Population growth has contributed 80% of ecological overshoot

William Rees is the originator of ecological footprint analysis, the influential approach to measuring sustainability. In a new article, he argues that humanity is deep into ecological overshoot and that we need to ratchet back our numbers and the size of our economies before nature does it for us.

by Philip Cafaro

William Rees has been a leading sustainability scholar for three decades. In a recently published article, The human eco-predicament: Overshoot and the population conundrum, Bill makes three interlocking claims:

The human enterprise is in overshoot, depleting essential ecosystems faster than they can regenerate and polluting the ecosphere beyond nature’s assimilative capacity.  

Mainstream approaches to alleviating various symptoms of overshoot merely reinforce the status quo.

The continuity of civilisation will require a cooperative, planned contraction of both the material economy and human populations, beginning with a transformation of the fundamental values … underpinning neoliberal capitalist industrial society.

How big a contraction? Rees estimates a sustainable global population at 1 to 2 billion people—provided citizens in wealthy nations are willing to reduce our individual ecofootprints to 25% their current size. But as he notes, “in the real world … the population is still growing and there is zero international interest in sizing the global economy to fit within carrying capacity or to share the world’s bounty more equitably.” While “zero interest” might be an exaggeration, it’s hard not to share his pessimism about such ideas going mainstream anytime soon.

For followers of this blog, perhaps the most interesting part of the paper is a section which argues that “while overconsumption and population growth have long been recognised as co-drivers of overshoot, population growth is currently the major contributor to total consumption growth and associated negative ecological impacts” throughout the world. Comparing changes in per capita ecofootprints and changes in population for all the world’s nations between 1960 and 2016, Rees finds that population growth has been the dominant driver in increased national ecofootprints for all four of the World Bank’s country groupings based on national income (see figure below).

Changes in ecological footprint, biocapacity and population for nations in the World Bank’s four average income brackets, 1961–2016. Source: William Rees, The human eco-predicament: Overshoot and the population conundrum. Vienna Yearbook of Population Research 21 (2023): 1–19.

It comes as no surprise that in low-income countries, with rapidly growing populations, population growth accounted for 100% of the growth in (still relatively small) national ecological footprints between 1960 and 2016. But it also accounted for 88%, 73% and 75% of the growth in ecofootprints during that same time for lower middle-income, upper middle-income, and high-income countries, respectively (see section 3 in Rees’ paper for more numbers and calculations).

Globally, according to Rees, “population growth accounted for 80% of the increase in the total human ecological footprint above what would have accrued had populations remained constant while income/consumption and per capita EFs increased” after 1960. Next time a friend tells you that “the problem’s consumption, not population,” you might want to send them the paper!

Rees is quick to remind readers that citizens of high-income countries make much greater per capita demands on nature than those in poorer countries, noting that “1.14 billion rich consumers (15% of the human population) lay claim to 57% of global biocapacity.” He criticizes an “egregious, inexcusable, yet still increasing material inequality between rich and poor people and nations in today’s world.” And he states: “globalisation and unfair terms of trade in world markets enable the citizens of wealthy countries to appropriate legally, by commercial means, several times their equitable share of Earth’s biocapacity from other countries and the global commons.”

Here Rees may be falling into what Gaia Baracetti calls the per capita fallacy: the view that many smaller ecological footprints are more virtuous than fewer, larger ones. After all, it isn’t clear that all differences in individual or national wealth are the result of injustice, or that absolute equality in wealth or resource use is demanded by justice. Poor people around the world want more consumption and wealth, and with the UN’s Sustainable Development Goals, the international community has committed to helping them achieve that. But this will inevitably increase demands on the biosphere, which is already overused by people.

While Rees stresses that population decline in rich countries would generate more ecological benefit than in poor countries, he observes that “the most significant social benefits from stable populations would accrue at the micro level to the low-income families of poor countries who would enjoy larger slices of the economic pie.” But he fails to mention that a four-fold increase in their populations since 1960 has given them smaller slices of the pie, contributing more than “unfair terms of trade” to today’s inequalities. He states that “Egregious and widening inequality is a separate socio-political problem.” But it is not separate, it is fundamentally linked to the diverging demographics of rich and poor countries. The main factor separating today’s emerging economies (e.g. in Southeastern Asia) from the least-developed countries was their success in lowering birth rates four decades ago. We must stop seeing the population issue as separate from, or even a distraction from inequalities, and start seeing it as instrumental in closing the gap.

