Warming trends increasingly dominate global ocean

Abstract

The ocean takes up about 93% of the global warming heat entering Earth’s climate system. In addition, the associated thermal expansion contributes substantially to sea-level rise. Hence, quantifying the oceanic heat uptake rate and its statistical significance has been a research focus. Here we use gridded ocean heat content maps to examine regional trends in ocean warming for 0–700 m depth from 1993–2019 and 1968–2019, periods based on sampling distributions. The maps are from four research groups, three based on ocean temperature alone and one combining ocean temperature with satellite altimeter sea-level anomalies. We show that use of longer periods results in larger percentages of ocean area with statistically significant warming trends and less ocean area covered by statistically significant cooling trends. We discuss relations of these patterns to climate phenomena, including the Pacific Decadal Oscillation, the Atlantic Meridional Overturning Circulation and global warming.

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Fig. 1: Upper-ocean heat content anomaly linear trends for 1993–2019.
Fig. 2: Upper-ocean heat content anomaly linear trends for 1968–2019.
Fig. 3: Mean fractions of the global ocean surface area with trends of upper-ocean heat content that are statistically significantly different from zero.

Data availability

The Ssalto/Duacs global maps of satellite-altimeter-derived sea-surface height anomalies used for the PMEL maps were downloaded in January 2019 and can be accessed at https://www.aviso.altimetry.fr/en/data/products/sea-surface-height-products/global.html. The in situ Argo data used for the PMEL maps (https://doi.org/10.17882/42182#61117) were downloaded from the US Argo Global Data Assembly Center in January 2019 and can be accessed at https://www.usgodae.org//argo/argo.html. The historical in situ temperature data other than Argo used for the PMEL maps were EN3 v2a from www.metoffice.gov.uk/hadobs. This version has been superseded, but historical non-Argo data in later versions are very similar. The ocean heat content maps from JMA can be accessed at https://www.data.jma.go.jp/gmd/kaiyou/english/ohc/ohc_global_en.html, those from IAP at http://159.226.119.60/cheng/ and those from NCEI at https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/.

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Acknowledgements

G.C.J. and J.M.L. are supported by the Global Ocean Monitoring and Observing programme, National Oceanic and Atmospheric Administration (NOAA), US Department of Commerce and NOAA Research. The Argo data used here were collected and made freely available by the International Argo Program and the national programmes that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). The Argo Program is part of the Global Ocean Observing System. The Ssalto/Duacs altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS) (http://www.marine.copernicus.eu). We thank chief editor B. Wake for helpful comments and suggestions. The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the authors and do not necessarily reflect the views of NOAA or the Department of Commerce. PMEL Contribution number 4968.

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Authors

Contributions

G.C.J and J.M.L designed the study. J.M.L. made the calculations and analysed the trends. G.C.J. wrote the manuscript. Both authors contributed to interpreting the results and improving the manuscript.

Corresponding author

Correspondence to Gregory C. Johnson.

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The authors declare no competing interests.

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Peer review information Nature Climate Change thanks Karina von Schuckmann and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Maps of means, standard deviations, and ratios of their magnitudes for the different 0–700 m ocean heat content trend estimates used.

Means of trends for (a) 1993–2019 are contoured over twice the range used for (b) 1968–2019. Similarly, the standard deviations for (c) 1993–2019 trends are contoured over twice the range used for (d) 1968–2019. The ratio of the mean trend magnitudes to their standard deviations are contoured on the same scale for (e) 1993–2019 and (f) 1968–2019. Latitudes are gridded at 30° intervals, and longitudes, centered on 150 °W, at 60° intervals (dotted lines).

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Johnson, G.C., Lyman, J.M. Warming trends increasingly dominate global ocean. Nat. Clim. Chang. 10, 757–761 (2020). https://doi.org/10.1038/s41558-020-0822-0

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