Earth System Dynamics Discussions www.earth-syst-dynam-discuss.net 2190-4995 3 1 2012 10.5194/esdd-3-1-2012 http://www.earth-syst-dynam-discuss.net/3/1/2012/ http://www.earth-syst-dynam-discuss.net/3/1/2012/esdd-3-1-2012.html http://www.earth-syst-dynam-discuss.net/3/1/2012/esdd-3-1-2012.pdf 1 29 2012-01-13 Comparison of physically- and economically-based CO₂-equivalences for methane O. Boucher olivier.boucher@lmd.jussieu.fr Laboratoire de Météorologie Dynamique, Institut Pierre Simon Laplace, UMR8539, CNRS – Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05, France There is a controversy on the role methane (and other short-lived species) should play in climate mitigation policies and no consensus on what an optimal methane CO₂-equivalence should be. We revisit this question by discussing the relative merits of physically-based (i.e. Global Warming Potential or GWP and Global Temperature change Potential or GTP) and socio-economically-based climate metrics. To this effect we use a simplified Global Damage Potential (GDP) that was introduced by earlier authors and investigate the uncertainties in the methane CO₂-equivalence that arise from physical and socio-economic factors. The median value of the methane GDP comes out very close to the widely used methane 100-year GWP because of various compensating effects. However there is a large spread in possible methane CO₂-equivalences (1–99% interval: 10.0–42.5; 5–95% interval: 12.5–38.0) that is essentially due to the choice in some socio-economic parameters (i.e. the damage cost function and the discount rate). The methane 100-year GTP falls outside these ranges. It is legitimate to increase the methane CO₂-equivalence in the future as global warming unfolds. 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