Plausible limits of population [now playing: outer space]

[Torco]

It has been said that earth supports a maximum number of people not too distant from the current human population, a few billion. I claim the planet can hold much more than 10 billion people.This eco-friendly treehugger fantasy that "the earth can't hold more than *10^9 people" or whatever small number is kinda fun. I here explore the carrying capacity of earth for humans.

Per square kilometer, earth has 50 people. a square kilometer is a pretty large space, its one kilometer by one kilometer. Cities can hold easily some 20 thousand people per square kilometer, perhaps even 100,000/km^2 if constructive techniques allow for arcologies and other fantasies, but if we stick to near-future tech, let's take a nice city that doesn't look impossibly crowded and stick with that [after all, cities would need parks and factories and the like]; L'hospitalet, which is pretty and livable and airy and you wouldn't say "omg this is an urban dystopia" or anything. 18k/km^2

Earth has 134,940,000 km2 of land; this means that if earth was one big city it would have something like 2,428,920 million people, which i don't know how americans would dub but is 2e12. [a trillion in short scale?] So let's have that as an upper number of people on earth is all of earth's land space was filled with medium-density city [areas would be much denser, of course, but there would also have to be roads, sewage plants, huge distribution hubs, and other parts of the übercity that wouldn't be inhabitable readily. We could set the scale much higher for something like trantor, where there are kilometers upon kilometer of stacked city and that would probably hold much more people. Let's call this scenario M1.

Let M2 be much more conservative; let all of earth's surface that isn't antarctica be as populated as india. Let india have 400 people per square kilometer [about right]. this gives us 5,3e10, called 53 billion in shortscale. India, however, is largely non-urbanized, so the world would basically look like it does today, just without large uninhabited areas.

Take it the other way, the way of food. How much food can earth produce ? [farmland and city aren't exclusive at all, rooftops are perfectly viables places to grow food in,but let's separate variables]. The answer is a lot. Assume that at maximum density the earth won't produce food [it can, but never mind]. You still got the sea! There are some 310,000,000 square kilometers of perfectly good sea just laying there! letting fish grow and then catching and eating them is a supremely inefficient way to eat from that sea.... on earth we're farmers, but on the sea we're basically hunter-gatherers! [and we know hunter-gatherers need much more surface per person to eat]. Assuming a 1% sun-to-food efficiency, hell, assuming a 0,01% efficiency a meter makes about 10 kcal a day of food [not an impossible ratio]. this is 3e15 kcal/day, enough to feed a trillion people, M1. and that's just the sea!! sure, everyone'd eat seaweed, but seaweed can be made as nutritious and tasty as we want to make it ! There are, also, HUGE reserves of energy in geothermal and other kinds of energy, and photosynthesis can be made more efficient, and we could tell clouds to go fuck themselves and stop killing our food [for which there'd be plenty incentive, at that point]. Sure, there are problems with the estimate. Lower it according to your own assumptions of technology, but M2 is pretty conservative, we *can* get there with current tech without even realizing we're getting there, albeit at a huge environmental cost. M1 is more fantastic, but amply possible. M1 would mean the obsolescence of nature, however: We'd effectively be a Kardashev-1 civilization we'd have made the entire planet, or a huge bit of it, a garden/farm system. Ecology would be exactly the same thing as agriculture; controlling living things to make food and other useful materials for you. This is hard, sure, no one's saying its gonna happen tomorrow: but consider this: a society that has domesticated an entire planet to the level of providing food for a trillion people *has a trillion pair of working hands to do so*. Malthus couldn't have been more wrong, resources don't grow linearly: resources come from work, and work comes from people. The only malthusian catastrophe would be beyond M1, say M0, where the sun plus geothermal energy plus nuclear just don't provide the needed energy to feed a population of, say, ten quadrillion people.

So yeah, how many people can the earth hold realisticall? what's the planetary carrying capacity? I don't know, but I guess from 40 billion to one trillion.

[KathTheDragon]

Very interesting research, Torque. However, they assume that humanity doesn't care about the environment. What would the numbers look like if we try to preserve our current ecosystem? Or how about if the entire population moved to the sea, and we used the land to farm?

