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The world's population is projected to reach its next major milestone on 15 November – and is still growing. But how many humans can the planet support? 

Marvel Studios were onto something when they gave Avengers super-villain Thanos his driving motivation. “This universe is finite, its resources, finite. If life is left unchecked, life will cease to exist,” he explained. With the mauve Malthusian’s plan to eliminate half the life in the universe by clicking his fingers, Marvel were keying into a hot-button topic: overpopulation. With the world population about to hit 8 billion, it’s a subject that is once again coming to the fore – on 15 November this year to be precise, the date when humanity is projected to hit that milestone.

But – oddly, with ecological disaster looming – the debate about whether the Earth is too crowded continues to become more controversial by the year. It touches on perhaps the most fundamental human right: the right to have children. Overpopulation criers point to the fact there were only 2.5 billion humans on the planet in 2050, and to our shrinking resources and wild spaces. The most renowned among them, naturalist David Attenborough, is blunt: “Either we limit our population growth, or the natural world will do it for us.” (Luckily, he hasn’t got any Infinity Stones.) Meanwhile, the opposing camp are quick to denounce the repression and social repercussions real-world population control entails, starting with China’s failed one-child policy. And, they elaborate, it’s far from certain that the Earth has reached the limits of its capacity. Who is right?

Overpopulated

Attenborough and co are aghast at the vast size of a world population that has grown at an accelerated rate since 1700: one UN forecast projects 11.2 billion people by 2100 (other estimates are lower). To the overpopulationists, this is nature dangerously unbalanced. To put it in perspective, there are between 170,000 to 300,000 chimpanzees on the planet; and even to draw comparisons with the species whose numbers we have artificially boosted, there are just under 1 billion cows and about 780 million pigs. 

The overpopulationists broadly follow in the tradition of British economist and demographer Thomas Malthus, whose 1798 “An Essay on the Principle of Population”, argued that population, when unchecked by constraints, would increase exponentially and eventually exhaust the resources needed to support it, which in contrast only grow arithmetically. As the world population surged at 2% per annum in the 1960s, population biologist Paul and Anne Ehrlich updated Malthusianism for the 20th century with their alarmist bestseller The Population Bomb. If such growth continued, they warned, environmental degradation and collapse, and global famine, were on the way.

Population growth in the west has flattened out, but continues in many parts of the developing world. Next year, India will overtake China as the world’s most populous country, with both behemoths currently hovering around 1.4 billion. The swelling middle-class in these 21st-century frontrunners aspires to the same consumption habits as in the west, intensifying the resource toll on the planet. In 1965, just before the Ehrlichs wrote The Population Bomb, with 3.3 billion people we only used 70% of the biocapacity the Earth is capable of generating per year. We reached 100% capacity in 1983, and now we run up a deficit, using up the equivalent of 1.75 Earths every 12 months.

Mankind has twice in modern history managed to increase agricultural production to enable sudden population spurts: during the Agricultural Revolution that began in Britain in the late 18th century and later spread to Europe; and in the second half of the 20th century, when new wheat varieties developed by US agronomist Norman Borlaug ushered in the Green Revolution. New crop technology, man-made fertilisers (possible since the invention of the Haber-Bosch process in 1909), pesticides and advanced irrigation reputedly tripled crop yields while using only 30% more land; a billion people worldwide were saved from starvation, and countries such as India and Pakistan became agriculturally self-sufficient.

But many think we have now exhausted such advances. This 2010 Mother Jones piece pointed out four limitations of the Green Revolution: the finite supplies available of the constituent ingredients to make fertilisers, especially phosphorus; pollution of ecosystems by fertilisers, pesticides and herbicides used to safeguard yields; stagnant crop yields in many areas of the world, including China, and with global warming threatening further decline; diminishing topsoil lost to intensive agriculture that driving erosion and desertification. 

Despite all this, the UN Food and Agriculture Organization estimates that food production will have to increase by around 70% by 2050 to feed the expanded world population. But with all available arable land utilised, it’s not clear how that is possible. Some experts believe that genetic crop modification is the only major tool left in the agricultural toolbox that can ensure food security at global level.

Population spikes, agricultural yields, environmental degradation: these are, however, are primarily human concerns. Maybe, the overpopulationists might say, that is the fundamental problem. As long as Homo sapiens remains at the centre of things, the diversity of nature will continue to be squashed into an ever-tinier portion of the globe, exploited and monetised until all life on Earth is under threat. Limiting the human population is essential to restore balance.

