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Timescales for detection of trends in the ocean carbon sink


The ocean has absorbed 41 per cent of all anthropogenic carbon emitted as a result of fossil fuel burning and cement manufacture1,2. The magnitude and the large-scale distribution of the ocean carbon sink is well quantified for recent decades3,4. In contrast, temporal changes in the oceanic carbon sink remain poorly understood5,6,7. It has proved difficult to distinguish between air-to-sea carbon flux trends that are due to anthropogenic climate change and those due to internal climate variability5,6,8,9,10,11,12,13. Here we use a modelling approach that allows for this separation14, revealing how the ocean carbon sink may be expected to change throughout this century in different oceanic regions. Our findings suggest that, owing to large internal climate variability, it is unlikely that changes in the rate of anthropogenic carbon uptake can be directly observed in most oceanic regions at present, but that this may become possible between 2020 and 2050 in some regions.

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Figure 1: Modelled and observed mean 1982–2011 CO2 flux in 15 ocean biomes.
Figure 2: Forced trends and internal variability of CESM-LE trends in sea-to-air CO2 flux.
Figure 3: Time of emergence for sea-to-air CO2 flux.


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The National Science Foundation sponsors National Center for Atmospheric Research, where the Community Earth System Model is developed. Computing resources were provided by the Climate Simulation Laboratory at NCAR’s Computational and Information Systems Laboratory, sponsored by the NSF and other agencies. NCAR’s Advanced Study Program sponsored D.J.P., K.L., M.C.L. and G.A.M. to initiate this analysis. We also thank NASA for funding (grants NNX11AF53G and NNX13AC53G to G.A.M., D.J.P., A.R.F. and N.S.L.). N.S.L. also thanks the NSF (grant OCE-1155240) and NOAA (grant NA12OAR4310058).

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Authors and Affiliations



G.A.M. conceived the analysis, which was further refined by all authors. K.L. coordinated inclusion of ocean biogeochemistry in CESM-LE. D.J.P. and A.R.F. did the analysis. All authors discussed results and contributed to writing the manuscript.

Corresponding author

Correspondence to Galen A. McKinley.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Comparison of 1982–2011 mean CO2 flux.

a, Data-based climatology (ref. 28). b, CESM large ensemble 32-member mean. c, Mean of 12 CMIP5 models.

Extended Data Figure 2 Forced trends and variability of CMIP5 trends in sea-to-air CO2 flux.

Forced trends for a, 1990–1999, b, 1990–2019 and c, 1990–2089. Grey areas are where the forced trend cannot be distinguished from the variability with 95% confidence (Methods). CO2 flux trend standard deviations, indicating the impact of variability on CO2 flux trends, for d, 1990–1999, e, 1990–2019 and f, 1990–2089. Negative values indicate increasing ocean carbon uptake.

Extended Data Table 1 Comparison of observed and modelled and CO2 flux variability for 1982–2011
Extended Data Table 2 Comparison of observed and modelled and CO2 flux trends for 1982–2011
Extended Data Table 3 CMIP5 models used in this work
Extended Data Table 4 Biome long names and mean time of emergence

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McKinley, G., Pilcher, D., Fay, A. et al. Timescales for detection of trends in the ocean carbon sink. Nature 530, 469–472 (2016).

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