Ecological Limit for Population

A society's population is supported by its economy, and a population's ecological limit is therefore tied to the economy's ecological limit.

For this reason, a population cannot expand beyond the point where the economy exhausts its lowest environmental budget. This statement can be clarified with the help of the following figure.

A population's ecological limit
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For a given average per capita rate of consumption (Q/P), the economy's ecological limit determines the population's ecological limit.

In this graph the independent variable is the population level on the horizontal axis. The vertical axis represents the economy's total outputs per unit of time. Moving up and down this axis thus represents changes in the economy's scale.

For simplicity, the model assumes that there is no trade, which means that all outputs are locally consumed.

The sloping line depicts the average per capita rate of consumption. It is assumed that ENL's principles have been applied, and that this consumption represents target output quantities that have been equitably distributed.

Further, ecological efficiencies have been maximized, and the economy's ecological limit is therefore as high as can be currently achieved.

As the slope of this line increases (rotates up), the economy's scale increases for a given population level, and average consumption therefore goes up. As the slope decreases (rotates down), the scale decreases and the average goes down.

The line thus relates a specific population level such as P1 to a specific economic scale such as S1.

As population increases from P1 the economy's scale increases from S1. When the scale reaches its ecological limit, the population has reached its ecological limit.

Any further increases in population would be impermissible by ENL principles because the economy would contribute to global overshoot.

Note that a higher consumption rate, and thus a steeper slope, would cause this ecological limit to be reached more quickly. Thus, the higher the consumption rate, the lower the sustainable population, and vice versa.

This model addresses all three of the factors underlying overshoot: population, per-capita consumption, and ecological efficiencies. It could therefore be used as the basis of ENL's overshoot model. However, per-capita consumption is represented here by the slope of a line, which is difficult for most people to intuitively grasp.

A different model has therefore been chosen a to deal with the overshoot issue — one that more clearly represents the three critical overshoot factors.

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