On Human Overpopulation

A recurring theme among a number of widely divergent political and environmental movements is that of human overpopulation. Often, the claim that there are too many humans has conspicuous racist overtones and is associated with ecofascism,¹ but claims of overpopulation are also made by people with very different political ideas. Much of the popular overpopulation discourse appears to be quite ignorant about what “overpopulation” even means, however, and about what it might imply, so I thought it might be useful to write a few words about this.

What even is “overpopulation”?

“Overpopulation” is a relative term – it means that a population has become larger than what its environment can (sustainably) support. If the concept is lifted out of its ecological context, it could also mean that there are more individuals of a certain kind than what is considered (by someone) to be desirable or tolerable. Thus, from an antisemite’s perspective there might be an overpopulation of Jews in his town or city if it has a Jewish population larger than zero, but this kind of decontextualized (i.e. non-ecological) “overpopulation” is metaphorical at best. The notion of overpopulation makes little sense without a clear and sufficiently precise definition and explanation of the limit that is exceeded (by the population concerned). That limit is usually called the “carrying capacity” of some environment or ecosystem, and thus, if one claims that there are too many humans on Earth, one is either claiming that the number of humans exceeds Earth’s carrying capacity, or hiding some other – probably racist – claim behind pseudo-scientific rhetoric.

So, this raises an obvious question: What is the carrying capacity of Earth? But that question doesn’t have a clear and simple answer – it depends on a lot of things. And for that reason, estimates of this number vary widely. A 2004 meta-analysis by Jeroen van den Bergh and Piet Rietveld includes estimates ranging from 0.7 to more than a 100 billion, for example.² They suggest that the median of “all method-oriented (objective) studies”, which is 7.7 billion, is the best estimate available.

The range of estimates is so large because different studies make very different assumptions about technology and the dispersion thereof, about the (continuing) availability of necessary resources, and about the limits set by our environment (and changes therein). Higher estimates tend to assume infinite sources of energy, as well as technologies that are bordering on science fiction, such as nuclear fusion, direct air capture (DAC) of carbon, and high-tech vertical farming. These thre examples are technologically possible, but they are also inefficient – nuclear fusion costs much more energy than it produces, for example, and DAC would have to break the laws of physics to make a significant contribution to overcoming climate change. Furthermore, given technological and economic limitations, as well as limited availability of necessary resources, these technologies can never be implemented at the scales assumed. In other words, higher estimates are indeed best thought of as science fiction, although they tend to be so unrealistic that the “science” classifier is dubious as well – perhaps, it is more appropriate to just call them “fiction”. This doesn’t imply that low estimates are automatically (much) better – some of those probably err in the other direction by making overly pessimistic assumptions about resource availability, technology, and pollution.

A number of recent estimates suggest a carrying capacity close to 3 billion. For example, the five authors (including Paul Ehrlich) of the very recent “Scientists’ warning on population” suggest a sustainable human population size of 2 to 4 billion,³ Christopher Tucker suggested 3 billion in a 2019 book, ⁴ and in The Lesser Dystopia (2019) I estimated a global population limit between 2.5 and 3 billion after taking necessary changes in agriculture and the food industry into account. Perhaps, this means that 3 billion is a good target number, but I’ll have more to say about this below.

The fascist roots of some (!) overpopulation discourse

Although the far right doesn’t have a monopoly on claims of human overpopulation, prominent expressions of the idea are often heavily influenced by fascist tropes, such as anti-urbanism and racism. One of the typical features of fascism is a disdain for cities and an idealization of the countryside.⁵ Hitler complained in Mein Kampf that cities lack culture and corrupt the youth, for example. There is an obvious association between the high population density of cities and the idea of overpopulation, and it’s equally obvious that significant de-urbanization (i.e. a return to a focus on rural live and much smaller cities) would only be possible if there would be much less people.⁶

Perhaps even more obvious than the anti-urbanism in much overpopulation rhetoric is its often barely hidden racism. It’s not uncommon that claims of overpopulation are made in response to data showing a higher birth rate in large parts of Africa, or among some other non-white population. Often, the claim of human overpopulation is merely an attempt to give a more sophisticated expression to there being too many “black”, “brown”, “yellow”, or other non-white people for one’s liking. As in “replacement theory”, there is a fear of white dominance being deteriorated, or white people becoming an endangered minority. And rather than explicitly calling for extermination of non-white people, this implicit call is packaged in overpopulation rhetoric.

