The contribution of Earth degassing to the atmospheric sulfur budget

Volcanic gases have contributed to the development of the Earth's atmosphere to a large extent. Today, the sulfur budget of the atmosphere is still much influenced by volcanic degassing. Even though the total flux of sulfur gases from quiescent and small eruptive volcanic sources is small compared with anthropogenic release, the geographical distribution and the height of the main sources lead to comparable effects in total atmospheric sulfur budget and also for the important radiative effects. In the upper troposphere the volcanic sources even determine the sulfur content of the atmosphere. When estimated volcanic sulfur emissions are processed and transported in an atmosphere chemistry-climate model, where the contribution of different sources is trace marked, one can estimate the relative contribution of the emittents to total sulfate aerosol radiative forcing. In the global mean the volcanic (-0.15 W/m(2)) is comparable with the anthropogenic (-0.17 W/m(2)) direct backscatter effect of sulfate aerosol. Only in the Northern hemisphere winter, when anthropogenic emissions have their maximum, do they have a stronger (-0.25 W/m(2)) effect than volcanic contributions (-0.15 W/m(2)). (C) 1998 Elsevier Science B.V. All rights reserved.