- In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point.
- The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction.
- We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.
The ocean’s conveyor belt
Ocean currents are driven by winds, tides and water density differences. In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic.
- The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a conveyor belt.
- A weaker conveyor belt transports less heat northward and also enables less heavy water to reach Greenland, which further weakens the conveyor belt’s strength.
What happens to the climate at the tipping point?
- Today’s more detailed climate models indicate a continued slowing of the conveyor belt’s strength under climate change.
- We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water.
The result: Dangerous cold in the North
- This cools the North American and European continents by a few degrees.
- The European climate is much more influenced by the Gulf Stream than other regions.
- We found that parts of Norway would experience temperature drops of more than 36 F (20 C).
- That might seem like a long time, but on typical climate time scales, it is abrupt.
- The conveyor belt shutting down would also affect sea level and precipitation patterns, which can push other ecosystems closer to their tipping points.
So, when will we see this tipping point?
- The big question – when will the Atlantic circulation reach a tipping point – remains unanswered.
- Once a threshold is reached, the tipping point is likely to follow in one to four decades.
The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the climate shifts are unstoppable on human time scales. It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.
- René van Westen receives funding from the European Research Council (ERC-AdG project 101055096, TAOC).
- Henk A. Dijkstra receives funding from the European Research Council (ERC-AdG project 101055096, TAOC, PI: Dijkstra).
