title: Testing anthropic selection: a climate change example.
abstract: Planetary anthropic selection, the idea that Earth has unusual properties since, otherwise, we would not be here to observe it, is a controversial idea. This paper proposes a methodology by which to test anthropic proposals by comparison of Earth to synthetic populations of Earth-like planets. The paper illustrates this approach by investigating possible anthropic selection for high (or low) rates of Milankovitch-driven climate change. Three separate tests are investigated: (1) Earth-Moon properties and their effect on obliquity; (2) Individual planet locations and their effect on eccentricity variation; (3) The overall structure of the Solar System and its effect on eccentricity variation. In all three cases, the actual Earth/Solar System has unusually low Milankovitch frequencies compared to similar alternative systems. All three results are statistically significant at the 5% or better level, and the probability of all three occurring by chance is less than 10(-5). It therefore appears that there has been anthropic selection for slow Milankovitch cycles. This implies possible selection for a stable climate, which, if true, undermines the Gaia hypothesis and also suggests that planets with Earth-like levels of biodiversity are likely to be very rare.
authors.affiliation: Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, UK. d.waltham@rhul.ac.uk
authors.forename: Dave
authors.initials: D
authors.lastname: Waltham
mesh_terms: D044822:Biodiversity; D057231:Climate Change; D018534:Earth, Planet; D018559:Exobiology / Q000379:methods*; D016081:Moon; D016083:Planets