A big chunk of the West Antarctic Ice Sheet is collapsing. Scientists announced in May that it’s now inevitable — though it will take decades or even centuries to happen. But the collapse will cause a big rise in sea level. Eric Rignot is the lead author of one of the studies that reached that conclusion, and he’s a glaciologist at NASA’s Jet Propulsion Laboratory and at UC-Irvine. He talked with Alex Chadwick.