Too Many People?

Populationists often accuse their critics of being “cornucopians”—of believing that the earth’s resources will never run out and that infinite growth is possible or desirable. Some people have indeed argued just that: the best known was Julian Simon, a business professor and best-selling author who denied that there were any limits to growth, because capitalism would always ensure that “just about any environmental and economic trend pertaining to basic human material welfare . . . will show improvement in the long run.”²

Simon claimed that “the standard of living has risen along with the size of the world’s population since the beginning of recorded time. There is no convincing economic reason why these trends toward a better life should not continue indefinitely.” He also said that “with present technology and without moving toward the much higher yields found under experimental conditions, the world can more than feed any foreseeable population increase.”³

In 1984 Simon predicted:

If present trends continue, the world in 2000 will be less crowded (though more populated), less polluted, more stable ecologically, and less vulnerable to resource-supply disruption than the world we live in now. Stresses involving population, resources, and environment will be less in the future than now . . . The world’s people will be richer in most ways than they are today . . . The outlook for food and other necessities of life will be better . . . life for most people on earth will be less precarious economically than it is now.⁴ [emphasis and ellipses in original]

Astonishingly, he republished that statement in 1996, without a word changed and with no suggestion that it didn’t seem likely to come true in the next four years. Simon’s ideological faith in the magic of what he called free markets blinded him to the realities of the world around him.

Simon’s cornucopianism led him directly into climate change denial. He seems to have believed that since the market couldn’t stop climate change, it must not be a real problem. In 1996, he confidently predicted that “global warming is likely to be simply another transient concern, barely worthy of consideration ten years from now.”⁵ So much for his crystal ball.

One of Simon’s co-thinkers, Jacqueline Kasun, carried the all growth is good argument to extremes. She rejected the view that population growth always leads to poverty or environmental damage, simply inverting the populationist claim that big is bad:

Population growth permits the easier acquisition as well as the more efficient use of the economic infrastructure—the modern transportation and communications systems, and the education, electrification, irrigation, and waste disposal systems. Population growth encourages agricultural investment—clearing and draining land, building barns and fences, improving the water supply. Population growth increases the size of the market, encouraging producers to specialize and use cost-saving methods of large-scale production. Population growth encourages governments, as well as parents, philanthropists, and taxpayers, to devote more resources to education. If wisely directed, these efforts can result in higher levels of competence in the labor force. Larger populations not only inspire more ideas but more exchanges, or improvements, of ideas among people, in a ratio that is necessarily more than proportional to the number of additional people.⁶

Despite their differences, cornucopians agree with the populationists in one important respect: both say population growth is the primary driver of economic growth. The difference is that the Ehrlichs think that’s a bad thing, while Kasun and Simon think it’s great.

When populationists accuse all critics of cornucopianism, they are in effect saying that only two positions are possible: either unlimited population growth is possible and desirable, or the human population is nearing (or has passed) an absolute limit that can’t be exceeded without causing a catastrophe. They deny, or don’t even consider, the possibility that humanity’s relationship with the earth can’t be reduced to numbers and arithmetic.

When the first wave of modern populationists claimed that certain countries were overpopulated, they were immediately challenged by critics who pointed out that other countries with less space supported more people. Paul Ehrlich’s opening chapter in The Population Bomb, describing his shock and fear at first seeing a crowded street in New Delhi, led many to point out that there were far more people per square mile in New York City.

An environment’s carrying capacity for a given kind of creature (living a given way of life) is the maximum persistently feasible load—just short of the load that would damage that environment’s ability to support life of that kind. Carrying capacity can be expressed quantitatively as the number of us, living in a given manner, which a given environment can support indefinitely.⁷

The term carrying capacity is borrowed from biology, where it is defined as the maximum number of members of a species that can survive indefinitely in a given environment, given the space and resources available. It is used to estimate how many members of a given species—elephants or salmon or bees—can live, eat, and reproduce in a defined area without depleting the environment and forcing a reduction in their numbers. The basic concept was originally developed in 1838 by Belgian mathematician Pierre Verhulst and independently reinvented by US statisticians Raymond Pearl and Lowell Reed in 1920. It holds that the growth of any given population can be described as an S-shaped or logistic curve, growing slowly at first, then speeding up, and then leveling off when it reaches carrying capacity, as in the figure below.

