The remaining carbon budget represents the total amount of CO2 that can still be emitted in the future while limiting global warming to a given temperature target. Remaining carbon budget estimates range widely, however, and this uncertainty can be used to either trivialize the most ambitious mitigation targets by characterizing them as impossible, or to argue that there is ample time to allow for a gradual transition to a low-carbon economy. Neither of these extremes is consistent with our best understanding of the policy implications of remaining carbon budgets. Understanding the scientific and socio-economic uncertainties affecting the size of the remaining carbon budgets, as well as the methodological choices and assumptions that underlie their calculation, is essential before applying them as a policy tool. Here we provide recommendations on how to calculate remaining carbon budgets in a traceable and transparent way, and discuss their uncertainties and implications for both international and national climate policies.
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The MAGICC7 model emulator is available from Z.R.J.N. upon request. Codes for producing the figures are available from H.D.M. or K.B.T. upon request.
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We are grateful for the opportunity to have discussed these and other issues at the International Workshop on the Remaining Carbon Budget, organized with the support of the Global Carbon Project, the CRESCENDO project, Stanford University, the University of Melbourne, and Simon Fraser University. H.D.M. has been supported by funding from the Concordia University Research Chair programme and the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant RGPIN-2017-04159). K.B.T., J.R., P.M.F., R.K. and R.S. were supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 820829 (CONSTRAIN project). J.G.C. was supported by the Australian National Environmental Science Program – Earth Systems and Climate Change Hub. P.F. and T.L.F. were supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 821003 (4C project). T.L.F. was also supported by the Swiss National Science Foundation under grant PP00P2_170687. A.H.M. and K.Z. are supported by the Natural Sciences and Engineering Research Council of Canada Discovery Grant Program. C.D.J. was supported by the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101) and by H2020 EU project CRESCENDO under grant agreement No. 641816. R.B.J. and J.G.C. acknowledge support from the Gordon and Betty Moore Foundation (GBMF5439). C.K. is supported by the US DOE, BER, RGMA program through the ECRP and RUBISCO projects.
The authors declare no competing interests.
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Matthews, H.D., Tokarska, K.B., Nicholls, Z.R.J. et al. Opportunities and challenges in using remaining carbon budgets to guide climate policy. Nat. Geosci. 13, 769–779 (2020). https://doi.org/10.1038/s41561-020-00663-3
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