Technical note: On comparing greenhouse gas emission metrics

Abstract. Many metrics for comparing greenhouse gas emissions can be expressed as an instantaneous global warming potential multiplied by the ratio of airborne fractions calculated in various ways. The forcing equivalent index (FEI) provides a specification equal radiative at all times expense generally precluding point-by-point equivalence over time. FEI terms asymptotic exponentially growing emissions. This reference against which other compared. Four are evaluated how closely they match timescale dependence FEI, with methane referenced to carbon dioxide used example. 100-year overestimates long-term role methane, while based on rates change overestimate short-term contribution. A recently proposed metric differences between 20 years apart good compromise. Analysis Laplace transforms leads alternative that gives closer agreement considering longer time periods. behaviour, is important when trading, illustrated simple examples four metrics.