Despite these caveats, Bill Rees may be right that any successful effort to achieve global ecological sustainability must find a way to distribute resources and share Earth’s limited assimilative capacities more fairly within and among societies. He makes a strong case that this also must involve decreasing human numbers and, for many of us, our personal demands on the natural world.

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27 thoughts on “Population growth has contributed 80% of ecological overshoot

  1. Well, D’uh. D’uh. (Please excuse my lame sarcasm.) I can only read the same information so many times. A well-written article, but of little use.

  2. As per Stephen’s post, DUH!!!!!!!!!!!!!

    And, if we had an honest, ethical ‘snooze’ media (which thanks to deregulation, we no longer do and that from a now-retired journalist FROM WHEN MEDIA WERE ETHICAL), they’d be headlining NATIONALLY that a significant portion of the United States, the American Southwest, is within 2 YEARS OR LESS of a TOTAL COLLAPSE OF THE COLORADO RIVER SYSTEM, meaning roughly 45 million people likely to face a lot of thirst, perhaps even forced moves from the region.

    Yet our clueless–or CORRUPT or outright senile–El Presidente Biden–happily circumvents or trashes immigration laws to the extent of now even going so far as to send buses to Mexicali, Mexico, to IN COOPERATION WITH THE MEXICAN GOVERNMENT “expedite’ the arrival of more ‘amnesty seekers,’ although not one in 99 of them actually QUALIFIES under, well, you know, the laws that BIDEN IS IGNORING! Even the Biden administration admits to one 12-month period of 2.1 MILLION over the border, though others say that number was closer to 3 million.

    Meanwhile, U.N. data–I long since stopped believing Census Bureau data–shows a net increase of one EVERY 20 SECONDS added to the U.S. population, plus the addition IN JUST 2 YEARS OF FIVE MILLION TO THE U.S. POPULATION! So, yeah, that’ll help the Southwest’s drought crisis.

    And, the ENTIRE COLORADO RIVER SYSTEM at the brink of collapse as our president shows his stunning leadership skills by ignoring drought and further exploding our population, so yes, as Stephen says, DUH!

  3. Humanity can throw up a Bach or an Einstein with little apparent effort, but is totally arrogant and clueless, about regulating their numbers.

    Some other force, way stronger than COVID-19, would have to do it for them. Wars, famines, mega pestilence, “natural” disasters, asteroid strike, who knows. It’s not something that can be modelled by IPCC.

  4. “We must stop seeing the population issue as separate from, or even a distraction from inequalities, and start seeing it as instrumental in closing the gap.”
    Inequality is a very important theme that in the overpopulation debate is often only addressed at the inter-country level (hence my “per capita fallacy” argument). But I do believe that reducing inequality needs to play a big role in our journey towards sustainability. It’s not just a matter of fairness: it’s also easier to get people to accept “sacrifices” (i.e. not getting something they want) if they don’t feel they are the only ones being forced to do them. Also, people want to do what others do, and if no one is out there showing that it’s great to have a gazillion kids or to fly to the other side of the world twice a year, they won’t even consider it.
    Part of the backlash against the climate change advocacy by scientists, celebrities and politicians is that people are always wondering: why am I the only one who should stop polluting while I’m struggling already, while they get to keep their high salaries and fly around the world in private jets??

