Under 2.5 miles of ice in southeastern Antarctica, a natural levee is about to break.
If it does, the world will look much, much different.
A study released Thursday in the journal Nature Climate Change revealed that East Antarctica's Totten Glacier is dangerously unstable.
Although other parts of Antarctica are melting in response to climate change, the instability of Totten could be the "biggest in the end, because it's continually unstable as you go toward the interior of the continent," Alan Aitken, a geologist at the University of Western Australia in Perth and an author of the study, told the Washington Post.
The Totten Glacier isn't Antarctica's largest glacier, but it's precariously perched upon a 1-mile-deep basin of snow and ice the size of California — which means it holds back more ice than any other place on the continent.
The problem? Totten is also one of Antarctica's most rapidly thinning glaciers. If it buckles into its basin, it could release enough ice to raise oceans an extra 4 to 6 feet by the end of the century.
The researchers recently discovered two zones where the glacier is particularly unstable. In past climate cycles, these zones shifted between stability and instability with periods of warming and cooling, with Totten contributing to sea-level rise and fall at that time.
Aitken said in a press release that Totten's weakening is being driven by unprecedented warming. We've already reached more than 1.8 degrees Fahrenheit of global warming since the industrial era; reaching 3.6 degrees Fahrenheit of global warming, he says, could push Totten's instability over the edge.
"If this was to happen again, with a warmer climate than today, it could lead to a rapid rise in sea level of over a meter (about 3 feet)," Aitken said in the release.
If global warming goes unabated and Totten retreats inland toward its basin, it could add as much as 9 feet to rising seas.
Aitken and his colleagues estimated that when Earth was about 4 degrees warmer than it is now, a melting Totten may have contributed to half of that period's sea levels, which stood dozens of feet higher than they do today.
There is some good news, though: Aitken says the tipping point for that kind of melt happens at 4.5 degrees of warming. If we can keep global warming to just 3.6 degrees, Totten just might make it.
