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 already been observed. There has been an average temperature increase of >0.05 °C/decade since 1957 across the continent, although it had been uneven.^[2] While 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 and more stable East Antarctica had been experiencing cooling until the 2000s.^[4][5] Around Antarctica, the Southern Ocean has absorbed more heat than any other ocean,^[6] with particularly strong warming at depths below 2,000 m (6,600 ft)^[7]: 1230 and around the West Antarctic, which has warmed by 1 °C (1.8 °F) since 1955.^[3]

The warming of Antarctica's territorial waters has caused the weakening or outright collapse of ice shelves, which float just offshore of glaciers and stabilize them. Many coastal glaciers have been losing mass and retreating, which causes net annual ice loss across Antarctica,^[7]: 1264 even as the East Antarctic ice sheet continues to gain ice inland. By 2100, net ice loss from Antarctica alone is expected to add about 11 cm (5 in) to global sea level rise. However, 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 overall 21st century sea level rise.^[8][9][10]

The fresh meltwater from the ice, 1100-1500 billion tons (GT) per year, dilutes the saline Antarctic bottom water,^[11][12] thus weakening the lower cell of the Southern Ocean overturning circulation.^[7]: 1240 Some research tentatively suggests a full collapse of the circulation may occur between 1.7 °C (3.1 °F) and 3 °C (5.4 °F) of global warming,^[13] although the full effects are expected to unfold over multiple centuries. They include less precipitation in the Southern Hemisphere but more in the Northern Hemisphere, and an eventual decline of fisheries in the Southern Ocean with a potential collapse of certain marine ecosystems.^[14] Furthermore, while many Antarctic species remain undiscovered, there are already documented increases in flora and large fauna such as penguins are already seen struggling to retain suitable habitat. On ice-free land, permafrost thaws, releasing not only greenhouse gases, but also formerly frozen pollution.^[15]

The West Antarctic ice sheet is likely to melt completely,^[16][17][18] unless temperatures are reduced by 2 °C (3.6 °F) below the levels of the year 2020.^[19] The loss of this ice sheet would take between 2,000 and 13,000 years,^[20][21] although several centuries of high emissions could shorten this timeframe to 500 years.^[22] 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.^[23] Isostatic rebound may contribute an additional 1 m (3 ft 3 in) to global sea levels over another 1,000 years.^[22] In contrast, the East Antarctic ice sheet is far more stable and 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.^[24] With a global warming of around 3 °C (5.4 °F), vulnerable areas like the Wilkes Basin and Aurora Basin may collapse over a period of around 2,000 years,^[20][21] potentially adding up to 6.4 m (21 ft 0 in) to sea levels.^[22] The complete melting and disappearance of the East Antarctic ice sheet would require at least 10,000 years, and it would only occur if global warming reaches 5 °C (9.0 °F) to 10 °C (18 °F).^[20][21]