What Is the Carrying Capacity of Earth?

Alex Casey, Communications Fellow, reports on a conversation she had with Joel E. Cohen, author of How Many People Can the Earth Support?

What Does Carrying Capacity Mean?

Did you know that the term we use to try to determine the number of people the planet can support is the same one used by sailors in the 1840s to weigh the amount of cargo a ship could safely carry?

Joel Cohen on March 2, 2011 | © El Programa DIA, Desarrollo de Inteligencia a través del arte

Carrying capacity became mainstream in the 1870s as a “poetic metaphor” in wildlife management, according to Joel E. Cohen, the professor and mathematician who tried to calculate a definitive number in his 1995 book How Many People Can the Earth Support? The term was further popularized in the 19th century as a way to measure human population growth. In the mid-twentieth century, so-called neo-Malthusians employed the term carrying capacity to identify the number of humans the Earth could support, according to Nathan Sayre, a geographer at UC Berkeley who published a paper on the limitations of carrying capacity as a concept in 2008.

Measuring a dynamic human carrying capacity involves more complications than a static ship, but it implies that there’s a definite upper limit to the planet’s population. An overarching question remains: With a resource-demanding 7.8 billion people today, how many more people can the world hold?

How to Calculate Carrying Capacity

Measuring carrying capacity is often attempted by calculating Earth’s available resources. Edward O. Wilson, a Harvard sociobiologist, estimated that Earth’s remaining arable land could support about ten billion vegetarians. In Prof. Wilson’s logic, Earth’s remaining 3.5 billion acres of land could produce two billion tons of grains annually.

In 2004, a group of Dutch authors recorded other estimates from a group of 94 scientists. The estimates ranged from 500 million to 1 sextillion (that’s 21 zeroes). Cohen told me that this range was particularly helpful because it proves that estimates depend on methodological differences and assumptions people make about the world they live in.

Average material consumption plays an important role in determining how many people the earth can support, according to Cohen. But so does resource inequality, future technologies, conflict resolution, economic systems, social demographics, physical environment preferences, risk assessments, population variability, sustainability time horizons and values, tastes, and fashions.

“It’s a dubious value in many of its applications. The existence of a carrying capacity in wildlife management is not supported. Animals change their environment and that changes their capacity,” Cohen said. “Humans change their worlds and that changes their capacities.”

There is no metric for what determines human carrying capacity that can be generalized on a community scale, let alone a world one. City-dwelling vegetarians who compost everything may jet around the country multiple times a week for business trips. Rural couples in Niger may struggle to meet the daily fresh water and food needs of their large families. Eco-conscious suburbanites may drive electric vehicles and have solar panels, but eat meat every night for dinner.

All of these ever-changing factors make it difficult to calculate the maximum population the earth can sustain. Moreover, how we consume, emit, treat the planet, practice sustainability, travel, vote in elections—in addition to all other socioeconomic, political, or cultural factors and practices—make it difficult to determine when an area has reached its true carrying capacity.

Did the mass exodus in the wake of Hurricane Katrina represent a breach of New Orleans’ carrying capacity, or was it a failure of the government to anticipate predictable problems when it allowed people to build in low-lying, flood-prone regions? Cohen says it was the latter.

This question becomes a bit more complicated as lower-income countries begin to experience prolonged drought due to declining water tables and variable weather patterns. An estimated 3.7 million people have been displaced as a direct result of climate change and violent conflict in the Sahel, a region that also experiences very high fertility. In Niger, the country with the highest total fertility rate in the world, the average woman will have about 7 children during her lifetime.

Do We Really Need to Estimate Earth’s Human Carrying Capacity?

Since the publication of Cohen’s groundbreaking work, some scientists have claimed that we’re already past the point of no return. The UN Secretary General said 2021 is the ‘make-or-break’ year for climate action. People are consuming Earth’s resources at 1.6 times the sustainable rate. Meanwhile, the world population continues to rise by 80 million a year.

