Abstract

Several methods exist to estimate the cumulative carbon emissions that would keep global warming to below a given temperature limit. Here we review estimates reported by the IPCC and the recent literature, and discuss the reasons underlying their differences. The most scientifically robust number — the carbon budget for CO2-induced warming only — is also the least relevant for real-world policy. Including all greenhouse gases and using methods based on scenarios that avoid instead of exceed a given temperature limit results in lower carbon budgets. For a >66% chance of limiting warming below the internationally agreed temperature limit of 2 °C relative to pre-industrial levels, the most appropriate carbon budget estimate is 590–1,240 GtCO2 from 2015 onwards. Variations within this range depend on the probability of staying below 2 °C and on end-of-century non-CO2 warming. Current CO2 emissions are about 40 GtCO2 yr−1, and global CO2 emissions thus have to be reduced urgently to keep within a 2 °C-compatible budget.

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Acknowledgements

We acknowledge the work by IAM modellers that contributed to the IPCC AR5 Scenario Database and the climate modelling teams contributing to CMIP5. We thank IIASA for hosting the IPCC AR5 Scenario Database, and M. Meinshausen for detailed comments and feedback on the manuscript.

Author information

Affiliations

  1. ENE Program, International Institute for Applied Systems Analysis (IIASA) Schlossplatz 1, A-2361 Laxenburg, Austria

    • Joeri Rogelj
    •  & Keywan Riahi
  2. Institute for Atmospheric and Climate Science, ETH Zurich, Universitätstrasse 16, CH-8092 Zürich, Switzerland

    • Joeri Rogelj
    •  & Reto Knutti
  3. Climate Analytics, Karl-Liebknechtstrasse 5, 10178 Berlin, Germany

    • Michiel Schaeffer
  4. Environmental Systems Analysis Group, Wageningen University and Research Centre, PO Box 47, 6700 AA Wageningen, the Netherlands

    • Michiel Schaeffer
  5. College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK

    • Pierre Friedlingstein
  6. Canadian Centre for Climate Modelling and Analysis, Environment Canada, University of Victoria, PO Box 1700, STN CSC, Victoria, British Columbia V8W 2Y2, Canada

    • Nathan P. Gillett
  7. PBL Netherlands Environmental Assessment Agency, PO Box 303, 3720 AH Bilthoven, the Netherlands

    • Detlef P. van Vuuren
  8. Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, the Netherlands

    • Detlef P. van Vuuren
  9. Graz University of Technology, Inffeldgasse, A-8010 Graz, Austria

    • Keywan Riahi
  10. ECI, School of Geography and the Environment, University of Oxford, Oxford OX1 3QY, UK

    • Myles Allen
  11. Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK

    • Myles Allen

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Contributions

All authors contributed to parts of the underlying research during the writing process of the IPCC AR5. J.R. coordinated the conception and the writing of the paper. J.R. carried out the research with significant contributions from M.S., and developed the TEB and TAB conceptual framework. J.R. produced the figures and wrote the first draft of the manuscript. All authors contributed to interpreting and discussing the results, and writing the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Joeri Rogelj.

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DOI

https://doi.org/10.1038/nclimate2868

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