Article

Emission budgets and pathways consistent with limiting warming to 1.5 °C

Received:
Accepted:
Published online:

Abstract

The Paris Agreement has opened debate on whether limiting warming to 1.5 °C is compatible with current emission pledges and warming of about 0.9 °C from the mid-nineteenth century to the present decade. We show that limiting cumulative post-2015 CO2 emissions to about 200 GtC would limit post-2015 warming to less than 0.6 °C in 66% of Earth system model members of the CMIP5 ensemble with no mitigation of other climate drivers, increasing to 240 GtC with ambitious non-CO2 mitigation. We combine a simple climate–carbon-cycle model with estimated ranges for key climate system properties from the IPCC Fifth Assessment Report. Assuming emissions peak and decline to below current levels by 2030, and continue thereafter on a much steeper decline, which would be historically unprecedented but consistent with a standard ambitious mitigation scenario (RCP2.6), results in a likely range of peak warming of 1.2–2.0 °C above the mid-nineteenth century. If CO2 emissions are continuously adjusted over time to limit 2100 warming to 1.5 °C, with ambitious non-CO2 mitigation, net future cumulative CO2 emissions are unlikely to prove less than 250 GtC and unlikely greater than 540 GtC. Hence, limiting warming to 1.5 °C is not yet a geophysical impossibility, but is likely to require delivery on strengthened pledges for 2030 followed by challengingly deep and rapid mitigation. Strengthening near-term emissions reductions would hedge against a high climate response or subsequent reduction rates proving economically, technically or politically unfeasible.

  • Subscribe to Nature Geoscience for full access:

    $59

    Subscribe

Additional access options:

Already a subscriber?  Log in  now or  Register  for online access.

References

  1. 1.

    Adoption of the Paris Agreement FCCC/CP/2015/L.9/Rev. 1 (UNFCCC, 2015);

  2. 2.

    , , & Embracing uncertainty in climate change policy. Nat. Clim. Change 5, 917–920 (2015).

  3. 3.

    , , & Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: the HadCRUT4 data set. J. Geophys. Res. 117, D08101 (2012).

  4. 4.

    et al. Energy system transformations for limiting end-of-century warming to below 1.5 °C. Nat. Clim. Change 5, 519–527 (2015).

  5. 5.

    , & What would it take to achieve the Paris temperature targets? Geophys. Res. Lett. 43, 7133–7142 (2016).

  6. 6.

    et al. Can Paris pledges avert severe climate change? Science 350, 1168–1169 (2015).

  7. 7.

    & Stabilizing climate requires near-zero emissions. Geophys. Res. Lett. 35, L04705 (2008).

  8. 8.

    et al. Warming caused by cumulative carbon emissions towards the trillionth tonne. Nature 458, 1163–1166 (2009).

  9. 9.

    et al. Greenhouse-gas emission targets for limiting global warming to 2 °C. Nature 458, 1158–1162 (2009).

  10. 10.

    , , & Setting cumulative emissions targets to reduce the risk of dangerous climate change. Proc. Natl Acad. Sci. USA 106, 16129–16134 (2009).

  11. 11.

    IPCC Climate Change 2014: Synthesis Report (eds Pachauri, R. K. & Meyer, L. A.) (Cambridge Univ. Press, 2009).

  12. 12.

    et al. Global carbon budget 2015. Earth Syst. Sci. Data 7, 349–396 (2015).

  13. 13.

    et al. Paris Agreement climate proposals need boost to keep warming well below 2 °C. Nature 534, 631–639 (2016).

  14. 14.

    et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 1029–1136 (IPCC, Cambridge Univ. Press, 2016).

  15. 15.

    et al. Differences between carbon budget estimates unravelled. Nat. Clim. Change 6, 245–252 (2016).

  16. 16.

    IPCC Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) (Cambridge Univ. Press, 2016).

  17. 17.

    , , & Reconciled climate response estimates from climate models and the energy budget of Earth. Nat. Clim. Change 6, 931–935 (2016).

  18. 18.

    et al. Estimating changes in global temperature since the pre-industrial period. Bull. Am. Meteorol. Soc. (2017).

  19. 19.

