You might have heard by now that:

... At a scientific conference on climate change held this week in Copenhagen, four environmental experts announced that sea levels appear to be rising almost twice as rapidly as had been forecast by the United Nations just two years ago. The warning is aimed at politicians who will meet in the same city in December to discuss the same subject and, perhaps, to thrash out an international agreement to counter it.
The reason for the rapid change in the predicted rise in sea levels is a rapid increase in the information available. In 2007, when the Intergovernmental Panel on Climate Change convened by the UN made its prediction that sea levels would rise by between 18cm and 59cm by 2100, a lack of knowledge about how the polar ice caps were behaving was behind much of the uncertainty. Since then they have been closely monitored, and the results are disturbing. Both the Greenland and the Antarctic caps have been melting at an accelerating rate. It is this melting ice that is raising sea levels much faster than had been expected. Indeed, scientists now reckon that sea levels will rise by between 50cm and 100cm by 2100, unless action is taken to curb climate change....

More on the actual studies which had been carried out in supporting the above in The Economist's article.