University of Washington
Seattle, WA 98195
Cloud condensation nuclei (CCN) are predominantly sulfate particles, and over the oceans the major source of sulfur for these particles appears to be dimethyl sulfide, a gas produced by marine biota (see Figure 26.1). The reflection of sunlight by marine stratiform clouds is a major feature of the Earth's radiation budget, and these clouds will reflect more sunlight if their liquid water is distributed among more CCN, thus forming more (and smaller) droplets. These facts form the basis of a proposal that marine biogenic sulfur may be an important factor in determining the Earth's climate. Key implications of this proposal are (1) the possibility of a biota-climate feedback loop if the production of biogenic sulfur is sensitive to changes in climate, (2) the possibility that anthropogenic sulfur emissions may be altering the global climate through this cloud-mediated mechanism, and (3) the possibility that anthropogenic pollution could alter climate by perturbing the sulfur-producing marine organisms.
References
Charlson, R.J., J.E. Lovelock, M.O. Andreae, and S.G. Warren, 1987: Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature, 326, 655-661.
Anderson, T.L., G.V. Wolfe, and S.G. Warren, 1992: Biological sulfur, clouds and climate. Encyclopedia of Earth System Science, Academic Press, 363-376.
Andreae, M.O., 1994: Climatic effects of changing atmospheric aerosol levels. World Survey of Climatology, 16, in press.
