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Human-induced changes to the global ocean water masses and their time of emergence

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Abstract

The World Ocean is rapidly changing, with global and regional modification of temperature and salinity, resulting in widespread and irreversible impacts. While the most pronounced observed temperature and salinity changes are located in the upper ocean, changes in water masses at depth have been identified and will probably strengthen in the future. Here, using 11 climate models, we define when anthropogenic temperature and salinity changes are expected to emerge from natural variability in the ocean interior along density surfaces. The models predict that in 2020, 20–55% of the Atlantic, Pacific and Indian basins have an emergent anthropogenic signal; reaching 40–65% in 2050 and 55–80% in 2080. The well-ventilated Southern Ocean water masses emerge very rapidly, as early as the 1980–1990s, while the Northern Hemisphere water masses emerge in the 2010–2030s. Our results highlight the importance of maintaining and augmenting an ocean observing system capable of detecting and monitoring persistent anthropogenic changes.

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Fig. 1: Observed and simulated salinity changes between 1950 and 2008, shown in patterns of 50-yr salinity changes, analysed on density surfaces.
Fig. 2: Anthropogenic salinity change along density surfaces.
Fig. 3: ToE and percentage of emergence in basin zonal means.
Fig. 4: Distribution of GSAT at emergence.

Data availability

All CMIP5 model data used in this paper are available through the Earth System Grid and freely available for download (https://esgf-node.llnl.gov/search/cmip5/).

Code availability

The analysis code for this paper is written in Python and is available on GitHub (https://github.com/ysilvy/ocean_toe_2020)54. The density binning code and data are available upon request to the authors.

Change history

  • 28 August 2020

    In the PDF version of this Article originally published online, Figs. 3 and 4 appeared in reverse order; this has now been amended. The HTML version was unaffected.

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Acknowledgements

We thank C. de Lavergne, A. Fedorov, P. Gleckler, J. Gregory, E. Hawkins, G. Madec, H. Mercier, J. Mignot, B. Santer and L. Terray for helpful discussions. We acknowledge the support from the Make Our Planet Great Again project ARCHANGE (Agence Nationale pour la Recherche project no. ANR-18-MPGA-0001) from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant no. 637770) and from the Centre National de la Recherche Scientifique. We also acknowledge the CMIP5 modelling groups, the ESGF and IPSL/ESPRI-MOD data distribution systems. The work of P.J.D. was prepared by Lawrence Livermore National Laboratory (LLNL) under contract no. DE-AC52-07NA27344 and is a contribution to the US Department of Energy, Office of Science, Climate and Environmental Sciences Division, Regional and Global Modeling and Analysis Program (LLNL release no. LLNL-JRNL-794900).

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The density binning of CMIP5 data was designed and performed by E.G. and P.J.D. All subsequent analysis for this paper was performed by Y.S. and supervised by E.G and J.-B.S. Observational data were provided by P.J.D. All authors contributed to interpreting the results and writing the manuscript.

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Correspondence to Yona Silvy.

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Peer review information Nature Climate Change thanks Veronique Lago, Nadya Vinogradova-Shiffer and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Silvy, Y., Guilyardi, E., Sallée, JB. et al. Human-induced changes to the global ocean water masses and their time of emergence. Nat. Clim. Chang. 10, 1030–1036 (2020). https://doi.org/10.1038/s41558-020-0878-x

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