Here’s what you’ll learn when you read this story:

• The Atlantic Meridional Overturning Circulation (AMOC) is slowing down, and if it collapses, Europe could be plunged into a new Ice Age.
• To prevent the AMOC from collapsing, researchers have proposed building a dam across the Bering Strait.
• Before a plan like this can be carried out, scientists will need improved data to create a more accurate projection of what will happen to the AMOC.

Something’s not right with the currents. The Atlantic Meridional Overturning Circulation, also known as AMOC, is something of a conveyor belt for the exchange of warm and cool water. But as global temperatures creep upward, its movement has grown sluggish, and some scientists even argue it’s headed towards collapse. The last time that happened, around 12,000 years ago, enormous ice sheets melting at the end of the last Ice Age flooded the North Atlantic with freshwater, shutting down the circulation and plunging much of the Northern Hemisphere into a deep freeze. The effects of another collapse are uncertain, but could be dire.

Previous studies warned that a full collapse could plunge western Europe into extreme cold winters and summer droughts, shift the tropical rainfall belt (which hundreds of millions of people depend on to grow food), and raise sea levels along the Atlantic coast by nearly two feet. In response, researchers Jelle Soons and Henk Dijkstra—both from the University of Utrecht in the Netherlands—have come up with a controversial idea to strengthen the weakening current before it’s too late. A study lsying out their work was recently published in the journal Science Advances.

Soons and Dijkstra propose building a dam over areas of the Bering Strait that were once part of a land bridge during the Pliocene Era. About 36,000 ago, during the last Ice Age, the freezing of water into glaciers and ice sheets caused a drastic lowering of sea levels, exposing a strip of land between Siberia and Alaska. The Bering Land Bridge allowed for the migration of humans and animals from Asia to the North American continent. Then, between 13,000 and 11,000 years ago, melting glaciers caused global ocean levels to rise, once again submerging the land bridge and affecting marine currents around the world. Rising temperatures heated the ocean, flooding it with freshwater from ice melt and more frequent rains. Because warm water with lower salinity takes longer to sink than colder, saltier water, ocean currents experienced a slowdown that caused the AMOC to collapse.

Soons and Dijkstra think that a similar collapse could be avoided in the near future by creating what they call an artificial closure of the Bering Strait (CBS for short)—essentially, a massive dam. “The results presented here indicate that an artificial CBS could be an effective climate intervention strategy to prevent an AMOC collapse under CO₂ [levels increasing],” the researchers said in their study. “For an active AMOC with a relatively saline North Atlantic, a closure will allow for a reduced freshwater transport out of the Arctic into the North Atlantic and hence cause an AMOC strengthening.”

Our planet’s oceans are currently experiencing changes resembling those at the end of the Ice Age 12,000 years ago. If waters in the North Atlantic are not dense enough to sink and cool off before flowing south, the Northern Hemisphere would experience drops in temperature like it hasn’t seen in over ten thousand years, and the Southern Hemisphere would grow unbearably hot. This is where Dijkstra and Soon’s hypothetical dam comes in. Simulating the climate from when the Bering Land Bridge was exposed (between 36,000 and 13,000 years ago) showed the researchers that the AMOC would have been stronger during that period, as an influx of freshwater coming in from the Pacific through the Bering Strait tends to progressively weaken the AMOC. Some of the researchers’ initial simulations were inconsistent, but running them on a supercomputer with an updated climate model showed that if a barrier were built across the strait by 2050, catastrophic damage to the AMOC would be avoided.

If this dam were built, half of it would be on one side of the two islands in the middle of the Bering Strait, and half would be on the other side. The problem is that measures like this one, which can potentially alter the planet, always carry heavy uncertainties. Scientists don’t even agree on the AMOC’s future, let alone how to fix its decline. Some blame its contemporary slowdown on anthropogenic climate change, while others think that natural shifts could be playing a role, given that humans didn’t cause the previous collapse. There’s also controversy around when the AMOC will collapse—predictions range from before the turn of the next century to several centuries in the future, though little doubt exists about the AMOC continuing to weaken. Unfortunately, not enough data has been collected yet to provide a more accurate outlook.

“We expect the [dam] to have a large impact onto the regional ecosystem, and so, particularly in this regard, we do want to stress that CO₂ mitigation efforts are the preferable option to avoid an AMOC collapse,” Soon and Dijkstra said. “But if this is not realized, this study showed that […] a man-made timely [closure] can prevent a collapse of the AMOC under particular climate forcing scenarios.”

It might not happen tomorrow, but the very real threat of what could transpire in the event of a collapse should at least have us shutting off a few more lights.