    A couple more thoughts:
    – sometimes I think that, if there were fewer people, and fewer poor people especially, in the world, inequality and waste would automatically decline because you can only overconsume if you have lots of workers making stuff for you (robots notwhistanding). For most people wasteful consumption might not even be worth it if they have to produce the stuff through their own labour
    – the national and individual levels are not quite the same. A nation can theoretially claim to be wealthy because it is prudent in its use of resources while trading fairly, or not trading, with the rest of the world. But an individual can never make that claim. Self-made billionaires do not exist. No man or woman can produce everything that is necessary to be rich, to survive even, alone. Anyone who is rich is rich thanks to others, especially in very complex systems such as our own, with massive public spending that supports the rich as well as the poor. Groups are one thing; individuals another

    1. Reducing economic inequality and achieving ecological sustainability both seem like worthwhile goals; perhaps the two most important goals facing current societies. I am less clear on their interrelationship.

      Gaia’s right: common folks are not going to change to more sustainable consumption patterns while jet setters continue their wasteful ways. At least not willingly.

      There are various kinds of economic inequality and various possibilities for addressing it. I’ve long thought that billionaires shouldn’t exist; allowing individuals to inflate their power and influence through such vast wealth does considerable harm to our democracies. Why not confiscate their wealth and use it to fund the transition to clean energy in the developing world?

      1. I think the relationship between inequality and sustainability actually goes both ways (unfortunately). I stand by what I said above, but it’s also true that things like hunting reserves for the wealthy probably played a role in conserving animals and habitats (excluding predators of course, as they competed with human hunters).
        You could theoretically have an extremely unequal society where a few people have vast wealth but the impact on the environment is small because everyone else is dirt poor. But what would be the point of such a society? People would not want to live in it for long and would leave or revolt if possible. You could sustain it only by extreme repression and locking them in (North Korea is probably an example of such a society – but its environment is also in a terrible state apparently).
        I think it’s more of an indirect relation – in an unequal society, what are people going to do to the environment, and how and why? What do the effects of inequality push people to do?
        A connection worth exploring on this blog? 🙂

  5. Yes definitely a connection worth exploring — by someone like you, who doesn’t try to tie everything up in a neat little bow. Rich, powerful people setting aside land as hunting preserves or protected areas have done a lot to preserve biodiversity. That doesn’t mean their power or wealth was justly achieved or fairly deployed vis a vis their fellow humans.

    1. There’s a huge literature on natural reserves, their relation to colonialism and racism (everyone’s favourite subjects), and the conflict with indigenous people who used to live in said reserves. Ecotourism is another example of nature kept for the rich at the expense of the locals or at least of their economic independence on the land.
      I’d write something about it if it didn’t require an enormous amount of research to be done well 🙂

  6. “Before nature does it for us.” I think that ship has passed and nature is already doing it for us. The idea of us taking charge, in a peaceful way, must be done before nature takes over and it will not be pretty, has been around for decades, and how many have listened!? Gaiabaracetti’s comment, “it’s also easier to get people to accept “sacrifices.” may be true for some but how many people, in the world, are willing to accept even a modicum of sacrifices. Right now the world seems to be locked in a fight for a shrinking amount of resources. Tribalism is running rampant and wars over resources are starting. A lot of what is written may work if everyone on the planet were sane and rational. Unfortunately we are not and that situation seems to get worse as the global situation gets worse. I know, a lot of Doom and Gloom but the opposite (and what is being practiced today is ‘Smile and Denial.’ My late partner and I came up with a reason based idea which is ‘Know and Grow.” The Overpopulation Project and comments here follow that saying but still it seems hard to see any positive results.
    I live in an island archipelago which is dependent on a system of ferries (the largest in the U.S.). This year the citizens received their annual property value assessments and it was the largest ever. Mine went up 25% and some went up 50%. The residents are mad and with our recent election only one (of numerous) levies failed. Several proposals, amending the county governance, also failed. We now have a new sheriff (the previous one was well liked and served a long time). It is a wealthy community and people have always been very generous with sharing the resources. Unfortunately, the county has failed to control growth and continue to put business and growth ahead of protecting the lands and this is the result. An amazingly beautiful place that has inspired people to put nature first is turning into a place where families and friends have split. Because of it’s location crime has yet to increase but that will come. If one can’t even take care of a few islands, what hope is there for the planet!?

