Opinion: The AMOC is weakening &ndash; time to take the evidence seriously

Rahmstorf, Stefan; Caesar, Levke

doi:10.5194/egusphere-2026-2110

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https://doi.org/10.5194/egusphere-2026-2110

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21 Apr 2026

| 21 Apr 2026

Opinion: The AMOC is weakening – time to take the evidence seriously

Stefan Rahmstorf and Levke Caesar

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) is a critical component of the climate system. Climate models have long predicted a slowing of the AMOC due to anthropogenic forcing, with a risk of passing tipping points in the future. The question of whether the AMOC is already weakening in response to global warming is still somewhat controversial. Continuous monitoring is only available for the past two decades, a period too short to tease apart contributions of natural variability and climate change. Reconstructions of AMOC strength going back further in time have different limitations which are debated in the literature. Here we review the state of this discussion. We conclude that the balance of multiple lines of evidence strongly supports a past and ongoing AMOC slowing in response to global warming.

Received: 13 Apr 2026 – Discussion started: 21 Apr 2026

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Stefan Rahmstorf and Levke Caesar

Status: final response (author comments only)

CC1:
'Trusting projections of the AMOC weakening is difficult…', Luis G. Lopez-Lemus, 22 Apr 2026

🖇️ Trusting projections of the Atlantic Meridional Ocean Circulation (AMOC) weakening is difficult because of significant discrepancies between observational data and climate model outputs regarding its historical trend:
https://doi.org/10.1038/s41467-024-55297-5
While the IPCC reports have indicated a weakening, the confidence in these findings have varied, and recent climate models (CMIP6) have shown a slight strengthening over historical periods, contrary to some proxy data suggesting a decline…
https://lnkd.in/gXDqSxSU
Studies investigating such weakening are based on so-called 'hosing' model experiments 'adding' freshwater to the entire North Atlantic to simulate ice melt, to document its effect on the AMOC, although this recent study highlights the limitations of these experiments and ways to make them more realistic…
https://doi.org/10.1016/j.ocemod.2025.102599
This observation-model discrepancy, along with the large natural variability of the AMOC and challenges in calibration, makes future AMOC projections uncertain and highlights the need for more direct observations and improved models, such as those from current monitoring programs.
https://lnkd.in/geMNxN7a

https://lnkd.in/gd3BiAWM

https://lnkd.in/gSBwRq6q

Citation: https://doi.org/10.5194/egusphere-2026-2110-CC1
- CC2:
  'Reply on CC1', Stefan Rahmstorf, 23 Apr 2026
  
  Future projections, e.g. by the CMIP6 models for the last IPCC report, are generally not hosing experiments, they don't have any freshwater added. See our Drijfhout et al. 2025 paper on the fate of AMOC in these CMIP6 projections:
  https://iopscience.iop.org/article/10.1088/1748-9326/adfa3b
  To reduce uncertainty in future projections, models can be compared to observations to find out which of the models are most realistic (so-called observational constraints), and that is what the recent Portman et al. 2026 study has done:
  https://www.science.org/doi/10.1126/sciadv.adx4298
  Hope that helps!
  
  Citation: https://doi.org/10.5194/egusphere-2026-2110-CC2
  - CC3: 'Reply on CC2', Luis G. Lopez-Lemus, 23 Apr 2026
    
    —Sure, both references are great … thank you!
    
    Citation: https://doi.org/10.5194/egusphere-2026-2110-CC3
RC1:
'Review of egusphere-2026-2110', Anonymous Referee #1, 08 May 2026

I have major concerns centred on the suitability and the selective content of this manuscript. I do not think that the Ocean Science journal is an appropriate place for an article with content as unbalanced as this.

