population," said Jevrejeva.
For a more thorough look at the IPCC's sea-rise predictions, and why they're likely underestimates, this RealClimate post is a good place to start. (It's readable, even for non-experts.)
And to see how this little ocean surge could affect the United States, check out this interactive map put out by Architecture2030, which lets you see the impact of various sea-level rises on different U.S. coastal cities. A 1.5-meter rise could, potentially, take out New Orleans, Atlantic City, NJ; San Mateo, CA; Galveston, TX; East Boston; and a long list of towns in Florida that would find themselves partially or wholly submerged. Of course, some of these cities could try building elaborate flood defenses. A country like, say, Bangladesh—most of which sits only one meter above sea level—might find it a bit harder to cope.