Recently identified post-fire carbon fluxes indicate that, to understand whether global fires represent a net carbon source or sink, one must consider both terrestrial carbon retention through pyrogenic carbon production and carbon losses via multiple pathways. Here these legacy source and sink pathways are quantified using a CMIP6 land surface model to estimate Earth’s fire carbon budget. Over the period 1901–2010, global pyrogenic carbon has driven an annual soil carbon accumulation of 337 TgC yr−1, offset by legacy carbon losses totalling −248 TgC yr−1. The residual of these values constrains the maximum annual pyrogenic carbon mineralization to 89 TgC yr−1 and the pyrogenic carbon mean residence time to 5,387 years, assuming a steady state. The residual is negative over forests and positive over grassland-savannahs (implying a potential sink), suggesting contrasting roles of vegetation in the fire carbon cycle. The paucity of observational constraints for representing pyrogenic carbon mineralization means that, without assuming a steady state, we are unable to determine the sign of the overall fire carbon balance. Constraining pyrogenic carbon mineralization rates, particularly over grassland-savannahs, is a critical research frontier that would enable a fuller understanding of fire’s role in the Earth system and inform attendant land use and conservation policy.
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The data for figure reconstruction in addition to data for tropical post drought-fire mortality and pyrogenic production and aquatic export are available online as source data and Supplementary Information, respectively, and are also deposited in the Zenodo digital repository (https://www.zenodo.org; https://doi.org/10.5281/zenodo.5789942), which is managed by the European Organization For Nuclear Research (CERN) and OpenAIRE. Owing to file size limitations we are unable to deposit primary data (model output) online. These are archived on the Obelix cluster and the repository managed by LSCE/IPSL, which can be made available upon request by contacting the corresponding author. Source data are provided with this paper.
The source code for this version of ORCHIDEE-MICT is available via https://forge.ipsl.jussieu.fr/orchidee/wiki/GroupActivities/CodeAvalaibilityPublication/ORCHIDEE_Biochar (https://doi.org/10.14768/054193dc-a5b0-4a51-bd11-3812e8f12307; Bowring 2021). Please follow the online instructions for accessing the code. We suggest that interested parties contact the corresponding author for latest code versions containing bug fixes, improvements or cleaner code. This software is governed by a CeCILL licence under French law and abiding by the rules of the distribution of free software. You can use, modify and/or redistribute the software under the terms of the CeCILL licence as circulated by CEA, CNRS and INRIA at the following URL: http://www.cecill.info (last accessed 20 November 2021).
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S.P.K.B. was supported by Swiss National Science Foundation (SNSF) grant no. SNSF 649 200021–178768 and would like to thank C. Yue, J. Chang and R. Lauerwald for discussions relating to ORCHIDEE modifications. M.W.J. was supported by the European Commission Horizon 2020 project VERIFY (grant no. 776810). P.C. was co-funded by the European Space Agency Climate Change Initiative ESA-CCI RECCAP2 project 1190 (ESRIN/ 4000123002/18/I-NB).
The authors declare no competing interests.
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Bowring, S.P.K., Jones, M.W., Ciais, P. et al. Pyrogenic carbon decomposition critical to resolving fire’s role in the Earth system. Nat. Geosci. 15, 135–142 (2022). https://doi.org/10.1038/s41561-021-00892-0