Add a New Ice Sheet ‘Tipping Point’ to Your Nightmares

The ice sheets are already scary. Greenland could be doomed with only a few fractions of a degree more warming. Antarctica’s ice shelves, the floating extensions of the ice sheet that help hold it back from falling in the sea, are facing “unavoidable” destruction. There is something called a “Doomsday Glacier,” and it isn’t doing great.

And now, more bad news: a study from the British Antarctic Survey finds a new tipping point in the ice sheet system, involving the “grounding zone” where floating ice and bedrock-based ice meet. Short version: projections of melting and subsequent sea level may yet still be underestimated.

The longer version is that the researchers, Alexander Bradley and Ian Hewitt, developed a model to estimate the effects of groundwater intrusion underneath the ice sheet, and the feedback loops between that water and melting of the ice above it. The results were ugly. They found that “as the grounding zone widens in response to melting, both temperature and flow velocity in the region increase, further enhancing melting.”

In other words, melting induces faster melting. At a certain point, this acceleration will pass a tipping point when ocean water will basically pour into the gap between ice and rock “in an unbounded manner,” inducing “runaway melting.” That excess and accelerated melt is not yet incorporated into global sea level rise models.

The authors don’t know when that tipping point will rear its head. And importantly, whenever we talk about melting ice sheets, we’re talking about decades and centuries rather than a few years; as I’ve written elsewhere, in some senses the reason we’re not absolutely quivering in fear and destroying every oil rig in the world right now is that the ice is melting too slowly for us to truly grasp what’s coming. It’s not so much a boulder rolling down a hill in your house’s direction as it is a crack in the foundation getting a little bigger every year until the house is at risk of falling down.

And the water will come. West Antartica’s melted ice alone could add upwards of 10 feet of sea level rise; throw in Greenland and you’re up past 30 feet. That’s enough to entirely submerge basically all of South Florida and southern Louisiana, the entire Shanghai region, and more or less all of the country of Bangladesh, not to mention completely destroy life in a number of small island nations. This may take centuries to fully unfold, but the new study suggests there may be more melt in the near term — on the order of decades — than previously thought.