Nearly 90 percent of the planet's ice is in Antarctica, and most of the rest is in Greenland. Go to the South Pole and you will be standing on nearly two miles of ice, at the North Pole just fifteen feet of it. Antarctica alone has six million cubic miles of ice—enough to raise the oceans by a height of two hundred feet if it all melted. But if all the water in the atmosphere fell as rain, evenly everywhere, the oceans would deepen by only an inch.

Sea level, incidentally, is an almost entirely notional concept. Seas are not level at all. Tides, winds, the Coriolis force, and other effects alter water levels considerably from one ocean to another and within oceans as well. The Pacific is about a foot and a half higher along its western edge—a consequence of the centrifugal force created by the Earth's spin. Just as when you pull on a tub of water the water tends to flow toward the other end, as if reluctant to come with you, so the eastward spin of Earth piles water up against the ocean's western margins.