David Thornalley writes:

Icy winds howl across a frozen Thames, ice floes block shipping in the Mersey docks, and crops fail across the UK. Meanwhile, the US east coast has been inundated by rising seas and there’s ecological chaos in the Amazon as the wet and dry season have switched around… The world has been upended. What’s going on?

While these scenes sound like something from a Hollywood disaster movie, a new scientific study investigating a key element of Earth’s climate system – the Atlantic Meridional Overturning Circulation (AMOC) – says this could occur for real as soon as 2050.

So what is it and why is it important? Are such catastrophic events, like those mentioned above, likely to happen if it disrupted, and what – if anything – can we do about it?

Why the AMOC matters and what’s changing

The AMOC – often called ‘the great ocean conveyor’ – is a large system of ocean currents that includes the Gulf Stream. It circulates warm, salty water from the tropics northward into the North Atlantic, where
it cools and becomes denser. As this water cools, it sinks and flows back southward at deeper levels, before eventually rising back to the surface throughout the rest of the ocean, creating a continuous loop
of circulation.

It transports vast amounts of heat around the Atlantic – equivalent to boiling about a thousand billion kettles. It’s responsible for 25 per cent of the total heat flowing into the northern hemisphere by the ocean and atmosphere. This heat warms the winds that blow in off the Atlantic over Northwest Europe, contributes to the relatively mild climate these regions experience and helps to stop Arctic sea ice from spreading down beyond Norway.

But its effects are felt more globally, too. If the AMOC gets weaker and causes the northern hemisphere to cool, all the climate belts of the world – including the equatorial rainfall belt – will be shifted further south. [Continue reading…]