7 ms·

What is the Limit to Human Population Growth?

45 points by sampsonjs 15y ago

graeme 15y ago
Population will almost certainly run into hard limits before mid-century. The author points out resource limits in passing, but it's worse than he admits. We run our civilization off of stored solar energy. That's what oil, natural gas and coal are. In a century we've used millions of years worth of stored solar energy. That's the energy that's powered the green revolution (along with non-renewable aquifers). Nuclear and our small sources of renewable are the only exceptions. The rest of our power comes from stored energy. And nuclear/renewables are generally built using stored fossil energy. Effectively, we're burning through capital, beyond a sustainable rate. If anyone has thought of a way out, please let me know. Meanwhile, if you've been looking for something meaningful to build that will be in demand, this is it.
- bryanlarsen 15y ago
  Have you taken a look at the estimates of how many years worth of coal, oil & natural gas we have left? In the 70's they said we had 20-30 years of oil left. They were right: we've basically run out of $10-20 oil, although Saudi Arabia still has some of that. But $100 oil? We've got enough of that to last this century, at least. Heck, the Canadian oil sands alone could probably power the world for most of this century. And we'll run out of oil before we run out of shale gas or coal -- we've probably got multiple centuries of that, at peak prices.
  - graeme 15y ago
    You're right, there's more left. But as it gets harder to extract, prices will rise. We're already reduced to blowing up mountaintops in Virginia to get coal, or melting the soil of Alberta to get tar. The energy return on investment (EROI) of those sources is much lower than the old Saudi oil. Optimistically, those sources might help ease a transition. We'd still have energy to power things, and the higher prices would encourage switching. But there are still dangers. We only have a limited amount of carbon we can still afford to put in the atmosphere. And it will be difficult to run all of our current activities and invest in new energy sources and do so as the price of energy rises. The question remains: if we switch, what are we switching to?We're currently using energy that was stored for us over millions of years. It's highly concentrated. Renewables must make do with incoming solar energy. Maybe people will warm to nuclear, but that has its own issues.
    - Retric 15y ago
      EROI for blowing up mountaintops in Virginia is significantly better than 1970's saudi Oil. It's also better than directly minding the stuff. Which is why the cost of coal is so 1/10th the price of Oil per unit energy. PS: People talk about Oil like it's the single most important energy source out there, but it's only important because it used to be so cheap.
      - schiffern 15y ago
        The EROI for blowing up mountaintops ignores the externalized costs of the activity: water pollution, habitat destruction (and the loss of associated ecosystem services), damage from explosive concussions, and ultimately a locality that sacrifices its long-term health for a handful of temporary jobs. And this argument even yields to the HN party line that states that the value of undeveloped natural spaces is zero.
        wlievens 15y ago
        It's a bit cynical to call that "the HN party line". There's surely a bunch of hardcore libertarians out here who would hold that opinion (by which I won't implicate that any libertarian would) but I doubt it's a majority.
        Retric 15y ago
        When it comes to energy, I am vary pro wind power and feel solar/fusion are both going to be viable in my lifetime. However, EROI is a measure of the amount of energy it costs to develop an energy source which is both a simple measurement and poorly understood by a lot of people. So, while I dislike coal for a number of reasons, I do feel the need to bring it up when people get all doom and gloom over Oil.
    - jacques_chester 15y ago
      You can make oil out of natural gas, coal, wood, hemp oil, cane sugar. Anything that has carbohydrates can, with an energy investment, be turned into a different carbohydrate. Gas and coal would be first because they're closer to petroleum and massively abundant, but there's no chemical reason why other substitutes can't be used in the very long term.
  - zeteo 15y ago
    Exactly. The price of oil reflects not so much its rarity as the difficulty in extraction. As the difficulty increases, companies like Solyndra will have a much easier time selling substitute products, and will stop going bankrupt despite heavy governmental assistance.
- lupatus 15y ago
