A geophysiologist's thoughts on the natural sulphur cycle

The climate depends on the atmospheric abundance of sulphur aerosols at all levels up to the stratopause. Volcanoes, combustion and biological emissions all contribute and usually result in cooling. The history of this topic is lively and goes back at least to the eighteenth century with Benjamin Franklin's comments on the cooling effects of the sulphuric acid aerosol from the Icelandic volcano, Laki. Mitchell first drew attention to the potential cooling effects of combustion aerosols. Charlson and his colleagues proposed that emissions of dimethyl sulphide (DMS) from ocean algae might also be important. More recently, Lovelock & Kump drew attention to the decline of biological sulphur emissions with global warming and the possible consequence of a positive feedback on climate change. The geophysiological aspects, which arose from the Gaia hypothesis in the early 1970s, form an important part of the account that follows.