Evaluation of Black Carbon Semi-Direct Radiative Effect in a Climate Model

A parameterization of liquid cloud optical properties with a mixture of black carbon is proposed. It is found that the changes in cloud optical properties due to mixture of black carbon can be treated as a perturbation to existing cloud optical property parameterizations in climate models.

Based on AMIP type climate model simulations, it is found that the cloud amount can be either enhanced or reduced when BC is included in clouds. For BC in clouds and above, the global annual mean enhancement of solar absorption is about 0.049 W/m2 and 0.57 W/m2 respectively. The BC semi-direct radiative forcing is estimated by subtracting the BC direct forcing from the BC total radiative forcing. The global annual mean of BC direct forcing and semi-direct forcing at TOA are 0.264 W/m2 and 0.213 W/m2, respectively.