The Thwaites Glacier is living out its last years of stability: the disintegration of its floating shelf has begun. As spectators of a predicted collapse, we witness the countdown of a colossus whose melting could raise the oceans by 65 centimetres.
The surface area of the Thwaites Glacier is comparable to that of Great Britain. It accounts for 8.7% of the ice sheet in West Antarctica. Located in the Amundsen Sea, it is fed by snowfall from the large Antarctic ice sheet. Downstream, this giant glacier ends in the sea with a floating ice shelf 120 kilometers wide, 50 kilometers long, and up to 1,200 meters thick. It slows the flow of ice, but its collapse is thought to be imminent. One of the most unstable in Antarctica, it could disintegrate within the decade. Thwaites alone could cause sea levels to rise by 65 centimeters if all the ice were to melt.
In the sights of glaciologists the world over
In 2018, the British polar research institute teamed up with its US counterpart to found the International Thwaites Glacier Collaboration. With a budget of $50 million, they spent five years observing the giant glacier with its fragile structure to understand the process of disintegration. In 2019, 100 scientists joined forces at Thwaites, located 1,600 kilometers from the British Rothera station.
Using the icebreaker Nathaniel B. Palmer, underwater robots and from camps on the ice cap and ice shelf, they studied its thickness, glacier flow and shear forces. They observed the submerged part of the glacier, its anchoring line and the traces it left in the sediments.
When ice turns liquid
In 2021, the discovery of a small amount of excess heat coming from beneath the ice did not bode well. The Earth’s crust is thinner than average under Thwaites, between 17 and 25 kilometers thick: it prevents meltwater from refreezing, and the meltwater acts as a lubricant on the flow of ice.
In 2023, researchers showed that the El Niño phenomenon, which usually occurs every four years, influences the melting of the Thwaites glacier. When it occurs, the Pacific trade winds slow down, allowing currents of warm water to pass through. Climate change is exacerbating El Niño, as described by IPCC experts.
In 2024, observations by the Nathaniel B. Palmer showed the circulation of warm water currents through a network of 800-meter-deep trenches beneath the anchor line, up to 60 kilometers beneath the ice giant.
The base gives way under the weight of change
The anchor line is the result of two contradictory forces: the flow of the glacier on the one hand, and melting caused by ocean heat on the other. Since the 1940s, the Thwaites anchor line has been retreating, as has that of neighbouring Pine Island. El Niño could have initiated this retreat, which has never stopped. Since the 1970s, the two glaciers have contributed 4% of the current rise in sea level.
Since the 1990s, the anchor line on which Thwaites rests has receded by 14 kilometers. It is weaker on its southeastern slope. This lateral weakening causes crevasses and cracks to form upstream on the glacier’s “banks”, where friction is stronger.
Mechanics run amok
The rate of retreat of the anchor line towards the coast has doubled since 1973, and its decline has been confirmed over the last 20 years. Thwaites was losing 4.6 gigatons of ice per year in the 1980s, and this figure increased eightfold between 2009 and 2017. In addition, the rate of flow has doubled over the last 30 years.
In 2013, seven subglacial lakes suddenly emptied of their water: seven cubic kilometers of fresh water (the volume of Loch Ness) were poured into the Amundsen Sea. A plume of cold water, mixing and rising warm water, can double the rate of melting. Scientists refer to this as a “turbo” effect.
Between 2014 and 2015, a spectacular retreat of the anchor line of several tens of kilometers was observed. By 2020, the retreat was reaching 10 meters per day. In October 2022, scientists discovered that the flow of ice in Antarctica is influenced by the seasons, accelerating by 15% in summer.
In 2022, at a depth of 700 meters, 160 parallel furrows were discovered in the sediments. These marks left by the action of the tide on the ice shelf show that it receded six kilometers in six months at one point over 200 years ago. According to scientists, this type of retreat could be 20 times faster in the future.
Today, the loss of ice is causing the Earth’s crust to rise more rapidly than in the late Holocene. At that time, warming was also taking place, but today’s rebound is much more violent.
Cracks, fractures, colossi adrift
The first signs of Thwaites’ weakness were observed in the shear zone in 1990. In 2002, B-22A, a 300 km² iceberg (three times the size of Paris), broke off before immediately running aground.
