For centuries, the enormous ice sheet covering the Arctic island of Greenland has been relatively stable.

So when NASA scientists realized that Greenland’s glaciers had begun melting much faster than expected, they were puzzled — and alarmed: If all of Greenland’s ice sheet were to melt, it’s estimated that sea level around the world would rise by about 20 feet, putting coastal cities from Miami to Mumbai at risk of catastrophic flooding.

Date: 

Thursday, September 20, 2018