Yes - and the oceans rapidly expand and stratify. We will generate more emissions from trying to produce fuel and shelter for displaced hundreds of millions or perhaps billions of people.
AMOC shut down stops the oceanic transfer of heat from the tropics to the poles (about 50% of the energy) that will have to be transferred by the atmosphere, the tropical atmosphere becomes extremely hot and wet - and that hot wet atmosphere then moves heat to the poles.
So for the higher latitudes,more extreme weather? More rain, more snow, more wind? Does the temperature still go down overall in the higher latitudes or does it go up?
I don’t know - I don’t think anyone does. We can draw broad conclusions, the Earth transfers heat and nutrients and dissolved gases using the overturning currents. That stops we know the atmosphere is wetter and there are going to be larger temp differences. Exact impacts? Not sure our current weather models will be able to predict the outcome with anything but terrible accuracy.
It's important to note that the regional cooling hypothesis is largely based on Younger Dryas proxy analogs, and the paleoclimatic regime isn't comparable to Anthropocene conditions. The YD initiated with significant glacial volume in the Northern Hemisphere; the Laurentide and Fennoscandinavian ice shelves. A weakening and collapse of the AMOC under these conditions demonstrates a drastic cooling response in sediment samples. It was the melt rate of the Laurentide that has been suggested as a factor for the freshwater influx that triggered a collapse when Lake Agassiz burst its banks and emptied entirely.
Based on current geophysical and meteorological conditions I'd estimate that the North Atlantic's maritime climates would transition into something much more continental; from a humid temperate Cfa Köppen classification, to a Dfa hot summer continental classification. Quite frankly, the publications that suggest a drastic temperature drop are absurd in their conclusions and base that finding purely on what their computer model suggests. It's effectively a secondary commentary as these models are designed to estimate the response of the AMOC to freshwater hosing, they're not really designed to provide a practical reconstruction of the meteorological response. A drop of ~10°c in London isn't happening, it's just not physically possible under the dynamics.
Totally agree. Even locally in northern EU the continued rise in CO2 would overwhelm the drop in heat transport within a decade or two. Meanwhile the rest of the globe continues with accelerated warming and transport north of even more heat energy in the atmosphere as the latent heat of condensation accelerates and drives heat energy northward in upper troposphere.
Potentially yes but it really depends on the model you look at as there are a range of outcomes but a good number of them would have northern Europe colder than preindustrial averages.
I’m aware Northern Europe would be significantly colder than the pre-industrial to the point where agriculture effectively stops. I’m wondering how significant the northern hemisphere average temperature reduction would be compared to say a 2.5C or 3C rise since the industrial revolution
Hard to predict exactly. It would depend on where exactly you’re talking about and when the Amoc collapses and how long after you’re measuring the effects as they likely will take a few decades to set in. But over time, I believe, based on what I’ve read and heard on the topic that full Amoc collapse could decrease North American temperatures, especially in Canada by 2-3 C, maybe more in some places like Northern Quebec. While Europe could see 2-3 C cooling in the south, places like Spain, Italy. And 5-10 C further North, like the UK, Germany & Norway etc. Everyone on here probably wouldn’t agree, but I strongly believe cooling of 5-10 C would be way worse than warming of 2-3 C elsewhere on earth
In 2022, a major review of tipping points had concluded that AMOC collapse would lower global temperatures by around 0.5 °C (0.90 °F), while regional temperatures in Europe would go down by between 4 °C (7.2 °F) and 10 °C (18 °F).[13][72]
In 2020, a study had assessed the impact of an AMOC collapse on farming and food production in Great Britain.[122] It found an average temperature drop of 3.4 °C (6.1 °F) (after the impact of warming was subtracted from collapse-induced cooling.) Moreover, AMOC collapse would lower rainfall during the growing season by around <123mm, which would in turn reduce the land area suitable for arable farming from the 32% to 7%. The net value of British farming would decline by around £346 million per year, or over 10%.[14]
In 2024, one modelling study suggested even more severe cooling in Europe - between 10 °C (18 °F) and 30 °C (54 °F) within a century for land and up to 18 °F (10 °C) on sea. This would result in sea ice reaching into the territorial waters of the British Isles and Denmark during winter
Stefan Rahmstorf from the Postdam Institute is a good source of info about this topic. At no point does he suggest that an AMOC collapse could be some kind of solution to global warming.
https://tos.org/oceanography/article/is-the-atlantic-overturning-circulation-approaching-a-tipping-point "A full shutdown of the AMOC would have truly devastating consequences for humanity and many marine and land ecosystems. Figure 15 shows the model of Liu et al. (2017) after a doubling of CO2, with an AMOC collapse caused by this CO2 increase. The cold air temperatures then expand to cover Iceland, Britain, and Scandinavia. The temperature contrast between northern and southern Europe increases by a massive 4°C, likely with major impact on weather, such as unprecedented storms."
It shows the northern hemisphere being cooler, but by how much relative to what? This is not some helpful global cooling, and the impacts are catastrophic.
"one modelling study"
One model is insufficient for science or policy and should never be cited in isolation, it's useless. Science is about repeatable findings and understanding probabilities and error margins.
What's the mechanism for this cooling? The AMOC is redistributing thermal energy from equatorial ocean surfaces to the poles and deep ocean... it makes sense that shutting this down would cool northern latitudes but how could the resultant build up in thermal energy in equatorial ocean surfaces have a cooling effect on equatorial regions?
