Maximum Sustainable Earth Population

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  • #1
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Main Question or Discussion Point

Climate change and environmentalism are some of my favourite areas of science and from both reading around and going to lectures I've got two figures for the maximum sustainable population of the earth, those being:

1 billion - from James Lovelock (one of his Gaia books)
1-2 billion - from the head of the Geoengineering department at Bristol

and I was wondering if anyone else knew of any other estimates, just so I can get a better idea on this subject.

I know all estimates have huge uncertainties, but an "in-the-ballpark-of" sort of figure would be appreciated,
 

Answers and Replies

  • #3
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Sustainable, as in, has no net effect upon world resources and can be maintained indefinately, using current technology. I think Lovelock's estimate was based upon average, developed country lifestyles.
 
  • #4
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I do not think the carrying capacity of the earth can be accurately predicted. One must take into account the effect of accelerating returns.

We don't even know what humans will be like 30 years hence. How much of our physiology will be enhanced? My mother sees better than I do now thanks to lens implants. What happens when we can all wear contacts that create virtual realities that mix with our physical ones? What if we cure heart diseases, cancers, HIV, and other maladies?

As our brain scanning technologies improve, we'll understand better how to improve our minds. Perhaps we'll find some way to enhance our intellectual and ethical being that enables some profound shift in our ability to socialize.

Unless we experience some catastrophic losses as a species, we'll need to find ways to support many times our current population as we continue to enjoy increasing lifespans.

I think it is most likely that our species will continue to learn to improve its understanding of the universe, and that we will use this knowledge to better ourselves and our circumstances. We do not have to stretch our imaginations very much to believe that we can inhabit the sea, the air, and even space as needed. Eventually, our social structures and infrastructures will evolve to support a nearly infinite number of people in completely sustainable ways. The entire earth will come to be regarded as a universally shared resource of our species, wherever we might reside.

Assuming of course, we don't screw things up too badly in the interim by doing something stupid like nuking ourselves.
 
  • #5
Evo
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I do not think the carrying capacity of the earth can be accurately predicted. One must take into account the effect of accelerating returns.

We don't even know what humans will be like 30 years hence. How much of our physiology will be enhanced? My mother sees better than I do now thanks to lens implants. What happens when we can all wear contacts that create virtual realities that mix with our physical ones? What if we cure heart diseases, cancers, HIV, and other maladies?

As our brain scanning technologies improve, we'll understand better how to improve our minds. Perhaps we'll find some way to enhance our intellectual and ethical being that enables some profound shift in our ability to socialize.

Unless we experience some catastrophic losses as a species, we'll need to find ways to support many times our current population as we continue to enjoy increasing lifespans.

I think it is most likely that our species will continue to learn to improve its understanding of the universe, and that we will use this knowledge to better ourselves and our circumstances. We do not have to stretch our imaginations very much to believe that we can inhabit the sea, the air, and even space as needed. Eventually, our social structures and infrastructures will evolve to support a nearly infinite number of people in completely sustainable ways. The entire earth will come to be regarded as a universally shared resource of our species, wherever we might reside.

Assuming of course, we don't screw things up too badly in the interim by doing something stupid like nuking ourselves.
Let's keep this scientific, and not science fiction.

We've already had dozens of threads identical to this, so unless there is some new peer reviewed research posted today that makes this an improvement to past discussion, this will also be closed. The science forum is not for idle speculation.
 
  • #6
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I know there have been many threads discussing the ethics of population control, but none seem to have any actual estimates, apart from 1 a couple of years ago. I started this thread just to see if anyone had any good, referenced numbers, rather than opinions.
 
  • #7
Dug
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Until you critically define "sustainability" you can't get an estimate. However, basic biomass and or life cycle analysis calculations can give us some rough estimates if we define productivity of the respective natural system.

