James Lovelock is a scientist/inventor. He's earned his living and funded his research by his inventions, largely of measuring devices. He proposed the Gaia hypothesis, that planet Earth could be viewed as a single self-maintaining biotic/abiotic organism, controlling its internal environment in homeostasis (within limits) much like any other organism. To do this, Gaia uses the water cycle, nitrogen cycle, and many others, everything from controlling atmospheric oxygen between asphyxiation and combustion, to maintaining ocean salinity.
Lovelock took a lot of flack for this. One of the criticisms leveled at the Gaia hypothesis was that Gaia must be an omniscient goddess, hardly what Lovelock was saying. In response to this, Watson and Lovelock published a simple cartoon system called DaisyWorld, where homeostasis is maintained by simple nonlinear feedback loops.
In DaisyWorld, daisies find 22.5 degrees Celsius just perfect. At that temperature their birthrate is a maximal 1.0. Their birthrate drops off to zero at 5 and 40 degrees Celsius. The deathrate is constant. The determination of temperature is a bit complex. Different color daisies, and bare ground, have different albedos, the amount of incoming light they reflect back off into space. An albedo of 1.0 is a perfect reflector and 0.0 is a perfect absorber. The effect of albedo on determining Earth's temperature is well-studied. Some values are mentioned in the Questions. The equations for this global temperature calculation are Under the Hood. They are nonlinear, permitting feedback loops.
There are two other details in the DaisyWorld model, solar input and insulation. In the Scenarios in this lab, solar input is allowed to vary from 0.6 to 2.0 times the base solar luminosity. Like our own sun, DaisyWorld's sun is getting brighter. The timescale on this is about 4 billion years before now (luminosity 1.0), and 10 billion after now until our sun's too hot for Earth to support life. Insulation (0 to 1.0) is the degree to which each color daisy's area maintains its own local temperature rather than equilibrating to the global temperature. Note that area is percent area of a completely flat world. There is no spatial structure, and the daisy display here is simply showing percentages. On the plot window, the first plot tracks the percent area barren and for each species.
With the daisies having no tricks at their disposal except color/albedo and birthrate, they maintain the living planet's temperature at a daisy-friendly 20-30 degrees in the face of the solar input doubling or tripling. The second plot shows the temperature of the living planet, versus what the temperature would be if the planet were all barren. In this way, Watson and Lovelock hoped to demonstrate the power of control by feedback loops, and thus how no omniscience or even sentience was implied by the Gaia hypothesis. Simple feedback was sufficient for homeostasis.
In this course, you're studying ecological models: cartoons of reality, based on a set of propositions of what is and is not important, and what happens as a result of that which is deemed important. These propositions are made by fiat, maybe inspired, possibly well-justified, but still by fiat. In this context, whether the Gaia hypothesis is "right" is not the question. The question is, What does this perspective/model enable one to see? What does it show and what does it hide? The Gaia system is too vast for a course example, but hopefully, DaisyWorld can provide an appreciation for its principles.
There are suggestions for thinking games to play here under Questions, plus some easier drill questions under Homework. Please spend some time on the model details Under the Hood, because you'll be seeing elaborated forms of DaisyWorld again in later labs. Outside readings are provided under References.
Ginger Booth, Jan 14, 1998