Greenland: a remote, mysterious island five times the size of California but with a population of just 56,000. The ice sheet that covers it is 700 miles wide and 1,500 miles long, and is composed of nearly three quadrillion tons of ice. For the last 150 years, explorers and scientists have sought to understand Greenland—at first hoping that it would serve as a gateway to the North Pole, and later coming to realize that it contained essential information about our climate. Locked within this vast and frozen white desert are some of the most profound secrets about our planet and its future. Greenland’s ice doesn’t just tell us where we’ve been. More urgently, it tells us where we’re headed.