There’s been a bit of media whiplash on the issue of AMOC slowing lately – ranging from the AMOC being “on the brink of collapse” to it being “more stable than previously thought”. AMOC, of course, refers to the Atlantic Meridional Overturning Circulation, one of the worlds major ocean circulation systems which keeps the northern Atlantic region (including Europe) exceptionally warm for its latitude. So what is this whiplash about?
As is often the case with such media whiplash, there isn’t much scientific substance behind it, except for the usual small incremental steps in the search for improved understanding. It is rare that one single paper overthrows our thinking, though media reports unfortunately often give that impression. Real science is more like a huge jigsaw puzzle, where each new piece adds a little bit.
The latest new piece is a new reconstruction of how the AMOC has changed over the past 60 years, by Jens Terhaar and colleagues. The background to this discussion is familiar to our regular readers (else just enter ‘AMOC’ in the RealClimate search field): proper measurements of the AMOC flow are only available since 2004 in the RAPID project, thus for earlier times we need to use indirect clues. One of these is the sea surface temperature ‘finger print’ of AMOC changes as discussed in our paper Caesar et al. 2018 (Fig. 1). There we used the cold blob temperature anomaly (Nov-May) as an index for AMOC strength. Other studies have used other sea surface temperature or salinity patterns as well as paleoclimatic proxy data (e.g. sediment grain sizes), and generally found an AMOC decline since the 19th Century superimposed by some decadal variability. The new paper critices our (i.e. Caesar et al) reconstruction and suggests a new method using surface heat fluxes from reanalysis data as an indicator of AMOC strength.
Here’s three questions about it.
1. Does the ‘cold blob’ work well as AMOC indicator?
We had tested that in the historic runs of 15 different CMIP5 climate models in Caesar et al. 2018 (our Fig. 5) and found it works very well, except for two outlier models which were known to not produce a realistic AMOC. Now Terhaar et al. redid this test with the new CMIP6 model generation und found it works less well, i.e. the uncertainty is larger (although for future simulations where the AMOC shows a significant decline in the models, our AMOC index also works well in their analysis).
Which raises the question: which models are better for this purpose: CMIP5 or CMIP6? One might think that newer models are better – but this does not seem to be the case for CMIP6. Irrespective of the AMOC, the CMIP6 models created substantial controversy when their results came out: the climate sensitivity of a subset of ‘hot models’ was far too high, these models did not reproduce past temperature evolution well (compared to observed data), and IPCC made the unprecedented move of not presenting future projections as straightforward model average plus/minus model spread, but instead used the new concept of “assessed global warming” where models are weighted according to how well they reproduce observational data.
In the North Atlantic, the historic runs of CMIP6 models on average do not reproduce the ‘cold blob’ despite this being such a striking feature of the observational data, as shown clearly in the Summary for Policy Makers of the IPCC AR6 (see Fig. 2 below). Of the 24 CMIP6 models, a full 23 underestimate the sea surface cooling in the ‘cold blob’. And most of the CMIP6 models even show a strengthening of the AMOC in the historic period, which past studies have shown to be linked to strong aerosol forcing in many of these models (e.g. Menary et al. 2020, Robson et al. 2022). The historic Northern Hemisphere temperature evolution in the models with a strong aerosol effect “is not consistent with observations” and they “simulate the wrong sign of subpolar North Atlantic surface salinity trends”, as Robson et al. write. Thus I consider CMIP6 models as less suited to test how well the ‘cold blob’ works as AMOC indicator than the CMIP5 models.
2. Is the new AMOC reconstruction method, based on the surface heat loss, better?
In the CMIP6 models it looks like that, and the link between AMOC heat transport and surface heat loss to the north makes physical sense. However, in the models the surface heat loss is perfectly known. In the real ocean that is not an observed quantity. It has to be taken from model simulations, the so-called reanalysis. While these simulations assimilate observational data, over most of the ocean surface these are basically sea surface temperatures, but surface heat loss depends also on air temperature, wind speed, humidity, radiation and cloud cover in complex ways, all of which are not accurately known. Therefore these surface heat loss data are much less accurate than sea surface temperature data and in my view not well suited to reconstruct the AMOC time evolution.
That is supported by the fact that two different reanalysis data sets were used, leading to quite different AMOC reconstructions. Also the AMOC time evolution they found differs from other reconstruction methods for the same time period (see point 3 below).
