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West Antarctic Ice Sheet

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

A topographic and bathymetric map of Antarctica without its ice sheets, assuming constant sea levels and no post-glacial rebound

Description Edit

It is estimated that the volume of the Antarctic ice sheet is about 25.4 million km3 (6.1 million cu mi), and the WAIS contains just under 10% of this, or 2.2 million km3 (530,000 cu mi).[1] 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)[2] in a process known as isostatic depression.

Under the force of its own weight, the ice sheet deforms and flows. The interior ice flows slowly over rough bedrock. In some circumstances, ice can flow faster in ice streams, separated by slow-flowing ice ridges. The inter-stream ridges are frozen to the bed while the bed beneath the ice streams consists of water-saturated sediments. Many of these sediments were deposited before the ice sheet occupied the region, when much of West Antarctica was covered by the ocean. The rapid ice-stream flow is a non-linear process still not fully understood; streams can start and stop for unclear reasons.[citation needed]

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.[3]

Climate change Edit

Warming and net ice loss Edit

The West Antarctic ice sheet (WAIS) has warmed by more than 0.1 °C (0.18 °F) per decade in the last fifty years, and the warming is the strongest in winter and spring. Although this is partly offset by fall cooling in East Antarctica, this effect was restricted to the 1980s and 1990s. The continent-wide average surface temperature trend of Antarctica is positive and statistically significant at >0.05 °C (0.090 °F)/decade since 1957.[4] This warming of WAIS is strongest in the Antarctic Peninsula. In 2012, the temperature records for the ice sheet were reanalyzed with a conclusion that since 1958, the West Antarctic ice sheet had warmed by 2.4 °C (4.3 °F), almost double the previous estimate. Some scientists now fear that the WAIS could now collapse like the Larsen B Ice Shelf did in 2002.[5]

A collage of footage and animation to explain the changes that are occurring on the West Antarctic Ice Sheet, narrated by glaciologist Eric Rignot

Indications that the West Antarctic Ice Sheet is losing mass at an increasing rate come from the Amundsen Sea sector, and three glaciers in particular: Pine Island Glacier, Thwaites Glacier and Smith Glacier.[6] Data reveals these three glaciers are losing more ice than is being replaced by snowfall. According to a preliminary analysis, the difference between the mass lost and mass replaced is about 60%. The melting of these three glaciers alone is contributing an estimated 0.24 millimetres (0.0094 inches) per year to the rise in the worldwide sea level.[7] There is growing evidence that this trend is accelerating: there has been a 75% increase in Antarctic ice mass loss in the ten years 1996–2006, with glacier acceleration a primary cause.[8] As of November 2012 the total mass loss from the West Antarctic Ice Sheet is estimated at 118 ± 9 gigatonnes per year mainly from the Amundsen Sea coast.[9]

Satellite measurements by ESA's CryoSat-2 revealed that the West Antarctic Ice Sheet is losing more than 150 cubic kilometres (36 cubic miles) of ice each year. The loss is especially pronounced at grounding lines, the area where the floating ice shelf meets the part resting on bedrock, and hence affects the ice shelf stability and flow rates.[10]

Potential collapse Edit

Large parts of the WAIS sit on a bed which is both below sea level and sloping downward inland.[A] This slope, and the low isostatic head, mean that the ice sheet is theoretically unstable: a small retreat could in theory destabilize the entire WAIS, leading to rapid disintegration. Current computer models do not account well for the complicated and uncertain physics necessary to simulate this process, and observations do not provide guidance, so predictions as to its rate of retreat remain uncertain. This has been known for decades.[11] It is considered one of the tipping points in the climate system.

2000s Edit

 
A map of West Antarctica

The possible disastrous outcome of a disintegration of the WAIS for global sea levels has been mentioned and assessed in the IPCC Third Assessment Report from 2001. However, it was not included in the IPCC Fourth Assessment Report. Jessica O'Reilly, Naomi Oreskes and Michael Oppenheimer discussed the case in a 2012 Social Studies of Science paper. According to them, IPCC authors were less certain about potential WAIS disintegration not only due to external new science results. As well pure internal "cultural" reasons, as changes of staff within the IPCC and externally, made it too difficult to project the range of possible futures for the WAIS as required.[12] Mike Hulme saw the issue as a showcase to urge for the integration of minority views in the IPCC and other major assessment processes.[13]

In January 2006, in a UK government-commissioned report, the head of the British Antarctic Survey, Chris Rapley, warned that this huge West Antarctic Ice Sheet may be starting to disintegrate. It has been hypothesised that this disintegration could raise sea levels by approximately 3.3 metres (11 ft).[14] (If the entire West Antarctic Ice Sheet were to melt, this would contribute 4.8 m (16 ft) to global sea level.)[15] Rapley said a previous (2001) Intergovernmental Panel on Climate Change (IPCC) report that played down the worries of the ice sheet's stability should be revised. "I would say it is now an awakened giant. There is real concern."[7]

