INSTAAR logo Landscapes and Water (GEOG 1011): GAIA HYPOTHESIS

Instuctor: Mark Williams
Telephone: 492-8830



The following web site on the Gaia Hypothesis is required reading:

Overview of the GAIA hypothesis

Following are my lecture notes; required reading: GAIA lecture notes


DaisyWorld was invented to explain how the Gaia Hypothesis did not require a sentient Earth, but only feedback loops. DaisyWorld demonstrates homeostasis via ecosystem feedback loops. In DaisyWorld, the assumption is that the energy emitted by the sun increases with time. With a bare earth, the air temperature would increase at the same rate. However, the simple addition of black and white daisies causes the air temperature to stabilize at the optimum temperature for daisy growth because of the different albedos associated with the two different daisy colors.

Albedo is a measure of the amount of incoming solar radiation that is reflected by a surface. A higher albedo means more energy is reflected, the surface absorbs less of the incoming energy, and the surface heats less than expected. A lower albedo means less energy is reflected, the surface absorbs more energy, and thus the surface temperature heats up.

The Gaia hypothesis states that the Earth's biosphere interacts with and regulates the physical conditions of the planet. This dynamic "geophysiology" is illustrated by Daisyworld, a planet in which the Earth's surface is modeled in terms of its (blackbody) temperature, with black and white "daisies" living on the surface within a narrow range of temperatures. Temperature is determined by incoming solar radiation and the color of the daisies locally covering Daisyworld's surface. Black daisies absorb light and heat the surface; white daisies reflect light and cool the surface. As Daisyworld evolves, the two sets of daisies germinate and die at different rates, altering local temperatures. Over a specific range of solar luminosities, the daisies steer the planetary system to a stable temperature range matching that required for optimal daisy growth ("homeostasis"). This is demonstrated in the following animation:

This animation provides a simple intro to DaisyWorld. Required reading.
Daisyworld animation; introduction

This animation provides a more realistic animation. Required reading. Please try different run scenarios.
Daisyworld animation; advance

The following web site provides more detailed information on how DaisyWorld works. Optional.
under the hood of Daisyworld: formulas