Science / Earth

The Doomsday Glacier could raise seas twice as much as scientists thought

New modelling of Thwaites Glacier in West Antarctica projects up to 30 millimetres of sea level rise by 2100 from this one glacier alone, double the previous estimate, and it happens even without any extra warming.

West Antarctica · October 18, 2026

The revision is simple to state and awkward to plan around. A study published on October 12 in Nature Communications, by a team at the University of California, Irvine and NASA's Jet Propulsion Laboratory led by Mattia Poinelli, projects that Thwaites Glacier could add up to 30 millimetres, about 1.2 inches, to global sea levels by 2100. That is roughly twice the 15.2 millimetre average of the earlier ISMIP6 model ensemble under the same conditions, and the new figure holds even if the climate stays at its recent average, with no additional warming at all.

The change is not a bigger guess. It is a different picture of what happens under the ice. Older models treated the grounding line, the boundary where the glacier leaves bedrock and starts to float, as a fixed line. Satellite radar shows something wider and messier: a grounding zone, sometimes kilometres wide, where tides lift the ice and warm seawater pushes deep underneath it. As Poinelli put it, satellite observations show a zone where warm ocean water is "reaching deep underneath the ice sheets and causing vigorous melting." Put that zone into the model and the glacier's recorded retreat since the 1990s suddenly matches, four times more pronounced than traditional models could reproduce.

Scale is why this one glacier gets its own headlines. Thwaites covers about 192,000 square kilometres, roughly the size of Senegal and larger than Florida, and it holds about 65 centimetres of potential sea level rise in total. Al Jazeera's summary of the research notes that ice loss from Thwaites already accounts for about four percent of all global sea level rise, that it has lost more than 1,000 billion tonnes of ice since 2000, and that it is still losing about 50 billion tonnes a year. It also acts as a plug. Behind it sits the far larger West Antarctic ice sheet, which it helps to hold back.

The simulations carry a second warning. In the runs that best match today's radar data, there is a 60 percent chance that the glacier's main trunk detaches from the Mouginot Ridge, an underwater ridge that currently helps to pin it in place, before the end of the century. A separate British Antarctic Survey study reported on October 13 reached a colder conclusion from the opposite direction: even in a hypothetical scenario with no ocean melting at all for 150 years, Thwaites kept losing ice, while its neighbour Pine Island Glacier recovered. One study says the melt was underestimated. The other says the decline may already be locked in.

Thirty millimetres sounds small until you price it the way a coastal city does, in higher storm surges, more frequent flooding and defences built for a lower sea. The honest reading of this week is not that collapse is imminent, the researchers do not project that by 2100, but that the planning number just doubled for the single most watched glacier on Earth. Cities from Miami to Mumbai build to the forecast they are given. This forecast just moved.