Melting Ice and Rising Seas

The Greenland and Antarctic ice sheets together hold enough frozen fresh water to raise global sea level by more than 65 meters if they were to melt entirely, and both are now losing mass at accelerating rates. Greenland loses roughly 270 billion tonnes of ice per year on average, through a combination of surface melting and the accelerated flow of outlet glaciers such as Jakobshavn Isbræ into the sea. In Antarctica, the East Antarctic Ice Sheet has remained comparatively stable, but the West Antarctic Ice Sheet is considered far more vulnerable, particularly the Thwaites Glacier — nicknamed the "Doomsday Glacier" by researchers because its potential collapse, driven by warm ocean water eroding its grounding line from below, could alone raise global sea level by more than half a meter and destabilize the wider basin around it. Satellite gravimetry missions such as GRACE and GRACE-FO have made it possible to track these mass changes with increasing precision since 2002.