The Atlantic Meridional Overturning Circulation (AMOC) ocean currents are vital in transporting heat from the tropics to the Northern Hemisphere, but new research suggests that climate change could put the AMOC out of action much sooner than we expected.
That could have profound, large-scale impacts on the planet in terms of weather patterns, disruptive agricultural practices, biodiversity and economic stability in the vast parts of the world that the AMOC affects.
The problem is the rate at which the Earth is warming and the ice in the Arctic is melting: According to the researchers’ new models, this rate of temperature rise means that the risk of hitting the tipping point for the AMOC going dormant is now an urgent concern. .
(University of Copenhagen)
“It’s alarming news,” says physicist Johannes Lohmann of the University of Copenhagen in Denmark. “Because if this is true, it diminishes our safe workspace.”
Lohmann and his colleague Peter Ditlevsen have adapted an existing climate change model in the oceans to study the consequences of an increased supply of freshwater in the North Atlantic Ocean, driven by the rapid melting of Greenland’s ice sheets.
The model showed that a faster freshwater change could cancel the AMOC much sooner. In a rate-induced roll-over scenario like this, the speed at which the change occurs, rather than a specific threshold, is what matters most – and once the tipping point is reached, there’s no turning back.
In other words, the speed at which we are expelling greenhouse gases and melting ice in Greenland leaves us little room for maneuver when it comes to protecting the climate systems that control global weather patterns. The same problem could also threaten other climate subsystems around the world, the researchers say.
“These tipping points have previously been shown in climate models, where meltwater is diverted very slowly into the ocean,” Lohmann told Molly Taft of Gizmodo. “In reality, the increase in melt water from Greenland is accelerating and cannot be considered slow.”
The AMOC works somewhat like a giant, loop-shaped seawater conveyor, redistributing water and heat around the Northern Hemisphere while the temperature, salinity and relative weight of the water fluctuate. It’s part of the reason that European winters are relatively mild, even in higher latitudes.
While it’s not clear exactly where the AMOC’s tipping point is, it’s been slowing down in recent years, and this new study suggests that the faster climate change gets, the greater the risk of these currents. An influx of cold fresh water from Greenland will likely prevent warm water from spreading north, scientists think.
Modeling climate change is incredibly complicated, with so many factors to consider, and Lohmann and Ditlevsen themselves admit that there is even more work to be done to find out the exact details of this rate-induced tipping scenario.
However, they hope it is a reminder of how urgent action is now on the climate crisis: our goals to reduce greenhouse gas emissions should be as ambitious as possible, regardless of the scenario that ultimately unfolds in the North Atlantic. We probably don’t have room for error anymore.
“Due to the chaotic dynamics of complex systems, there is no well-defined critical rate of parameter change, which severely limits the predictability of the qualitative long-term behavior,” the researchers write in their paper.
“The results show that the safe working space of elements of the Earth system with regard to future emissions may be smaller than previously thought.”
The research is published in PNAS