CO<Subscript>2</Subscript> equivalences for short-lived climate forcers

With advancing climate change there is a growing need to include short-lived climate forcings in cost-efficient mitigation strategies to achieve international climate policy targets. Tools are required to compare the climate impact of perturbations with distinctively different atmospheric lifetimes and atmospheric properties. We present a generic approach for relating the climate effect of short-lived climate forcers (SLCF) to that of CO<Subscript>2</Subscript> emissions. We distinguish between three alternative types of metric-based factors that can be used to derive CO<Subscript>2</Subscript> equivalences for SLCF: based on forcing, activity and fossil fuel consumption. We derive numerical values for a wide range of parameter assumptions and apply the resulting generalised approach to the practical example of aviation-induced cloudiness. The evaluation of CO<Subscript>2</Subscript> equivalences for SLCF tends to be more sensitive to SLCF specific physical uncertainties and the normative choice of a discount rate than to the choice of a physical or economic metric approach. The ability of physical metrics to approximate economic-based metrics alters with changing atmospheric concentration levels and trends. Under reference conditions, physical CO<Subscript>2</Subscript> equivalences for SLCF provide sufficient proxies for economic ones. The latter, however, allow detailed insight into structural uncertainties. They provide CO<Subscript>2</Subscript> equivalences for SLCF in short term strategies in the face of failing climate policies, and a temporal evolution of CO<Subscript>2</Subscript> equivalences over time that is noticeably better in line with cost-efficient climate stabilisation. Copyright Springer Science+Business Media Dordrecht 2014