Scientists are warning that Antarctica's Thwaites Glacier, long dubbed the "Doomsday Glacier" for its outsized potential to destabilise global coastlines, may be more dangerous than previously projected. A new analysis suggests that seawater intruding beneath the glacier is accelerating ice loss in ways that could roughly double its sea-level contribution by 2100 compared with earlier forecasts.
The updated modelling adds urgency to one of climate science's most closely watched questions: how fast can a marine-based glacier collapse when warm ocean water reaches its underside? Thwaites sits on a vulnerable bed of rock below sea level in West Antarctica, making it especially sensitive to ocean-driven melting. Once seawater gains access beneath the ice shelf and grounding line, it can erode the glacier from below, thinning the ice and making it more likely to retreat inland.
Ocean Heat Below Ice
The new findings reinforce a central concern among glaciologists: the ocean, not just the atmosphere, is now a decisive driver of Antarctic ice loss. Even if surface air temperatures stabilise, warm water circulating under Thwaites can continue to eat away at the glacier's base. That means the system may remain on a path of decline despite broader climate progress, complicating assumptions that slower warming alone will be enough to halt the damage.
Researchers say the glacier's response is not linear. Small changes in ocean access can trigger much larger losses because the ice sheet rests on a bed that slopes downward inland. That geometry can create a self-reinforcing retreat, where thinning ice allows more seawater intrusion, which in turn causes more thinning. The result is a feedback loop that can accelerate sea-level rise over time.
The revised estimate does not mean an abrupt collapse is certain, but it does indicate that the glacier's contribution to sea-level rise may be materially underestimated in some earlier scenarios. For coastal planners, that distinction matters. Even modest upward revisions in Antarctic ice loss can translate into higher flood risk, more expensive defences, and tighter adaptation timelines for low-lying cities and island states.
Why Thwaites Matters
Thwaites is not just another glacier. It is widely viewed as a critical weak point in the West Antarctic Ice Sheet, a region that holds enough ice to raise global sea levels by several metres if fully destabilised over long periods. While that full outcome is not imminent, Thwaites is seen as a potential gateway to broader ice-sheet retreat because of its scale and location.
The glacier's importance is magnified by the fact that sea-level rise is already reshaping risk calculations worldwide. Higher oceans intensify storm surge, worsen tidal flooding, and increase the frequency of so-called nuisance floods in coastal infrastructure. In practical terms, every additional millimetre of sea-level rise compounds the burden on ports, power plants, transport networks, and densely populated shorelines.
The latest research also underscores a broader climate transition reality: the most consequential risks are increasingly coming from systems that respond slowly but irreversibly. Unlike emissions, which can be reduced through policy and technology, ice-sheet dynamics unfold over decades and centuries. That makes early warning especially valuable, because once a glacier crosses certain thresholds, the process can be difficult or impossible to reverse on human timescales.
Forecasts Under Pressure
The new projection arrives amid a wider effort to refine climate models with better data on sub-ice ocean circulation, grounding-line behaviour, and ice-shelf fracture. Those improvements are changing the picture of Antarctica from a static frozen reserve into a dynamic and highly sensitive component of the Earth system.
For policymakers, the message is sobering but clear: adaptation assumptions built on older, lower-end sea-level estimates may no longer be robust enough. Infrastructure designed for the coming decades must account for the possibility that Antarctic contributions could accelerate faster than expected, especially if ocean warming continues to penetrate vulnerable glacier fronts.
At the same time, the findings do not eliminate the role of mitigation. Cutting greenhouse-gas emissions remains essential to slowing ocean warming and limiting the long-term scale of ice-sheet loss. But the new analysis suggests that even aggressive climate action may not immediately stop Thwaites from retreating, because the glacier is already exposed to a warming ocean system that can keep working against it.
In that sense, Thwaites has become a test case for the climate era: a reminder that the costs of warming are not confined to future generations, and that some of the planet's most consequential changes are already underway beneath the ice.