Gabriel Oxenstierna, Ph.D
The Atlantic Meridional Overturning Circulation (AMOC) is one of Earth’s major ocean circulation systems—it redistributes heat on our planet and is a key driver of climate variability. There is a northward transport of heat throughout the Atlantic, comprising one quarter of the global heat flux (reaching a maximum of 1.3PW at 25°N).
Figur 1. AMOC is the Atlantic section of the global Meridional Overturning Circulation (MOC). One part of it is the Gulf stream, that transports heat northwards from the tropics.
The heat transport is a balance of the northward flux of the warm Gulf Stream, Ekman pumping, and southward fluxes of cooler thermocline, and cold North Atlantic deep water. The circulation is completed after a very long time as the deep waters rise to the surface again in the Southern Ocean. The turnover period of AMOC is many hundreds of years.
Forecasts of cascading tipping points
Several studies have found evidence that both the Gulf stream and the AMOC have weakened during the last 40 years or so.[1][2][3] One highly publicized report warns that a continued weakening would have “severe impacts” and increase the risk of “cascading problems” for other major Earth systems, “such as the Antarctic ice sheet, tropical monsoon systems and Amazon rainforest” – see the figure below illustrating the major climate crisis teleconnections related to AMOC.[4] Climate crise effects would occur in many other areas as well. Stormier weather, more floods, collapsed plankton production, and widespread oxygen death in the oceans (anoxia) are forecast. The issue of AMOC’s whereabouts is therefore of great interest.
Figur 2. AMOC is a centerpiece in the cascades of tipping points thought up by alarmist researchers.[4]
What the IPCC says
The IPCC AR6 report highlights AMOC as a main building block in the climate and that it potentially is one of the most important ‘tipping points’.[5] Over the years, the IPCC has had dramatic projections for the AMOC. In the latest climate report (AR6) they claim that the AMOC currently is at its weakest for the last 1600 years and forecast a dramatic future decline.
Figur 3. AMOC-flow anomalies according to IPCC model simulations. The thick grey and black lines are the history as simulated by the two latest model generations. The colored lines are forecasts from the models according to selected emissions scenarios. Flows are in Sverdrups (Sv, million cubic meters per second). Source: AR6 WG1 fig. 9.10, which is taken from [3]
The IPCC claims that AMOC is “very likely” to weaken over the 21st century under all emission scenarios.[ch 4.3.2.3] An almost monotonous reduction by 25 to 50 percent in 2100 is predicted, depending on which scenario is chosen.
IPCC only has “medium confidence” that there will not be an “abrupt collapse” before 2100. If it collapsed, the world’s weather patterns would be dramatically impacted.
Model fudging begets a history revision…
For the historical part, figure 3 is model based.[3] Comparing the modelled history in the older CMIP5 and the newer CMIP6 computer model ensembles, we see that AMOC is bumped up in CMIP6, especially during the second half of the 20th century up until 1990. As a result of this history revision in the models, the CMIP6 models now show a much more pronounced weakening from around 1980.
The revised history neatly fits the narrative that a decline in the AMOC is mainly caused by increased levels of greenhouse gases, i.e., that it is caused by anthropogenic global warming (AGW).
…but no decline seen in recent data from the Atlantic
Recently, we got an update from the measuring stations called RAPID, which directly measure the various flows that together constitute AMOC. RAPID measures AMOC at a series of stations, located at 26.5 N. The flows are measured in the Gulf Stream, another part is the Ekman transport, and finally the southbound return flow of different layers of cold water. These three components together form AMOC, see the red time series in the figure below (copied from the RAPID website).
Figur 4. Readings of the AMOC flows in Sverdrups (Sv). (A)MOC is the red curve with a flow of 16.8 ±4.6Sv. It comprises the Gulf stream (green, 31.3 ±3.1 Sv), the Ekman transport (black, 3.7 ±3.5 Sv), and the cold, deep southbound flow (lila, -18.2 ±3.4 Sv). The latest data are up until March 2022. Source: RAPID.
As can be seen from the figure, the AMOC did have a certain decrease at the very beginning of the RAPID measurement period, from 2004 until 2010, but after that AMOC is trend-stable. The Gulf stream shows a slight decrease, in line with the above-mentioned research, whereas the other components are stable. Volatility is also stable over time within a fairly large short-term variability.
Data collected directly in the Atlantic Ocean thus do not provide any support for the IPCC’s forecasts of an ongoing collapse of the AMOC.
IPCC’s forecasts disputed by field research
In recent years, a number of research reports have been published that put the IPCC forecasts into question.[6][7] Some of the researchers behind RAPID write that they can’t find any signs of a weakening AMOC during the last 30 years.[6] This is the very period where the revised history from IPCC claims there is a steep decline, due to their climate models. Reality vs. fiction.
