Tides are pumping warm water under Thwaites, and scientists now say it could add twice the sea rise expected by 2100

The story

The biggest glacier on the planet may be giving up its ice faster than anyone thought. A new study from researchers at UCLA and NASA's Jet Propulsion Laboratory says Thwaites Glacier in West Antarctica could add about 30 millimeters, roughly 1.2 inches, to global sea levels by 2100. That is about double earlier estimates, and it holds even if warming doesn't speed up.

The reason is what happens where the ice meets the seabed. Older models treated that boundary as a fixed line. The new work describes a wider zone where the tides lift and drop the ice, pushing warm ocean water deep underneath and melting it from below. Lead author Mattia Poinelli calls the process tidal pumping.

That melting is loosening the glacier's grip on the Mouginot Ridge, an underwater stretch of bedrock that currently helps hold it steady. The team puts the chance that Thwaites breaks free of it before the end of the century at 60 percent.

Thwaites covers about 192,000 square kilometers, bigger than Florida and close to the size of Senegal, which is how it earned the nickname Doomsday Glacier. It already accounts for around 4 percent of sea level rise worldwide and has shed more than a trillion tonnes of ice since 2000, and it is still losing about 50 billion tonnes a year. Along with neighbors like Pine Island Glacier, it acts as a plug holding back the far larger West Antarctic ice sheet.

Scientists caution that more research is needed to pin down exact numbers. But a separate study from the British Antarctic Survey in July found Thwaites will keep losing ice for at least another 150 years, even if the ocean around it cooled dramatically.