the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Apr 2026
Opinion: The AMOC is weakening – time to take the evidence seriously
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.
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Status: open (until 16 Jun 2026)
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CC1: 'Trusting projections of the AMOC weakening is difficult…', Luis G. Lopez-Lemus, 22 Apr 2026
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CC2: 'Reply on CC1', Stefan Rahmstorf, 23 Apr 2026
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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
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—Sure, both references are great … thank you!
Citation: https://doi.org/10.5194/egusphere-2026-2110-CC3
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CC3: 'Reply on CC2', Luis G. Lopez-Lemus, 23 Apr 2026
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CC2: 'Reply on CC1', Stefan Rahmstorf, 23 Apr 2026
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RC1: 'Review of egusphere-2026-2110', Anonymous Referee #1, 08 May 2026
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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 20th 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
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—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
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CC4: 'Reply on RC1', Luis G. Lopez-Lemus, 09 May 2026
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🖇️ 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