Rapley said, "Parts of the Antarctic ice sheet that rest on bedrock below sea level have begun to discharge ice fast enough to make a significant contribution to sea level rise. Understanding the reason for this change is urgent in order to be able to predict how much ice may ultimately be discharged and over what timescale. Current computer models do not include the effect of liquid water on ice sheet sliding and flow, and so provide only conservative estimates of future behaviour."[16]

Polar ice experts from the US and UK met at the University of Texas at Austin in March, 2007 for the West Antarctic Links to Sea-Level Estimation (WALSE) Workshop.[17] The experts discussed a new hypothesis that explains the observed increased melting of the West Antarctic Ice Sheet. They proposed that changes in air circulation patterns have led to increased upwelling of warm, deep ocean water along the coast of Antarctica and that this warm water has increased melting of floating ice shelves at the edge of the ice sheet.[17] An ocean model has shown how changes in winds can help channel the water along deep troughs on the sea floor, toward the ice shelves of outlet glaciers.[18] The exact cause of the changes in circulation patterns is not known and they may be due to natural variability. However, this connection between the atmosphere and upwelling of deep ocean water provides a mechanism by which human induced climate changes could cause an accelerated loss of ice from the WAIS.[18] Recently published data collected from satellites support this hypothesis, suggesting that the West Antarctic Ice Sheet is beginning to show signs of instability.[6][19]

After 2010 Edit

On 12 May 2014, it was announced that two teams of scientists said the long-feared collapse of the Ice Sheet had begun, kicking off what they say will be a centuries-long, "unstoppable" process that could raise sea levels by 1.2 to 3.6 metres (3.9 to 11.8 ft)[20][21] They estimate that rapid drawdown of Thwaites Glacier will begin in 200 – 1000 years.[22] (Scientific source articles: Rignot et al. 2014 [23] and Joughin et al. 2014.[24]) More recent research suggests that a partial collapse of Thwaites Glacier could occur sooner, as the ice shelf that restricts the eastern third of the glacier's flow is now showing instability, as warming waters undermine the grounding zone, where the glacier connects to its floating ice shelf.[25][26] According to Ted Scambos, a glaciologist at the University of Colorado Boulder and a leader of the International Thwaites Glacier Collaboration, in a 2021 interview from McMurdo Station, "Things are evolving really rapidly here. It's daunting."[26]

Later in 2014, the IPCC Fifth Assessment Report discussed the possibility of the collapse of marine-based sectors of the Antarctic ice sheet. It expressed medium confidence that if such an event were to occur, it would not add more than several tenths of a metre to sea level rise during this period. In the absence of a collapse, it estimated that the gradual ice loss would most likely add around 6 cm to sea level rise under the Representative Concentration Pathway 2.6 (a scenario of strong climate change mitigation), and 4 cm under RCP 8.5, a scenario where the greenhouse gas emissions continue to increase at a high rate for the rest of the century. The reason why a scenario of much greater warming sees a lower contribution to sea level rise is because the more intense effects of climate change on the water cycle result in an increased precipitation over the ice sheet, which would freeze on the surface, and this increase in the surface mass balance (SMB) would counteract a larger fraction of the ice loss. The uncertainty in the way different climate change models simulate both ice sheet dynamics and the water cycle means that for RCP 2.6 and RCP 8.5, the 5%-95% confidence interval ranges from a 4 cm decrease in sea levels to a 16 cm rise, and an 8 cm decrease to a 14 cm rise, respectively.[27]

In 2016, improved computer modeling revealed that the breakup of glaciers could lead to a steep rise in sea levels much more quickly than previously projected. "We're in danger of handing young people a situation that's out of their control," according to James E. Hansen, the leader of a number of climate scientists who worked together to compile the study.[28] In 2018, scientists concluded that high sea levels some 125,000 years ago, which were 6–9 m (20–30 ft) higher than today, were most likely due to the absence of the WAIS, and found evidence that the ice sheet collapsed under climate conditions similar to those of today.[29][30]

In 2021, these modeling improvements were represented in the IPCC Sixth Assessment Report, where the end-of-century Antarctic sea ice loss is much more aggressive, and contribution from ice sheet collapse processes is now included in the 5-95% range. It now estimates that under the SSP1-2.6, which corresponds to the Fifth Report's RCP 2.6 and includes aggressive mitigation and is largely in accordance with the goals of the Paris Agreement, the median sea level rise contribution from the Antarctica is around 11 cm, with a likely (17-85%) range of 3 to 27 cm, and only the very likely (5-95%) range includes the chance of an 1 cm reduction to sea level rise, which is as likely as a 41 cm increase in sea levels due to ice sheet collapse going well underway. Under the "moderate" SSP2-4.5 scenario, the figures are very similar, as winter precipitation over the ice sheet rises in tandem with increased ice loss from the atmospheric and ocean warming: the median estimate is also 11 cm, with a likely range of 3 to 29 cm, and the very likely range of -1 to 46 cm. However, increases in precipitation can no longer keep up with or outpace the increased ice sheet breakdown if the emissions increase indefinitely under SSP5-8.5: its median contribution is 12 cm, with a likely range of 3 to 34 cm, and the very likely range of 0 to 57 cm.[27] It had also cited the limited-confidence (based on just three studies) predictions of the earlier IPCC SROCC about sea level rise by the year 2300: it suggested that sea level rise contribution would not go much further beyond the 2100 levels under the 2.6 scenario (16 cm median, 37 cm maximum), but would accelerate to a median of 1.46 metres (with a minimum and a maximum of 60 cm and 2.89 metres) under the 8.5 scenario. Likewise, it had acknowledged the possibility of a West Antarctic ice sheet tipping point around 1.5°C, but noted that it was much less likely at that level than at 2°C, while it would become practically certain around 3°C.[27]

