78°44′03″S 133°16′41″W / 78.73417°S 133.27806°W / -78.73417; -133.27806
123-624: 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 ,
246-685: A conspiracy among climate scientists to make up global warming, and said Doran's study definitively proved there was no warming in Antarctica outside of the Peninsula. Relatively few scientists responded to the book at the time, but it was mentioned in a 2006 US Senate hearing in support of climate change denial . Peter Doran published a statement in The New York Times decrying the misinterpretation of his work. The British Antarctic Survey and NASA also issued statements affirming
369-481: A doubling time of 10, 20 or 40 years, which would then lead to multi-meter sea level rise in 50, 100 or 200 years. However, it remains a minority view amongst the scientific community. For comparison, a 2020 survey of 106 experts found that their 5%–95% confidence interval of 2100 sea level rise for the high-emission scenario RCP8.5 was 45–165 cm ( 17 + 1 ⁄ 2 –65 in). Their high-level projections also included both ice sheet and ice cliff instability:
492-467: A flexible material and anchored to the Amundsen Sea floor would be able to interrupt warm water flow. This approach would reduce costs and increase the longevity of the material (conservatively estimated at 25 years for curtain elements and up to 100 years for the foundations) relative to more rigid structures. With them in place, Thwaites Ice Shelf and Pine Island Ice Shelf would presumably regrow to
615-492: A high albedo (reflectivity), adds to the albedo of the ice sheets' own bright, white surface. Antarctica's coldness means it is the only place on Earth where an atmospheric temperature inversion occurs every winter; elsewhere on Earth, the atmosphere is at its warmest near the surface and becomes cooler as elevation increases. During the Antarctic winter, the surface of central Antarctica becomes cooler than middle layers of
738-429: 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
861-550: A major land mass, but the bed of the WAIS is, in places, more than 2,500 meters (8,200 feet) below sea level . It would be seabed if the ice sheet were not there. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf , the Filchner-Ronne Ice Shelf , and outlet glaciers that drain into
984-485: A minimum of 10,000 years. The Antarctic ice sheet covers an area of almost 14 million square kilometres (5.4 million square miles) and contains 26.5 million cubic kilometres (6,400,000 cubic miles) of ice. A cubic kilometer of ice weighs approximately 0.92 metric gigatonnes, meaning that the ice sheet weighs about 24,380,000 gigatonnes. This ice is equivalent to around 61% of all fresh water on Earth. The only other currently existing ice sheet on Earth
1107-600: A point where only minor and isolated ice caps remained, such as during the Marine isotope stage 31 ~1.07 million years ago, or the Eemian period ~130,000 years ago. West Antarctica has experienced statistically significant warming in recent decades, although there is some uncertainty about its magnitude. In 2015, the warming of the WAIS between 1976 and 2012 was calculated as a range between 0.08 °C (0.14 °F) per decade and 0.96 °C (1.73 °F) per decade. In 2009,
1230-538: A rate of 1100-1500 billion tons (GT) per year. This meltwater 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. Paleoclimate research and improved modelling show that the West Antarctic ice sheet is very likely to disappear even if
1353-542: A role as well though models of the changes suggest declining CO 2 levels to have been more important. The Western Antarctic ice sheet declined somewhat during the warm early Pliocene epoch, approximately five to three million years ago; during this time the Ross Sea opened up. But there was no significant decline in the land-based Eastern Antarctic ice sheet. 90°S 0°E / 90°S 0°E / -90; 0 Ice stream An ice stream
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#17327727559651476-428: A state they last had a century ago, thus stabilizing these glaciers. To achieve this, the curtains would have to be placed at a depth of around 600 metres (0.37 miles) (to avoid damage from icebergs which would be regularly drifting above) and be 80 km (50 mi) long. The authors acknowledged that while work on this scale would be unprecedented and face many challenges in the Antarctic (including polar night and
1599-511: A very long time from start to end for the ice sheet to disappear, some research indicates that the only way to stop its complete meltdown once triggered, is by lowering the global temperature to 1 °C (1.8 °F) below the preindustrial level; i.e. 2 °C (3.6 °F) below the temperature of 2020. Other researchers have proposed engineering interventions to stabilize Thwaites and Pine Island Glaciers before they are lost. For instance, 2019 research estimated that moving some ocean water from
1722-407: A way which would be difficult to reverse and constitute an example of tipping points in the climate system . This would be similar to some projections for Atlantic meridional overturning circulation (AMOC), which is also affected by the ocean warming and by meltwater flows from the declining Greenland ice sheet . However, Southern Hemisphere is only inhabited by 10% of the world's population, and
1845-404: Is a region of fast-moving ice within an ice sheet . It is a type of glacier , a body of ice that moves under its own weight. They can move upwards of 1,000 metres (3,300 ft) a year, and can be up to 50 kilometres (31 mi) in width, and hundreds of kilometers in length. They tend to be about 2 km (1.2 mi) deep at the thickest, and constitute the majority of the ice that leaves
1968-436: 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
2091-475: Is almost negligible. As ice streams diminish in size, the pressure they exert on surrounding features like glaciers reduces, allowing the glacier that feeds into the sea to speed up and discharge more quickly, rising sea level. This rise in sea level affects both topography and bathymetry in the regions directly affected by the ice stream in question. As a result of this rise in sea level, albeit slow and almost minute in short scales but large over longer scales,
