Scientists are raising alarm bells after two studies found that the Gulf Stream—an ocean current key to regulating Earth's climate—is the weakest it's been in 1,600 years, the Guardian reports. The culprit is apparently melting sea ice and glaciers, which inject fresh water into the North Atlantic and weaken the stream. "Fiddling with [the Gulf Stream] is very dangerous, because you may well trigger some surprises," says climate scientist Stefan Rahmstorf. "I wish I knew where this critical tipping point is, but that is unfortunately just what we don’t know." If the stream dies, scientists say, its equatorial heat would stop reaching the North Atlantic—plunging Europe into bone-numbing winters and affecting weather worldwide. Even subtler changes "could wreak havoc" on the Atlantic Ocean's "delicate ecosystems," Smithsonian reports.
The studies differ in approach and timeline but both say the Gulf Stream has diminished by about 15%, Nature reports. One study spotted it by measuring sediment on the ocean floor and says the problem began when the Little Ice Age subsided around 1850. The other, which analyzed sea surface temperatures combined with advanced climate simulations, says the decline started around 50 years ago. But both see human-influenced climate change as a cause, Nature says. And with Greenland's huge ice cap melting at a historic rate, some say the Paris climate agreement is our only hope. "If we can keep the temperature rise to well below 2C as agreed in the Paris agreement, I think we run a small risk of crossing this collapse tipping point," says Rahmstorf. (Meanwhile the Doomsday Clock has ticked 30 seconds closer to "midnight.")