Field-experiment constraints on the enhancement of the terrestrial carbon sink by CO2 fertilization

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Abstract

Clarifying how increased atmospheric CO2 concentration (eCO2) contributes to accelerated land carbon sequestration remains important since this process is the largest negative feedback in the coupled carbon–climate system. Here, we constrain the sensitivity of the terrestrial carbon sink to eCO2 over the temperate Northern Hemisphere for the past five decades, using 12 terrestrial ecosystem models and data from seven CO2 enrichment experiments. This constraint uses the heuristic finding that the northern temperate carbon sink sensitivity to eCO2 is linearly related to the site-scale sensitivity across the models. The emerging data-constrained eCO2 sensitivity is 0.64 ± 0.28 PgC yr−1 per hundred ppm of eCO2. Extrapolating worldwide, this northern temperate sensitivity projects the global terrestrial carbon sink to increase by 3.5 ± 1.9 PgC yr−1 for an increase in CO2 of 100 ppm. This value suggests that CO2 fertilization alone explains most of the observed increase in global land carbon sink since the 1960s. More CO2 enrichment experiments, particularly in boreal, arctic and tropical ecosystems, are required to explain further the responsible processes.

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Fig. 1: Effect of eCO2 on the change in the global residual terrestrial sink during the past five decades.
Fig. 2: Emergent constraints on the sensitivity of the Northern Hemisphere temperate terrestrial carbon sink to eCO2.

Data availability

Driver data of MsTMIP models are available from https://doi.org/10.3334/ORNLDAAC/1220. The outputs of MsTMIP models are available from https://doi.org/10.3334/ORNLDAAC/1225. Global Carbon Budget 2017 data (Global_Carbon_Budget_2017v1.3.xlsx) are available from https://doi.org/10.18160/GCP-2017. CRU climatology data (CRU CL v. 2.0) are available from https://crudata.uea.ac.uk/cru/data/hrg/.

Code availability

The code for fitting the two-box model, as given in equation (3), is shown in Supplementary Information.

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Acknowledgements

This study was supported by the Strategic Priority Research Program (A) of the Chinese Academy of Sciences (Grant XDA20050101), the National Key R&D Program of China (2017YFA0604702), and the National Natural Science Foundation of China (41861134036, 41701089). The full list of acknowledgements is provided in the Supplementary Information.

Author information

S.P., Y.L., T.G. and P.C. designed the study. Y.L. performed the analysis. Y.L. and S.P. drafted the paper. All authors contributed to the interpretation of the results and to the text.

Correspondence to Shilong Piao.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Description, Supplementary Figs. 1–25 and Tables 1–4, Supplementary References and full list of acknowledgements.

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