2214-465: Is also possible, but it would require very high warming and a lot of time: In 2022, an extensive assessment of tipping points in the climate system published in Science Magazine concluded that the ice sheet would take a minimum of 10,000 years to fully melt. It would most likely be committed to complete disappearance only once the global warming reaches about 7.5 °C (13.5 °F), with
2337-460: Is bedrock, and not made of sediments, the speed will decrease. The bedrock acts to slow down the ice stream as it incises and deforms it. Flow velocity of the ice stream is not entirely constant, but in short time scales of days to weeks, it can be treated as such, over long scales, however, it is variable, depending on how the conditions of thickness, temperature, water accumulation, stresses, and base material have changed. The Antarctic Ice Sheet
2460-412: 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
2583-476: Is drained to the sea by several ice streams. The largest in East Antarctica is Lambert Glacier . In West Antarctica the large Pine Island and Thwaites Glaciers are currently the most out of balance, with a total net mass loss of 85 gigatonnes (84 billion long tons; 94 billion short tons) per year measured in 2006. Antarctica has many ice streams that carry billions of tons of ice to
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#17327727559652706-410: Is exceeded is considered one of the tipping points in the climate system . Earlier research suggested it may withstand up to 3 °C (5.4 °F) before it would melt irreversibly, but 1.5 °C (2.7 °F) was eventually considered a more likely threshold. By 2023, multiple lines of evidence suggested that the real tipping point was around 1 °C (1.8 °F), which has already been reached in
2829-710: Is expected to add about 11 cm (4.3 in) to global sea-level rise. Other processes may cause West Antarctica to contribute more to sea-level rise. Marine ice-sheet instability is the potential for warm water currents to enter between the seafloor and the base of the ice sheet once the sheet is no longer heavy enough to displace such flows. Marine ice-cliff instability may cause ice cliffs taller than 100 m (330 ft) to collapse under their own weight once they are no longer buttressed by ice shelves. This process has never been observed and it only occurs in some models. By 2100, these processes may increase sea-level rise caused by Antarctica to 41 cm (16 in) under
2952-470: 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
3075-545: Is lost through them. While East Antarctica is generally stable, ice loss in West Antarctica has increased by 59% in the past 10 years and by 140% in the Antarctic peninsula . Ice streams control much of the ice sheet mass budget as they dictate the amount of discharge that comes off an ice sheet. Geomorphic features such as bathymetric troughs indicate where paleo-ice streams in Antarctica extended during
3198-474: Is most strongly affected by winds and precipitation , and the larger lower cell, which is defined by the temperature and salinity of Antarctic bottom water . Since the 1970s, the upper cell has strengthened by 50–60%, while the lower cell has weakened by 10–20%. Some of this was as the result of the natural cycle of Interdecadal Pacific Oscillation , but large flows of meltwater also had a clear effect, The circulation may lose half of its strength by 2050 under
3321-399: Is one half of the global thermohaline circulation , with the better-known Atlantic meridional overturning circulation being the other. Southern Ocean absorbs by far the most heat and is also the strongest carbon sink of any ocean. Both properties are affected by the strength of the overturning circulation. The overturning circulation consists of two parts – the smaller upper cell, which
3444-421: Is one of the reasons why it is so difficult for oceans to freeze or evaporate. Water is also a poor conductor of heat, so increased thickness will not only increase the amount of heat that can be retained, but also make more energy required for heat to be lost. In addition to thickness, water, and stresses, sediment and bedrock play a key role in the rate at which ice streams drain. If the underlying sediment
3567-484: Is that thicker ice results in faster velocity. As the thicker an ice stream is, the greater the driving stress at the bed, and thus the greater the velocity. In addition to driving stress, ice streams have better insulation as the thickness of ice increases, due to it retaining higher temperatures better, it can increase the rate of deformation, as well as basal sliding. As a substance's volume increases, it requires more energy per unit volume to raise its temperature, which
3690-705: Is the Greenland ice sheet in the Arctic . The Antarctic ice sheet is divided by the Transantarctic Mountains into two unequal sections called the East Antarctic Ice Sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS). Some glaciologists consider ice cover over the relatively small Antarctic Peninsula (also in West Antarctica) to be the third ice sheet in Antarctica, in part because its drainage basins are very distinct from
3813-510: 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. Its surface is nearly continuous, and the only ice-free areas on the continent are the dry valleys, nunataks of the Antarctic mountain ranges , and sparse coastal bedrock . However, it is often subdivided into East Antarctic ice sheet (EAIS), West Antarctic ice sheet (WAIS), and Antarctic Peninsula (AP), due to
West Antarctic Ice Sheet - Misplaced Pages Continue
3936-434: Is to lower the global temperature to 1 °C (1.8 °F) below the pre-industrial level, to 2 °C (3.6 °F) below the temperature of 2020. Other researchers said a climate engineering intervention to stabilize the ice sheet's glaciers may delay its loss by centuries and give the environment more time to adapt. This is an uncertain proposal and would be one of the most-expensive projects ever attempted. Otherwise,
