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Long-term climate implications of twenty-first century options for carbon dioxide emission mitigation


Long-term future warming is primarily constrained by cumulative emissions of carbon dioxide1,2,3,4. Previous studies have estimated that humankind has already emitted about 50% of the total amount allowed if warming, relative to pre-industrial, is to stay below 2 °C (refs 1, 2). Carbon dioxide emissions will thus need to decrease substantially in the future if this target is to be met. Here we show how links between near-term decisions, long-term behaviour and climate sensitivity uncertainties constrain options for emissions mitigation. Using a model of intermediate complexity5,6, we explore the implications of non-zero long-term global emissions, combined with various near-term mitigation rates or delays in action. For a median climate sensitivity, a long-term 90% emission reduction relative to the present-day level is incompatible with a 2 °C target within the coming millennium. Zero or negative emissions can be compatible with the target if medium to high emission-reduction rates begin within the next two decades. For a high climate sensitivity, however, even negative emissions would require a global mitigation rate at least as great as the highest rate considered feasible by economic models7,8 to be implemented within the coming decade. Only a low climate sensitivity would allow for a longer delay in mitigation action and a more conservative mitigation rate, and would still require at least 90% phase-out of emissions thereafter.

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Figure 1: Long-term effect of zero emissions.
Figure 2: Long-term effect of non-zero positive and negative long-term emissions.
Figure 3: Global peak temperature accounting for uncertainty in climate sensitivity.


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The authors wish to thank D. Matthews, J. Daniel and T. Sanford for helpful discussions and R. Flecker for creating Fig. 3.

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P.F. and S.S. designed the work and the experiments, P.F. performed the model simulations, G-K.P. provided the model code, G-K.P. and R.K. gave guidance on the use of the model, P.F. led the writing of the paper with contributions from all other authors.

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Correspondence to P. Friedlingstein.

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The authors declare no competing financial interests.

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Friedlingstein, P., Solomon, S., Plattner, GK. et al. Long-term climate implications of twenty-first century options for carbon dioxide emission mitigation. Nature Clim Change 1, 457–461 (2011).

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