In 2022, an extensive assessment of tipping points in the climate system was published in the Science Magazine. For the West Antarctic Ice Sheet, the paper concluded that it would most likely be committed to long-term disintegration around 1.5°C of global warming, but the threshold could be between 1°C (in which case it is already set in motion, and may only be stopped if the warming is reversed, or perhaps even reduced to levels below the preindustrial) and 3°C. It suggested that once the threshold is crossed, the collapse of the entire ice sheet would most likely take place over 2000 years, although the overall certainty is limited, and it could take as long as 13,000 years, or as little as 500 years. It had also factored in the contribution of ice-albedo feedback after a total loss of the ice sheet: global temperatures would be increased by 0.05°C, while the local temperatures would increase by around 1°C.[31][32]

West Antarctic Rift System Edit

The West Antarctic Rift System (WARS) is one of the major active continental rifts on Earth.[33] In 2017, geologists from Edinburgh University discovered 91 volcanoes located two kilometres below the icy surface, making it the largest volcanic region on Earth.[34] The WARS 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.[35] Sub-ice volcanism has been detected and proposed to influence ice flow.[36] 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,[37][38] which would act to accelerate ice-sheet disintegration at more intense levels of climate change.[39]

Engineering options for stabilization Edit

In the Amundsen Sea, Thwaites Glacier and Pine Island Glacier are considered part of Antarctica's "weak underbelly", as they are prone to collapse and complete disappearance over the next several centuries, and their loss would then trigger the loss of the entire ice sheet.[11][40][41] Consequently, some scientists have suggested stabilizing them via climate engineering aiming to block warm water flows from the ocean.

 
A proposed "underwater sill" blocking 50% of warm water flows heading for the glacier could have the potential to delay its collapse and the resultant sea level rise by many centuries.[42]

Some engineering interventions have been proposed for Thwaites Glacier and the nearby Pine Island Glacier to stabilize its ice physically, or to preserve it by blocking the flow of warm ocean water, which currently renders the collapse of these two glaciers practically inevitable even without further warming.[43][44] A proposal from 2018 included building sills at 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 still 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.[42] Further, some researchers dissented, arguing that this proposal could be ineffective, or even accelerate sea level rise.[45] The original authors have suggested attempting this intervention on smaller sites, like the Jakobshavn Glacier in Greenland, as a test run,[42][44] as well as acknowledging 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.[42]

In 2023, a modified proposal was tabled: it was proposed that an installation of underwater "curtains", made out of a flexible material and anchored to Amundsen Sea floor would be able to interrupt warm water flow while reducing costs and increasing their longevity (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 be able to regrow to a state they last had a century ago, thus stabilizing these glaciers.[46][47][44] 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 Arctic (including polar night and 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.[46][47]

 
Diagram of a proposed "curtain".[46]
The authors estimated that this project would take a decade to construct, at $40–80 billion initial cost, while the ongoing maintenance would cost $1–2 billion a year.[46][47] Yet, a single seawall capable of protecting the entire New York City may cost twice as much on its own,[44] and the global costs of adaptation to sea level rise caused by the glaciers' collapse are estimated to reach $40 billion annually:[46][47] The authors also suggested that their proposal would be competitive with the other "climate engineering" proposals like stratospheric aerosol injection (SAI) or carbon dioxide removal (CDR), as while those would stop a much larger spectrum of climate change impacts, their estimated annual costs range from $7–70 billion for SAI to $160–4500 billion for CDR powerful enough to help meet the 1.5 °C (2.7 °F) Paris Agreement target.[46][47]

See also Edit

Notes Edit

  1. ^ In this case, the ice is effectively moving upslope towards the sea.

References Edit

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External links Edit

  • WAIS – West Antarctic Ice Sheet Initiative – A multidisciplinary study of rapid climate change and future sea level. Sponsored by National Science Foundation Office of Polar Programs and NASA Earth Science.
  • U.S. National Snow and Ice Data Center Antarctic Data
  • Crystal Ball: Scientists Race to Foretell West Antarctica's Unclear Future
  • "Structure Found Deep Within West Antarctic Ice Sheet", ScienceDaily, September 2004

