Collapse of Critical Atlantic Current Is No Longer Low-Likelihood, Study Finds

An anonymous reader quotes a report from The Guardian: 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. The research found that if carbon emissions continued to rise, 70% of the model runs led to collapse, while an intermediate level of emissions resulted in collapse in 37% of the models. Even in the case of low future emissions, an Amoc shutdown happened in 25% of the models.

Scientists have warned previously that Amoc collapse must be avoided 'at all costs.' It would shift the tropical rainfall belt on which many millions of people rely to grow their food, plunge western Europe into extreme cold winters and summer droughts, and add 50cm to already rising sea levels. The new results are 'quite shocking, because I used to say that the chance of Amoc collapsing as a result of global warming was less than 10%,' said Prof Stefan Rahmstorf, at the Potsdam Institute for Climate Impact Research in Germany, who was part of the study team. 'Now even in a low-emission scenario, sticking to the Paris agreement, it looks like it may be more like 25%. 'These numbers are not very certain, but we are talking about a matter of risk assessment where even a 10% chance of an Amoc collapse would be far too high,' added Rahmstorf. 'We found that the tipping point where the shutdown becomes inevitable is probably in the next 10 to 20 years or so. That is quite a shocking finding as well and why we have to act really fast in cutting down emissions.'

'Observations in the deep [far North Atlantic] already show a downward trend over the past five to 10 years, consistent with the models' projections,' said Prof Sybren Drijfhout, at the Royal Netherlands Meteorological Institute, who was also part of the team. 'Even in some intermediate and low-emission scenarios, the Amoc slows drastically by 2100 and completely shuts off thereafter. That shows the shutdown risk is more serious than many people realize.'

The findings have been published in the journal Environmental Research Letters.

Read more of this story at Slashdot.