Now comes the news that the West Antarctic isn’t the only concern. In fact, it may not even be the biggest one.

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In the much larger East Antarctica, where melting has the potential to raise sea level by 53 meters (174 feet), there’s a small ice volume called the Wilkes Basin. It carries significance well beyond its size. According to a study published this week in Nature Climate Change, if it melts, it would trigger an “irreversible discharge” of the entire basin, causing an unstoppable sea level rise of up to 4 meters. “East Antarctica may become a large contributor to future sea-level rise on timescales beyond a century,” the study says.

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“East Antarctica’s Wilkes Basin is like a bottle on a slant,” lead author Matthias Mengel said. “Once uncorked, it empties out.”

The most jarring conclusion? Once the ice begins its flow out of the broken “ice cork,” there’s no stopping it.

“Until recently, only West Antarctica was considered unstable, but now we know that its 10 times bigger counterpart in the East might also be at risk,” explained Anders Levermann, another author on the study.

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The findings come at a time when scientists from the United Nations to the National Climate Assessment are warning of the looming effects of global warming. “Climate change, once considered an issue for a distant future, has moved firmly into the present,” a recent National Climate Assessment says.

Last month, the U.N. also released a report saying that it is nearly too late to reverse global warming. “The window is shutting very rapidly on [limiting global warming to] the 2 degrees target,” Johan Rockstrom, director of the Stockholm Resilience Centre, told Reuters. “The debate is drifting to ‘maybe we can adapt to 2 degrees, maybe 3 or even 4.'”

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Until now the East Antarctic has been considered the more stable of the two. “The East Antarctic ice sheet has long been considered to be stable even under a warmer climate, in contrast to its West Antarctic counterpart,” Mengel said in a statement. “We have now shown that this may not be true. … The future sea-level contribution of the East Antarctic ice sheet may be significantly higher than previously estimated.”

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“It sounds plausible,” Tony Payne, a professor of glaciology at Bristol University, told Reuters. East Antarctica “could contribute meters to sea level rise over thousands of years,” he said.

Indeed, the process, though significant, appears to be slow. The study found that it may take as many as 200 years for the cork to melt. And after it goes, it will take another several thousand years for the basin to empty into the sea.

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Still, with many of the world’s most populous cities — Mumbai, Tokyo, New York — near the ocean, every inch in sea rise counts.