[Ars Lande]

A very intriguing thought experiment. But I'll still cling to my tree and say it won't work.

With the M1 hypothesis, you'll probably wreck something somewhere down the road. Even assuming a clear energy source, you'd still have a lot of waste heat to get rid of, and possible changes to the albedo of Earth. All moving towards a rapidly heating planet.
Plus, you have to handle the refuse produced by one trillion humans. You've also disturbed the climate to a massive extent, and caused soil erosion on a massive scale. And that's ignoring the psychological factors. How long before the primate territorial instincts are triggered?

The M2 is a lot more viable, though I wonder about the long-term consequences. The environmental cost is enormous and I don't think there's a way to keep the damage under control - the Earth biosphere is just too big, with too many factors at play.

The trouble with Earth's biosphere and climate are that they're completely unpredictable. Who knows about the consequences of global warming? Judging from the available models, it could end up with no consequences at all, with minor - or even beneficial - consequences, or a global catastrophe.

[Herr Dunkel]

Interesting, and I third it, Torco.
This is one of the basis of my sci-fi world - the species don't really care about the enviroment and have developed efficent ways of exploiting it.
Both of your scenarios assume a lack of regard for the enviroment.
I'd say the range from fourty to eighty billion is just about allright.

[Ars Lande]

Interesting, and I third it, Torco.
This is one of the basis of my sci-fi world - the species don't really care about the enviroment and have developed efficent ways of exploiting it.
Both of your scenarios assume a lack of regard for the enviroment.
I'd say the range from fourty to eighty billion is just about allright.

A neat idea for a conworld, who doesn't like a good dystopia?
Still, you guys are revealing a tree-hugger side of me I didn't know existed.
Just for the sake of contradiction: how do you propose to destroy the environment while not destroying the population it supports? (Well, unless your people are content to live on spirulina and fish, that is!)

[Herr Dunkel]

Interesting, and I third it, Torco.
This is one of the basis of my sci-fi world - the species don't really care about the enviroment and have developed efficent ways of exploiting it.
Both of your scenarios assume a lack of regard for the enviroment.
I'd say the range from fourty to eighty billion is just about allright.

A neat idea for a conworld, who doesn't like a good dystopia?
Still, you guys are revealing a tree-hugger side of me I didn't know existed.
Just for the sake of contradiction: how do you propose to destroy the environment while not destroying the population it supports? (Well, unless your people are content to live on spirulina and fish, that is!)

Farm buildings are the solution in my conworld - hydroponics does wonders.
My conworld's in transition from M2 to M1 in a good majority of civilised areas (huge cities, farms still exist but are being supplanted by "food factories" so to speak), so dystopia, ho!
It's not a sustainable position, not really, but it serves them good as they continuously strip away at the planet's crust for more rocks and build higher and higher buildings to house more people.

[KathTheDragon]

Well, once a society's got into a mindset of 'take what you want, give nothing back', the only practical way to snap them out of it is for them to destroy their eco-sphere and cause a massive failure of civilisation. Assuming they survive, of course.

[Herr Dunkel]

Sometimes, they just plain don't learn.

[Salmoneus]

A very intriguing thought experiment. But I'll still cling to my tree and say it won't work.

With the M1 hypothesis, you'll probably wreck something somewhere down the road. Even assuming a clear energy source, you'd still have a lot of waste heat to get rid of, and possible changes to the albedo of Earth. All moving towards a rapidly heating planet.

Who cares? I mean, in Torco's scenarios, humanity has vast technological abilities. At which point, why would they care what the average global temperature was? That's only a problem if you want traditional food-from-the-soil farming going on. Otherwise, not a problem. Assuming that we're not into cytherean territory here - and I'd think that a humanity that sophisticated could easily avoid that problem. The waste heat itself shouldn't matter - nothing we'll produce will be on the order of existing sunlight anyway.

Plus, you have to handle the refuse produced by one trillion humans. You've also disturbed the climate to a massive extent, and caused soil erosion on a massive scale. And that's ignoring the psychological factors. How long before the primate territorial instincts are triggered?

