PNNL

Abstract

Multi-gas greenhouse emission targets require that different emissions be combined into an aggregate total. The Global Warming Potential (GWP) index is currently used for this purpose, despite various criticisms of the underlying concept. It is not possible to uniquely define a single metric that perfectly captures the different impacts of emissions of substances with widely disparate atmospheric lifetimes, which leads to a wide range of possible index values. We examine the sensitivity of emissions and climate outcomes to the value of the index used to aggregate methane emissions using a technologically detailed integrated assessment model. We find that the sensitivity to index value is of order 4-14% in terms of methane emissions and 2% in terms of total radiative forcing, using index values between 4 and 70 for methane, with larger regional differences in some cases. The sensitivity to index value is much higher in economic terms, with total 2-gas mitigation cost decreasing 4-5% for a lower index and increasing 10-13% for a larger index, with even larger changes if the emissions reduction targets are small. The sensitivity to index value also depends on the assumed maximum amount of mitigation available in each sector. Evaluation of the maximum mitigation potential for major sources of non-CO2 greenhouse gases would greatly aid analysis