On the NYT’s Green blog, Justin Gillis says, “Sea level does not rise evenly everywhere in the world; gravity shifts and other factors cause the rise to be lumpy….” Gillis describes the difficulty of collecting good data to make predictions:
As I’ve noted previously on the Green blog, scientists are cautious about claiming that the shift is permanent because sea level rise varies on a time scale of decades and can be influenced by short-term factors. The ocean seems to have risen briskly during a warm spell in the 1920s and 1930s, for instance, then to have slowed down when volcanic eruptions cooled the Earth in the middle of the 20th century. But the recent measurements are certainly cause for worry.
There’s a related post about melting sea ice here.