Wonderland model
Encyclopedia

Governing equations


Denote the four state variables as: (population), (per capita output), (stock of natural capital) and (pollution flow per unit of output). Let and
, then the state variables evolve in discrete time

Discrete time
Discrete time is the discontinuity of a function's time domain that results from sampling a variable at a finite interval. For example, consider a newspaper that reports the price of crude oil once every day at 6:00AM. The newspaper is described as sampling the cost at a frequency of once per 24...

, according to the following difference equations (Sanderson, 1994).

 




 


Altogether, these equations depend upon 15 parameters.

Sector Parameter
Economic
Demographic
Anthropogenic


 


and represent the birth rate

Birth rate
Crude birth rate is the nativity or childbirths per 1,000 people per year . Another word used interchangeably with "birth rate" is "natality". When the crude birth rate is subtracted from the crude death rate, it reveals the rate of natural increase...

 and death rate respectively. Both saturate as per capita output rises, in agreement with empirical studies (Cohen, 1995).


The form of follows from the IPAT Hypothesis.

System behavior

Using the Scenario analysis
Scenario analysis
Scenario analysis is a process of analyzing possible future events by considering alternative possible outcomes . Thus, the scenario analysis, which is a main method of projections, does not try to show one exact picture of the future. Instead, it presents consciously several alternative future...

 technique, Sanderson (1994) studied two possible futures for the idealized world described by Wonderland. One future entitled Dream, held out the possibility of unending sustainable growth, while the other termed Horror, ended in environmental collapse and eventual extinction of the population. Subsequent work (Kohring, 2006) showed that the parameters of the model can be bisected into two sets, one which always produces sustainable futures and one which always ends in collapse and extinction. Additionally, the equations of Wonderland exhibit chaotic behavior (Gröller, et al., 1996, Wegenkittl, et al., 1997, Leeves and Herbert, 1998).

Avoiding collapse

In the basic model it is impossible to avoid or recover from the environmental collapse seen in the Horror scenario without changes to the model itself. Two such changes have been studied:
pollution abatement and pollution avoidance
Pollution prevention
Pollution prevention ' describes activities that reduce the amount of pollution generated by a process, whether it is consumer consumption, driving, or industrial production...

.

Pollution abatement

Abating the effects of pollution draws funds from other sources to pay for cleaning up the environment (Sanderson, 1994). This decreases the value of entering into the equations for birth, , and death, :

 




 



The time evolution of is unaffected because those goods and services needed for pollution abatement must also be considered part of the overall output. The impact of these changes on the environment is expressed by changes to :

 




 



These changes introduce three new parameters into the model:

Sector Parameter
Policy Levers


 


By adjusting the policy levers, it is possible to cleanup a polluted environment and recover from the collapse seen in the Horror scenario. However, the recovery is only temporary, after a brief time of robust growth the system again collapses, leading to endless cycles of collapse followed by recovery. Abating pollution does not alter the fundamental division of the parameters into the two sets of sustainable and unsustainable futures (Kohring, 2006).

Pollution avoidance

Pollution avoidance
Pollution prevention
Pollution prevention ' describes activities that reduce the amount of pollution generated by a process, whether it is consumer consumption, driving, or industrial production...

 aims to prevent pollution from entering into the environment, by making its production unprofitable. This is modeled by means of a pollution tax (Herbert and Leeves, 1998, Lempert, et al., 2003):

 




 



The new parameters for the pollution avoidance model are:

Sector Parameter
Policy Levers


 



With these changes, it is possible to raise the tax rate, , such that the system never collapses and the horror scenario is avoided altogether. Regardless of the other parameters, it is always possible to increase in order to avoid collapse thereby enabling unending sustainable growth (Kohring, 2006).

Production function

Instead of the relatively simple economic growth equation used for some researchers use a Cobb–Douglas production function instead (Leeves and Herbert, 2002).

Multiple countries

The standard form of the Wonderland model contains a single, homogeneous entity. Herbert et al. (2005) extended Wonderland to a multi-country model by allowing the different entities to use different sets parameters and assuming the outputs are coupled through trade flows.

Differential equations

Originally developed in terms of discrete time, finite difference equations, it is often recast as a set of continuous time differential equations (Gröller, et al., 1996)
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