This is true. I believe there are theories that suggest that the absence of thermohaline circulation would be supplemented by atmospheric circulation, as a more clearly defined and larger equator to pole temperature gradient induces the dynamics required for natural heat circulation.
In plain English: excess heat still gets circulated, but by other circulations.
Just eyeballing the energy that has to be moved with the atmosphere's low thermoconductivity and energy density, it seems like atmospheric convection would have to flow at a fairly serious pace to establish equilibrium. But, I suppose a lot could get moved about stored as latent heat in evaporated water.
There's also a weird wrinkle in that the AMOC stopping could lead to a larger polar freeze/thaw cycle that could start the AMOC back up again, possibly even stronger than it is, so could we see wild stuttering like centennial ice ages or something?!
I'm not overly convinced by the cooling theories. The more you read about the rationale behind it, the less viable it sounds. The analogs they employ to suggest widespread cooling are questionable at best. The Younger Dryas is a commonly cited analog, but they neglect to account for the fact the YD began with a significant portion of the Northern Hemisphere already dominated by ice shelves. North America had the Laurentide, which buried the entirety of eastern Canada, whereas Scandinavia had the Fennoscandinavian that dominated Northern Europe. The ocean between Norway and Greenland was entirely frozen. So when you account for these factors, it makes sense why the computing models usually suggest a drastic cooling trend based on sediment proxy data. Of course there would have been drastic cooling if most of the upper latitudes were already experiencing near glacial conditions. To add to that, the originator of the regional cooling in response to ocean circulation collapse during the YD eventually grew critical of this theory. There's some suggestion that these glaciers exist due to such a strong current existing in the Atlantic in the first place. With the opening of the Drake Passage, a strong circulation formed in the North Atlantic and introduced a larger volume of precipitation. So there's an ironic situation where the thermohaline circulation provided the conditions needed for glacial growth but also act as a buffer against further encroachment. As a demonstration of this hypothesis; during the last glacial maximum, it's estimated that Sakhalin maintained a temperate climate while comparable latitudes in Europe were either frozen or tundra grassland. Reconstructions suggest that North America and Europe saw the greatest extent of glacial encroachment whilst other regions saw significantly less encroachment. If you look up "last glacial maximum maps" you can see how Europe and North America were so disproportionately frozen.
Another commonly cited analog is the so-called Little Ice Age, which is a terrible analog as there's no strong case to suggest it was a consequence of AMOC changes. Granted, the LIA saw bitterly cold winters and scorching hot summers, which suggests it could have been attributed to AMOC decline/collapse, but the coldest winters observed in Europe during the LIA correlate with significant volcanic activity and ash sediments found in ice core samples. The Little Ice Age wasn't unrelentingly cold either, there are still some record warm CET annual averages from that period that haven't yet been beaten, and the infamous Great Fire of London occurred in 1666 after a long period of drought and persistent heat.
And as a purely unscientific analysis, reconstructions suggest that Northern Hemisphere permanent ice formation has been gradually shrinking with each interglacial to glacial cycle. That is, to say, the extent of year round ice under interglacial conditions has shrunk with each successive glacial maximum progressing into interglacial conditions. The volume of interglacial permanent ice formation is comparatively lower than during preceding interglacials.
I see what you mean, the "last glacial maximum" maps have a dramatic imbalance in glacial distribution. It does seem tempting to attribute it to variation in AMOC behavior because that region of the North Atlantic (NA) involves the coupling of a few different complicated effects that could force relatively large temperature differentials via feedback. It seems very difficult to precisely parametrize the thermal vs saline forces alone, and that local region of deep-diving water in the NA would be a point where huge volatility could emerge. The vertical flow of currents is probably difficult to model.
When you say "the opening of the Drake passage" are you referring to this as a distant but highly influential event that generated the AMOC as we know it now?
When I was looking into the Pliocene there was still healthy debate about whether the Isthmus of Panama had closed with an error-margin of 10 million years or so, and I even saw it suggested somewhere that the ocean was dominated by a circum-equatorial current during the Pliocene, but I couldn't find much to support that claim. The Drake passage seems to have more uncertainty.
Is the AMOC state in paleoclimatology inferred by a process of exclusion, because it may be difficult to detect physical evidence of its behavior? In medicine there are some annoying disorders that can't be diagnosed via biomarkers in any way, so differential diagnosis is accomplished via an iterative process of increasingly invasive pathology testing until every thing that could be diagnosed by operational criteria has been excluded. When you're left with the only possibility being the illness that can't be diagnosed by fitting the symptoms to a set of operational criteria that satisfy a threshold for diagnosis, you can be tentatively assurred you've landed upon the correct illness. These are sometimes called a 'wastebasket diagnosis'.
The AMOC appears to be a canonical motif in climate models, if you remove it most (or even all) models would probably collapse. A neuroscientist would probably call it a 'canonical circuit' in climate models. This leads to an unsettling thought that climate models rely on a critical assumption in the stable behavior of the AMOC, but its state at any moment in history is inferred via the same process a doctor uses to establish a wastebasket diagnosis :/
The only reason I can think for an AMOC halt cooling the planet average is because thermal radiation to space goes as absolute temperature to the 4th power, so if you split a surface into half hotter and half colder, the thermal radiation would increase since not a linear average. Meaning, the planet would reject more heat to Space.
Simple arithmetic example:
avg of equal ground temperatures: (1\^4 +1\^4)/2 = 1
avg of colder and hotter equal-split temperatures: (0.5\^4 + 1.5\^4)/2 = 2.56
Water vapor is a much stronger greenhouse gas than CO2, so more would warm the planet. But, when it forms water droplets (clouds), they reflect sunlight. Cloud interaction in the radiant exchange is complicated, and varies depending on altitude. In the Stratosphere, they form ice crystals which act differently than liquid droplets.
