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Will the human race succumb to overpopulation?

August 2021

More than 200 year ago, Malthus worried about the planet's "carrying capacity" and back then there were only one billion humans on this planet. Today we are 8 billion. Those who were born at the end of World War II have seen the population triple.

In 1968 Paul Ehrlich of Stanford University and his wife Anne published a study titled "The Population Bomb" in which he warned that the planet was already overcrowded. Back then the population was half what it is today. In 1970 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." To stem population growth, poor countries took draconian measures: India under Indira Gandhi enacted forced sterilization of millions of men and China adopted a "one-child" policy.

Ehrlich's prediction was obviously wrong: the "end" didn't come. In fact, today we generally live in a wealthier world: when "The Population Bomb" was published, one out of four people in the world was hungry, whereas today it is more like one out of ten. In 1980 Paul Ehrlich and economist Julian Simon made a bet: Ehrlich bet that the price of five key metals would increase astronomically whereas Simon bet that they would not. Simon won. In 2011 another famous bet took place, this time between economist David Lam of the University of Michigan and demographer Stan Becker of Johns Hopkins University: Lam bet that food would get cheaper over the next decade, whereas Becker bet that food would get more expensive. Becker won this one.

A 2017 report by the United Nations Population Division reignited the discussion: it calculated that the world's population would be 10 billion by 2050 and 11 billion by 2100 (report). This prompted, for example, David Attenborough at the World Economic Forum (2018) to argue that "the planet can't cope with overpopulation" (paper). Mathis Wackernagel, co-founder of Global Footprint Network, wrote that: "Our current economies are running a Ponzi scheme with our planet. We are borrowing the Earth's future resources to operate our economies in the present. We are digging ourselves deeper and deeper into ecological debt." (paper) In 2021 a team of 17 of the world's most famous ecologists (including Paul Ehrlich) described three major crises facing life on Earth: climate disruption, biodiversity decline and human overconsumption and overpopulation (paper). John Bongaarts of the Population Council was less catastrophic but nonetheless warned of a gradual deterioration in quality of life: the rich will be able to thrive for a while, but most of humankind will pay a terrible price over the next few decades.

The counter-argument, of course, is that so many thinkers have worried about overpopulation for centuries, and they always turn out wrong: the world on average is way richer than it was in 1968 when the Chinese, the Indians, the Africans and the South Americans were starving, sometimes to death. Today the Chinese have skyscrapers and high-speed trains, and food is their last concern.

The problem with the 2017 United Nations report is that it used only statistical analysis based on fertility rates and death rates. It didn't take into account the drivers of fertility, such as education levels among women and access to contraception. Adjusting the calculations for the predictable increase in women's education in "Empty Planet" (2020) and contraception availability, the Canadian journalist John Ibbitson and the political scientist Darrell Bricker reached the opposite conclusion: that human population will soon start declining, and that the world risks having too few people (summary). The Austrian demographer] Wolfgang Lutz says that the most important reproductive organ for human beings is our mind: cultural shifts (such as more educated and independent female population) can have bigger consequences on population growth than anything else. In other words, predictions about population growth should take into accounts cultural variables.

The "optimists" generally use variations on this argument: a demographic transition always take place as societies get wealthier and healthier because people tend to start having less children. When both birthrates and death rates are high, the population is low and stable. When technology (notably medicine) reduces child mortality, initially birthrates remain high and the population grows rapidly, but this lasts only for one or two generations. As people feel more secure in their financial outcome and as women's rights increase, birthrates start to decline. Children are no longer an economic asset but a cost. Birthrates begin to fall and the population stabilizes again. If birthrates fall below replacement reproduction (because people prefer to enjoy a life of travel and career rather than a costly and demanding life of parenting), population begins shrinking.

And soon this line of thinking leads to a new kind of apocalyptic pessimism: that humankind will shrink to self-extinction. In 2020 Stein Emil Vollset of the University of Washington calculated that the world's population will peak at 9.7 billion in 2064 and decline to 8.8 billion by the end of the century, and the population of some countries (notably Japan and Italy) will shrink by half in the next 80 years (while sub-Saharan Africa's population will triple). The problem for future generations will be of a different nature: too many old people and too few young people (he estimated 2.4 billion people over the age of 65 forecast by 2100, compared with 1.7 billion under the age of 20). For example, China's population will increase slightly but its working-age population will decline from 950 million in 2017 to about 360 million by 2100. Fewer workers and taxpayers will have to provide and fund expensive social security and health care systems (paper).

Meanwhile, regardless of what will happen to the world's population, there is no consensus among experts about the Earth's "carrying capacity", the largest population that it could support indefinitely. Heinz-Wilhelm Strubenhoff of the World Bank Group thinks that (quote) "we could quite easily provide food for 10 billion people on the planet" (paper).

After the covid pandemic (that spread faster also because of the highest densities of population in the history of the world) one can also wonder if greater populations constitute greater opportunities for deadly viruses.

The fundamental paradox of "sustainability" is that: economists and governments want populations to keep growing so that economies are healty and at the same time, for ethical reasons, we want everybody to have all the luxuries that, say, US citizens enjoy (air conditioning, a car, appliances, and plenty of energy). Notoriously, the average middle-class US family consumes a lot more food, water and energy than in the rest of the world, sometimes several times more, so the experiment of giving everybody the same luxuries has never been done. There is no consensus on what is the maximum number of people with the US standard of living that the Earth can afford.

Incidentally, that standard of living is a shifting target because, barring wars and natural disasters, it keeps increasing: the luxuries of a generation become the necessities of the next generation. Air conditioning is a typical example: my parents wouldn't even dream of installing an air conditioning system and were perfectly happy to sweat it out through our long hot summers, but younger generations won't go to school or to work if the air conditioning is not working.

Can technology overcome today's problems? As ecologist Carl Safina of Stony Brook University wrote: "New technology that serves the same values that have caused the current array of problems will likely accelerate those problems."

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