Glacier Cliffs Are Crumbling Faster Than Models Predicted, But a Doomsday Scenario Looks Less Likely

A Long-Debated Theory Gets Its Biggest Test Yet

For years, one of the most unsettling questions in climate science has been whether Earth's towering glacier cliffs could trigger a catastrophic, self-sustaining collapse — sending seas surging far faster than any current projection. A sweeping new study published in the journal Science has now delivered the most rigorous real-world test of that theory, and the answer is complicated: the cliffs are breaking apart faster than scientists thought, but they're also pulling back from the brink before triggering a runaway disaster.

The study, led by the Woods Hole Oceanographic Institution (WHOI), provides the most comprehensive observational analysis yet of the towering ice cliffs that fringe Earth's ice sheets, giving scientists new evidence to evaluate a long-debated process that could influence future sea level rise. Researchers used satellite laser altimetry — a technique that measures surface elevation by timing laser pulses traveling from a satellite to Earth's surface and back — to calculate cliff heights and compare them with ice thickness, water depth, crevassing, and calving rates across thousands of locations.

What the Satellites Revealed

The Marine Ice-Cliff Instability (MICI) theory proposes that extremely tall ice cliffs, taller than about 100 meters above the waterline, can become structurally unstable and trigger a cycle of rapid, self-sustaining ice loss. Because that process has never been directly observed, scientists have debated whether it should be included in projections of future sea level rise.

To test the theory against real-world observations, researchers analyzed the characteristics of ice cliffs using 15,330 individual satellite observations collected around the margins of Earth's ice sheets. They found that ice cliffs that collapsed did so at a much faster rate than scientists had predicted — but these collapsing cliffs also quickly stabilized, instead of continuing to erode the larger ice sheet. The researchers also observed that the average ice cliff height was about 30 meters, with only a few rare cliffs surpassing 100 meters.

"We found that when the cliffs were retreating, they were doing so faster than what has been modeled, which would mean more ice loss and higher contributions of sea level rise," said lead author Caroline Needell. "But because we found that the retreat was short-lived, and all the glaciers eventually stabilized, that would suggest that things won't be so bad. We don't see this runaway effect."

Why This Matters for Coastal Communities

Global sea level has already risen by more than eight inches since 1880, and scientists project it will continue to rise throughout this century as ice sheets lose mass. More accurate projections are increasingly important for coastal communities, where rising sea levels can worsen flooding, accelerate erosion, damage infrastructure, and intensify storm-surge impacts.

The results suggest that some estimates of higher and faster sea level rise, which have been dismissed by some scientists, could be more likely than previously thought. "High-end sea level rise associated with really rapidly breaking cliffs has been somewhat dismissed as being an unlikely scenario, but maybe we shouldn't rule out some of the higher estimates," said Jeremy Bassis, a professor at the University of Michigan and co-author of the study.

While earlier models suggested cliffs taller than 100 meters would trigger a runaway collapse, the study found that collapsing cliffs retreat faster than predicted but quickly stabilize, preventing a cascading effect. Factors like thicker mélange — a mix of broken icebergs and sea ice — and deeper surrounding water also stabilize cliffs, even those exceeding the critical height.

What Comes Next

"Understanding how ice sheets lose mass is key to improving projections of future sea level rise," said Catherine Walker, a glaciologist at WHOI and study author. "To make better predictions, we need observations that show how glaciers behave where they meet the ocean and help us improve the models we use to understand future change."

Walker said the group plans to run the same analysis on every glacier that feeds an Antarctic ice shelf, with a key question being what happens when glaciers can't thin fast enough to stabilize retreat — which might happen in places like Thwaites in the future. That glacier has long been considered one of the most vulnerable on the planet. The findings highlight the need to consider bed topography and ice thinning rates in predicting sea level rise, and while the study suggests a less dire scenario than previously thought, it underscores the complexity of ice cliff dynamics. In short, the doomsday clock hasn't been stopped — scientists have simply gotten a much clearer look at its gears.