Maximum Sustainable Earth Population

Kracatoan

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,

Borek

Define "sustainable". And a lot depends on the level/way of life. See this post:

http://www.physicsforums.com/showpos...2&postcount=10

from this thread:

http://www.physicsforums.com/showthread.php?t=391197

Kracatoan

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.

socean

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.

Evo

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.

Kracatoan

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.

Dug

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:
http://www.youtube.com/watch?v=4BbkQiQyaYc - 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.

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.

TechnoPagan

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.

So basically, to be sustainable, we would need an energy source beaming down to us from outer space. I'll work on it.

Dug

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.

Kracatoan

A most interesting point, I'd never thought of that perspetive before.

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.

mugaliens

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?

PRDan4th

Yes, H2 from H2O.

qraal

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.

Evo

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.

Phrak

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.

qraal

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.