Antarctica's 'Doomsday Glacier' May Double Earlier Sea Level Rise Estimates

When the researchers built this broader zone into their simulations, the model reproduced the glacier's historical changes from the 1990s to the present far better than before — changes that were four times more pronounced than conventional models captured.

How does seawater get under a glacier?

The mechanism is blunt. Seawater travels several kilometers beneath ice still anchored to the seafloor. As tides rise and fall, that water lifts the ice and repeatedly exposes its underside to warm, pressurized seawater. Ocean currents — themselves altered by climate change — deliver the warm water to Antarctica's coastline.

The evidence is not purely simulated. The team compared its results against more than two decades of satellite observations, plus synthetic aperture radar measurements from Finland's ICEYE satellite constellation. Those radar data showed fluctuations extending across several kilometers of the grounding zone along the glacier's main trunk.

What does this change for coastal cities?

The practical question is flooding. If the new model holds, scientists have been systematically underestimating how much ice Thwaites will surrender, and coastal regions face greater flood exposure in the coming decades than earlier assessments assumed.

"We have documented and quantified 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 happening on the undersides of glaciers like Thwaites is leading to an even greater sense of alarm," said co-author Eric Rignot, professor of Earth system science at UC Irvine. "Most projections up to the present have struggled to match the rapidity of the mass loss because of missing physics; our new model with more complete physics is able to match the record and then produces projections that are twice as large as before."

Could the glacier lose its anchor?

The study also flags a specific tipping point. Water moving beneath Thwaites is weakening its grip on underwater ridges that hold it in place. The glacier's main trunk is currently pinned by the Mouginot Ridge. Once that ridge unpins, Poinelli said, "the glacier will continually retreat across a predominantly retrograde seafloor toward its next topographic high, the South Ridge."

That is not a distant hypothetical. When the model includes a grounding zone 4 to 6 kilometers across, it gives a 60% probability that Thwaites detaches from Mouginot Ridge before 2100.

A caveat, though — and there always is one. This is a single model, and a model is only as good as its physics and its calibration. Poinelli defends the approach: "When you factor in key physical processes and calibrate against historical observations, you gain a reliable pathway for narrowing uncertainty in projections." The model does match the observed record better than its predecessors. That is encouraging. It is not proof. Twenty-two years of observations and one satellite constellation underpin the claims; continued monitoring will tell whether the doubling holds.

For now, the safest reading is this: the plausible worst case for Thwaites just got worse, and coastal planners should treat 30 millimeters of sea level rise from one glacier alone as a live possibility rather than a tail risk.