Future changes in global warming potentials under representative concentrationpathways

Abstract

Global warming potentials (GWPs) are the metrics currently used to compareemissions of different greenhouse gases under the United Nations FrameworkConvention on Climate Change. Future changes in greenhouse gas concentrationswill alter GWPs because the radiative efficiencies of marginal changes inCO2,CH4 andN2O depend on their background concentrations, the removal ofCO2 is influenced by climate–carbon cycle feedbacks, and atmospheric residence times ofCH4 andN2O also depend on ambient temperature and other environmental changes. Wecalculated the currently foreseeable future changes in the absolute GWP ofCO2, which acts as the denominator for the calculation of all GWPs, and specifically the GWPs ofCH4 andN2O, alongfour representative concentration pathways (RCPs) up to the year 2100. We find that the absolute GWPof CO2 decreases under all RCPs, although for longer time horizons this decrease is smaller than forshort time horizons due to increased climate–carbon cycle feedbacks. The 100-year GWP ofCH4 would increase up to 20% under the lowest RCP by 2100 but would decreaseby up to 10% by mid-century under the highest RCP. The 100-year GWP ofN2O would increase by more than 30% by 2100 under the highest RCP but would vary by lessthan 10% under other scenarios. These changes are not negligible but are mostly smallerthan the changes that would result from choosing a different time horizon for GWPs, orfrom choosing altogether different metrics for comparing greenhouse gas emissions, such asglobal temperature change potentials.