The regular ‘Atlantic Circulation Collapse’ story

Risking making AMOCkery of climate science with unrealistic scenarios in global models is nothing new, but this one keeps coming back like a bad penny, as NZW explains. Returning to the same faulty predictions time and again gets the headlines but is easily debunked. In this case, the researchers intend to re-run their model with ‘global warming included’, but if everything else is the same, including ‘adding unrealistically large quantities of fresh water all at once’, many of the criticisms will still apply.
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One of the many regular climate scare stories you can rely on is the one about failing currents in the Atlantic Ocean bringing cold climate chaos to Europe, says Net Zero Watch.

It’s one of the most favourite doomsday speculations, based on computer models pushed to the edge – but who cares, it’s a good shock-horror story and it pops up regularly.

Actually we should care because it’s well known that most people only register the top line of any news story — especially a climate disaster prediction – while they don’t take-in or even read up on the context and the qualifications.

That’s when the headline becomes accepted as fact and takes its place as an undisputed example of the looming climate catastrophe.
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If some of the headlines in recent days are to be believed we are headed for a global climate disaster because of a slowdown in the circulation of the northern Atlantic Ocean predicted by computer models. But are we? No.

I suspect that people are thinking about the wrong thing here. This is not about the North Atlantic Drift – the current that brings warm water to Northern Europe from the Gulf of Mexico. That is a consequence of the Earth’s rotation and the distribution of the continents and it’s not going to change as long as the Earth keeps turning. This story is about another [topic].

Michael Le Page in New Scientist says that the Atlantic current shutdown is a real danger, but then backtracks qualifying what he means by “real danger,” when he adds:

The most detailed computer model run so far shows that melting ice sheets could cause the collapse of the major ocean current that warms Europe, but it’s still unclear how likely this is to happen.”
. . .
It is the case that it has declined 15% since 1950 and is possibly in its “weakest” state in more than a millennium, but no one really knows whether this is significant. Some studies have suggested the tipping point could happen between next year and 2095. However, the UK Met Office said large, rapid changes in AMOC were “very unlikely” in the 21st century.
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But, as I have said, when you look a little closer into this research and the media coverage, the dramatic headlines start to dissolve. New Scientist goes on to say that the modelling has proved tricky and the prediction of a shutdown involves adding unrealistically large quantities of fresh water all at once. Also in some recent simulations no shutdown took place suggesting that there is no potential tipping point at all.

New Dutch computer simulations added fresh water gradually, that eventually shut down the overturning circulation, causing temperatures to rise in the southern hemisphere, but plummet in Europe. The researchers say that some of the changes seen in the model ahead of the collapse correspond with changes being seen in the real Atlantic in recent decades.

But then the story flip-flops again. The freshwater added is about 80 times more than is currently entering the ocean as Greenland’s ice sheet melts. “So that is absurd and not very realistic,” van Westen now says! So perhaps the headlines describing this research should have included the words ‘absurd’ and ‘not very realistic’?

In addition the simulation didn’t involve any global warming. The team will now rerun the simulation to include it.

Full article here.