Greenland Ice Sheet

The Greenland ice sheet is the second-largest body of ice on Earth, covering roughly 1.7 million square kilometers, about 80 percent of the island. Its ice is up to about 3 kilometers thick, and if all of it melted, global sea level would rise by around 7 meters.

Snow that falls on the interior compacts over centuries into ice, which flows slowly outward under its own weight toward the coast. Most of the ice leaves through fast-moving outlet glaciers, such as Jakobshavn Isbræ, that end in fjords. There the ice either melts or breaks off as icebergs, a process called calving. The deep cores drilled at Summit, such as GRIP and GISP2, record more than 100,000 years of past climate, including abrupt warmings at the end of the last ice age.

Satellite gravity and altimetry measurements show that the ice sheet has been losing mass since the 1990s, on the order of 250 billion tonnes of ice a year on average since 2002, with large year-to-year swings. Warmer air drives more surface melt, and warmer ocean water eats at the glacier fronts. The loss of bright snow also lowers the albedo, so the surface absorbs more sunlight, a feedback described in ice-albedo feedback. Greenland is warming faster than the global average because of Arctic amplification.

Greenland now adds more to sea level rise than any other single ice mass, and meltwater can also freshen the North Atlantic, which scientists study for effects on the Atlantic meridional overturning circulation. Whether parts of the ice sheet have tipping points beyond which loss becomes self-sustaining is an active research question, and it is one of the central subjects of cryosphere dynamics.