I think given the context and claim being made it would benefit ALL OF US to have the purporter of the claim back their claim up. If you can't see that then I am sad for you.
That requesting citations is appropriate for this forum. It's not some esoteric practice that's only useful to professors. If you make a claim, you should be able to verify where it came from... unless you made it up (which is fine, as long as you acknowledge it).
It should be noted that the publications that suggest a drop in average temperatures are; (a) generally not accounting for the atmospheric dynamic response, which I'll explain below, and (b) it's an average annual drop. Europe's zonal temperature anomaly relative to its latitude is more positively pronounced during meteorological winter. During the summer months, this same anomaly has a cooling tendency.
Expanding on (a), there's a lot of more recent research that suggests that an AMOC collapse results in an aggressive continentalisation of maritime Europe's climate. Winters get colder, but summers get hotter. Both seasons observe a drastic drop in precipitation. The most recent publication by Oltmanns, Holliday et al. even demonstrates that a cooler freshwater anomaly in the North Atlantic results in hotter and drier summers for the northern half of Europe. It's generally well known that a sluggish and even absent current would result in more extreme weather in Europe, which would include more persistent hot weather.
It's also generally observed that the computing methodology has issues. The Royal Society has discussed this issue somewhat extensively. For example, they generally do a poor job of accounting for the warming tendency of GHGs under a collapse scenario. Drijfhout attempted to resolve this and concluded that the effects of anthropogenic warming would be reversed for 15-20 years before a warming trend continues. The issue is that the climatology models are limited in how they can reproduce non-linear elements.
But if the AMOC collapses, it's not cooling that we should worry about. Such a drastic change in ocean circulation would almost certainly destabilise methane hydrate reserves. When that happens, we're pretty much heading for a hothouse state. Methane is an incredibly potent greenhouse gas and has been implicated in historic runaway warming events, and it has been demonstrated that it would only take minimal disturbance of the AMOC to see a catastrophic destabilisation event.
I can add citations for anyone who's interested, Reddit app is really glitchy and it's already crashed today and lost me an entire post.
--**Atmospheric feedback discussions:**
* [Decelerating Atlantic meridional overturning circulation main cause of future west European summer atmospheric circulation changes](https://iopscience.iop.org/article/10.1088/1748-9326/10/9/094007) (Haarsma, Selten, Drijfhout. 2015)
* [Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context](https://www.nature.com/articles/s41467-017-02699-3) (Trouet, Babst, Meko. 2018)
* [What is the North Atlantic Oscillation (NAO)?](https://www.worldclimateservice.com/2021/08/26/north-atlantic-oscillation/) from the World Climate Service briefly describes the northern hemisphere summer cooling tendency (JJA negative temperature anomaly relative to latitude) observed in maritime Europe due to westerlies induced by North Atlantic circulation.
--**Colder winters, hotter summers:**
* [European summer weather linked to North Atlantic freshwater anomalies in preceding years](https://wcd.copernicus.org/articles/5/109/2024/) (Oltmanns, Holliday et al. 2024)
* [Long-term drought intensification over Europe driven by the weakening trend of the Atlantic Meridional Overturning Circulation](https://www.sciencedirect.com/science/article/pii/S2214581822001896) (Ionita, Nagavciuc et al. 2022)
* [Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2018PA003341) (Bromley, Putnam et al. 2018)
* [Warm summers during the Younger Dryas cold reversal](https://www.nature.com/articles/s41467-018-04071-5) (Schenk, Väliranta et al. 2018)
-- **Computer model reconstruction issues:**
* [Challenges simulating the AMOC in climate models](https://royalsocietypublishing.org/doi/10.1098/rsta.2022.0187) (Jackson, Hewitt et al. 2023)
* [Can we trust projections of AMOC weakening based on climate models that cannot reproduce the past?](https://royalsocietypublishing.org/doi/full/10.1098/rsta.2022.0193) (McCarthy & Caeser. 2023)
* [Competition between global warming and an abrupt collapse of the AMOC in Earth’s energy imbalance](https://www.nature.com/articles/srep14877) (Drijfhout. 2015)
--**Methane and ice age termination theorem:**
* [Evidence for massive methane hydrate destabilization during the penultimate interglacial warming](https://www.pnas.org/doi/full/10.1073/pnas.2201871119) (Weldeab, Schneider et al. 2022) specifies the correlation between AMOC stability and methane hydrate destabilisation.
* [Atmospheric Methane: Comparison Between Methane's Record in 2006–2022 and During Glacial Terminations](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GB007875) (Nisbet, Manning et al. 2023)
---
I've linked the academic releases but there are numerous outlets that discuss their findings in a more concise way if you want something more brief.
Thanks for this. The AMOC literature is so vast it’s hard to know where to start. McCarthy & Caesar 2023 discussion about why models and observations and SST-based proxies don’t always match is something I’ve been wondering about.
I also have this problem there is a ton of reading to do on it and there seems to be a range of different outcomes predicted by different models/studies
If the AMOC shuts down the oceans stratify and become anoxic, killing life below a few 100m, we go to an equitable climate, with with vast flooding and massive storms, all the ice on the planet rapidly melts and yeah. AMOC shutdown is endgame, not a handy little warming hiatus. It means we are full on in the transition to hot house conditions.
Yep, if AMOC gets to the point where it actually ceases, things have by definition spiralled beyond our control in any meaningful way. It implies a full state change of our planetary climate, being that it's such a central pillar of our current climate.