And there is another issue: we’ve previously looked at ERA5 surface heat flux trend, as shown here from my article in Oceanography 2024:
You see in both figures (in temperature as well as surface heat flux) the AMOC slowdown ‘fingerprint’ which includes both the ‘cold blob’ and a warming along the American coast due to a northward Gulf Stream shift, which is also a symptom of AMOC weakening. However, Terhaar et al. integrate over the whole northern Atlantic north of 26 °N so that the red area of increasing heat loss largely compensates for the blue area of decreasing heat loss. So in their analysis these two things cancel, while in the established concept of the ‘fingerprint’ (see Zhang 2008: Coherent surface-subsurface fingerprint of the Atlantic meridional overturning circulation) these two things both reinforce the evidence for an AMOC weakening.
3. How do these new reconstructions compare to others?
Here is how the Terhaar reconstructions (bottom two) compare:
The reconstruction at the bottom using a reanalysis product from Japan doesn’t resemble anything, while the blue one using the European ERA5 reanalysis at least has the 1980s minimum and early 2000s maximum in common with other data, albeit with much smaller amplitude; it is a lot smoother. Thus it also misses the strong AMOC decline 2004-2010 and subsequent partial recovery seen in the RAPID measurements as well as the Caesar and Worthington reconstructions. A main reason for the lack of significant trend in the Terhaar reconstructions further is the time interval they used; for the same time span the Caesar reconstruction also does not show an even remotely significant trend (p-value is only 0.5), so in this respect our reconstructions actually agree for the period they overlap. The fact that ours shows a significant AMOC decline is because of the stable AMOC we find during 1900-1960, which is stronger than in the following sixty years. Here our reconstruction method shows its advantage in that reliable and accurate sea surface temperature data exist so far back in time.
Hence, I do not believe that the new attempt to reconstruct the AMOC is more reliable than earlier methods based on temperature or salinity patterns, on density changes in the ‘cold blob’ region, or on various paleoclimatic proxy data, which have concluded there is a weakening. But since we don’t have direct current measurements going far enough back in time, some uncertainty about that remains. The new study however does not change my assessment of AMOC weakening in any way.
And all agree that the AMOC will weaken in response to global warming in future and that this poses a serious risk, whether this weakening has already emerged from natural variability in the limited observational data we have, or not. Hence the open letter of 44 experts presented in October at the Arctic Circle Assembly (see video of my plenary presentation there), which says:
We, the undersigned, are scientists working in the field of climate research and feel it is urgent to draw the attention of the Nordic Council of Ministers to the serious risk of a major ocean circulation change in the Atlantic. A string of scientific studies in the past few years suggests that this risk has so far been greatly underestimated. Such an ocean circulation change would have devastating and irreversible impacts especially for Nordic countries, but also for other parts of the world.
Post script
Since I’m sometimes asked about that: last year a data study by Volkov et al. revised the slowing trend of the Florida current as well as the AMOC. Contrary to ‘climate skeptics’ claims, it has no impact on our long-term estimate of ~3 Sv slowing since 1950, i.e. -0.4 Sv/decade (Caesar et al. 2018). Both the original and the revised trend estimates for the RAPID section data (see Figure) suggest the recent AMOC weakening since 2004 is steeper than the long-term trend we estimated.
thank you–this is helpful
Many thanks for this long expected update . Your candor regarding the signal emergence problem recalls Michael Oppenheimer’s in dealing with decadal global temperature data back in 1990 before CMIPS evolved.
Given the comparative wealth of SST anomaly reconstructions we now enjoy, might RC provide some parallel global maps of decadal trends in seasonal wind velocity ?
As to the cold blob and the high winds and seas that attend it, now that AI’s are getting good at data mining, it might be possible to augment the relatively short satellite sea state record by recruiting re-insurance quants to examine that much longer proxy for North Atlantic weather, LLoyds Shipping News?
To a first approximation, ocean crossing times fall as wind anomalies rise, witness how many vessels have literally been left at sea by the phenomenal winds of last week’s primary focus of climate communication, storm Eowyn.
That approximation holds for sailing ships, which post 1850 shipping records distinguish from those under fossil fuel propulsion. Their speed and fuel economy in contrast tends to fall as wave heights increase with rising winds.
