160 feet. That’s how much sea levels could rise if the entire Antarctic ice sheet disintegrated.

What would that mean for the world? We’re already witnessing the sinking of small island nations thanks to a warming ocean and the melting of glaciers at both poles. But if the Antarctic ice sheet melts, we’d see an increase in ocean volume dramatic enough to alter the entire world map.

Even wealthy cities like London and New York that can afford sea walls and other coastal defenses would be calling uncle by the turn of the next century. The ocean would swallow and destroy the world’s greatest metropolises, perched strategically by water.

Recently, the New York Times published “Antarctic Dispatches,” a three-part series on this disaster brewing in Antarctica. Reporter Justin Gillis toured the icy continent on a Columbia University expedition. He calls the prospective melting of Antarctica “a potential apocalypse, depending on exactly how fast it happened.”

This wouldn’t be the first time humans have experienced massive flooding (a subject covered extensively in Brian Fagan’s The Attacking Ocean, which I’m currently listening to on CD in my car).

When the Ice Age drew to a close thousands of years ago, the melting of ice sheets that covered Russia, Europe, and North America flooded some of the places that our hunter/gatherer ancestors called home. These deluges may even explain the common trope of flooding in mythology ranging from Hindu lore to Noah and the Ark.

But when this flooding occurred many thousands of years ago, there were but a few million primitive humans inhabiting the Earth. These mobile communities had plenty of space to which to relocate.

When oceans redraw our coasts now, they impact a world filled with 7.5 billion-and-counting people, who are by comparison immobile and made further immobilized by borders and immigration restrictions. It’s no longer so simple to pick up and go.

Today, the Greenland and Antarctic sheets are among the last remnants of the Ice Age, but they might not be around for long.

After presenting stunning visualizations of ice flow patterns, Gillis is kind enough to end on a hopeful note: it’s not too late to sharply cut greenhouse gas emissions and avert some of the forecasted melting. While we are already locked into a certain amount of warming that will increase sea levels, we could avert the fate of nearly 200 feet of sea level rise in the next couple centuries.