Fugitive Methane and the Role of Atmospheric Half-Life

Because methane has an initial GWP (global warming potential) 120x that of carbon dioxide, concern about leaked “fugitive” methane often dominates discussions of natural gas policy. But this high GWP can easily be misinterpreted to conclude that natural gas is a much greater greenhouse danger when used for electric power generation vs. coal. In determining policy, particularly with regard to legacy issues (global warming for future generations) it is essential to take full account of the short 8.6-year lifetime of methane in the atmosphere. Moreover, the Intergovernmental Panel on Climate Change use of time “horizon” must be understood properly; it refers to an average from the present, not a time that lies in the future. The IPCC GWP value cannot be used directly to estimate the effect unless careful account is taken of the lighter weight of the methane molecule compared to that of carbon dioxide. We discusses severalways to take these issues into account, and show that for a wide range of leakages and legacy goals, fugitive methane is typically not a critical issue, and that even with a few percent leakage, natural gas is preferable to coal for legacy global warming considerations.