Thwaites Glacier
Thwaites Glacier | |
---|---|
"Doomsday Glacier" | |
Type | Tidewater valley |
Location | Walgreen Coast, Marie Byrd Land, Antarctic |
Coordinates | 75°30′S 106°45′W / 75.500°S 106.750°W |
Area | 192,000 km2 (74,000 sq mi)[1] |
Width | 120 km (75 mi)[2] |
Thickness | 800–1,200 metres (0.50–0.75 miles)[1] |
Lowest elevation | Below sea level |
Terminus | Pine Island Bay, part of the Amundsen Sea |
Status | Receding |
Thwaites Glacier is an unusually broad and vast
Thwaites Glacier is closely monitored for its potential to elevate sea levels.[4] Since the 1980s, Thwaites and Pine Island Glacier have been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, in part because they seem vulnerable to irreversible retreat and collapse even under relatively little warming, yet also because if they go, the entire ice sheet is likely to eventually follow.[5][6][7] This hypothesis is based on both theoretical studies of the stability of marine ice sheets and observations of large changes on these two glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces have lowered, and their grounding lines have retreated.[8] They are believed very likely to eventually collapse even without any further warming.[9][10][11] The outsized danger Thwaites poses has led to some reporters nicknaming it the Doomsday Glacier,[12][13][14][15][16] although this nickname is controversial among scientists.[17]
The Thwaites Ice Shelf, a floating ice shelf which braces and restrains the eastern portion of Thwaites Glacier, is likely to collapse within a decade from 2021.[5][18][19][20] The glacier's outflow is likely to accelerate substantially after the shelf's disappearance; while the outflow currently accounts for 4% of global sea level rise, it would quickly reach 5%, before accelerating further. The amount of ice from Thwaites likely to be lost in this century will only amount to several centimetres of sea level rise,[1][21] but its breakdown will rapidly accelerate in the 22nd and 23rd centuries,[10] and the volume of ice contained in the entire glacier can ultimately contribute 65 cm (25+1⁄2 in) to global sea level rise,[5] which is more than twice the total sea level rise to date.[22] Some researchers have proposed engineering interventions to stabilize the glacier,[10][23][24] but they are very new, costly and their success uncertain.[25]
Location and features
Thwaites Glacier is located at the northern edge of the
The third Antarctic expedition of
Thwaites Glacier Tongue and Thwaites Iceberg Tongue
The Thwaites Glacier Tongue, or Western Glacier Tongue (75°0′S 106°50′W / 75.000°S 106.833°W) was a narrow, floating part of the glacier, located about 30 mi (48 km) east of
Post-2010 break-up and current state
Thwaites Glacier Tongue had also experienced destructive changes, eventually shortening to 40 mi (64 km) long and 20 mi (32 km) wide.[28] By 2012, it went from an ice tongue firmly attached to the rest of the glacier to a series of icebergs floating next to each other, each no larger than 1–5 kilometres (0.62–3.11 mi) in width and only held in place by sea ice. The final remainder of the old glacier tongue, with an area of 470 square kilometres (180 sq mi), disintegrated in 2016. This "melange" of icebergs is still referred to by its old name, as it continues to occupy a substantial amount of area and may retain a stabilizing effect on the glacier. However, future retreat of the surrounding sea ice is likely to trigger disintegration of ever-larger sections, like during the 2019 disintegration of icebergs on its western margin.[29] In 2023, scientists found that ice tongue retreat rates are subject to wide fluctuations after its break-up: over six years of observations, annual retreat accelerated by as much as 40% (from around 4 kilometres (2.5 mi) to 6 kilometres (3.7 mi) per year) twice, before slowing back down. These researchers have also repurposed a machine learning algorithm normally used in microbiology to identify crevasses in the remains of the ice tongue and project how they may affect its stability.[32][26]
Iceberg B-22a
On 15 March 2002, a notable calving event took place, when the
Thwaites Ice Shelf
Glaciers in Antarctica commonly have
Subglacial features
Swamp-like canal areas and streams underlie the glacier. The upstream swamp canals feed streams, while the dry areas between those streams retard flow of the glacier. Due to this friction, the glacier is considered stable in the short term.[41] As warming progresses, these streams expand and form larger structures underneath the glacier.[11] The largest one to date was discovered by NASA researchers in 2019 – an underwater cavity formed mostly in the previous three years, nearly 350 m (1,148+1⁄2 ft) tall and 4 km (2.5 mi) wide, with an area two-thirds the size of Manhattan.[42][43]
In 2014, the area underneath Thwaites Glacier was found to have heat flow from
Importance
Between 1992 and 2017, Thwaites Glacier retreated at between 0.3 km (0.19 mi) and 0.8 km (0.50 mi) annually, depending on the sector,[42] and experienced a net loss of over 600 billion tons of ice as the result.[48] This loss had caused about 4% of the global sea level rise over that period.[18][43] If all of the ice contained within Thwaites Glacier melted (which is expected to take place over multiple centuries),[5][9][49] it would be sufficient to raise the global sea level by 65 cm (25+1⁄2 in).[50] This is more than twice as large as all of the sea level rise which occurred between 1901 and 2018 (estimated at 15–25 cm (6–10 in)),[22]: 5 though only a fraction of the total sea level rise which would be seen in the future, particularly under high warming.[22]: 21
Fears of the entire
Once the potential contribution of Thwaites to future sea level rise became better known, some stories have started to refer to it as the "Doomsday Glacier". The first known usage of that nickname was in a May 2017 Rolling Stone magazine article by Jeff Goodell,[12] and it has subsequently been used more widely.[13][14][15][16] While some scientists have embraced the name,[55] many others, including leading researchers like Ted Scambos, Eric Rignot, Helen Fricker and Robert Larter have criticized it as alarmist and inaccurate.[17]
Observations and predictions
Early observations
In 2001, an analysis of
In 2011, an analysis of IceBridge data showed a rock ridge 700 m (2,300 ft) tall, which helps to anchor the glacier and slows its glacier's slide into the sea.[60] In early 2013, a minor speedup of ice flow was detected, which was later attributed to the activity of subglacial lakes upstream of the grounding line.[61][62] Altogether, annual ice loss had increased substantially since Rignot's 2001 analysis: from around 16 billion tonnes of ice between 1992 and 1996[56] to about 50 billion tons between 2002 and 2016. Cumulative ice loss over those 14 years was equivalent to a global sea level rise of 2.07 mm.[1]
A 2014 paper noted that while the Thwaites Glacier was expected to add less than 0.25 mm of global sea level rise per year over the 21st century, this would eventually increase to over 1 mm per year during its "rapid collapse" phase.
