John Feeney

Lately it appears more people are beginning to consider the problem of human population size as it relates to carrying capacity. Nevertheless, misunderstanding abounds. Since my focus is elsewhere right now, and I have no plan to write on this topic for publication in the near future, I offer a few thoughts here. This is merely a quick sketch with much detail, some points of logic, and additional convincing evidence omitted. I may flesh it out sometime in the future.

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Have we exceeded the earth's carrying capacity for humans? Many observers conclude there is no way to answer the question with any confidence. I believe their view stems from an assumption which fails to hold up to analysis. It is the common notion that, through human ingenuity, we've been able, through the course of history, to increase carrying capacity.

This idea is based on the correct observation that the advent of agriculture and our later use of fossil fuels were central among those developments which allowed us to grow the human population as enormously as we have. It does not follow, however, that these developments increased carrying capacity.

The error here is in failing to account properly for overshoot. Animal populations regularly overshoot or grow beyond carrying capacity. It is simple enough to demonstrate this has happened with the human population. Agriculture and fossil fuels have not increased carrying capacity; they have merely led to our overshooting it, supported by what William Catton calls "phantom carrying capacity." It is not carrying capacity at all, and is only temporary. [1]

This is especially easy to see with regard to oil depletion. Oil is a finite resource. Relying on it, therefore, to support global food production can only be temporary.

But here are two less widely recognized observations which also support my point: First, agriculture as we know it has always been unsustainable. It has brought with it soil erosion and an inevitable depletion of soil nutrients at rates far faster than their natural rates of renewal. This is comparable to our depletion of finite resources such as oil. It may have taken ten thousand years for us to see this, but that is barely an eye blink in human history. [2]

Second, consider that none of the processes which have allowed our numbers to explode has come without cost to the web of life. We know well enough about the environmental impacts of extracting and burning fossil fuels. Less discussed is the cost of agriculture to other species. Cultivation agriculture means the elimination of all life from a piece of land, turning it then exclusively to human use. [3] [4] Multiply this by over a billion hectares and we see clearly how agriculture has been the primary driver of the Sixth Mass Extinction of species in Earth's history, the direct destruction of Earth's life support systems.

Not only have we not increased carrying capacity, we have decreased it. It's simple ecology. We depend on the web of life for our own survival. When a species consumes resources faster than they are renewed, degrading the habitat on which it depends, it erodes carrying capacity.

The damage we have done to the biosphere and the web of life has temporarily allowed us to grow our numbers but has reduced carrying capacity. This may be hard to believe when we consider that for nearly all of human history, prior to exploding into the billions, our numbers never exceeded more than a few million. It underscores the shocking degree by which we've overshot carrying capacity.

No, there is no evidence we have increased carrying capacity. Rather, basic principles of ecology reveal we have managed only to overshoot it by an incredible margin.

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For some underlying fundamentals of carrying capacity please see the article Six Steps to "Getting" the Global Ecological Crisis.

[1] For much more see Catton's classic text, Overshoot.

[2] For more detail see Agriculture: Unsustainable Resource Depletion Began 10,000 Years Ago by soil scientist Peter Salonius.

[3] For an illuminating description of this process see Lierre Kieth's The Vegetarian Myth.

[4] Even a major improvement such as permaculture may suffer from a similar problem of turning the land excessively to human consumption. As I understand it, however, it is structured to be practiced on a scale small enough -- and with constraints against large populations --  that it might prove sustainable under conditions of a much smaller human population. This is not to suggest it as an "alternative" to agricululture, without which humans did quite well for most of our history.