The intricate fragility of oceanic dynamics are frighteningly underestimated in my experience. There's definitely a degree of linear assumption in how the ocean and atmosphere respond to concurrent changes in either system.
Anoxia would be a huge concern if we see a breakdown of thermohaline circulation, and to a degree we can already observe some of the precursors.
You're right in thinking that a collapse would be a prelude to a hothouse state. It has been demonstrated that even a minimal disruption in oceanic circulation would be sufficient enough to destabilise methane hydrate reserves, which would almost certainly result in an ice age termination event. Atmospheric methane concentrations is the more underestimated danger we're facing right now as it has been estimated that current levels are sufficient enough to confirm an ice age termination is already occurring, and that's before we've even seen the full potential of permafrost thaw and methane hydrate destabilisation. Should that happen, we're pretty much looking at a Rockström scenario where the climatic regimes below the 60th parallels are too extreme for human civilisation.
Basically, I'm not seeing any potential for any regional cooling of any kind, actually the direct opposite. Publications by Weldead, Schneider et al. and Nisbet, Manning et al. actually demonstrate that an AMOC collapse can indeed result in a rapid termination of glacial conditions and the formation of a hyperthermal event.
>If the AMOC shuts down
Do people assume from this comment that the entire oceans heat and mass transfer system ceases. It seem to me that the conclusions drawn from "If the AMOC shuts down" is a conclusion draw from a total shut down.
Turbulence, mass and heat transfer, convection, conduction typically described as currents will continue. No amount of human intervention or sanctions will prevent this or any other influence of this scale.
Continents are drifting at a faster rate that sea levels are rising. This has an influence on currents. I suggest though that it would be delusional to think we can change this to some idealistically desired condition.
No, doesn’t work like that.
You, like many, are failing to see that average temperatures are just that: average over time. A decrease of say, 10°C in Europe does NOT mean you tack on roughly ten degrees to the temperatures all year.
Were the AMOC to collapse, reputable research suggests European winters will get catastrophically cold AND summers will be even more hellish infernos.
So no, if we tank out ocean current system, greenhouse gasses are not going to help us.
As im living in Europe/Germany I would really like to understand what AMOC collapse means for the climate here. Will it be „just“ more continental or will it be like a new ice age here?
Only northern europe gets cooler, and that only temporarily. The rest of the planet burns.
But to answer your question, it doesn't fucking matter.
1. If/When the AMOC shuts down, we're fucked.
2. We're already fucked. About a dozen unstoppable feedback loops start at 2C, and we've already pumped more than enough CO2 to get us to 2C and we don't have a way to remove carbon at that scale or speed, we don't have a way to get to net zero emissions, and even if we did, it's too late.
I believe there is not enough geological carbon that would allow it. We should have passed peak oil already in 2018, and we likely are forced to ramp down fossil energy production due to progressive depletion of the resource, even if for some countries it would be highly advantageous to pollute as much as possible. (Doubtful claim, but you made it.)
My understanding is that RCP 8.5 requires maintaining and even increasing carbon emissions from where they are now, which should be counterfactual as all regions of the world are expected to enter in decline of carbon production by 2025. This includes coal, whose use should go up by factor of 5, IIRC, for RCP 8.5 to happen. While there is coal around, there's probably no way to increase mining by factor of 5.
If AMOC halts, that won't effect the planet's energy budget with the Sun and Space, so the total planet would still keep warming. Europe would cool, but sorry you can't heat up the whole planet and let those in the Tropics wither just so you can stay warmer. That assumes humans could do anything about it anyway.
Re planet warming, all focus is on the average planet temperature, but warming has been very uneven. The Arctic has warmed 4x the rest of the planet, which would seem nice, but Inuit complain about the changes, while holding their hands out for donations. Warming in California has been in warmer nights, not hotter days, which seems pretty tolerable.
2 of my proffessors working in the field, independently ridiculed the paper for being bad science. According to them, it won‘t break down anytime soon (next few hundred years).
Anyway, shutting down wouldn‘t help I don‘t think. The biggest polliters on the northern hemisphere would have even less inclination to slow down GHG production, since theyr temperature will sink eith amoc collapse.
Love all the "if" language in here...it's already happening. It won't be like day after tomorrow, it will start slow then faster, and faster. Which is literally what's happening now, weakening. We're so screwed and so few people see it
It is interesting to talk about this subject, but I suggest to not dwell on it, and give it your energy. There are more important things in life. Yes this is important, but what can you really do?
No, we cannot time our CO2 emissions to "game" the system. The heat effects are delayed, nonlinear, and persist for thousands of years.
It's not global cooling. It's just northern Europe. The rest of the planet gets hot.
Yes - and the oceans rapidly expand and stratify. We will generate more emissions from trying to produce fuel and shelter for displaced hundreds of millions or perhaps billions of people. AMOC shut down stops the oceanic transfer of heat from the tropics to the poles (about 50% of the energy) that will have to be transferred by the atmosphere, the tropical atmosphere becomes extremely hot and wet - and that hot wet atmosphere then moves heat to the poles.
So for the higher latitudes,more extreme weather? More rain, more snow, more wind? Does the temperature still go down overall in the higher latitudes or does it go up?
I don’t know - I don’t think anyone does. We can draw broad conclusions, the Earth transfers heat and nutrients and dissolved gases using the overturning currents. That stops we know the atmosphere is wetter and there are going to be larger temp differences. Exact impacts? Not sure our current weather models will be able to predict the outcome with anything but terrible accuracy.