    1. I think we still don’t know whether the imperative to grow and always be wealthier and have as much as possible is rooted in our culture or in our genes (and any other species would do the same). This would make a big difference.
      History has proven people are willing to make enormous sacrifices, including of their own lives, if they are shared fairly and if they believe in the ultimate goal. Whether such a mindset can be sustained indefinitely is a different matter.

  7. Interesting piece Phillip, thank you. I would be interested to know how the wealthiest have managed to decrease their eco-footprint in recent decades?

    1. The claim is that average per capita ecofootprint has declined in the last few years in wealthy countries. But because of population increase, total ecofootprint and available biocapacity per person have both declined.

      Yes, I was surprised by this as well. The details will be found in the Global Footprint Network’s recent yearly reports. The Rees article I report on here simply reports their results.

      1. I think “standards of living” are declining for significant chunks of the population in the wealthier countries. At least this is what it looks like talking to people and hearing the news. It’s not a bad thing given how wasteful our societies are, but very unequally distributed.

  8. I agree with the basic reasoning of this paper by William Rees, but his calculations are somewhat crude. When he says that “the 54% increase in high-income population since 1961 accounts for 75% of the 3.2 billion gha increase in high-income consumers’ demand on nature”, this number should be corrected to 68%. Indeed, William Rees obtains this result using the EF per capita of the year 2016, while he should use the EF per capita of the year at mid term between 1961 and 2016, lets say the average of the EF of these two years. Same for the other 2 cases, where we should have 55% instead of 72% for upper middle-income countries, and 75% instead of 88% for lower middle income countries.
    I have the feeling that there may be other flaws in this caluclations, which I have not been able to find yet, although it looks like elementary arithmetics!
    Anyway, if I do the same reasoning as regards global GHG emissions, taking the values of the last IPCC report, I obtain the results that population growth should account for 85% of the increase in emissions between 1990 and 2019 (William Rees would obtain 88%). This is far above what I have seen in the litterature, although there are only very few publications on the subject.
    I can send the calculation on excel file if anybody is intersted.

    1. Marc,

      thanks for weighing in. I will have go back to the Rees paper to assess your main point.

      Regarding the contrast between Rees’ finding regarding population’s contribution to humanity’s total ecological footprint (he claims 80%), and recent estimates of population’s contribution to climate change (about 40% over the past three decades, according to the IPCC), I would note that EF analysis looks at a wider range of human impacts than climate change.

      1. PS I should have said “recent estimates of population’s contribution to increases in greenhouse gas emissions” in the comment above; that is more exact than “population’s contribution to climate change.”

      2. Phil, Marc Gillet, Bill Rees, and Gaia —

        Is it possible for you four to trim off the errors and tighten up the numbers of Bill’s welcome paper?

        If the data are then peer-reviewed, the striking findings are important enough to be aired much more widely than in the Vienna Yearbook of Popul Res. Let’s go!

        IMHO, Phil’s well-meaning but under-reflected idea to “confiscate the wealth” of billionaires should be dropped, fast. History teaches us that one sure way to agitate uproar and regretful violence is to march in under a “confiscation” flag.

        If minimum wage laws made sense, and maximum wealth levels make sense
        (agreed on by way of democratic debate and voting — old fashioned democracy),
        then a gradual decline would be tolerable. Grandfathering in those who earned their wealth by the old rules seems a more fair way than the autocratic-like confiscation maneuver.

        Let’s keep our eye on the ball here: Bill’s valuable legwork and the cogent insights of you peers. Version 2.0 of the paper could also do with a better title, one that conveys the key finding. (Most all scientific research tackle puzzles and “conundrums” and hence that fact need not waste space in the title; instead, let’s position the remarkable find up front — with eloquence.)

        We want others to cooperate. Shall we show them how?


  9. Few experts in population biology, related fields of science, demography and economics appear ready and willing to see what is in front of naked eyes. Too many experts have confused cause and effect and thereby vitiated the coherence of mind and clarity of vision required to sensibly interpret evidence of whatsoever could be objectively correlated with reality. As a consequence, they appear to find the ecological science of human population dynamics simultaneously unbelievable yet virtualy irrefutable.

