Is the Atlantic Overturning Circulation Approaching a Tipping Point?

[LetItSnow]

To my non-scientist (but I’d like to think still smart!) brain it just confuses me as a concept. Because, yes, on one hand it makes sense the idea that if it stopped our region would become very cold with a large drop in annual temperature due to an uninterrupted feed of colder air from the Artic - but if it occurred in a couple of decades from now (or hundreds of years) when the Artic would be considerably less cold than it is today, then how could there be a 10C annual drop?  I really don’t know. I feel like the idea of that big drop in temperature is focused on what the climate is like now. But if it happened in 2125 would it 

Knowing our luck if it collapsed we’d still have marginality issues!!! 45C summers and 7C anticyclonic gloom in winter… The cracked ruins of what’s left of the M4 will still mark the boundary line. 

[Jacob]

 LetItSnow Climate change would offset the impact of 10C, and most studies don't even predict a drop that severe nor take the offset into account. Winter temperatures would still drop more than summer temperatures too

[raz.org.rain]

 Penguin16 because the studies that simulate a 10-15°c drop are highly idealised and assume a preindustrial baseline. It's also acknowledged that these models have an inherent cooling bias in their simulations, overestimate cryospheric stability and generally don't factor in atmospheric feedbacks. More recent reconstructions have suggested a much less substantial temperature drop and clarify that they don't account for atmospheric feedbacks that would further mitigate any hypothetical cooling.

[raz.org.rain]

 Jacob summer temperatures wouldn't drop, thats the thing. It's impractical in practice. Paleoclimate evidence suggests that didn't even occur during the last glacial maximum when conditions were considerably more conductive to glacial development. Bromley et al. discussed this higher seasonality response.

[Jacob]

 raz.org.rain the most recent one I know predicts a 15C February drop in London

[Jacob]

 raz.org.rain I found this very recent study which still predicts an annual drop of >6C for the entire UK, and a fraction of a degree cooling in summer, so winters could still potentially cool by >12C widely https://www.nature.com/articles/s41467-025-55888-w.pdf 

Also a less recent study predicts a much more minor drop in temperature https://arxiv.org/pdf/2407.19909 

Edited January 19 by Jacob

[raz.org.rain]

 Jacob the Lu et al. study principally discusses AMOC collapse in the context of the last glacial maximum. In their present climate simulations they use a preindustrial constraint (<280ppm). I'm also unsure of why their paleoclimate simulation suggests a summer cooling response when proxy data says the opposite, but I guess that's an example of the linear assumptions and cooling biases noted in simulation models.

[Jacob]

 

48 minutes ago, raz.org.rain said:

cooling biases noted in simulation models

Can you send any links to evidence of the cooling bias?

[raz.org.rain]

 Jacob there are a few papers that discuss model simulation biases such as Bellomo et al.'s publication that mentions an overestimation of hypothetical sea ice feedbacks which are unrealistic in practice, hence the simulated results aren't fully representative of potential climatic responses. I could've sworn there's a paper that discusses CMIP bias issues but can't find it now. There's definitely a few papers that discuss the absense of atmospheric feedbacks in model simulations, it's been noted that this often results in unrealistic cooling feedbacks in simulations. 

[Jacob]

One study suggests a cooling of 14-16C in the UK following an AMOC collapse in the Younger Dryas without considering the cooling bias of models (f rom my knowledge) into account. I doubt the impacts would be the same this time considering climate change and the fac tthat we're not covered by ice caps https://www.nature.com/articles/s41598-024-53591-2.pdf

Edited January 20 by Jacob

[BLAST FROM THE PAST]

On the impacts of the amount of cooling that would occur if it shutdown…..I cannot see a reason why it wouldn’t be as high as modelled.  One must ask, look at the arctic outbreak currently across the pond….if the arctic has already warmed so much how can a warm arctic still produce cold plunges that match or beat previous cold plunges from a colder arctic?

 

BFTP

[cheeky_monkey]

i dont know what all the panic is about ..even if the UK winter temps did drop by lets say 5c it would be no colder than say nova scotia in the winter time and still way warmer than i am..i have no issues living in a cold climate neither do hundreds of millions of people in Scandinavia North America etc..its not like we get blizzards/snow and its -40c everyday ..most of the time it is dry sunny and pretty benign 

[Jacob]

This new study predicts an AMOC tipping point with a similar amount of freshwater forcing (around 0.54?) as the study which predicted a 95% chance of a tipping point between 2025 and 2095 https://egusphere.copernicus.org/preprints/2025/egusphere-2025-14/egusphere-2025-14.pdf but the tipping point is also slower

Another suggests that there would be a tipping point at 3C warming https://arxiv.org/pdf/2407.19909 at 0.53Sv

Edited January 23 by Jacob

[Jacob]

This study suggests that our summers won't be any warmer from an AMOC collapse, and heatwaves would only be more severe in East Europe: https://iopscience.iop.org/article/10.1088/1748-9326/ada3e7/pdf

[Jacob]

This study predicts a tipping point at 0.36Sv of freshwater forcing, which is far lower than other studies https://arxiv.org/html/2410.16277v2

[raz.org.rain]

 Jacob their conclusions seem to contradict a lot of observations declared in other studies, although they do briefly mention a lack of consistency among ensembles. They don't seem to clarify control presets but I'd imagine a preindustrial constraint. And as Vautard et al. and Kornhuber et al. both clarify, simulation models consistently underestimate atmospheric dynamic feedbacks in Western Europe and subsequent heat extremes. It's a good example of how relying entirely on model outputs often isn't ideal, we need to investigate where they're known to fall short, but there's rarely incentive to do that.

[Jacob]

This study predicts that after the tipping point, there would be an extremely quick decline instantly over 30 years before this decline slows, making it much harder to adapt tohttps://www.nature.com/articles/s41598-023-43143-5.pdf

[Cambrian]

A bit more mainstream coverage here :

Could the UK actually get colder with global warming?

WWW.BBC.CO.UK

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Some scientists fear the risk of a collapse to warm Atlantic currents has not been taken seriously.

Discussion of potential AMOC collapse and the cold blob and possible effects on the UK and Europe. Some great explanations and graphics.

I cannot recall such credence being offered before by anyone at the BBC Weather and Climate teams.

[Jacob]

The AMOC is having some much larger temp contrasts than normal. 12C difference over a very small section of the ocean, this can be a sign of the AMOC slowing down or being about to collapse

[Jacob]

What do people think about the modelled climate impacts on this? I'm aware that this study is old news but not that many people seem to mention the climate impacts om this study compared to others

https://www.science.org/doi/10.1126/sciadv.adk1189

I know that this is caused by it incorporating  sea ice albedo feedbacks

Edited April 26 by Jacob

[Jacob]

While the seas around the UK temporally bask in warm SST anomalies, the Gulf Stream is being overcome with ludicrous cold anomalies. Maybe the AMOC tipping point is imminent?

[Thunderboom]

How bad would it be for us will we see major snowstorms like the us?

Edited May 23 by Thunderboom

[Cheshire Freeze]

 Jacob hopefully soon enough the jet stream pulls south during winter. That would set us up with some interesting weather.

[raz.org.rain]

 Thunderboom it's more likely that Atlantic windstorms would intensify. This was suggested as a potential net warming feedback in some of the older research as it would hypothetically introduce warmer air masses. 

 Cheshire Freeze some recent reanalysis suggests that we could actually see a northward expansion of Hadley cells when accounting for anthropogenic warming, I guess it's a case of be careful what you wish for 

[Thunderboom]

So stormy winters then but will our storms be more powerful than now