Major Shortcomings:
The title tells us that the manuscript is an opinion, and this has two problems. First: a manuscript in which the authors claim to review the state of a scientific discussion but under the banner of ‘Opinion’ choose to highlight only the papers they feel sit well with their narrative, doesn’t fulfil the criteria of scientific excellence which is required for publication in this journal.
Second: It is not clear what the the opinion actually is – is it the statement in the title and the final sentence, claiming that someone is not taking evidence seriously? If so, who is that someone? What is meant by taking it seriously? There is no explanation about these statements, no evidence to support them, no view of what the alternative should look like.
The first paragraph of the Introduction makes a statement that there is widespread perception that evidence for AMOC weakening is inconclusive, so here it looks like the opinion may anyway be that all statements like that are wrong. The paper then sets out a story using papers that are in line with their opinion that the AMOC has weakened since the mid 20^th century, ignores other papers that dispute the lines of reasoning, and either omits or dismisses the scientific validity of published journal papers that show evidence that is not in line with the opinion. The incomplete selection of papers mentioned makes it unsuitable for publication in its present form in this journal.
There is certainly a place for a review of the state of knowledge of whether the AMOC has weakened in the past 100 years or so - a review that brings clarity by carefully bringing together all the available evidence. But this manuscript does not meet that need because it is selective and biased in content.
Expanding on the major shortcoming that this being a one-sided collection of papers, next I highlight the key areas where this is most obvious.
The ‘cold blob’ and temperature fingerprints. The authors fail to mention most of the studies that provide evidence of other causes of surface temperature change in the subpolar gyre, or that provide evidence that the link between surface temperature in the SPG and the AMOC is model-dependent and highly questionable. The small number of papers they chose to mention are dismissed as having weaknesses that make their evidence unimportant. They don’t comment on the major differences between the left and right panels in Fig 2. This is a very selective effort that does not review all evidence in the literature.
Under salinity fingerprints some of the statements are evidenced by publications, but there is no mention of papers that provide evidence of mechanisms that have led to increased salinity north of the Gulf Stream and lower salinity in the pathway of the North Atlantic Current and in the gyre, not all of which are AMOC related and instead involve Arctic waters.
The discussion of reanalysis products comes closest to acknowledging that there is mixed evidence for decline in the AMOC since the 1950s. But instead of saying that, the authors choose to dismiss reanalysis products are unreliable and therefore “not yet suited to reconstruct the past AMOC”. It is inconsistent to make this argument for reanalyses yet not for subpolar surface temperature.
In the Proxy data section the authors fail to cite the other studies that do not support their story.
Additional specific comments:
l25-26, the speculation of a continuation for another 80 years of the trend in the AMOC recorded at 26°N over 20 years has no evidence to support it. It would be better presented as a plausible scenario in the context of other plausible scenarios.
I find many of the trend lines in Fig 3 unevidenced and unconvincing. In some cases the authors have applied smoothing to the data originally reported in the cited papers which has acted to create a trend where none was reported by the original papers. In all cases they have removed any quantification of uncertainty that was reported in the original papers, and so the reader has no indication that some of the trends cannot be viewed as robust. The time series in this figure have been carefully curated to fit the narrative, with any evidence that goes against it excluded or not commented on.
Under the section “Is there evidence against an AMOC slowing” the opinion takes a strange turn. The authors seem to be saying that statistical significance is irrelevant in the case of time series that show no significant trend, and that any trend negative against time is good enough to support their argument that there has been a decline. This allows Rahmstorf and Caesar to disagree with the careful analysis of original authors that state there is no evidence of weakening in their own data. The argument is dressed up as a lesson in interpreting statistics, but the evidence given to support their concluding remarks is weak at best, and could be construed as misleading.

Citation: https://doi.org/10.5194/egusphere-2026-2110-RC1
- CC4: 'Reply on RC1', Luis G. Lopez-Lemus, 09 May 2026
  
  —I concur…
  
  Confidence in projections regarding the weakening of the Atlantic Meridional Overturning Circulation (AMOC) remains limited due to substantial discrepancies between observational data and climate model outputs concerning its historical trends.
  https://doi.org/10.1038/s41467-024-55297-5
  While reports from the IPCC indicate a weakening trend, the certainty of these findings varies. Recent climate models (CMIP6) have demonstrated a slight strengthening during historical periods, which contrasts with certain proxy data suggesting a decline.
  https://lnkd.in/gXDqSxSU
  Studies investigating this weakening utilize so-called 'hosing' model experiments, which involve 'adding' freshwater to the entire North Atlantic to simulate ice melt and document its effect on the AMOC. However, recent research highlights the limitations of these experiments and proposes methods to enhance their realism.
  https://doi.org/10.1016/j.ocemod.2025.102599
  The discrepancy between observations and models, combined with the significant natural variability of the AMOC and calibration challenges, renders future AMOC projections uncertain. This underscores the necessity for more direct observations and improved models, such as those derived from current monitoring programs.
  https://lnkd.in/geMNxN7a (https://lnkd.in/geMNxN7a)
  
  https://lnkd.in/gd3BiAWM (https://lnkd.in/gd3BiAWM)
  
  https://lnkd.in/gSBwRq6q (https://lnkd.in/gSBwRq6q)
  