Soil erosion doesn't matter if you're not farming. Nor does the climate (not once you have proper hurricane-proofing). And human refuse is just fertiliser, so that shouldn't be a problem - in fact, it'll be a bonus.
The psychological elements are an issue, but then primates are good at living in crowded conditions, and humans have shown themselves able to adapt to far higher densities. Torco's assuming a paltry 18kpsqkm. London in 1680 is estimated to have had around 45kpsqkm (like modern Manila, for that matter), two and a half times more dense. And people smelled a lot more back then and were a lot more violent.

The M2 is a lot more viable, though I wonder about the long-term consequences. The environmental cost is enormous and I don't think there's a way to keep the damage under control - the Earth biosphere is just too big, with too many factors at play.

For the most part, the biosphere is also self-correcting. And again, why does the biosphere matter on a high-population world?


However, Torco is also wrong. Or at least doesn't fully portray the situation. Theoretically you can fit as many people onto earth as you can physically fit - the only question is how much energy you're willing to spend to do it.
Let's assume nuclear fission is our energy source. We've got uranium, at present rates, to last up to 70 years, or 8500, or 47000, depending on the estimate. The larger numbers probably involve more risk and more cost (they involve breeder reactors). Scale that up to nuclear supplying most of our needs, and then scale up the population to two trillion, and fission gives us power for somewhere between a couple of days and about ten years. And that assumes current energy use - obviously, if it's a giant city-world, energy use per capita is likely to be far higher.

So energy would have to basically all be solar power, I think. The sun gives us maybe more than twice as much energy as uranium will ever give us, EVERY YEAR. Although only half reaches the surface. And let's, for sake of argument, not pave over the ocean, only all the city-land, giving us only a third of that. Doing some VERY rough arithmetic, it looks like we currently use about 6x10^20 joules a year, and the sun gives us about 6x10^23 joules a year, so solar power can give us a thousand times more power than we currently use. Actually I get it around 1200 times more than we currently use. That's a lot. But current photovoltaics are less than 50% efficient, and we're covering the entire land area of earth with them. So let's say 50% efficient cells everywhere, including antarctica, for a conservative estimate.

Scale the population up to two trillion then, and we're left with... every person on earth can use about twice as much energy as they do now! Yay! But wait: lots of the world doesn't use much energy at all, due to the horrible poverty we have. So let's scale everyone up to the level of europe. That'll double the energy consumption.

So, in very rough maths, in a world city in which the entire land area of the planet is covered in today's best, most expensive photovoltaics, a population of two trillion people would be able to have similar energy use to modern europe. But would a city-world be able to keep itself to such a low energy use? Well, for one thing, if all the food comes from the seas, then the parts of the world city in kazakstan will be a very long way away from food! A huge amount of our food comes from near by us, but in this world it would all have to be transported (and if people aren't living on boats it'll also cost more to collect the food, because an area of sea able to support current agricultural yields would be huge). And at the moment most of our heating and cooling is done by the atmosphere - but you'd have a huge part of the human species living in cities in what's now the sahara desert, and an even huger part in what's now siberia. So much energy required! Even if we just up the estimate from 'modern europe' to 'modern usa' that imperils the scenario - we'd have to make our photovoltaics 100% efficient. And if we thought this continent-spanning city-world might use as much energy on average as, say, warm louisiana or cold alaska or north dakota, we'd be looking at needing between 300% and 400% efficiency...

In my view, then: a population of trillions, with conceivable technology, is not feasible. Billions, we have. Tens of billions, I can't imagine any reason why not in the long run. I think once you start entering the hundreds of billions, however, you start getting into serious trouble.



It's also worth bearing in mind that the real problem isn't the maximum capacity, but our ability to expand rapidly. Sure, we could build cities all across the sahara... but it would cause us a lot of unappealing difficulties if we tried to do that.


Realistically? I think with current energy and food resources, we're probably looking at a population between 10 and 20 billion, or slightly more than we'll hit. If something dramatically reduces energy prices, we could have several times that.

