Direct radiative forcing by anthropogenic airborne mineral aerosols

AIRBORNE mineral dust can have a significant effect on the Earth's radiation budget, as it can both scatter sunlight back to space (leading to negative radiative forcing), and absorb solar and infrared radiation (leading to positive forcing)1,2. The effects of mineral aerosols on the radiation budget are important relative to those of other types of aerosols—such as sulphate and smoke particles—due to the widespread distribution and large optical depth of mineral dust. Various human activities, such as land use practices, can result in additional loading of dust, increasing the radiative forcing. Previous studies have attempted to estimate the radiative effects of both the natural and anthropogenic components of the dust3,4. Here we use estimates of anthropogenic dust inputs and observations of dust optical properties to show that although the key quantities contributing to the evaluation of the direct solar radiative forcing by dust generated through human activities have a wide range of uncertainty, the forcing by anthropogenically generated mineral aerosols may be comparable to the forcing by other anthropogenic aerosols. On a regional scale the forcing due to mineral aerosols can greatly exceed that due to sulphate aerosols and can be comparable to that of clouds. Our analysis enables us to highlight the key quantities that need to be better characterized to reduce the (currently large) uncertainties in these estimates.