Russell said:
AI in it’s various forms has been good at data mining.for several decades. It’s more a matter of whether one believes what it’s telling you. This is a case that I documented almost 9 years ago:
https://geoenergymath.com/2016/02/13/qbo-model-validation/
In this situation, a wind model was initially proposed via a physical mechanism, and then an AI symbolic regression algorithm cross-validated the results. It essentially data-mined the QBO time-series and found and matched precisely the same values that the physical mechanism would demand. That was after 10 trillion fitting calculations — what would now be considered a mild form of data mining.. (In comparison, my physical model did a single multiple regression calculation)
Published in 2019 in Mathematical Geoenergy.
How well are the new CMIP7 models doing?
[Response: They haven’t started yet (soon though). – gavin]
“And all agree that the AMOC will weaken in response to global warming in future and that this poses a serious risk, whether this weakening has already emerged from natural variability in the limited observational data we have, or not.”
The call for urgent reductions in CO2 emissions cannot solve the problem or lower the risk because that takes none of the CO2 already added out of the atmosphere to lower global temperatures. It does leave carbon in the ground. More importantly, it will make the availability of transportation fuels less and less available and at higher costs to continue the transition to renewables and EVs. Bottom line? The decision leaves us between the proverbial rock and a hard place.
Ken the Denier, 26 Jan: “The call for urgent reductions in CO2 emissions cannot solve the problem or lower the risk because that takes none of the CO2 already added out of the atmosphere””
“All or nothing” fallacy, again. The likelihood/magnitude of the weakening of AMOC in the +1.5 or 2C world is NOT THE SAME as in the +3C or +5C world, genius.
As for your trying to hijack the new thread to spread your old claim – that to reduce CO2 emissions we need to … increase Co2 emissions – repeating a lie won’t make it true. Didn’t before, won’t now.
Denier? liar? Please explain how to feed eight billion stakeholders who will be doing the work transporting, installing and phasing in renewables during the transition away from fossil fuels.
It’s been said that you can ignore reality but not the consequences of ignoring them.
Ken Towe says 27 Jan “Denier? liar?”
Yes, Denier, liar. Ken Towe is what Ken Towe does:
– pushes the denier’s standard narrative, using typical denier’s fallacies of “all or nothing” and related “reductio at absurdum”.
– discourage reductions in GHG emissions: “reductions in CO2 emissions cannot solve the problem because that takes none of the CO2 already added out of the atmosphere” thus ignoring the fact the problem will be MUCH worse if we continue ADDING CO2 thanks to discouragement from the sense of the reductions
– promotes the further increases in CO2 concentrations as a way to …decrease CO2 concentration – again using the “all or nothing” fallacy – NOBODY normal proposed the near future where our use of fossil fuels abruptly drops to ZERO – yet this is behind Ken the Denier threats that the “urgent reductions in CO2 emissions” would make impossible to feed “8 billion”.
Thus in one short paragraph Ken Towe discredits renewables for the inability to correct the problem created by … fossil fuels, and his solution is … more fossil fuels that would make that problem much worse.
So yes, Ken Towe, your are both a “denier” and a “liar”. By their fruits you shall know them.
It’s been accurately said that you can ignore reality but you cannot ignore the consequences of that action.
Perhaps I’m missing your point here, but surely the higher the cost of fossil fuels for transportation (or anything else), the greater will be the economic pressure to move quickly to replace them by renewable energy sources? Your argument appears to assume that fossil fuels are essential to ‘continue the transition’ to renewable sources. This is like saying that when I go on a diet, candy and chocolate bars are needed to ‘transition’ to a healthy diet based on fruit and vegetables. There is a glaring logical fallacy at the core of your argument.
“Your argument appears to assume that fossil fuels are essential to ‘continue the transition’ to renewable sources.”
Exactly.. Solar, wind and nuclear projects don’t install themselves and neither do EVs. There are no EVs transporting food to the eight billion stakeholders depending on fossil fuels to do it. That means more oil will be needed, not less. Starvation is not an option.
Total nonsense. Current and reducing levels of fossil fuels are sufficient to build renewables and rapidly, provided existing energy is used slightly more efficiently.
I accept your point in part, but I don’t see why *more* oil will be needed than we have now. As EVs replace ICEs, the amount of oil needed will decline over time. And you fail to take peak oil into account. Even by OPEC’s estimates, peak oil will be here in 20 years, after which production will decline irreversibly. The future then will be renewable energy.
Rory Allen: – “Even by OPEC’s estimates, peak oil will be here in 20 years, after which production will decline irreversibly.”
I’d suggest there are accumulating indicators that global peak oil supply is already here. Only in hindsight will we know for sure.