[brandrinn]

All Earth carrying capacity equations forget that the Earth must be inhabited by people, and people never explore the practical limits of what they can do. We have the internet. That means we could all be doing online masters programs with every spare minute of our days. We should all be quintuple doctorates by now. Instead we look at pictures of cats and bondage porn (hopefully not at the same time). Having the means to live at Manhattan densities while farming spirulina on our rooftops doesn't mean we ever would. This must be taken into account when calculating carrying capacity.

[Salmoneus]

All Earth carrying capacity equations forget that the Earth must be inhabited by people, and people never explore the practical limits of what they can do. We have the internet. That means we could all be doing online masters programs with every spare minute of our days. We should all be quintuple doctorates by now. Instead we look at pictures of cats and bondage porn (hopefully not at the same time). Having the means to live at Manhattan densities while farming spirulina on our rooftops doesn't mean we ever would. This must be taken into account when calculating carrying capacity.

Yes and no. I think it's worthwile to have a sense of what is possible and what isn't, in order to deduce what might be probable and what might not.

[Ars Lande]

Who cares? I mean, in Torco's scenarios, humanity has vast technological abilities. At which point, why would they care what the average global temperature was?

Plus, you have to handle the refuse produced by one trillion humans. You've also disturbed the climate to a massive extent, and caused soil erosion on a massive scale. And that's ignoring the psychological factors. How long before the primate territorial instincts are triggered?
Soil erosion doesn't matter if you're not farming. Nor does the climate (not once you have proper hurricane-proofing). And human refuse is just fertiliser, so that shouldn't be a problem - in fact, it'll be a bonus.

All good points, but as you pointed out below, how do you get from here to there? Soil erosion, pollution and waste heat are not a problem when you already have huge enclosed cities and massive radiators to get rid of the heat, but how do you build these when, in the meantime, you're dealing with the consequences of the damage you've already done?

The psychological elements are an issue, but then primates are good at living in crowded conditions, and humans have shown themselves able to adapt to far higher densities. Torco's assuming a paltry 18kpsqkm. London in 1680 is estimated to have had around 45kpsqkm (like modern Manila, for that matter), two and a half times more dense. And people smelled a lot more back then and were a lot more violent.

I'll grant you this, but people could get away from the city and still can, or at least hope to. In Torco's scenario, there's no escape.

Your point about energy consumption is very interesting.
Assuming solar panels are placed on Earth, it seems that half the land area of the Earth would be covered with solar panels, with a very conservative estimate of energy use per capita. This does not work out, because I used the average energy use per capita of the United States, and with all the krill factories and air conditioning, you'll need a lot more than that.

If your panels are in orbit, you get a more manageable size, about that of Russia. But... one square meter of current, space based solar arrays weighs one kilogram. That's really inefficient, let's assume 10 grams instead. That means 1.5*10^8 tons, which Wolfram Alpha diligently informs me is on the same order of magnitude as the total weight of 6 billion humans. You won't put this into orbit.

[KathTheDragon]

What if you filled the seas with wind turbines? How much extra energy would that bring in?

[Herr Dunkel]

What if you filled the seas with wind turbines? How much extra energy would that bring in?

It'd be a net loss, since you don't have wind underwater.

[Ars Lande]

The highest class of wind turbines get about 1000 W/sq meter, almost 10 times as much as an ideal solar panel. So, theoretically, you'd get a lot more.

I have no idea how these gigantic fields of turbines would interact with wind patterns, so I can't see how to calculate this. I'll try a very wild guess:
Some research has been done though, I read a figure of 1700 TW of total, global wind power. That's from Wikipedia, but it'll do.
Assuming 10kW per person (the low estimate I mentioned early) and 50% efficiency that's enough to support an extra 170 billion.

So your approach could work, in theory. I have no idea about the specifics, but I suspect it'd be a very hairy engineering problem to get this kind of efficiency.

