Karin Kuhlemann[1]

Original article published in The Ecological Citizen Vol 1 No 2 2018


Human population growth is slowing down, but there is no end in sight: we are due to reach 11 billion towards the end of this century, and to continue expanding our numbers well into the next. This article discusses why focusing on the rate of population growth as the central problem amounts to a mistaken and misleading approach to thinking about the issue, as does the suggestion that we should aim to “stabilize” population size. Our current population size is already unsustainable, which poses great risks to human beings and wildlife alike. The aim must be to reverse human population growth rather than merely to slow it down or lock it in at some arbitrary, unsustainable size.

High fertility rates are largely a product of social norms. But social norms can change, and this is a powerful argument for active and honest dialogue about the problem of unsustainable human population growth.


Human numbers were relatively stable during thousands of years, slowly edging up until reaching our first billion around 1804[2]. After this, growth accelerated, then exploded. By 1927, when beloved naturalist Sir David Attenborough was a baby, humanity had already notched up the second billion. By the time Attenborough narrated the first Life on Earth series in the late 1970s, our numbers had more than doubled again. We are now on course for to reach our third doubling by 2023; there will be 8 billion of us then. Population growth is slowing down, but there is no end in sight: we are due to reach 11 billion towards the end of this century and to continue expanding our numbers well into the next[3]. The number of people added to this planet every year (~80 million) has not changed much since the late 1970s, but it translates into an ever-smaller rate of growth because our absolute numbers are getting larger and larger. For many, this means there is no problem left to solve.

In this article, I briefly discuss how problematising population growth in terms of the speed of growth amounts to a mistaken and misleading approach to thinking about the issue, as do suggestions that we should aim to “stabilise” population size (whether at the national or global level). Population size is not a neutral factor and poses great risks to human beings and wildlife alike. Logically and morally, the aim must be to reverse population growth rather than to merely slow it down or lock it in at arbitrary, unsustainable size. High fertility rates are largely a product of social norms. But social norms can change, and this is a powerful argument for active and honest engagement with the problematic of population growth by scientists, activists and policy-makers.

First, a clarification. In this paper I criticize rhetorical arguments about the problematic of population growth which are frequently put forward by economists, futurists, and policy-makers, but sometimes also by natural scientists and even population concern activists. Any of these actors might be motivated by political expediency, ideological commitment, or a sincere belief that their positions are empirically sound. Whether or not genuinely endorsed by those who proffer them, the arguments I attack are commonly presented to the public as though they represent sound reasons for dismissing concern about population growth, and this is a problem. As I attempt to demonstrate, even a fairly cursory examination shows these arguments to be fallacious. I make no claim that my criticisms or counter-arguments are novel. On the contrary, I take the logical and moral incongruences I identify as fairly self-evident to anyone who has given serious thought to the subject of population and sustainability.

The future of population growth is not set in stone. But if we get the problem wrong, we are bound to misunderstand our options about what can or should to be done to mitigate the risks to all life on this planet, both human and wild.

Too fast, or too much growth?

Concerns about population growth are often articulated in terms of the growth being too fast. Supposedly, we should aim at slowing down growth or stabilising our numbers. In its most intellectually reprehensible incarnation, this framing of the problem translates into the argument that there is nothing to worry about because the rate of population growth is already slowing down. The easiest way to solve a complex ethical and practical problem, as ever, is to deny that it exists.

Current declines in fertility rates are neither irreversible nor inevitable, which is why multiple UN population projections have had to be adjusted upwards in recent years. But more importantly, the rhetoric of “slower growth” or “stable population size” erroneously and misleadingly implies that population size is a neutral factor. If a “stable” population is an ideal outcome, or at least a population that is not growing as fast, then it must follow that any population size is fine; the problem is merely that there is change, or the change is too fast. But this is not the case, however much it may suit one’s ideological inclinations or political aims.

From an environmental sustainability perspective, what matters is the current and cumulative effect of absolute population size, not the rate at which our numbers grow. It makes a great deal of difference to the prospects for human security and wellbeing, and for wildlife survival, if our population is 2 billion, 7 billion, 11 billion or, indeed, 16 billion. Whether a population is sustainable turns on how many consumers there are, consuming as they can be realistically expected to consume[4]. If there are more consumers than can be sustained, the risks will turn principally on how many more and for how long there is an imbalance.

