Ice sheets can vanish 20 times faster than satellites have measured
Beneath the Norwegian seafloor, ancient ridges pressed into sediment by a retreating ice sheet have delivered a warning across millennia: ice does not surrender slowly. New research reveals that during Earth's last great warming, ice sheets collapsed at rates twenty times faster than anything our satellites have yet witnessed in Antarctica — a discovery that reframes how humanity must reckon with the fragility of its coastlines. The geometry of the seafloor, not merely the warmth of the ocean, may determine how quickly the world's great frozen reserves surrender to the sea.
- Seafloor ridges formed by tidal pulses thousands of years ago reveal that ice sheets once retreated at 600 metres per day — a speed that current satellite records have never captured and climate models have not fully accounted for.
- The danger is structural: where ice rests on flat seafloor, as little as half a metre of daily melt can sever its grip on the bed, triggering buoyancy-driven collapse that unfolds over days or months before the geometry shifts and retreat slows.
- Thwaites Glacier in West Antarctica — already retreating and now just four kilometres from exactly this kind of flat, vulnerable terrain — carries enough ice to raise global sea levels by 65 centimetres if its drainage basin collapses.
- The broader Antarctic Ice Sheet, if lost entirely, would submerge the world's coastlines by more than 57 metres, threatening hundreds of cities and displacing millions of people who have built their lives at the water's edge.
- Scientists are now racing to incorporate this pulsed, nonlinear retreat behaviour into sea-level models, recognising that ice sheets do not fade gradually but can lurch catastrophically before stabilising — a rhythm the geological record has always known.
Beneath the Norwegian seafloor, a pattern of small ridges — each one etched by the daily pulse of tides against a retreating ice sheet — has preserved a message from the last ice age. By measuring the spacing between these corrugations, researchers determined that the Scandinavian Ice Sheet once retreated at rates reaching 600 metres per day. That figure is twenty times faster than anything satellites have recorded in Antarctica over the past half-century, and it changes the terms of the conversation about sea-level rise.
The Antarctic Ice Sheet covers an area larger than the United States and Mexico combined. Its complete loss would raise global seas by more than 57 metres. Satellite observations have tracked West Antarctic ice retreating at up to 30 metres per day — alarming enough — but that record spans only decades, a thin slice of geological time. To understand how ice truly behaves under sustained warming, researchers turned to the last deglaciation, the period between roughly 20,000 and 11,000 years ago, when Earth last made the transition out of an ice age.
What the ancient record shows is that retreat is not gradual. Ice sheets can hold relatively stable for years, then lurch backward in violent pulses before stabilising again. The trigger is the shape of the seafloor beneath the ice: on flat beds, only minimal daily melting is needed to make ice buoyant enough to lose its grip on the ground and float free. These collapses unfold over days to months before the ice sheet's changing geometry slows the retreat.
Thwaites Glacier sits at the centre of this concern. Already retreating and closely watched, it now lies just four kilometres from a flat region of its bed — precisely the terrain this research identifies as most dangerous. A rapid-retreat pulse there could cascade into the collapse of the entire Thwaites drainage basin, contributing 65 centimetres to global sea levels on its own. The work underscores an urgent need: climate models must account for this pulsed, nonlinear behaviour, and scientists must map the hidden contours of ice sheet beds to understand where the next sudden lurch may begin.
Beneath the Norwegian seafloor lies a record written in ridges. These small corrugations, each one to two meters high, were etched into the seabed thousands of years ago by the rhythmic pulse of a retreating ice sheet. Two ridges formed each day, one at each low tide, as the Scandinavian Ice Sheet rose and fell with the ocean's rhythm. By measuring the space between them, researchers discovered something that should concern anyone living near a coast: ice sheets can vanish far faster than we thought.
The Antarctic Ice Sheet sprawls across an area larger than the United States and Mexico combined. If it melted entirely, global sea levels would rise by more than 57 meters—enough to flood hundreds of cities worldwide. Satellite data collected over the past 50 years shows that grounded ice in West Antarctica's coastal regions has been disappearing at up to 30 meters per day. But that satellite record is brief, a mere snapshot of geological time. To understand how ice sheets truly behave under warming conditions, researchers looked backward, studying the last deglaciation—the period between roughly 20,000 and 11,000 years ago when Earth transitioned from an ice age to the warmer climate we inhabit now.
What they found was startling. During that ancient warming period, the Scandinavian Ice Sheet underwent pulses of retreat reaching 600 meters per day. That is 20 times faster than anything satellites have yet measured in Antarctica. The mechanism behind this catastrophic speed lies in the shape of the seafloor. Where ice sheets rest on flat beds, only about half a meter of daily melting is needed to trigger what researchers call buoyancy-driven collapse. The ice becomes so lightly attached to its foundation that it essentially floats free, retreating almost instantaneously. These pulses of extreme retreat typically last days to months before the ice sheet's geometry changes and the brakes engage once more.
The implications for Antarctica are sobering. Thwaites Glacier, a vast and unstable mass of ice in West Antarctica, has been retreating steadily since satellites began watching it. Today it sits just four kilometers away from a flat region of its bed—the kind of terrain that, according to this research, is most vulnerable to catastrophic collapse. If Thwaites enters one of these rapid-retreat pulses, the consequences would ripple outward. Ice losses there could accelerate the collapse of the entire Thwaites drainage basin, a region containing enough ice to raise global sea levels by 65 centimeters on its own.
The research reveals a troubling nonlinearity in how ice sheets respond to warming. They do not retreat at steady rates. Instead, they can remain relatively stable for years or decades, then suddenly lurch backward in violent bursts before stabilizing again. This pulsed behavior, observed in the geological record, is likely to characterize the future as well. The challenge for climate scientists is incorporating this short-timescale mechanism into computer models that predict sea-level rise. Understanding the shape of ice sheet beds—where they are flat and vulnerable, where they slope and resist—has become critical to forecasting how quickly our coasts will change.
Notable Quotes
Ice sheets on flat regions are most vulnerable to extremely rapid retreat over much shorter timescales— Research findings on ice sheet behavior
The Hearth Conversation Another angle on the story
How did you actually measure something that happened 15,000 years ago?
The tides did the measuring for us. When an ice sheet retreats, it rises and falls with the ocean twice a day. Each time it rests on the seafloor at low tide, it pushes sediment into a ridge. Two tides, two ridges, every single day. The spacing between them tells you exactly how far the ice retreated in 24 hours.
And you found these ridges on the Norwegian seafloor?
Yes. They're preserved there like tree rings, except instead of recording years, they record days of ice sheet collapse. The Scandinavian Ice Sheet left this detailed archive behind.
Why does it matter that Thwaites Glacier is four kilometers from a flat bed?
Because flat beds are the danger zones. On steep terrain, ice sheets cling to the rock. On flat ground, they barely grip at all. Once they start floating, they can move 600 meters in a single day. Thwaites is approaching that threshold.
Could that actually happen soon?
The research suggests it's possible under current melting rates. We don't know when, but the conditions are aligning. That's why this matters now.
What happens if Thwaites collapses?
It doesn't just disappear. Its collapse destabilizes the ice behind it, like dominoes. The entire drainage basin could follow, raising sea levels by 65 centimeters. That's not catastrophic on a geological timescale, but for cities built at sea level, it's transformative.
So we're watching a slow-motion disaster unfold?
We're watching a system approach a tipping point. The ice sheet isn't moving yet, but the ground beneath it is changing. When it does move, it may move faster than we can adapt.