4059-417: Is too porous , allowing for too much water to seep into it, and therefore become saturated , it will be incapable of supporting the shear stress the ice stream places on the bed. The best type of sediment for increased speed of drainage is soft, deformable sediment, that allows the ice stream to flow over the combination of sediment and till , while supporting against shear stress . If the underlying surface
4182-601: The Amundsen Sea to the top of the Thwaites and Pine Island Glacier area and freezing it to create at least 7400 billion tonnes of snow would stabilize the ice sheet. This would be enormously expensive, as an equivalent of 12,000 wind turbines would be required to provide power just to move the water to the ice sheet, even before desalinating it (to avoid enhancing surface melt with salt) and turning it to snow. It also assumed local water temperature remaining at early 21st century levels, rather than tripling unavoidably by 2100 as
4305-466: The Amundsen Sea . Thwaites Glacier and Pine Island Glacier are the two most important outlet glaciers. Antarctica is the coldest, driest continent on Earth, and has the highest average elevation. Antarctica's dryness means the air contains little water vapor and conducts heat poorly. The Southern Ocean surrounding the continent is far more effective at absorbing heat than any other ocean. The presence of extensive, year-around sea ice , which has
4428-541: The CMIP6 models - the most advanced generation available as of early 2020s. One study suggests that the circulation would lose half its strength by 2050 under the worst climate change scenario , with greater losses occurring afterwards. It is possible that the South Ocean overturning circulation may not simply continue to weaken in response to increased warming and freshening, but will eventually collapse outright, in
4551-403: The East Antarctic Ice Sheet adds meltwater to the Southern Ocean , at a total rate of 1100–1500 billion tons (GT) per year. This meltwater is fresh, and when it mixes with ocean water, the ocean becomes fresher (less salty) as well. This results in the increased stratification and stabilization of the ocean layers, which has a significant impact on Southern Ocean overturning circulation . It
4674-501: The Eemian , and about 0.9 m (2 ft 11 in) between 318,000 and 339,000 years ago, during the Marine Isotope Stage 9 . Neither Wilkes nor the other subglacial basins were lost entirely, but estimates suggest that they would be committed to disappearance once the global warming reaches 3 °C (5.4 °F) - the plausible temperature range is between 2 °C (3.6 °F) and 6 °C (11 °F). Then,
4797-576: The Greenland ice sheet into the sea include Helheim Glacier , Jakobshavn Isbræ and Kangerdlugssuaq Glacier . With significantly more surface melt, only 50% of ice mass is lost through ice streams in Greenland, but they still are one of the primary modes of ice loss. the Northeast Greenland Ice Stream, at 600 km (370 mi) long, drains roughly 12% of the entire ice sheet through three outlet glaciers. Earlier in
4920-568: The Last Glacial Maximum (LGM). Analysis of landforms diagnostic of paleo-ice streams, revealed considerable asynchronicity in individual ice stream retreat histories. This notion is important when considering how the underlying geomorphology of ice streams control at what rate and how they retreat. Furthermore, this reinforces the importance of internal factors such as bed characteristic, slope , and drainage basin size in determining ice stream dynamics. Ice streams that drain
5043-727: The McMurdo Dry Valleys in East Antarctica had experienced cooling of 0.7 °C per decade, a local trend that was confirmed by subsequent research at McMurdo. Multiple journalists said these findings were "contradictory" to global warming, even though the paper noted the limited data and found warming over 42% of the continent. What became known as the Antarctic Cooling Controversy received further attention in 2004, when Michael Crichton wrote that novel State of Fear , which said
West Antarctic Ice Sheet - Misplaced Pages Continue
5166-492: 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 ( 19 ⁄ 64 ± 5 ⁄ 32 in) to
5289-409: The 20th century, with the only uncertainty being the magnitude. During 2012-2013, estimates based on WAIS Divide ice cores and revised temperature records from Byrd Station suggested a much-larger West-Antarctica warming of 2.4 °C (4.3 °F) since 1958, or around 0.46 °C (0.83 °F) per decade, although there has been uncertainty about it. In 2022, a study narrowed the warming of
5412-779: The 21st century, but is likely to weaken its carbon sink once it is complete, which would be closer to 2300. Other likely impacts include a decline in precipitation in the Southern Hemisphere countries like Australia (with a corresponding increase in the Northern Hemisphere ), and an eventual decline of fisheries in the Southern Ocean, which could lead to a potential collapse of certain marine ecosystems . Due to limited research to date, few specifics are currently known. The same ice sheet topography which makes marine ice sheet instability possible in
5535-701: The Central area of the West Antarctic Ice Sheet between 1959 and 2000 to 0.31 °C (0.56 °F) per decade, and conclusively attributed it to increases in greenhouse gas concentrations caused by human activity. Between 2000 and 2020, local changes in atmospheric circulation patterns like the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) slowed or partially reversed
5658-550: The EAIS in addition to the erosion of the WAIS. This Antarctica-only sea level rise would be in addition to ice losses from the Greenland ice sheet and mountain glaciers , as well as the thermal expansion of ocean water. If the warming were to remain at elevated levels for a long time, then the East Antarctic Ice Sheet would eventually become the dominant contributor to sea level rise, simply because it contains
5781-720: The EAIS would play an increasingly larger role in sea level rise occurring after 2100. According to the most recent reports of the Intergovernmental Panel on Climate Change ( SROCC and the IPCC Sixth Assessment Report ), the most intense climate change scenario , where the anthropogenic emissions increase continuously, RCP8.5 , would result in Antarctica alone losing a median of 1.46 m (4 ft 9 in) ( confidence interval between 60 cm (2.0 ft) and 2.89 m (9 ft 6 in)) by 2300, which would involve some loss from