In my work we have found that max. biomass for natural systems is relatively uniform - whether you talk about fish, birds, pigs, cows or humans - as it relates to the total available organics in the respective system. However, when you start having nutrient and energy inputs into the system - all things "natural" go by the way side. Even in natural systems you can get more of one species - if that species can occupy the niches of other species and displace them and or if that species can make use of waste nutrients before the algae and bacteria get to them - or use the algae and bacteria. We need to remember that biomass in natural systems is limited by nutrient, energy, and for us oxygen.

Unfortunately, for the case of humans our entire existence since the early 1800s has been increasing by the use of fossil fuels, petro-chemical fertilizers, fossil-chemical energy inputs and of course our displacing other species. We are so far beyond "natural" systems in terms of human population today it's - well bizarre. Bizarre when you consider that 85% of human food is produced using petro-chemical fertilizers and 95% of our food require petro-fuels to get from the field to your mouth. Bizarre when you consider that all commercial human food production uses mined phosphates that are now estimated to peak in 30 years and be essentially gone in 50 years. So, it's bizarre that we are knowingly letting our population get far, far, beyond our food production capacity without petro-chemicals which we know are available only in finite quantities which have apparently already peaked in availability.

Perhaps the simplest answer is to say that the demonstrable natural maximum sustainable human population was reached just before industrial revolution - when first coal and then oil started providing energy and nutrient inputs far above natural levels. One of the most dramatic examples of human population growth as a response to unnatural energy and nutrient inputs can be found here:
- or you can visit Bangladesh during the rainy season.

So the bottom line from a practical standpoint regarding human population sustainability is really about our ability to produce food for humans. And as food production technology stands today - it is limited by the amount of petro-chemical fertilizers available. If nothing changes dramatically technologically in food production in the next 50 years - well let's just say that we in the US we will have finally licked our obesity epidemic.
 
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  • #8
DrClapeyron
You would have to consider the lag time it takes to regenerate a resource after using it, and factor in consumption rates. It takes like millions of years for ore bodies, oil, gas, top soil and such to form. Seems like an ungodly amount of guess work. I would maximum sustainablity can't happen because all the usefull energy on Earth will be used up eventually.
 
  • #9
You would have to consider the lag time it takes to regenerate a resource after using it, and factor in consumption rates. It takes like millions of years for ore bodies, oil, gas, top soil and such to form.
Well, yes, it does take a long time for these resources to form, but it doesn't take that long to recycle them. Using mulching and composting we can create new topsoil. We don't have to wait for a car to rust away to iron ore, then re-refine it. We can just recycle the metal and use it over and over.

I would maximum sustainablity can't happen because all the usefull energy on Earth will be used up eventually.
So basically, to be sustainable, we would need an energy source beaming down to us from outer space. I'll work on it.
 
  • #10
Dug
5
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So basically, to be sustainable, we would need an energy source beaming down to us from outer space. I'll work on it.[/QUOTE]

That is the exact point. Solar does just that - beams down from space. Relatedly we get tide, wind, and wave - all off planet energy sources available to us in forms that don't diminish our on planet critical resources. We can't on one had scare hell out of people over peak oil - and then on the other promote the development of biofuels that will require the use of petroleum based fertilizers to have any significant impact on our energy needs. Our inability to produce sufficient food once we use up readily available petroleum and phosphate resources - is a far more serious problem than just running out of cheap fuel. By prioritizing the development of off-planet energy sources like solar- we can extend critical finite resources on the planet and hopefully develop technologies to manage our species population such that it doesn't self destruct and or until we can achieve successful off planet colonizations such that the species can keep growing. What most people don't realize is that our current economic system (capitalism) doesn't work in declining population models = declining market size and ultimately declining demand. Allowing politics to mis-direct technological alternative energy development toward petro-chemically fertilized biofuels is dangerous, self-destructive and a willfully ignorant mistake for all of us.
 
  • #11
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What most people don't realize is that our current economic system (capitalism) doesn't work in declining population models = declining market size and ultimately declining demand.
A most interesting point, I'd never thought of that perspetive before.

