Revised 24 May 2019

 In the summer of 1970, Professor Jay Forrester of MIT presented a global computer model to the Club of Rome conference in Cambridge, Massachusetts. This global model which took into account over 100 factors including population, agricultural production, natural resources, industrial production, and pollution, enabled the analysis of the behaviour and dynamic relationships of these factors. 

An international team under the direction of Professor Dennis Meadows was set up to examine five basic factors that determine and ultimately limit growth on our planet. Many different model runs were made based on different inputs of the physical aspects of humankind’s behaviour. In all model runs capital and population growth were allowed to continue until they reached some natural limits. 

The results of the study were published in the book The Limits to Growth.  When population and capital growth were allowed to grow without human constraints, there was no policy that avoided the scenario of an exponential growth of population and capital followed by collapse. Some policies delayed collapse, but a collapse scenario by the year 2100 and earlier were common to all model runs without human constraint. 

Figure 1: Business as Usual Model of Collapse 

In the process of seeking the requirements for global equilibrium, constraints on population and capital growth were each tested separately. It was found that the collapse scenario also applied for these conditions. When simultaneous constraints on population and capital growth were tested, global equilibrium was achieved. 

The Limits to Growth made the following four points:

    1. National policies that existed prior to and in 1972 promoted exponential growth in population and material consumption.
    2. There are limits to growth because the Earth is finite.
    3. Exponential growth on a finite planet will inevitably stop either voluntarily or due to mounting global pressures. 
    4. The sooner we act to slow down exponential growth and stop growth in population and material consumption, the more possibilities will be available for future generations. 

The minimum requirements for global equilibrium, or steady state, were defined as being: 

    1. "The capital plant and the population are constant in size. The birth rate equals the death rate and the capital investment rate equals the depreciation rate. 
    2. All input and output rates - births, deaths, investment, and depreciation - are kept to a minimum. 

The levels of capital and population and the ratio of the two are set in accordance with the values of the society. They may be deliberately revised and slowly adjusted as the advance of technology creates new options." (Meadows et al., 1972, pp 173-4)

The above minimum requirements for steady state in a human ecosystem are equivalent to the conditions for climax in other ecosystems.