The Impact of Daisies on Climate: A Story of Survival

1. In the beginning of Daisyworld, God created a young star and a barren planet, cold and distant from its sun. As time went on the star grew hotter (click to see graph)

2. On Daisyworld’s barren surface there was no life, but two types of daisy were ready to spring into action as soon as conditions were right. Black daisies and white daisies shared all the same characteristics except colour. As soon as the planet reached optimum temperature for daisy growth, flowers would spread across the rocky surface. The young sun continued to heat, bringing the temperatures closer to the optimum for daisy growth. Ideal temperatures for daisies

3. Although Daisyworld’s temperature was generally too low for daisy growth, a few sheltered spots near the equator could just support daisy growth. Black daisies grew best because their dark colour absorbed the faint heat from the sun, warming the surroundings. The first few colonies of daisies caused rapid local warming. Soon it was warm enough for more and more black daisies - which in turn raised the planet’s temperature faster than the sun’s slow heating could achieve. Ideal temperatures for daisies

4. After this rapid warming - set off by the black daisies - Daisyworld was now warm enough for white daisies to grow as well. The white daisies had a high albedo and so cooled their surroundings, consequently they favoured the hotter regions of the globe (which they cooled) whilst the black daisies spread to the poles, warming the cooler regions. Between them the black and white daisies moderated the temperature of the entire planet. But still the sun grew hotter.

5. Millions of years later the sun is still growing hotter and Daisyworld would be baking under its heat - were it not for the covering of white daisies which have now replaced the black ones over most of the globe. The black daisies could no longer survive because they absorbed too much heat, pushing the local temperatures too high for daisy survival. Eventually the equator is too hot even for white daisies and the planet’s temperature begins to rise as daisies die.

6. The sun is too hot to allow life to grow on Daisyworld. Only in the most shaded polar areas do a few white daisies still survive by reflecting the tremendous heat from the now mature sun. Within a few centuries Daisyworld will be devoid of life.

7. T1 Daisyworld is dead. But look at the difference the daisies made. The graph shows the actual temperature curve created by the daisies. They moderated climate so that it was suitable for daisies for time T1 (click to see labels). Without the daisies, the temperature would have risen in a straight line, so life would only have been possible for time T2 (click to see labels). Optimum temps for daisies T2 The daisies - therefore - moderated climate in a way that benefited their survival - an example of global homeostasis and the Gaia hypothesis at work.