    We do not have a food production problem. Food harvests are abundant; food is sufficient to feed the human community plus many more. The problem is food redistribution. Granted the fair and equitable redistribution of available food to the human community writ large would lead in all likelihood to a temporary, exacerbating increase in absolute global human population numbers; however, limiting total global food production that humans consume would in the course of space-time return Homo sapiens to balance within the natural world.

    Consider biomimicry, the design and production of materials, structures, and systems that are modeled on biological entities and processes. For a moment let us assume that nature has the answers to the problems human beings have induced by relentlessly increasing the human food supply, and must now confront and overcome. By following the laws of the natural world, by changing our way to conform with nature, humans would consciously and deliberately mimic nature’s way where we find that all resources (including food to feed a growing population) are categorically limited by the size and finite resources of the planet which is our planetary home, the house humans have filled beyond its natural carrying capacity through the massive deployment of complex systems and inventive technologies.

    One of the worst mistakes of the second half of the 20th Century has been and continues to be generated by the United Nations. A delusion in the form of a meme, or unquestioned cultural transmission, has been viewed as real and spread virally by misusing the imprimatur of science upon which the meme is not actually based. Large scale human organizations have held tightly to versions of the same meme prior to this time period. Most experts became captives of a satisfying false cultural transmission: humans must continuously increase food production to feed a growing population. This misperception/misconception of reality cloaks our view of the way the world really works with regard to the population dynamics of all species within the evolutionary ‘tree of life’, including Homo sapiens.

    There are hallmarks that define a deluded cultural transmission. They include political convenience, economic expediency, social suitability, religious tolerance, and legalization. All seem necessary for a false meme to become culturally prescribed. Purveyors of false memes willfully ignore the questioning of ideas upon which their misinformation is based — a hallmark of science. Without the support of science we find ourselves in a festering haze of delusion.

    With regard to its population dynamics, our evolving memetic species has a vital task. Substitute a scientifically founded meme for the unquestioned false one. Then the new meme would be: increases in the total production of food for human consumption lead to a global population increase of H. sapiens. We would acknowledge not only that we have a food distribution problem but also a problem derived from our tragic failure to use available ways and means to prevent unwanted births humanely.

    How the human community chooses to act in response to this daunting predicament is something others more capable than I will have to address and find a way to overcome. Years ago, before the 21st century began to unfold, my spouse advised me not to communicate the ecological science of human population dynamics until I had a solution to the existential situation disclosed by the evidence. I told her then and say to all now, I do not have answers to the thorny questions or solutions to difficult problems the heretofore uncontested science raises. Please allow me to add the belief that any program of action to rein in the size of the human population by limiting the human food supply must begin by taking simultaneous steps to feed the human community as well as to save the flourishing of life (i.e., biodiversity) as we know it.

    It is neither necessary nor sustainable to continue increasing food production to feed a growing human population. To the contrary, such a determination ultimately carries with it profoundly harmful consequences. In the case of H. sapiens the species eats itself out of house and home.

    Steven Earl Salmony, Ph.D., M.P.A. is a retired practicing psychologist. In 2001 Steve founded the AWAREness Campaign on the Human Population to raise consciousness of the colossal threat that the unbridled, near exponential growth of absolute global human population numbers poses for life as it is known to us. His campaign has focused upon the best available science of human population dynamics and the topic of human overpopulation of earth in our time. He can be reached at sesalmony@aol.com.

    1. “The problem is food redistribution.”
      Well, yes and no. If people live where food isn’t produced in sufficient quantities, to me that is a food *production* problem, because there is no guarantee that the food they need will get to them, and because doing so has economic and environmental costs. Also, countries that are producing extra food should in time lower their production to leave space for wildlife. It doesn’t make sense to me to preserve wildlife in Africa or the Amazon by forcing the US or Europe to destroy their own environment in order to produce food for the people in poorer, greener countries. I want forests too! I want people in SS Africa to produce their own local, nutritious food.
      You can rely on trade for things that aren’t life and death. But, as the war in Ukraine has shown, to depend on others for things such as food, energy or heating is extremely dangerous.

