Thwaites Glacier is a very large and wide glacier in Antarctica, located east of Mount Murphy on the Walgreen Coast of Marie Byrd Land. It was first seen by researchers in 1940, mapped between 1959 and 1966, and officially named in 1967 after Fredrik T. Thwaites, an American glaciologist. The glacier flows into Pine Island Bay, which is part of the Amundsen Sea, and moves at speeds faster than 2 kilometers (1.2 miles) per year near its grounding line. Its fastest-moving ice is found between 50 and 100 kilometers (31 and 62 miles) east of Mount Murphy. Like other parts of the cryosphere, it has been harmed by climate change and shows one of the clearest examples of glaciers moving backward since 1850.
Thwaites Glacier is closely watched because it could raise sea levels. Since the 1980s, Thwaites and Pine Island Glacier have been called the "weak underbelly" of the West Antarctic Ice Sheet. This is because they may retreat and collapse even with small amounts of warming, and if they do, the entire ice sheet might follow. This idea comes from studies about ice sheet stability and observations of changes in these glaciers. In recent years, both glaciers have moved faster, their surfaces have lowered, and their grounding lines have moved backward. Scientists believe they may collapse even without more warming. Because of this, some reporters have called Thwaites the "Doomsday Glacier," though scientists disagree with this name.
The Thwaites Ice Shelf, a floating piece of ice that holds back part of Thwaites Glacier, may collapse within a decade after 2021. Once the ice shelf is gone, the glacier’s movement is likely to speed up. Right now, Thwaites contributes 4% of global sea level rise, but this could quickly rise to 5% and increase further. Over this century, Thwaites may lose enough ice to raise sea levels by several centimeters. However, ice loss will likely speed up in the 22nd and 23rd centuries. The entire glacier contains enough ice to raise global sea levels by 65 centimeters (25.5 inches), more than double the total rise so far. Scientists have suggested engineering projects to slow the glacier, but these ideas are new, expensive, and uncertain in their success.
Location and features
Thwaites Glacier is located at the northern edge of the West Antarctic Ice Sheet, near Pine Island Glacier. Both glaciers lose ice from their grounding line into Pine Island Bay, which is part of the Amundsen Sea. The fastest ice movement happens between 50 and 100 kilometers east of Mount Murphy, where ice can move more than 2 kilometers per year. Thwaites Glacier is the widest glacier in the world, measuring 120 kilometers across. It covers an area of 192,000 square kilometers, larger than the U.S. state of Florida (170,000 square kilometers) and slightly smaller than the island of Great Britain (209,000 square kilometers). The glacier is also very thick, with ice ranging from 800 to 1,200 meters in height. Because of its size, large amounts of ice are released when ice calving events occur at the glacier’s marine terminus, where the grounding line meets the sea. The largest calving events, on the glacier’s western side, can be detected by seismometers up to 1,600 kilometers away.
The third Antarctic expedition by Richard E. Byrd in 1940 is believed to be the first official sighting of Thwaites Glacier’s coastline. Detailed maps of the glacier’s surface were created between 1959 and 1966. In 1967, the glacier was officially named after Fredrik T. Thwaites, a respected glacial geologist and professor at the University of Wisconsin–Madison, even though he never visited the glacier. Researchers at McMurdo Station study the glacier, including the International Thwaites Glacier Collaboration (ITGC).
The Thwaites Glacier Tongue, also called the Western Glacier Tongue, was a floating part of the glacier located about 48 kilometers east of Mount Murphy. It was first mapped using 65,000 aerial photographs from Operation Highjump in 1947. At that time, it was 95 kilometers long and 60 kilometers wide. By 1967, during Operation Deepfreeze, the glacier tongue had moved 75 kilometers north and experienced major ice calving events, forming the Thwaites Iceberg Tongue, a group of icebergs covering an area 150 kilometers long and 35 to 65 kilometers wide. These icebergs drifted into the Amundsen Sea, about 32 kilometers northeast of Bear Peninsula. Over time, the iceberg tongue shrank, and by 2012, it had broken into smaller icebergs floating near each other. The last remaining part of the old glacier tongue, covering 470 square kilometers, disintegrated in 2016. This collection of icebergs is still called by its old name and may help stabilize the glacier. However, if surrounding sea ice continues to retreat, more icebergs may break off. In 2019, icebergs on the glacier’s western edge disintegrated, and scientists found that ice tongue retreat rates can change rapidly, with retreat increasing by up to 40% in some years. Researchers used a machine learning tool from microbiology to study cracks in the remaining ice and predict how they might affect stability.
On March 15, 2002, a major calving event occurred when an iceberg named B-22 broke off. B-22 was about 85 kilometers long and 65 kilometers wide, covering an area similar to Rhode Island. Most of the iceberg broke apart quickly, but the largest piece, B-22A, drifted near the glacier. In 2012, B-22A became stuck on the seafloor 53 kilometers from the glacier, temporarily stabilizing the area. In 2022, it began moving again and is expected to remain in the ocean for a long time.