west, antarctic, sheet, 73417, 27806, 73417, 27806, western, antarctic, sheet, wais, segment, continental, sheet, that, covers, west, antarctica, portion, antarctica, side, transantarctic, mountains, that, lies, western, hemisphere, wais, classified, marine, b. 78 44 03 S 133 16 41 W 78 73417 S 133 27806 W 78 73417 133 27806 The Western 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 The WAIS 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 A topographic and bathymetric map of Antarctica without its ice sheets assuming constant sea levels and no post glacial reboundContents 1 Description 2 Climate change 2 1 Warming and net ice loss 2 2 Potential collapse 2 2 1 2000s 2 2 2 After 2010 3 West Antarctic Rift System 4 Engineering options for stabilization 5 See also 6 Notes 7 References 8 External linksDescription EditSee also Ice sheet dynamics It is estimated that the volume of the Antarctic ice sheet is about 25 4 million km3 6 1 million cu mi and the WAIS contains just under 10 of this or 2 2 million km3 530 000 cu mi 1 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 2 in a process known as isostatic depression Under the force of its own weight the ice sheet deforms and flows The interior ice flows slowly over rough bedrock In some circumstances ice can flow faster in ice streams separated by slow flowing ice ridges The inter stream ridges are frozen to the bed while the bed beneath the ice streams consists of water saturated sediments Many of these sediments were deposited before the ice sheet occupied the region when much of West Antarctica was covered by the ocean The rapid ice stream flow is a non linear process still not fully understood streams can start and stop for unclear reasons citation needed 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 3 Climate change EditWarming and net ice loss Edit The West Antarctic ice sheet WAIS has warmed by more than 0 1 C 0 18 F per decade in the last fifty years and the warming is the strongest in winter and spring Although this is partly offset by fall cooling in East Antarctica this effect was restricted to the 1980s and 1990s The continent wide average surface temperature trend of Antarctica is positive and statistically significant at gt 0 05 C 0 090 F decade since 1957 4 This warming of WAIS is strongest in the Antarctic Peninsula In 2012 the temperature records for the ice sheet were reanalyzed with a conclusion that since 1958 the West Antarctic ice sheet had warmed by 2 4 C 4 3 F almost double the previous estimate Some scientists now fear that the WAIS could now collapse like the Larsen B Ice Shelf did in 2002 5 source source source source source source source source A collage of footage and animation to explain the changes that are occurring on the West Antarctic Ice Sheet narrated by glaciologist Eric RignotIndications that the West Antarctic Ice Sheet is losing mass at an increasing rate come from the Amundsen Sea sector and three glaciers in particular Pine Island Glacier Thwaites Glacier and Smith Glacier 6 Data reveals these three glaciers are losing more ice than is being replaced by snowfall According to a preliminary analysis the difference between the mass lost and mass replaced is about 60 The melting of these three glaciers alone is contributing an estimated 0 24 millimetres 0 0094 inches per year to the rise in the worldwide sea level 7 There is growing evidence that this trend is accelerating there has been a 75 increase in Antarctic ice mass loss in the ten years 1996 2006 with glacier acceleration a primary cause 8 As of November 2012 the total mass loss from the West Antarctic Ice Sheet is estimated at 118 9 gigatonnes per year mainly from the Amundsen Sea coast 9 Satellite measurements by ESA s CryoSat 2 revealed that the West Antarctic Ice Sheet is losing more than 150 cubic kilometres 36 cubic miles of ice each year The loss is especially pronounced at grounding lines the area where the floating ice shelf meets the part resting on bedrock and hence affects the ice shelf stability and flow rates 10 Potential collapse Edit See also Marine ice sheet instability Large parts of the WAIS sit on a bed which is both below sea level and sloping downward inland A This slope and the low isostatic head mean that the ice sheet is theoretically unstable a small retreat could in theory destabilize the entire WAIS leading to rapid disintegration Current computer models do not account well for the complicated and uncertain physics necessary to simulate this process and observations do not provide guidance so predictions as to its rate of retreat remain uncertain This has been known for decades 11 It is considered one of the tipping points in the climate system 2000s Edit A map of West AntarcticaThe possible disastrous outcome of a disintegration of the WAIS for global sea levels has been mentioned and assessed in the IPCC Third Assessment Report from 2001 However it was not included in the IPCC Fourth Assessment Report Jessica O Reilly Naomi Oreskes and Michael Oppenheimer discussed the case in a 2012 Social Studies of Science paper According to them IPCC authors were less certain about potential WAIS disintegration not only due to external new science results As well pure internal cultural reasons as changes of staff within the IPCC and externally made it too difficult to project the range of possible futures for the WAIS as required 12 Mike Hulme saw the issue as a showcase to urge for the integration of minority views in the IPCC and other major assessment processes 13 In January 2006 in a UK