The Concept of ‘ G aia’

Abstract The Gaia theory of James Lovelock proposes that the Earth is a self‐regulating system, or super‐organism, maintaining conditions hospitable to contemporary planetary biota. Objections to this theory, concerning its alleged untestability and circularity, are considered and countered. Favourable evidence includes Lovelock's Daisyworld model of a planet regulating its own temperatures and thus maintaining homeostasis, and his discoveries of actual regulatory mechanisms such as the biological generation of dimethyl sulphide, which removes sulfur from the oceans and seeds clouds whose albedo reduces solar radiation (a negative feedback mechanism). After some decades of scepticism, sections of the scientific community have partially endorsed Gaia theory, accepting that the Earth system behaves as if self‐regulating. Whether or not this theory is acceptable in full, it has drawn attention to the need for preserving planetary biological cycles and for the planetary dimension to be incorporated in ethical decision‐making, and thus for a planetary ethic. Key Concepts James Lovelock hypothesises that the planetary physical and biological system is a self‐regulating super‐organism. There were precedents before Lovelock for ascribing life either to the planet or to the universe. James W. Kirchner presents Gaia hypotheses as either unoriginal or untestable. Lovelock demonstrates that Gaia theory is both original and testable, albeit indirectly. Lovelock's theory can readily escape the charge of circularity. Predictions of Gaia theory include the existence of biologically generated mechanisms of planetary regulation. Lovelock's discovery of dimethyl sulphide discloses such a mechanism for the regulation of oceanic sulfur. Both atmospheric oxygen and atmospheric nitrogen turn out to be biologically generated and maintained. Philosophers such as Stephen Clark and Mary Midgley have made Gaia a symbol for the planetary thinking currently needed. The Amsterdam Declaration of planetary scientists (Moore et al ., 2001) accepted aspects of Gaia theory, without explicitly accepting the theory's planetary goal.