The researchers write that AMOC rather seems to be “a decadal oscillation, which is superimposed on a multidecadal cycle”. Paleoclimatic records also show distinct multidecadal variability of the AMOC.
Which are then the dominant feedbacks and their associated timescales in AMOC’s natural variability? Is AMOC variability periodic, or quasi-periodic? The timescales, as well as the mechanisms behind these natural variations remain unexplained. This is no wonder, given the current’s extended turnaround time (100’s of years). The IPCC itself is not too sure about the state of the AMOC: “Given the large discrepancy between modelled and reconstructed AMOC in the twentieth century and the uncertainty over the realism of the 20th century modelled AMOC response (Section 3.5.4.1), we have low confidence in both.” (p. 9-32)
Summing up
- The model makers have managed to create an impression of a steeper decline in the AMOC from 1990 and onwards by manipulating the models from the CMIP5 to the CMIP6 model generations. This manipulation of the history fits the climate crisis narrative that a decline in the AMOC is caused by greenhouse gas emissions and AGW.
- The IPCC is not too convinced and gives a “low confidence” to the models. This doesn’t stop the IPCC from forecasting a sharp and monotonous decrease of the AMOC as “very likely“. They promote a climate crisis narrative entirely built on models they themselves give a low confidence rating.
- The issue of natural variability is pertinent to all discussions on the AMOC, but remains unresolved. This doesn’t stop the IPCC from giving the primary role in AMOC developments to the effects of greenhouse gas emissions and AGW.
- The empirical data on the water flows in the various strands of the AMOC in the Atlantic show no decline in the last 30 years. The AMOC is stable and doesn’t show any sign of decline.
References
[1] Robust Weakening of the Gulf Stream During the Past Four Decades Observed in the Florida Straits, Piecuch and Beal, 2023, https://doi.org/10.1029/2023GL105170
[2] Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation, Niklas Boers, Nature 2021, https://doi.org/10.1038/s41558-021-01097-4
[3] Aerosol-Forced AMOC Changes in CMIP6 Historical Simulations, Menary and 13 co-authors, 2020, https://doi.org/10.1029/2020GL088166
[5] IPCC SROCC “Extremes, Abrupt Changes and Managing Risks”, Chapter 6.7, https://www.ipcc.ch/site/assets/uploads/sites/3/2022/03/08_SROCC_Ch06_FINAL.pdf
[4] Exceeding 1.5°C global warming could trigger multiple climate tipping points, Armstrong McKay and 5 co-authors, Science 2022, https://doi.org/10.1126/science.abn7950
[6] A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline, Worthington and 5 co-authors, 2021, https://doi.org/10.5194/os-17-285-2021
[7] A stable Atlantic Meridional Overturning Circulation in a changing North Atlantic Ocean since the 1990s, Fu and 4 co-authors, Science 2022, https://doi.org/10.1126/sciadv.abc7836
Gabriel Oxenstierna is a PhD at Stockholm University and one of the Clintel signatories.
Models, all the way down. Again.
Moreover — unskilled, not-fit-for-purpose, “low confidence” models — along with unjustified-by-data “tuning” (again).
And revising history again, like the alarmists did with the temperature record, to demonize CO2 and promote the CAGW narrative.
Yes, and it’s the very same models that are used for making all the future scenarios, that are one of the main foundations for climate policies.
If the models fail with a fundamental aspect of our climate like the AMOC, they are not to be trusted in other aspects either. As the say themselves, “low confidence”.
They should also stick to modelling the distant past. Looking at figure 3, the modelled range was much tighter then.
Even the data had to be modeled! Garbage in, garbage in the middle, and garbage all the way out.
But even with their modeled data they show AMOC speeding up during the fossil fueled post war reconstruction and big v8 period – and when CO2 was rising roughly as fast as now.
The colour legend for figure 3 is mistaken, has switched the colours for Gulf and Ekman, and Ekman is green not black.
Great post still.
Just a thought, what would a huge windfarm polluted coast off the US do to the AMOC? Would the prevailing winds being interfered with, slow down surface currents, so that green fascists have a self-fulfilling prophecy?
In June 2022 we entered a Grand Solar Minimum. The last GSM, the Maunder Minimum ran from approximately 1645 to 1715. The predominant effect on the weather was cold and excessive precipitation in all its forms, rain, hail, sleet, snow. This resulted in crop destruction, starvation of people and animals, great hardship and death. Currently 1 acre of land produces 7 times the crop that a similar acre produced in the Maunder Minimum. That is how we feed the massive population.
Great cold and hardship is coming just as it did around 1300AD and the MM. Now it’s our turn.
You need to think on.
“Currently 1 acre of land produces 7 times the crop that a similar acre produced in the Maunder Minimum.”
Written as though sun and temperature were primary causes.
