Climatic variability of cloud radiative forcing

Abstract Multiple‐regression models have been developed relating interannual departures of the Earth Radiation Budget Satellite net, long‐wave, and short‐wave cloud radiative forcing primarily to variations in the International Satellite Cloud Climatology Project cloud amounts for low, middle and high clouds, and cloud water. These models are used to evaluate the effects on cloud radiative forcing of specified and observed changes in cloud properties. The calculated changes of cloud forcing due to 16.5% increases in low‐, middleand high‐cloud amounts and 25% increases in cloud water are compared with those of a radiative‐transfer model. the two methods have results which agree with respect to the signs of the responses and the order of the significance of the independent variables for net cloud forcing. Overall, variations in cloud water have the largest effect on net cloud forcing; those in high cloud have the largest effect on long‐wave cloud forcing; those in cloud water make the largest contributions to short‐wave cloud forcing. Using the statistical models forced by one‐standard‐deviation variations in cloud properties, variations in high cloud are shown to have increased importance relative to the results for the 16.5 and 25% perturbations. In addition, variations in clear‐sky planetary albedo and long‐wave flux are also found to be important at higher latitudes. In a small sample of observed short‐term climate‐change scenarios, compensations amongst the effects of the variables alter the magnitude, and in two cases the sign, of the change in net cloud forcing relative to those resulting from uniform variations of the cloud properties.