No overconsumption impact.

Climate change is not the only form of environmental damage we are inflicting upon the Earth. Might we face other environmental existential risks through overpopulation, running out of critical resources or biodiversity loss?

When environmentalism rose to prominence in the 1960s and 1970s, one major concern was overpopulation. It was widely feared that humanity’s rapidly growing population would far outstrip the Earth’s capacity to feed people, precipitating an environmental and humanitarian catastrophe. The most prominent advocate of this view, Paul Ehrlich, painted an apocalyptic vision of the near future: “Most of the people who are going to die in the greatest cataclysm in the history of man have already been born.”93 This catastrophe would come soon and pose a direct existential risk. Ehrlich predicted: “Sometime in the next 15 years, the end will come—and by ‘the end’ I mean an utter breakdown of the capacity of the planet to support humanity.”94

These confident predictions of doom were thoroughly mistaken. Instead of rising to unprecedented heights, the prevalence of famine dramatically declined. Less than a quarter as many people died of famine in the 1970s as in the 1960s, and the rate has since halved again.95 Instead of dwindling to a point of crisis, the amount of food per person has steadily risen over the last fifty years. We now have 24 percent more food per person than when Ehrlich’s book, The Population Bomb, was published in 1968.

Much of the credit for this is owed to the Green Revolution, in which developing countries rose to the challenge of feeding their people. They did so by modernizing their farming, with improved fertilizers, irrigation, automation and grain varieties.96 Perhaps the greatest single contribution was from Norman Borlaug, who received the Nobel Prize for his work breeding the new, high-yield varieties of wheat, and who may be responsible for saving more lives than anyone else in history.97

But the improvements in agriculture are just part of the story. The entire picture of overpopulation has changed. Population growth is almost always presented as an exponential process—increasing by a fixed percentage each year—but in fact that is rarely the case. From about 1800 to 1960 the world population was growing much faster than an exponential. The annual growth rate was itself growing from 0.4 percent all the way to an unprecedented rate of 2.2 percent in 1962. These trends rightly warranted significant concern about the human and environmental consequences of this rapid population increase.

But suddenly, the situation changed. The population growth rate started to rapidly decline. So far it has halved, and it continues to fall. Population is now increasing in a roughly linear manner, with a fixed number of people being added each year instead of a fixed proportion. This change has been driven not by the feared increase in death rates, but by a dramatic change in fertility, as more and more countries have undergone the demographic transition to a small family size. In 1950, the average number of children born to each woman was 5.05. It is now just 2.47—not so far above the replacement rate of 2.1 children per woman.98

While we can’t know what will happen in the future, the current trends point to a rapid stabilization of the population. The current linear increase is likely to be an inflection point in the history of human population: the point where the curve finally starts to level off. We may never again see the rapid population growth of the mid-twentieth century. In the last eighty years, population grew threefold. In the next eighty years (to 2100) it is expected to go up just 50 percent, to about 11 billion. For every person alive now, we’ll have to make room for an extra half a person. This will be a challenge, but a much easier one than last century.