Antarctic ice sheet

The Antarctic ice sheet is a continental glacier covering 98% of the Antarctic continent, with an area of 14 million square kilometres (5.4 million square miles) and an average thickness of over 2 kilometres (1.2 mi). It is the largest of Earth's two current ice sheets, containing 26.5 million cubic kilometres (6,400,000 cubic miles) of ice, which is equivalent to 61% of all fresh water on Earth.

For the purposes of study, the ice sheet is often subdivided into three geographic regions based on topography, ice flow, and mass balance: The East Antarctic ice sheet (EAIS), West Antarctic ice sheet (WAIS), and Antarctic Peninsula (AP). The WAIS and EAIS are approximately divided along the Transantarctic Mountains, and the AP is defined by its more geographically distinct drainage basins. All three regions have negative mass balance trends and have lost significant volumes of ice over the observational record, accounting for about 10% of recent rates of global mean sea level rise (1993-2020).

Basin distinctions notwithstanding, the ice sheet surface is nearly continuous over the continent, disrupted only regionally by dry valleys, nunataks of the Antararctic mountain ranges, and sparse coastal bedrock—features which often show evidence of past ice cover over the Late Cenozoic Ice Age.

Because the East Antarctic ice sheet is over 10 times larger than the West Antarctic ice sheet and located at a higher elevation, it is less vulnerable to climate change than the West. In the 20th century, it had been one of the only places on Earth which displayed limited cooling instead of warming, even as the West Antarctic ice sheet warmed by over 0.1 °C/decade from 1950s to 2000, producing an average warming trend of >0.05 °C/decade since 1957 across the whole continent. EAIS also started to display a clear warming trend after 2000 (while the warming of the WAIS slowed), but as of early 2020s, there is still net mass gain over the EAIS (due to increased precipitation freezing on top of the ice sheet), yet the ice loss from the WAIS glaciers such as Thwaites and Pine Island Glacier is far greater.

By 2100, net ice loss from Antarctica alone would add around 11 cm (5 in) to the global sea level rise. Further, the way WAIS is located deep below the sea level leaves it vulnerable to marine ice sheet instability, which is difficult to simulate in ice sheet models. If instability is triggered before 2100, it has the potential to increase total sea level rise caused by Antarctica by tens of centimeters more, particularly with high overall warming. Ice loss from Antarctica also generates fresh meltwater, at a rate of 1100-1500 billion tons (GT) per year.^: 1240 It dilutes the saline Antarctic bottom water, which weakens the lower cell of the Southern Ocean overturning circulation and may even contribute to its collapse, although this will likely take place over multiple centuries.

The two parts of the ice sheet also have a very different long-term outlook. Paleoclimate research and improved modelling show that the West Antarctic ice sheet is very likely to disappear even if the warming does not progress any further, and only reducing the warming to 2 °C (3.6 °F) below the temperature of 2020 may save it. It is believed that the loss of the ice sheet would take place between 2,000 and 13,000 years, although several centuries of high emissions may shorten this to 500 years. 3.3 m (10 ft 10 in) of sea level rise would occur if the ice sheet collapses but leaves ice caps on the mountains behind, and 4.3 m (14 ft 1 in) if those melt as well. Isostatic rebound may also add around 1 m (3 ft 3 in) to the global sea levels over another 1,000 years. On the other hand, the East Antarctic ice sheet is far more stable and may only cause 0.5 m (1 ft 8 in) - 0.9 m (2 ft 11 in) of sea level rise from the current level of warming, which is a small fraction of the 53.3 m (175 ft) contained in the full ice sheet. Around 3 °C (5.4 °F), vulnerable locations like Wilkes Basin and Aurora Basin may collapse over a period of around 2,000 years, which would add up to 6.4 m (21 ft 0 in) to sea levels. The loss of the entire ice sheet would require global warming in a range between 5 °C (9.0 °F) and 10 °C (18 °F), and a minimum of 10,000 years.