Allowing politics to mis-direct technological alternative energy development toward petro-chemically fertilized biofuels is dangerous, self-destructive and a willfully ignorant mistake for all of us.
Indeed, it is most irritating that politicians are butting much emphasis on biofuels, when that land could be put to much better use growing food.
 
  • #12
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Indeed, it is most irritating that politicians are butting much emphasis on biofuels, when that land could be put to much better use growing food.
Agreed. Arable land isn't exactly in plentiful supply. It's stupid using arable land to gather energy from the sun in the form of biofuel here in the U.S. when there's more than enough desert which can be used for that purpose to gather energy in the form of electricity.

Question: Given plentiful electricity, can fuel be synthesized from raw, non-biological materials?
 
  • #13
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Agreed. Arable land isn't exactly in plentiful supply. It's stupid using arable land to gather energy from the sun in the form of biofuel here in the U.S. when there's more than enough desert which can be used for that purpose to gather energy in the form of electricity.

Question: Given plentiful electricity, can fuel be synthesized from raw, non-biological materials?
Yes, H2 from H2O.
 
  • #14
780
3
Climate change and environmentalism are some of my favourite areas of science and from both reading around and going to lectures I've got two figures for the maximum sustainable population of the earth, those being:

1 billion - from James Lovelock (one of his Gaia books)
1-2 billion - from the head of the Geoengineering department at Bristol

and I was wondering if anyone else knew of any other estimates, just so I can get a better idea on this subject.

I know all estimates have huge uncertainties, but an "in-the-ballpark-of" sort of figure would be appreciated,
Depends on what's meant by sustainable. The thermodynamic limits are considerably higher, but the end state is perhaps unpalatable. If we assume half the biomass is in humans and the other half is in food species - probably a highly efficient algae - then we can equate the two and derive a limit. Active humans need ~8,700 KJ per day (~100 J/s bioenergy released) and we might engineer food plants to be ~1% efficient at energy storage. Earth absorbs ~122,000 TW from the Sun per second, thus a food energy potential of ~1220 TW.day/day. Assuming rapid harvest and processing, then the maximum human population sustainable is ~12.2 trillion people. A bit knife-edge because there's no reserve, but that's a design problem, not physics.

Doing away with the middleman entirely, powering humans directly via sunlight with 100% efficiency then the sustainable limit is ~1.22 quadrillion people.
 
  • #15
Evo
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Doing away with the middleman entirely, powering humans directly via sunlight with 100% efficiency then the sustainable limit is ~1.22 quadrillion people.
Post the peer reviewed scientific study that shows that food, clean water, suitable housing, waste control, schooling, jobs, medical care and transportation could be physically and economically viable to sustain that many people.

This is getting absolutely ridiculous.
 
  • #16
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Gas, coal and crude sustain world population. Gasoline is condensed, liquid sunlight with an energy density of 34 billion Joules per cubic meter. Take a google world tour and you will see crude oil and coal put to use, visible as green circles that have turned deserts green with corn. Usually, at the center of each is a well and pump. These are not fueled by punny solar cells nor windmills.

In all of history, an unprecedented bounty of energy per capita fuels population and the lifestyles to which we have come to think of as 'normal'.

current world population stands at about 7 billion, by the way. It seems James Lovelock, et al were a bit inconsiderate of our ingenuity in clawing wealth out of the ground if they gave it a thought at all.
 
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  • #17
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Post the peer reviewed scientific study that shows that food, clean water, suitable housing, waste control, schooling, jobs, medical care and transportation could be physically and economically viable to sustain that many people.

This is getting absolutely ridiculous.
You clearly missed my point - if it was just a matter of physics then the limit is huge. Clearly there's a lot of other dissipative processes involved in sustaining human life and the question was kind of vague in it's terms.
 
