Ice Sheets

An ice sheet is a continent-sized mass of glacier ice covering more than 50,000 square kilometers. Earth currently has two ice sheets: Greenland (about 1.7 million square kilometers, holding about 2.85 million cubic kilometers of ice) and Antarctica (about 14 million square kilometers, holding about 27 million cubic kilometers of ice). Antarctica is divided into the East Antarctic Ice Sheet (EAIS, which is enormous, mostly grounded above sea level, and relatively stable) and the West Antarctic Ice Sheet (WAIS, which is smaller, mostly grounded below sea level, and more vulnerable to ocean warming). Together the two ice sheets contain enough water to raise global sea level by about 65 meters if they were to fully melt, though that would take millennia even under extreme warming.

Both ice sheets are currently losing mass. Greenland is losing about 250-300 billion tonnes of ice per year on average, with year-to-year variation. Antarctica is losing about 100-150 billion tonnes per year, with most of the loss concentrated in West Antarctica. The mechanisms include surface melting (especially on Greenland during increasingly warm summers), iceberg calving (where outlet glaciers shed icebergs into the ocean), and submarine melting (where warm ocean water melts ice from below at outlet glacier termini and ice shelf bases). Some specific outlet glaciers, like Greenland is Jakobshavn and Antarctica is Thwaites and Pine Island, are losing mass particularly fast and have been called the "doomsday glaciers" because of their potential contribution to sea-level rise.

Ice sheet research is a major scientific frontier. Satellite missions like ICESat-2 (NASA, measuring ice elevation with laser altimetry), GRACE-FO (NASA/German collaboration, measuring ice mass through gravity changes), and CryoSat-2 (ESA, measuring ice topography with radar) provide global coverage. Field expeditions traverse ice sheets to install instruments, drill ice cores, and study glacier dynamics in detail. Numerical models simulate ice sheet evolution under different climate scenarios. Each line of research contributes to projections of future sea-level rise. Current estimates suggest sea level could rise about 0.3-1.0 meters by 2100 depending on emissions, with much higher rises possible after 2100 if rapid Antarctic ice loss occurs. Strong climate adaptation requires planning for these changes, while strong climate mitigation aims to keep them manageable.

Ice sheets are the largest and most consequential ice features on Earth. The next lesson covers their direct effect on the rest of the planet: sea-level rise.