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Reply to: Evidence lacking for a pending collapse of the Atlantic Meridional Overturning Circulation

Nature Climate Change volume 14, pages 43–47 (2024)Cite this article

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The Original Article was published on 30 November 2023

replying to X. Chen & K.-K. Tung Nature Climate Change https://doi.org/10.1038/s41558-023-01877-0 (2023)

On the basis of analyses of spatial patterns of Atlantic sea surface temperatures (SSTs) and salinity concentrations, together with four SST- and four salinity-based fingerprints of the Atlantic Meridional Overturning Circulation (AMOC) introduced in previous studies, Boers1 concluded that the stability of the AMOC may have declined during the past century. Chen and Tung2 raise three concerns in their comment: (1) the two AMOC fingerprints that are based on subpolar North Atlantic salinity fields have the wrong sign, (2) the positive trends of the restoring rate λ inferred in Boers1 and interpreted as a stability decline are caused by non-stationary coverage of observational data, and (3) a general criticism of SST-based AMOC fingerprints. Here I respond to each of their concerns, arguing that the fingerprints’ sign does not matter for the stability analysis and that their way to test the effect of non-stationary data coverage is flawed, and demonstrate that the autocorrelation and restoring rate λ are robust against non-stationary observational coverage. Note that the stability decline inferred by Boers1 remains statistically significant when accounting for the effects of non-stationary observational coverage3 and that it has since been confirmed on longer timescales using independent data4.

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Fig. 1: EWS for SST- and salinity-based AMOC indices.
Fig. 2: Effect of different gap-filling procedures on CSD indicators, exemplified for the SPG index SNN1 and the Southern Atlantic index SS.

Data availability

No additional data were used in this response.

Code availability

All Python code used is available at https://github.com/niklasboers/AMOC_EWS.

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Authors and Affiliations

  1. Earth System Modelling, School of Engineering and Design, Technical University of Munich, Munich, Germany

    Niklas Boers

  2. Potsdam Institute for Climate Impact Research, Potsdam, Germany

    Niklas Boers

  3. Department of Mathematics and Global Systems Institute, University of Exeter, Exeter, UK

    Niklas Boers

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  1. Niklas Boers
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Correspondence to Niklas Boers.

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Boers, N. Reply to: Evidence lacking for a pending collapse of the Atlantic Meridional Overturning Circulation. Nat. Clim. Chang. 14, 43–47 (2024). https://doi.org/10.1038/s41558-023-01878-z

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