  As The Futurist discusses in depth[1], annual world oil consumption has been hovering around 32 billion barrels since about 1982. That means oil consumption, at $100/barrel, is $3.2 trillion, or 5% of nominal world GDP. My take away from that is technology has made the oil supply a non-issue. And, it will continue not being a problem for the foreseeable future. It is not a hard resource limit. [1] http://www.singularity2050.com/2011/07/the-end-of-petrotyranny.html http://www.singularity2050.com/2011/07/the-end-of-petrotyran...
bryanlarsen 15y ago
One of the most annoying things things in science fiction is this plot line: the earth is running out of food, so several hundred thousand people get on a big ark ship to the nearest star. They then feed themselves in a few cubic kilometres simply using nuclear energy to power giant greenhouses. Why couldn't they have done that on earth? Using nuclear power plants to desalinate water and power vertical greenhouses, back of the envelope calculations show the maximum population of the earth at somewhere around 1 TRILLION people. Sure, that would make food more expensive, but given how dramatically the cost of food has dropped over time, we could deal with it. For example, the price of a bushel of wheat has been within an order of magnitude of 1 UK pound for the last 1000 years. The price of everything else has increased over time, but wheat hasn't.
- tsuyoshi 15y ago
  Right, so energy can be substituted for arable land. But I wonder if the real limit to human population is mineral-based, rather than energy-based. Every person needs a certain portion of different minerals: calcium, iron, potassium, magnesium, phosphorus, zinc, selenium, etc. Maybe we would run out of one of those minerals before we would run out of energy? This could be a topic for science fiction. We run out of zinc, and then have to send an unmanned spaceship over to some other galaxy to mine some zinc... but there would have to be some other complication, because unmanned spaceflight is boring.
  - ctdonath 15y ago
    Pot growers manage to substitute energy for arable land.
  - jacques_chester 15y ago
    I once calculated that at a constant doubling rate of every 15 years, the human race would need to use all of the resources of the asteroid belt in about 12,000 years. There's a lot of stuff out there.
  - bryanlarsen 15y ago
    We're not going to run out of minerals. Choose a mineral, any mineral, even a trace mineral. Look on Wikipedia to see what percentage of the earth's crust it makes up. (for example, iron is 5%). Do the math and realize that we've got thousands to millions of years worth of minerals left. Sure, we can run out of "easy" deposits. We did that for Copper decades ago. Copper mines today are essentially giant processing plants that extract the tiny amount of copper in pretty much ordinary dirt -- "copper ore" these days only has about 10 times as much copper per kg as the stuff in your backyard.
VladRussian 15y ago
if to look at civilization development through energy harnessed/controlled, our civilization has been through the following stages: 1. at human body energy level by gathering/hunting (ie. what nature provided) 2. at human body energy level, managed/renewable. I.e. agriculture. 3. at industrial energy level by gathering - fossil fuels, nuclear fission. we're at the end of the stage 3. with stage 4. "managed/renewable industrial level" (solar/wind and nuclear fusion) appearing on the horizon. Increasing available energy levels allows for increased population growth. There is no limit in sight. The Moon and Mars are waiting :)
zeteo 15y ago
Even assuming a limit exists, without hard numbers this discussion is a waste of time. There is a huge practical difference between a limit of 8 billion and one of 20 billion; especially as these same UN population models, which the author mentions, predict that world population may stabilize, or even start declining, by 2050 (http://www.un.org/esa/population/publications/popnews/Newsltr_87.pdf http://www.un.org/esa/population/publications/popnews/Newslt...)
whackberry 15y ago
The limit is right about what we have now.
reasonattlm 15y ago
The only hard limits for human-style organisms on an earth-type planet are thermodynamic. Using 1970s technology, the earth could support hundreds of billions. e.g.: http://www.acceleratingfuture.com/michael/blog/2006/09/overpopulation-no-problem/ http://www.acceleratingfuture.com/michael/blog/2006/09/overp... When you look at the simple figures that show that to be true, it somewhat puts the ridiculous debates over billions into context. i.e. they're not really debates over capacity and resources, they're debates over organization and (lack of) understanding the nature of progress and achievement.
- icegreentea 15y ago
  The linked article misses or glosses over a crucial part of sustaining the population. As the New Yorker article touches on, the real rate limiting factor in growing food is not sunlight, or even water, but really phosphorous, nitrogen, and other fertilizers nutrients. The only way to have a long term sustainable food system is to have one where the majority of these nutrients are redirected from human waste back into growing food.