government commissioned report the head of the British Antarctic Survey Chris Rapley warned that this huge West Antarctic Ice Sheet may be starting to disintegrate It has been hypothesised that this disintegration could raise sea levels by approximately 3 3 metres 11 ft 14 If the entire West Antarctic Ice Sheet were to melt this would contribute 4 8 m 16 ft to global sea level 15 Rapley said a previous 2001 Intergovernmental Panel on Climate Change IPCC report that played down the worries of the ice sheet s stability should be revised I would say it is now an awakened giant There is real concern 7 Rapley said Parts of the Antarctic ice sheet that rest on bedrock below sea level have begun to discharge ice fast enough to make a significant contribution to sea level rise Understanding the reason for this change is urgent in order to be able to predict how much ice may ultimately be discharged and over what timescale Current computer models do not include the effect of liquid water on ice sheet sliding and flow and so provide only conservative estimates of future behaviour 16 Polar ice experts from the US and UK met at the University of Texas at Austin in March 2007 for the West Antarctic Links to Sea Level Estimation WALSE Workshop 17 The experts discussed a new hypothesis that explains the observed increased melting of the West Antarctic Ice Sheet They proposed that changes in air circulation patterns have led to increased upwelling of warm deep ocean water along the coast of Antarctica and that this warm water has increased melting of floating ice shelves at the edge of the ice sheet 17 An ocean model has shown how changes in winds can help channel the water along deep troughs on the sea floor toward the ice shelves of outlet glaciers 18 The exact cause of the changes in circulation patterns is not known and they may be due to natural variability However this connection between the atmosphere and upwelling of deep ocean water provides a mechanism by which human induced climate changes could cause an accelerated loss of ice from the WAIS 18 Recently published data collected from satellites support this hypothesis suggesting that the West Antarctic Ice Sheet is beginning to show signs of instability 6 19 After 2010 Edit On 12 May 2014 it was announced that two teams of scientists said the long feared collapse of the Ice Sheet had begun kicking off what they say will be a centuries long unstoppable process that could raise sea levels by 1 2 to 3 6 metres 3 9 to 11 8 ft 20 21 They estimate that rapid drawdown of Thwaites Glacier will begin in 200 1000 years 22 Scientific source articles Rignot et al 2014 23 and Joughin et al 2014 24 More recent research suggests that a partial collapse of Thwaites Glacier could occur sooner as the ice shelf that restricts the eastern third of the glacier s flow is now showing instability as warming waters undermine the grounding zone where the glacier connects to its floating ice shelf 25 26 According to Ted Scambos a glaciologist at the University of Colorado Boulder and a leader of the International Thwaites Glacier Collaboration in a 2021 interview from McMurdo Station Things are evolving really rapidly here It s daunting 26 Later in 2014 the IPCC Fifth Assessment Report discussed the possibility of the collapse of marine based sectors of the Antarctic ice sheet It expressed medium confidence that if such an event were to occur it would not add more than several tenths of a metre to sea level rise during this period In the absence of a collapse it estimated that the gradual ice loss would most likely add around 6 cm to sea level rise under the Representative Concentration Pathway 2 6 a scenario of strong climate change mitigation and 4 cm under RCP 8 5 a scenario where the greenhouse gas emissions continue to increase at a high rate for the rest of the century The reason why a scenario of much greater warming sees a lower contribution to sea level rise is because the more intense effects of climate change on the water cycle result in an increased precipitation over the ice sheet which would freeze on the surface and this increase in the surface mass balance SMB would counteract a larger fraction of the ice loss The uncertainty in the way different climate change models simulate both ice sheet dynamics and the water cycle means that for RCP 2 6 and RCP 8 5 the 5 95 confidence interval ranges from a 4 cm decrease in sea levels to a 16 cm rise and an 8 cm decrease to a 14 cm rise respectively 27 In 2016 improved computer modeling revealed that the breakup of glaciers could lead to a steep rise in sea levels much more quickly than previously projected We re in danger of handing young people a situation that s out of their control according to James E Hansen the leader of a number of climate scientists who worked together to compile the study 28 In 2018 scientists concluded that high sea levels some 125 000 years ago which were 6 9 m 20 30 ft higher than today were most likely due to the absence of the WAIS and found evidence that the ice sheet collapsed under climate conditions similar to those of today 29 30 In 2021 these modeling improvements were represented in the IPCC Sixth Assessment Report where the end of century Antarctic sea ice loss is much more aggressive and contribution from ice sheet collapse processes is now included in the 5 95 range It now estimates that under the SSP1 2 6 which corresponds to the Fifth Report s RCP 2 6 and includes aggressive mitigation and is largely in accordance with the goals of the Paris Agreement the