Although this hasnít been subject to much exposure, most of the ice sheet over the Western Antarctic bulge is actually below sea level- that is the mile thick ice sits on the ocean bottom. What we think of as the continent of Antarctica doesnít exist- the Western bulge is actually just a few islands. Rivers of ice within this sheet are flowing to the sea at hugely higher rates (several feet a day). If sea water were to penetrate underneath the floor of this sheet and melt and lubricate it, it is conceivable that the entire thing could catastrophically rip loose and plunge in the ocean through the Ross Sea and Ice Shelf (which has been breaking up). That would raise worldwide sea levels by 16-20 feet and flood every seaside city in the world, after shattering them with devastating tidal waves. Imagine if a 90 mile long 6000 ft high 1/4 mile wide chunk of ice cap snaps off into the ocean. Though some of the Day After Tomorrow movie is scientific gibberish (the instant freezing)- the smashing and flooding of major cities by water is something we may see in our lifetimes.


Note: Map is from Nat. Geographic 1963, more modern ones show much less actual land.