The radiative forcing (or effect) due to aerosol-cloud interactions (RFaci) is the radiative forcing (or radiative effect - if the perturbation is internally generated) due to the change in number or size distribution of cloud droplets or ice crystals that is the proximate result of an aerosol perturbation - with other variables (in particular total cloud water content) remaining equal. In liquid clouds - an increase in cloud droplet concentration and surface area would increase the cloud albedo. This effect is also known as the cloud albedo effect - first indirect effect - or Twomey effect. It is a largely theoretical concept that cannot readily be isolated in observations or comprehensive process models due to the rapidity and ubiquity of rapid adjustments. This is contrasted with the effective radiative forcing (or effect) due to aerosol-cloud interactions (ERFaci)