Antarctic glaciers often have ice shelves, which are large floating ice masses that help stabilize the glacier. The Thwaites Ice Shelf is 45 kilometers wide and at least 587 meters thick. It rests partially on an underwater mountain 50 kilometers offshore. The ice shelf protects the eastern part of the glacier, though the western side was previously covered by the ice tongue. Even though the ice shelf is relatively small, it helps prevent large calving events on that side. Some scientists suggest that if the ice shelf collapses, the glacier’s edge could become too tall to remain stable, leading to a chain reaction of collapse. However, other studies argue that losing the ice shelf might not significantly change the glacier’s movement.
Swamp-like canals and streams lie beneath the glacier. These canals feed streams, and the dry areas between them slow the glacier’s movement. This friction makes the glacier stable in the short term. As temperatures rise, these streams grow and form larger structures under the glacier. In 2019, NASA discovered an underwater cavity under Thwaites Glacier that was nearly 350 meters tall and 4 kilometers wide, covering an area two-thirds the size of Manhattan.
In 2014, scientists found that geothermal heat flow beneath Thwaites Glacier was nearly twice the global average and 3.5 times higher in hotspots. By 2017, researchers mapped 138 volcanoes under the West Antarctic Ice Sheet, 91 of which were previously unknown. Marie Byrd Land, where Thwaites and Pine Island Glaciers are located, has about one volcano per 11,200 square kilometers. This density is high but lower than in other regions like the East African Rift or Antarctica’s central rift. Heat from magma under these volcanoes can increase melting, and the risk of eruptions may rise as more ice is lost due to isostatic rebound. Marie Byrd Land and the central rift also contain most of West Antarctica’s 29 volcanoes taller than 1 kilometer, even though they are completely covered by ice.
Importance
From 1992 to 2017, Thwaites Glacier moved backward by 0.3 km (0.19 mi) to 0.8 km (0.50 mi) each year, depending on the area studied. During this time, it lost more than 600 billion tons of ice. This loss contributed to about 4% of the global rise in sea levels during the same period. If all the ice in Thwaites Glacier melted (a process expected to take many centuries), it would raise global sea levels by 65 cm (25.5 in). This amount is more than twice the total sea level rise that happened between 1901 and 2018 (estimated at 15–25 cm [6–10 in]). However, it would still be a small part of the sea level rise expected in the future, especially if global warming continues strongly.
Concerns about the West Antarctic Ice Sheet (WAIS) collapsing quickly due to rising global temperatures were first raised in a 1968 study by glaciologist J. H. Mercer. These concerns were repeated in a 1978 study by Mercer and another in 1973. In 1981, scientists proposed that the Amundsen Sea region, including Thwaites and Pine Island Glaciers, was the weakest part of the WAIS. They suggested that the collapse of these glaciers could lead to the collapse of the entire ice sheet. This idea was based on radar data from research flights in the 1960s and 1970s, which showed that the glacier bed in Pine Island Bay slopes downward and lies far below sea level. This shape, along with nearby strong ocean currents, makes these glaciers especially sensitive to increases in ocean warmth. Later research confirmed that Thwaites Glacier is likely to have the greatest short-term effect on sea levels and could disappear even with the climate changes already observed. Scientists now agree that losing Thwaites Glacier may lead to the loss of the entire WAIS, which would raise sea levels by about 3.3 m (10 ft) over several centuries or millennia.
After the role of Thwaites Glacier in future sea level rise became more widely understood, some media began calling it the "Doomsday Glacier." This nickname first appeared in a 2017 article by Jeff Goodell in Rolling Stone magazine and has since been used more often. While some scientists have accepted this name, others, including experts like Ted Scambos, Eric Rignot, Helen Fricker, and Robert Larter, have criticized it as exaggerated and misleading.
Observations and predictions
In 2001, scientists studied data from Earth satellites and found that the grounding line of Thwaites Glacier had moved back by 1.4 km between 1992 and 1996. The glacier was losing ice quickly, about 16 billion tonnes each year, which meant the retreat would likely continue. Later research showed that for every 0.1 °C rise in ocean temperature, melting at the glacier’s base would increase by about 1 meter per year. In 2002, scientists from Chile and NASA used a plane to collect data, confirming that the glacier was thinning and retreating faster. They found that the shape of the seabed did not stop the glacier from retreating quickly. These findings led to more studies by the University of Texas in 2004–2005 and NASA’s IceBridge Campaign from 2009–2018. Data from IceBridge showed that parts of the glacier are 1.5 miles below sea level, making them very vulnerable.
