Toward a Future for Gaia Theory

The three papers in this issue of Climatic Change (Kirchner, 2002; Kleidon, 2002; Lenton, 2002) are probably the most concentrated effort in recent years by several prominent theoreticians of the biosphere to set forth their views on the current status and future of Gaia theory. (Also see the forthcoming volume by M.I.T. Press of the proceedings from the Second Chapman Conference on the Gaia Hypothesis, Valencia, Spain, 2000.) The three papers offer strikingly different renderings. Axel Kleidon asks whether life on global scales enhances itself by improving environmental conditions through its activities. His analysis suggests ‘yes.’ He further recommends that primary production measured in carbon units should be utilized as a ‘metric’ (my term) for Gaia theory. In contrast, Timothy Lenton focuses not as much on environmental parameters but on whether a global system with life, compared to a sterile planet, will be more resistant to change and also more resilient in its rapidity of response to change. Lenton concludes, tentatively at least, that the Gaia system does enhance regulation and that this regulation will tend to accumulate over time. The message in the third paper, by James Kirchner, runs counter to both Kleidon and Lenton. Kirchner uses evolutionary arguments to show why we should expect Gaia neither to be more stably regulated than an abiotic system nor produce an enhanced environment for life. Overall, I am most in agreement with Kirchner. As I will emphasize, the dynamics of evolutionary adaptation have far too often been neglected by Gaia theorists. In this essay I will concentrate first on the arguments advanced by Kleidon and Lenton, looking both at their shortfalls and positive offerings. Eventually I will try to use ideas from all three papers to sketch out what I see as tasks for the future of Gaia theory, which involves the ongoing search for general principles of the biosphere.