When you have a lot of frozen water, you not only have a lot of water, but you have gravitational effects, and lots of bouncy, bouncy if the stuff melts, which slightly changes the shape of the Earth.
The West Antarctic Ice Sheet (WAIS) is big enough, that if it goes away, these things and more have to be considered. In a recent Science report, Mitrovica, Gomez and Clark discuss how global sea levels would rise if the WAIS collapsed.
Most models of sea level rise are relatively unsophisticated. Clark and Lingle added gravitational and rebound effects. Sea levels in the far south, near the sheet DECREASE because the gravitational attraction of the ice sheet for sea water in the area and elastic rebound. The effects extends out as far north as Peru. The Science report adds some more spice to the model
The sea-level theory adopted by Clark and Lingle does not allow for shoreline migration, including the inundation and adjustment of regions vacated by grounded, marine-based ice cover, or any feedback onto sea level of Earth rotation changes. We show a projection based on a sea-level theory (6) that overcomes these limitations. These results show a highly accentuated sea-level rise in the oceans bordering North America and in the Indian Ocean. Coastal sites in North America would experience a rise 30% higher than the (effective eustatic value) EEV.Figure B shows the results of their calculation and C the differences between the two
In particular, the collapse of the WAIS leads to a displacement of the south rotation pole of 100 m x EEV toward the West Antarctic; this shift drives a sea-level rise in North America and the Indian Ocean and a fall over South America and Asia relative to the EEVSea level at Washington, DC is 6.3 m (the Potomac is tidal up to Georgetown) 1.3 m higher than the generic 5 m from Clark and Lingle's model. The Capital is safe (but the front steps are wet). The White Houseboat will float.