International Thwaites Glacier Collaboration
In 2017, British and American research institutions founded a 5-year research mission named International Thwaites Glacier Collaboration (ITGC).[63][64][18][65] The mission involves over 100 scientists and support staff, with an estimated cost of $50 million across the entire research period.[1]
In 2020, ITGC researchers discovered that at the glacier's baseline, the temperature of the water is already over 2 °C (36 °F) above
In 2021, further ITGC research suggested that the Thwaites Ice Shelf, which currently restrains the eastern portion of the Thwaites Glacier, could start to collapse within five years.[69][18][20] This would lead to a greater outflow from the glacier, increasing its annual contribution to sea level rise from 4% to 5% in the near term.[2][5][19] In December 2021, ITGC glaciologist Erin Pettit noted in an interview that Thwaites, along with the rest of the West Antarctic Ice Sheet, would start to see major losses "within decades" after the ice shelf's failure, and this would be especially pronounced if the anthropogenic emission trajectory does not decrease by then. In her own words: "We’ll start to see some of that before I leave this Earth."[5]
Other recent research
A 2022 study described the "rapid retreat" of the Thwaites Glacier, inferring its past movement in the pre-satellite era by analyzing "ribs" left behind after seabed gouging by ice. It found that at some point in the last two centuries, the glacier moved 2.1 km (1.3 mi) per year, twice the rate it did between 2011–2019. This rate of retreat could reoccur if the glacier recedes and is dislodged beyond a sea bed that is currently keeping it somewhat stable.[70][16][65] In 2023, researchers found that at the end of Last Glacial Maximum, an ice sheet covering what is now Norway retreated at 50 to 600 meters per day over the course of several days to months, far faster than any rate observed today, because its "bed", the ground it rested on, was completely flat. As Thwaites Glacier continues to retreat, the grounding line will eventually reach a similarly flat portion, and the researchers suggested that a part of the glacier could then disappear similarly quickly. This finding does not change the annual average melting rate for the rest of the glacier.[71][72]
A model created in 2023 suggested that as the outer ice at Thwaites melts due to warm water currents, it erodes in a way which strengthens the flow of those currents. While this
Predicted timelines for glacier collapse
A 2014 study, using satellite measurements and computer models, predicted that only the lowest possible warming offered any chance of preserving Thwaites Glacier: otherwise, it will inevitably reach the point of "rapid and irreversible collapse" in the next 200 to 900 years. Once that happens, its retreat would add over 1 mm to the global annual sea level rise, up until it disappears.[75][76][7][77][9][78]
A 2022 assessment of tipping points in the climate system did not consider Thwaites Glacier on its own, but it did note that the entire West Antarctic Ice Sheet would most likely take 2,000 years to disintegrate entirely once it crosses its tipping point, and the minimum plausible timescale is 500 years, and could be as long as 13,000 years. It also noted that this tipping point for the entire ice sheet is no more than 3 °C (5.4 °F) of global warming away, and is very likely to be triggered around the near-future levels of 1.5 °C (2.7 °F): at worst, it may have even been triggered by now, after the warming passed 1 °C (1.8 °F) in the early 21st century.[79][80]
In May 2023, a modelling study considered the future of Thwaites Glacier over the course of 500 years. Due to computational limitations, it was only able to simulate about two-thirds of the glacier catchment (volume of ice equivalent to 40 cm (15+1⁄2 in) of the global sea level rise, rather than the 65 cm (25+1⁄2 in) contained in the full glacier). It found that the uncertainty about glacier bed friction was almost as important as the future ocean temperature. Another finding was that lower-resolution models (those which simulated the glacier as a "mesh" of 20 km2 (7.7 sq mi) areas) consistently estimated faster break-up than the more detailed models with mesh size of 6.5 km2 (2.5 sq mi). While in the less-detailed models, practically the entirety of the simulated area was lost around a 250-year mark under the combination of high warming and low friction, higher-resolution simulation showed that about quarter would remain under those conditions, to be lost over 100 more years. Under high warming yet high seabed friction, a quarter was still left at the end of 500 years in the detailed simulations. The same outcome occurred under low warming and low friction. With low warming and high friction, over half of the studied area remained after 500 years.[49]
Engineering options for stabilization
Some engineering interventions have been proposed for Thwaites Glacier and the nearby
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.[23][24][81] 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 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.[23][24]
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.[23][24] Yet, a single seawall capable of protecting the entire New York City may cost twice as much on its own,[81] and the global costs of adaptation to sea level rise caused by the glaciers' collapse are estimated to reach $40 billion annually:[23][24] 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.[23][24]
See also
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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.
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Sources
- This article incorporates public domain material from "Thwaites Glacier". Geographic Names Information System. United States Geological Survey.