Awesome /s But seriously thanks for your thoughtful responses.
It's important to note that the regional cooling hypothesis is largely based on Younger Dryas proxy analogs, and the paleoclimatic regime isn't comparable to Anthropocene conditions. The YD initiated with significant glacial volume in the Northern Hemisphere; the Laurentide and Fennoscandinavian ice shelves. A weakening and collapse of the AMOC under these conditions demonstrates a drastic cooling response in sediment samples. It was the melt rate of the Laurentide that has been suggested as a factor for the freshwater influx that triggered a collapse when Lake Agassiz burst its banks and emptied entirely. Based on current geophysical and meteorological conditions I'd estimate that the North Atlantic's maritime climates would transition into something much more continental; from a humid temperate Cfa Köppen classification, to a Dfa hot summer continental classification. Quite frankly, the publications that suggest a drastic temperature drop are absurd in their conclusions and base that finding purely on what their computer model suggests. It's effectively a secondary commentary as these models are designed to estimate the response of the AMOC to freshwater hosing, they're not really designed to provide a practical reconstruction of the meteorological response. A drop of ~10°c in London isn't happening, it's just not physically possible under the dynamics.
Fabulous comment, thank you!
Totally agree. Even locally in northern EU the continued rise in CO2 would overwhelm the drop in heat transport within a decade or two. Meanwhile the rest of the globe continues with accelerated warming and transport north of even more heat energy in the atmosphere as the latent heat of condensation accelerates and drives heat energy northward in upper troposphere.
Canada, the US (mainly the northeast) and Russia too will experience significant cooling in the case of full AMOC shutdown
Cooler than the pre-industrial average?
Potentially yes but it really depends on the model you look at as there are a range of outcomes but a good number of them would have northern Europe colder than preindustrial averages.
I’m aware Northern Europe would be significantly colder than the pre-industrial to the point where agriculture effectively stops. I’m wondering how significant the northern hemisphere average temperature reduction would be compared to say a 2.5C or 3C rise since the industrial revolution
Hard to predict exactly. It would depend on where exactly you’re talking about and when the Amoc collapses and how long after you’re measuring the effects as they likely will take a few decades to set in. But over time, I believe, based on what I’ve read and heard on the topic that full Amoc collapse could decrease North American temperatures, especially in Canada by 2-3 C, maybe more in some places like Northern Quebec. While Europe could see 2-3 C cooling in the south, places like Spain, Italy. And 5-10 C further North, like the UK, Germany & Norway etc. Everyone on here probably wouldn’t agree, but I strongly believe cooling of 5-10 C would be way worse than warming of 2-3 C elsewhere on earth
At least we in the developed west get one or two more generations to continue fucking everything up before the planet burns to a crisp /s
In 2022, a major review of tipping points had concluded that AMOC collapse would lower global temperatures by around 0.5 °C (0.90 °F), while regional temperatures in Europe would go down by between 4 °C (7.2 °F) and 10 °C (18 °F).[13][72] In 2020, a study had assessed the impact of an AMOC collapse on farming and food production in Great Britain.[122] It found an average temperature drop of 3.4 °C (6.1 °F) (after the impact of warming was subtracted from collapse-induced cooling.) Moreover, AMOC collapse would lower rainfall during the growing season by around <123mm, which would in turn reduce the land area suitable for arable farming from the 32% to 7%. The net value of British farming would decline by around £346 million per year, or over 10%.[14] In 2024, one modelling study suggested even more severe cooling in Europe - between 10 °C (18 °F) and 30 °C (54 °F) within a century for land and up to 18 °F (10 °C) on sea. This would result in sea ice reaching into the territorial waters of the British Isles and Denmark during winter
Stefan Rahmstorf from the Postdam Institute is a good source of info about this topic. At no point does he suggest that an AMOC collapse could be some kind of solution to global warming. https://tos.org/oceanography/article/is-the-atlantic-overturning-circulation-approaching-a-tipping-point "A full shutdown of the AMOC would have truly devastating consequences for humanity and many marine and land ecosystems. Figure 15 shows the model of Liu et al. (2017) after a doubling of CO2, with an AMOC collapse caused by this CO2 increase. The cold air temperatures then expand to cover Iceland, Britain, and Scandinavia. The temperature contrast between northern and southern Europe increases by a massive 4°C, likely with major impact on weather, such as unprecedented storms."
This study is amazing. Figure 2 shows clearly that a collapse would lower temperatures all over the world, not just Europe
It shows the northern hemisphere being cooler, but by how much relative to what? This is not some helpful global cooling, and the impacts are catastrophic.
"one modelling study" One model is insufficient for science or policy and should never be cited in isolation, it's useless. Science is about repeatable findings and understanding probabilities and error margins.
What's the mechanism for this cooling? The AMOC is redistributing thermal energy from equatorial ocean surfaces to the poles and deep ocean... it makes sense that shutting this down would cool northern latitudes but how could the resultant build up in thermal energy in equatorial ocean surfaces have a cooling effect on equatorial regions?
This is true. I believe there are theories that suggest that the absence of thermohaline circulation would be supplemented by atmospheric circulation, as a more clearly defined and larger equator to pole temperature gradient induces the dynamics required for natural heat circulation. In plain English: excess heat still gets circulated, but by other circulations.