  10. davykydd, wealth taxes change all the time. In the 1930s in the US the highest income tax was 75%. No revolution by the super rich happened then.
    If anything, it would make revolt by the poorest less likely. Look at the gilet jaunes in France to see a small taste of what happens when only the middle- and lower classes are expected to make sacrifices.
    As for the numbers, I am certainly not qualified to touch them, but others here are.

    1. Gaia, thanks for your reflections. And good of you to speak about graduated income taxes.

      Nonetheless, my point was about Phil’s wording, “confiscation.” Citizens do not pay annual income confiscations, they pay income taxes. At the store, customers do not have their money confiscated, they pay sales tax. These are two different concepts, not innocent synonyms.
      Since the Overpopulation Project aspires to reach audiences beyond our own silo, it behooves us to speak with tact and care about people’s wealth. “Confiscation” simply won’t do, will it?

      1. I see your point. I can’t speak for Phil, and I agree the word “confiscation” might frighten a few people and not be necessary, but he was talking about billionaires, a small minority with a personal wealth so big it actually destabilizes societies and gives them more power as individuals than is compatible with a democracy. An argument could be made that there should be a maximum amount of wealth an individual is legally allowed to keep, and anything about that should be redistributed or used for public spending. We don’t allow people to “own” countries, for example, do we? I’m actually hoping to write a book on this, so I don’t think I can argue convincingly in just the space of a comment.

  11. There’s a major methodological error in this analysis.

    Hundreds of millions of people across the world have increased their consumption by moving to higher-income nations. Those are increases in consumption, not population, but the paper falsely attributes them to the population side of the issue. This causes three separate errors:

    #1: Higher-income countries are registered as having contributed to a population increase, when the actual issue was people moving to increase consumption and global population did not change as a result of their move.

    #2: Since the average immigrant uses below-average resources in the wealthy country, per-capita consumption in the wealthy nation decreases. But no one’s consumption actually decreased, just some people changed categories.

    #3: Since the average emigrant from a low-income country was using above-average resources, per-capita consumption in that poorer country declines when they leave. But no one’s consumption actually declined, they just changed categories.

    I’m also unsure why 1961 is taken as a reasonable baseline. Were people going out of their way to conserve resources in 1961? We’re they issuing efficient technology? Comparing our consumption rates to 1961 is like comparing our Covid deaths to 2022. It’s a completely artificial starting point, and the degree of consumption increase since 1961 bears little relevance to the question of how far above acceptable our consumption has become.

  12. Hi Jon, you make a couple of valid points. However, I’m not sure if the volume of international migration is as large as you believe. It was running at about 3 million per year, with about 1 million of those transferring from a poor country to a rich country. That number has crept up in the last half decade, so I’m not sure what it is, but still relatively modest at a global scale. Nevertheless, it does account for most of the current population growth in developed countries, if not the growth since 1961 – for most developed countries, most of that growth has been from the post-war baby boom and the momentum it created, but that momentum has now largely played out. A few countries – especially the Anglophone “new world” countries, have had a large share of their growth from immigration. Per capita footprint has mainly come down through more efficient vehicles and heating/cooling/lighting, rather than individual choices to consume less. That is a real thing, not a category shift. Then, as Gaia points out, a great many residents of wealthy countries are getting poorer – not just migrants. The excesses of the rich are often in how they consume other people’s labour rather than natural resources (although clearly resources come into it too).

    The more important point is what this decomposition of impacts says about the policies that are needed. Whether the additional people are through the airport or the maternity ward, developed countries need to recognise that population growth is antithetical to environmental sustainability. A sustainable population policy includes limiting immigration to levels that don’t fuel population growth (i.e. levels that only make up for lower-than-replacement fertility). If you say, it’s not population growth, just people consuming more because they moved, then there is no clear message for developed countries to use population policy to reduce their ecological footprint.

    On the other point, the choice of baseline really changes nothing. Obviously, if the study was looking to reveal the impact of specific initiatives or policies active over a specific time, then the baseline should be immediately before that. In this case, it is a data availability issue – he’s using the earliest period in which data was available for calculating ecological footprint of nations.

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