US petroleum geologist Art Berman said in early 2024:
“I’m quite confident that before this decade is over we’re going to see some serious supply concerns by markets for both oil and natural gas, and it would not surprise me if that happened in a year or two, ah, as opposed to, you know, the five or six years that we have remaining in this decade.”
https://www.youtube.com/watch?v=rv85LTMO8TQ&t=2233s
I’d suggest we don’t need to wait long to see whether Art Berman is correct or not…
More recently, Art Berman said:
“…the United States absolutely does not have the capability to, you know, it’s not like we have 4 million barrels a day of spare capacity sitting around that we could just turn on, nor do we have 4 million barrels a day of proved reserves that could be somehow, um, drilled, developed and, and, you know, brought on-stream in any kind of a meaningful time frame. So this ‘drill, baby, drill’ thing is just, it, it’s, it’s pure garbage, okay? The United States is producing more oil today, under Biden, who, everybody in my industry thinks is like the most negative, um, for the oil and gas industry of any President in history, and yet United States oil and gas productions are at record high. Which kind of goes back to my point that the President and party don’t really have very much effect on that.”
https://youtu.be/ZHlm7uoIvbc?t=1970
And there’s also this sobering analysis:
https://www.artberman.com/blog/beginning-of-the-end-for-the-permian/
Peak Diesel is the portion of an oil barrel that really matters. Diesel is the lifeblood of the global economy.
https://crashoil.blogspot.com/2024/01/el-pico-del-diesel-edicion-de-2023.html
KT: There are no EVs transporting food to the eight billion stakeholders depending on fossil fuels to do it. That means more oil will be needed, not less. Starvation is not an option.
BPL: That oil is being used NOW. As EVs replace ICE vehicles (and EV trucks are already being deployed), [t]hat means LESS oil will be needed, not MORE.
There. Fixed it for you.
BPL: Perhaps KT is unaware that nearly 40% of rail transport globally has already been electrified. Turkey for one has completed most of its electrification of rail already.
The USA of course lags significantly as they always do with rail and climate mitigation in general. But other countries have managed to do this without exhausting their ff supplies somehow.
It just may be vaguely barely possible given the will (sarcasm). But the USA has precious little will for such things at the moment.
But war over resources is an option?
KT: The call for urgent reductions in CO2 emissions cannot solve the problem or lower the risk because that takes none of the CO2 already added out of the atmosphere to lower global temperatures.
BPL: It would stop making things worse.
But as I also said, it does keep carbon in the ground. That makes life for people who depend on transportation worse because EVs are not yet able to do that job.
KT: But as I also said, it does keep carbon in the ground. That makes life for people who depend on transportation worse because EVs are not yet able to do that job.
BPL: Existing oil drilling is enough to power the existing transportation system. No one is saying that we should immediately keep all oil in the ground. Merely that we replace it with other things as quickly as possible. That means we will use LESS oil, not MORE. We don’t need MORE oil to do the job existing oil is already doing.
KT: it does keep carbon in the ground. That makes life for people who depend on transportation worse because EVs are not yet able to do that job.
BPL: I think I may have pinpointed where the fallacy lies. Existing fossil fuels are enough to do the job of running the existing economy, including the transportation of renewable power materials and parts which are reducing the amount of fossil fuels needed. You seem to be saying we need more fossil fuel exploration and exploitation. No. As renewables increase, fossil fuels decrease. We do not need more, we need less.
Carl Wunsch of MIT is very critical of the concept.
http://www.masterresource.org/debate-issues/amoc-alarmism-doesnt-stick/
Interesting link. On a separate but related point, Carl Wunsch is no stranger to controversy. In 2007 a Guardian article contained the following:
‘A leading US climate scientist is considering legal action after he says he was duped into appearing in a Channel 4 documentary that claimed man-made global warming is a myth. Carl Wunsch, professor of physical oceanography at the Massachusetts Institute of Technology, said the film, The Great Global Warming Swindle, was ‘grossly distorted’ and ‘as close to pure propaganda as anything since World War Two’.
He says his comments in the film were taken out of context and that he would not have agreed to take part if he had known it would argue that man-made global warming was not a serious threat. ‘I thought they were trying to educate the public about the complexities of climate change,’ he said. ‘This seems like a deliberate attempt to exploit someone who is on the other side of the issue.’ He is considering a complaint to Ofcom, the broadcast regulator.
The film, shown on Thursday, was made by Martin Durkin. In 1997, he produced a similar series for Channel 4 called Against Nature, which attacked many of the claims of the environmental movement.’
