flooding

Last week, scientists warned that a massive chunk of the West Antarctica Ice Sheet will eventually drift into the sea and melt, raising sea levels at least 10 feet higher than previous predictions.

Even before the announcement, scientists at the nonprofit research organization Climate Central predicted that surging seas could put the homes of nearly 5 million Americans underwater by the end of this century.

The nation's capital is not exactly a beach town. But the cherry-tree-lined Tidal Basin, fed by the Potomac River, laps at the steps of the Jefferson Memorial. And, especially since Superstorm Sandy, officials in Washington have a clear idea of what would happen in a worst-case storm scenario.

"The water would go across the World War II memorial, come up 17th Street," says Tony Vidal of the U.S. Army Corps of Engineers. "And there are actually three spots where the water would come up where we don't have ... a closure structure right now."