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).
It's a nice math problem, but it misses one key element: Relativity. If most of the universe's human population is expanding away from earth at a speed approaching c, the population growth rate in the earth's frame of reference would slow down -- people might still be breeding at the same rate in their own reference frames, but from the perspective of the earth all the fast-moving people would be living their lives very slowly.
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.
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.
So by dividing current farmland by population and rounding the result up a bit, each person gets a plot 47x47m for 603 sq ft for living and the rest for farmland. Assuming half the land is rank (unusable) wilderness, that roughs out to an optimistic carrying capacity of 33000M people.
But that’s not taking into account high-efficiency farming or compact housing.
So methinks the alarm has been prematurely sounded. We’re still a ways from 33 billion occupants, and between technology and nature methinks that issue will be...adjusted.
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.
I've always wondered why more people don't discuss a future based around the idea of practically unlimited nuclear energy + practically unlimited clean water from desalinization + practically unlimited hydrogen from electrolysis.
It seems that that would solve a vast number of problems, no?
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/Newslt...)
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.
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.
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.
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.
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
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.
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.:
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.
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.
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.
[+] [-] tzs|14 years ago|reply
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).
[+] [-] cperciva|14 years ago|reply
[+] [-] zeteo|14 years ago|reply
[+] [-] bryanlarsen|14 years ago|reply
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.
[+] [-] ctdonath|14 years ago|reply
149M sq km total land
15M sq km farmland
7000M people
So by dividing current farmland by population and rounding the result up a bit, each person gets a plot 47x47m for 603 sq ft for living and the rest for farmland. Assuming half the land is rank (unusable) wilderness, that roughs out to an optimistic carrying capacity of 33000M people.
But that’s not taking into account high-efficiency farming or compact housing.
So methinks the alarm has been prematurely sounded. We’re still a ways from 33 billion occupants, and between technology and nature methinks that issue will be...adjusted.
[+] [-] tsuyoshi|14 years ago|reply
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.
[+] [-] bdunbar|14 years ago|reply
I cannot think of a story with that plot. But I am not the world's biggest fan: what story is that?
Why couldn't they have done that on earth?
Because 'people stay home and grow food' is not a very exciting story.
[+] [-] sneak|14 years ago|reply
It seems that that would solve a vast number of problems, no?
[+] [-] doyoulikeworms|14 years ago|reply
By what measure? Over the long run, prices have surely fallen for just about everything.
[+] [-] zeteo|14 years ago|reply
[+] [-] forkandwait|14 years ago|reply
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.
[+] [-] graeme|14 years ago|reply
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|14 years ago|reply
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.
[+] [-] lupatus|14 years ago|reply
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-petrotyran...
[+] [-] TerraHertz|14 years ago|reply
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
[+] [-] wlievens|14 years ago|reply
[+] [-] curt|14 years ago|reply
[+] [-] VladRussian|14 years ago|reply
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 :)
[+] [-] reasonattlm|14 years ago|reply
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|14 years ago|reply
[+] [-] spullara|14 years ago|reply
[+] [-] mark_up|14 years ago|reply
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[+] [-] whackberry|14 years ago|reply