Climate change in Antarctica

Climate change caused by greenhouse gas emissions from human activities occurs everywhere on Earth, and while Antarctica is less vulnerable to it than any other continent,^[1] climate change in Antarctica has been observed. Since 1959, there has been an average temperature increase of >0.05 °C/decade since 1957 across the continent, although it had been uneven.^[2] West Antarctica warmed by over 0.1 °C/decade from the 1950s to the 2000s, and the exposed Antarctic Peninsula has warmed by 3 °C (5.4 °F) since the mid-20th century.^[3] The colder, stabler East Antarctica had been experiencing cooling until the 2000s.^[4][5] Around Antarctica, the Southern Ocean has absorbed more oceanic heat than any other ocean,^[6] and has seen strong warming at depths below 2,000 m (6,600 ft).^[7]: 1230 Around the West Antarctic, the ocean has warmed by 1 °C (1.8 °F) since 1955.^[3]

The warming of the Southern Ocean around Antarctica has caused the weakening or collapse of ice shelves, which float just offshore of glaciers and stabilize them. Many coastal glaciers have been losing mass and retreating, causing net-annual ice loss across Antarctica,^[7]: 1264 although the East Antarctic ice sheet continues to gain ice inland. By 2100, net ice loss from Antarctica is expected to add about 11 cm (5 in) to global sea level rise. Marine ice sheet instability may cause West Antarctica to contribute tens of centimeters more if it is triggered before 2100.^[7]: 1270 With higher warming, instability would be much more likely, and could double global, 21st-century sea-level rise.^[8][9][10]

The fresh, 1100-1500 billion tons (GT) per year of meltwater from the ice dilutes the saline Antarctic bottom water,^[11][12] weakening the lower cell of the Southern Ocean overturning circulation (SOOC).^[7]: 1240 According to some research, a full collapse of the SOOC may occur a between 1.7 °C (3.1 °F) and 3 °C (5.4 °F) of global warming,^[13] although the full effects are expected to occur over multiple centuries; these include less precipitation in the Southern Hemisphere but more in the Northern Hemisphere, an eventual decline of fisheries in the Southern Ocean and a potential collapse of certain marine ecosystems.^[14] While many Antarctic species remain undiscovered, there are documented increases in Antarctic flora,^[15] and large fauna such as penguins are already having difficulty retaining suitable habitat. On ice-free land, permafrost thaws release greenhouse gases and formerly frozen pollution.^[16]

The West Antarctic ice sheet is likely to completely melt^[17][18][19] unless temperatures are reduced by 2 °C (3.6 °F) below 2020 levels.^[20] The loss of this ice sheet would take between 2,000 and 13,000 years,^[21][22] although several centuries of high greenhouse emissions could shorten this time to 500 years.^[23] A sea-level rise of 3.3 m (10 ft 10 in) would occur if the ice sheet collapses, leaving ice caps on the mountains, and 4.3 m (14 ft 1 in) if those ice caps also melt.^[24] Isostatic rebound may contribute an additional 1 m (3 ft 3 in) to global sea levels over another 1,000 years.^[23] The far-stabler East Antarctic ice sheet may only cause a sea-level rise of 0.5 m (1 ft 8 in) – 0.9 m (2 ft 11 in) from the current level of warming, a small fraction of the 53.3 m (175 ft) contained in the full ice sheet.^[25] With global warming of around 3 °C (5.4 °F), vulnerable areas like Wilkes Basin and Aurora Basin may collapse over around 2,000 years,^[21][22] potentially adding up to 6.4 m (21 ft 0 in) to sea levels.^[23] The complete melting and disappearance of the East Antarctic ice sheet would require at least 10,000 years and would only occur if global warming reaches 5 °C (9.0 °F) to 10 °C (18 °F).^[21][22]