If there are too many people, we should somehow “cull the herd” to assure that there are less. Although this is rarely stated explicitly, it is often clearly implied. And which part of the herd should be culled? The answer to that question is also rarely stated explicitly, but tends to be equally clearly implied: the disposable poor who don’t contribute anything to our “Great Civilization”, black people in Africa “who breed like rats”, and so forth. Ideas like these are almost never stated this explicitly, but all too often it is very clear that this is exactly what some overpopulation advocate has in mind.

“Culling the herd”

Aside from being atrocious, the idea of “culling the herd” is also interesting, because it exposes some nonsensical hidden assumptions in nearly all overpopulation rhetoric. Although these assumptions are probably ideologically motivated, they coincide with – and are thus reinforced by – important aspects of the ecological notion of overpopulation in the context of non-human animals. These assumptions are the following. (1) There are – on an ecological scale – no significant differences between individuals belonging to the same population with regards to their individual impact on the ecosystem. That is, while one lion might eat a bit more than another, these differences are largely insignificant. (2) Barring exceptions, the members of a species in an ecosystem cannot significantly change their “ways of life” and roles within that ecosystem. A lion cannot suddenly decide to become a vegetarian, or learn more efficient ways of producing food than by hunting prey.

In case of humans, both of these assumptions are obviously absurd. Both with regards to consumption and environmental impact, there are enormous differences between people. According to a report by SEI and Oxfam from 2020, the richest 10% of people are responsible for about half of all carbon emissions, for example.⁷ According to an even more recent report by Autonomy, the richest 1% of the UK population emits more in one year, than the bottom 10% in two decades.⁸ And the UN estimates in its latest Emissions Gap Report that the top 1% is responsible for 17% of all emissions.⁹ Hence, if we arrange the poorest to richest percentiles from left to right, and measure their environmental impact, the curve we get looks something like this:¹⁰

Continuing the lions analogy, this would correspond to a situation in which most lions kill a zebra once every now and then, while one lion kills hundreds a day. Park rangers wouldn’t call that a lion overpopulation problem – they’d just shoot that one problematic lion. In case of humans, it is dubious to call this an “overpopulation” problem for the same reasons.

If it is assumed that individuals cannot change their life styles and environmental impacts and that culling is the only way to remedy the supposed “overpopulation” problem, then culling the poor would be stupidly inefficient. (It would be like keeping the one problematic lion alive and killing all other lions.) But this is exactly what is often implicitly suggested by human overpopulation advocates. They point at high birth rates and poverty in Africa, suggesting that that causes (or even is) the overpopulation problem, and thus that that needs to be remedied. From a mathematical point of view, this implicit suggestion makes absolutely no sense, however. (And neither does it make sense from any other sane point of view.) If – in a situation corresponding to the graph above – you’d need to reduce the environmental impact by 10%, you could do so by culling the poorest 41% of the population indeed, but you’d achieve the same result by culling the richest 0.9%. (See the table below for these percentages at other levels of reduction.¹¹) Hence, under the assumptions mentioned at the beginning of this paragraph, if you’d want to do something about supposed overpopulation, you shouldn’t cull the poor, but rather, you should start at the top. To solve “overpopulation”, you’d have to “cull” Elon Musk, Jeff Bezos, and so forth; not poor Africans, Indians, or Chinese.

Similarly, if Jeroen van den Bergh and Piet Rietveld’s estimate of a carrying capacity of 7.7 billion is right, this could be achieved by culling either the 24% poorest people, or the 0.2% richest people. And if the 3 billion estimate is right, these percentages rise to 94.5% and 19.1%, respectively. But all of this is nonsense, of course – these “culling percentages” critically depend on the aforementioned two assumptions and utterly ignore the real cause of the problem that is conveniently misrepresented as “overpopulation”.

Carrying capacity is conditional

In addition to being overly simplistic and callous, the “culling the herd” approach to what is called “overpopulation” makes a further error: it lifts carrying capacities out of their contexts, while it is their contexts that give these numbers meaning. As far as I know, no serious scholar argues that merely reducing global population would solve any major problems. Such a way of understanding those numbers get things the wrong way around. In a sense, the number follows from what might be a “solution”, rather than that it is (or even summarizes) a solution.

