Large ocean current could be on the brink of a devastating ‘tipping point’

Atlantic Meridional Overturning Circulation (AMOC) ocean currents are essential in transporting heat from the tropics to the northern hemisphere, but new research suggests climate change could shut down AMOC much sooner than expected.

This could have profound and large-scale impacts on the planet in terms of weather patterns, disruption of agricultural practices, biodiversity and economic stability in the vast regions of the world that AMOC influences.

The problem is the rate at which the Earth is heating up and melting ice in the Arctic: according to the researchers’ new models, this rate of temperature rise means that the risk of reaching the tipping point of the Dormant AMOC is now a pressing concern. .

(University of Copenhagen)

“This is worrying news,” says physicist Johannes Lohmann of the University of Copenhagen in Denmark. “Because if this is true, it reduces our secure workspace.”

Lohmann and his colleague Peter Ditlevsen adapted an existing oceanic climate change model to study the consequences of an increase in the rate of freshwater inflow to the North Atlantic Ocean, due to the rapid melting of the Greenland ice caps.

The model showed that a faster rate of freshwater change could cancel AMOC much sooner. In a rate-induced tipping scenario like this, it is the speed at which the change occurs, rather than a specific threshold, that is most important – and once that tipping point is reached, it is not. there is no going back.

In other words, the rate at which we are expelling greenhouse gases and melting ice in Greenland leaves us with very little leeway to protect the climate systems that control global weather conditions. The same problem could also threaten other climate subsystems around the world, the researchers say.

“These tipping points have already been shown in climate models, where meltwater is introduced very slowly into the ocean,” Lohmann told Molly Taft at Gizmodo. “In reality, increases in Greenland’s meltwater are accelerating and cannot be considered slow.”

AMOC works much like a giant looping seawater conveyor belt, redistributing water and heat around the northern hemisphere as temperature, salinity, and the relative weight of the water fluctuate. This is part of the reason why European winters are relatively mild, even in higher latitudes.

While it’s unclear exactly where AMOC’s tipping point is, it has slowed in recent years, and this new study suggests that the faster the climate change, the more at risk these currents are. An influx of cold freshwater from Greenland is likely to prevent warm water from spilling north, scientists believe.

Modeling climate change is incredibly complicated, with so many factors to consider, and Lohmann and Ditlevsen themselves admit that there is still work to be done to determine the exact details of this rate-induced switch scenario.

However, they hope this will serve as a reminder of just how urgent action against the climate crisis is now: our targets for reducing greenhouse gas emissions must be as ambitious as possible, whatever scenario ends up unfolding. in the North Atlantic. We probably no longer have a margin of error.

“Due to the chaotic dynamics of complex systems, there is no well-defined critical rate of change in parameter, which severely limits the predictability of long-term qualitative behavior,” the researchers write in their paper.

“The results show that the safe operating space of elements of the Earth system with respect to future emissions may be smaller than previously thought.”

The research was published in PNAS.