Western Greenland Ice Sheet Nears Tipping Point

PNAS, May 17

Unlike Antarctica with its protective ice shelves, the stability of Greenland’s ice sheet depends on its sheer altitude: three kilometers high at some points, the temperature at the “top” of the ice sheet rarely falls below freezing, even in summer. However, as the ice sheet loses mass, its altitude lowers, exposing more and more of the central portions to above-freezing temperatures and melt. Once the ice sheet drops enough in elevation, complete loss becomes inevitable because it stays above freezing for greater periods each year, which cannot be offset by winter snowfall. Previous estimates of the temperature threshold beyond which Greenland ice loss is irreversible averaged around 1.6°C above pre-industrial, but with large ranges between about 0.8-3.2°C. This detailed study of the central western ice sheet, largely drained by the large Illulisaat (Jakobshavn) glacier, shows that this threshold could be quite close, potentially already at today’s 1.2°C, at least for this portion of Greenland. Reconstruction of the height changes of the central-western Greenland ice sheet since 1880 shows loss of elevation, and thus instability at an accelerating rate. Ice loss from Greenland already has measurable impacts on global sea level, and may also be impacting Earth’s largest ocean circulation systems. Even this partial section of Greenland holds 1-2 meters of global sea-level rise,

https://www.pnas.org/content/118/21/e2024192118