Warming caused by cumulative carbon emissions towards the trillionth tonne (original) (raw)

Nature volume 458, pages 1163–1166 (2009)Cite this article

Abstract

Global efforts to mitigate climate change are guided by projections of future temperatures1. But the eventual equilibrium global mean temperature associated with a given stabilization level of atmospheric greenhouse gas concentrations remains uncertain1,2,3, complicating the setting of stabilization targets to avoid potentially dangerous levels of global warming4,5,6,7,8. Similar problems apply to the carbon cycle: observations currently provide only a weak constraint on the response to future emissions9,10,11. Here we use ensemble simulations of simple climate-carbon-cycle models constrained by observations and projections from more comprehensive models to simulate the temperature response to a broad range of carbon dioxide emission pathways. We find that the peak warming caused by a given cumulative carbon dioxide emission is better constrained than the warming response to a stabilization scenario. Furthermore, the relationship between cumulative emissions and peak warming is remarkably insensitive to the emission pathway (timing of emissions or peak emission rate). Hence policy targets based on limiting cumulative emissions of carbon dioxide are likely to be more robust to scientific uncertainty than emission-rate or concentration targets. Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO2), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 °C above pre-industrial temperatures, with a 5–95% confidence interval of 1.3–3.9 °C.

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Figure 1: Idealized carbon dioxide emission scenarios and response to benchmark scenario.

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Figure 2: Peak CO 2 -induced warming as a function of total cumulative emissions 1750–2500 for 250 idealized emission scenarios.

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Figure 3: Warming commitment for selected scenarios shownin Fig. 1a .

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Acknowledgements

We thank N. Gillett, K. Shine and T. Stocker for suggestions, P. Stott for estimates of twentieth-century-attributable warming, J. Welby for help calibrating the simple climate model. P. Friedlingstein and the C4MIP modelling community for model output and I. Tracey for help with the manuscript. M.R.A. and D.J.F. acknowledge support from NERC and the FP6 ENSEMBLES project. M.R.A. received additional support from the International Detection and Attribution Working Group (IDAG), supported by the DOE Office of Science, Office of Biological and Environmental Research and NOAA Climate Program Office, and from the British Council. C.H. acknowledges the CEH Science Budget Fund. C.D.J. and J.A.L. were supported by the Joint DECC, Defra and MoD Integrated Climate Programme (DECC/Defra GA01101; MoD CBC/2B/0417_Annex C5).

Author Contributions M.R.A. and D.J.F. designed, tested and ran the simple climate model. C.H., C.D.J. and J.A.L. developed and tuned HadSCCCM1 and C.H. and J.A.L. ran the simulations; M.M. ran the MAGICC model contributing to Fig. 3 and N.M. advised on statistical analysis. All authors contributed to writing the paper.

Author information

Authors and Affiliations

  1. Department of Physics, University of Oxford, OX1 3PU, UK,
    Myles R. Allen & David J. Frame
  2. Smith School of Enterprise and the Environment, University of Oxford, OX1 2BQ, UK ,
    David J. Frame
  3. Centre for Ecology and Hydrology, Wallingford, OX10 8BB, UK ,
    Chris Huntingford
  4. Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK ,
    Chris D. Jones
  5. Department of Meteorology, Met Office Hadley Centre (Reading Unit), University of Reading, RG6 6BB, Reading, UK,
    Jason A. Lowe
  6. Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany
    Malte Meinshausen
  7. Department of Statistics, University of Oxford, OX1 3TG, UK,
    Nicolai Meinshausen

Authors

  1. Myles R. Allen
  2. David J. Frame
  3. Chris Huntingford
  4. Chris D. Jones
  5. Jason A. Lowe
  6. Malte Meinshausen
  7. Nicolai Meinshausen

Corresponding author

Correspondence toMyles R. Allen.

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Allen, M., Frame, D., Huntingford, C. et al. Warming caused by cumulative carbon emissions towards the trillionth tonne.Nature 458, 1163–1166 (2009). https://doi.org/10.1038/nature08019

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Editorial Summary

Climate change: target acquisition

How quickly greenhouse-gas emissions need to be reduced in order to avoid what has been termed dangerous climate change is of fundamental importance. Two papers in this issue tackle the question from different standpoints, yet come to broadly similar conclusions. Meinshausen et al. relate the cumulative emission of greenhouse gasses by 2050 to the probability of exceeding the 2 °C of global warming above pre-industrial temperatures adopted by more than 100 countries as the threshold of dangerous climate change. They find that only about a third of economically recoverable oil, gas and coal reserves can be burned if global warming of 2 °C is to be avoided by 2100, an amount of fossil fuel that would be burned by 2029 if consumption remains at today's levels. Allen et al. use a combined climate and carbon cycle model to produce simulations spanning a range of climate futures consistent with the changes already observed. The 500 billionth tonne of anthropogenic carbon since 1750 was recently released into the atmosphere, and Allen et al. find that releasing a trillion tonnes of carbon in total is likely to cause a peak warming exceeding the 'acceptable' 2 °C temperature increase. Every tonne released thereafter increases the committed maximum warming in a predictable way, regardless of when it is released. Any effective climate mitigation regime must therefore achieve a cap on cumulative carbon dioxide emissions — one trillion tonnes would be a possible though optimistic target. In News and Views, Gavin Schmidt and David Archer consider these papers and other recent work focusing on establishing achievable emissions targets.

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