This description is taken from the original documentation. The model diagram is shown below.
The model has the three state variables (stocks): population, environmental pollution, and production capacity (all standardized to an initial value of 1).
The population increases by births and is reduced by deaths. The number of births per year depends on the size of the population, the birth rate, and a birth control parameter. It is also affected by the consumption level and by the quality of environment.
The respective environmental pollution arises from the interplay of environmental degradation and regeneration. The amount of degradation depends on population, its consumption level and the specific degradation rate. Regeneration is determined by the specific regeneration rate, the damage threshold, the quality of environment and current environmental pollution. The quality of environment is all the higher the smaller the environmental pollution is in relation to the damage threshold. If the environmental pollution exceeds the damage threshold (quality of environment less than 1), then the regeneration mechanism of environmental pollution changes: the regeneration rate no longer corresponds to existing environmental pollution but to the (smaller) value of the damage threshold.
The level of production capacity changes by the capacity increase rate. This depends with a logistic saturation function on consumption level that in turn corresponds to available production capacity. The capacity increase corresponds to the parameters growth rate and consumption goal; it is also affected by environmental pollution.
To explore the behaviour of the model, simply move the sliders for the initial stock value or the parameter value, and the graphs will be updated.
The final value for Population is . The maximum value for Environmental pollution is and occurred at time .
Plot of population against time
Plot of Environmental pollution and Production capacity against time
This model is a Systo re-implementation of the Miniworld model (model Z605) presented in Bossel, H. (2007). System zoo: 3. Norderstedt: Books on Demand GmbH, p. 116-124.
This link provides a partial preview of the chapter describing the model.