The high circulation of the twisted southern Atlantic circulation (AMOC) is vital in transporting heat from the tropics to the northern hemisphere, but new research suggests that climate change could take AMOC out of action much faster than we anticipated.
This could have a profound, large-scale impact on the planet in terms of weather patterns, growing agricultural practices, biodiversity and economic stability in the vast areas of the world that AMOC influences.
The problem is how fast the Earth is warming and melting ice in the Arctic: according to new models by researchers, this rate of temperature rise means that the risk of reaching the peak for AMOC to remain inactive is now an urgent concern.
(University of Copenhagen)
“This is worrying news,” says physicist Johannes Lohmann of the University of Copenhagen in Denmark. “Because if that’s true, it reduces our safe operating space.”
Lohmann and his colleague Peter Ditlevsen adapted an existing model of ocean climate change to study the consequences of an increased rate of freshwater entry into the North Atlantic Ocean due to the rapid melting of ice sheets in Greenland.
The model showed that a faster freshwater change rate could cancel AMOC much earlier. In a rate-induced tipping scenario like this, the most important thing is the rate at which the change occurs, rather than a specific threshold, and once the tipping point is reached, there is no turning back.
In other words, the speed with which we eliminate greenhouse gases and melt ice in Greenland leaves us very little room for maneuver when it comes to protecting climate systems that control global weather patterns. The same problem could threaten other climate subsystems around the world, say researchers.
“These high points were previously shown in climate models, in which meltwater is introduced very slowly into the ocean,” Lohmann told Molly Taft at Gizmodo. “In reality, the growth of molten water in Greenland is accelerating and cannot be considered slow.”
AMOC works a bit like a huge, looping, seawater conveyor belt, redistributing water and heat around the northern hemisphere as water temperature, salt and relative weight fluctuate. It is part of the reason why European winters are relatively mild even at higher latitudes.
Although it is not clear exactly where the peak of the AMOC is, it has slowed in recent years, and this new study suggests that the faster climate change becomes, the more exposed they are to these currents. An influx of cold fresh water from Greenland could stop the spread of hot water to the north, scientists believe.
Climate change modeling is incredibly complicated, with so many factors to consider, and Lohmann and Ditlevsen themselves acknowledge that there is more work to be done to find out the exact details of this rate-induced tipping scenario.
However, they hope that it will act as a reminder of how urgent action is being taken against the climate crisis: our targets for reducing greenhouse gas emissions must be as ambitious as possible, regardless of the scenario that ultimately ends. will take place in the North Atlantic. We probably have no room for error.
“Due to the chaotic dynamics of complex systems, there is no well-defined critical rate of parameter change, 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 the elements of the Earth system in terms of future emissions could be smaller than previously thought.”
The research was published in PNAS.