median sea level rise contribution from the Antarctica is around 11 cm with a likely 17 85 range of 3 to 27 cm and only the very likely 5 95 range includes the chance of an 1 cm reduction to sea level rise which is as likely as a 41 cm increase in sea levels due to ice sheet collapse going well underway Under the moderate SSP2 4 5 scenario the figures are very similar as winter precipitation over the ice sheet rises in tandem with increased ice loss from the atmospheric and ocean warming the median estimate is also 11 cm with a likely range of 3 to 29 cm and the very likely range of 1 to 46 cm However increases in precipitation can no longer keep up with or outpace the increased ice sheet breakdown if the emissions increase indefinitely under SSP5 8 5 its median contribution is 12 cm with a likely range of 3 to 34 cm and the very likely range of 0 to 57 cm 27 It had also cited the limited confidence based on just three studies predictions of the earlier IPCC SROCC about sea level rise by the year 2300 it suggested that sea level rise contribution would not go much further beyond the 2100 levels under the 2 6 scenario 16 cm median 37 cm maximum but would accelerate to a median of 1 46 metres with a minimum and a maximum of 60 cm and 2 89 metres under the 8 5 scenario Likewise it had acknowledged the possibility of a West Antarctic ice sheet tipping point around 1 5 C but noted that it was much less likely at that level than at 2 C while it would become practically certain around 3 C 27 In 2022 an extensive assessment of tipping points in the climate system was published in the Science Magazine For the West Antarctic Ice Sheet the paper concluded that it would most likely be committed to long term disintegration around 1 5 C of global warming but the threshold could be between 1 C in which case it is already set in motion and may only be stopped if the warming is reversed or perhaps even reduced to levels below the preindustrial and 3 C It suggested that once the threshold is crossed the collapse of the entire ice sheet would most likely take place over 2000 years although the overall certainty is limited and it could take as long as 13 000 years or as little as 500 years It had also factored in the contribution of ice albedo feedback after a total loss of the ice sheet global temperatures would be increased by 0 05 C while the local temperatures would increase by around 1 C 31 32 West Antarctic Rift System EditSee also Glaciovolcanism The West Antarctic Rift System WARS is one of the major active continental rifts on Earth 33 In 2017 geologists from Edinburgh University discovered 91 volcanoes located two kilometres below the icy surface making it the largest volcanic region on Earth 34 The WARS 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 35 Sub ice volcanism has been detected and proposed to influence ice flow 36 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 37 38 which would act to accelerate ice sheet disintegration at more intense levels of climate change 39 Engineering options for stabilization EditIn the Amundsen Sea Thwaites Glacier and Pine Island Glacier are considered part of Antarctica s weak underbelly as they are prone to collapse and complete disappearance over the next several centuries and their loss would then trigger the loss of the entire ice sheet 11 40 41 Consequently some scientists have suggested stabilizing them via climate engineering aiming to block warm water flows from the ocean This section is an excerpt from Thwaites Glacier Engineering options for stabilization edit A proposed underwater sill blocking 50 of warm water flows heading for the glacier could have the potential to delay its collapse and the resultant sea level rise by many centuries 42 Some engineering interventions have been proposed for Thwaites Glacier and the nearby Pine Island Glacier to stabilize its ice physically or to preserve it by blocking the flow of warm ocean water which currently renders the collapse of these two glaciers practically inevitable even without further warming 43 44 A proposal from 2018 included building sills at 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 still 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 42 Further some researchers dissented arguing that this proposal could be ineffective or even accelerate sea level rise 45 The original authors have suggested attempting this intervention on smaller sites like the Jakobshavn Glacier in Greenland as a test run 42 44 as well as acknowledging 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 42 In 2023 a modified proposal was tabled it was proposed that an installation of underwater curtains made out of a flexible material and anchored to Amundsen Sea floor would be able to interrupt warm water flow while reducing costs and increasing their longevity 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 be able to regrow to a state they last had a century ago thus stabilizing these glaciers 46 47 44 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 Arctic including polar night and 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 46 47 Diagram of a proposed curtain 46 The authors estimated that this project would take a decade to construct at 40 80 billion initial cost while the ongoing maintenance would cost 1 2 billion a year 46 47 Yet a single seawall capable of protecting the entire New York City may cost twice as much on its own 44 and the global costs of adaptation to sea level rise caused by the glaciers collapse are estimated to reach 40 billion annually 