Ever since the writing of Thomas Malthus in the early 1800s, and especially since Paul Ehrlich’s publication of “The Population Bomb” in 1968, there has been a lot of learned skull-scratching over what the sustainable human population of Planet Earth might “really” be over the long haul.
This question is intrinsically tied to the issue of ecological overshoot so ably described by William R. Catton Jr. in his 1980 book “Overshoot:The Ecological Basis of Revolutionary Change”. How much have we already pushed our population and consumption levels above the long-term carrying capacity of the planet?
In this article I outline my current thoughts on carrying capacity and overshoot, and present five estimates for the size of a sustainable human population.
“Carrying capacity” is a well-known ecological term that has an obvious and fairly intuitive meaning: “The maximum population size of a species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment.”
Unfortunately that definition becomes more nebulous and controversial the closer you look at it, especially when we are talking about the planetary carrying capacity for human beings. Ecologists will claim that our numbers have already well surpassed the planet’s carrying capacity, while others (notably economists and politicians…) claim we are nowhere near it yet!
This confusion may arise because we tend to confuse two very different understandings of the phrase “carrying capacity”. For this discussion I will call these the “subjective” view and the “objective” views of carrying capacity.
The subjective view is carrying capacity as seen by a member of the species in question. Rather than coming from a rational, analytical assessment of the overall situation, it is an experiential judgement.
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