Daisy, daisy, give me your answer do

The short talk will describe one of the simplest possible biosphere models, which incorporates both climate and an evolving plantlife and can be used to model the response of a planetary ecosystem to external driving (a warming sun, the greenhouse effect, nuclear winter etc.).

The model is based on Lovelock's ''daisyworld'' model, extended on to a 2D grid to allow for evolution, and simplified by having a single species. Each point on the grid may be inhabited by ''daisies'' which are a particular shade of grey, and grow best at 22^o. Paler daisies reflect sunlight and lead to a local cooling of the environment, darker daisies absorb sunlight and locally warm their environment. Stochastic rules determines how the daisies die, or spread to adjacent grid points. New daisies may mutate to have a slightly different colour from their parents.

The daisyworld system is self-regulating, maintaining over a range of external heating (''insolation''). Curvature of the planet gives rise to different environments, but the daisies colour (''albedo'') evolves preferentialy to maintain the local temperature at the optimum 22^o. Under extremes of insolation the self regulation breaks down and the daisies die, and we examine the signatures of the system immediately preceding collapse.

Work by Graeme Ackland, Michael Clark and Werner von Bloh.