There are two fundamental shifts that must occur to both heighten standards of living and lower climate-related disasters, according to Cohen. The first is food. Right now, 22 percent of the world’s children under five suffer from poor nutrition. Cohen says we must grow enough food to adequately feed the next generation’s future problem solvers.

Voluntary contraception and education are next. An estimated 218 million women in low- and middle-income countries have an unmet need for contraception. According to Cohen, 100 percent of pregnancies should be intended and all women should be able to access the education, services, and supplies needed to control their fertility. When women attain bodily autonomy, they make better choices about factors that affect climate change mitigation (e.g. family size) and adaptation (e.g. where to live).

Contraception in and of itself is a form of climate preparedness; it enables women and families to make better decisions to live better lives. Family planning programs and contraceptive services have had enormous success in promoting health, development, and gender equality since they were introduced in the 1960s. They’ve also had a tremendous effect on the trajectory of human population growth. The global fertility rate has declined from 4.9 children per woman in 1965-1970 to 2.4 today, and the rate of population growth has declined from its peak of 2.05% a year to 0.98%.

With dedicated investments in international family planning and primary and secondary education, especially for girls, we could further slow population growth through smaller families, which would improve health and development outcomes while shrinking humanity’s ecological footprint.

“Do we really need to estimate Earth’s human carrying capacity?” Cohen asked. “Wouldn’t it make sense to use the available knowledge and resources we have to try to fix problems our species and other species face today?”

Perhaps this should be the question we ask, rather than going in circles trying to calculate our lifestyle-dependent upper limit.

An earlier post about carrying capacity, published in April 2017, has been replaced with this updated version.

33 thoughts on “What Is the Carrying Capacity of Earth?

  1. I think it is around 1 billion. With that population recycling and renewables could sustain the population for quite sometime. We still will have to actively sequester carbon. It will happen by slow reduction of population or a biological crash. The latter would not be pretty.

      • There are currently more people on the planet than many scientists believe is sustainable long term, which is what carrying capacity refers to. A population of any species can live in overshoot for a while, but eventually lack of sustainability will catch up with it, causing suffering and strife.

          • That goal will most likely be hit. If each continent had 12 billion people there is no room for other species to thrive. !2 billion is 2x the amount that we have right now. Imagne twice the amount of people will just kill all other existing life.

        • 88 billion. Is our max 12 billion people per continent.

          But I wouldn’t try to hit that. Maybe just do 12 billion-24 billion max.

  2. Huge research papers predict; Sustainable carrying capacity of Mother earth as on today is 3 billion people depending on replenishment of renewable resources. Different sections of people are in rat race of survival like the tribes of ancient ages. One particular section of tribes want to multiply and capture the world to spread their tribal laws in name of religion . Other sections are also multiplying for survival / existence. There will never be any agreement on this issue and we will be extinct within next one hundred years as predicted by numerous specialists. We have already ignited the suicidal bomb for extinction of human species on earth and there is no escape from it

  3. People cannot continue reproducing at will. The cc is somewhat dependent upon lifestyle, governing systems and how we apply our technologies. Currently, as a whole, humans are not doing much to show that our cc is 10 billion or more. I believe based on our current path, we max out at 4 to 5 billion. Currently, we are on a path to extinction.

  4. We already know the answer to this question, because before 1820 humanity was living off of human, animal, and vegetable (i.e. wood) power only. So the answer is one billion people. Anything else is above the carrying capacity for our species.

  5. How about limiting it to 2 billion people? The current population could be reduced by attrition. That’s enough and that many people would not strain the environment. There is a limit and reproducing carelessly endangers our long-term survival and the survival of other species with whom we share the planet.

