If much of the ice sitting on the Antarctic continent or on the Greenland Shelf melts, water will pour into the oceans, raising their level. Most people will presumably get out of the way in time to avoid drowning (this will all take some time to happen), but an enormous fraction of the Earth's population would be homeless. In addition, the warmer oceans may support more powerful storms, with the resulting damage. The dissolved CO2
will turn the oceans too acidic and kill off the corral reefs, and all the life they support, even aside from the temperature changes. It might make more sense to switch to small efficient cars, public transportation, etc.
p.s. I guess you're thinking about the arctic ice, which mostly floats and will not directly affect the sea levels much. As it melts, it might shut down the Gulf Stream, but that's another story.
By the way, there is an additional effect due to the thermal expansion of ocean water when it warms up. There are various estimates but it seems that about half of the ocean level rise could be attributed to this effect.
(published on 04/16/07)