  - billswift 15y ago
    That is merely a matter of attitude. Right now post-processed sewerage isn't used for food production in most First World countries, but it could be. It is often used on golf courses, and there have been experiments in bagging it and selling it to landscape gardeners as a replacement for bagged cow manure. In the DC area, there was Com-Pro in the 1990s, for example, though I heard it was taken off the market for lack of sales even though it was less than half the price of bagged cow manure. If there was serious need for fertilizer, it could easily be satisfied.
mark_up 15y ago
Anyone really interested in this should watch Albert Bartlett's lecture "Arithmetic, Population, and Energy". It blew my mind when I first watched it two years ago: http://www.youtube.com/watch?v=F-QA2rkpBSY http://www.youtube.com/watch?v=F-QA2rkpBSY
tzs 15y ago
Here's a shot at an upper limit (idea ripped off from an Isaac Asimov essay I read a long time ago--late '70s most likely, but I re-did the calculations myself since I couldn't remember his numbers). Imagine all humanity packed into a very large sphere, with each human allocated a mere 1 cubic meter of space. As the population expands, we have to enlarge the sphere to make room. Starting with the current population, how long can a 1% growth rate be sustained before the frontier of the human sphere would have to expand faster than the speed of light to make room for the new humans? That's a pretty good hard upper bound on long 1% growth can be sustained. If my calculations are right, it's about 9000 years from now. (That fits with my recollection of Asimov's result).
- zeteo 15y ago
  I'd say the chances that the speed of light is still infinite, 9000 years from now, are rather slim. After all, Newton's system was radically corrected after 320 years, and even Aristotle's only held sway for about 2000. Einstein's has held well for the past 106 years, but an additional 9000 years of observation, experiment and theorizing will probably improve it a bit.
  - prayag 15y ago
    Speed of light as a limit on speed of information or matter is a universal constant. There is a reason why it is called a universal constant, no amount of observation or experimentation would change this universal fact. Of course, the science and technology would change, we would have better understanding of the universe but I doubt we would find anything that would defy the speed of light.
  - Tloewald 15y ago
    If there's some neat trick we are going to figure out in 9000 years to get around the speed of light then the galaxy / universe would have been overrun by advanced alien civilizations already. Who knows, we may have "sublimed" or been uploaded, but we won't be tooling around at warp 9 in velour uniforms.
    - 15y ago
forkandwait 15y ago
All developed nations are either right at replacement rates (USA) or well below (Japan, former Soviet nations etc). The developing nations (Thailand, Brazil, etc) are approaching replacement quickly. That leaves Africa and the poorer parts of large heterogeneous nations like India. Some of us demographers think that as we continue to develop, population growth rates will go to under replacement and then sort of bounce around replacement after that due to social reasons.
spullara 15y ago
If you take the title of this article at face value, why are we limiting ourselves to Earth? Seems like the limit of human population growth is likely at least a quadrillion based on current sky surveys and likely transportation mechanisms.
curt 15y ago
This is bogus. Hate all this overpopulation nonsense. Every developed country in the world other than the US has a negative replacement rate (births - deaths). The developing world is rapidly slowly as well. If I remember right the world only has another 50 years or so of positive growth. Not only that but the demographic skew in the developing world in male-female will likely cause it to slow even faster. The slowing growth and shrinking populations will be the huge problem of this century because our social structure in its current form can't survive a shrinking population.
TerraHertz 15y ago
The practical limits are much more esoteric than Malthus imagined. First limit: that population limit that some group of people with the power for force their beliefs on everyone else, thinks is ideal. Not like some group, of, oh, let's call them Elites, might decide the limit was radically less than the present population, and plan to use multiple means including mass contagion, war and economic collapse to force depopulation or anything. See: Georgia Guide Stones. Second limit: The number of people alive at the point when some technological singularity occurs, making 'population' a moot concept. For example: http://everist.org/texts/Fermis_Urbex_Paradox.txt http://everist.org/texts/Fermis_Urbex_Paradox.txt
- wlievens 15y ago
  I just read your scifi short in that folder. Nice writing, and interesting ideas in there.