The risks from an unsustainable pattern of resources use do not crystallise overnight. Consider a situation where your one and only source of livelihood is withdrawals from a bank account into which someone placed a large deposit (precise amount unknown). Even if you repeatedly withdraw from the account more than it is earning in interest rates, it may take a long time to empty the account completely; you may come to think it will never happen, even though it is the logical end-point of your trajectory. You may be a very optimistic person who is counting on interest rates going up in future, or on finding a way to diminish your withdrawals before the capital is completely gone. (Another way of looking at it, of course, is that you are reckless with your finances.) But for the time being, your withdrawals are unsustainable. They do not stop being unsustainable because things might change in future. The longer the unsustainable withdrawals go on for, the harder it becomes for you to mitigate the risk that you’ll run out of money. In particular, the longer you keep up your unsustainable withdrawals, the less leeway you’ll have to deal with unexpected expenses, falling interest rates, or simply having misjudged how much there is in the account. As with our planet’s resources, there is no safety net in this thought experiment.

I am quite willing to concede that, from the perspective of provision of public services, the speed of population growth is indeed an independent problem. Rapid population growth can create something of a Red Queen race for societies, where continuously increased public expenditure is needed simply to keep up with growing demand for school places, hospital beds, housing, sanitation, public transport, etc.  

But in so far as one accepts that at least some needful resources are finite and depletable – in so far as one accepts that sustainability is or can be an issue independently of the capacity of social structures to adapt to population growth – then it simply cannot be logically supposed that the solution lies in ensuring growth eventually stops, yielding a stable population size. That a population’s size is stable in no way entails sustainability. It may be sustainable, or it may be far too large. This turns on a range of factors, most notably on how big that ‘stable’ population is and on the state of the resource base on which it depends.

Framing population stabilisation as a policy goal – independently of any sustainability assessment – is simply false and bound to mislead the public about the nature of the problem.  It reflects an unthinking acceptance of the premise that populations must not shrink, that whatever arbitrary size a population grows to must be locked in and accommodated somehow. The fear of population “decline” or “ageing” is primal and tribal, reflecting macho anxieties of a bygone era where survival was about how many young men one could round up for waging war or fighting off invasions. It makes no sense in today’s world, where the main threats to the long-term viability of human societies are ultimately rooted on there being too many of us, men and women, young and old, doing damage simply by peacefully leading our own lives.

Population, affluence and technology

It is trivially true that the environmental impact of any given population size is modulated by affluence and by the technology available (in addition to cultural and institutional particularities). This broadly corresponds to the familiar “IPAT identity”[5] formula: impact = population x affluence x technology. However, it is often mistakenly assumed that more advanced technology translates into a reduced impact, or that people living in poverty have next to no environmental impact or will remain poor for ever.

Technology can be used to increase efficiency in resource use, allowing us to make more with less. But it can also be used to extract resources faster and more cheaply, masking their scarcity, encouraging overuse, or otherwise accelerating resource depletion. As the Aldo Leopold put it nearly 70 years ago, “few educated people realize that the marvellous advances in technique made during recent decades are improvements in the pump, rather than the well.[6]”  There is mounting evidence that the predominant relationship between technology and resource use is one of improvements to the pump, that is, facilitating their extraction rather than creating more resources. A related phenomenon is described in economics as Jevons’ paradox[7], where greater technological efficiency in the use of a resource ultimately increases its overall consumption. In addition, technology can also be used to convert one environmental problem into another, for example where freshwater scarcity is “resolved” via desalination plants that consume vast amounts of fossil fuels, decimate marine life, or generate serious pollution.

