Direct Radiative Forcing of Black Carbon Particles: A Global Climate Model Perspective

Black carbon (BC) particles in the atmosphere have profound impacts on air quality, human health, weather, and climate. Although BC represents a key short-lived climate forcer, its direct radiative forcing remains highly uncertain. In particular, the results of absorption enhancement of BC particles during atmospheric aging from available in-situ measurements and laboratory studies are conflicting, leading to large uncertainty in global radiation budget and climate variability. Using a global climate model, the BC forcing change due to the mass absorption cross-section (MAC) enhancement is evaluated, on the basis of the most recently available experimental and field studies. Moreover, the observed MAC enhancement associated with accumulation mode aerosols is implemented in NCAR CAM5. The forcing calculations include both direct radiative forcing and forcing due to the cloud adjustment, in particular the BC semi-direct effects. Atmospheric implications of our results are discussed.