The possible climatic effects of the secular increase of aerosols from man's activities have been coupled with the microphysics of the aerosol properties. The magnitude of the critical aerosol absorption coefficient to backscatter coefficient, (babs/ bbs)critical, was estimated for a model atmosphere corresponding to cooling or heating of the earth with increasing aerosol concentration. The babs/bbs ratio was calculated with Mie theory assuming a Junge particle size distribution and spherical particles as a function of the imaginary part of the particle refractive index (particle light absorption) and the size distribution slope. Comparing the babs/bbs ratio calculated from Mie theory to the critical babs/ bbs, cooling might ensue if the imaginary part is less than 10−3 while heating may result if it is greater than 0.1.