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Ratcheting of climate pledges needed to limit peak global warming

Nature Climate Change volume 12, pages 1129–1135 (2022)Cite this article

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Abstract

The new and updated emission reduction pledges submitted by countries ahead of the Twenty-Sixth Conference of Parties represent a meaningful strengthening of global ambition compared to the 2015 Paris pledges. Yet, limiting global warming below 1.5 °C this century will require countries to ratchet ambition for 2030 and beyond. Here, we explore a suite of emissions pathways to show that ratcheting near-term ambition through 2030 will be crucial to limiting peak temperature changes. Delaying ratcheting ambition to beyond 2030 could still deliver end-of-century temperature change of less than 1.5 °C but would result in higher temperature overshoot over many decades with the potential for adverse consequences. Ratcheting near-term ambition would also deliver benefits from enhanced non-CO2 mitigation and facilitate faster transitions to net-zero emissions systems in major economies.

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Fig. 1: Global GHG emissions in the pathways modelled using the GCAM.
Fig. 2: Temperature change in 2100 (inner bars) and peak temperature change (outer bars) outcomes of the emissions pathways explored in this study.
Fig. 3: GHG emissions by sector and species in a subset of the pathways explored in the study.
Fig. 4: Cumulative GHG emissions by region in a subset of the pathways explored in the study.
Fig. 5: Year of net-zero CO2 emissions in a subset of the pathways explored in the study.

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Data availability

Country ratings from the CAT are publicly available at https://climateactiontracker.org/countries/. The latest (v.2020) Human Development Index is publicly available at https://hdr.undp.org/data-center/human-development-index#/indicies/HDI. The datasets generated during and analysed in the current study are available from a public repository (https://doi.org/10.5281/zenodo.7069063). Source data are provided with this paper.

Code availability

GCAM is an open-source community model available at https://github.com/JGCRI/gcam-core/releases. The version of GCAM and additional input files associated with this study are available at https://doi.org/10.5281/zenodo.7069066.

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Acknowledgements

The research described in this paper was conducted with support from the US EPA IAA DW-089-92460001 (G.I., Y.O., J.E., J.F., S.W. and H.M.). The views and opinions expressed in this paper are those of the authors alone and do not necessarily state or reflect those of the Environmental Protection Agency or the US Government and no official endorsement should be inferred.

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Author notes

  1. These authors contributed equally: Gokul Iyer, Yang Ou.

Authors and Affiliations

  1. Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland, College Park, MD, USA

    Gokul Iyer, Yang Ou, James Edmonds, Jay Fuhrman, Stephanie Waldhoff & Haewon McJeon

  2. US Environmental Protection Agency, Washington, DC, USA

    Allen A. Fawcett & James McFarland

  3. Center for Global Sustainability, School of Public Policy, University of Maryland, College Park, MD, USA

    Nathan Hultman

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Contributions

G.I. and Y.O. contributed equally to this study. G.I., Y.O., J.E., A.A.F., N.H. and H.M. designed the research. G.I. wrote the first draft of the paper. Y.O. conducted the simulations. G.I., Y.O., J.E., J.F., S.W. and H.M. contributed to the modelling tools. J.M. contributed to the writing of the paper. All authors contributed to writing the paper.

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Correspondence to Haewon McJeon.

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Nature Climate Change thanks Matthias Weitzel, Ioannis Dafnomilis and Kate Dooley for their contribution to the peer review of this work.

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Iyer, G., Ou, Y., Edmonds, J. et al. Ratcheting of climate pledges needed to limit peak global warming. Nat. Clim. Chang. 12, 1129–1135 (2022). https://doi.org/10.1038/s41558-022-01508-0

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