5904-652: The East Antarctica interior demonstrated clear warming over those two decades. In particular, the South Pole warmed by 0.61 ± 0.34 °C per decade between 1990 and 2020, which is three times the global average. The Antarctica-wide warming trend continued after 2000, and in February 2020, the continent recorded its highest temperature of 18.3 °C, which is one degree higher than the previous record of 17.5 °C in March 2015. By 2100, net ice loss from Antarctica
6027-533: The Holocene, the ice stream system of northeast Greenland reached much farther into Greenland's interior compared to the present day. The northeast Greenland ice stream behaves similarly to the Ross ice streams of West Antarctica with fast flow and a weak bed with low driving stresses. The basal shear stress balances the driving stress for several hundred kilometers in the center of the ice stream. Further upstream,
6150-459: The Southern Ocean overturning circulation has historically received much less attention than the AMOC. Some preliminary research suggests that such a collapse may become likely once global warming reaches levels between 1.7 °C (3.1 °F) and 3 °C (5.4 °F), but there is far less certainty than with the estimates for most other tipping points in the climate system . Even if initiated in
6273-528: The Thwaites' grounding line to either physically reinforce it, or to block some fraction of warm water flow. The former would be the simplest intervention, yet equivalent to "the largest civil engineering projects that humanity has ever attempted". It is also only 30% likely to work. Constructions blocking even 50% of the warm water flow are expected to be far more effective, yet far more difficult as well. Some researchers argued that this proposal could be ineffective, or even accelerate sea level rise. The authors of
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#17327727559656396-479: The WAIS warmed by over 0.1 °C/decade from 1950s to 2000, with an average warming trend of >0.05 °C/decade since 1957 across the whole continent. 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
6519-595: The WAIS. Collectively, these ice sheets have an average thickness of around 2 kilometres (1.2 mi), Even the Transantarctic Mountains are largely covered by ice, with only some mountain summits and the McMurdo Dry Valleys being ice-free in the present. Some coastal areas also have exposed bedrock that is not covered by ice. During the Late Cenozoic Ice Age , many of those areas had been covered by ice as well. The EAIS rests on
6642-520: The West Antarctic Ice Sheet loses ice due to the warming ocean water melting its coastal glaciers, it inevitably contributes to sea level rise . However, projections are complicated by additional processes that are difficult to model, such as meltwater from the ice sheet itself changing local circulation due to being warmer and fresher than the ocean water. Another complicated process is hydrofracturing, where meltwater collecting atop
6765-504: The West Antarctic ice sheet would cause around 3.3 m (10 ft 10 in) of sea-level rise. This kind of collapse is now considered almost inevitable because it appears to have occurred during the Eemian period 125,000 years ago, when temperatures were similar to those in the early 21st century. The Amundsen Sea also appears to be warming at rates that, if continued, make the ice sheet's collapse inevitable. The only way to reverse ice loss from West Antarctica once triggered
6888-569: The West Antarctic ice sheet, which is much smaller than the East Antarctic ice sheet and is grounded deep below sea level, is considered highly vulnerable. The melting of all of the ice in West Antarctica would increase global sea-level rise to 4.3 m (14 ft 1 in). Mountain ice caps that are not in contact with water are less vulnerable than the majority of the ice sheet, which is located below sea level. The collapse of
7011-423: The West Antarctica around 125,000 years ago, during Marine Isotope Stage 5 . Since that period was only 0.5 °C (0.90 °F) to 1.5 °C (2.7 °F) warmer than the preindustrial period, the current levels of warming are also likely to be sufficient to eventually melt the ice sheet. Further, oceanographic research explains how this irreversible melting would occur, by indicating that water temperatures in
7134-487: The atmosphere; this means greenhouse gases trap heat in the middle atmosphere, and reduce its flow toward the surface and toward space, rather than preventing the flow of heat from the lower atmosphere to the upper layers. This effect lasts until the end of the Antarctic winter. Early climate models predicted temperature trends over Antarctica would emerge more slowly and be more subtle than those elsewhere. There were fewer than twenty permanent weather stations across
7257-453: The average annual rate of mass loss since 2002, equivalent to 0.4 millimetres (0.016 inches) of annual sea level rise. Coastal glaciers are typically buttressed by ice shelves , which are massive blocks of floating ice next to a glacier. Yet, the ice shelves melt relatively quickly, as they are constantly in contact with the warming ocean water. Glacier retreat accelerates substantially once they collapse and stop providing structural support to
7380-493: The bed only deepens upstream. This means that as the ice sheet loses mass to melting, an increasing fraction of its height becomes exposed to warm water flows that are no longer displaced by its mass. This hypothesis is known as marine ice sheet instability (MISI) and it has the potential to greatly accelerate ice losses. The lack of knowledge about its specifics introduces substantial uncertainty into projections of 21st century sea level rise. WAIS could be even more vulnerable under
7503-410: The continent and only two in the continent's interior. Automatic weather stations were deployed relatively late, and their observational record was brief for much of the 20th century satellite temperature measurements began in 1981 and are typically limited to cloud-free conditions. Thus, datasets representing the entire continent only began to appear by the very end of the 20th century. The exception