  • #18
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You clearly missed my point - if it was just a matter of physics then the limit is huge. Clearly there's a lot of other dissipative processes involved in sustaining human life and the question was kind of vague in it's terms.
A more critical point is that a lot of people seem to be talking about "sustainable" based on agricultural practices that seem heavily labour intensive, yet don't seem inclined to be the ones doing the hard work. Clearly they have no idea of what agricultural, pre-industrial, societies were like.
 
  • #19
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Current world population stands at about 7 billion, by the way. It seems James Lovelock, et al were a bit inconsiderate of our ingenuity in clawing wealth out of the ground if they gave it a thought at all.
There is a difference between maximum possible population and maximum sustainable population. Naturally a population can exceed the limit of its sustainiblity for a short while, however the length of time such a large population can last for is definately finite.
 
  • #20
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Can you clearly state a definition of "sustainable" including a nominal span of years somewhere less the remaining life of the sun? Also, when considering environmental values, which do you wish to be unconsidered such as sunspot activity and asteroid impact perhaps.
 
  • #21
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Levels of technology are very important to this question. If we all suddenly had to use only roman technology, the Earth's population would probably be cut in half within 2 years.

So a major problem with this calculation is that even if you could define "Sustainable", it is possible that technological advancement might increase the sustainable population faster then the actual population is growing. Advancements in solar and wind have certainly increased the hypothetical sustainable population. What if we discovered cheap fusion? Or seaweed that makes oil?
 
  • #22
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First we have to define "sustainable". One obvious limitation is the lifespan of the Sun, which has already been mentioned, so we cannot mean indefinitely sustainable, and the only really long term hope for mankind is to get off the Earth, but for now lets assume "sustainable" means for as long as the Sun lasts. See http://en.wikipedia.org/wiki/Earth#Future

Secondly, by "sustainable population" do we mean just the human population or do we wish to sustain the diversity of life on Earth? If we do, then we should be aware that even the current human population of 7 to 8 billion is already threatening the survival of many other species on Earth.

Next, to obtain a ball park figure for sustainable population we should ignore all fossil fuels as a source of energy, as they cannot be replaced at any reasonable pace, so the base survival figure should be based on solar energy. The average number of Joules of sunlight per square meter of the Earth's surface is approximately 14.2 MJ/day. For the entire Earth's surface the potentially available energy (PE) is 14.2*5.1*10^14 = 7.24*10^15 MJ/day.

If we care about diversity of life on Earth then obviously we cannot cover the entire Earth with solar panels and some areas will have to be left natural. Even if we do not care about diversity, if the Earth is entirely covered by solar energy panels there will no room for plants or algae and so there will be no CO2 recycling or oxygen production. Additionally if we use a very large fraction of the Earth's surface for solar energy production there will be artificial climate change implications. Thus there is limit to the Earth's surface that can be used for solar energy production and bearing in mind that 2/3 of the surface is ocean, a figure for the fraction of surface area that is exploitable (EA) might be somewhere in the region of say 2% of the total surface area, so that gives a figure of PE*EA = 1.44*10^14 MJ/day.

Now we need to take into consideration the conversion efficiency (CE) rate that we can convert exploitable solar energy into usable energy. Photo voltaic cells have an average conversion efficiency of solar power into electricity of around 20%. Systems that covert solar energy directly into home or water heating can be more efficient, but we have to bear in mind the energy costs of constructing solar power systems. When we take into account the energy to manufacture solar power systems and deduct this from the energy captured from the devices, the effective efficiencies are much lower. In fact some calculations show that more energy is used in manufacturing some of these devices, than is ever recovered and they only exist because of government subsidies. Taking into account manufacturing energy costs we might guess that the conversion efficiency is somewhere in the region of 5% and that might be generous. This makes the total usable energy PE*EA*CE = 7.24*10^12 MJ/day.