    • Be incredibly careful when proposing an attrition approach. If the rate of reproduction is slashed, the mean age of the population will become much older. In countries with older populations, like Italy, quality of life decreases as the productive portion of the population cannot generate enough resources to care for the elderly. Currently, Italy is rich enough to use resources from other countries to compensate, but that will not be possible globally. Consider also the oppression that would have to take place to mandate population decline. Mandatory contraception is the opposite of body autonomy, and anyone who claims to be feminist or “pro-choice” and supports ideas like the ones advocated in this article betrays their own values. Families will be jailed and their children will be taken from them and human dignity will be eroded. It’s crucial that intellectuals get off their high horses and have real empathy and realize they don’t have the silver bullet to become the savior of ordinary people around the world.

  6. This depends on whether we want other life on Earth to survive too. If we do and we want to continue our current lifestyle, I think the answer is closer to 2 billion. Part of the reason that it is lower than the current population is because we use fossil fuel based fertiliser, which is a finite resource. If we stopped eating ruminants we could increase that number, or if we produced them more intensively.

  7. I deal with nutrition, i wrote a book “in good health without diet” and I tell you this: if we want to live really healthy as our distant ancestors (30.000 years ago) were but at the same time much longer not having to endure hypothermia or infections and having unlimited natural resources available, allowing them to be recycled one hundred million would be the maximum figure

  8. Thinking we can survive without the other life on earth is irrational. Considering we need a heathy biosphere to survive, I say carrying capacity is 2 billion. New knowledge and technology raised it from the per 1820’s one billion, but new knowledge and technology can only raise it so much.
    Of course, carrying capacity depends on population X per capita consumption. For most of the developed world, that would mean about one million. because they enjoy running through nature like a mad bull in a china shop. The fewer the people, the more destructive the elite of this world will get.
    So the question is: Can humans evolve to a species that accepts earths limitations and tries to live within them?

    • Great turn of phrase – ‘The fewer the people, the more destructive the elite of this world will get.’ Couldn’t agree more. I fear for our youngest inhabitants, and theirs. We’re way past the tipping point. Climate(see food supply) and microbiological organisms will be the great winnowers. One can only hope this happens sooner rather than later – before all of the rest of the plant and animal life on the planet is destroyed

  9. I think that regardless of actual carrying capacity it’s important to note something; if we exceed this capacity, some event will occur to balance it, but EXTINCTION and ANNIHILATION (words present in more than a few comments) are extremely unlikely. A mass die-off would obviously be likely, but with the exception of nuclear war (and maybe even then) almost any event that kills of billions will still see significant amounts of survivors (even something like 3000 survivors would be biological capable of repopulation) . We’re not facing extinction of species, we’re facing the extinction of our existing civilization without change. Simply, the dilemma is we reduce/sustain population at a feasible level, or biology and chemistry will reduce it for us in a less pleasant way.

  10. I am just checking if the 19 thoughts are provided by readers or if they had been hand selected by the author for a school report.

    • The comments on this website are submitted by readers. Population Connection staff approve comments, assuming they aren’t spam and don’t contain abusive language.

  11. So far I’ve not heard it pointed out that: The rich have always known that the real value of their fortune is “how much labor will it buy?” This because almost all things humans value are merely frozen labor. When the worker are numerous and poor, they will work for peanuts. During a depression the purchasing power of the rich leaps upward as wages drop. This is probably the prime reason that the vast majority of humanity has never heard of population overshoot. Population overshoot makes the rich giddy.

  12. It’s not about space it’s about resources. It’s about access to food and water to sustain a large population. We are projected to hit somewhere between 9 and 11 billion. Whether or not we will be able to sustain this number depends on whether or not agricultural technology keeps advancing. And if you think drinking sea water is an option it’s not really a usable solution right now. Did you know you could fit the entire population of humans on Earth shoulder to shoulder in Los angles. It’s not space it’s food and resources. This is what we call carrying capacity, the amount of people that can be sustained based on the resources we have. If population continues to grow as projected our population should hit 11 billion by 2100. You can trust me I’m in AP human geography.