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#17327727559657626-482: The currently insufficient numbers of specialized polar ships and underwater vessels), it would also not require any new technology and there is already experience of laying down pipelines at such depths. 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
7749-405: The direction and magnitude of ice streams. Ice streams have various impacts on the surrounding event. The most obvious one is the development of large topographic lows and valleys after an ice stream has been completely drained from the ice sheet itself. The topographic lows are formed by glacial erosion as the stream carves through the underlain material, eroding it and pushing sediment into
7872-454: The disappearance of the West Antarctic ice sheet would take an estimated 2,000 years. The loss of West Antarctica ice would take at least 500 years and possibly as long as 13,000 years. Once the ice sheet is lost, the isostatic rebound of the land previously covered by the ice sheet would result in an additional 1 m (3 ft 3 in) of sea-level rise over the following 1,000 years. If global warming were to reach higher levels, then
7995-418: 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 km (6.46 million cu mi), while the WAIS contains about 2.1 million km (530,000 cu mi) in ice that is above the sea level, and ~1 million km (240,000 cu mi) in ice that
8118-488: The early 21st century. This includes paleoclimate evidence from the Eemian period, such as analysis of silt isotopes in the Bellingshausen Sea , or the genomic history of Antarctica's Turquet's octopus . The former shows specific patterns in silt deposition and the latter genetic connections between currently separate subpopulations; both are impossible unless there was no ice outside of mountain caps in
8241-461: The entire Amundsen Sea are already committed to increase at triple the historical rate throughout the 21st century. However, while the West Antarctic Ice Sheet is likely to be committed to disappearance, it would take a long time. Its most vulnerable parts like Thwaites Glacier, which holds about 65 cm ( 25 + 1 ⁄ 2 in) of sea level rise equivalent, are believed to require "centuries" to collapse entirely. Thwaites' ice loss over
8364-508: The experts found ice cliff instability research to be just as, or even more influential, as the IPCC Fifth Assessment report. Consequently, when the IPCC Sixth Assessment Report (AR6) was published in 2021–2022, it estimated that while the median increase in sea level rise from the West Antarctic ice sheet melt by 2100 would be ~11 cm (5 in) under all emission scenarios (since the increased warming would intensify
8487-410: 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
8610-404: 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. The West Antarctic Rift System (WARS) is one of
8733-422: The future. 2023 research had also shown that much of the glacier may survive 500 years into the future. Consequently, the entire WAIS would most likely take around 2,000 years to disintegrate entirely once it crosses its tipping point. Under the highest warming scenario RCP8.5 , this may be shortened to around 500 years, while the longest potential timescale for its disappearance is around 13,000 years. In 1978, it
8856-480: The glacier, and once warm water can flow to the glacier unimpeded. Most ice losses occur at the Amundsen Sea Embayment and its three most vulnerable glaciers – Thwaites Glacier , Pine Island Glacier and Smith Glacier . Around 2005, they were thought to lose 60% more mass than what they have gained, and to contribute about 0.24 millimetres (0.0094 inches) per year to global sea level rise . Of
8979-631: 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
9102-443: 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
9225-482: The ice sheet is so reflective, its loss would also have some effect on the ice-albedo feedback . A total loss would increase the global temperatures by 0.05 °C (0.090 °F), while the local temperatures would increase by around 1 °C (1.8 °F). Estimates of isostatic rebound after the loss of East Antarctica's subglacial basins suggest sea level rise contributions of between 8 cm (3.1 in) and 57 cm (1 ft 10 in). While it would take
9348-431: The ice sheet may pool into fractures and force them open, further damaging its integrity. Climate change alters winds above Antarctica, which can also affect surface current circulation, but the importance of this process has been disputed. Most importantly, the WAIS has a complex topography which magnifies its vulnerability. The grounding lines of its glaciers are below the sea level by several hundred metres or more, and
9471-408: The ice. In 1981, the Amundsen Sea region had first been described by the researchers as "the weak underbelly" of the WAIS, with the hypothesis that the collapse of Thwaites Glacier and Pine Island Glacier would trigger the collapse of the entire ice sheet. This had been supported by subsequent research. Now, the potential for the West Antarctic Ice Sheet to disappear after a certain temperature
9594-581: The icy surface, making it the largest volcanic region on Earth. Fast-moving ice streams in the Siple Coast adjacent to the east edge of the Ross Ice Shelf are influenced by the lubrication provided by water-saturated till within fault-bounded grabens within the rift, which would act to accelerate ice-sheet disintegration at more intense levels of climate change. Like the other ice sheets, West Antarctic Ice Sheet had undergone significant changes in size during its history. Until around 400,000 years ago,
9717-822: The initiation of the ice stream (established by looking at velocity data) is caused by a weak bed . Ice streams can also occur in ice fields that are significantly smaller than the Antarctic and Greenland ice sheets. In the Patagonian region of southern South America there are three main icefields - the North Patagonian Icefield, South Patagonian Icefield, and Cordillera Darwin Icefield that all exhibit ice streams. Ice streams are also important for ice sheet dynamics of Iceland's ice fields. In Iceland, areas with reticulated ridges, ribbed moraines , and trunk-flow zones have demonstrated no control over