One hopes he is not being misquoted or manipulated a second time by the climate science denial industry.
Carl Wunsch along with his colleague Walter Munk have done seminal work on ocean currents and the forces driving them, w/ dynamics influenced by the Coriolis effect, winds, and tidal forces, significantly contributing to physical oceanography. Munk’s “Abyssal Recipes” paper with Wunsch addressed how mixing processes in the deep ocean maintain global thermohaline circulation. They emphasized the importance of vertical mixing processes, driven by wind, tides, and topography, in sustaining the overturning circulation.
I follow his work because of the influence of tides, which I think is important.
However, he has shown mixed judgment in the past. In particular, he OK’d a peer-reviewed AGW paper by Patrick Frank. To remedy this, on PubPeer, Wunsch unendorsed his review, but after over 3oo comments, the paper has still not been retracted https://pubpeer.com/publications/391B1C150212A84C6051D7A2A7F119#5
Read through the comment thread and you will see why he’s referred to as PFrank the Crank.
The lesson learned is to be careful on giving ammunition to an adversary. That’s unfortunate, as it bleeds into a risk adverse mode to potentially groundbreaking discoveries.
I read as far as your assertion of Michael “Climategate” Mann then stopped and did a little research before continuing. ANY author still pushing “Climategate” as some sort of serious issue–hell ANY sort of issue at all–deserves no further consideration as to any being sort of honest purveyor of honest information. But I find there’s more…
I’m also at a complete loss to figure out how anyone interested in actual science would be swayed by a person displaying the scientific, moral, and ethical credentials of a nonscientist whose “primary job was preparing speeches for chairman and CEO Ken Lay”!!! That would be an ACTUAL “-gate” of rather serious proportions that one _should_ consider in reading him unlike the fake “-gate” he tries to create in his piece.
To his credit, Mr. Bradbury was at least not actually charged with any specific crime of his own while writing Mr. Lay’s speeches. However one really has to ask exactly how he could be ignorant of all the criminal behavior around him in the executive suite if he is so smart, informed, and honest.
My guess is the feds really didn’t care about the speechwriter as anyone significant. Anyway, why anyone here should consider him worth listening to at all here about anything at all serious is utterly beyond _my_ ken..
But all that’s just a personal opinion “to the man”.
____________________________
With regard to the honesty of his scientific interpretation of Wunsch’s reply to him I note Wunsch specifically states TO HIM in the blog entry:
“To clarify however: I am *not* a climate skeptic, and I regard the threat of major climate change as very real and very worrisome. In that context, one can argue that alarming the public about elements such as the behavior of the AMOC could lead to useful actual political and scientific/engineering progress and precautions.
Where I become conflicted is when the particular science is mis-interpreted and mis-understood. Turning the AMOC on and off as an explanation of major past and possible future change has become a go-to-story for people who want a simple explanation of a very complicated system.”
And note, he even attached his own paper though warning you it was perhaps too technical;. Since you ignored it, I guess it was. However, in your absence the author has conveniently posted a copy of it on his site http://ocean.mit.edu/~cwunsch/papersonline/AMOC_collapse.pdf (or was it his 2013 paper here: https://journals.ametsoc.org/view/journals/clim/26/18/jcli-d-12-00478.1.xml?tab_body=pdf ?) both of which most basically assert the variations in the limited data at these early dates are not yet sufficient to be definitive stating (2013): “The testing of such inferences against adequate databases is a problem left for other times and places.”
Hint: He is NOT “very critical of the concept”. He has significant research in the area even. He IS quite critical (2022) of simple-minded interpretations and of those who categorically assert compensatory currents cannot arise or that any other highly specific prediction has definitive evidence for it as of yet. That is a pretty much main stream view across the field of actual researchers regardless of any propaganda stating otherwise from the silliest eco-greenie to silliest former Cato-funded, former ENRON speechwriters.
I highly suspect he would include your own blog entry in the simple-minded pile as well.
A collection of insults as arguments. https://www.desmog.com/robert-l-bradley-jr/
Ph.D., political economy, International College, Los Angeles.1
M.A., economics, the University of Houston.2
B.A., economics, Rollins College.3
“Robert Bradley Jr. is the founder and CEO of Institute for Energy Research (IER). Bradley spent nearly 20 years in the business world including 16 years at Enron where he served as corporate director of public policy analysis and as a speech writer for Kenneth L. Lay.