Affluence is a similarly multivalent factor. A wealthier population will typically consume much more than a poorer population of the same size, but will also be better able to invest into the development of new technologies that may reduce their impact on resources – or amplify it.  But there is nothing inherently “environmentally friendly” about poverty.  In much of the world, those who are struggling to find opportunities in the formal economy will turn to extractivist activities[8] to make a living for themselves and their families, often to devastating results: empty forests where most wildlife has been hunted down[9], rampant deforestation for wood fuel and growing food[10], overfished rivers and bays[11]. In addition, it is clear that some environments are better able to support larger human populations than others. Poverty-stricken, rapidly growing populations are too often found in drought-prone, resource-poor, fragile environments such as the Sahel and the Horn of Africa. In such areas, mere subsistence activities are enough to over-exploit natural resources, driving desertification and worsening the already chronic food insecurity[12]

The contribution of population size to our environmental impact is comparatively unambiguous. For any given level of affluence, use of technology, or environmental constraints, and regardless of which way these factors pull, a smaller population size will mean a smaller environmental impact, slower resource depletion, and a greater range of alternatives for coping with resource scarcity (for example, relocating elsewhere). Conversely, a bigger population will have a greater environmental impact, a faster rate of resource depletion, fewer alternatives for coping with scarcity due to the concatenation of multiple scarcities and to greater competition for resources, and a greater number of human lives at risk than what would otherwise be the case.

Population size always matters, and in today’s world, a smaller population is a more resilient one.

The irrelevance of current food production

It is often suggested that we ought not to worry about population growth because we already produce enough food to feed 10 billion people. Supposedly we can, or should, let population growth run its course, whatever it may prove to be, because we are safe on the food front. There are at least three reasons why this reasoning is fallacious.

First, answering the question of how much food is produced now is not answering the question of how much food we can expect to produce over the foreseeable future. Current resource use in agriculture is unsustainable,[13] and this is without taking into account the potentially devastating impact of climate change. Discussions about food waste and expansion of the agricultural frontier typically ignore the reality that not all waste can be prevented, that most productive land worldwide is already in use for agriculture[14], and that what is left is natural habitat that supports important ecosystem services and provides critical sanctuary for what remains of the world’s wildlife.

Secondly, even if it were possible to sustainably produce enough food to feed a population of 10 or even 11 billion – and we have no reason to be confident it will be[15] – food production is not the only issue. People’s ability to earn a livelihood matters to their ability to secure enough food and other basic resources for themselves and their families, to their ability to live lives of dignity, and to the fiscal sustainability of their societies. The International Labour Office has been chronicling a global trend towards higher unemployment and underemployment for years, due to job creation not keeping up with growth in the number of new labour market entrants. This has particularly affected younger workers[16], reflecting the morally problematic asymmetry of all population growth externalities: the costs and risks of population growth are typically worse for younger generations than for the older generations who have made the choices that created or added to the risks. As if these population growth-driven trends were not enough of a threat to the livelihoods of younger generations, in recent years there has been growing concern about the scope for developments in artificial intelligence to cause unprecedented levels of unemployment without concomitant creation of new jobs for those displaced[17], potentially vastly aggravating fiscal unsustainability problems that are already widespread[18]

And thirdly, even if it were possible to secure food and decent livelihoods for 11 billion people, our population may keep on growing well past that already enormous size. This is the trajectory indicated by the latest UN population projections[19] sees the global population continuing to grow well into the 22nd century, and its projected size for 2100 might prove optimistic. Population projections for countries experiencing high fertility are particularly uncertain; these are the countries which are projected to drive the bulk of global population growth from 2050 onwards. Even slightly slower than anticipated fertility declines could result in a much larger population size. The UN’s “high” variant projection assumes fertility rates will remain half a child higher, on average, than the “medium” variant. This yields a 2100 population of over 16 billion. It may be thought that the high variant assumes an increase in fertility; on the contrary, it still builds in a substantial reduction in fertility rates relative to today’s levels. A straightforward extrapolation of current fertility rates would yield a population of well over 25 billion by 2100[20].

While many remain steadfastly optimistic about the prospects for producing enough food to feed 11 billion in a climate changed world with damaged soils and not enough water, this author is not aware of any credible proposals for feeding a world of 16 billion or more.

Already unsustainable

Our current population’s impact on the natural resources on which we depend suggests 7 billion is already an unsustainable population size. Further population growth will increase systemic risks to food security and livelihoods, in particular climate change, mounting unemployment and sub-employment, degradation of agricultural soils, overfishing, and freshwater scarcity.