S. Rahmstorf’ hobby horse, the AMOC decline… 😀
The latest one, 8/23
The AMOC: tipping this century, or not?
A few weeks ago, a study by Copenhagen University researchers Peter and Susanne Ditlevsen concluded that the Atlantic Meridional Overturning Circulation (AMOC) is likely to pass a tipping point already this century, most probably around mid-century. Given the catastrophic consequences of an AMOC breakdown, the study made quite a few headlines but also met some skepticism. Now that the dust has settled, here some thoughts on the criticisms that have been raised about this study.
“likely”
Very scientific.
“most probably around mid-century”
Conveniently “over the horizon” for those making the predictions..
Well done! The sober view of the little-understood AMOC that is presented here is a good antidote to the alarmist presentations on ever-present climate change that permeate most media reports. What often betrays the lack of scientific expertise in such presentations is the misattribution of the wind-driven Gulf Stream to much slower thermohaline effects, which are of lower order as physical drivers. As long as Earth continues to spin and winds blow we will have the Gulf Stream conveying warm water northward and eastward, no matter what its density.
did IPCC explained what is the connection between the greenhouse emission with the variation of the ocean circulation? is thrr a sort of mechanism that relates both fenomenon? on what are the models based?
Magic. The high priests of the climate cult are the only ones that can channel the magic, interpret and counter the evil magic spewing forth across the land and harness the power of unicorn farts to save their chosen followers.
They simply ASSUME it. There is now, not only no data proving their speculation about the properties of CO2 (i.e , that it can CAUSE, via any mechanism, not by alteration of the AMOC or by ANY physical mechanism, meaningful shifts in the climate zones of the earth),
there is now, years of ANTI-data making it highly likely that their conjecture is wrong:
CO2 EMISSIONS UP GREATLY. WARMING NOT.
Game over.
(as Richard Page said in other words)
They get the oceans wrong (AMOC). They get the atmosphere wrong (Tropospheric Hot Spot). They get the land wrong (UHI). Just where does CliSciFi get it right?
Sadly, what the Alarmists have gotten “right” is funding of their house of cards.
“Right” as in “good at”, not “correct”.
“what is the connection between the greenhouse emission with the variation of the ocean circulation?”
I would say “magic” but Richard already beat me to it.
There is no established connection between CO2 and this circulation. It’s all pure speculation, and not very good speculation at that.
So what you are saying is they are liars. Just say that.
Fudging, misdirection and weasel words aside, yes.
You have to allow for the possibilty that they are True Believers and actually believe what they say. Humans can be very good at fooling themselves sometimes. And, in today’s world, they have a lot of assistance in believing false narratives, promoted by the Mass/Leftwing Media.
The other alternative is they are liars.
It’s one or the other because what they say has no basis in fact.
No. Belief has nothing to do with it. Telling lies is being a liar. Period. Full stop. End of debate. A lie is a lie, they have been telling lies for decades.
There might be a slight possibility that they are not always really true believers, might even have some doubts, but to admit that would mean no publications and loss of job. However, I’m not going to bet on it. 🙂
As 2hotel9 implied, whether they are true believers or grifters, they have lied; as in what they say has been proven to have no basis in truth or reality. Their motivations may be many, varied and complex but, objectively, they are telling lies and have been caught doing so. The shameful part is that, once caught in a lie, they seem to double down rather than admit it’s wrong.
“As 2hotel9 implied, whether they are true believers or grifters, they have lied”
I agree they have not told the truth, but I’m talking about motivation here. If someone thinks they are telling the truth, even though it is not true, it’s not a deliberate lie, it is a mistake.
This is a well presented article. It appears that WUWT is a place where facts can get oxygen.
Could this paper ever make it to modern “scientific” journals?
Thanks Rick, much appreciated!
Ya, might be an idea to search for publication with a deepened study into how the IPCC got into this rabbit hole of tipping points related to AMOC and esp. the subpolar ocean gyres. I think it started with the IPCC report in 2013, continued with the SROCC report, based on a range of papers published around 10 years ago.
Scale creep. Every time they release a paper or a report it has to top the previous one or their alarmism goes into reverse. As more and more wild claims are put out they steadily grow more and more shrill and outlandish – the IPCC now has a tiger by the tail and no way of letting go.
That’s why those computer models keep getting hotter. It’s necessary to have ever new scary stories about the climate in order to keep the public in a panic and keep the money rolling in.
if their new computer models predicted less warming, then they might as well close up shop. So they are not going to do that.
It’s always going to be “worse than we thought” when it comes to climate alarmist predictions. It’s their “bread and butter”.
Interesting stuff on AMOC here too
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080940
Haven’t they discovered CO2 will stop the Coriolis effect?
Who you going to believe; your lying eyes, or climate modelers with their nearly perfect record for predicting climate disasters!? Is climatology closely linked to economics? Besides the grift, I mean!
