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West Antarctic Ice Sheet
78°44′03″S 133°16′41″W / 78.73417°S 133.27806°W
The West Antarctic Ice Sheet (WAIS) is the sector of the Antarctic Ice Sheet covering West Antarctica. The WAIS is a marine ice sheet, as the majority of its ice is grounded well below sea level, on rock and sediment that would be the ocean floor if the ice were to retreat. The ice sheet first formed about 27 million years ago, likely fed partially by advancing glaciers of the older East Antarctic Ice Sheet . The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.
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, and a substantial retreat of its coastal glaciers since at least the 1990s. Estimates suggest it added around 7.6 ± 3.9 mm (0.30 ± 0.15 in) to the global sea level rise between 1992 and 2017, and has been losing ice in the 2010s at a rate equivalent to 0.4 millimetres (0.016 inches) of annual sea level rise. While some of its losses are offset by the growth of the 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. Fresh meltwater from WAIS also contributes to ocean stratification and dilutes the formation of salty Antarctic bottom water, which destabilizes Southern Ocean overturning circulation.
In the long term, the West Antarctic Ice Sheet is likely to disappear due to the warming which has already occurred. Paleoclimate evidence suggests that this has already happened during the Eemian period, when the global temperatures were similar to the early 21st century. It is believed that the loss of the ice sheet would take place between 2,000 and 13,000 years in the future, 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. Total sea level rise from West Antarctica increases to 4.3 m (14 ft 1 in) if they melt as well, but this would require a higher level of warming. 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.
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. 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, but it would be extraordinarily difficult and may not account for the ongoing acceleration of ocean warming in the area. 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.
The total volume of the entire Antarctic ice sheet is estimated at 26.92 million km3 (6.46 million cu mi), while the WAIS contains about 2.1 million km3 (530,000 cu mi) in ice that is above the sea level, and ~1 million km3 (240,000 cu mi) in ice that is below it. The weight of the ice has caused the underlying rock to sink by between 0.5 and 1 kilometre (0.31 and 0.62 miles) in a process known as isostatic depression.
Under the force of its own weight, the ice sheet deforms and flows slowly over rough bedrock. Ice ridges are the areas where ice sheet movement is slow because it is frozen to the bed, while ice streams flow much faster because there is liquid water in the sediments beneath them. Those are either the marine sediments which used to cover the ocean floor before the ice sheet froze above them, or they have been created due to erosion from the constant friction of ice against the bedrock. The water in these sediments stays liquid because the Earth's crust below the ice streams is thin and conducts heat from geothermal activity, and because the friction also generates heat, particularly at the margins between ice streams and ice ridges.
When ice reaches the coast, it either calves or continues to flow outward onto the water. The result is a large, floating ice shelf affixed to the continent. These ice shelves restrain the flow of ice into the ocean for as long as they are present.
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West Antarctic Ice Sheet AI simulator
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West Antarctic Ice Sheet
78°44′03″S 133°16′41″W / 78.73417°S 133.27806°W
The West Antarctic Ice Sheet (WAIS) is the sector of the Antarctic Ice Sheet covering West Antarctica. The WAIS is a marine ice sheet, as the majority of its ice is grounded well below sea level, on rock and sediment that would be the ocean floor if the ice were to retreat. The ice sheet first formed about 27 million years ago, likely fed partially by advancing glaciers of the older East Antarctic Ice Sheet . The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.
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, and a substantial retreat of its coastal glaciers since at least the 1990s. Estimates suggest it added around 7.6 ± 3.9 mm (0.30 ± 0.15 in) to the global sea level rise between 1992 and 2017, and has been losing ice in the 2010s at a rate equivalent to 0.4 millimetres (0.016 inches) of annual sea level rise. While some of its losses are offset by the growth of the 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. Fresh meltwater from WAIS also contributes to ocean stratification and dilutes the formation of salty Antarctic bottom water, which destabilizes Southern Ocean overturning circulation.
In the long term, the West Antarctic Ice Sheet is likely to disappear due to the warming which has already occurred. Paleoclimate evidence suggests that this has already happened during the Eemian period, when the global temperatures were similar to the early 21st century. It is believed that the loss of the ice sheet would take place between 2,000 and 13,000 years in the future, 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. Total sea level rise from West Antarctica increases to 4.3 m (14 ft 1 in) if they melt as well, but this would require a higher level of warming. 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.
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. 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, but it would be extraordinarily difficult and may not account for the ongoing acceleration of ocean warming in the area. 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.
The total volume of the entire Antarctic ice sheet is estimated at 26.92 million km3 (6.46 million cu mi), while the WAIS contains about 2.1 million km3 (530,000 cu mi) in ice that is above the sea level, and ~1 million km3 (240,000 cu mi) in ice that is below it. The weight of the ice has caused the underlying rock to sink by between 0.5 and 1 kilometre (0.31 and 0.62 miles) in a process known as isostatic depression.
Under the force of its own weight, the ice sheet deforms and flows slowly over rough bedrock. Ice ridges are the areas where ice sheet movement is slow because it is frozen to the bed, while ice streams flow much faster because there is liquid water in the sediments beneath them. Those are either the marine sediments which used to cover the ocean floor before the ice sheet froze above them, or they have been created due to erosion from the constant friction of ice against the bedrock. The water in these sediments stays liquid because the Earth's crust below the ice streams is thin and conducts heat from geothermal activity, and because the friction also generates heat, particularly at the margins between ice streams and ice ridges.
When ice reaches the coast, it either calves or continues to flow outward onto the water. The result is a large, floating ice shelf affixed to the continent. These ice shelves restrain the flow of ice into the ocean for as long as they are present.