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

Journal name:
Nature Climate Change
Year published:
Published online

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.

At a glance


  1. Long-term effect of zero emissions.
    Figure 1: Long-term effect of zero emissions.

    Illustrative scenarios where emissions are instantaneously cut by 100% (a and b), compared with scenarios where emissions decrease today following a mitigation rate of 5%, 3% and 1% (c and d, blue, green and red lines respectively) and where emissions start decreasing globally in 10, 20 or 30 years at a 3%yr−1 mitigation rate (e and f, blue, green and red lines respectively). The left panels show atmospheric CO2 concentration (ppmv) and the right panels show global surface temperature change relative to the pre-industrial (°C). The instantaneous mitigation case of a,b is reproduced on c,d (black lines) as the ‘baseline’ case (infinite mitigation rate). Similarly, the 3% mitigation rate with no delay case (c,d, green lines) is reproduced on e,f (black lines) as the ‘baseline’ case (no delay in mitigation). Also shown on each temperature panel is the 2°C isoline (thin black line).

  2. Long-term effect of non-zero positive and negative long-term emissions.
    Figure 2: Long-term effect of non-zero positive and negative long-term emissions.

    Illustrative scenarios where emissions eventually decrease by 90% relative to the present-day level (top four panels) or by 105% relative to the present-day level (negative emissions, through carbon capture and storage) (bottom four panels). As in Fig. 1, three mitigation rates are investigated as well as three delays in emission mitigation. The instantaneous mitigation cases are also shown on a,b and e,f (black lines) as the ‘baseline’ case (infinite mitigation rate). Similarly, the 3% mitigation rate with no delay cases (a,b and e,f, green lines) are shown on c,d and g,h respectively (black line) as the ‘baseline’ cases (no delay in mitigation). Also shown on each temperature panel is the 2°C isoline (thin black line).

  3. Global peak temperature accounting for uncertainty in climate sensitivity.
    Figure 3: Global peak temperature accounting for uncertainty in climate sensitivity.

    Global peak temperature change reached within the next 1,000 years for the three levels of long-term mitigation: 100% reduction (left panel, square symbols), 90% reduction (middle panel, circle symbols) and 105% reduction (right panel, diamond symbols). Symbols are for the median climate sensitivity (3°C), while error bars shows the ‘likely’ range (more than 66% probability) for low (2°C) and high (4.5°C) climate sensitivities. Within each panel, black symbols represent immediate and instantaneous emissions reduction; dark blue, green, light blue and red symbols represent global emissions mitigation starting today or delayed by 10, 20 and 30 years respectively; mitigation rates are indicated as 1% (open symbols), 3% (filled symbols) and 5% (symbols bordered in black).


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Author information


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

    • P. Friedlingstein
  2. Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado 80309, USA

    • S. Solomon
  3. Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland

    • G-K. Plattner
  4. Institute for Atmospheric and Climate Science, ETH Zurich, Universitätstrasse 16, CH-8092 Zürich, Switzerland

    • R. Knutti
  5. Laboratoire des Sciences du Climat et de l’Environment, UMR CEA-CNRS-UVSQ, Bat. 709, CE, L’Orme des Merisiers, 91191 Gif-sur-Yvette, France

    • P. Ciais
  6. CSIRO Marine and Atmospheric Research, Clunies Ross Street, Black Mountain, Acton, Australian Capital Territory 2601, Australia

    • M. R. Raupach


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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The authors declare no competing financial interests.

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