A new study has found that global warming has caused an “almost complete loss of stability” in the network of currents that weave their way through the North Atlantic Ocean, a series of currents that, if they were to collapse entirely, would result in a domino effect of systemic climate disasters around the world.
This study, conducted at the Potsdam Institute for Climate Impact Research in Germany, has charted key indicators that reflect the health of what is called the Atlantic meridional overturning circulation (AMOC), including more than a century of water temperature and salinity records, and found that the stability of the AMOC is rapidly approaching a tipping point that might see the currents shutting down entirely.
“The signs of destabilization being visible already is something that I wouldn’t have expected and that I find scary,” explains study author Niklas Boers. “It’s something you just can’t [allow to] happen.”
The AMOC is a network of currents that zig-zag northward from the west coast of Africa across to the Caribbean, and then tracking northeast towards northern Europe. Under normal circumstances, the warm water from this southern stream cools when it meets the currents flowing south from the Arctic; this cooling causes the water to sink into the depths where it joins another current that runs south, deep under the Atlantic, to continue its journey through the world’s oceans.
However, the accelerated melt of glaciers in Greenland has caused a large amount of fresh water to flood into the ocean where this downward convection takes place, and this fresh water, being less dense than salt water, inhibits the sinking of the current’s waters, slowing the flow of the entire system.
If the AMOC grinds to a halt entirely, this creates a bottleneck in the overall system of water circulating through the world’s oceans, with far-reaching consequences: sea-level rise would accelerate along the east coast of North America; rain patterns in India, South America and West Africa would be disrupted, potentially starving the crops that billions rely on for nourishment; Europe would see an intensification in storm activity, along with a dramatic drop in temperature; and despite being at the opposite end of the Earth, the ice sheets of Antarctica would be put under increased strain from warming ocean waters.
This desalination effect on the AMOC was last seen close to the end of the last ice age: as the world began to warm back up, a massive glacial lake that covered much of what are the modern-day Canadian provinces of Manitoba and Ontario abruptly emptied into the North Atlantic. The sudden flood of fresh water shut down the AMOC, disrupting the flow of warm water to northern Europe and plunging the planet back into a mini ice age that lasted for 1,200 years known as the Younger Dryas.
Due to the complex factors that govern the health of the AMOC, Boers is unable to provide a forecast of exactly how close the AMOC is to failing this time around, although he is able to offer that “the critical threshold is most likely much closer than we would have expected.”
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