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Emission pathways consistent with a 2 °C global temperature limit


In recent years, international climate policy has increasingly focused on limiting temperature rise, as opposed to achieving greenhouse-gas-concentration-related objectives. The agreements reached at the United Nations Framework Convention on Climate Change conference in Cancun in 2010 recognize that countries should take urgent action to limit the increase in global average temperature to less than 2 °C relative to pre-industrial levels1. If this is to be achieved, policymakers need robust information about the amounts of future greenhouse-gas emissions that are consistent with such temperature limits. This, in turn, requires an understanding of both the technical and economic implications of reducing emissions and the processes that link emissions to temperature. Here we consider both of these aspects by reanalysing a large set of published emission scenarios from integrated assessment models in a risk-based climate modelling framework. We find that in the set of scenarios with a ‘likely’ (greater than 66%) chance of staying below 2 °C, emissions peak between 2010 and 2020 and fall to a median level of 44 Gt of CO2 equivalent in 2020 (compared with estimated median emissions across the scenario set of 48 Gt of CO2 equivalent in 2010). Our analysis confirms that if the mechanisms needed to enable an early peak in global emissions followed by steep reductions are not put in place, there is a significant risk that the 2 °C target will not be achieved.

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Figure 1: Emission ranges of published IAM scenarios, colour coded as a function of the likely (greater than 66% probability) avoided global average temperature increase.

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The authors gratefully thank everyone involved in the UNEP Emissions Gap Report, and acknowledge the contributions of all modelling groups that provided data and information, all co-authors from the UNEP Emissions Gap Report and others who provided comments, in particular B. Knopf, G. Luderer, E. Sawin, B. O’Neill, B. Ward, N. Ranger, V. Bossetti and R. Knutti. J.R. was supported by the Swiss National Science Foundation (project 200021-135067). J.L. was supported by the Joint DECC/Defra Met Office Hadley Centre Climate Programme (GA01101) and the AVOID programme (GA0215).

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J.R., W.H., J.L., K.R., B.M., M.M. and D.P.v.V. designed the research. M.M. developed the climate model set-up. J.R. carried out the research. All authors discussed the results and contributed to writing the paper.

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Correspondence to Joeri Rogelj.

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The authors declare no competing financial interests.

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Rogelj, J., Hare, W., Lowe, J. et al. Emission pathways consistent with a 2 °C global temperature limit. Nature Clim Change 1, 413–418 (2011).

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