46 47 The authors also suggested that their proposal would be competitive with the other climate engineering proposals like stratospheric aerosol injection SAI or carbon dioxide removal CDR as while those would stop a much larger spectrum of climate change impacts their estimated annual costs range from 7 70 billion for SAI to 160 4500 billion for CDR powerful enough to help meet the 1 5 C 2 7 F Paris Agreement target 46 47 See also EditEast Antarctic Ice Sheet List of glaciers in the Antarctic Retreat of glaciers since 1850 WAIS Divide Ice Core Drilling ProjectNotes Edit In this case the ice is effectively moving upslope towards the sea References Edit Lythe Matthew B Vaughan David G June 2001 BEDMAP A new ice thickness and subglacial topographic model of Antarctica PDF Journal of Geophysical Research 106 B6 11335 11352 Bibcode 2001JGR 10611335L doi 10 1029 2000JB900449 Anderson John B 1999 Antarctic marine geology Cambridge University Press p 59 ISBN 978 0 521 59317 5 Ice Shelves Antarctic and Southern Ocean Coalition Archived February 3 2006 at the Wayback Machine Steig E J Schneider D P Rutherford S D Mann M E Comiso J C Shindell D T 2009 Warming of the Antarctic ice sheet surface since the 1957 International Geophysical Year Nature 457 7228 459 462 Bibcode 2009Natur 457 459S doi 10 1038 nature07669 PMID 19158794 S2CID 4410477 Matt McGrath 23 December 2012 West Antarctic Ice Sheet warming twice earlier estimate BBC News Retrieved 16 February 2013 a b Rignot E 2008 Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR data Geophysical Research Letters 35 12 L12505 Bibcode 2008GeoRL 3512505R doi 10 1029 2008GL033365 a b Jenny Hogan Antarctic ice sheet is an awakened giant New Scientist February 2 2005 Rignot E Bamber J L Van Den Broeke M R Davis C Li Y Van De Berg W J Van Meijgaard E 2008 Recent Antarctic ice mass loss from radar interferometry and regional climate modelling Nature Geoscience 1 2 106 Bibcode 2008NatGe 1 106R doi 10 1038 ngeo102 S2CID 784105 King M A Bingham R J Moore P Whitehouse P L Bentley M J Milne G A 2012 Lower satellite gravimetry estimates of Antarctic sea level contribution Nature 491 7425 586 589 Bibcode 2012Natur 491 586K doi 10 1038 nature11621 PMID 23086145 S2CID 4414976 ESA December 11 2013 Antarctica s ice loss on the rise a b Hughes Terence J 1981 The weak underbelly of the West Antarctic ice sheet Journal of Glaciology The Rapid Disintegration of Projections The West Antarctic Ice Sheet and the Intergovernmental Panel on Climate Change Jessica O Reilly Naomi Oreskes Michael Oppenheimer Social Studies of Science June 26 2012 doi 10 1177 0306312712448130 Mike Hulme Lessons from the IPCC do scientific assessments need to be consensual to be authoritative in eds Doubleday R and Willesden J March 2013 page 142 ff Bamber J L Riva R E M Vermeersen B L A LeBroq A M 2009 Reassessment of the potential sea level rise from a collapse of the West Antarctic Ice Sheet Science 324 5929 901 3 Bibcode 2009Sci 324 901B doi 10 1126 science 1169335 PMID 19443778 S2CID 11083712 Bamber J L Riva R E M Vermeersen B L A LeBroq A M 2009 Reassessment of the potential sea level rise from a collapse of the West Antarctic Ice Sheet Supporting Online Material Science 324 5929 901 3 Bibcode 2009Sci 324 901B doi 10 1126 science 1169335 PMID 19443778 S2CID 11083712 West Antarctic ice sheet Waking the sleeping giant Symposium February 19 2006 a b Statement Thinning of West Antarctic Ice Sheet Demands Improved Monitoring to Reduce Uncertainty over Potential Sea Level Rise Jsg utexas edu Retrieved 26 October 2017 a b Thoma M Jenkins A Holland D Jacobs S 2008 Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf Antarctica PDF Geophysical Research Letters 35 18 L18602 Bibcode 2008GeoRL 3518602T doi 10 1029 2008GL034939 S2CID 55937812 Kaufman Mark 2008 Escalating Ice Loss Found in Antarctica Sheets Melting in an Area Once Thought to Be Unaffected by Global Warming Washington Post January 14 p A01 online Scientists warn of rising sea levels as huge Antarctic ice sheet slowly melts Ctvnews ca 12 May 2014 Retrieved 26 October 2017 Justin Gillis March 30 2016 Climate Model Predicts West Antarctic Ice Sheet Could Melt Rapidly New York Times Boyle Alan 12 May 2014 West Antarctic Ice Sheet s Collapse Triggers Sea Level Warning NBC News Retrieved 12 May 2014 Rignot E J Mouginot M Morlighem H Seroussi and B Scheuch May 12 2014 Widespread rapid grounding line retreat of Pine Island Thwaites Smith and Kohler glaciers West Antarctica from 1992 to 2011 Geophysical Research Letters 41 10 3502 3509 Bibcode 2014GeoRL 41 3502R doi 10 1002 2014GL060140 S2CID 55646040 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Joughin Ian Benjamin E Smith Brooke Medley May 12 2014 Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin West Antarctica Science 344 6185 735 738 Bibcode 2014Sci 344 735J doi 10 1126 science 1249055 PMID 24821948 S2CID 206554077 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link The Threat from Thwaites The Retreat of Antarctica s Riskiest Glacier Press release Cooperative Institute for Research in Environmental Sciences University of Colorado Boulder 2021 12 13 Retrieved 2021 12 14 a b Kaplan Sarah December 13 2021 Crucial Antarctic ice shelf could fail within five years scientists say The Washington Post Washington DC Retrieved December 14 2021 a b c Fox Kemper B Hewitt H T Xiao C Adalgeirsdottir G Drijfhout S S Edwards T L Golledge N R Hemer M Kopp R E Krinner G Mix A 2021 Masson Delmotte V Zhai P Pirani A Connors S L Pean C Berger S Caud N Chen Y Goldfarb L eds