9840-420: The large differences in topography , ice flow , and glacier mass balance between the three regions. 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 WAIS. In the 20th century, EAIS had been one of the only places on Earth which displayed limited cooling instead of warming, even as
9963-491: The largest amount of ice. Sustained ice loss from the EAIS would begin with the significant erosion of the so-called subglacial basins, such as Totten Glacier and Wilkes Basin , which are located in vulnerable locations below the sea level. Evidence from the Pleistocene shows that Wilkes Basin had likely lost enough ice to add 0.5 m (1 ft 8 in) to sea levels between 115,000 and 129,000 years ago, during
10086-542: The limited information about MISI for a long time. In 2001, IPCC Third Assessment Report mentioned the possibility of such disintegration and provided a vague long-term estimate for what it then described as a hypothetical. In 2007, the IPCC Fourth Assessment Report omitted any mention of it due to increased uncertainty, and a number of scientists criticized that decision as excessively conservative. The 2013/2014 IPCC Fifth Assessment Report (AR5)
10209-416: The limited recovery during 2010s. Since the 1970s, the upper cell has strengthened by 3-4 sverdrup (Sv; represents a flow of 1 million cubic meters per second), or 50-60% of its flow, while the lower cell has weakened by a similar amount, but because of its larger volume, these changes represent a 10-20% weakening. While these effects weren't fully caused by climate change, with some role played by
10332-433: 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
10455-435: 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
10578-435: The low-emission RCP2.6 scenario was followed, only contributing a median of 16 cm (5 in). On the other hand, even the minimum estimate of West Antarctica melting under the high-emission scenario would be no less than 60 cm (0 ft), while the median would amount to 1.46 m (5 ft) and the maximum to 2.89 m (10 ft). Ice loss from the West Antarctic Ice Sheet (along with much smaller losses from
10701-422: The low-emission scenario and by 57 cm (22 in) under the high-emission scenario. Ice loss from Antarctica also generates more fresh meltwater , at a rate of 1100-1500 billion tons (GT) per year. This meltwater then mixes back into the Southern Ocean, which makes its water fresher. This freshening of the Southern Ocean results in increased stratification and stabilization of its layers, and this has
10824-451: The major active continental rifts on Earth. It is believed to have a major influence on ice flows in West Antarctica. In western Marie Byrd Land , active glaciers flow through fault-bounded valleys ( grabens ) of the WARS. Sub-ice volcanism has been detected and is known to influence ice flows. In 2017, geologists from Edinburgh University discovered 91 volcanoes located two kilometres below
10947-626: The minimum and the maximum range between 5 °C (9.0 °F) and 10 °C (18 °F). Another estimate suggested that at least 6 °C (11 °F) would be needed to melt two thirds of its volume. The icing of Antarctica began in the Late Palaeocene or middle Eocene between 60 and 45.5 million years ago and escalated during the Eocene–Oligocene extinction event about 34 million years ago. CO 2 levels were then about 760 ppm and had been decreasing from earlier levels in
11070-470: The most-recent reports of the Intergovernmental Panel on Climate Change ( SROCC and the IPCC Sixth Assessment Report ), there will be a median rise of 16 cm (6.3 in) and maximum rise of 37 cm (15 in) under the low-emission scenario. The highest-emission scenario results in a median rise of 1.46 m (5 ft) with a minimum of 60 cm (2 ft) and a maximum of 2.89 m ( 9 + 1 ⁄ 2 ft). Over longer timescales,
11193-418: 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
11316-462: The natural cycle of Interdecadal Pacific Oscillation , they are likely to worsen in the future. As of early 2020s, climate models ' best, limited-confidence estimate is that the lower cell would continue to weaken, while the upper cell may strengthen by around 20% over the 21st century. A key reason for the uncertainty is limited certainty about future ice loss from Antarctica and the poor and inconsistent representation of ocean stratification in even
11439-548: The near future, the circulation's collapse is unlikely to be complete until close to 2300, Similarly, impacts such as the reduction in precipitation in the Southern Hemisphere , with a corresponding increase in the North , or a decline of fisheries in the Southern Ocean with a potential collapse of certain marine ecosystems , are also expected to unfold over multiple centuries. Sea levels will continue to rise long after 2100 but potentially at very different rates. According to
11562-423: The next 30 years would likely be around 5 mm of sea level rise between 2018 and 2050, and between 14 and 42 mm over 100 years. Other research also suggests that Thwaites Glacier would add less than 0.25 mm of global sea level rise per year over the 21st century, although it would increase to over 1 mm per year during its "rapid collapse" phase, which it expected to occur between 200 and 900 years in
11685-491: The original proposal suggested attempting this intervention on smaller sites, like the Jakobshavn Glacier in Greenland , as a test. They also acknowledged that this intervention cannot prevent sea level rise from the increased ocean heat content , and would be ineffective in the long run without greenhouse gas emission reductions. In 2023, it was proposed that an installation of underwater curtains , made of
11808-542: The past 1.4 million years, and so their melting would require a larger level of warming. 2021 research indicates that isostatic rebound , after the loss of the main portion of the ice sheet, would ultimately add another 1.02 m (3 ft 4 in) to global sea levels. While this effect would start to increase sea levels before 2100, it would take 1000 years for it to cause 83 cm (2 ft 9 in) of sea level rise – at which point, West Antarctica would be 610 m (2,001 ft 4 in) higher than now. Because
