Clear-Sky Direct Aerosol Radiative Forcing Uncertainty Associated with Aerosol Optical Properties Based on CMIP6 models

Abstract The direct perturbation of anthropogenic aerosols on Earth’s energy balance [i.e., aerosol radiative forcing (DARF)] remains uncertain in climate models. These uncertainties critically depend optical properties, primarily depth (AOD), single scattering albedo (SSA), and the asymmetry factor g . In this study, we investigate intermodel spread DARF across 14 global models within phase 6 Coupled Model Intercomparison Project (CMIP6), using unified transfer calculation parameter assumptions. mean for clear sky 2014 with respect to 1850 is estimated as ?0.77 ± 0.52 W m ?2 assuming an externally mixed state ?0.68 0.53 internally state. We further conduct a quantitative analysis find that globally, external mixing assumption, AOD dominant factor, whose results 36% total uncertainty. For internal SSA becomes major which also leads vertical distribution combined contribute ?30% Regionally, uncertainty typically more sensitive where absorbing fraction high, such South Asia central Africa. Substantial differences between model-averaged observed parameters are still noticed, general yielding closer agreement observations. Our highlight importance absorption properties estimation.