  Citation: https://doi.org/10.5194/egusphere-2026-2110-CC4
- AC1: 'Reply on RC1', Stefan Rahmstorf, 27 May 2026
  
  We thank the reviewer for these comments and are happy to provide a first response.
  We note that our article is an opinion article and thus not a comprehensive review paper. It therefore presents our assessment of the balance of evidence in the scientific literature, without being able to discuss everything. We would welcome if the reviewer mentions which further paper(s) they would have liked us to discuss.
  Regarding Fig. 3, the LOWESS smoothing of data is a standard technique if the longer-term evolution is of interest rather than short-term variability. The linear trend lines shown in the figure are in all cases computed from the original unsmoothed data. We did not “create a trend”. For full transparency and reproducibility, all analysis scripts and data sources used are publicly available in our GitLab repository as linked in our manuscript and can be independently inspected and reproduced by interested readers.
  Concerning the combination of evidence from multiple independent sets of uncertain data, the established approach is known as Bayesian inference, in honour of Thomas Bayes who developed the basic theorem in the 1740s. A good explanation with the formula to compute the probability of a hypothesis in view of various data is e.g. found on Wikipedia.
  For a simple illustration, let us just distinguish two hypotheses for AMOC change: AMOC has slowed or it has increased (neglecting the infinitesimal chance that the trend is exactly 0.00 Sv/decade).
  If we have no evidence, both are equally likely and the prior probability is 50% for both hypotheses.
  Now let’s assume we have three independent data sets, each suggesting a 75% probability that AMOC has weakened. Those three independent lines of evidence could e.g. be the northern Atlantic ‘cold blob’, the ‘salinity pile-up’ in the subtropical South Atlantic and the northward Gulf Stream shift (in reality there's more lines of evidence).
  Accounting for these three strands of evidence, the posterior probability according to Bayes’ Theorem then is:
  P(AMOC slowing | 3 data series) = 0.5 * 0.75^3 / (0.5 * 0.75^3 + 0.5 * 0.25^3) = 0.96
  In other words, the three data sets combined imply a 96% chance that AMOC has slowed (which is “extremely likely” in IPCC terms), despite each data set by itself being far from significant at the 95% level.
  We thank the reviewer for the opportunity to clarify our arguments.
  
  Citation: https://doi.org/10.5194/egusphere-2026-2110-AC1
CC5:
'Comment on egusphere-2026-2110', Michael Mayer, 12 Jun 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2110/egusphere-2026-2110-CC5-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2026-2110-CC5
- AC2: 'Reply on CC5', Stefan Rahmstorf, 15 Jun 2026
  
  Thank you for this helpful comment! We will take this into account when revising the manuscript.
  
  Citation: https://doi.org/10.5194/egusphere-2026-2110-AC2
- CC7:
  'Reply on CC5', Jens Terhaar, 15 Jun 2026
  
  I would not have submitted this comment had our paper (Terhaar et al., 2025) not been explicitly discussed in the open review discussion around this preprint. In the first part of this comment, I therefore address the question of uncertainties in air-sea heat flux estimates from reanalysis products and their implications for the reconstruction of Terhaar et al. (2025), including an extended multi-product reconstruction. Since our paper also examined SST-based AMOC reconstructions, I use this opportunity in the second part to discuss uncertainties in this proxy that, in my view, have not been adequately acknowledged in the paper under discussion or in Caesar et al. (2018).
  
  Citation: https://doi.org/10.5194/egusphere-2026-2110-CC7
  - CC8: 'Reply on CC7', Michael Mayer, 16 Jun 2026
    
    The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2110/egusphere-2026-2110-CC8-supplement.pdf
    
    Citation: https://doi.org/10.5194/egusphere-2026-2110-CC8
    
    CC9: 'Reply on CC8', Jens Terhaar, 17 Jun 2026
    
    I am aware that this response is longer than it probably should be, and not as concise as I would have liked, but it is the best I could manage before the discussion closes, and despite its length I believe it is a clear and well-argued reply to the points raised.
    
    Citation: https://doi.org/10.5194/egusphere-2026-2110-CC9
CC6:
'Comment on egusphere-2026-2110', Susanna Winkelbauer, 12 Jun 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2110/egusphere-2026-2110-CC6-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2026-2110-CC6
- AC3: 'Reply on CC6', Stefan Rahmstorf, 15 Jun 2026
  
  Thank you for this helpful comment! We will take this into account when revising the manuscript.
  