    , , & Sensitivity of carbon budgets to permafrost carbon feedbacks and non-CO2 forcings. Environ. Res. Lett. 10, 125003 (2015).

  20. 20.

    et al. Multi-model simulations of aerosol and ozone radiative forcing due to anthropogenic emission changes during the period 1990–2015. Atmos. Chem. Phys. 17, 2709–2720 (2017).

  21. 21.

    et al. RCP 2.6: exploring the possibility to keep global mean temperature increase below 2 °C. Climatic Change 109, 95–116 (2011).

  22. 22.

    et al. RCP 8.5-A scenario of comparatively high greenhouse gas emissions. Climatic Change 109, 33–57 (2011).

  23. 23.

    IPCC Climate Change 2014: Mitigation of Climate Change (eds Edenhofer, O. et al.) (Cambridge Univ. Press, 2011).

  24. 24.

    et al. in Climate Change 2014: Mitigation of Climate Change (eds Edenhofer, O. et al.) 413–510 (IPCC, Cambridge Univ. Press, 2011).

  25. 25.

    Inhomogeneous forcing and transient climate sensitivity. Nat. Clim. Change 4, 18–21 (2014).

  26. 26.

    & The impact of forcing efficacy on the equilibrium climate sensitivity. Geophys. Res. Lett. 41, 3565–3568 (2014).

  27. 27.

    , , & Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere–ocean climate models. Geophys. Res. Lett. 39, L09712 (2012).

  28. 28.

    et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 659–740 (IPCC, Cambirdge Univ. Press, 2012).

  29. 29.

    , , & A modified impulse-response representation of the global near-surface air temperature and atmospheric concentration response to carbon dioxide emissions. Atmos. Chem. Phys. 17, 7213–7228 (2017).

  30. 30.

    et al. The UVic Earth System Climate Model: model description, climatology, and applications to past, present and future climates. Atmos.-Ocean 39, 361–428 (2001).

  31. 31.

    et al. Historical and idealized climate model experiments: an intercomparison of Earth system models of intermediate complexity. Clim. Past 9, 1111–1140 (2013).

  32. 32.

    et al. Long-term climate change commitment and reversibility: an EMIC intercomparison. J. Clim. 26, 5782–5809 (2013).

  33. 33.

    , , & The cumulative carbon budget and its implications. Oxford Rev. Econ. Policy 32, 323–342 (2016).

  34. 34.

    , & Climate-society feedbacks and the avoidance of dangerous climate change. Nat. Clim. Change 2, 668–671 (2012).

  35. 35.

    Rethinking the lower bound on aerosol radiative forcing. J. Clim. 28, 4794–4819 (2015).

  36. 36.

    , , & Radiative forcing of carbon dioxide, methane, and nitrous oxide: a significant revision of the methane radiative forcing. Geophys. Res. Lett. 43, 12614–12623 (2016).

  37. 37.

    Emission Gap Report 2015 (UNEP, 2016).

  38. 38.

    et al. Understanding the origin of Paris Agreement emission uncertainties. Nat. Commun. 8, 15748 (2017).

  39. 39.

    , , & Climate implications of GWP-based reductions in greenhouse gas emissions. Geophys. Res. Lett. 27, 409–412 (2000).

  40. 40.

    Short-lived climate pollution. Annu. Rev. Earth Planet. Sci. 42, 341–379 (2014).

  41. 41.

    et al. New use of global warming potentials to compare cumulative and short-lived climate pollutants. Nat. Clim. Change 6, 773–776 (2016).

  42. 42.

    et al. The role of short-lived climate pollutants in meeting temperature goals. Nat. Clim. Change 3, 8–11 (2013).

  43. 43.

    , , & The ‘2 °C capital stock’ for electricity generation: committed cumulative carbon emissions from the electricity generation sector and the transition to a green economy. Appl. Energy 179, 1395–1408 (2016).

  44. 44.

    et al. Locked into Copenhagen pledges—implications of short-term emission targets for the cost and feasibility of long-term climate goals. Technol. Forecast. Soc. Change 90, 8–23 (2015).

  45. 45.

    et al. Biophysical and economic limits to negative CO2 emissions. Nat. Clim. Change 6, 4–50 (2015).

