Twenty-six million cubic kilometres of ice sit on Antarctica
The Antarctic ice sheet blankets ninety-eight percent of the continent across 14 million square kilometres, averaging more than two kilometres thick and holding about 26.5 million cubic kilometres of ice. It is Earth’s largest ice sheet—and its western half is the climate risk that keeps modelers awake.
East Antarctica’s sheet dwarfs the West by more than tenfold and sits higher, so it proved less sensitive; parts even showed limited twentieth-century cooling while the west warmed. By 2100 Antarctica alone may add around eleven centimetres of global sea-level rise, and marine ice-sheet instability under the west is hard to simulate. Paleoclimate work suggests the West Antarctic Ice Sheet is very likely doomed without cooling some two degrees below 2020 temperatures, with loss spanning centuries to millennia if triggered.
At roughly 0.92 gigatonnes per cubic kilometre, the whole sheet weighs on the order of 24 million gigatonnes.
The Transantarctic Mountains split the ice into the larger East Antarctic sheet and the smaller West Antarctic one, and some glaciologists count the Antarctic Peninsula's cover as a third. The eastern ice rests on solid land, but the western sheet's bed lies in places more than 2,500 metres below sea level and would be seabed without its burden. That makes it a marine-based sheet whose margins float out as the Ross and Filchner-Ronne ice shelves. Greenland's is the only other ice sheet on Earth today.
Antarctica began icing over between roughly 60 and 45.5 million years ago, and glaciation surged around 34 million years ago as carbon dioxide fell past a tipping point near 600 parts per million. The western sheet shrank during the warm early Pliocene, when the Ross Sea opened, while the eastern one held firm. Today melting pours 1,100 to 1,500 billion tonnes of fresh water a year into the Southern Ocean, layering it more strongly and weakening parts of its overturning circulation, which could eventually collapse.
Source: Antarctic ice sheet
