As Tyler Cowen said a while ago, uncertainty in the accuracy of climate models is not our friend and not an argument for inaction. The unexpectedly-rapid melting of the Artic icecap is the first sign that perhaps our climate modelers have been too optimistic.
So let me turn the mike over to Brad Plumer to talk about sea-level rising:
ADVENTURES ON THE HIGH SEAS: The AP interviewed two dozen climate experts and found pretty firm agreement about the fact that sea levels are going to rise at least a meter in the near future, "regardless of any future action to curb greenhouse gases." All told, a rise that big would swamp a big chunk of the U.S. coastline—areas that are seriously at risk include Jamestown, the Louisiana wetlands, parts of Florida, North Carolina, Texas, South Carolina, and so on. Remarkably, even John Christy, who often gets hyped in skeptic circles, thinks we should prepare for a meter's worth of rising seas.
Now, a couple things: Even if a one-meter rise is likely to happen regardless of what we do about greenhouse gases, curbing those gases is still critical. After all, the rate of sea-level rise matters-—a one-meter rise that took place over 50 years would be much, much more catastrophic than a one-meter rise over, say, two centuries (which would at least gives us some time to adapt). And, of course, there's always the high likelihood that sea levels could rise even higher than a meter, if CO2 levels continue increasing without end. Not a happy thought.
(As a sidenote, "skeptics" like Bjorn Lomborg love to say that the IPCC only predicted, at worst, a rise of 8 inches by the end of the century. This was always false, seeing as how the IPCC explicitly said they weren't including "the full effect of changes in ice flow" in their prediction. Maybe that's well-known by now, but seeing as how Lomborg got to peddle this line on the Colbert Report recently without being challenged, it's worth hitting this again and again.)