The current that ferries water around the Atlantic stabilises the climate for millions. Now it is getting weaker, which could bring more extreme heatwaves and floods
THE northern hemisphere is roasting. Greece is battling lethal wildfires, and even the UK’s weather has been so hot and dry that record-breaking fires have broken out in its usually damp climes. In Oman on the Arabian peninsula, thermometers registered the hottest night on record anywhere on Earth on 28 June: the temperature never fell below 42.6°C.
Climatologists have been quick to point out that extremes are to be expected in a warming world. But there may be more to it than that. The ongoing European heatwave may have been made worse by a consequence of climate change rearing its head after decades of Cassandra-like warnings. For more than a century, the oceans have been changing right under our noses, as a powerful Atlantic current has weakened. The result, it seems increasingly likely, is more extremes of both heat and cold on both sides of the Atlantic – and the prospect of even more dramatic switches to come.
The object of concern is the Atlantic ocean conveyor belt, also known as the Atlantic meridional overturning circulation or AMOC. It is part of a global network of currents that push all the water in the oceans up and down the length, breadth and depth of the various interconnected basins. From the tropical Atlantic off the coast of South America, warm surface water flows north towards Greenland and western Europe, bringing with it an uncharacteristically warm climate, carried by the Gulf Stream.
The water becomes saltier as it evaporates, and cools as it moves north. Both factors make it denser so that by the time …