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Realization of Paris Agreement pledges may limit warming just below 2 °C

Abstract

Over the last five years prior to the Glasgow Climate Pact1, 154 Parties have submitted new or updated 2030 mitigation goals in their nationally determined contributions and 76 have put forward longer-term pledges. Quantifications of the pledges before the 2021 United Nations Climate Change Conference (COP26) suggested a less than 50 per cent chance of keeping warming below 2 degrees Celsius2,3,4,5. Here we show that warming can be kept just below 2 degrees Celsius if all conditional and unconditional pledges are implemented in full and on time. Peak warming could be limited to 1.9–2.0 degrees Celsius (5%–95% range 1.4–2.8 °C) in the full implementation case—building on a probabilistic characterization of Earth system uncertainties in line with the Working Group I contribution to the Sixth Assessment Report6 of the Intergovernmental Panel on Climate Change (IPCC). We retrospectively project twenty-first-century warming to show how the aggregate level of ambition changed from 2015 to 2021. Our results rely on the extrapolation of time-limited targets beyond 2030 or 2050, characteristics of the IPCC 1.5 °C Special Report (SR1.5) scenario database7 and the full implementation of pledges. More pessimistic assumptions on these factors would lead to higher temperature projections. A second, independent emissions modelling framework projected peak warming of 1.8 degrees Celsius, supporting the finding that realized pledges could limit warming to just below 2 degrees Celsius. Limiting warming not only to ‘just below’ but to ‘well below’ 2 degrees Celsius or 1.5 degrees Celsius urgently requires policies and actions to bring about steep emission reductions this decade, aligned with mid-century global net-zero CO2 emissions.

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Fig. 1: Number of countries that have NDCs, long-term targets and net-zero emission targets and their share of global CO2 emissions.
Fig. 2: Although some near-term pledges are estimated to be very weak, implying potentially substantial overachievement (hot air), countries with long-term targets envisage substantial per capita emission reductions.
Fig. 3: Global mean temperature projections based on 2030 NDCs show a wide range, whereas those based also on long-term targets stay just around or below 2 °C—with limited additional effects by the GMP.
Fig. 4: Pledges submitted at the time of the Paris Agreement (2015) and up to after COP26 show a strong recent decrease in projected cumulative emissions.
Fig. 5: Pledges submitted at the time of the Paris Agreement (2015) and up to after COP26 indicate the possibility of emission peaking before 2030 and lowering median warming.

Data availability

The data archive for this study is available at https://doi.org/10.5281/zenodo.5886866, which includes the scenario data, temperature outcomes and supplementary tables48. Country-level emission quantifications of NDCs and LT-LEDs (the ‘NDC Factsheets’)49 are available at https://doi.org/10.5281/zenodo.5768669 and are also interactively available at https://climate-resource.com/tools/ndcs. The source data PRIMAP-hist CR is provided at https://doi.org/10.5281/zenodo.5494497Source data are provided with this paper.

Code availability

The analysis code used in this study is provided by Silicone (version 1.2.1) for the infilling, available at https://github.com/GranthamImperial/silicone, and by the Anaeris package (version 0.2.0+41.g6ddf6e5) for the harmonization, available at https://github.com/iiasa/aneris. The climate model MAGICC7.5 is in the process of becoming open source (re-factoring ongoing), the model is available as an interactive mode at http://live.magicc.org. The source code for extrapolating and infilling of the NDC scenarios are available at https://gitlab.com/climate-resource/ndc-realisations-2021.

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Acknowledgements

We acknowledge discussions and collaborations with several colleagues of the UNEP Gap report team and the IAM modellers contributing to the SR1.5 and ENGAGE scenario databases. M.M. is the recipient of an Australian Research Council (ARC) Future Fellowship (grant number FT130100809). C.M., L.C. and B.H. state that the views expressed in this article are in the author’s personal capacity and do not necessarily reflect the views of the United Nations, United Nations Climate Change or the International Energy Agency.

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Contributions

All authors contributed to writing the study. M.M. designed the study and quantified the NDCs for the bottom-up NDC analysis; J.L. performed the global harmonization, climate model runs and analysis; C.M. and L.C. provided the analysis of net-zero emission targets and the IEA scenarios; Z.N. provided the code base for the probabilistic climate model analysis and analysis of the ENGAGE database; and J.G. provided the PRIMAP-hist data.

Corresponding author

Correspondence to Malte Meinshausen.

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Nature thanks Kalyn Dorheim, Zeke Hausfather and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 CO2 emissions for various scenarios.

Total CO2 emissions of the considered scenarios A and B, the 2030 extension scenarios ‘a’ to ‘h’ (Extended Data Table 2), the SSP scenarios (dashed grey lines) and the SR1.5 scenario database. As in Fig. 3b, but for total CO2 emissions instead of GHG emissions.

Source data

Extended Data Fig. 2 Sensitivity test of database temperature projections in the ENGAGE database31.

The 25 closest scenarios in terms of their 2050 GHG emissions (GWP-100 AR6, excluding LULUCF) to this study’s scenario A (thick blue line, Extended Data Table 2) are selected (thin coloured lines). For the respective emission level around 30 GtCO2e by 2050, more of the selected ENGAGE scenarios suggest lower post-2050 GHG emission levels than our scenario A, which had been extrapolated using an equal-quantile-walk approach on the basis of the SR1.5 scenario database7.

Source data

Extended Data Table 1 2100 warming relative to 1850–1900 of comparison studies shown in sidebars of Fig. 3a, c
Extended Data Table 2 Overview of shown pathways and their characteristics

Source data

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Meinshausen, M., Lewis, J., McGlade, C. et al. Realization of Paris Agreement pledges may limit warming just below 2 °C. Nature 604, 304–309 (2022). https://doi.org/10.1038/s41586-022-04553-z

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