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What size of human population can earth sustain?

  1. Jul 8, 2009 #1
    A friend of mine said that currently, the "wealthy" 1.5 billion people on earth consume as much as the poor other 4.5 billion. He also said there are not enough resources (corruption, etc, aside) to have the others live the "rich" life style.

    Which begs the question... how much human life can earth sustain? During the 20th century, the population went from something like 1.5 to 5 billion.... i think prognoses are 9 billion for 2050, but "only" 9.5 billion for 2150. Could overpopulation become an issue during our life times?
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  3. Jul 8, 2009 #2
    I read somewhere that the population in developed countries double every 37 years, so I would expect there be at least 10 billion people by 2050, however there is still plenty of space for growth yet. I mean look at Australia, its practically empty.
  4. Jul 8, 2009 #3


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    For clarity, are you intending you question to be answered in the context of the current resource distribution, a more uniform resource distribution, or something else?
  5. Jul 8, 2009 #4
    Well it's not so much a space issue, but rather a resources/energy/pollution/susceptibility to war/epidemic/etc-issue.
  6. Jul 8, 2009 #5
    As time goes on we will develope more efficient use of resources, means of making more land arable, means of making more varieties of crops easily grown, cheaper easier desalinization for drinking water, ect ect.
    Also as nations become more developed the number of children per family decreases. So if we 'make the poorer richer' we may eventually see a decline in population growth.
  7. Jul 8, 2009 #6
    A realistic scenario, which would be close to the current resource distribution. Well, i'd be interested on your thoughts about this regardless, but to answer your question: i'm not talking about a hypothetical situation with optimal resource distribution.
  8. Jul 8, 2009 #7
    How many people can be supported depends on too many factors to arrive at a definite number. For example, what standard of living you expect them to have? Eg. how much fresh water can each person consume given that rainfalls don't respond to population size? What sources of energy can replace depleted fossil fuels currently needed to farm for food? How many non-human species are we willing to sacrifice in the reallocation of planetary resources to support human life? What life expectancy do we want to achieve? Will climate change affect food and water utilization?

    My impression is that a sustainable population that does not damage its environment, does not eliminate other species, provides an abundance of water, food and other resources for all would be something less than what we currently have. So I would guess a number lower than 6 billion under our current state of technology.
  9. Jul 8, 2009 #8
    The Earth can probably support a hundred billion people. The question is for how long.
    Why would we get a 3 billion person increase in 50 years, but only a 500 million person increase in the next 100 years?
  10. Jul 8, 2009 #9
    Not enough food and water for more? Limitless growth within a limited world is an impossibility. At some point human population will either stabilize to a steady state or crash.
  11. Jul 8, 2009 #10


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    I think the earth could sustain over 30 billion people. But I agree broadly with the UN 2050 population projections, which have population roughly stabilizing around 10 billion. Getting above, say, twice that would require substantial wealth redistribution.
  12. Jul 8, 2009 #11
    With the current status-quo, the earth can not even support the 6 billion we have right now for the next 50 years. With significant changes in technology/lifestyle/ways that we live we may be able to support those numbers that the UN projects.
    Last edited: Jul 8, 2009
  13. Jul 8, 2009 #12


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    The models assume that as GDP for a 3rd world country rises then it's birth rate declines to 1st world levels - which for most is negative growth.
    The assumption is also that you never go backward - so no country drops back to 3rd world levels because of war or natural disaster.
  14. Jul 8, 2009 #13


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    That's the current trend. Values and cultural traits may change in the future where maybe they will choose to get more children.
  15. Jul 8, 2009 #14
    I think overpopulation or sustainability would never be a real issue because you cannot go over the limit (i.e. have more people than the resources required to sustain them. Is it even possible?). More concerning would be the number of people dying each year because of the less resources.

    Resource distribution (rich/poor people) is not related to the sustainability.
  16. Jul 8, 2009 #15
    That also means the nation's ability to produce go down and you need immigrants. I don't think negative growth is desired.
  17. Jul 8, 2009 #16
    Has anyone bothered to calculate how long it will take at the current rate of greenhouse gas emissions for the atmosphere to be lost?
  18. Jul 8, 2009 #17
    That is certainly a possibility. There are current subcultures in first world nations such as the mormons that still prefer larger families. I'm not sure that it is very likely to become common though. The general trend accross all cultures seems to be a decrease in family size, but I guess you never know.
  19. Jul 8, 2009 #18
    You are strictly correct: it's not possible for anything to exceed its maximum possible. But I don't think of overpopulation in technical terms, I find it to be a subjective point of view. When members of a population suffer (a relative term) from resource shortages (another relative term) then I call that overpopulation (yet another relative). If I think the planet is overpopulated, it is because of my own standard of living which I consider normal. But it cannot be made available to everyone. There just isn't enough planet to provide it to all. Or conversely, there are too many humans per planet to permit it. With luck we can learn new technological tricks to alleviate this but we cannot grow a bigger planet. One thing we can do is stabilize our population. Two well-fed kids beat eight hungry ones, and contraception is cheaper than a lifetime of food for six more.