  46. 46.

    et al. Reaching peak emissions. Nat. Clim. Change 6, 7–10 (2015).

  47. 47.

    et al. A review of Chinese CO2 emission projections to 2030: the role of economic structure and policy. Clim. Policy 15, S7–S39 (2015).

  48. 48.

    & China’s changing economy: implications for its carbon dioxide emissions. Clim. Policy 17, 423–442 (2017).

  49. 49.

    et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 95–1028 (IPCC, Cambridge Univ. Press, 2017).

  50. 50.

    Solution to the paradox of climate sensitivity. Climatic Change 113, 163–179 (2012).

  51. 51.

    Energy budget constraints on climate sensitivity in light of inconstant climate feedbacks. Nat. Clim. Change 7, 331–335 (2017).

  52. 52.

    et al. Model structure in observational constraints on transient climate response. Climatic Change 131, 199–211 (2015).

  53. 53.

    , & Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6–Part 1: Model description and calibration. Atmos. Chem. Phys. 11, 1417–1456 (2011).

  54. 54.

    et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 33–115 (IPCC, Cambirdge Univ. Press, 2011).

Download references

Acknowledgements

The authors would like to thank E. Hawkins, R. Pierrehumbert, G. Peters, R. Knutti, D. van Vuuren, K. Riahi and E. Kriegler for useful discussions and/or comments on an earlier draft. R.J.M. and P.F. acknowledge support from the Natural Environment Research Council project NE/P014844/1; R.J.M. and M.R.A. from the Oxford Martin Net Zero Carbon Investment Initiative (co-I Cameron Hepburn); M.R.A. from the Oxford Martin Programme on Resource Stewardship; and J.S.F. and R.B.S. from the Research Council of Norway through projects 235548 and 261728. H.D.M. acknowledges support from the Natural Sciences and Engineering Research Council of Canada. D.J.F. acknowledges support from the Deep South National Science Challenge and an internal grant from Victoria University of Wellington.

Author information

Affiliations

  1. College of Engineering, Mathematical and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK

    • Richard J. Millar
    •  & Pierre Friedlingstein
  2. Environmental Change Institute, University of Oxford, South Parks Road, Oxford OX1 3QY, UK

    • Richard J. Millar
    •  & Myles R. Allen
  3. Center for International Climate and Environmental Research—Oslo (CICERO), PO Box 1129, Blindern, 0318 Oslo, Norway

    • Jan S. Fuglestvedt
    •  & Ragnhild B. Skeie
  4. Energy Program, International Institute for Applied Systems Analysis (IIASA), 2361 Laxenburg, Austria

    • Joeri Rogelj
  5. Institute for Atmospheric and Climate Science, ETH Zurich, Universitätstrasse 16, 8006 Zurich, Switzerland

    • Joeri Rogelj
  6. Institute for Sustainable Resources, University College London, London WC1H 0NN, UK

    • Michael J. Grubb
  7. Concordia University, Montreal, Québec H3G 1M8, Canada

    • H. Damon Matthews
  8. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK

    • Piers M. Forster
  9. New Zealand Climate Change Research Institute, Victoria University of Wellington, PO Box 600, Wellington, New Zealand

    • David J. Frame
  10. Department of Physics, University of Oxford, Oxford OX1 3PJ, UK

    • Myles R. Allen

Authors

  1. Search for Richard J. Millar in:

  2. Search for Jan S. Fuglestvedt in:

  3. Search for Pierre Friedlingstein in:

  4. Search for Joeri Rogelj in:

  5. Search for Michael J. Grubb in:

  6. Search for H. Damon Matthews in:

  7. Search for Ragnhild B. Skeie in:

  8. Search for Piers M. Forster in:

  9. Search for David J. Frame in:

  10. Search for Myles R. Allen in:

Contributions

R.J.M. conducted the analysis and produced Figs 2 and 3. J.R. conducted the CMIP5 analysis and produced Fig. 1. H.D.M. conducted the integrations with the UVic ESCM. R.J.M. produced an initial draft of the manuscript along with J.S.F., M.G., P.F. and M.R.A. All authors contributed to the experimental design, interpretation and revisions of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Richard J. Millar.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information