The climate changing gas dimethyl sulphide is being made by microbes at the rate of more than 200 million tonnes a year in the world’s seas. The source of the dimethyl sulphide gas is another sulphur compound made by many seaweeds and marine plankton as an anti-stress protection. Some marine bacteria can break down this compound to release chemical energy, and dimethyl sulphide is given off as a by-product, with about 10% finding its way up into the atmosphere.