In a recent Nature Sustainability paper, a team of scientists concluded that the Earth can sustain, at most, only 7 billion people at subsistence levels of consumption (and this June saw us at 7.6 billion). Achieving “high life satisfaction” for everyone, however, would transgress the Earth’s biophysical boundaries, leading to ecological collapse. Despite its seeming scientific precision, the claim is old, not new – the latest iteration of the longstanding assertion that our population and consumption might soon exceed the Earth’s fixed “carrying capacity”.
From the 18th-century arguments of Reverend Thomas Robert Malthus onwards, prophets of environmental doom have imagined that in response to abundance, humans would respond with more – more children and more consumption. Like protozoa or fruit flies, we keep breeding and keep consuming until the resources that allow continuing growth are exhausted.
In reality, human fertility and consumption work nothing like this. Affluence and modernisation bring falling, not rising fertility rates. As our material circumstances improve, we have fewer children, not more. The explosion of human population over the past 200 years has not been a result of rising fertility rates but rather falling mortality rates. With better public health, nutrition, physical infrastructure and public safety, we live much longer.
Today, in the United States, Europe, Japan, much of Latin America, even parts of India, fertility rates are below replacement, that is, the average number of children born per woman is below two. Much of the rest of the world will likely follow suit over the next few decades. As a result, most demographers project that the human population will peak, and then begin a slow decline, in some cases before the end of this century.
For this reason, today’s warnings of impending ecological collapse mostly focus on rising consumption, not population growth. As many now acknowledge, our social biology might not function like protozoa, but capitalism does. It cannot survive without endless growth of material consumption.
Some environmental scientists claim that we have already surpassed the Earth’s carrying capacity. But this view is deeply ahistorical, assuming carrying capacity to be static.
In fact, we have been engineering our environments to more productively serve human needs for tens of millennia. We cleared forests for grasslands and agriculture. We selected and bred plants and animals that were more nutritious, fertile and abundant. It took six times as much farmland to feed a single person 9,000 years ago, at the dawn of the Neolithic revolution, than it does today, even as almost all of us eat much richer diets. What the palaeoarchaeological record strongly suggests is that carrying capacity is not fixed. It is many orders of magnitude greater than it was when we began our journey on this planet. There is no particular reason to think that we will not be able to continue to raise carrying capacity further. Nuclear and solar energy are both clearly capable of providing large quantities of energy for large numbers of people without producing much carbon emissions. Modern, intensive agricultural systems are similarly capable of meeting the dietary needs of many more people. A planet with a lot more chickens, corn and nuclear power might not be the idyll that many wish for, but it would clearly be one that would be capable of supporting a lot more people consuming a lot more stuff for a very long time.
Viewing humans in the same way we view single-celled organisms or insects risks treating them that way. Malthus argued against Poor Laws, in the belief that they only incentivised the poor to reproduce. Ehrlich argued against food aid for poor countries for similar reasons, and inspired population-control measures of enormous cruelty. Today, demands to impose planetary boundaries globally are couched in redistributive and egalitarian rhetoric, so as to avoid any suggestion that doing so might condemn billions to deep agrarian poverty.
We are not fruit flies, programmed to reproduce until our population collapses. Nor are we cattle, whose numbers must be managed. To understand the human experience on the planet is to understand that we have remade the planet again and again to serve our needs and our dreams. Today, the aspirations of billions depend upon continuing to do just that.