Chapter 9 Ocean Cryosphere and Sea Level Change PDF Climate Change 2021 The Physical Science Basis Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Cambridge University Press Cambridge UK and New York NY USA 1270 1272 Justin Gillis March 22 2016 Scientists Warn of Perilous Climate Shift Within Decades Not Centuries New York Times Voosen Paul 2018 12 18 Discovery of recent Antarctic ice sheet collapse raises fears of a new global flood Science Retrieved 2018 12 28 Turney Chris S M Fogwill Christopher J Golledge Nicholas R McKay Nicholas P Sebille Erik van Jones Richard T Etheridge David Rubino Mauro Thornton David P Davies Siwan M Ramsey Christopher Bronk 2020 02 11 Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica Proceedings of the National Academy of Sciences 117 8 3996 4006 Bibcode 2020PNAS 117 3996T doi 10 1073 pnas 1902469117 ISSN 0027 8424 PMC 7049167 PMID 32047039 Armstrong McKay David Abrams Jesse Winkelmann Ricarda Sakschewski Boris Loriani Sina Fetzer Ingo Cornell Sarah Rockstrom Johan Staal Arie Lenton Timothy 9 September 2022 Exceeding 1 5 C global warming could trigger multiple climate tipping points Science 377 6611 eabn7950 doi 10 1126 science abn7950 hdl 10871 131584 ISSN 0036 8075 PMID 36074831 S2CID 252161375 Armstrong McKay David 9 September 2022 Exceeding 1 5 C global warming could trigger multiple climate tipping points paper explainer climatetippingpoints info Retrieved 2 October 2022 The Antarctic Rift Plume vs Plate Dynamics MantlePlumes org Scientists discover 91 volcanoes below Antarctic ice sheet The Guardian 12 August 2017 Retrieved 13 August 2017 Luyendyk Bruce P Wilson Douglas S Siddoway Christine S 2003 10 01 Eastern margin of the Ross Sea Rift in western Marie Byrd Land Antarctica Crustal structure and tectonic development Geochemistry Geophysics Geosystems 4 10 1090 Bibcode 2003GGG 4 1090L doi 10 1029 2002GC000462 ISSN 1525 2027 Blankenship Donald D Bell Robin E Hodge Steven M Brozena John M Behrendt John C Finn Carol A 1993 Active volcanism beneath the West Antarctic ice sheet and implications for ice sheet stability Nature 361 6412 526 529 Bibcode 1993Natur 361 526B doi 10 1038 361526a0 ISSN 1476 4687 S2CID 4267792 Studinger Michael Bell Robin E Blankenship Donald D Finn Carol A Arko Robert A Morse David L Joughin Ian 2001 09 15 Subglacial sediments A regional geological template for ice flow in West Antarctica Geophysical Research Letters 28 18 3493 3496 Bibcode 2001GeoRL 28 3493S doi 10 1029 2000GL011788 ISSN 1944 8007 Peters Leo E Anandakrishnan Sridhar Alley Richard B Winberry J Paul Voigt Donald E Smith Andrew M Morse David L 2006 01 01 Subglacial sediments as a control on the onset and location of two Siple Coast ice streams West Antarctica Journal of Geophysical Research Solid Earth 111 B1 Bibcode 2006JGRB 111 1302P doi 10 1029 2005JB003766 ISSN 2156 2202 Veen C J Van Der Whillans I M 1993 New and improved determinations of velocity of Ice Streams B and C West Antarctica Journal of Glaciology 39 133 483 590 doi 10 3189 S0022143000016373 ISSN 1727 5652 Feldmann J Levermann A November 17 2015 Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin Proceedings of the National Academy of Sciences 112 46 14191 14196 Bibcode 2015PNAS 11214191F doi 10 1073 pnas 1512482112 PMC 4655561 PMID 26578762 Voosen Paul 13 December 2021 Ice shelf holding back keystone Antarctic glacier within years of failure Science Magazine Retrieved 22 October 2022 Because Thwaites sits below sea level on ground that dips away from the coast the warm water is likely to melt its way inland beneath the glacier itself freeing its underbelly from bedrock A collapse of the entire glacier which some researchers think is only centuries away would raise global sea level by 65 centimeters a b c d Wolovick Michael J Moore John C 20 September 2018 Stopping the flood could we use targeted geoengineering to mitigate sea level rise The Cryosphere 12 9 2955 2967 Bibcode 2018TCry 12 2955W doi 10 5194 tc 12 2955 2018 S2CID 52969664 Joughin I 16 May 2014 Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin West Antarctica Science 344 6185 735 738 Bibcode 2014Sci 344 735J doi 10 1126 science 1249055 PMID 24821948 S2CID 206554077 a b c d James Temple 14 January 2022 The radical intervention that might save the doomsday glacier MIT Technology Review Retrieved 19 July 2023 Moon Twila A 25 April 2018 Geoengineering might speed glacier melt Nature 556 7702 436 Bibcode 2018Natur 556R 436M doi 10 1038 d41586 018 04897 5 PMID 29695853 a b c d e f Wolovick Michael Moore John Keefer Bowie 27 March 2023 Feasibility of ice sheet conservation using seabed anchored curtains PNAS Nexus 2 3 pgad053 doi 10 1093 pnasnexus pgad053 PMC 10062297 PMID 37007716 a b c d e Wolovick Michael Moore John Keefer Bowie 27 March 2023 The potential for stabilizing Amundsen Sea glaciers via underwater curtains PNAS Nexus 2 4 pgad103 doi 10 1093 pnasnexus pgad103 PMC 10118300 PMID 37091546 External links EditWAIS West Antarctic Ice Sheet Initiative A multidisciplinary study of rapid climate change and future sea level Sponsored by National Science Foundation Office of Polar Programs and NASA Earth Science U S National Snow and Ice Data Center Antarctic Data Crystal Ball Scientists Race to Foretell West Antarctica s Unclear Future Structure Found Deep Within West Antarctic Ice Sheet ScienceDaily September 2004 Retrieved from https en wikipedia org w index php title West Antarctic Ice Sheet amp oldid 1170120251, wikipedia, wiki, book, books, library,

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