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created with NetLogo
view/download model file: sd-dw1.nlogo
This is an adaptation of the original Daisyworld model of Lovelock and Watson, done as a 2D vectorfield using the NetLogo System Dynamics Modeler. It is easy because a STELLA model may be found online at: www.carleton.edu/departments/GOEL/DaveSTELLQA/Daisyworld/daisyworld_model.htm
thanks to Dave Bice.
Read Dave Bice's paper for details. Each tick represents 20,000 years of daisyworld time. Solar luminosity (solar-lum) starts at 0.6 and increases with each tick. Daisie areas (black and white) increase accoding to the growth factors and death rates. The average planetary temperature (avg-temp) is determined by the average albedo according to the Stefan-Boltzmann law. The local temperatures over the black and white daisies are computed by making slight corrections to the average temperature. The parabolic growth laws for daisies (following Dave Bice) have the same optimum temperature for both colors of daisies, although in the original model of Lovelock and Watson, white daisies preferred a temperature warmer than that for black daisies.
As we have not included any sliders, one must change the model by editing the System Dynamics diagram.
Notice that this vectorfield in the plane always has a unique point attractor. The location of this attractor moves with time, as the solar luminosity is ever on the rise.
Try changing the initial values and the albedos of the three areas. The three areas should always add up to one.
This model, originally programmed by Dave Bice in STELLA, is very easy to do in NetLogo because of the System Dynamics Modeler.
Check out the daisyworld model in the NetLogo Model Library under Biology. It is a distributed model, showing a small exemplary patch of dirt under the microscope as individual daisies multiply and die. Our model is an aggregate model, as is the original of Lovelock and Watson, depending only on the total areas covered by white and black daisies.
Many thanks to David Bingham for the revolutionary STELLA program of 1987, to Dave Bice for his adaptation of Daisyworld, and to Uri Wilensky and the NetLogo team for their System Dynamics Modeler. This is, as far as we know, the first freeware version of STELLA.