Not overpopulated

Those who believe talk of overpopulation is exaggerated can point to one fact: that the world growth rate has been gradually slowing since the early 1960s, when it peaked at 2.2% a year. In 2021, it was 0.9%; based on falling fertility rates in many areas of the world, it will eventually level out – though it is not clear when. One UN estimate projects a global population peak at the end of the century, but others, including The Lancet and the Wittgenstein Center, are plumping for earlier, around 2060-2070. After that, it’s thought the world population will slowly decline, hopefully alleviating pressure on the Earth’s resources.

Most of this continuing expansion will be in sub-Saharan Africa, whose population – on current average growth rates of 2.6% – is expected to double by 2050. Three-quarters of population growth over the next 80 years will happen in the region. Nigeria, with a projected 400 million people by mid-century, will likely replace the USA as the world’s third most populated country. 

Overpopulationists sometimes label this news a demographic “time bomb”. But their opponents point out an inherent unfairness, or even racism, to these arguments. Pressurising developing countries to control their population not only denies them a chance at the economic prosperity the developed world has enjoyed for over two centuries, it also obscures the true crux of the overpopulation issue: that it is rich nations’ excessive consumption habits that is driving resources over-exploitation, not sheer weight of numbers. The average American, for example, uses roughly 77,000 kilowatt-hours of energy a year, compared to 7,000 for the average Indian and 400 if you are from the Democrat Republic of Congo.

The west insisting that the Global South limit its population is, in the eyes of many, an unwelcome revival of patrician 19th-century paranoia about the uncontrolled reproduction of an impoverished underclass. Eugenics was sometimes used to justify family planning for these undesirables – an ideology that also underpinned the abhorrent forced sterilisation of US ethnic minorities in the 1970s. As well as the ethical aspects, this kind of coercive population control often backfires, as in the case of the gender disparity and numerous human rights infringements that followed China’s one-child policy. When it comes to 21st-century Africa, a strong possibility is the birth rate will naturally stabilise as countries become more affluent, people start to have less children, and the populace ages. In general terms, this is already happening: when The Population Bomb was published, more than 120 countries had fertility rates (the average number of children born to each woman) over five; now that’s down to 10 countries.

All this is to reassure those who say the world population needs to drop. But perhaps it doesn’t. Perhaps we are still capable of – to focus on food security – wringing out more juice from the Earth’s agricultural productivity; we’ve done it twice, confounding Malthus and the Ehrlichs, and maybe the present-day naysayers can be proved wrong too. 

If food production must increase by over two-thirds to meet global needs by 2050, many point out that – despite the 768 million currently going hungry – in ideal circumstances we could feed the existing population. One-third of all food produced for human consumption (about 1.3 billion tonnes) is wasted or lost, and this shortfall could help close the gap by mid-century. Shifting towards plant-based diets would reduce demand for cultivatable land for raising animals for meat, and for growing animal feed. Given the uncertainty over how much further our food systems can be stretched in an era of climate extremes, maximising their efficiency in terms of sustainable production is vital if the world is to avoid mass starvation. And one more thing: we can produce all the food we like, but if impoverished people don’t have ready access to it, it means little.

It’s just as well that feeding 10 billion might be possible, because those at the very relaxed end of the debate would like to see humanity keep on growing. If average global fertility falls below 2.1, the level needed to assure a broadly stable population, then our numbers will decline. This implies that countries below this replacement rate will experience labour shortages without enough new people being born to eventually enter the job market; already in this position for decades, most western countries have relied on immigration to fill the gap. South Korea, whose 2021 birth rate was 0.81, is head of the list of countries feeling the demographic heat. But its economy is still growing, showing that population prediction is rarely an exact science.

Ultimately, it is not merely about the statistics, as Alex Ezeh, professor of Global Health at Drexel University, Pennsylvania, explains to BBC Future: “I think the conversation about size and numbers is a misplaced conversation. Think of a city that is doubling every 10 years – and that's a number of cities in Africa – which government really has the resources to improve every infrastructure that currently exists every 10 years, in order to maintain the correct level of coverage of those services?”

Crucial in assessing the dangers of population growth is whether the right socio-economic conditions are in place to give those people an acceptable standard of living over a given time frame. Says Ezeh: "When economists think about it, a large population is great for many different outcomes, but do you achieve that large population in 10 years or 100 years or 1,000 years? The longer it takes to get there, you can put in place the right structures in the system that will support that population."

Written By: Phil Hoad ( Olivium's Editor in chief )


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