In 2011, a 30-kilometer crack appeared on the platform of neighboring Pine Island. The following year, a crack 11 kilometers long and 400 meters thick opened in five minutes, at a speed of 35 meters per second, followed by the calving of a giant 720 km² iceberg (Singapore).
In 2019, Thwaites suffered two huge cracks, followed by the calving of B-49, covering 260 km². In 2020, it broke away. Scientists are wondering whether these could be the first signs of a more widespread disintegration of the ice shelves, as already observed with Larsen A and B in the Weddell Sea.
In September 2022, the International Thwaites Glacier Collaboration discovered that calving (the detachment of chunks of ice from the front of the glacier), in addition to underwater and atmospheric melting, was accentuating the glacier’s decline.
Towards collapse?
In March 2023, the UAV (Underwater vehicle) Icefin showed that melting beneath the platform was still increasing, but at a slower rate than previously estimated: 2 to 5 meters of melted ice per year, rather than 14 to 32. A layer of colder meltwater protects the flat surfaces. On the other hand, the stepped arches and crevasses below the surface concentrate most of the melt. Hot water penetrates more easily. The evolution of the platform’s architecture would therefore play a more important role in its destabilization than the simple loss of thickness.
During the southern hemisphere summer of 2023, the giant iceberg B-22A broke away from the seabed after 22 years. It is now light enough to float and enter ocean currents.
Finally, a September 2024 study estimates that the Thwaites ice shelf is in the final stages of disintegration, which should occur within the decade. Its internal structure threatens to collapse. Other researchers believe that the collapse of the entire Thwaites glacier will not occur before the end of the century.
On the brink of the irreversible, the spreading
In the Amundsen Sea, Pine Island has exceeded a critical threshold, which has since been maintained by a rise in temperature above 1.2°C. The slope of the seabed is fuelling its retreat. Under these conditions, melting is irreversible. Even below the Paris Agreement threshold (1.5°C), warming at the end of the century will be three times faster than in the 20th century, and retreat will continue to accelerate.
Thwaites is not yet as bad off as Pine Island. The north-western front still rests on landforms that hold it in place, but it is in danger of breaking away from the submarine ridges. The rate of retreat would increase from 600 meters per year to 2 kilometers per year.
Since 1990, the destabilization phenomenon has spread to the whole of Antarctica. In as yet unaffected regions of the continent, some platforms have begun to behave like Larsen, now Pine Island and Thwaites in their early stages of destabilization. The Shirase Glacier (Queen Maud Land), in 2017, showed abnormal decomposition of its front and melting by the foot at a rate of 7 to 16 meters.
In May 2025, researchers showed that ice flows can be redirected from one watershed to another depending on glacier flow velocity. Thwaites is already dragging the ice of Kohler Glacier down with it.
Overall, the glaciers in Antarctica have not yet reached the point of total collapse. Anchor lines could reach this point in 300 to 500 years. After that, every degree of further warming will bring total disintegration closer.
However, there is still time to reabsorb excess carbon emissions and cool the climate. One possible path is the IPCC’s SSP1-1.9 scenario, based on international cooperation, massive use of renewable energy, reduced consumption, and strong environmental protection.
Illusory remedies for a deep-seated problem
Technological solutions have been put forward, such as the idea of an insulating curtain to prevent the intrusion of warm ocean currents in 2020. But other researchers have shown that they would slow down the melting effect without stopping it, and that they would not restore the glacier. They would therefore not prevent sea-level rise. What’s more, the management of underwater curtains and their mode of governance would be incompatible with the current Antarctic Treaty.
This year saw the start of the UN’s International Year of Glaciers, as well as the Decade of the Cryosphere. In 2017, 2019 and 2022, in Beijing, Prague and Berlin, the British and the USA discussed the Thwaites case, a major symbol of rising waters and global warming, before the signatory countries of the Antarctic Treaty.
But in Milan in 2025, the United States withdrew from the UN and polar sciences, a regrettable position. On the front of global warming, climate catastrophes and rising sea levels, the Thwaites Glacier is still holding out, and behind it, its allies are melting like snow in the sun. Winston Churchill once said, “Attitude is a small thing that makes a big difference.”