Yet their work—and the work of other sea-level-rise scientists—still warns of potential catastrophe for our children and grandchildren. If every country meets its current commitment under the Paris Agreement, the Earth will warm about 2.7 degrees Celsius by the end of the century compared with its pre-industrial average. In their new research, DeConto and his colleagues say that there’s a tipping point, somewhere between 2 and 3 degrees Celsius of temperature rise, after which the West Antarctic Ice Sheet will slip into rapid and shattering collapse.

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Their new research also raises the marginal risk of disaster. Officially, the Paris Agreement aims to keep global warming from exceeding 2 degrees Celsius, though many experts consider that goal fanciful. And even in that extremely optimistic scenario, West Antarctica still switches into unavoidable collapse about 10 percent of the time, according to the new research.

Their short-term revisions also barely change their long-term forecast of West Antarctic disintegration. If emissions keep rising, they warn that global sea level could rise by more than 26 feet by 2300.

These new results have not yet been peer-reviewed. DeConto, a professor at the University of Massachusetts at Amherst, presented them to other scientists last month at the fall meeting of the American Geophysical Union, the largest annual conference of Earth scientists in the world. He and his colleagues declined to comment for this story in keeping with an academic custom not to discuss new work with the press before its publication.

The new results inform one of the biggest outstanding questions—and most fervent debates—concerning how climate change will reshape our world: How much will the seas rise, and how fast will that upheaval occur? DeConto and several other American glaciologists—including Richard Alley, a professor at Penn State and a co-author of the new research—represent something like the vanguard of that discussion. They champion an idea called “marine ice-cliff instability,” or MICI, which maintains that West Antarctic glaciers will eventually crumble under their own weight. By the middle of next century, they warn, this mechanism could send ocean levels soaring at a rate of several feet per decade. For reference: Along the U.S. East Coast, the Atlantic Ocean has risen by only about a foot over the last 12 decades.

While “marine ice-cliff instability” might be clunky, the idea is cinematic. It holds that warm ocean waters will eventually chew away the floating ice shelves that gird Antarctic glaciers today. With these ice shelves gone, the glaciers will stand naked on the seafloor: towering, fragile cliffs of ice. Imagine a 300-foot-tall shard of sapphire rising from the ocean and stretching for miles in both directions, and you will have a sense of the awesome prospect of this new geography. You will also have a sense of its dangerous physics, because ice cannot support itself at such heights. As MICI kicks in, those sapphire walls will crack, buckle, and begin rapidly birthing hundred-foot splinters of frozen freshwater into the sea. And thus the oceans will rise.