AMOC ...

New modelling suggests the tipping point that makes an Amoc shutdown inevitable is likely to be passed within a few decades. Photograph: Henrik Egede-Lassen/Zoomedia/PA

Years ago, I talked to a good friend who had a senior position at NOAA. A conservative Republican but keen on science and close to the researchers, he said ... "These assholes have no idea what's coming. " Why the strong language? Because he's right. The fools in this administration and business all over the world are doing business as usual and Gaia is responding. We are bad stewards of the planet and, due to the two laws of thermodynamics, there's always a cost and in our case, payment is past due.

The collapse of a critical Atlantic current can no longer be considered a low-likelihood event, a study has concluded, making deep cuts to fossil fuel emissions even more urgent to avoid the catastrophic impact.

The Atlantic meridional overturning circulation (Amoc) is a major part of the global climate system. It brings sun-warmed tropical water to Europe and the Arctic, where it cools and sinks to form a deep return current. The Amoc was already known to be at its weakest in 1,600 years as a result of the climate crisis.

Climate models recently indicated that a collapse before 2100 was unlikely but the new analysis examined models that were run for longer, to 2300 and 2500. These show the tipping point that makes an Amoc shutdown inevitable is likely to be passed within a few decades, but that the collapse itself may not happen until 50 to 100 years later.

Guardian graphic. Source: Noaa, S Rahmstorf et al from
the Potsdam Institute for Climate Impact Research (PIK)

‘We don’t know where the tipping point is’:
climate expert on potential collapse of Atlantic circulation

What would be the consequences of Amoc breakdown?

This has happened repeatedly in Earth’s history, most recently during the last ice age, when big ice masses slid into the ocean – so-called Heinrich events – adding meltwater that diluted the salinity of the north Atlantic. These are among the most massive upheavals of climate conditions in Earth’s history.

The effects include a cooling of the northern hemisphere, particularly northwestern Europe. There would also be a shift of the tropical rainfall belt to the south, which is bad because the rains will move away from the rainforests to regions that are not used to so much rainfall. So this will mean droughts in some regions and floods in others.

Amoc collapse would also have a major impact on the northern Atlantic sea level, which would rise by half a metre or so, in addition to the rise caused by global heating. It would also reduce the CO2 uptake of the ocean because Amoc sinking in the northern Atlantic takes a lot of CO2 down into the deep oceans where it is safely locked away from the atmosphere.

Amoc collapse would also change the nutrient supply and reduce the oxygen of the deep oceans. This would have a massive effect on marine biology and the entire ecosystem of the northern Atlantic.

The rate of melting in Greenland could affect the tipping rate of the
Atlantic meridional overturning circulation. Photograph: Luis Leamus/Alamy

In essence, an accelerant to the ongoing Holocene 6th Extinction.