Reversing Overshoot

In general, the term "overshoot" means to violate a limit. If a landing airplane overshoots a runway, for example, this means it violates the runway's length limit and ends up in a field beyond the tarmac. When applied to the global environment, "overshoot" has two related but distinct interpretations.

The first is when humankind ignores the fact that nonrenewable resources will one day be effectively depleted, and grows beyond the Earth's capacity to sustainably support its production level through renewable resources alone.

This is a violation of the resource limit, and is therefore called resource overshoot.

If this problem is left unaddressed, our species will eventually experience a sharp drop in consumption, a population die-off, or both.

Resource overshoot is best exemplified by peak oil — the decline in conventional fossil-fuel extraction after the historical maximum was reached early in the 21st century. The global population skyrocketed due to the ready availability of these fuels, and this population cannot be supported at current consumption levels once the fuels become prohibitively scarce.

The second interpretation of overshoot is when humankind exceeds the biosphere's capacity to safely absorb the environmental effects of our economic activities. This is a violation of the impact limit, and is therefore called impact overshoot.

Impact overshoot is far more serious than resource overshoot because it imperils the biosphere as a whole by undermining the integrity of the planet's ecosystems. The clearest example of impact overshoot is global warming, or climate change, which has the potential to turn a verdant Earth into a lifeless Venus.

When the word "overshoot" is used by itself in ENL, it refers to the two types together. Thus, to reverse overshoot means to overcome resource overshoot and reach resource sustainability, and to overcome impact overshoot and reach impact sustainability.

The economic factor that links the two types of overshoot is the global economy's output rate — the quantity of outputs produced and consumed by the world's population over a specified period of time. This is similar to the "output quantity" (quantity/time) that is used in many ENL graphs with reference to a specific output or the economy as a whole.

The global output rate is central because it indicates the level of humankind's economic activities which, in conjunction with ecological efficiencies, is responsible for humankind's violation of the planet's environmental constraints.

These concepts are graphically depicted in the following figure.

Overshoot concepts
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Resource overshoot occurs when humankind's output rate exceeds the resource limit — the maximum sustainable rate in the absence of nonrenewable resources. Impact overshoot occurs when this rate exceeds the impact limit — the maximum rate consistent with environmental integrity. Resource sustainability and impact sustainability are achieved when the output rates falls below these limits. The two limits rise when ecological efficiencies increase, and fall when they decline.

Humankind's output rate is shown on the vertical axis. The horizontal axis represents a compressed timeline of human history. The output rate increased gradually for much of humankind's existence, but skyrocketed after the advent of capitalism around 1500AD.

Resource overshoot occurred first as nonrenewable resources were used to increase population and per-capita consumption beyond the resource limit.

Impact overshoot followed when the soaring toxins, pollutants, and habitat destruction violated the planet's impact limit.

On the assumption that contractionary revolutions are successful and rapid contraction occurs on a global scale, the output rate will decrease sharply in the future. This will achieve first impact sustainability and then resource sustainability. As with overshoot, the term "sustainability" by itself refers to both types.

One of the main challenges faced by ENL analysts is how to effectively apply the framework to the task of reversing overshoot and achieving sustainable well-being after a contractionary revolution.

ENL is simply a collection of analytical tools, whereas overshoot is an ecological crisis. It is not immediately obvious how the tools should be brought to bear on the crisis.

Let us address this by first identifying a major shortcoming of ENL's existing tools in dealing with overshoot. See the following figure, which represents the entire world economy.

Reversing overshoot — existing ENL tools
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The current output rate for the world economy is above its ecological limit, which is the biosphere's impact limit. The economy is thus in impact overshoot. This can be reversed by increasing ecological efficiencies, thereby shifting the impact limit to the right, and by decreasing the output rate. In this standard ENL graph, however, population and average consumption rate are aggregated as quantity divided by time.

The graph indicates that the economy's current output rate is well above its ecological limit. Since we are considering the world economy, the ecological limit is equivalent to the biosphere's impact limit, which means that the economy is in impact overshoot.

As shown, this can be rectified by increasing the appropriate ecological efficiencies, thereby raising the impact limit, and by decreasing the economy's output rate.

Here these two factors meet at the optimum output rate, thus achieving both optimum scale and overshoot reversal.

The problem with this model is that it does not clearly depict two of the key factors driving overshoot: the global population level and its average consumption rate. Although both are represented in the graph, they appear as a single quantity: the output rate (quantity/time) on the horizontal axis.

This means that, for the purpose of analyzing overshoot and its reversal, output rate is an over-aggregation.

If we are to consider these factors separately, the output rate must disaggregated into its two components. This disaggregation is shown in ENL's treatment of the population's ecological limit, where the average consumption rate is represented by the slope of a line, which is too abstract for present purposes.

ENL thus includes an overshoot model, which explicitly represents the three critical factors. With all three overshoot factors — population, average consumption rate, and ecological efficiencies — clearly visible, analysts can properly orient their ENL analysis during the post-revolutionary period of rapid contraction.

In developing this model ecological efficiencies are initially ignored for simplicity. When the term "environmental effects" is used, it refers to both environmental damage and resource depletion.

Contents of this section:

Four Approaches to Overshoot The overshoot model is intended primarily to help contractionary leaders strategize overshoot reversal in a post-revolutionary situation and to guide the attendant ENL analysis. However, it is also useful in a pre-revolutionary situation for characterizing contractionism and its alternatives. Read on…
Overshoot Model The output rate is disaggregated by first noting that output quantity is equal to population (P) multiplied by the average consumption level (Q/P). That is: Read on…
Shrinking Economies The phrase, "shrinking economies" refers to rapid contraction in regions that have undergone contractionary revolutions. The particular emphasis is on the rich capitalist countries, which during their history have contributed heavily to overshoot and which will, in their post-revolutionary periods, bear the greatest responsibility for its reversal. Read on…

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