The Intergovernmental Panel for Climate Change recognises population growth as a primary driver of climate change[21], along with economic growth. The IPCC warns that climate change may have severe impacts on food security via higher temperatures, precipitation changes, increased frequency of extreme weather events, the spread of new pests and ocean acidification. Estimates suggest that some 200 million people could be displaced by climate change over the next 40 years[22]. Food production is a major contributor to greenhouse gas emissions and a dominant force behind diversity loss, degradation of land and depletion of freshwater sources, among other serious environmental impacts. Simultaneously, agriculture is the most weather-dependant of all human activities, and extensively reliant on the same natural resources and ecosystem services[23] it is degrading.

The Food and Agricultural Organisation identifies population growth and economic growth as the primary drivers of the ongoing loss and degradation of agricultural soils, which in turn is a major threat to food security[24]. Global marine fisheries landings have been declining since the late 1980s due to overfishing[25]. The FAO’s analysis of assessed stocks has found a downward trend in biologically sustainable fish stocks since 1974; some 30% of fisheries are already overfished and a further 60% are “fully fished”[26], with pressures on fish stocks largely driven by population growth (but also economic growth).  Around 1.4 billion people live in areas where ground water is being drawn at a faster rate than it can be replenished[27]. The UN projects that almost half the world’s population will be living in areas of high water stress by 2030, potentially displacing as many as 700 million people[28]. Water scarcity is driven principally by population growth and – what else – economic growth, is set to be worsened by climate change, and is thought to be a major driver of armed conflict, in particular in Africa[29]. Some of the most water stressed countries are also experiencing very high population growth rates[30]. The UN estimates that nearly 80% of the jobs constituting the global workforce depend on access to an adequate water supply[31].

Population growth contributes to and amplifies every one of these risks while increasing the number of people exposed to those risks. In addition, by expanding the reach and intensity of human pressures on the natural environment, human population growth poses an existential threat to countless other species.

The most recent doubling of our numbers was accompanied by a loss of over half of wildlife numbers, driven by destruction of natural habitats and harvesting of wildlife to meet human needs and aggravated by environmental fouling from human activities.[32]  This involves a combination of thinning of wildlife populations and eradication of countless species. A sixth mass extinction event is ongoing, the worst spate of species loss since the Cretaceous-Tertiary extinction event that saw the end of non-avian dinosaurs and many other lineages of life[33]. Even if our human population eventually stops growing and shrinks back to a sustainable size, the species pushed to extinction along the way will be lost forever.

Those of a particularly extreme speciesist or anthropocentric moral outlook may believe that there is no inherent wrong in causing other species to go extinct. Let us assume, for the sake of argument, that the interests of human beings are the only moral considerations that count. Even then, humanity’s impact on the natural world is a serious moral wrong of reckless risking of livelihoods and safety nets. Many millions of people in Africa, Asia and Latin America rely on wildlife resources for their livelihoods and as a buffer to see them through times of hardship, such as unemployment and crop failures.[34] More generally, the world’s poor are often highly dependent on natural resources for their livelihoods, and the most vulnerable to the effects of defaunation and environmental degradation[35].

For those of us who reject anthropocentrism, or at least do not endorse such an extreme version of it, the permanent loss of biodiversity is a profound moral wrong to the species being annihilated by humanity’s reckless expansionist project. It is also a moral wrong to future generations, condemned to live in a biologically impoverished world where such iconic fauna as elephants, sea turtles, snow leopards, orangutans, rhinos, gorillas and tigers no longer exist in the wild, or at all.

Ideas, values, and behaviours

When we accept a large risk, we must have in mind an even greater benefit that justifies taking that risk, or else we are behaving irrationally and recklessly. Most people should be able to recognise that it is wrong to expose younger and future generations to enormous risks, and bring entire lineages of life to an end, for as trivial a reason as our reluctance to adjust our own behaviour and attitudes in response to changing circumstances, or as disreputable a reason as treating children and wildlife as means to the ends of today’s parents and consumers. We are supposedly a rational species. We have been aware of population growth for decades, and reliable and inexpensive birth control methods have been available for over 50 years. And yet, we hold on to the idea that cultural and individual preferences about family size should be left to drift along, as if the future of humanity and of countless other creatures was not sufficiently important to warrant conscious effort to mitigate population growth.