Just eyeballing the energy that has to be moved with the atmosphere's low thermoconductivity and energy density, it seems like atmospheric convection would have to flow at a fairly serious pace to establish equilibrium. But, I suppose a lot could get moved about stored as latent heat in evaporated water. There's also a weird wrinkle in that the AMOC stopping could lead to a larger polar freeze/thaw cycle that could start the AMOC back up again, possibly even stronger than it is, so could we see wild stuttering like centennial ice ages or something?!
I'm not overly convinced by the cooling theories. The more you read about the rationale behind it, the less viable it sounds. The analogs they employ to suggest widespread cooling are questionable at best. The Younger Dryas is a commonly cited analog, but they neglect to account for the fact the YD began with a significant portion of the Northern Hemisphere already dominated by ice shelves. North America had the Laurentide, which buried the entirety of eastern Canada, whereas Scandinavia had the Fennoscandinavian that dominated Northern Europe. The ocean between Norway and Greenland was entirely frozen. So when you account for these factors, it makes sense why the computing models usually suggest a drastic cooling trend based on sediment proxy data. Of course there would have been drastic cooling if most of the upper latitudes were already experiencing near glacial conditions. To add to that, the originator of the regional cooling in response to ocean circulation collapse during the YD eventually grew critical of this theory. There's some suggestion that these glaciers exist due to such a strong current existing in the Atlantic in the first place. With the opening of the Drake Passage, a strong circulation formed in the North Atlantic and introduced a larger volume of precipitation. So there's an ironic situation where the thermohaline circulation provided the conditions needed for glacial growth but also act as a buffer against further encroachment. As a demonstration of this hypothesis; during the last glacial maximum, it's estimated that Sakhalin maintained a temperate climate while comparable latitudes in Europe were either frozen or tundra grassland. Reconstructions suggest that North America and Europe saw the greatest extent of glacial encroachment whilst other regions saw significantly less encroachment. If you look up "last glacial maximum maps" you can see how Europe and North America were so disproportionately frozen. Another commonly cited analog is the so-called Little Ice Age, which is a terrible analog as there's no strong case to suggest it was a consequence of AMOC changes. Granted, the LIA saw bitterly cold winters and scorching hot summers, which suggests it could have been attributed to AMOC decline/collapse, but the coldest winters observed in Europe during the LIA correlate with significant volcanic activity and ash sediments found in ice core samples. The Little Ice Age wasn't unrelentingly cold either, there are still some record warm CET annual averages from that period that haven't yet been beaten, and the infamous Great Fire of London occurred in 1666 after a long period of drought and persistent heat. And as a purely unscientific analysis, reconstructions suggest that Northern Hemisphere permanent ice formation has been gradually shrinking with each interglacial to glacial cycle. That is, to say, the extent of year round ice under interglacial conditions has shrunk with each successive glacial maximum progressing into interglacial conditions. The volume of interglacial permanent ice formation is comparatively lower than during preceding interglacials.
I see what you mean, the "last glacial maximum" maps have a dramatic imbalance in glacial distribution. It does seem tempting to attribute it to variation in AMOC behavior because that region of the North Atlantic (NA) involves the coupling of a few different complicated effects that could force relatively large temperature differentials via feedback. It seems very difficult to precisely parametrize the thermal vs saline forces alone, and that local region of deep-diving water in the NA would be a point where huge volatility could emerge. The vertical flow of currents is probably difficult to model. When you say "the opening of the Drake passage" are you referring to this as a distant but highly influential event that generated the AMOC as we know it now? When I was looking into the Pliocene there was still healthy debate about whether the Isthmus of Panama had closed with an error-margin of 10 million years or so, and I even saw it suggested somewhere that the ocean was dominated by a circum-equatorial current during the Pliocene, but I couldn't find much to support that claim. The Drake passage seems to have more uncertainty. Is the AMOC state in paleoclimatology inferred by a process of exclusion, because it may be difficult to detect physical evidence of its behavior? In medicine there are some annoying disorders that can't be diagnosed via biomarkers in any way, so differential diagnosis is accomplished via an iterative process of increasingly invasive pathology testing until every thing that could be diagnosed by operational criteria has been excluded. When you're left with the only possibility being the illness that can't be diagnosed by fitting the symptoms to a set of operational criteria that satisfy a threshold for diagnosis, you can be tentatively assurred you've landed upon the correct illness. These are sometimes called a 'wastebasket diagnosis'. The AMOC appears to be a canonical motif in climate models, if you remove it most (or even all) models would probably collapse. A neuroscientist would probably call it a 'canonical circuit' in climate models. This leads to an unsettling thought that climate models rely on a critical assumption in the stable behavior of the AMOC, but its state at any moment in history is inferred via the same process a doctor uses to establish a wastebasket diagnosis :/
The only reason I can think for an AMOC halt cooling the planet average is because thermal radiation to space goes as absolute temperature to the 4th power, so if you split a surface into half hotter and half colder, the thermal radiation would increase since not a linear average. Meaning, the planet would reject more heat to Space.
Hard to see it cooling though, it would just slow heating. The increased atmospheric water vapor would also form a good blanket.
Simple arithmetic example: avg of equal ground temperatures: (1\^4 +1\^4)/2 = 1 avg of colder and hotter equal-split temperatures: (0.5\^4 + 1.5\^4)/2 = 2.56 Water vapor is a much stronger greenhouse gas than CO2, so more would warm the planet. But, when it forms water droplets (clouds), they reflect sunlight. Cloud interaction in the radiant exchange is complicated, and varies depending on altitude. In the Stratosphere, they form ice crystals which act differently than liquid droplets.
You seem to think the AMOC breaking down would change the laws of thermodynamics.