45 points by sampsonjs 15y ago

Population will almost certainly run into hard limits before mid-century. The author points out resource limits in passing, but it's worse than he admits. We run our civilization off of stored solar energy. That's what oil, natural gas and coal are. In a century we've used millions of years worth of stored solar energy. That's the energy that's powered the green revolution (along with non-renewable aquifers). Nuclear and our small sources of renewable are the only exceptions. The rest of our power comes from stored energy. And nuclear/renewables are generally built using stored fossil energy. Effectively, we're burning through capital, beyond a sustainable rate. If anyone has thought of a way out, please let me know. Meanwhile, if you've been looking for something meaningful to build that will be in demand, this is it.

bryanlarsen 15y ago
Have you taken a look at the estimates of how many years worth of coal, oil & natural gas we have left? In the 70's they said we had 20-30 years of oil left. They were right: we've basically run out of $10-20 oil, although Saudi Arabia still has some of that. But $100 oil? We've got enough of that to last this century, at least. Heck, the Canadian oil sands alone could probably power the world for most of this century. And we'll run out of oil before we run out of shale gas or coal -- we've probably got multiple centuries of that, at peak prices.
- graeme 15y ago
  You're right, there's more left. But as it gets harder to extract, prices will rise. We're already reduced to blowing up mountaintops in Virginia to get coal, or melting the soil of Alberta to get tar. The energy return on investment (EROI) of those sources is much lower than the old Saudi oil. Optimistically, those sources might help ease a transition. We'd still have energy to power things, and the higher prices would encourage switching. But there are still dangers. We only have a limited amount of carbon we can still afford to put in the atmosphere. And it will be difficult to run all of our current activities and invest in new energy sources and do so as the price of energy rises. The question remains: if we switch, what are we switching to?We're currently using energy that was stored for us over millions of years. It's highly concentrated. Renewables must make do with incoming solar energy. Maybe people will warm to nuclear, but that has its own issues.
  - Retric 15y ago
    EROI for blowing up mountaintops in Virginia is significantly better than 1970's saudi Oil. It's also better than directly minding the stuff. Which is why the cost of coal is so 1/10th the price of Oil per unit energy. PS: People talk about Oil like it's the single most important energy source out there, but it's only important because it used to be so cheap.
    - schiffern 15y ago
      The EROI for blowing up mountaintops ignores the externalized costs of the activity: water pollution, habitat destruction (and the loss of associated ecosystem services), damage from explosive concussions, and ultimately a locality that sacrifices its long-term health for a handful of temporary jobs. And this argument even yields to the HN party line that states that the value of undeveloped natural spaces is zero.
      - wlievens 15y ago
        It's a bit cynical to call that "the HN party line". There's surely a bunch of hardcore libertarians out here who would hold that opinion (by which I won't implicate that any libertarian would) but I doubt it's a majority.
      - Retric 15y ago
        When it comes to energy, I am vary pro wind power and feel solar/fusion are both going to be viable in my lifetime. However, EROI is a measure of the amount of energy it costs to develop an energy source which is both a simple measurement and poorly understood by a lot of people. So, while I dislike coal for a number of reasons, I do feel the need to bring it up when people get all doom and gloom over Oil.
  - jacques_chester 15y ago
    You can make oil out of natural gas, coal, wood, hemp oil, cane sugar. Anything that has carbohydrates can, with an energy investment, be turned into a different carbohydrate. Gas and coal would be first because they're closer to petroleum and massively abundant, but there's no chemical reason why other substitutes can't be used in the very long term.
- zeteo 15y ago
  Exactly. The price of oil reflects not so much its rarity as the difficulty in extraction. As the difficulty increases, companies like Solyndra will have a much easier time selling substitute products, and will stop going bankrupt despite heavy governmental assistance.
lupatus 15y ago
As The Futurist discusses in depth[1], annual world oil consumption has been hovering around 32 billion barrels since about 1982. That means oil consumption, at $100/barrel, is $3.2 trillion, or 5% of nominal world GDP. My take away from that is technology has made the oil supply a non-issue. And, it will continue not being a problem for the foreseeable future. It is not a hard resource limit. [1] http://www.singularity2050.com/2011/07/the-end-of-petrotyranny.html http://www.singularity2050.com/2011/07/the-end-of-petrotyran...