Where population growth is acknowledged to be a problem, it is commonly suggested that the way to address it is by educating girls, tackling gender discrimination or lifting people out of poverty. Ensuring women and girls are treated with equal respect and afforded the same educational and economic opportunities as men and boys is a matter of justice and basic human decency. The same applies to efforts to secure for everyone the at least the minimum material resources needed for lives free from fear and want. However, it is important to note that tackling gender inequality and absolute poverty are neither preconditions[36]  to fertility declines nor reliable ways to achieve declines that are as deep and fast as they need to be to adequately mitigate unsustainable population trajectories.[37] Conversely, high fertility rates pose a formidable obstacle to securing improvements to gender equality and to economic and educational opportunities[38].

Women who are unable to control their bodies can be confidently predicted to bear more children than those who can, and education tends to make larger families less appealing. But it would be a mistake to surmise that women having large families necessarily do so out of ignorance or because they have no choice. It seems more likely that ideas about the role of women and the (instrumental versus intrinsic) value of children spring from the same socio-cultural fountain as preferences about family size. The weight of the evidence suggests the most important factors driving population growth today are persistent preferences for larger family sizes[39] and unintended births resulting from non-use of contraception even where it is available, often due to cultural/religious objections [40]. Both factors are amenable to changes in values and social norms that have a tremendous bearing on individual attitudes and reproductive behaviour, as exemplified by the many successful ideational change campaigns employing entertaining television and radio shows[41].

But the case for changes in values and social norms is undermined whenever and wherever those best placed to understand and explain the risks that are driven or aggravated by population growth stay silent on it, and even more so if the only voices speaking on population are pro-natalist ideologues representing capitalist, patriarchal or religious interests.  An unconscionable population +-taboo[42] has developed whereby scientists, activists and policy makers talk around population growth and gloss over or omit reference to the need for smaller family sizes when discussing climate change, food or livelihood insecurity, loss of biodiversity and environmental degradation. In doing so, these actors are complicit in creating an environmentally impoverished world in which many millions, possibly billions of people may starve, become displaced, or have no hope of securing decent livelihoods. This needs to change.

What can be done?

Fundamentally, we must foster a shared sense of responsibility for the size of our human population, and adjust our behaviours and ways of thinking. In the oft-quoted words of Stanislaw Jerzy Lec, no snowflake in an avalanche ever feels responsible. But we all are. Even the childless by choice are still consumers, and as social beings we all make a contribution, however small, to what ideas live or die.

The logical and ethical response to unsustainable population growth is to reject the primitive rhetoric that irrationally fears population de-growth and ageing while embracing speculative gambles with our collective futures. It is to confront those who promote population growth on the ethically repugnant premise that human beings exist to serve the needs of a supposedly ever-growing capitalist economy, or the political goals of religious leaders. It is to embrace, rather than fear, sub-replacement fertility.

In order for younger and future generations to have a shot at decent lives in a world that is not an environmental wasteland, social ideas about what a normal family looks like need to change.  A one-child family ideal is a very small family indeed, but one that prioritises the life chances of children, the long-term stability of human societies, and the survival of the world’s wildlife over the immediate preferences and desires of prospective parents. This is what makes sense, and how it should be. 


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[1] Doctoral candidate at University College London, School of Public Policy

[2] Based on historical estimates of world population compiled by the US Census Bureau (https://www.census.gov/population/international/data/worldpop/table_history.php)

[3] See United Nations (2015) and Gerland et al (2014)

[4] In the original (and rather more eloquent) words of Paul and Anne Ehrlich (1990: 37-40): “Overpopulation is defined by the animals that occupy the turf, behaving as they normally behave, not by a hypothetical group that might be substituted for them.”

[5] Holdren and Ehrlich (1974); Ehrlich and Ehrlich (1990).

[6] Leopold (1949) p. 223.

[7] Alcott (2004); Magee and Devezas (2016)

[8] See for example Kerr et al (2004), Duffy and St John (2013), Harrison (2011), Nasi et al (2011), Slingenberg et al (2009), Sreekar et al (2015), McDonald (2016), Gettleman (2015), Lall (2013).

[9] Nasi et al (2008); Nasi et al (2011); Harrison (2011); Nellemann et al (2014); UNEP (2016); Long et al (2017). See also Panjabi (2014) and Maxwell et al (2016).

[10] Kerr et al (2004); Some et al (2007); McCarthy (2011); Hosonuma et al (2012); Nellemann et al (2014); Sedano et al (2016); FAO (2016).

