Daisyworld model

The Daisyworld model described here was published by Andrew J. Watson & James E. Lovelock in "Biological homeostasis of the global environment: the parable of Daisyworld" in 1983.

Daisyworld is a theoretical cloudless planet with negligible greenhouse gases where only black and white daisies live. The white ones have a higher albedo (\(\alpha\)) than the black ones.

To begin with, Daisyworld's atmosphere is very cool and black daisies, thrive best at cooler temperatures. The more black daisies grow on the planet, the more solar radiation they absorb, causing them to warm up and thus radiate heat to their surroundings, warming the planet. At some point, the planet is too warm for the black daisies and the white daisies begin to grow, because they thrive best at warmer temperatures. And while the planet is covered with more and more white daisies, they begin to reflect more and more energy back into space because their albedo is higher. When more energy is reflected, the colder it gets on the planet and the more uncomfortable it becomes for the white daisies. And as you can imagine, more and more black daisies are now thriving.

☞ White daisies reflect more energy, so the albedo is higher and the planet cools down - they work against the sun (negaitve feedback). The black daisies like the cold, grow up, absorb and store the energy, so the planet gets warmer - they work with the sun (positive feedback). 22.5°C is the optimal growth temperature for both black and white daisies. Together they regulate the planets temperature producing a stable environment despite the changes in solar radiation.

☞ It illustrates how a change in one environmental condition can cause a change in a second condition, which in turn can change the first condition in a feedback loop. In this case feedback is related to the different albedo of different vegetation types.