DIRECT RADIATIVE FORCING BY ANTHROPOGENIC AIRBORNE MINERAL AEROSOLS

AIRBORNE mineral dust can have a significant effect on the Earth's rad iation budget, as it can both scatter sunlight back to space (leading to negative radiative forcing), and absorb solar and infrared radiatio n (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 widesprea d distribution and large optical depth of mineral dust, Various human activities, such as land use practices, can result in additional loadi ng of dust, increasing the radiative forcing, Previous studies have at tempted to estimate the radiative effects of both the natural and anth ropogenic components of the dust(3,4). Here we use estimates of anthro pogenic dust inputs and observations of dust optical properties to sho w that although the key quantities contributing to the evaluation of t he direct solar radiative forcing by dust generated through human acti vities have a wide range of uncertainty, the forcing by anthropogenica lly generated mineral aerosols may be comparable to the forcing by oth er anthropogenic aerosols, On a regional scale the forcing due to mine ral 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.