“Robert Bradley has been associated with a range of conservative and free-market think tanks; he was an adjunct scholar at the Cato Institute and Competitive Enterprise Institute CEI), an Energy and Climate Change Fellow at the Institute of Economic Affairs (IEA) in London, and an honorary senior research fellow at the Center for Energy Economics. He has been a member of the Academic Review Committee for the Institute for Humane Studies at George Mason University.
“He is also the author of several books including Climate Alarmism Reconsidered (2003) and Renewable Energy: Not Cheap, Not ‘Green’ (Cato Institute, 1997), and formerly ran the website Political Capitalism.org.”
Dr. Wunsch’s collection of insults discredits him sufficiently to be ignored by those who are real as opposed to fake skeptics.
Susan Anderson: Dr. Wunsch’s collection of insults discredits him sufficiently to be ignored by those who are real as opposed to fake skeptics.
Did you mean “Dr. Bradley’s collection of insults”? AFAICT from quotes attributed to Carl Wunsch here, Wunsch actually was ‘very critical” of simplistic alarmist arguments for AMOC collapse and an ensuing “ice age”. Well, so am I. Wunsch nonetheless “regard[s] the threat of major climate change as very real and very worrisome”. IOW, he’s not a denier, and explicitly supports the broad consensus of his climate-specialist peers. He does not strike me as a fake skeptic, nor should his publication record be ignored by real ones. The AMS even dedicated a special issue of the Journal of Physical Oceanography to him in 2006 (journals.ametsoc.org/collection/carl-wunsch).
Mal, you make an important point. For some reason I found the insults attributed to Dr. Wunsch somewhere, and can’t now verify how I came to do that that. With hindsight I see his reputation has once again been ‘swindled’. I owe him and you all an apology for increasing the harm to Dr. Wunsch’s reputation. The following (from 2007) will I hope enhance the record.
“In the part of the “Swindle” film where I am describing the fact that the ocean tends to expel carbon dioxide where it is warm, and to absorb it where it is cold, my intent was to explain that warming the ocean could be dangerous—because it is such a gigantic reservoir of carbon. By its placement in the film, it appears that I am saying that since carbon dioxide exists in the ocean in such large quantities, human influence must not be very important — diametrically opposite to the point I was making — which is that global warming is both real and threatening in many different ways, some unexpected.”
“it is easy to be misquoted or quoted out context. My experience in the past is that these things do happen, but usually inadvertently — most reporters really do want to get it right.
“Channel 4 now says they were making a film in a series of “polemics”. There is nothing in the communication we had (much of it on the telephone or with the film crew on the day they were in Boston) that suggested they were making a film that was one-sided, anti-educational, and misleading. I took them at face value—clearly a great error. I knew I had no control over the actual content, but it never occurred to me that I was dealing with people who already had a reputation for distortion and exaggeration.”
https://www.realclimate.org/index.php/archives/2007/03/swindled-carl-wunsch-responds/
&
https://www.realclimate.org/index.php/archives/2007/03/swindled/#comment-27434
This is further confirmation of the malign intent of Enron Bradley’s bad behavior. The kidnapping of Dr. Revelle’s work comes to mind.
SA: “He is also the author of several books including Climate Alarmism Reconsidered (2003) and Renewable Energy: Not Cheap, Not ‘Green’ (Cato Institute, 1997), and formerly ran the website Political Capitalism.org.”
BPL: In other words, a career denier.
Unsurprising, since Wunsch has been proclaiming that an AMOC collapse is “scientifically impossible” for going on 20 years, regardless of what the science says. Note the strawman fallacy of attacking the plot of a science fiction movie rather than addressing the concerns of climate scientists:
“The notion that the Gulf Stream would or could ‘shut off’ or that with global warming Britain would go into a ‘new ice age’ are either scientifically impossible or so unlikely as to threaten our credibility as a scientific discipline if we proclaim their reality.”
— Letter from Carl Wunsch to RealClimate, March 2007 (written after Wunsch appeared in the propaganda film “The Great Global Warming Swindle”)
https://www.realclimate.org/index.php/archives/2007/03/swindled-carl-wunsch-responds/
[Response: Of course, to my knowledge no scientist has ever claimed the Gulf Stream could shut off (only the AMOC), or that this would cause a “new ice age” (which to us scientists implies major continental ice sheets). Such terms have been used by some journalists.]
