How many people can the Earth support?

Posted: 1 September 2000

Author: Joel E. Cohen
W.W. Norton, New York and London, 1995, US$30

Given the impossibility of the task, maybe it is fitting that a book answering this title question should be written by a New York City comedian. But besides doing stand-up humour, the author holds two doctorates and heads Rockefeller University's Laboratory on Populations, which makes him worth reading as much for his scientific rigour as for his wry commentaries on other writers' conclusions about the planet's capacity to house more humans.

Cohen questions the question itself after examining some of the 66 scientific answers to it that have been published over the years - the first from 1679, (13.4 billion), and the last four from 1994 (ranging from 3 to 44 billion). In between are some truly eye-popping numbers - Paul Ehrlich's well-known 1971 estimate of 0.5 billion when the world population was already 3.7 billion, and tongue-in-cheek physicist's estimate of a billion billion, based on the global warming potential of heat radiation from human skin.

The book finds considerable flex in the very definitions of human carrying capacity. An appendix lists 26 different explanations that accompany some of the calculations already mentioned from Garrett Hardin's bluntly stated "This question evokes a reply of no human use" to Donella Meadow's (of Club of Rome fame) slippery caveat, "carrying capacity is a dynamic concept. It is always changing with...the pressure exerted by the species being carried."

This is not to say the entire exercise is fruitless. The 1992 Rio Conference's Agenda 21 document calls for estimating national human carrying capacities in the context of basic human needs, sustainable development, critical natural resources, and environmental protection. But in an age of world trade, consumerism, and cultural exchange, Cohen persuasively shows how global carrying capacity is no longer simply a sum of its national or regional parts.

Although over the last decade there has been more, rather than less, variations in the hard estimates, there does seem to be a rough consensus that the earth is now approaching an upper limit. One half of the estimates are under 7.7 billion, which if correct means we will not be able to sustain our currently projected world population for long.

And thus Cohen ends with a three-choice menu for balancing population and resources in the future. We can bake a bigger pie (increase production), put fewer forks on the table (reduce our numbers), or learn better manners (change the way rich and poor countries interact). While he obviously believes in moving on all fronts together, his advocacy for the neglected third option is what makes this book so appealing.

Reviewer: Louis Werner

Reviewer Info: Louis Werner is a writer and film-maker with a special interest in population.