44 Scientists Sign Off On Warning That Atlantic Current Shutdown Risks Have Been "Greatly Underestimated"

[hatrack]

The dangers of a collapse of the main Atlantic Ocean circulation, known as Amoc, have been “greatly underestimated” and would have devastating and irreversible impacts, according to an open letter released at the weekend by 44 experts from 15 countries. One of the signatories, Stefan Rahmstorf, an oceanographer and climatologist who heads the Earth system analysis department at the Potsdam Institute for Climate Impact Research in Germany, explains here why he has recently upgraded his risk assessment of an Amoc breakdown as a result of global heating – and what that means for Britain, Europe and the wider world.

What is Amoc?

Amoc, or the Atlantic meridional overturning circulation, is a system of ocean currents that brings heat into the northern Atlantic. Warm surface water from the tropics flows north and releases its heat in the subpolar Atlantic, south of Greenland and west of Britain and Ireland. Then it cools and sinks to a depth of between 2,000m to 3,000 metres before returning south as a cold current. Amoc is one of our planet’s largest heat transport systems, moving the equivalent of 50 times the human energy use, and it has a particularly strong impact on the climate in Europe, affects the ocean’s CO2 uptake and oxygen supply, as well as rainfall patterns in the tropics.

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What is the range of forecasts?

Until a few years ago, the general thinking in the Intergovernmental Panel on Climate Change (IPCC) was that the probability of crossing the tipping point this century was less than 10%. Since then, there have been a number of studies suggesting a collapse would probably be triggered this century, possibly in the next few decades. So my risk assessment has really changed. I am now very concerned that we may push Amoc over this tipping point in the next decades. If you ask me my gut feeling, I would say the risk that we cross the tipping point this century is about 50/50. I wouldn’t rule it out completely, because it would be very hard to tell from observations. Nothing dramatic happens at the tipping point. That just means Amoc is then doomed and it will slowly die, but that process could take 50 to 100 years. Because the Amoc is already weakening we can’t be entirely sure whether we already passed a tipping point, but I would say this is most likely not the case, so it is not too late to prevent this.

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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.

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https://www.theguardian.com/environment/2024/oct/23/we-dont-know-where-the-tipping-point-is-climate-expert-on-potential-collapse-of-atlantic-circulation

[markodochartaigh]

1. Paul Beckwith has a

couple of interesting videos on this. Here is one:

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