Recent United Nations population projections paint a comforting picture of immanent population stabilization. But what if they are wrong? Global population growth does not appear to be slowing as quickly as UN demographers have predicted, making widespread famines and run-away climate change more likely in the coming decades.
By Jane O’Sullivan
The Elon Musks of this world think there can never be enough humans. When we fill up Earth, we will conquer the Universe! But most people think population growth is not a problem because it’s stopping soon anyway. Those “population alarmists” must be naïve, or motivated by racism. But what if growth is not stopping as soon as we think, and what if those extra numbers make it impossible to avoid widespread famines and run-away climate change?
In a newly published paper, I show how the UN projections have consistently underestimated global population growth this century. According to the UN’s 2022 data, there were 253 million more people on Earth in mid-2022 than the UN expected there would be in its projection from the year 2000. While they then estimated an annual increment under 80 million and falling, the actual increase has been roughly 90 million per year, with no sure sign of diminishing.
There are several rival projections, the most widely known being the Wittgenstein Centre (the “shared socioeconomic pathways” or SSP series), Institute for Health Metrics and Evaluation (IHME) and the Stockholm Resilience Centre’s “Earth4All” project. All three anticipate far more rapid deceleration and lower peak population than does the UN. Hence, all are even further from reality.
Worryingly, these unrealistically low projections are being used in research efforts to model sustainable futures, which explore what it would take to avoid dangerous climate change and meet everyone’s needs within planetary limits for resource use and environmental damage. The SSP projections are particularly widely used in modelling. They then present sustainability as a viable (if highly challenging) possibility, when greater population numbers would breach environmental limits even under the most techno-optimist scenarios.
One reason for this underestimation is attributing fertility decline to socioeconomic circumstances, such as reducing infant mortality, improving girls’ education, urbanisation and industrialisation. None of the models assigns any importance to deliberate interventions such as voluntary family planning programs. While family size does correlate with each of those factors, all of the models treat fertility as the ‘dependent variable’, not considering how family planning programs might have contributed to lowering infant mortality, improving girls’ access to schooling and accelerating industrialisation and income growth.
The UN’s model is calibrated over the decades in which family planning programs were well supported and many countries had relatively rapid fertility transitions. However, since this support was withdrawn in the 1990s, fertility declines slowed globally and even reversed in a few countries. The UN doesn’t seem to have adjusted its calibration to account for this slow-down. On the contrary, it has recently recalibrated to increase the rate of future fertility decline, with no apparent evidence to back this change. Its rhetoric flatly denies that past family planning programs played any role at all, and is silent on its own projections’ poor record at predicting growth over the past two decades.
Regular readers of this blog might recall my critiques of each of these projections (here, here, here, here and here). In my most recent paper, I bring these together in the context of scenarios for sustainable futures. While few such studies have explored the influence of different population assumptions, those that did have found it impossible to achieve sustainable food systems and low enough emissions to avoid more than 2oC of global heating, no matter how rapidly and universally we change our production technologies and consumption behaviours, if the world population exceeds 10 billion. Yet, at this point it seems that only massive calamities will prevent the human population exceeding 10 billion.
Letting nature do the culling for us is not in anyone’s preferred playbook. Nobel Laureate Henry Kendall once said, “If we don’t halt population growth with justice and compassion, it will be done for us by nature, brutally and without pity—and will leave a ravaged world.”
If we go down in wars, famines and environmental disasters, we will take a great deal of biodiversity with us. Hungry people eat the roots of plants, the bark of trees, and anything that crawls, digs, swims or flies, if they can lay their hands on them. Protected areas become a meaningless concept. Hunger soon gives way to violence and failed states.
What would it take to avoid these calamities? The only answer is a much faster fall in birth rates in all high-fertility countries than is happening now. Such fast transitions have happened in the past, but only when contraception and small families were strongly promoted through active family planning programs.
It is an extraordinary tragedy that the global community shuns this opportunity, on the grounds that we are defending the poor from abominations like China’s one-child policy. We should instead be championing the great family planning successes such as in Thailand, Tunisia, Costa Rica, South Korea and Iran. Instead of emulating these successes, the high-fertility countries in Africa and elsewhere are being served an insipid and ineffectual reproductive health agenda, in denial of the harms wrought by population growth. It is supposedly centring women’s rights but effectively impedes women’s emancipation through lack of funding and political will for the services they need to avoid unwanted pregnancies, and through lack of a clear motive to challenge the patriarchal cultures that limit women’s roles to motherhood.
Population projections, like all complex modelling exercises, are rarely questioned because their details are difficult for the average person to fathom. However, models are only as good as their assumptions and data. The current crop of global population projections embed the myth that rapid fertility decline can be achieved through indirect socioeconomic drivers, together with the myth that direct promotion of contraception and small families is ineffective and incompatible with human rights.
Lulled by these fantasies, plans for achieving sustainable futures exclude population measures. We need a more integrated approach across the environmental and social justice agenda, which acknowledges the essential role of rapid population stabilisation in climate change mitigation, biodiversity protection, poverty reduction, food security and world peace. Unless we take a more proactive approach to ending population growth very soon, we will miss our last chance to avoid a hungry, hothouse world.