  Citation: https://doi.org/10.5194/egusphere-2026-2110-AC3
RC2:
'Comment on egusphere-2026-2110', Anonymous Referee #2, 16 Jun 2026
Review of “Opinion: The AMOC is weakening – time to take the evidence seriously” by Rahmstorf and Caesar
Overview
The authors present a summary of the AMOC literature, arriving at the conclusion that the AMOC has weakened by about 2 Sv +/- 1 Sv since the mid 20^th century (line 255). The authors contend that the significance of this trend becomes apparent when combining many different lines of evidence, despite each individual line of evidence not exceeding traditional significance thresholds. The manuscript is structured by proceeding through each group of measurements and discussing their findings, and then compiling their results in a discussion and conclusions section at the end.
I found the manuscript to be thought-provoking but not convincing. If indeed the various streams of AMOC data can be considered statistically independent from one another, then the combination of their results is a powerful tool that could be leveraged to tease out a coherent signal from the noise. Thus I find the approach the authors use to be compelling. However, the execution of this approach is insufficient to prove their point, and the analysis presented herein is not close to meeting the level of scientific rigor required of a peer-reviewed manuscript. I also found the presentation and writing to be lacking, and I elaborate on these points below.
In essence, the authors are making a quantitative argument without doing the necessary analysis, and then framing it as an opinion. The topics discussed in this manuscript are not subject to opinion – they are inherently quantitative and thus the topic is not suitable to an opinion piece. If the article were written in a way that explains why the authors believe the current literature on AMOC proxies leans towards detection of a decline, that would be an opinion. But the authors are instead trying to make the case that the AMOC decline is now statistically significant, a claim that - if true - has big ramifications for the field and is also entirely quantifiable. I would encourage the authors to conduct the necessary analysis to test this hypothesis.
If the authors decide to pursue this quantitative assessment, then they need to ensure the following conditions hold:
The compilation of AMOC indices must be comprehensive and rigorous. The data should not be cherry-picked from available AMOC reconstructions, as is done in this current manuscript under discussion.

The various lines of evidence must be statistically independent, and the noise in their relationship must be uncorrelated.

Unfortunately, I found that the authors did not compile a comprehensive list of evidence, repeatedly discarding information that contradicts their hypothesis of a declining AMOC for insufficient reasons, and neglecting other, more comprehensive, compilations of AMOC time series that have already been published. Furthermore, the authors made no attempt to demonstrate the second point, that any of these data are statistically independent from one another. In fact, the opposite is likely true, that many of the lines of evidence presented in this summary are correlated to one another, and thus this meta-analysis approach to look at coherent signals is faulty unless the cross-correlations are properly estimated. Thus, ultimately I disagree with the authors, I do not believe the combination of AMOC indices demonstrates that there is a statistically significant decline of the AMOC. For the above-mentioned reasons, I recommend the paper be rejected.

Major issues identified
I will first elaborate on the point #1 presented above, that the authors used only a subset of available AMOC reconstructions. I start by pointing the authors to a list of relevant papers that were not included in the current manuscript, then I discuss why the authors’ attempt to discard some of the indices they do cite is not justified. I then elaborate on the lack of uncertainty quantification in the paper, and identify a few major citation issues in the text. I then list some minor edits the authors should consider if they decide to pursue publication elsewhere.
Relevant papers not included in this meta-analysis:

There are three reviews that would be a good starting point for this meta-analysis (organized in chronological order):
Frajka-Williams E, Ansorge IJ, Baehr J, Bryden HL, Chidichimo MP, Cunningham SA, Danabasoglu G, Dong S, Donohue KA, Elipot S, Heimbach P, Holliday NP, Hummels R, Jackson LC, Karstensen J, Lankhorst M, Le Bras IA, Lozier MS, McDonagh EL, Meinen CS, Mercier H, Moat BI, Perez RC, Piecuch CG, Rhein M, Srokosz MA, Trenberth KE, Bacon S, Forget G, Goni G, Kieke D, Koelling J, Lamont T, McCarthy GD, Mertens C, Send U, Smeed DA, Speich S, van den Berg M, Volkov D and Wilson C (2019) Atlantic Meridional Overturning Circulation: Observed Transport and Variability. Front. Mar. Sci. 6:260. doi: 10.3389/fmars.2019.00260

