Thwaites 'Doomsday Glacier' could drive twice the sea-level rise by 2100, new model finds

Scientists have long known that Antarctica's Thwaites Glacier is retreating. What they did not fully account for was the relentless tide-driven pump pushing warm seawater miles beneath it — and a new study published Monday in the journal Nature Communications suggests that missing piece alone could double the glacier's contribution to sea-level rise by the end of this century.

Glaciologists from the University of California, Irvine and NASA's Jet Propulsion Laboratory developed a new ice-sheet model that treats the glacier's base not as a fixed line but as a 'grounding zone' — a region up to 4–6 kilometres wide where seawater constantly flushes in and out with the tides, lifting and lowering the ice in a process called 'tidal pumping.' When that process was built into their simulations, Thwaites' projected contribution to global sea levels by 2100 jumped to 1.2 inches (30 mm) — roughly twice what earlier models predicted — even assuming no additional global warming beyond current levels.

Deep underneath the ice sheets and causing vigorous melting.— Mattia Poinelli, lead author and project scientist, UCLA

Thwaites spans roughly 192,000 square kilometres — about the size of Senegal and larger than the US state of Florida — making it the world's largest glacier. It sits on the Walgreen Coast of Marie Byrd Land in remote West Antarctica and has been closely monitored since scientists identified its rapid melt in the 1980s. Ice loss from Thwaites currently accounts for about 4 percent of all global sea-level rise, and the glacier has shed more than 1,000 billion tonnes of ice since 2000, losing around 50 billion tonnes per year, according to Al Jazeera.

The stakes of getting the projections right are enormous. Thwaites holds enough water to raise global sea levels by more than 2 feet on its own if it were to collapse entirely, according to CNN. Because it also acts as a physical barrier holding back the broader West Antarctic Ice Sheet — roughly 14 times Thwaites' size — its failure could ultimately contribute around 10 feet of sea-level rise, threatening coastal cities from Miami to Manila. The International Thwaites Glacier Collaboration puts the figure for Thwaites alone at around 65 centimetres of eventual rise, according to Times of India.

The key to the new findings lies in how the glacier meets the sea. At what researchers call the 'grounding line,' the ice transitions from resting on bedrock to floating on the ocean as an ice shelf. Previous models treated this boundary as largely fixed and stable. Satellite data, however, shows it is a dynamic zone where tidal action repeatedly drives relatively warm ocean water deep beneath the ice, accelerating melt from below. The land beneath Thwaites also slopes downward toward the Antarctic interior, meaning as the glacier retreats, progressively more ice is exposed to that warm water — a self-reinforcing feedback that NASA has identified as a major concern.

The study found that this accelerated melting is hastening the 'unpinning' of Thwaites from the Mouginot Ridge, an underwater bedrock feature that currently stabilises the glacier from below. The researchers calculate a 60 percent probability that Thwaites will detach from the ridge entirely by 2100, after which the glacier is likely to retreat rapidly down the sloping bedrock toward the next major ridge.

The results predict greater risk of and exposure for coastal flooding than anticipated in the coming decades.— Eric Rignot, report co-author and professor of Earth system science, UC Irvine

Outside researchers called the findings significant but urged caution. Ted Scambos, a senior research scientist at the University of Colorado Boulder's Earth Science and Observation Center who was not involved in the study, said the work could be 'a real gamechanger for sea level forecasting from Thwaites,' according to CNN. But Robert Larter, a marine geophysicist at the British Antarctic Survey who was also not involved, noted that the environment beneath Thwaites is 'even more complex than the paper describes' and that direct observational data from under the glacier is still needed.

The reality is that there is a lot we still need to find out about grounding zone processes to be able to make confident predictions about how fast ice will be lost.— Robert Larter, marine geophysicist, British Antarctic Survey

The research team plans to travel to Thwaites in 2028 to deploy instruments capable of directly documenting the tidal flushing of seawater beneath the ice — data that could sharpen or revise the current projections. A separate study by the British Antarctic Survey, published in Geophysical Research Letters in July, found that Thwaites will continue losing ice for at least 150 years even under the most extreme ocean-cooling conditions scientists could model in simulation, underscoring that some degree of continued rise is now effectively locked in.

We have been aware of the impacts of climate change on our planet's sensitive ice sheets for decades, but a mounting realization gained in recent years of what is really happening on the undersides of glaciers like Thwaites is leading to an even greater sense of alarm. Even if we do, we can expect higher sea levels in the future resulting from the damage that has already been done.— Eric Rignot, report co-author and professor of Earth system science, UC Irvine

Scientists say the most effective near-term lever remains cutting greenhouse gas emissions to limit further ocean warming — the primary driver of Thwaites' melt. But researchers are also calling for stronger coastal protection, improved flood planning, and restoration of natural barriers such as mangroves to prepare for the sea-level rise that is already unavoidable, according to Times of India.

Why it matters — Even a 1.2-inch rise in global sea levels significantly amplifies coastal flooding risk worldwide, and the study suggests that risk has been systematically underestimated — with some degree of further rise now locked in regardless of emissions cuts.

Sources differ on Comparative size of Thwaites Glacier: Roughly the size of Senegal (~192,000 sq km); larger than Florida (aljazeera.com) vs Roughly the size of Britain (timesofindia.indiatimes.com)

Reported by aljazeera.com, cnn.com, timesofindia.indiatimes.com