For generations, the mild and temperate climate of north-western Europe has been credited to one legendary force: the Gulf Stream. This idea is so deeply entrenched in our cultural identity that in James Joyce’s Ulysses, the protagonist Stephen Dedalus refuses to take a bath, arguing that “all Ireland is washed by the Gulf Stream”.

However, the Gulf Stream is just one part of a much more complex system called the Atlantic Meridional Overturning Circulation or AMOC.

To explain this better, scientists often use the image of a giant ocean conveyor belt, where warm waters move northwards across the surface of the Atlantic from the tropics. As these waters reach the North Atlantic, they release their heat into the atmosphere, much like a radiator. The AMOC also carries the moisture that gives us our temperate landscape. After the waters have released their heat, they become colder and denser, which makes them sink into the deep ocean. These waters then return southward, at great depths.

When scientists talk about the AMOC “slowing down” or “changing,” they are essentially describing a reduction in the strength of our natural radiator. Specifically, they measure how much water is moving north and south at different depths across the Atlantic. This allows them to estimate how much heat is being carried from the tropics toward the North Atlantic and back again at depth.

More than a conveyor belt

Although this “conveyor belt” analogy is a helpful starting point,........

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