The Atlantic current is something of a poster child for possible climate “tipping points”, beyond which systems that have been responding gradually and incrementally to global warming could undergo sudden and dramatic change
. The Atlantic Meridional Overturning Circulation is a stream of water which, as it flows from the southern to the northern part of the Atlantic, grows cooler and saltier. Eventually it sinks to the ocean floor, 3km down, and flows back across the abyssal plain. Mounting evidence suggests that theAMOC
Another reason is that its tipping-point nature is not open to question. Theory, modelling and reconstructions of prehistoric climate all support the idea thatis “bistable”. Rather than just gradually getting stronger or weaker, it can go suddenly from “on” to “off” if pushed too far, and does so in a way that makes it very hard to flip it back on again. It was one of the first such instabilities clearly demonstrated in the climate system.
That would have dire effects. Northern Europe would get both colder—bringing worse winters, more powerful storms inland and shorter growing seasons—and drier, making summers more prone to drought. The impact on agriculture would be far greater than that caused by warming alone, hitting poorer countries hardest.
The stick in question is a freshening of the water in the North Atlantic caused by increased rainfall and melting ice, both expected results of warming caused by greenhouse gases. The climate models used by the Intergovernmental Panel on Climate Change show this leading to a weakening of the circulation over this century, an outcome the panel sees as “very likely” . But they do not show it weakening enough to cross the tipping point and shut itself down.
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