The ocean currents of the Atlantic Southern Reversal Circulation (AMOC) are vital for transporting heat from the tropics to the Northern Hemisphere, but new research suggests that climate change could knock AMOC out of action much sooner than we anticipate.
That could have large-scale and profound impacts on the planet in terms of weather patterns, altering agricultural practices, biodiversity, and economic stability in the vast areas of the world that AMOC influences.
The problem is the rate at which the Earth is warming and melting ice in the Arctic: according to the researchers’ new models, this rate of increase in temperature means that the risk of reaching the tipping point for the AMOC Going idle is now an urgent concern. .
“This is worrying news,” says physicist Johannes Lohmann of the University of Copenhagen in Denmark. “Because if this is true, it reduces our safe operating space.”
Lohmann and his colleague Peter Ditlevsen adapted an existing ocean climate change model to study the consequences of a higher rate of freshwater inflow into the North Atlantic Ocean, driven by the rapid melting of the Greenland ice sheets.
The model showed that a faster rate of freshwater change could cancel the AMOC much earlier. In a rate-induced rollover scenario like this, what matters most is the speed at which change is occurring, rather than a specific threshold, and once the tipping point is reached, there is no turning back.
In other words, the speed at which we are expelling greenhouse gases and melting the ice in Greenland leaves us very little room to maneuver when it comes to protecting the weather systems that keep global weather patterns in check. The same problem could also threaten other climate subsystems around the world, the researchers say.
“These tipping points have been shown previously in climate models, where meltwater is very slowly entering the ocean,” Lohmann told Molly Taft on Gizmodo. “Greenland’s meltwater increases are actually accelerating and cannot be considered slow.”
The AMOC functions a bit like a giant looped seawater conveyor belt, redistributing water and heat throughout the Northern Hemisphere as the temperature, salinity, and relative weight of the water fluctuate. It is part of the reason why European winters are relatively mild even at higher latitudes.
While it’s unclear exactly where the AMOC’s tipping point is, it has slowed in recent years, and this new study suggests that the faster climate change becomes, the more risk these currents run. An influx of cool fresh water from Greenland is likely to prevent the warm water from spreading north, scientists believe.
Modeling climate change is incredibly complicated, with so many factors to take into account, and Lohmann and Ditlevsen themselves admit that there is more work to be done to uncover the exact details of this rate-induced tipping scenario.
However, they hope it will act as a reminder of how urgent action is in the climate crisis now: Our goals to reduce greenhouse gas emissions must be as ambitious as possible, whatever scenario eventually ends up unfolding in the future. 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, severely limiting 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 could be less than previously thought.”
The research has been published in PNAS.