Link required.
https://en.m.wikipedia.org/wiki/North_Atlantic_Current#Climate_change
Wikipedia is not a valid citation. You need to link to the thing they purport to be summarizing.
Why don't you go get it professor, this is reddit FFS not MIT.
I think given the context and claim being made it would benefit ALL OF US to have the purporter of the claim back their claim up. If you can't see that then I am sad for you.
Are you a climate denialist? What is your point?
It's a sub for discussing climate science, are you lost?
What is your point?
That requesting citations is appropriate for this forum. It's not some esoteric practice that's only useful to professors. If you make a claim, you should be able to verify where it came from... unless you made it up (which is fine, as long as you acknowledge it).
It should be noted that the publications that suggest a drop in average temperatures are; (a) generally not accounting for the atmospheric dynamic response, which I'll explain below, and (b) it's an average annual drop. Europe's zonal temperature anomaly relative to its latitude is more positively pronounced during meteorological winter. During the summer months, this same anomaly has a cooling tendency. Expanding on (a), there's a lot of more recent research that suggests that an AMOC collapse results in an aggressive continentalisation of maritime Europe's climate. Winters get colder, but summers get hotter. Both seasons observe a drastic drop in precipitation. The most recent publication by Oltmanns, Holliday et al. even demonstrates that a cooler freshwater anomaly in the North Atlantic results in hotter and drier summers for the northern half of Europe. It's generally well known that a sluggish and even absent current would result in more extreme weather in Europe, which would include more persistent hot weather. It's also generally observed that the computing methodology has issues. The Royal Society has discussed this issue somewhat extensively. For example, they generally do a poor job of accounting for the warming tendency of GHGs under a collapse scenario. Drijfhout attempted to resolve this and concluded that the effects of anthropogenic warming would be reversed for 15-20 years before a warming trend continues. The issue is that the climatology models are limited in how they can reproduce non-linear elements. But if the AMOC collapses, it's not cooling that we should worry about. Such a drastic change in ocean circulation would almost certainly destabilise methane hydrate reserves. When that happens, we're pretty much heading for a hothouse state. Methane is an incredibly potent greenhouse gas and has been implicated in historic runaway warming events, and it has been demonstrated that it would only take minimal disturbance of the AMOC to see a catastrophic destabilisation event. I can add citations for anyone who's interested, Reddit app is really glitchy and it's already crashed today and lost me an entire post.
Yes please to citations, thanks!
--**Atmospheric feedback discussions:** * [Decelerating Atlantic meridional overturning circulation main cause of future west European summer atmospheric circulation changes](https://iopscience.iop.org/article/10.1088/1748-9326/10/9/094007) (Haarsma, Selten, Drijfhout. 2015) * [Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context](https://www.nature.com/articles/s41467-017-02699-3) (Trouet, Babst, Meko. 2018) * [What is the North Atlantic Oscillation (NAO)?](https://www.worldclimateservice.com/2021/08/26/north-atlantic-oscillation/) from the World Climate Service briefly describes the northern hemisphere summer cooling tendency (JJA negative temperature anomaly relative to latitude) observed in maritime Europe due to westerlies induced by North Atlantic circulation. --**Colder winters, hotter summers:** * [European summer weather linked to North Atlantic freshwater anomalies in preceding years](https://wcd.copernicus.org/articles/5/109/2024/) (Oltmanns, Holliday et al. 2024) * [Long-term drought intensification over Europe driven by the weakening trend of the Atlantic Meridional Overturning Circulation](https://www.sciencedirect.com/science/article/pii/S2214581822001896) (Ionita, Nagavciuc et al. 2022) * [Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2018PA003341) (Bromley, Putnam et al. 2018) * [Warm summers during the Younger Dryas cold reversal](https://www.nature.com/articles/s41467-018-04071-5) (Schenk, Väliranta et al. 2018) -- **Computer model reconstruction issues:** * [Challenges simulating the AMOC in climate models](https://royalsocietypublishing.org/doi/10.1098/rsta.2022.0187) (Jackson, Hewitt et al. 2023) * [Can we trust projections of AMOC weakening based on climate models that cannot reproduce the past?](https://royalsocietypublishing.org/doi/full/10.1098/rsta.2022.0193) (McCarthy & Caeser. 2023) * [Competition between global warming and an abrupt collapse of the AMOC in Earth’s energy imbalance](https://www.nature.com/articles/srep14877) (Drijfhout. 2015) --**Methane and ice age termination theorem:** * [Evidence for massive methane hydrate destabilization during the penultimate interglacial warming](https://www.pnas.org/doi/full/10.1073/pnas.2201871119) (Weldeab, Schneider et al. 2022) specifies the correlation between AMOC stability and methane hydrate destabilisation. * [Atmospheric Methane: Comparison Between Methane's Record in 2006–2022 and During Glacial Terminations](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GB007875) (Nisbet, Manning et al. 2023) --- I've linked the academic releases but there are numerous outlets that discuss their findings in a more concise way if you want something more brief.
Thanks for this. The AMOC literature is so vast it’s hard to know where to start. McCarthy & Caesar 2023 discussion about why models and observations and SST-based proxies don’t always match is something I’ve been wondering about.
I also have this problem there is a ton of reading to do on it and there seems to be a range of different outcomes predicted by different models/studies
Not to mention a full collapse in fisheries due to the stoppage of general nutrient circulation relied upon ocean ecosystems.
Great post thanks for posting this info
If the AMOC shuts down the oceans stratify and become anoxic, killing life below a few 100m, we go to an equitable climate, with with vast flooding and massive storms, all the ice on the planet rapidly melts and yeah. AMOC shutdown is endgame, not a handy little warming hiatus. It means we are full on in the transition to hot house conditions.