11931-500: The sea a year. The Pine Island and Thwaites streams have the highest amount of net discharge in west Antarctica while Lambert Glacier leads the way in East Antarctica . The rate at which the Antarctic ice sheet is losing mass is accelerating and the past and ongoing acceleration of ice streams and outlet glaciers is considered to be a significant, if not the dominant cause of this recent imbalance. Ice streams hold serious implications for sea level rise as 90% of Antarctica's ice mass
12054-566: The sea level. Further, it had been shown in 2021 that the Thwaites Ice Shelf , which restrains the eastern portion of the Thwaites Glacier, could start to collapse within five years. The glacier would start to see major losses "within decades" after the ice shelf's failure, and its annual contribution to sea level rise would increase from the current 4% to 5%, although it would still take centuries to disappear entirely. As
12177-399: The sheet through ice streams, which can be one of many factors causing small stage sheet collapse. In addition to this collapse, ice streams also act to increase the global sea level . As ice streams drain into the surrounding ocean, not only does this increase the sea level due to displacement of the ice runoff, but also by increasing the volumetric content of the oceans themselves, but this
12300-428: The sheet. In Antarctica, the ice streams account for approximately 90% of the sheet's mass loss per year, and approximately 50% of the mass loss in Greenland. The shear forces cause deformation and recrystallization that drive the movement, this movement then causes topographic lows and valleys to form after all of the material in the ice sheet has been discharged. Sediment also plays an important role in flow velocity;
12423-511: The short term, also leaves it vulnerable to disappearing in response to even seemingly limited changes in temperature. This suggestion had first been presented in a 1968 paper by glaciologist J. H. Mercer. In the 1970s, radar measurements from research flights revealed that glacier beds in Pine Island Bay slope downwards at an angle, well below the sea level . Thus, even a limited warming of ocean currents ice would effectively undermine
12546-406: The single largest impact on the long-term properties of Southern Ocean circulation. These changes in the Southern Ocean cause the upper cell circulation to speed up, accelerating the flow of major currents, while the lower cell circulation slows down, as it is dependent on the highly saline Antarctic bottom water , which already appears to have been observably weakened by the freshening, in spite of
12669-505: The so-called marine ice cliff instability hypothesis (MICI). It suggests that when a glacier's ice shelf melts, it would not just retreat faster, but rapidly collapse under its own weight if the height of its cliffs was greater than 100 m (330 ft). This particular process has never been observed and was even ruled out by some of the more detailed modelling, but it still adds to the uncertainty in sea level projections. The Intergovernmental Panel on Climate Change has wrestled with
12792-659: The softer and more easily deformed the sediment present, the easier it is for flow velocity to be higher. Most ice streams contain a layer of water at the bottom, which lubricates flow and acts to increase speed. Ice streams are typically found in areas of low topography , surrounded by slower moving, higher topography ice sheets. The low topography arises as a result of various factors, the most prominent being that water accumulates at topographic lows. As water accumulates, its presence increases basal sliding and therefore velocity , which causes an increase in sheet discharge. Another factor causing ice streams to be found in low regions
12915-507: The state of WAIS was largely governed by the effects of solar variation on heat content of the Southern Ocean , and it waxed and waned in accordance with a 41,000-year-long cycle. Around 80,000 years ago, its size was comparable to now, but then it grew substantially larger, until its extent reached the margins of Antarctica's continental shelves during the Last Glacial Maximum ~30,000 years ago. It then shrunk to around its preindustrial state some 3,000 years ago. It also at times shrunk to
13038-511: The strength of climate science after the hearing. By 2009, researchers were able to combine historical weather-station data with satellite measurements to create consistent temperature records going back to 1957 that demonstrated warming of >0.05 °C/decade since 1957 across the continent, with cooling in East Antarctica offset by the average temperature increase of at least 0.176 ± 0.06 °C per decade in West Antarctica. Subsequent research confirmed clear warming over West Antarctica in
13161-599: The subglacial basins would gradually collapse over a period of around 2,000 years, although it may be as fast as 500 years or as slow as 10,000 years. Their loss would ultimately add between 1.4 m (4 ft 7 in) and 6.4 m (21 ft 0 in) to sea levels, depending on the ice sheet model used. Isostatic rebound of the newly ice-free land would also add 8 cm (3.1 in) and 57 cm (1 ft 10 in), respectively. The entire East Antarctic Ice Sheet holds enough ice to raise global sea levels by 53.3 m (175 ft). Its complete melting
13284-531: The surface would be gaining mass . This is possible because effects of climate change on the water cycle would add more snow to the surface of the ice sheet, which is soon compressed into more ice, and this could offset some of the losses from the coasts. Afterwards, several major publications in the late 2010s (including the Fourth United States National Climate Assessment in 2017) suggested that if instability
13407-539: The thousands of ppm. Carbon dioxide decrease, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation. The glaciation was favored by an interval when the Earth's orbit favored cool summers but oxygen isotope ratio cycle marker changes were too large to be explained by Antarctic ice-sheet growth alone indicating an ice age of some size. The opening of the Drake Passage may have played
