New Study Doubles Sea Level Rise Forecast Tied to Antarctica's Doomsday Glacier

A Glacier That Could Reshape the World's Coastlines

Thwaites Glacier in West Antarctica — nicknamed the Doomsday Glacier because of the catastrophe its collapse would trigger — is a massive wildcard when it comes to forecasting global sea level rise. And according to alarming new research published this week, scientists have been significantly underestimating just how fast it's deteriorating.

The planet's widest glacier is melting "more aggressively" than previously projected, meaning its impacts on global sea level rise could be double current estimates, according to new research by a team of glaciologists. Thwaites measures 80 miles — roughly 120 kilometers — across, making it one of the most consequential bodies of ice on Earth. It has been retreating for decades and its melting ice currently contributes around 4% to global sea level rise.

The Hidden Mechanism Scientists Missed

For years, researchers modeled Thwaites using a concept called the "grounding line" — the point where the glacier lifts off the seafloor and begins floating. The problem? That model turns out to be far too simplistic. Glaciologists had long based their assumptions on this grounding line as a discrete, narrow, and mostly stable boundary where ice leaves the land and begins floating on water.

Satellite data now reveals the grounding line is actually a "grounding zone," sometimes miles wide, where seawater constantly flushes in and out with the tides, lifting and lowering the thick ice in a process known as "tidal pumping." This allows relatively warm ocean water to penetrate "deep underneath the ice sheets," causing vigorous melting. By adjusting a computer model of Thwaites to incorporate this grounding zone, the researchers were able to reconstruct historical glacier change from the 1990s to the present that is four times more pronounced than traditional models had shown.

Researchers identified a grounding zone about 6 kilometers wide at the glacier's center and 2 kilometers wide along its flanks — and detected irregular seawater intrusions extending a further 6 kilometers inland during spring tides. That warm water seeping beneath the ice isn't just a curiosity. It's actively accelerating the glacier's collapse from the inside out.

What the New Numbers Actually Mean

When scientists adjusted their models to include the concept of a grounding zone, they found Thwaites could contribute up to 1.2 inches of sea level rise by 2100 — twice previous estimates — even without further global warming, according to the findings published in the journal Nature Communications. While 1.2 inches may not sound dramatic on its own, it is Thwaites' contribution in isolation. The broader stakes are far more severe.

Thwaites holds enough water to raise sea levels by more than 2 feet if it were to collapse entirely. Because it also acts as a cork holding back the vast Antarctic ice sheet, it could ultimately lead to around 10 feet of sea level rise, devastating coastal communities from Miami to Manila. The new study also found that the melting processes at Thwaites' grounding zone are accelerating the "unpinning" of ice from a large ridge called the Mouginot Ridge, and there is a 60% chance that it will be unpinned by the end of the century — after which the glacier is likely to retreat quickly down the sloping bedrock toward the next major ridge.

What Comes Next for Scientists

Glaciologists from the University of California, Irvine and NASA's Jet Propulsion Laboratory developed the new ice sheet model that is driving this reassessment. But they are quick to acknowledge that more direct observation is urgently 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," said Robert Larter, a marine geophysicist at British Antarctic Survey.

Getting observational data from Thwaites' grounding line is the next step, with scientists planning to travel there in 2028 to deploy instruments capable of documenting the flushing in and out of seawater. The International Thwaites Glacier Collaboration has identified tidal pumping as an unresolved research question, including how it interacts with meltwater drainage, sediments, and ice — and has called for continued monitoring and measurements beneath the glacier to test and improve models. The science is moving fast, but so is the ice — and the window to fully understand what is coming may be narrower than anyone hoped.