Moffa-Sánchez, P., Moreno-Chamarro, E., Reynolds, D.J., Ortega, P., Cunningham, L., Swingedouw, D., Amrhein, D.E., Halfar, J., Jonkers, L., Jungclaus, J.H., Perner, K., Wanamaker, A. and Yeager, S. (2019), Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review. Paleoceanography and Paleoclimatology, 34: 1399-1436. https://doi.org/10.1029/2018PA003508

Jackson, L.C., Biastoch, A., Buckley, M.W., Desbruyères, D., Frajka-Williams, E., Moat, B., and Robson, J. The evolution of the North Atlantic Meridional Overturning Circulation since 1980. Nat Rev Earth Environ 3, 241–254 (2022). https://doi.org/10.1038/s43017-022-00263-2

These three papers summarize many AMOC reconstructions that were not included in the current analysis. In addition, I point the authors to two special issues focused on the AMOC:
An AGU special issue in Reviews of Geophysics and JGR-Oceans: (https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)1944-9208.AMOC)

A Royal Society special collection: (https://royalsocietypublishing.org/rsta/issue/381/2262).

Should the authors decide to resubmit an updated version of this manuscript elsewhere, I recommend they consult a wider group of AMOC experts to ensure that they comprehensively review the literature rather than select a small subset of papers. The papers mentioned here may not be comprehensive, after all, they are just based on one person’s knowledge of the literature. A wider group of experts should be consulted to provide a rigorous assessment for this meta-analysis framework.
Other (non-review) papers that should be included in a meta-analysis (some of which are reviewed in the review papers cited above, but not all): Grist et al. (2009); Josey et al. (2009); Lozier et al. (2010); Meinen et al. (2013); Grist et al. (2014); Williams et al. (2014); Hummels et al. (2015); Mercier et al. (2015); Delworth et al. (2016); Jackson et al. (2016); Karspeck et al. (2017); Rossby et al. (2017); Chen and Tung (2018); Våge et al., (2018); Desbruyères et al. (2019); Jackson et al. (2019); Rossby et al. (2020); Tsubouchi et al. (2021); Smedsrud et al. (2022); Årthun et al. (2023); Chidichimo et al. (2023); Le Bras et al. (2023); Wett et al. (2023); Årthun et al. (2025); Fox et al. (2026); Hans et al. (2026)

2. Papers discarded for unjustified reasons:
The authors also cite a few papers that they believe should be discarded from this meta-analysis. Notably, no papers that found a decline in the AMOC were discarded. Each of these papers that were discarded (Fraser and Cunningham, 2021; Li et al., 2021; He et al., 2022; Rossby et al., 2022; and Terhaar et al., 2025) either disagree about the suitability of the subpolar SST index derived in Rahmstorf et al. (2015) and Caesar et al. (2018), and/or find no decline in the AMOC. Fraser and Cunningham (2021) and Rossby et al. (2022) were discarded due to issues with historical data coverage and knowledge of a level of no motion. No information was presented in this current manuscript under discussion to make the case that data coverage was indeed inhibiting the interpretation of these results, and thus without compelling evidence to remove these results from the record, there is no reason to discard them. In fact, the data used in Rahmstorf et al. (2026) to reconstruct the ocean heat content in the subpolar North Atlantic are the same that are used in Fraser and Cunningham (2021).
Furthermore, the case for removing Li et al. (2021) and He et al. (2022) was confounding – the authors claim that these papers should be discarded because they use slab ocean models without an active ocean circulation. That is indeed the point of those papers – that they can recreate the warming hole without ocean advection, and thus the divergence of oceanic MHT is not required to recreate the subpolar warming hole. Using that choice of methodology as reason to discard these papers is not justified.
The case for removing Terhaar et al. (2025) from consideration was due to the quality of the reanalysis surface heat flux data as well as the lack of an OHC tendency term in the budgets. Similar to the point raised above regarding the historical OHC data, these same surface heat flux data are used in Rahmstorf et al. (2026) as well as Li et al. (in review), which was co-authored by lead author Rahmstorf. In the latter paper, the authors used these data to reconstruct the AMOC through the Wålin water mass transformation framework. The authors find a decline in the AMOC (which appears due to the addition of mixing, not from the surface fluxes), yet the authors of the current paper under discussion do not question those results. Regarding the lack of an OHC tendency term in the Terhaar et al. (2025) paper, those authors show that if the OHC tendency term were included, it would lead to a stronger AMOC increase in their reconstruction. Hence the title of the paper ends with “indicates no decline since the 1960s”; the authors cannot rule out an increase using their methods due to their lack of an OHC tendency term.
To conclude this section, the authors of the manuscript under discussion did not include important AMOC proxies in their analysis, and did not make a compelling case of why removing certain AMOC proxies that disagreed with their premise was valid. Thus it is not surprising that the proxies remaining proxies in their meta-analysis consist of a subset of AMOC indices that demonstrate a declining trend.

