On the planetary capacity to sustain human populations

This essay investigates the limiting capacity of the planet to support humans, making various assumptions about current practices and the intensities of per caput resource consumption. Supposing people to be exclusively vegetarian, consuming cereals produced by present methods, at the highest reported yields, and also eschewing the cultivation of non-edible crops, the Earth is argued to be capable of sustaining a population up to 55 billion. Consuming mixed diets including meat and beverages while continuing to raise non-food crops reduces the capacity by 7- to 10-fold, closer to the actual population at the present time. When the availability and distribution of exploitable water supplies are considered, it is difficult to argue for a sustainable population much exceeding 10 billion, without considerable changes in the equity of supply. All such extrapolations are subject to unknown consequences of rapid and chaotic climate change. The possibility that the rate of human population growth may be stabilising for other reasons, with numbers perhaps peaking at 10 to 11 billion, may yet allow increasingly widespread and severe water shortages to be avoided. This coincidence offers the opportunity to improve human sustainability through new social structures and new, cleaner, more resource-efficient technologies. They need to be directed towards solving inequities in resource use—not only of food and energy, but especially also of water. Though ultimately speculative and polemical, the essay is a genuine attempt to promote the case for recognising our real problems and the need to evolve strategies for survival.