Future changes in global warming potentials under representative concentration pathways

摘要

Global warming potentials (GWPs) are the metrics currently used to compare emissions of different greenhouse gases under the United Nations Framework Convention on Climate Change. Future changes in greenhouse gas concentrations will alter GWPs because the radiative efficiencies of marginal changes in CO2, CH4 and N2O depend on their background concentrations, the removal of CO2 is influenced by climate–carbon cycle feedbacks, and atmospheric residence times of CH4 and N2O also depend on ambient temperature and other environmental changes. We calculated the currently foreseeable future changes in the absolute GWP of CO2, which acts as the denominator for the calculation of all GWPs, and specifically the GWPs of CH4 and N2O, along four representative concentration pathways (RCPs) up to the year 2100. We find that the absolute GWP of CO2 decreases under all RCPs, although for longer time horizons this decrease is smaller than for short time horizons due to increased climate–carbon cycle feedbacks. The 100-year GWP of CH4 would increase up to 20% under the lowest RCP by 2100 but would decrease by up to 10% by mid-century under the highest RCP. The 100-year GWP of N2O would increase by more than 30% by 2100 under the highest RCP but would vary by less than 10% under other scenarios. These changes are not negligible but are mostly smaller than the changes that would result from choosing a different time horizon for GWPs, or from choosing altogether different metrics for comparing greenhouse gas emissions, such as global temperature change potentials.