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Timelines for mitigating methane emissions from energy technologies

Energy technologies emitting differing proportions of methane and carbon dioxide vary in their relative climate impacts over time, due to the different atmospheric lifetimes of the two gases. Standard technology comparisons using the global warming potential (GWP) emissions equivalency metric do not reveal these dynamic impacts, and may not provide the information needed to assess technologies and emissions mitigation opportunities in the context of broader climate policy goals. Here we formulate a portfolio optimization model that incorporates changes in technology impacts as a radiative forcing (RF) stabilization target is approached. An optimal portfolio, maximizing allowed energy consumption while meeting the RF target, is obtained by year-wise minimization of the marginal RF impact in an intended stabilization year. The optimal portfolio calls for using certain higher methane-emitting technologies prior to an optimal switching year, followed by methane-light technologies as the stabilization year approaches. The model is applied to transportation technology pairs and shows that, by accounting for the differing decay behavior of gases, optimal switching portfolios allow energy consumption gains of up to 50% compared to relying on the higher methane-emitting technology alone. The results allow for estimates of target timelines for mitigating methane emissions from energy technologies.