3. Lack of uncertainty quantification
I found that the current manuscript also misconstrued the uncertainty in previous work. Figure 3 was especially problematic in this regard because there were no estimates of uncertainty and the authors applied a smoothing filter that changed the time scale of the reconstructions. Given the importance of uncertainty to the underlying motivation for this paper, I was surprised to see a meta-analysis of these different metrics without any accompanying estimates of uncertainty. To this point, at least three of the authors of the proxies shown in Figure 3 clearly identify that the declines in their estimates are not statistically significant given the noise in the relationship (e.g. Frajka-Williams, 2015; Worthington et al. 2021; Chafik et al., 2022), yet their time series are reproduced here without error bars and temporally smoothed, which gives the impression that there is a statistically significant decline. Given that the suitability of these AMOC proxies are often time-scale dependent (e.g. Terhaar et al., 2025), applying a smoothing filter that is not used in the original work is misleading.
Figure 4 is similar in this regard. It also does not show uncertainties (with the exception of Thornalley et al. (2018) subsurface T), and the y-axis only refers to relative strength of the AMOC. Thus without a quantitative y-axis, it is hard to interpret the statistical significance of the declines shown. I.e., is the variability in each time series consistent across proxies? And are each of the proxies similarly related to the AMOC? This figure also omits a large data set of historical proxies compiled in Moffa-Sanchez et al. (2019) these data largely disagree with the findings shown here.

4. Incorrect citations:
I also found that the text repeatedly cited incorrect papers. Some of these errors can be easily corrected by changing the citations, while some of the claims in this paper are simply not justified by the literature (of which I am aware). It should be noted that for two well-established authors to repeatedly reference information that is not supported by the cited papers goes beyond sloppy writing – it seriously undermines the scientific process.
An example of an easily fixed error appears on lines 64 and 210: the authors reference Zhang (2008) as evidence that the Gulf Stream shifts northward to conserve vorticity when the AMOC weakens. In fact, Zhang (2008) make no mention of vorticity conservation. The correct references for that work would be: Zhang and Vallis (2007), Joyce and Zhang (2010), and/or Peña-Molino and Joyce (2008). I was not as concerned with this error as the ones that follow because the correct lead author was acknowledged (but the authors should be careful to cite the correct paper by the lead author).
A more problematic error was on line 142, when the authors cite Majumder et al. (2016) as an example of a paper that found “an accelerated weakening of the Atlantic overturning circulation since the 1980s”. This is categorically untrue – that information is not in that paper.
And on lines 183-185, the authors cite Forget et al. (2015) as identifying an AMOC decline in ECCO-v4r4. I was unable to identify any mention of such a trend in that paper (not even a statistically insignificant one). Similarly, the authors cite an AMOC decline in GLORSY12V1 from Lellouche et al. (2021). Instead, Jackson et al. (2019) report almost no trend in these products from 1993-2016 (see their Fig. 11h).
Another citation issue is in the caption of Fig. 3: multiple papers were cited in the caption for unknown reasons because their time series were not included in the figure (e.g. Kanzow et al. 2010; Stepanov and Haines, 2014; Wett et al., 2023; Dotto et al., 2025). Some of these figures were cited next to time lags, so it was unclear if that time lag is what is being referenced. For example, Dotto et al. (2025) finds an increase in the volume transport in the eastern subpolar gyre, and the authors note that this could take ~10 years for this trend to show up in the AMOC. But the current paper under discussion cites Dotto et al. (2025) as evidence that it takes 10 years of lag for “productivity signals” to appear, which does not make sense given the content of Dotto et al. (2025).

