Remember that scene from The Day After Tomorrow where Dennis Quaid tells everybody about the breakdown of the Atlantic current that carries warm water north from the tropics? Sure you do. Within minutes, tornadoes are everywhere, tsunamis are destroying the coast, and New York City is sent back into another ice age. I’ll remind you:
Unfortunately, this wasn’t all Hollywood bullshit. A new ice age may not be imminent, but the current in question—the Atlantic meridional overturning circulation, or AMOC to its friends—really is weakening, mostly due to the melting of the polar ice cap and the Greenland ice sheet, which makes the ocean water less salty. This means the coast off Greenland is cooling and the coast off of New York City is warming (Dennis got that part wrong). Here’s a picture from a new study in Nature that shows how observation matches with climate models:
That’s a pretty close fit. And if you’re the kind of person who’d really prefer to see this in complicated chart form—and who isn’t?—a second paper in Nature has you covered:
All three of these charts show a dramatic change at the start of the industrial era. The authors believe that this change was probably kicked off by the end of the Little Ice Age, but has since continued for other reasons:
This suggests either hysteresis of the AMOC in response to an early climate forcing—natural (solar, volcanic) or anthropogenic (greenhouse gases, aerosols, land-use change)—or that continued climate forcing, such as the melting of the Greenland Ice Sheet, has been sufficient to keep the AMOC weak or cause further weakening.
So there you have it. If this keeps up, it’s not New York that will start to freeze over, it’s Europe. Right now, they’re kept relatively toasty, even though London is about as far north as Newfoundland, because the AMOC pushes warm water from the equator up their coast. If that stops, it’s going to get pretty chilly in Britain. For more, Chris Mooney has a good writeup in the Washington Post.