Most of the integrated assessment modelling literature focuses on cost-effective pathways towards given temperature goals. Conversely, using seven diverse integrated assessment models, we project global energy CO2 emissions trajectories on the basis of near-term mitigation efforts and two assumptions on how these efforts continue post-2030. Despite finding a wide range of emissions by 2050, nearly all the scenarios have median warming of less than 3 °C in 2100. However, the most optimistic scenario is still insufficient to limit global warming to 2 °C. We furthermore highlight key modelling choices inherent to projecting where emissions are headed. First, emissions are more sensitive to the choice of integrated assessment model than to the assumed mitigation effort, highlighting the importance of heterogeneous model intercomparisons. Differences across models reflect diversity in baseline assumptions and impacts of near-term mitigation efforts. Second, the common practice of using economy-wide carbon prices to represent policy exaggerates carbon capture and storage use compared with explicitly modelling policies.
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The code for the analysis in this paper is available upon request to the corresponding author. The code availability for the individual models used in this paper varies and contact should be made to individual modelling groups. The GCAM model is available for download from https://github.com/JGCRI/gcam-core. Detailed model documentation for all seven models is available online at https://www.i2am-paris.eu/detailed_model_doc.
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I.S., A.A.-K., H.B., L.C., E.D., H.D., A.G., S.G., A.H., A.C.K., A.K., S.M., J.M., A.N., S.P., G.P.P., J.R., D.-J.v.d.V. and M.V. acknowledge support from the H2020 European Commission Project PARIS REINFORCE (grant no. 820846). N.G. was supported by the Natural Environment Research Council (NERC) (grant no. NE/L002515/1) as well as the Department for Business, Energy and Industrial Strategy (BEIS).
The authors declare no competing interests.
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a, Implementation of CP_Price scenarios. First, current policies are explicitly implemented to 2030, and the resulting emissions in 2030 are recorded. Second, models are re-run to reach the same levels of emissions as in the previous step using a carbon price (C1) alone. Third, scenarios are extended post-2030 by growing the carbon price (C1) with GDP per capita. The resulting emissions pathways (P1(t)) are recorded. Fourth, models are re-run with current policies explicitly implemented to 2030, and as constant or minimum bounds on effort post-2030. The emissions pathways achieved in the previous step (P1(t)) are implemented as upper bounds on emissions. b, Implementation of NDC_Price scenarios follows the implementation of CP_Price scenarios, except for the first step. First, current policies are explicitly implemented to 2030. Then, the emissions levels achieved in 2030 in each model region are compared with NDC targets. When additional effort is required to achieve NDC targets, this is implemented on top of current policies. See Supplementary Text 2 for the full scenario protocol.
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Sognnaes, I., Gambhir, A., van de Ven, DJ. et al. A multi-model analysis of long-term emissions and warming implications of current mitigation efforts. Nat. Clim. Chang. 11, 1055–1062 (2021). https://doi.org/10.1038/s41558-021-01206-3
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