Doomsday Glacier Thwaites May Add Twice the Projected Sea Level Rise, New Study Finds

Thwaites Glacier in West Antarctica is the widest glacier on the planet, roughly the size of Florida, and it sits in one of the least reachable places on Earth. A new study says it is losing ice more aggressively than forecasts have assumed, and that its contribution to sea level rise by 2100 could be double what is currently projected.

The work comes from glaciologists at the University of California, Irvine and NASA's Jet Propulsion Laboratory. It was published on Monday in the journal Nature Communications. Their central finding is that when they adjusted ice sheet models to reflect what satellites show happening where the glacier meets the sea, Thwaites could add up to 1.2 inches of sea level rise by 2100. That is twice earlier estimates, and the team says it would happen even without further global warming.

The change concerns what scientists call the grounding line, the point where ice lifts off the seabed and begins to float as an ice shelf. Typical models have treated that line as fixed and mostly stable. Satellite data, though, shows it is really a grounding zone, sometimes miles wide, where seawater flows in and out with the tides, raising and lowering the thick ice in a process known as tidal pumping. Mattia Poinelli, the lead author, a project scientist at UCLA who was at UC Irvine when the study was done, said this lets relatively warm ocean water reach deep beneath the ice and cause vigorous melting.

The geography adds to the problem. The land under Thwaites slopes downward, so as the glacier thins and retreats, more ice is exposed to warm water. Two underwater ridges pin the ice and keep it from flowing into the ocean faster. The study found that melting in the grounding zone is speeding the unpinning of ice from the larger one, the Mouginot Ridge. It puts the chance of that unpinning by the end of the century at 60 percent. After that, the glacier would likely retreat quickly down the sloping bedrock toward the next major ridge.

The stakes explain the glacier's nickname, the Doomsday Glacier. Thwaites has been retreating for decades and currently accounts for about 4 percent of global sea level rise. If it collapsed, its own water could raise seas by more than 2 feet. It also acts like a cork for the vast Antarctic ice sheet behind it, and its loss could ultimately lead to around 10 feet of rise, a threat to coastal communities from Miami to Manila.

Against that backdrop, 1.2 inches may sound small, but the authors say it is enough to greatly magnify coastal dangers. Eric Rignot, a study author and professor of Earth system science at UC Irvine, said the results predict greater risk and exposure for coastal flooding in the coming decades than had been anticipated.

Outside scientists see the work as significant but unfinished. Ted Scambos of the University of Colorado Boulder, who was not involved, called it potentially a real gamechanger for forecasting sea level rise from Thwaites. Robert Larter, a marine geophysicist at British Antarctic Survey, also not involved, said much remains unknown about grounding zone processes before anyone can confidently predict how fast the ice will go. He added that conditions beneath Thwaites are even more complex than the paper describes.

The next step is direct observation. Rignot said the team plans to travel to the glacier in 2028 and deploy instruments to record seawater moving in and out of the grounding zone. He said the world must cut planet-heating pollution now to limit the damage, but warned that even if it does, higher sea levels should be expected from harm already done.