Will black carbon mitigation dampen aerosol indirect forcing?

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-gcloud albedo effect-h) 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 +0.13-2 0.33 W m.2 (HF) and + 0.31 ±0.33 W m.-2 (HC). Copyright © 2010 by the American Geophysical Union.