Commonly, natural populations fluctuate. Some vary with no apparent regularity, while others, such as lemmings, wax and wane cyclically. Some, such as locusts, are prone to occasional outbreaks in which population skyrockets and then plummets. Populations of many species grow wildly in response to unusually benign conditions, and then collapse. Some populations can even seem stable over considerable periods, but seldom if ever does a natural population rise sharply and then stabilize in the form of [a] sigmoid curve.⁸

Insects behave in very predictable ways and can’t choose to live differently; if their population growth can’t be accurately described using carrying capacity theory, then it’s very unlikely to be a useful guide to human populations that live, produce, and reproduce in a multitude of different ways. After a careful review of attempts by ecologists to use carrying capacity as a guide to human environmental impacts, environmentalist Irmi Seidl and economist Clem Tisdell conclude:

An academic disservice has been done by those who claim that carrying capacities in applied and human ecology are scientific and objectively determined. Only in controlled conditions does such a claim seem tenable . . . This view is untenable as far as social carrying capacities are concerned and in relation to most applied ecology issues because value judgments inevitably become an integral part of the concept. Carrying capacities alter according to variations in value judgments and objectives. In human society, institutional arrangements are likely to alter the carrying capacities and desired levels of populations, and carrying capacities in the shorter term may differ greatly from those in the longer term. Carrying capacities are far from being universal constants.⁹

The work of demographer Joel Cohen is particularly devastating for the concept of human carrying capacity. In a 1995 article in Science , he wrote:

Human carrying capacity depends both on natural constraints, which are not fully understood, and on individual and collective choices concerning the average level and distribution of material well-being, technology, political institutions, economic arrangements, family structure, migration and other demographic arrangements, physical, chemical, and biological environments, variability and risk, the time horizon, and values, tastes, and fashions. How many people Earth can support depends in part on how many will wear cotton and how many polyester; on how many will eat meat and how many bean sprouts; on how many will want parks and how many will want parking lots. These choices will change in time and so will the number of people Earth can support.¹⁰

And in his book How Many People Can the Earth Support?:

The Earth’s capacity to support people is determined partly by processes that the human and natural sciences have yet to understand, and partly by choices that we and our descendants have yet to make. A numerical estimate of how many people the Earth can support may be a useful index of present human activities and of present understanding of how to live on the Earth; it cannot predict the constraints or possibilities that lie in the future . . .

At any given time, a current but changing human carrying capacity is defined by the current states of technology; of the physical, chemical, and biological environment; of social, political, and economic institutions; of levels and styles of living; and of values, preferences, and moral judgments.¹¹

Cohen’s book includes twenty-six different published definitions of human carrying capacity. He points out that they “vary very widely and occasionally contradict one another.” Human carrying capacity, he concludes, “is a collection of concepts with no single generally accepted meaning.”¹²

In a 2010 article on demographic trends, Cohen summarized what he learned from studying attempts to quantify the earth’s carrying capacity:

Estimates made in the past half a century ranged from less than one billion to more than 1,000 billion. I learned that these estimates are political numbers, intended to persuade people either that too many humans are already on Earth or that there is no problem with continuing rapid population growth. By contrast, scientific numbers are intended to describe reality. Because no estimates of human carrying capacity have explicitly addressed the questions raised above, taking into account the diversity of views about their answers in different societies and cultures at different times, no scientific estimates of sustainable human population size can be said to exist.¹⁴

Populationist writers frequently make a logical leap in their arguments. They start with a true but abstract point: infinite growth is impossible on a finite planet. But they jump from there to the conclusion that the environmental crisis proves that we have exceeded the maximum number of people the earth can support, which simply doesn’t follow. For example, the amount of CO₂ in the atmosphere has reached a point where dangerous climate change is likely—but that shows human activity has to change, not that there are too many people.

One day, when we have broad agreement on the answers to all of Joel Cohen’s questions, and when we have eliminated the gross waste, destruction, and inequities of capitalism, we may be able to measure the earth’s carrying capacity scientifically. If so, humanity may then decide to consciously limit its numbers. Since the birth rate is already below replacement levels in much of the world, that probably won’t be a difficult task. But today, science provides no support for a populationist program.