[11] Stobutzki et al (2006); Salayo et al (2008); Keskar et al, 2017.

[12] United Nations (2007), IPCC (2014), Lifland (2012)

[13] International Food Policy Research Institute (2016), The Government Office for Science (2011)

[14] See for example Tilman et al (2002), Cassman (1999), Young (1999)

[15] Schade and Pimentel (2010)

[16] ILO (1996), (2007), (2012), (2013), (2014), (2016a), (2016b), (2017)

[17] See for example Frey and Osborne (2013).

[18] See for example The World Economic Forum’s 2017 report on global risks, which (as with previous reports) ranks fiscal unsustainability and unemployment/underemployment, along with a host of man-made environmental and humanitarian crises, as high impact, high likelihood risks.

[19] United Nations (2015)

[20] There was no “business as usual” (constant fertility) graph in the UN’s 2015 projections, perhaps because the BAU graph in the 2012 projections was thought to be alarmistic. It is fair to say that a human population of over 25 billion is improbable.

[21] Pachauri et al (2015)

[22] Laczko and International Organization for Migration (2009)

[23] Daily (1997)

[24] FAO (2015). See also Blum (2003)

[25] Mora et al (2009)

[26] FAO, 2016

[27] FAO (2009), (2012)

[28] Secretariat of the United Nations Convention to Combat Desertification (2014)

[29] Ibid

[30] UNDP (2006); see also United Nations (2012)

[31] Unesco et al (2016)

[32] World Wide Fund for Nature (2016)

[33] Ceballos et al (2015), Barnosky et al (2011), Dirzo et al (2014), McCauley et al (2015)

[34] Nasi et al (2008), Schulte-Herbrüggen et al (2013), Ntuli and Muchapondwa (2015)

[35] OECD (2008)

[36] See Campbell and Bedford (2009) for a useful summary.

[37] See Garenne (2012) and Grant (2015) for sobering data on the limited impact of education on fertility rates in Sub-Saharan Africa, and Myrskylä et al (2009) on how advanced levels of socio-economic development can reverse fertility declines.

[38] The population of many Sub-Saharan African countries is set to at least quintuple over this century (See UN, 2015), greatly depressing the scope for those societies to provide decent education and livelihood opportunities for rapidly enlarging cohorts of young people. See for example McNay (2005), Ashraf et al (2013), and Grant (2015). See also Anderson and Kohler (2015) and Recoules (2011) on how low fertility may boost gender equality and how gender equality may in turn boost fertility rates. The relationship between fertility and gender equality appears to be far more complex than commonly assumed.

[39] Westoff (2010); Bongaarts (2011); Bongaarts and Casterline (2013); Madsen (2015). See also INS and ICF International (2013).  

[40] This reflects the difference between unmet demand and unmet need for contraception. Where a woman would like to avoid pregnancy but does not intend to use contraception, there is unmet need but no unmet demand. For example, 65% of people in Pakistan, 54% of people in Nigeria and 52% of people in Ghana personally believe that using contraceptives is morally unacceptable; it does not necessarily follow that very large families are wanted [See Poushter (2014) and Pew (2014)]. A recent review of demographic and health surveys [Sedgh et al, 2016] found that a substantial proportion of women in developing countries did not seek family planning services even though they wanted to avoid pregnancy. Opposition to contraception was cited as a reason by 23% of those women, particularly among married women, while lack of knowledge or access to contraception, was cited by fewer than 10% of respondents. The same study confirmed that a preference for large family sizes remains the norm across most of Africa. See also Casterline and Agyei-Mensah (2017). Even if all women who have an unmet need for contraception used it, fertility in sub-Saharan Africa in particular would remain well above replacement levels [Bongaarts, 2011]. One of the most often encountered forms of instrumental valuing of children is parent’s expectation of financial support in old age. Unsurprisingly, there seems to be a robust correlation between increased social security benefits and reduced fertility rates – see Boldrin et al (2015).

[41] See for example Westoff and Koffman (2011), Basten (2009), Ashton et al (2015)

[42] See for example Mora (2014), Coole (2013), Campbell and Bedford (2009), Campbell (2007), Betts (2004), Orenstein (2004), Butler (2004); Beck and Kolankiewicz (2000), Grimes (1998), Maher (1997), Catton Jr, 1996.

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