Objective● Understand how aerosol effects on

clouds can best be estimated from model simulations

Approach● Add diagnostic calculations of the

cloudy-sky and clear-sky energy balance

● Estimate “clean-sky” cloud radiative forcing from the diagnosed cloudy- and clear-sky energy balance with aerosol scattering/absorption neglected

● Compare the clean-sky estimate with the conventional estimate that includes scattering and absorption by aerosols

Estimating Aerosol Effects on Clouds

Ghan SJ. 2013. “Technical Note: Estimating aerosol effects on cloud radiative forcing.” Atmospheric Chemistry and Physics 13: 9971-9974. DOI:10.5194/acp-13-9971-2013.

Impact● The bias in previous estimates of aerosol effects on

clouds has been identified and corrected.

CAM5.1 simulations of present-day and preindustrial difference in five-year annual mean top-of-atmosphere shortwave cloud radiative forcing (top, left), clean-sky shortwave cloud radiative forcing (top right), the difference (bottom left) and the surface albedo forcing (bottom right).