The contributions of atmospheric factors to surface shortwave irradiance (S) variability was investigated, using radiative transfer calculations to examine all sky (both cloud-free and cloudy) conditions. We defined the sensitivities of S to differential increases from given values of cloud, aerosol, and water vapor as potential radiative forcing (PRF). Thus, the expected change in S due to one factor would be the product of the PRF and the change in that factor. Geographical features of the PRF were described over China in January and July, and then the PRF was applied to evaluate the relative contributions of related factors to S variability over Jinan (the central-eastern China) during 1984 and 1990. Although some shortcomings were pointed out, the usefulness of the PRF was confirmed for determining the relative contributions. In particular, to use accurate aerosol absorption properties was suggested to be crucial for quantitative radiation budget estimates.