[Torco]

Hell, we all woke up feeling hippy and treehuggy, didn't we ? Come on, a totally domesticated planet wouldn't look like trantor, it would more look like a huge garden full of peppers and onions and pomegranate trees everywhere! who wouldn't want to live there! no more thisles, and edible chocolate-flavoured grass everywhere. I, for one, welcome nature's death.
not really, i don't know, i was just meditating on realistic limits, irrespective of moral concerns... because population growth's not gonna be a volitive thing: no one's gonna want earth's population to grow to half a trillion or whatever, but it may, and what are you gonna do, forced sterilizations? concentration camps? deport people to mars? one child policies? [come to think of it, might work!]

Very interesting research, Torque. However, they assume that humanity doesn't care about the environment. What would the numbers look like if we try to preserve our current ecosystem? Or how about if the entire population moved to the sea, and we used the land to farm?

M2 would, for the most part, keep our current environment's broadest features.. if we wanted to have no print on the ecosystem, however <as in generate no change>, I think we'd either have to keep population stable and reduce our standard of living dramatically, or reduce our population dramatically and still reduce our standard of living not dramatically. I think the idea that we will not wholly transform the planet eventually is misguided, though: what we *do* is to take the natural world and reshape it in a form more useful to us: unless someone stops us, yeah, we'll get to kardashev 1 most likely. kardashev-1 is ecology's wet dream and ecologism's worse nightmare.

With the M1 hypothesis, you'll probably wreck something somewhere down the road. Even assuming a clear energy source, you'd still have a lot of waste heat to get rid of, and possible changes to the albedo of Earth. All moving towards a rapidly heating planet.
Plus, you have to handle the refuse produced by one trillion humans. You've also disturbed the climate to a massive extent, and caused soil erosion on a massive scale. And that's ignoring the psychological factors. How long before the primate territorial instincts are triggered?

zero... there'll always be war, and we will surely make mistakes and fuck up and generate huge disasters in the process, but if people gonna keep breeding that's gonna be the only way to go [unless we stop breeding and we all become europpeans with an average fertility of 1 xD]

Sure its unpredictable now, but it could be predicted further down the line; plus, doesn't matter how unpredictable, disasters won't kill us unless they're HUGE disasters.

This is one of the basis of my sci-fi world - the species don't really care about the enviroment and have developed efficent ways of exploiting it.

This is one of the basis for *this* world

Sal's right about solar, except there's also geothermal; cooling down the earth's gonna yield a lot of energy... and warming up the surface as surplus heat would probably be pretty synergetic in the long run, freeing antartica for permanent human settlement. His more conservative estimate isn't delusional by any stretch of the imagination, but it does have assumptions that i think are wrong:

a) constant energy expenditure. Indeed there's something to be said for technology's ability to increase efficiency through infrastructure and machines: if you had a vacuum-sealed maglev that went from vladivostok, a massive center of seaweed distribution, to afghanistan, you'd need really little energy to move all that food, because maglevs without atmosphere need only break inertia. There are even more efficient means, i bet. making our photovoltaics 80% efficient is pretty possible, i don't know of a reason why the tech itself wouldn't allow it. Take good enough insulation, underground cities, and energy consumption in cold places wouldn't be a problem. hot places will need ventilation, though, sure. Basically we can and will live better with less energy percapita
b) solar isn't the only power source available: there's probably fusion <which isn't far away>, there's geothermal, which we already know how to do. I'm not talking fifth millenium tech here. Still, I agree, I thought of a trillion as something like an absolute upper limit barring magic [ huge energy stations on mercury that transmit energy to earth someway, which might as well be].

I think this question's better adressed by what would stop growth. If we all were to suddenly triplicate, for example, what would we do, would we kill each other? well, okay, we might in africa and the middle east, but in the rest of the civilize world we'd start growing food in cities, developping the food industry towards cheap and not towards tasty [say goodbye to meat, for instance]

All Earth carrying capacity equations forget that the Earth must be inhabited by people, and people never explore the practical limits of what they can do. We have the internet. That means we could all be doing online masters programs with every spare minute of our days. We should all be quintuple doctorates by now. Instead we look at pictures of cats and bondage porn (hopefully not at the same time). Having the means to live at Manhattan densities while farming spirulina on our rooftops doesn't mean we ever would. This must be taken into account when calculating carrying capacity.

yes, but again people won't choose for there to be 100 billion folks in the world, there'll just *be* 100 billion people in the world and they'll have to deal with it *somehow*. So the question isn't how much energy you're willing to invest in it, but how much energy you *can*.