Yep, if AMOC gets to the point where it actually ceases, things have by definition spiralled beyond our control in any meaningful way. It implies a full state change of our planetary climate, being that it's such a central pillar of our current climate.
The intricate fragility of oceanic dynamics are frighteningly underestimated in my experience. There's definitely a degree of linear assumption in how the ocean and atmosphere respond to concurrent changes in either system. Anoxia would be a huge concern if we see a breakdown of thermohaline circulation, and to a degree we can already observe some of the precursors. You're right in thinking that a collapse would be a prelude to a hothouse state. It has been demonstrated that even a minimal disruption in oceanic circulation would be sufficient enough to destabilise methane hydrate reserves, which would almost certainly result in an ice age termination event. Atmospheric methane concentrations is the more underestimated danger we're facing right now as it has been estimated that current levels are sufficient enough to confirm an ice age termination is already occurring, and that's before we've even seen the full potential of permafrost thaw and methane hydrate destabilisation. Should that happen, we're pretty much looking at a Rockström scenario where the climatic regimes below the 60th parallels are too extreme for human civilisation. Basically, I'm not seeing any potential for any regional cooling of any kind, actually the direct opposite. Publications by Weldead, Schneider et al. and Nisbet, Manning et al. actually demonstrate that an AMOC collapse can indeed result in a rapid termination of glacial conditions and the formation of a hyperthermal event.
>If the AMOC shuts down Do people assume from this comment that the entire oceans heat and mass transfer system ceases. It seem to me that the conclusions drawn from "If the AMOC shuts down" is a conclusion draw from a total shut down. Turbulence, mass and heat transfer, convection, conduction typically described as currents will continue. No amount of human intervention or sanctions will prevent this or any other influence of this scale. Continents are drifting at a faster rate that sea levels are rising. This has an influence on currents. I suggest though that it would be delusional to think we can change this to some idealistically desired condition.
No, doesn’t work like that. You, like many, are failing to see that average temperatures are just that: average over time. A decrease of say, 10°C in Europe does NOT mean you tack on roughly ten degrees to the temperatures all year. Were the AMOC to collapse, reputable research suggests European winters will get catastrophically cold AND summers will be even more hellish infernos. So no, if we tank out ocean current system, greenhouse gasses are not going to help us.
nope
I think if the AMOC shuts down, it might be a wake up call to pay more attention and hopefully our efforts would increase.
This implies that we have reduced emissions…
As im living in Europe/Germany I would really like to understand what AMOC collapse means for the climate here. Will it be „just“ more continental or will it be like a new ice age here?
[I wouldn't expect it to get colder](https://arstechnica.com/science/2024/03/how-melting-arctic-ice-leads-to-european-drought-and-heatwaves/)
Thank you for sharing - interesting read!
The range given for the cooling is quite vast, so it will be hard to say. We’re waiting for you in southern Romania if it gets too cold 😄
Only northern europe gets cooler, and that only temporarily. The rest of the planet burns. But to answer your question, it doesn't fucking matter. 1. If/When the AMOC shuts down, we're fucked. 2. We're already fucked. About a dozen unstoppable feedback loops start at 2C, and we've already pumped more than enough CO2 to get us to 2C and we don't have a way to remove carbon at that scale or speed, we don't have a way to get to net zero emissions, and even if we did, it's too late.
*on reducing, typo
I think the polar regions will be colder. The equator will be hotter. And in between will be windy and unpredictable.
The results from any change and the effects on the economy are what will most influence changes.
I believe there is not enough geological carbon that would allow it. We should have passed peak oil already in 2018, and we likely are forced to ramp down fossil energy production due to progressive depletion of the resource, even if for some countries it would be highly advantageous to pollute as much as possible. (Doubtful claim, but you made it.) My understanding is that RCP 8.5 requires maintaining and even increasing carbon emissions from where they are now, which should be counterfactual as all regions of the world are expected to enter in decline of carbon production by 2025. This includes coal, whose use should go up by factor of 5, IIRC, for RCP 8.5 to happen. While there is coal around, there's probably no way to increase mining by factor of 5.
If AMOC halts, that won't effect the planet's energy budget with the Sun and Space, so the total planet would still keep warming. Europe would cool, but sorry you can't heat up the whole planet and let those in the Tropics wither just so you can stay warmer. That assumes humans could do anything about it anyway. Re planet warming, all focus is on the average planet temperature, but warming has been very uneven. The Arctic has warmed 4x the rest of the planet, which would seem nice, but Inuit complain about the changes, while holding their hands out for donations. Warming in California has been in warmer nights, not hotter days, which seems pretty tolerable.
2 of my proffessors working in the field, independently ridiculed the paper for being bad science. According to them, it won‘t break down anytime soon (next few hundred years). Anyway, shutting down wouldn‘t help I don‘t think. The biggest polliters on the northern hemisphere would have even less inclination to slow down GHG production, since theyr temperature will sink eith amoc collapse.
Love all the "if" language in here...it's already happening. It won't be like day after tomorrow, it will start slow then faster, and faster. Which is literally what's happening now, weakening. We're so screwed and so few people see it
Can you please elaborate on this with sources? I would've assumed it's an immediate effect.
It is interesting to talk about this subject, but I suggest to not dwell on it, and give it your energy. There are more important things in life. Yes this is important, but what can you really do?
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Except for fires, drought, storms.
Both can be bad or worse than the other. We want stability, not climate change.