To their dismay, DeConto and Pollard had realized that Antarctica might be more vulnerable than previously thought. Increasing temperatures would attack the ice in two ways: warmer air would melt it from above, forming pools on the surface, and warming ocean currents would eat at the underside of the sheet, creating large cracks. The pools on the surface could drain through the cracks, widening them and splitting the ice sheet into unstable pieces that would fall apart under their own weight. The remaining chunks, surrounded by warm water and air, would melt quickly, like the ice cubes in a cocktail. If the two men were correct, melting Antarctic ice could by itself raise the world's oceans more than three feet by 2100, enough to swamp Miami, Tokyo, Mumbai, New Orleans, and many other cities. By 2500 the rise could be as much as fifty feet.