Off the coast of West Antarctica sits a glacier so large and so unstable that scientists have nicknamed it the “Doomsday Glacier.” Thwaites Glacier spans an area comparable to Florida or Britain, and the ice locked inside it holds enough water to raise global sea levels by more than two feet on its own. That figure alone would reshape coastlines, but the greater fear is what Thwaites could unleash behind it.
Researchers watch the glacier closely because it sits at a vulnerable point in the Antarctic ice sheet, exposed to warm ocean water and retreating in ways that are difficult to reverse. Its behavior over the coming decades and centuries is one of the largest uncertainties in projections of how high the seas will climb.
Why one glacier carries so much water
Thwaites is not an ordinary river of ice. It is one of the widest glaciers on the planet, draining a vast basin of the West Antarctic Ice Sheet directly into the ocean. The International Thwaites Glacier Collaboration notes that the glacier already accounts for roughly 4 percent of global sea-level rise, an outsized share for a single ice stream, and that the ice it contains could raise seas by about 65 centimeters if it were lost entirely.
Sixty-five centimeters is a little over two feet, enough to redraw the map of low-lying coastal cities, flood-prone deltas, and island nations around the world. That total would not arrive overnight; the process plays out over many decades. But even a fraction of it, added on top of the rise already underway from warming oceans and melting ice elsewhere, would sharply increase the frequency of coastal flooding and the reach of storm surges.
The cork in a much larger bottle
The reason Thwaites earns its ominous nickname is that its own ice is only part of the story. The glacier acts like a cork holding back a far larger volume of ice inland. Much of the West Antarctic Ice Sheet rests on bedrock that lies below sea level, sloping downward toward the interior of the continent. That configuration makes it prone to a runaway process: once the glacier’s grounding line, the point where ice lifts off the seabed and begins to float, retreats into deeper water, the retreat can accelerate on its own.
If Thwaites were to collapse and stop buttressing the ice behind it, scientists estimate the wider destabilization of the West Antarctic Ice Sheet could eventually add several feet more to sea level, potentially on the order of 10 feet over long timescales. According to Britannica’s overview of the glacier, this buttressing role is exactly why its potential collapse commands so much attention: the direct contribution is large, and the indirect one is far larger.
Warm water working from below
The threat to Thwaites comes mostly from beneath the surface. Relatively warm, dense ocean water is reaching the underside of the floating ice shelf that extends from the glacier, melting it from below and loosening its grip on the seabed. Expeditions that have sent instruments and robotic vehicles beneath the ice have found evidence of warm water carving channels and reaching vulnerable points where the glacier meets the ground.
As that ice shelf thins and fractures, it loses its ability to slow the flow of ice from land into the sea. The floating portion has developed large cracks, and scientists have warned that parts of it could break apart, removing another brake on the glacier’s advance into the ocean. Measurements of the glacier’s speed and thickness, tracked in part through satellite observations compiled by programs such as NASA’s climate monitoring effort, show ice that is flowing faster and thinning in the areas most exposed to warm water.
How fast, and how certain
One of the hardest questions is timing. Some research has suggested that a rapid, catastrophic collapse of Thwaites within this century is less likely than earlier worst-case scenarios implied, offering a measure of reassurance. But the same work generally finds that the glacier is still set to retreat further and faster through the coming centuries, and it cannot rule out a broader collapse of the West Antarctic Ice Sheet over longer timescales.
That uncertainty is itself part of the concern. Because the physics of grounding-line retreat can tip from gradual to abrupt, projections carry a wide range, and planners along vulnerable coasts have to prepare for outcomes that span many feet of possible rise. The difference between the low and high ends of those estimates translates directly into decisions about seawalls, development, and where hundreds of millions of people can safely live.
Thwaites has become a symbol of that stakes-and-uncertainty problem. It is a single glacier at the far edge of the planet, yet its stability is tied to the future of coastlines everywhere. Whether it retreats slowly or crosses a threshold into faster collapse, the ice held in and behind Thwaites represents one of the clearest links between what is happening in remote Antarctica and the height of the water lapping at cities thousands of miles away.
This article was researched and drafted with the assistance of AI and reviewed before publication.
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