Daisyworld

A model planet with nothing on it but grey ground and two kinds of daisy. Black daisies absorb more sunlight than the ground and warm their surroundings; white daisies reflect more and cool them. Brighten the sun and compare the planet with daisies against the same planet with no life at all.

Daisies on the planet:

White0%
Black0%
Bare ground100%

Planet temperature (°C)

With daisies
Same planet, no life
Daisies can grow (5 to 40 °C)
Best for daisies (22.5 °C)

What covers the surface

Sun brightness 0.60×

In this mode the sun brightens by itself. Switch to Steady sun to hold it where you choose.

With daisies

−9.2 °C

No life

−9.2 °C

Sun brightness

0.60×

Planet albedo

0.50

Try an experiment

The first four run the sun from dim to bright. The last two hold it steady and disturb the planet instead.

What to notice

On the lifeless planet the temperature simply follows the sun. The dashed line is that planet, drawn on every run so you always have it to compare against.
With both daisies, the solid line stays between about 20 °C and 27 °C for most of the run, while the dashed line climbs by more than 50 °C.
Watch which colour is winning at each point in the run, and what that does to the planet's albedo.
Look at how quickly things change at the two ends of the run, once they start to change.
Nothing on the planet plans anything. Each daisy simply grows where the temperature suits it.

About the model

Andrew Watson and James Lovelock published Daisyworld in 1983 to show that the life on a planet can regulate its temperature without anything planning it. It is deliberately simple: no atmosphere, clouds or greenhouse gases, one kind of plant in two colours, and a temperature that responds instantly to the sun. It is a model of an idea, not of the Earth.

Albedo: bare ground 0.50, white daisies 0.75, black daisies 0.25. The planet's albedo is the average, weighted by how much of the surface each covers.
Temperature: the planet warms until the heat it radiates equals the sunlight it absorbs. A patch of black daisies runs warmer than the planet as a whole and a patch of white daisies cooler.
Growth: both kinds grow fastest at 22.5 °C and not at all below 5 °C or above 40 °C, and a fixed share dies back all the time. They can only spread onto bare ground.
Seeds: each kind switched on always keeps 1% of the surface, so it can spread again when conditions allow.
Sun brightness is a multiple of 917 W m⁻², the model's reference sunlight. 1.00 is not a claim about our own Sun.

Source: Watson, A.J. and Lovelock, J.E. (1983) Biological homeostasis of the global environment: the parable of Daisyworld. Tellus B 35(4), 284–289.