A carrying capacity is derived from a set of assumptions and is meaningless outside the context of those assumptions. What such numbers mean is that a sustainable human populations on Earth could have a certain size in certain conditions. If those conditions are different from the present condition (i.e. from the way things are now), then the carrying capacity that is relevant to those counterfactual conditions does not apply to the present conditions (and thus, “culling the herd” is useless).¹²

Take my 2.5~3 billion estimate as an example – that number doesn’t represent some hypothetical sustainable population size in the world as we know it now. Rather, it resulted from an analysis that rejected science fiction “solutions”, that realistically accounted for resource limitations, and that took several kinds of potentially catastrophic pollution into account. In that analysis energy was the main limiting factor, but other problems also severely limited the productivity of agriculture and many other industries. In such circumstances Earth could feed about 2.5 to 3 billion people according to my estimate.¹³ Any number above that would require unsustainable use of energy and other resources. (For further details, see The Lesser Dystopia.) The point of that analysis is not that Earth is overpopulated and that we should reduce population, but that we would have to radically transform agriculture, manufacturing industry, and much else to avoid catastrophic climate breakdown. Unfortunately, that transformation would create another problem, namely that we cannot feed the current global population that way, but that doesn’t mean that the whole problem can be reduced to an “overpopulation” problem.

Much the same applies to most other serious attempts to estimate a sustainable human population size. Arguably, that isn’t even what those attempts are really trying to estimate at all. Rather, those numbers (i.e. sustainable population sizes or carrying capacities) are byproducts of attempts to determine a sustainable way of living for humanity as a whole on this planet.

Human overpopulation rhetoric makes no sense because it ignores all of this. It is mere rhetoric. There is no “overpopulation problem” in case of the lions example above. There is a very different kind of problem and treating it as an issue of overpopulation is not going to solve it.¹⁴ Likewise, the main problem that mankind faces isn’t really an overpopulation problem either, and treating it as such won’t solve it. The primary problem is not how many of us there are, but what we are doing,¹⁵ and especially what some of us are doing. But if you want to think of it as an overpopulation problem anyway, then at least take a sensible and efficient approach: cull the rich.

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1. Jordan Dyett & Cassidy Thomas (2019), “Overpopulation Discourse: Patriarchy, Racism, and the Specter of Ecofascism”, Perspectives on Global Development and Technology 18: 205–24.
2. Jeroen van den Bergh & Piet Rietveld (2004), “Reconsidering the Limits to World Population: Meta-analysis and Meta-prediction”, BioScience 54.3: 195–204.
3. Eileen Crist et al. (2022), “Scientists’ warning on population”, Science of the Total Environment 845.157166.
4. Christopher Tucker (2019), A Planet of 3 Billion: Mapping Humanity’s Long History of Ecological Destruction and Finding Our Way to a Resilient Future A Global Citizen’s Guide to Saving the Planet (Atlas Observatory Press).
5. Anti-urbanism is not the exclusive domain of fascism. The idea has Romantic roots and can also be found in other ideologies and movements that can be traced to the Romantic revolt against Enlightenment thought, such as anarcho-primitivism.
6. The fascist idealization of the countryside conflicts with its appeal to the mob, which is largely an urban phenomenon, of course, but fascism has never been a coherent ideology. In the contrary, it tends to reject coherence and embraces irrationality.
7. Sivan Karth et al. (2020), The Carbon Inequality Era: An Assessment of the Global Distribution of Consumption Emissions among Individuals from 1990 to 2015 and Beyond (Stockholm Environment Institute & Oxfam).
8. Luiz Garcia & Will Stronge (2022), A Climate Fund for Climate Action (Autonomy).
9. UN (2022), The Closing Window / Emissions Gap Report 2022 (United Nations Environment Programme).
10. For a very similar curve, see the SEI/Oxfam report, p. 6. Both the UN report and the report by Autonomy suggest that its even more skewed than the graph shown here suggests.
11. An environmental impact reduction of 20% (second row) would require culling either the poorest 59.1% or the richest 2.1%.
12. And since counterfactual conditions typically involve changes in the ways of life of many (if not most) people, estimates of carrying capacity tend to violate the second assumption (i.e. no lifestyle changes) mentioned above.
13. But these numbers drop significantly at higher levels of average global warming.
14. Except if one (accidentally?) ends up culling the problematic lion, of course, but the analogy breaks down there, because merely “culling” Elon Musk, Jeff Bezos, and similar parasites isn’t going to save us.
15. How we are living and making a living, particularly.