    EDIT: typo.
    Last edited: Jul 8, 2009
  20. Jul 8, 2009 #19


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    I didn't say the model was correct - just that this is the reason for the dip in the curve!

    An interesting second effect seen in europe is that as countries become 'more devloped' you get a huge drop in the birth rate as women have a chance of an education and a career, then a couple of generations later you get a bounce back as those women have the political power to demand better conditions, maternity rights etc. So you have Spain/Greece with birth rates of 1.2-1.4 and Scandanavia back up above 2.0
  21. Jul 8, 2009 #20


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    Yes, you can when you're talking about sustainability. If you have a large stockpile of a critical resource because it was once produced faster than it could be consumed, then it allows more people to use the resource than is sustainable .... for as long as the stockpile lasts.

    Fossil fuels, for example - it takes a lot of plants and a long time to create a stockpile, but there were a few billion years where consumption was virtually zero. Now, consumption is more than 400 times faster than development was (it would be more accurate to say that annual fossil fuel consumption is the equivalent of more than 400 years worth of the Earth's plant life since not all plant life turns into useable fossil fuels - i.e. the consumption rate is way more than 400 times the rate of development).

    At that ratio, you may as well call it a non-renewable resource and ignore the sustainability issue.

    You might have had the same situation on Easter Island, where the population exceeded what the island could support in one key resource - trees (either because of overpopulation or by climatic events). Regardless of the cause, once the consumption of trees exceeded what could be replaced, life still went on as normal until the sockpile of trees was gone. With almost complete deforestation, the soil erosion, loss of crops, etc, have a lot quicker effect on the population.

    In other words, unless all resources are developed at the same rate they're consumed (no surplus), you'll eventually create a situation that can support overpopulation temporarily ... at least until the surplus is consumed, at which point you have devastating consequences (of course, since climate changes because of one reason or another, having no surpluses would be equally devastating - the surplus just changes the timing of the devestation).
  22. Jul 8, 2009 #21
    Estimating an exaflop to run a human mind and sufficiently render a natural environment, and estimating a cubic centimeter, or roughly 10^23 atoms in a three dimensional molecular computer operating at an exaflop, which should ultimately be possible.

    10^50 atoms in the earth.

    With the presumption that the majority of it can be utilized for computation and power can be provided,

    1000000000000000000000000000 people.

    So it appears the planet can support up to ten trillion quadrillion people. 7 billion seems quite tame in comparison, but clearly we will have to change our approach.
  23. Jul 8, 2009 #22
    Personally I think if we can survive the next 100-10000 years and become a space traveling civilization with the ability to mine enormous amounts of minerals and harvest the suns energy, there will be no need for earth anymore (to a major extent) and we will expand quite radically from that point.

    The hard part is reaching that point and not getting destroyed by some natural event or human made disaster or war.

    (But I suspect with current conditions the earth can support ~10 billion people)
  24. Jul 8, 2009 #23
    Personally, i find it hard to imagine the luxury of the western world to still be as great as it is right now, as little as 100 years from now. Everything we've done in the 20th century is just SO EXTREMELY far ahead of anything we've done the 10.000 years before that. We've waged the biggest wars. We can, at any instant, effectively wipe out humanity using nuclear bombs. Global communication (Internet, TV) is something that is unimaginably far ahead of anything preceding. Science is at a very high level to the degree that we have a basic understanding of virtually all practical events in our nature. We don't have to worry about food or shelter (still talking about the western world). We can travel to any part of the world in little time. We've explored space and have launched and are using artificial satellites.

    It's just remarkable the gigantic technological steps we've taking during the last century. By comparison, in a millennium, a time stretch 10 times longer, from 500-1500, as humanity we've done very little except for kill ourselves and re-distribute land. What a horrible, miserable period of time the middle ages were.

    But, my point (in this post, not the thread) is: how long can we sustain this huge, upward arc the likes of which we've never seen? What if a terrorist obtains a nuclear weapon and unleashed a chain of events that leads to our extermination? I stand very positive in life, but i'm not at all sure of how life will be 100 years from now.
  25. Jul 8, 2009 #24


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    What are you talking about? Worldwide, the rate of growth is declining:

  26. Jul 9, 2009 #25
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