bryanlarsen 15y ago

One of the most annoying things things in science fiction is this plot line: the earth is running out of food, so several hundred thousand people get on a big ark ship to the nearest star. They then feed themselves in a few cubic kilometres simply using nuclear energy to power giant greenhouses. Why couldn't they have done that on earth? Using nuclear power plants to desalinate water and power vertical greenhouses, back of the envelope calculations show the maximum population of the earth at somewhere around 1 TRILLION people. Sure, that would make food more expensive, but given how dramatically the cost of food has dropped over time, we could deal with it. For example, the price of a bushel of wheat has been within an order of magnitude of 1 UK pound for the last 1000 years. The price of everything else has increased over time, but wheat hasn't.

tsuyoshi 15y ago
Right, so energy can be substituted for arable land. But I wonder if the real limit to human population is mineral-based, rather than energy-based. Every person needs a certain portion of different minerals: calcium, iron, potassium, magnesium, phosphorus, zinc, selenium, etc. Maybe we would run out of one of those minerals before we would run out of energy? This could be a topic for science fiction. We run out of zinc, and then have to send an unmanned spaceship over to some other galaxy to mine some zinc... but there would have to be some other complication, because unmanned spaceflight is boring.
- ctdonath 15y ago
  Pot growers manage to substitute energy for arable land.
- jacques_chester 15y ago
  I once calculated that at a constant doubling rate of every 15 years, the human race would need to use all of the resources of the asteroid belt in about 12,000 years. There's a lot of stuff out there.
- bryanlarsen 15y ago
  We're not going to run out of minerals. Choose a mineral, any mineral, even a trace mineral. Look on Wikipedia to see what percentage of the earth's crust it makes up. (for example, iron is 5%). Do the math and realize that we've got thousands to millions of years worth of minerals left. Sure, we can run out of "easy" deposits. We did that for Copper decades ago. Copper mines today are essentially giant processing plants that extract the tiny amount of copper in pretty much ordinary dirt -- "copper ore" these days only has about 10 times as much copper per kg as the stuff in your backyard.

VladRussian 15y ago

if to look at civilization development through energy harnessed/controlled, our civilization has been through the following stages: 1. at human body energy level by gathering/hunting (ie. what nature provided) 2. at human body energy level, managed/renewable. I.e. agriculture. 3. at industrial energy level by gathering - fossil fuels, nuclear fission. we're at the end of the stage 3. with stage 4. "managed/renewable industrial level" (solar/wind and nuclear fusion) appearing on the horizon. Increasing available energy levels allows for increased population growth. There is no limit in sight. The Moon and Mars are waiting :)

zeteo 15y ago

Even assuming a limit exists, without hard numbers this discussion is a waste of time. There is a huge practical difference between a limit of 8 billion and one of 20 billion; especially as these same UN population models, which the author mentions, predict that world population may stabilize, or even start declining, by 2050 (http://www.un.org/esa/population/publications/popnews/Newsltr_87.pdf http://www.un.org/esa/population/publications/popnews/Newslt...)

whackberry 15y ago

The limit is right about what we have now.

reasonattlm 15y ago

The only hard limits for human-style organisms on an earth-type planet are thermodynamic. Using 1970s technology, the earth could support hundreds of billions. e.g.: http://www.acceleratingfuture.com/michael/blog/2006/09/overpopulation-no-problem/ http://www.acceleratingfuture.com/michael/blog/2006/09/overp... When you look at the simple figures that show that to be true, it somewhat puts the ridiculous debates over billions into context. i.e. they're not really debates over capacity and resources, they're debates over organization and (lack of) understanding the nature of progress and achievement.