Thank you, Gavin. Once again, by paying attention to Wunsch’s own words, as opposed to interpretation of them by motivated others, one recognizes his understanding of how much the long-term, cumulative, collective scientific enterprise, with its sometimes ambiguous but ever-flowing benefits to people’s lives, depends on disciplined reticence by its practitioners. Hence the principle of least drama in peer-reviewed publication. You yourself are another exemplar, for which I’m grateful. It cements your authority as a source for accurate understanding of climate reality, free of motivated bullshit. How else could I have learned so much from RC?
If Stefan is the author of the in-line reply to Secular Animist, I apologize. Everything I said applies equally to him as to Gavin.
Was the Cold Blob present (as in, observable) in 2022?
Seems ‘gone’ by 2023.
Stefan, how do these recent papers bear on the issue?
I see one as “it’s complicated (surprise surprise!), and you get a better fit to observations if you include more stuff”, and the other as “Oops, some of that meltwater has stalled in its journey, but is getting close to a tipping point”.
Weakening of the Atlantic Meridional Overturning Circulation driven by subarctic freshening since the mid-twentieth century (read-only link).
Arctic freshwater anomaly transiting to the North Atlantic delayed within a buffer zone.
And Wunsch is even more critical of API cheerleaders with forty year track records of ignoring climate science.
As an old oil patch PR hand, Robert ” Enron” Bartley is in no position to complain about Michael” Hockey Stick ” Mann, There’s no point in predicating climate communication on hyperbole when the reality is bad enough.
Here is what Carl said
“I’m aware of the fuss going on about the AMOC… however: I am *not* a climate skeptic, and I regard the threat of major climate change as very real and very worrisome.
In that context, one can argue that alarming the public about elements such as the behavior of the AMOC could lead to useful actual political and scientific/engineering progress and precautions.. Where I become conflicted is when the particular science is mis-interpreted and mis-understood.”
And here is the paper Bradley fails to link:
http://ocean.mit.edu/~cwunsch/papersonline/AMOC_collapse.pdf
Thx Steffan for the update,
wondered how that new study was evaluated and yes fully agree atmospheric forcings on latent heat make it messy this method.
That the AMOC declined already in the 50s seems to me unlikely as this current would then be highly unstable but who knows..
Current models seem not to be able to simulate the AMOC as all these involved small scale physics would have to be resolved as it is the most complex current system that exist with the processes of a whole basin involved, melting of glaciers and see ice, small scale vertical mixing processes, eddies being important for currents, strength and position of low pressure systems impacting northward water transport, blocking patterns, up to the Beaufort Gyre and its evolution.
Just the issue with winter storms and the intensifying Gulf Stream front as a birthplace for low pressure systems moving northeast ward and that these stronger winter storms could now be fueled by subsurface water accumulating in the North Atlantic – this one “Recent acceleration in global ocean heat accumulation by mode and intermediate waters” https://www.nature.com/articles/s41467-023-42468-z with this one: “Sea Surface Salinity Reemergence in an Updated North Atlantic In Situ Salinity Dataset”; https://journals.ametsoc.org/view/journals/clim/34/22/JCLI-D-20-0840.1.xml whit this one: “Midlatitude Oceanic Fronts Strengthen the Hydrological Cycle Between Cyclones and Anticyclones”; https://doi.org/10.1029/2023GL106187 and the supplementing study: “Key Role of the Ocean Western Boundary currents in shaping the Northern Hemisphere climate”; https://doi.org/10.1038/s41598-019-39392-y and ad this recent paper on the tug of war that could exist between wind driven gyre circulation and buoyancy driven subpolar convective cell: “Unraveling how winds and surface heat fluxes control the Atlantic Ocean’s meridional heat transport”; https://essopenarchive.org/users/845439/articles/1253016-unraveling-how-winds-and-surface-heat-fluxes-control-the-atlantic-ocean-s-meridional-heat-transport?commit=8fa70291b49e2db125e44cd17667989b58693e77 with this preprint that the gyres in the NOrth Atlantic could intensify: “Impact of the North Atlantic Oscillation on the subtropical and subpolar gyres”; https://essopenarchive.org/users/845439/articles/1233954-impact-of-the-north-atlantic-oscillation-on-the-subtropical-and-subpolar-gyres?commit=102ca64de12ef4ce516bfeb96ada50a6370f7289 –
Just want to say things could become messy up there and highly difficult to simulate as the AMOC in its processes is fully integrated in Earth system changes being often triggered from remote areas like the North Pacific – these intensifying ocean fronts could become a game changer…
But fully agree that this current could collapse, but somehow I have the feeling with all these data points that it is quite stable – here I collect AMOC changes: https://drive.google.com/file/d/1QmJjXa22GqqKIwI73At8nSqoWSXX6fCI/view?usp=drive_link
Guess the immanent first time sea ice free Arctic during summer will roll a new set of dice into the mess.
