Improved Attribution of Climate Forcing to Emissions

TLDR

Evaluating multicomponent climate‑change mitigation strategies requires understanding the diverse direct and indirect effects of emissions, as methane, ozone, and aerosols are chemically linked and a single pollutant can influence multiple species. The authors used a coupled composition‑climate model to compute atmospheric composition changes, historical radiative forcing, and unit‑emission forcing from aerosol and tropospheric ozone precursors. Gas‑aerosol interactions markedly shift the relative importance of emissions, revealing that methane has a larger radiative impact than assumed in current carbon‑trading schemes or the Kyoto Protocol, and that mitigation assessments must incorporate these interactions.

Abstract

Evaluating multicomponent climate change mitigation strategies requires knowledge of the diverse direct and indirect effects of emissions. Methane, ozone, and aerosols are linked through atmospheric chemistry so that emissions of a single pollutant can affect several species. We calculated atmospheric composition changes, historical radiative forcing, and forcing per unit of emission due to aerosol and tropospheric ozone precursor emissions in a coupled composition-climate model. We found that gas-aerosol interactions substantially alter the relative importance of the various emissions. In particular, methane emissions have a larger impact than that used in current carbon-trading schemes or in the Kyoto Protocol. Thus, assessments of multigas mitigation policies, as well as any separate efforts to mitigate warming from short-lived pollutants, should include gas-aerosol interactions.