Minor edits identified
Fig. 2: I do not see the similarity between panels a and b that the authors reference. Instead, I see opposing signs between the two panels in the key regions near the Grand Banks (red in panel a and blue in panel b). Another interpretation of the SST dipole between the subtropical and subpolar gyres is the North Atlantic Oscillation (Hurrell, 1997; Deser et al., 2010).
Fig. 3: Are the lags used from the papers cited or from the current authors’ opinion on what the lag should be? If the latter, it is disingenuous to reproduce someone else’s AMOC reconstruction with an altered time axis. At the very least, there should be large caveats provided in the caption showing where this reproduction of the given AMOC index differs from that provided in the original paper.
L. 131-134: I do not understand what the authors are arguing here. That there has been a long-term freshening in the eastern subpolar North Atlantic?
L. 144: Zhu et al. (2023) also demonstrate that the subpolar SST index has no statistically significant trend, but that part seems to be omitted from this sentence.
Section 8. I do not follow the authors’ logic in this section. It seems like the dynamic pressure calculations cited in this section do not find trends? And these authors are arguing that is due to an issue with the barotropic reference velocity? This section requires some clarification, specifically how it aligns with information presented in the other sections.
L. 221: The authors write that there are several studies often cited as evidence against an AMOC weakening, but do not cite any papers. Please include citations for these papers.
L. 231-234: For this to be true, the indicators need to be independent. The lines of evidence presented herein cannot be considered independent from one another.
L. 255: Which indicators indicate a 2 Sv weakening since mid-20^th century? And where is this +/- 1 Sv error bar coming from? This is the central conclusion of the paper, so it deserves elaboration and references.
L. 259-260: I found this last sentence “It is therefore high time to stop wavering and to take this evidence seriously” to be incredibly condescending. It implies that scientists who disagree with the authors are not “taking the evidence seriously”. To turn it around, I believe these authors need to do some soul-searching and decide whether they can truly be neutral arbiters of the data, or if their preconceived notions preclude them from performing rigorous science. I worry their approach is to wait long enough until the weakening is apparent and statistically significant, to then tell everyone that they were right all along. There is a broad consensus in the field that the AMOC will weaken into the future, and the importance of this weakening is widely appreciated. We are all taking the evidence seriously, the difference is that we are taking ALL the evidence seriously.

References
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Citation: https://doi.org/10.5194/egusphere-2026-2110-RC2
EC1:
'Comment on egusphere-2026-2110', Sjoerd Groeskamp, 19 Jun 2026
Dear Stefan Rahmstorf and Levke Caesar
We thank you for submitting your opinion piece to Ocean Science. The open discussion of your manuscript is now closed. Based on the extensive review comments, multiple extensive community comments, and based on my own reading, it appears very unlikely that you will be able to fix the provided criticism upon revision. I discourage submission of a revised manuscript. Instead, I hope you can use some of the pointers and suggestions of the referees to reshape your manuscript and find another journal where this work may find a place. Below is a summary of the main reasons brought up by the reviewers and community comments.
The reasons not to publish this opinion piece are the following:
There are concerns about a bias in the used literature towards ones that fit in the narrative. The list of cited literature showing an AMOC time series is incomplete and biased towards decline. Papers that are showing an increase or no trend are discarded for invalid reasons.

The Bayesian statistical approach is compelling, but the underlying assumption - that all lines of evidence are independent from each other – is not met.

Figure 3 lacks to show and quantify the uncertainty estimates of the used data in combination with the used smoothing. Some of the original studies show no statistically significant trend in their original work, but are here presented as if they do, and likely would not when the uncertainty would be added. This has been considered misleading.

The authors are making a quantitative argument without doing the necessary analysis and then framing it as an opinion. An opinion piece is an assessment based on existing literature. I agree with the reviewers that here an extra analysis is applied, and that this analysis is not properly reviewed, but is fundamental to the opinion. This mixes up science and opinion in an unclear manner.

This opinion attributes citations to claims that are not in the papers that are cited.

The community comments (particularly CC5-CC9) discuss the level of uncertainty in different air-sea flux products and ocean reanalysis products. To me, the arguments used in this discussion are not well reflected in the opinion piece and could change the conclusion.

Sjoerd Groeskamp
Citation: https://doi.org/10.5194/egusphere-2026-2110-EC1

Stefan Rahmstorf and Levke Caesar

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Short summary

The Atlantic Ocean circulation has a big impact on climate, not only on European temperatures. There has been a longstanding concern that it could slow down or even shut down in response to global warming. While climate models predict that, it is debated whether a slowing is already underway. Here we discuss the available data and conclude that it is very likely that indeed the circulation is already slowing down.


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