ice-sheets Earth Science

The Greenland Ice Sheet averages 1.6 kilometers thick over roughly 1.7 million square kilometers; melting it entirely would raise global sea level by about 7.4 meters, redrawing most coastlines. Feedbacks make it worse: meltwater pools darken the surface and soak up more sunshine, while thinning marine-terminating glaciers retreat and speed up, shipping interior ice seaward faster. Because ice sheets respond with lag and irreversibility, past a threshold of mass loss they may keep shrinking even if temperatures stabilize — making Greenland one of the most-watched tipping systems in IPCC assessments.

Snow piles up layer by layer in polar regions, sealing each era's air as bubbles when it compacts to ice. A core is therefore a two-sided archive: oxygen-18 and deuterium ratios in the water reconstruct past temperatures, the trapped bubbles give direct readings of atmospheric carbon dioxide and methane up to eight hundred thousand years back, and sulfate spikes mark great eruptions. The EPICA Dome C core spans 800 millennia, showing CO2 never exceeded 300 ppm — today it exceeds 420 ppm, making ice cores among the hardest evidence of human influence on climate.