In 2011, IceBridge data revealed a tall rock ridge that helps hold the glacier in place and slows its movement toward the sea. In 2013, scientists noticed a slight increase in ice flow speed, which was later linked to water under the glacier. Ice loss had grown significantly since 2001, rising from about 16 billion tonnes per year to 50 billion tonnes between 2002 and 2016. Over 14 years, this loss raised global sea levels by 2.07 mm.
A 2014 study suggested that Thwaites Glacier would add less than 0.25 mm to sea levels each year in the 21st century, but this could rise to over 1 mm per year during a phase of rapid collapse. In 2018, scientists estimated that ice loss from Thwaites alone over the next 30 years could raise sea levels by 5 mm. However, predictions for 100 years were less certain, ranging from 14 to 42 mm, depending on how the ice sheet changes. Models could not account for the possibility of the eastern ice shelf breaking apart completely.
In 2017, British and American scientists started the International Thwaites Glacier Collaboration (ITGC), a five-year mission involving over 100 researchers and costing about $50 million. In 2020, ITGC found that water at the glacier’s base was over 2 °C above freezing. A 2023 study used a robotic submarine to explore the glacier’s underside and found cracks where melting was faster. These cracks covered 10% of the glacier’s base but caused 27% of its ice loss. Researchers also found that the mixing of fresh meltwater with salty ocean water slowed melting more than models predicted.
In 2021, ITGC scientists warned that the Thwaites Ice Shelf, which holds back part of the glacier, could collapse within five years. This would increase the glacier’s contribution to sea level rise from 4% to 5%. In 2021, scientist Erin Pettit said major ice loss from Thwaites and the West Antarctic Ice Sheet could happen within decades after the ice shelf collapses, especially if global warming does not slow.
A 2022 study used seabed features to estimate that Thwaites moved 2.1 km per year in the past two centuries, twice the rate observed between 2011 and 2019. If the glacier retreats beyond a stable seabed, it could retreat at similar speeds again. In 2023, researchers found that during the Last Glacial Maximum, an ice sheet over Norway retreated up to 600 meters per day, much faster than today. Thwaites could retreat quickly if it reaches a flat seabed. However, this does not change the glacier’s overall melting rate.
A 2023 model showed that melting at Thwaites strengthens warm ocean currents, increasing melting by 30% over 12 years. This effect could cause similar acceleration in the next century, even if ocean temperatures stop rising. Other 2023 research predicted that water temperatures in the Amundsen Sea could rise three times faster than historical rates, worsening the glacier’s situation.
In 2024, researchers found that Thwaites has a wider grounding zone (2–6 km) regularly exposed to water, and some areas are flooded by meltwater during strong tides. This increased exposure could double previous ice loss projections.
A 2014 study predicted that only the lowest warming levels
Engineering options for stabilization
Some engineering plans have been suggested to help stabilize Thwaites Glacier and nearby Pine Island Glacier. These plans aim to stop warm ocean water from reaching the glaciers, which could otherwise cause them to collapse even without more global warming. A 2018 idea proposed building barriers at the grounding line of Thwaites Glacier, where the glacier meets the sea floor. These barriers could either strengthen the glacier or block some of the warm water. Strengthening the grounding line would be the simplest option, but it would be as large as the biggest civil engineering projects ever built. This method has only a 30% chance of success. Blocking half of the warm water flow might work better, but it would be much harder. Some scientists believe this plan might not work or could even make sea levels rise faster. The original proposal suggested testing the idea on smaller glaciers, like Jakobshavn Glacier in Greenland, first. The researchers also noted that this method would not stop sea level rise caused by warmer oceans and would not work long-term without reducing greenhouse gas emissions.
In 2023, a new plan was proposed to install underwater curtains made of flexible material and anchored to the sea floor in the Amundsen Sea. These curtains could stop warm water from reaching the glaciers. This method might cost less and last longer than rigid structures. The curtains could help the Thwaites and Pine Island ice shelves grow back to a size they had a century ago, which might stabilize the glaciers. To work, the curtains would need to be placed about 600 meters deep (to avoid damage from icebergs) and be 80 kilometers long. The plan would face challenges in Antarctica, such as the long polar night and a lack of specialized ships, but it would not need new technology. Similar methods have already been used to lay pipelines at such depths.
The authors estimated the project would take about 10 years to build, with an initial cost of $40 to $80 billion. Annual maintenance would cost $1 to $2 billion. A single seawall to protect New York City might cost twice as much. Global costs to adapt to sea level rise from glacier collapse are estimated at $40 billion each year. The authors compared their plan to other climate solutions, like stratospheric aerosol injection (SAI) or carbon dioxide removal (CDR). These methods could address more climate issues, but their yearly costs range from $7 to $70 billion for SAI and $160 to $4,500 billion for CDR strong enough to meet the 1.5°C Paris Agreement target.