Looking at:
a) the tortuous, pole-to-pole paths indicative-only of average major flow directions of ocean currents comprising the overall AMOC, as shown in Figure 1, and reasoning that each of these currents must vary considerably in actual geographic position as the NH-SH seasons (and associated weather) shift over the course of a one-year Earth orbit,
b) the SH coupling of those Atlantic Ocean currents with Antarctic Ocean currents, and thus with Pacific Ocean and Indian Ocean circulation currents, as shown also in Figure 1, and
c) the combined variability and measurement uncertainty of flow measurements of just a few of the major component currents contributing to the AMOC (±10-20%), as indicated in Figure 4 (with evidence of a quasi-periodic signal component of one-year period visible in all four plotted parameters), one can easily see that modeling such will be tantamount to GIGO and that none of the science in this matter is “settled”.
Predicting “tipping points” if one understands the above issues? . . . PFFTHFPTH !
Data? What do you mean by data? This are raw measurement instrument numbers and require to be fully computer aligned to our model before they can be considered as Data /sarc
Feeling dense, didn’t the last collapse require the draining of Lake Agassiz?
Since I’ve been hearing of the potential of the collapse since High School in 1990, I’m giving up that it will happen in my lifetime.
That is certainly one theory although, it should be said that we are still only hypothesising that the AMOC actually collapsed at that point – there is veey little evidence to say definitively that it actually occurred.
Ugh ‘very’. I want the edit button back.
Please!
Not to worry Richard, my old eyes saw very, I had to go back to see the problem.
“In the latest climate report (AR6) they claim that the AMOC currently is at its weakest for the last 1600 years and forecast a dramatic future decline.”
They were measuring the AMOC 1600 years ago? Yeah, right. They knew what the AMOC was doing in 423? That is really hard to believe. The chart only goes back 173 years.
Which is, in itself, a big red flag – long-term direct observational data of the AMOC really only started in 2004 although there were readings taken in 1957 and 1981. 173 years? More like about 60 years.
This is from research quoted by IPCC, in SROCC chapter 6.7, and it’s based on proxy records:
“Palaeo-proxies also highlight that the historical era
may exhibit an unprecedented low AMOC over the last 1,600 years
(Sherwood et al. 2011; Rahmstorf et al. 2015; Thibodeau et al.
2018; Thornalley et al. 2018).”
Apparently paleo-climate proxies are fine for things like the AMOC. However, paleo-climate temperature proxies are wrong because they show that it was warmer in the past. One wonders how the Earth managed to survive all those tipping points.
Paleoclimatology proxies also show that Earth previously had atmospheric CO2 concentration levels 8-10 times higher than today’s level of 420 ppm . . . and yet Earth survived, indeed flourished, and self-recovered from such levels without there being any tipping points or runaway climate catastrophe.
Of course, the IPCC dare not mention such science-based evidence regarding Earth’s climate resiliency.
“They were measuring the AMOC 1600 years ago?”
That was my first thought, too. 🙂
It would be comical, if it wasn’t for the fact that these wild predictions have such dire consequence for society, causing Western politicians to ruin their economies trying to control the AMOC by trying to control CO2.
No connection has ever been made between CO2 and any weather phenomenon on Earth, and that includes any connection to the AMOC.
Story Tip
The UHI is very clear in some of the satellite images here but no mention of how this affects global temperature or UK records.
Maybe it could be used to adjust temperature records to account for UHI?
I have low confidence in the IPCC.
That’s more than I have.
Very nice post. I will add AMOC decline to my short list of big failed predictions.
I thought Piltdown Mann proved that the ocean cycles don’t exist and that all variations are co2 and gremlin caused
Another effective rebuttal to claims of AMOC collapse was published in July:
https://www.sciencemediacentre.org/expert-reaction-to-paper-warning-of-a-collapse-of-the-atlantic-meridional-overturning-circulation/
For example:
The RAPID programme (see diagram at top) measures daily flows of water at several depths between the North Atlantic and Arctic oceans, and its scientific coordinator, Prof Meric Srokosz, National Oceanography Centre, University of Southampton, said:
“While the possible collapse of the AMOC with significant climatic impacts is a concern, providing a warning of its collapse is problematic as a long set of observations is required. In this paper the warning depends on using proxy AMOC data (here based on sea surface temperature, SST) as direct continuous AMOC measurements are only available since 2004. The warning comes from applying statistical techniques to a long time series (over a century) of proxy AMOC data, but the warning is only as good as the proxy data are in representing the true AMOC. So, this warning needs to be treated with caution as there is no consensus as to which proxies can accurately capture the behaviour of the AMOC over the long term.”
My synopsis:
https://rclutz.com/2023/07/26/no-cnn-gulf-stream-is-not-collapsing/