The Oceans Are Going to Rise—but When?

The uniquely vulnerable West Antarctic Ice Sheet holds enough water to raise global sea levels by 5 meters. But when that will happen—and how fast—is anything but settled.

The original version of this story appeared in Quanta Magazine.

In May 2014, NASA announced at a press conference that a portion of the West Antarctic Ice Sheet appeared to have reached a point of irreversible retreat. Glaciers flowing toward the sea at the periphery of the 2-kilometer-thick sheet of ice were losing ice faster than snowfall could replenish them, causing their edges to recede inland. With that, the question was no longer whether the West Antarctic Ice Sheet would disappear, but when. When those glaciers go, sea levels will rise by more than a meter, inundating land currently inhabited by 230 million people. And that would be just the first act before the collapse of the entire ice sheet ...