  13. Many people discuss availability of resources when discussing the carrying capacity of our planet. I like to include a second discussion with my students. I include the discussion of how we buffer the human impact. Pollution of our air and waterways; degradation and depletion of our soil are just a few of the impacts that reduce the viability of fundamental resources such as water. Water is life’s essence!
    I think the actual population of people that can be sustained is based upon how much science and technology can ‘step in’ to solve some problems. For example, modified crops such as corn have been with us for years in attempt to increase available food. However, the nutrient level of our processed food is anything to be desired. Science has yet to cause major change in the buffering of our existence. This is mainly due to political will and apathy of the population.
    Just wanted to share my thoughts since I came across this site. Peace out dudes & dudettes

  14. As of April 2021, the population of the Earth was 7.9 billion, and I would argue that the maximum sustainable population of the Earth would be approximately two-thirds of that number, or 6 billion people. Although it is not an entirely pleasant thing to think about, eventually it will necessarily involve some kind of social control. That is, a limitation on the number of children each person is allowed to have. The real question then becomes, when, and how,  should we begin ? 

  15. The problem is Capitalism and Socialism, how we structure and incentivize our current societies. We need to switch to what is called a Resource Based Economy with the guidance of all our Technology, with all nations working as one. The earth could support probably up 20-30 billion people maybe more. We have the technology. We have the brain power. But moving to this kind of world means moving away this “Employer”, “Employee” structure.

  16. There is a limit to how far we can push nature to increase the cc of earth. We try to treat the complex questions as if they have simple answers. They don’t! In the United States, we may get away with depending on science to solve our population crisis. But will that happen in central Africa? The Amazon tropical forests us to be a Co2 absorbers. giving off oxygen. Recently it became a carbon dioxide emitter adding to the atmospheric carbon load. What happens as more and more of the forests burn due to climate change? What happens as sea currents and weather patterns change as a result of the thawing of the Antarctic Ice shelf, Will the earth have enough potable water for the population of the earth?

  17. IMHO, this and almost every study, report, article on Earth’s carrying capacity for humans seems fatally flawed, they exclude all other life on Earth. I offer, instead, bringing into this study the needs of all life on Earth, thus: Earth’s natural carrying capacity for humans should be based on how many people can any given area support in good health without negatively impacting the health of all the other species living in the same area.
    Through the vast majority of Homo sapiens sapiens accepted presence on Earth it has been variously estimated that our population ranged between one and ten million of us, and this range continued for between two and three hundred thousand years, at least; it was not until the advent of sedentary agriculture that these numbers began to be exceeded. With each injection of new technology our population increase followed suit.
    Almost myopically human carrying capacity studies have excluded the needs of any and all the other species we share the Earth with, and therein lies the crux of what I see is mankind’s ultimate dilemma: people are inextricably intertwined with what now is called the “web of life”; that is, either directly or indirectly all life is dependent on all other life on Earth. Yes, we might be able to continue to exist without other life, but not for long: we do not produce the oxygen we need to survive; oxygen is produced by the dynamic interactions of many other species, which in turn, is dependent at their root on the continued trickle of nutrients weathered from rock and soil, washed back into the soil and into the streams, rivers, lakes and oceans of the world. Somewhat euphemistically this has been called “The Gaia Effect.”
    Our technology can not replace such interdependence, and to date has only succeeded in shoving aside the needs of all other life on Earth to make room for our ever burgeoning numbers. To me this if folly akin to eating one’s own home.
    Having said all that I ask: what stable population size is necessary to provide a equitable, healthy human population where everyone has all the benefits of hi-technology as well? 500 million of us, a billion or two billion of us? Could a billion of us equally employing hi-technology be enough to sustain such technologies, steady-state? Why must advancing technological prowess always be coupled to ever growing population numbers. Excluding religious edicts I don’t think it does; “be fruitful and multiply” is the bane of all life on Earth, our own as well eventually.
    For the safe, heathy continuation of mankind’s existence a new paradigm needs to come about that sees the rights of all life on Earth protected, if not absolutely equal to ours, at the very least on a par with ours.

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