But what I really wonder is if there is enough Ice to destabilize the AMOC – never saw here a study, but could it be that known AMOC collapse events mostly happened when much more ice existed up there?
The cold blob is another issue, this new study thinks that only strong AMOC changes have n impact on the SST south of Greenland: “Nonstationarity of the Atlantic Meridional Overturning Circulation’s Fingerprint on Sea Surface Temperature”; https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL109789 – the last years the cold blob seems to vanish during winter, with this winter being gone – but would accordingly to the above study anyway no real meaning: https://earth.nullschool.net/#current/ocean/primary/waves/anim=off/overlay=sea_surface_temp_anomaly/orthographic=-22.41,34.10,526
Last some new studies on recent changes as the freshwater impulse from 2012-2017 or so shows now effects and we could see now a substantial weakening of the AMOC currently underway or not – nice real world experiment on AMOC stability I guess:
This study is a nice one consequences of the extreme freshwater impulse in the Irminger sea the most imortant deep convection site: “Recent Freshening of the Subpolar North Atlantic Increased the Transport of Lighter Waters of the Irminger Current From 2014 to 2022”; https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JC021184 – seems to me quite extreme an effect…
Then we have this data point: Convective mixing continued to deepen after 2015 because the 2012-2015 winter mixing events preconditioned the water column to be susceptible to deep convection in three more years. The progressively intensified 2012-2018 winter convections generated the largest and densest class of Labrador Sea Water since 1995. Convection weakened afterwards, rapidly shoaling by 800 m per year in the winters of 2021 and 2023. Distinct processes were responsible for these two convective shutdowns. In 2021, a collapse and an eastward shift of the stratospheric polar vortex, and a weakening and a southwestward shift of the Icelandic Low resulted in extremely low surface cooling and convection depth. In 2023, by contrast, convective shutdown was caused by extensive upper layer freshening originated from extreme Arctic sea-ice melt due to Arctic Amplification of Global Warming.
Intensification and shutdown of deep convection in the Labrador Sea were caused by changes in atmospheric and freshwater dynamics”; https://www.nature.com/articles/s43247-024-01296-9
Then I spoke with an oceanographer that in 2022 a shut down of deep convection happened – but here I do not know…
All these years I had the feeling that the observational results went into the direction of a more stable AMOC, but with these most recent changes due to the freshwater impulse and e.g. sea ice retreat all seems open to me as it does not look like that anyone can predict anymore what ill happen up there. Even an extreme increase in northward water transport driven by the atmosphere seems possible that triggers a sudden shut down of the AMOC caused by sudden extreme sea ice losses..
So its stays interesting up there…
All the best
Jan
p.s. sorry for the chaos, but Earth system changes are complex and interconnected :D
[Response: Yes, particularly if you look at short-term variability (months, years, decades) which is highly affected by weather and other vagaries of the atmosphere… Stefan]
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I would argue the AMO needs to be figured out before the AMOC, as much of the underlying AMO data is applied to infer what is happening with the AMOC — such as SSTs in inferring the gradients driving the AMOC flow.
Think in terms of AMO multidecadal change conflating with AMOC variability. A seeming collapse is only a slow transient that will eventually reverse according t historical AMO trends.
@Stefan Why is in these AMOC discussions never the deep ocean aka Antarctica Bottom Water (AABW) transport – current mentioned which is also slowing and connects with the AMOC later? According to the combined dataset for AABW which includes wind, thermal and meltwater it has slowed about twice as much as the AMOC.
Antarctic ice melt slows Deep Ocean Current with potential Impact on World’s Climate for Centuries https://climatestate.com/2023/04/16/antarctic-ice-melt-slows-deep-ocean-current-with-potential-impact-on-worlds-climate-for-centuries/
This paper from 2023 appears relevant and concluded with the following suggestion
Evolution of Atlantic Meridional Overturning Circulation since the last glaciation: model simulations and relevance to present and future https://royalsocietypublishing.org/doi/10.1098/rsta.2022.0190
Jan, from the abstract of the first paper I linked to above:
Oops, I guess I messed up the blockquotes. The second quote starts with Nevertheless, and the rest should be read as inline text.