West Antarctic Ice Sheet

78°44′03″S 133°16′41″W / 78.73417°S 133.27806°W / -78.73417; -133.27806

West Antarctic ice sheet
Type	Ice sheet
Area	<1,970,000 km2 (760,000 sq mi)[1]
Thickness	~1.05 km (0.7 mi) (average),[2] ~2 km (1.2 mi) (maximum)[1]
Status	Receding

The West Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. It is classified as a marine-based ice sheet, meaning that its bed lies well below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.^[1]

As a smaller part of Antarctica, WAIS is also more strongly affected by climate change. There has been warming over the ice sheet since the 1950s,^[3][4] and a substantial retreat of its coastal glaciers since at least the 1990s.^[5] Estimates suggest it added around 7.6 ± 3.9 mm (19⁄64 ± 5⁄32 in) to the global sea level rise between 1992 and 2017,^[6] and has been losing ice in the 2010s at a rate equivalent to 0.4 millimetres (0.016 inches) of annual sea level rise.^[7] While some of its losses are offset by the growth of East Antarctic ice sheet, Antarctica as a whole will most likely lose enough ice by 2100 to add 11 cm (4.3 in) to sea levels. Further, marine ice sheet instability may increase this amount by tens of centimeters, particularly under high warming.^[8] Fresh meltwater from WAIS also contributes to ocean stratification and dilutes the formation of salty Antarctic bottom water, which destabilizes Southern Ocean overturning circulation.^[8][9][10]

In the long term, the West Antarctic Ice Sheet is likely to disappear due to the warming which has already occurred.^[11] Paleoclimate evidence suggests that this has already happened during the Eemian period, when the global temperatures were similar to the early 21st century.^[12][13] It is believed that the loss of the ice sheet would take place between 2,000 and 13,000 years,^[14][15] although several centuries of high emissions may shorten this to 500 years.^[16] 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. Total sea level rise from West Antarctica increases to 4.3 m (14 ft 1 in) if they melt as well,^[2] but this would require a higher level of warming.^[17] Isostatic rebound of ice-free land may also add around 1 m (3 ft 3 in) to the global sea levels over another 1,000 years.^[16]

The preservation of WAIS may require a persistent reduction of global temperatures to 1 °C (1.8 °F) below the preindustrial level, or to 2 °C (3.6 °F) below the temperature of 2020.^[18] Because the collapse of the ice sheet would be preceded by the loss of Thwaites Glacier and Pine Island Glacier, some have instead proposed interventions to preserve them. In theory, adding thousands of gigatonnes of artificially created snow could stabilize them,^[19] but it would be extraordinarily difficult and may not account for the ongoing acceleration of ocean warming in the area.^[11] Others suggest that building obstacles to warm water flows beneath glaciers would be able to delay the disappearance of the ice sheet by many centuries, but it would still require one of the largest civil engineering interventions in history.