Now that we have a rough total potentially usable solar energy figure, we can in principle estimate the maximum sustainable population, if we know the average energy consumption per person. An average person consumes 1800 calories of food per day. This equates to 0.0075 MJ per day which is almost negligible even if takes ten times that in raw solar energy to produce the food. I say it almost negligible, because In 2008, total worldwide energy consumption was 474×10^12 MJ/year. This equates to an average energy consumption (EC) per person worldwide of about 200 MJ/day. Compare this to an average consumption of 895 MJ/day/person in the USA. This is energy used for home heating, air conditioning, cooking, refrigeration, entertainment devices, hot water, lighting, manufacturing energy costs, waste and water treatment, and vehicle fuel and they make food energy requirement pale into insignificance. There are countries that consume more than USA, but if we assume in the future that the worst users cut back their consumption a bit and that third world countries aspire to a living standard similar to that of the USA and other first world countries, then EC= 800 MJ/day per person might be a conservative estimate of usage in the future.

Now we can do a very rough estimate of a solar sustainable world population (SP) using SP = PE*EA*CE/EC = 7.24*10^12/800 = approx 9 billion people.

Of course you are free to come up with your own future projections for EA, CE and EC (and I invite you do so), but you should be aware that even with the current population we are causing climate change, fighting over resources like oil, water, land and threatening the survival of various species, so bear in mind that there is more to sustainability, than just theoretical availability of energy.

Note: I have only considered solar energy which includes indirectly wind power. Wave power might be considered as lunar power and independent of solar power. If we extracted 100% off all available wave power, would this have any consequences on the rotation rate of the Moon or the Earth? It certainly would have an effect on sea life affecting migration routes etc. Fusion power might be another option, but the means to reliably produce usable power from fusion has yet to be demonstrated and perhaps more resources should be put into fusion research.
 
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  • #23
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Dietary calories are 1,000 thermal calories. Thus 1,800 cal/day = (1800 x 4184 J)/day = 7.53 MJ/day.

On average the Sun supplies ~(1360/4)*0.7 ~240 W/sq.metre of energy per second to the Earth - 20.36 MJ/day. Autotrophs store a tiny fraction of the incident photon-stream:

(1)the total productivity is ~275-300 billion tonnes of "sugars" (storage molecules) per year - as 1 mole (mu = 0.03 kg) is energetically ~480 KJ, that equates to ~10^16 moles @ 480 KJ/mole = 4,800 exajoules of primary production per year.

(2) Total surface area is 510 x 10^12 sq.metres thus total supply of Solar energy is ~10,575 exajoules/day. There's 365.25 days per calendar year, so total captured by primary producers is ~0.124%.

(3) What happens then depends on how we assume the future of primary production utilization relates to the population future. Wandering away from physics into social engineering and quasi-Eugenics/Nazism...
 
  • #24
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I guess another question is, who would want to live on a planet that is sitting at the maximum level of sustainability. Is there any room in this situation for any other species, or would we only allow species to exist that directly contribute to the food chain, or other necessary production process?

And as others have said, that level of sustainability would change as technology finds new ways to reap more from the same piece of dirt, or whatever.

Technically, I guess it would be possible for a person to be maintained in an artificial environment that nutritionally sustains them and could stimulate the muscles artificially, provide the person stimulation through virtual reality. Ever seen The Matrix? These environments could even be stacked up in multi levels, further reducing the amount of planet surface area that each person uses.

In a situation like that you could live in an area of say 2 cubic metres, leaving the rest of the space you occupy now for other people, or for food production. But like I said, would you really like to live like that?
 
  • #25
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Maybe you misunderstand sustainability. There aren't levels of sustainability. Something is either sustainable or it isn't. How you live under sustainability is irrelevant. The example you could is possibly sustainable but so could something else that is more comfortable, natural, and less science fiction. It doesn't matter about the differences what matters is that it is sustainable. If it's sustainable it's sustainable there aren't degrees. Trying to achieve sustainability seems to me to be rather a hit or miss endeavor.
 

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