13530-460: The three, Thwaites Glacier is the best-known, to the point of being nicknamed the "Doomsday Glacier" by some in the press, although many scientists consider it alarmist and inaccurate. The reason for concern about Thwaites is because it had been experiencing substantial mass loss since at least the early 1990s, while its local seabed topography provides no obstacles to rapid retreat, with its most vulnerable parts located 1.5 mi (2.4 km) below
13653-422: 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 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
13776-667: The warming of West Antarctica , with the Antarctic Peninsula experiencing cooling from 2002. While a variability in those patterns is natural, ozone depletion had also led the SAM to be stronger than it had been in the past 600 years of observations. Studies predicted a reversal in the SAM once the ozone layer began to recover following the Montreal Protocol , starting from 2002, and these changes are consistent with their predictions. As these patterns reversed,
13899-481: The warming of the region since 1957 was estimated as exceeding 0.1 °C (0.18 °F) per decade. This warming is strongest in the Antarctic Peninsula . In 2012, research found that the West Antarctic ice sheet had warmed by 2.4 °C (4.3 °F) since 1958 – around 0.46 °C (0.83 °F) per decade, which was almost double the 2009 estimate. In 2022, Central WAIS warming between 1959 and 2000
14022-408: The water beneath the ice stream and through the drainage system. These low topographic areas can be up to a few kilometers in depth, and up to hundreds of kilometers in length. The resulting low regions act as a new drainage system for the ice sheet, as it allows movement of material through topographic low to increase, since the stream has left the sheet. Another problem arises from the discharge of
14145-462: The water cycle and increase snowfall accumulation over the ice sheet at about the same rate as it would increase ice loss), it can conceivably contribute up to 41 cm (16 in) by 2100 under the low-emission scenario and up to 57 cm (22 in) under the highest-emission one, due to the aforementioned uncertainties. It had also been suggested that by the year 2300, Antarctica's role in sea level rise would only slightly increase from 2100 if
14268-437: The worst climate change scenario , and decline even more afterwards. In the long run, the circulation could collapse entirely: potentially between 1.7 °C (3.1 °F) and 3 °C (5.4 °F), though this is much less certain than with the other tipping points in the climate system . This collapse would likely require multiple centuries to unfold: it is not expected to diminish Southern Ocean heat and carbon uptake during
14391-453: Was again unable to describe the risk, but it stated with medium confidence that MISI could add up to several tens of centimeters to 21st century sea level rise. The report projected that in the absence of instability, WAIS would cause around 6 cm (2.4 in) of sea level rise under the low-emission scenario RCP2.6 . High emission scenario RCP8.5 would have slightly lower retreat of WAIS at 4 cm (1.6 in), due to calculations that
14514-503: Was believed that the loss of the ice sheet would cause around 5 m (16 ft 5 in) of sea level rise, Later improvements in modelling had shown that the collapse of the ice grounded below the sea level would cause ~3.3 m (10 ft 10 in) of sea level rise, The additional melting of all the ice caps in West Antarctica that are not in contact with water would increase it to 4.3 m (14 ft 1 in). However, those ice caps have been continuously present for at least
14637-416: Was discovered by later research. Some engineering interventions have been proposed for Thwaites Glacier and the nearby Pine Island Glacier to physically stabilize its ice or to preserve it. These interventions would block the flow of warm ocean water, which currently renders the collapse of these two glaciers practically inevitable even without further warming. A proposal from 2018 included building sills at
14760-477: Was estimated at 0.31 °C (0.56 °F) per decade, with this change conclusively attributed to increases in greenhouse gas concentrations. The continually increasing ocean heat content forces the melting and retreat of ice sheet's coastal glaciers. Normally, glacier mass balance offsets coastal losses through gains from snowfall at the surface, but between 1996 and 2006, Antarctic ice mass loss had already increased by 75%. Between 2005 and 2010, WAIS melting
14883-501: Was the Antarctic Peninsula , where warming was pronounced and well-documented; it was eventually found to have warmed by 3 °C (5.4 °F) since the mid 20th century. Based on this limited data, several papers published in the early 2000s said there had been an overall cooling over continental Antarctica outside the Peninsula. A 2002 analysis led by Peter Doran received widespread media coverage after it also indicated stronger cooling than warming between 1966 and 2000, and found
15006-549: Was thought to have added 0.28 millimetres (0.011 inches) to global sea levels every year. Around 2012, the total mass loss from the West Antarctic Ice Sheet was estimated at 118 ± 9 gigatonnes per year . Subsequent satellite observations revealed that the West Antarctic ice loss increased from 53 ± 29 gigatonnes per year in 1992 to 159 ± 26 gigatonnes per year in 2017, resulting in 7.6 ± 3.9 mm ( 19 ⁄ 64 ± 5 ⁄ 32 in) of Antarctica sea level rise. By 2023, ~150 gigatonnes per year became
15129-487: Was triggered, then the overall sea level rise (combining the melting of West Antarctica with that of the Greenland ice sheet and mountain glaciers , as well as the thermal expansion of seawater) from the high-emission climate change scenario could double, potentially exceeding 2 m (5 ft) by 2100 in the worst case. A 2016 study led by Jim Hansen presented a hypothesis of vulnerable ice sheet collapse leading to near-term exponential sea level rise acceleration, with
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