Why? It has to do with one of the stranger mechanisms in ice physics. Glaciers, it turns out, don’t just alleviate sea-level rise by freezing water and keeping it out of the ocean. Their gravity fields are strong enough that they actually attract ocean water from elsewhere on the planet. The farther you go from a certain patch of glacier, the greater the gravitational effects—and West Antartica is very far from the United States. So Thwaites and Pine Island glaciers essentially swaddle themselves with water that would otherwise slosh against the beaches of the East Coast.
But if West Antarctica’s ice melts, and it loses mass, then its gravitational field will also lose its protective power. And North America will suffer the consequences. For example, for every bit of West Antarctic ice that tumbles into the sea, sea levels in Boston will bear an additional sort of gravity tax of 25 percent.
“For every centimeter [of sea-level rise] from West Antarctica, Boston feels one and a quarter centimeters. And that extends down the East Coast,” said DeConto.