icegreentea 15y ago
The linked article misses or glosses over a crucial part of sustaining the population. As the New Yorker article touches on, the real rate limiting factor in growing food is not sunlight, or even water, but really phosphorous, nitrogen, and other fertilizers nutrients. The only way to have a long term sustainable food system is to have one where the majority of these nutrients are redirected from human waste back into growing food.
- billswift 15y ago
  That is merely a matter of attitude. Right now post-processed sewerage isn't used for food production in most First World countries, but it could be. It is often used on golf courses, and there have been experiments in bagging it and selling it to landscape gardeners as a replacement for bagged cow manure. In the DC area, there was Com-Pro in the 1990s, for example, though I heard it was taken off the market for lack of sales even though it was less than half the price of bagged cow manure. If there was serious need for fertilizer, it could easily be satisfied.

mark_up 15y ago

Anyone really interested in this should watch Albert Bartlett's lecture "Arithmetic, Population, and Energy". It blew my mind when I first watched it two years ago: http://www.youtube.com/watch?v=F-QA2rkpBSY http://www.youtube.com/watch?v=F-QA2rkpBSY

tzs 15y ago

Here's a shot at an upper limit (idea ripped off from an Isaac Asimov essay I read a long time ago--late '70s most likely, but I re-did the calculations myself since I couldn't remember his numbers). Imagine all humanity packed into a very large sphere, with each human allocated a mere 1 cubic meter of space. As the population expands, we have to enlarge the sphere to make room. Starting with the current population, how long can a 1% growth rate be sustained before the frontier of the human sphere would have to expand faster than the speed of light to make room for the new humans? That's a pretty good hard upper bound on long 1% growth can be sustained. If my calculations are right, it's about 9000 years from now. (That fits with my recollection of Asimov's result).

zeteo 15y ago
I'd say the chances that the speed of light is still infinite, 9000 years from now, are rather slim. After all, Newton's system was radically corrected after 320 years, and even Aristotle's only held sway for about 2000. Einstein's has held well for the past 106 years, but an additional 9000 years of observation, experiment and theorizing will probably improve it a bit.
- prayag 15y ago
  Speed of light as a limit on speed of information or matter is a universal constant. There is a reason why it is called a universal constant, no amount of observation or experimentation would change this universal fact. Of course, the science and technology would change, we would have better understanding of the universe but I doubt we would find anything that would defy the speed of light.
- Tloewald 15y ago
  If there's some neat trick we are going to figure out in 9000 years to get around the speed of light then the galaxy / universe would have been overrun by advanced alien civilizations already. Who knows, we may have "sublimed" or been uploaded, but we won't be tooling around at warp 9 in velour uniforms.
  - 15y ago

forkandwait 15y ago

All developed nations are either right at replacement rates (USA) or well below (Japan, former Soviet nations etc). The developing nations (Thailand, Brazil, etc) are approaching replacement quickly. That leaves Africa and the poorer parts of large heterogeneous nations like India. Some of us demographers think that as we continue to develop, population growth rates will go to under replacement and then sort of bounce around replacement after that due to social reasons.

spullara 15y ago

If you take the title of this article at face value, why are we limiting ourselves to Earth? Seems like the limit of human population growth is likely at least a quadrillion based on current sky surveys and likely transportation mechanisms.

curt 15y ago

This is bogus. Hate all this overpopulation nonsense. Every developed country in the world other than the US has a negative replacement rate (births - deaths). The developing world is rapidly slowly as well. If I remember right the world only has another 50 years or so of positive growth. Not only that but the demographic skew in the developing world in male-female will likely cause it to slow even faster. The slowing growth and shrinking populations will be the huge problem of this century because our social structure in its current form can't survive a shrinking population.

TerraHertz 15y ago

The practical limits are much more esoteric than Malthus imagined. First limit: that population limit that some group of people with the power for force their beliefs on everyone else, thinks is ideal. Not like some group, of, oh, let's call them Elites, might decide the limit was radically less than the present population, and plan to use multiple means including mass contagion, war and economic collapse to force depopulation or anything. See: Georgia Guide Stones. Second limit: The number of people alive at the point when some technological singularity occurs, making 'population' a moot concept. For example: http://everist.org/texts/Fermis_Urbex_Paradox.txt http://everist.org/texts/Fermis_Urbex_Paradox.txt

wlievens 15y ago
I just read your scifi short in that folder. Nice writing, and interesting ideas in there.