Will black carbon mitigation dampen aerosol indirect forcing?

Abstract

If mitigation of black carbon (BC) particulate matter is accompanied by a decrease in particle number emissions, and thereby by a decrease in global cloud condensation nuclei (CCN) concentrations, a decrease in global cloud radiative forcing (a reverse “cloud albedo effect”) results. We consider two present‐day mitigation scenarios: 50% reduction of primary black carbon/organic carbon (BC/OC) mass and number emissions from fossil fuel combustion (termed HF), and 50% reduction of primary BC/OC mass and number emissions from all primary carbonaceous sources (fossil fuel, domestic biofuel, and biomass burning) (termed HC). Radiative forcing effects of these scenarios are assessed through present‐day equilibrium climate simulations. Global average top‐of‐the‐atmosphere changes in radiative forcing for the two scenarios, relative to present day conditions, are +0.13 ± 0.33 W m−2 (HF) and + 0.31 ± 0.33 W m−2 (HC).