Among many potential planetary “tipping points” — sudden and irreversible changes threatened by global warming — one of the more alarming is the possible collapse of the ocean circulation that sustains the Gulf Stream and, therefore, the mild climate of western Europe.
The Atlantic Meridional Overturning Circulation (Amoc) is like an immense marine conveyor that carries warm equatorial water northwards in the ocean’s upper layers while cooler water flows southward at greater depths. The heat transfer is equivalent to 10 Hiroshima-sized atomic bombs exploding every second, says Andrew Meijers, deputy science leader of the British Antarctic Survey’s polar oceans team.
Climate models have long predicted that Amoc will weaken as the world warms — and observations confirm that this is happening. Direct evidence has only been available since 2004. Then, a UK-US project called Rapid started continuous monitoring with an array of instruments across the Atlantic from Morocco to Florida, which measured temperature, salinity and current velocities from the surface to the sea floor.