Exploring Daisyworld

Student Worksheet

Daisyworld, originally proposed by Watson & Lovelock in 1983, is a simple model of a planet that illustrates systems behavior and shows how climate can be considered in terms of systems concepts. Daisyworld has only two species of life on its surface, white and black daisies. The planet is assumed to be well-watered, with all rain falling at night so that the days are cloudless. The atmospheric water vapor and CO2 are assumed to remain constant, so that the greenhouse gaseffect of the planet does not change.

In today’s activity, you will run a Daisyworld computer model and consider what Daisyworld teaches us about system behavior and climate sensitivity. This version of the model available on the web was written by Carla Chicchiero from Italy, who specializes in mathematics and web design.

Accessing the Daisyworld Model:

1) Log on to

2) Click on Daisyworld in the left column.

3) Click on “Go” at the lower right.

Daisyworld Model:

This Daisyworld model has both white and black daisies. White daisies reflect solar energy; black daisies absorb it. The colonization of Daisyworld is shown graphically on the left. The time history of “climate” (global average temperature) is shown in the graph on the right.

Parameter / Explanation / Valid Numerical Values*
Black Daisy Heat Rate (BDHR) / Fraction of solar energy absorbed by black daisies: default 0.001 / Range = 0 - 1
0=No energy absorbed
1=All energy absorbed
White Daisy Cool Rate (WDCR) / Fraction of solar energy reflected by white daisies: default 0.001 / Range = 0 – 1
0=No energy reflected
1=All energy reflected
Temperature for White Daisy Life / Minimum and maximum temperatures for survival of white daisies: default min 40 to max 50 / Tmin < Tmax
Temperature for Black Daisy Life / Minimum and maximum temperatures for survival of black daisies: default min 20 to max 30 / Tmin < Tmax
Sun Heat Rate in Different Climates / Fraction of solar energy received in each latitude zone: default: Pole=0.4,Zone 2=0.6,Zone 3=0.8,Equator=1 / Range = 0 – 1
0 = No energy received
1 = All energy received
Initial Temperature of the World / Initial temperature in each latitude zone: default Pole-8, 2-10, 3-12, equator-17

* Note that, in some cases, the model will run with values outside of these ranges; care should be taken in interpreting the results.

Note that the controls for Daisyworld are on the right side under the line graph:

  • Back – return to initial screen
  • Stop – stop the current simulation
  • Start – start a simulation
  • Default – return all parameters in boxes to original values

Daisyworld Experiments

1)Black Daisies Only Case: Set BDHR to 0.1 and the temperature for white daisy life to 4000 (min) and 5000 (max). This scenario explores the case of only black daisies growing on the planet. Leave the “sun heat rate in different climates” and the “initial temperature of the world” unchanged (i.e. at their default settings).

a)Where do the black daisies start growing first? Why?

b)Where do the black daisies die off first? Why?

c)Do the black daisies ever colonize all zones of the planet (i.e., from the equator to the poles) simultaneously? Why or why not?

d)Do the black daisies act as a positive feedback or as a negative feedback on the planet’s temperature?

e)Do the black daisies cause the planet’s temperature to become more stable (i.e., toward equilibrium) or less stable (i.e., away from equilibrium)?

2)White Daisies Only Case: Set WDCR to 0.1 and the temperature for black daisy life to 2000 (min) and 3000 (max). This scenario explores the case of only white daisies growing on the planet. Leave the “sun heat rate in different climates” and the “initial temperature of the world” unchanged (i.e. at their default settings).

a)On the line graph, after the white daisies colonize the planet, the temperature of the planet is lower with the white daisies than with no daisies. How do the white daisies cool the planet?

b)Do the white daisies act as a positive feedback or negative feedback on the planet’s temperature?

c)Do the white daisies cause the planet’s temperature to be more stable or less stable?

d)Do the white daisies ever colonize all zones of the planet (i.e., from the equator to the poles) simultaneously? Why or why not?

3)Default Case: Return the parameters to the default setting. Then set both BDHR and WDCR to 0.1.

a)What type of daisies grow first? Why?

b)What type of daisies die off first? Why?

c)What type of daisies populate the planet’s surfacefor the longest amount of time? Why?

d)Compare the temperature versus time graph for the “without daisies” case and the case with both black and white daisies that you just ran. How does the growth of daisies cause the large difference between these two cases?

4)Describe how what you’ve modeled here can be extended and used to understand Earth and its systems.

1

Created by Dr. Donna Witter, Kent State University