Years from now, when scientists look for a precise moment when the Earth’s climate began to inexorably change, they may mark this week. Two separate studies Monday appeared to confirm a fear scientists have harbored for decades: major glaciers in the West Antarctic Ice Sheet are irrevocably destabilized, and their slide into the ocean will swell the world’s oceans by four feet.

Glaciers in West Antarctica “have passed the point of no return,” said Eric Rignot, the author of a study from the University of California at Irvine and NASA published in Geophysical Research Letters. It “will be a major contributor to sea level rise in the decades and centuries to come.”

Thomas P. Wagner, another NASA researcher who studies polar ice, was equally grave in an interview with the New York Times. “This is really happening,” he said. “There’s nothing to stop it now. But you are still limited by the physics of how fast the ice can flow.”

What does this mean for the planet and the human species? Likely a lot.

Here are some critical questions and answers.

Q: Why is the collapse of an ice sheet so important?

A: The science of global warming comes down to ice. Though Earth’s warming, the planet is currently in an ice age, and great sheets of ice at the poles — think Greenland and Antarctica — have not always existed. In the past, sea levels were actually significantly higher than they are in this era’s environment, which allowed contemporary civilization to thrive.

If all of the ice was to melt at the poles, the National Academy of Sciences predicts the sea level rise approximately 60 meters — about 200 feet. That would result in “storm surges more likely to cause severe impacts” and “coastal inundation.”

A new study by researchers at NASA and the University of California at Irvine finds a rapidly melting section of the West Antarctic Ice Sheet appears to be in an irreversible state of decline, with nothing to stop the glaciers in this area from melting into the sea. (NASA)

Q: Should coastal cities be worried?

A: Yes. But not immediately. Scientists expect six glaciers to drain into Antarctica’s Amundsen Sea, driving sea levels up four feet — but these things take time. “The good news is that while the word ‘collapse’ implies a sudden change, the fastest scenario is 200 years, and the longest is more than 1,000 years,” a University of Washington press release about its climate-change study said. “The bad news is that such a collapse may be inevitable.”

You can probably guess which cities are among the most at risk if seas rise: Miami, New Orleans, Hong Kong, Tokyo and pretty much all of the Maldives.

Q: How did researchers come to this conclusion?

A: Both teams of scientists came to a strikingly similar conclusions about West Antarctic’s glacial collapse — but through very different means. The NASA study used satellite radar to scrutinize several glaciers hugging the Amundsen Sea that contain enough water to raise sea levels by four feet. They found a “continuous and rapid retreat,” and that there is “no [major] obstacle that would prevent the glaciers from further retreat.”

The University of Washington researchers used computer simulations to come to the same conclusion, but with an added caveat: One of the glaciers, Thwaites, acts as a “linchpin” on the rest of the ice sheet — which contains an additional 13 feet of global sea rise. “In our model simulations it looks like all the feedbacks tend to point toward it actually accelerating over time,” explained lead author Ian Joughlin. “There’s no real stabilizing mechanism we can see.”

Q: What’s the endgame? 

A: A very different planet. Some scientists say the collapse of West Antarctica is only the beginning. Regardless of Monday’s findings we may have already triggered nearly 70 feet of additional sea rise.

Others contend that East Antarctica, long thought to be stable, is more at risk than the western side of the continent. “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, the co-author of another global warming study released last week.