I'll grant you this, but people could get away from the city and still can, or at least hope to. In Torco's scenario, there's no escape.

THE INTERNET, OF COURSE!
also, a very realistic MMO that's nothing but farmland forever and ever and ever, where people can live out their jeffersonian homesteading fantasies to their heart's content. They'll probably have to do some sort of work within that virtual reality thing to pay for the subscription to the service, probably consumer surveys xD.

Yes, but turbines get wind from places without turbines; if we cover the earth with turbines there'd be no wind for the turbines to garner.

[KathTheDragon]

What if you filled the seas with wind turbines? How much extra energy would that bring in?

It'd be a net loss, since you don't have wind underwater.

Muppet. You put wind turbines on top of the water. On giant stilts.

[Hallow XIII]

What if you filled the seas with wind turbines? How much extra energy would that bring in?

It'd be a net loss, since you don't have wind underwater.

Muppet. You put wind turbines on top of the water. On giant stilts.

There's a reason we don't do that already. Namely, the ludicrously long stilts would either be macerated by the ocean currents or have to be really, really thick. You'd have to postulate the existence of some kind of sciency implausible plasma-stilt or something.

[KathTheDragon]

We've already assumed ridiculous things. What's one more? Besides, engineering with carbon nano-tubes will have come a long way. Build your stilts out of that, and they should the incredibly stong.

[Radius Solis]

Also, wind and ocean currents are not infinite energy supplies. The energy a windmill turbine takes from the wind reduces its speed equivalently (more so, because it's far from perfectly efficient). So there's only so many windmills you can put up before they all become useless because they stop the air from moving around enough to turn them - and you will reach that point long, long before you have enough windmills to supply energy to the kind of population figures we're talking about here.

[KathTheDragon]

Hm... Well, if we've already got as much solar as we can, and wind and water energy isn't enough... Geothermal does seem like the only available source. How much can that bring in?

[brandrinn]

OK, I'll bite. How much light do we actually need? If humans spend 8 hours in total darkness, and the other 16 hours using indoor light, then the vast majority of sunlight that falls on the Earth is superfluous. We could just cover the entire surface of the planet in solar panels, and use some of the resulting electricity to light our homes, including a handful of "sunlight" rooms where you can go and pretend to be on a beach. The plants will die, but as long as our machines can make amino acids more efficiently than plants, that's irrelevant. The entire net insolation can be used for electricity, 174 petawatts according to Wikipedia. At 20% efficiency (typical for top quality solar panels), you could provide American levels of energy consumption to 25 trillion people (that's 25*10^12).

[Torco]

Except in order to maintain life on a planet entirely covered with solar panels you'd need a bit more than current american energy consumption. I mean just to make food for a person you need 3kw/h per day <at perfect efficiency> or 300kw/h <at 1% efficiency, like plants>. Also,moving around the water and the food and blablabla. I think that grants lowering the estimate from 2e13 to somewhere between 2e11~2e12

In pure terms, the earth has 1e32 joules of heat, and most of it is renewable as it comes from radioactive decay.a *lot* of energy can come from geothermal, if the tech be available.

[KathTheDragon]

So in theory, the Earth alone could sustain us, if we learned how to tap into it? That's good news for us, and it allows us to preserve the eco-system!

[Torco]

So in theory, the Earth alone could sustain us, if we learned how to tap into it? That's good news for us, and it allows us to preserve the eco-system!

It probably wouldn't, though: in fact, it would probably precipitate its destruction: if your livelihood were to come entirely from the depths of the earth, what incentive have you to keep the surface world nice and harmonious? you'd just delve more deeply and more greedily into the earth, and throw your waste, including your waste heat, up into the surface. Global warming and greenhouse effect in a world covered in resistant strands of insect and thistles.