We’ve predicted and broken human population limits for centuries

http://nautil.us/issue/29/scaling/will-the-earth-ever-fill-up

by DiabloD3 • 11 years ago

26 79 11 years ago

x5n12• 11 years ago

i think we need to define limits in terms of energy. there is a certain amount of energy that comes in from the sun that life then uses to decrease entropy. that energy can be used by any form of life to do work. we broke those limits by in part by displacing a lot of other life. so yes we can probably push the limits even more and displace yet much more life on the planet. at some point however that fact will effect us unpredictably.

iofj• 11 years ago

i think we need to define limits in terms of energy

Ok. Let's do that. The earth receives about 10,000 exajoule per day (3850000 per year) [1]. Daily human caloric intake is 2500 calories [2]. Let's say inefficiency and the fact that you actually need food, not pure energy, let's say that means 20% efficiency, so 12500 calories per human daily. 12500 calories is about 50k joules. Things like running a tv/computer/... would be peanuts on top of that so they "come free".

So divide one by the other. The earth, without space based power, can keep about 1e18 humans alive on this planet using just earth-based solar power.

Plus you have to keep into account what humans actually do : they convert chemical energy into heat. If we cover the planet in solar panels, why couldn't we recover most of that human-generated heat ? Let's say we can recover 99% of energy that we put into humans back out, that's another factor of 100 right there.

We could use nuclear to increase that number to 1e30 or so for a millenium and if you count fusion based power, the numbers become completely ridiculous.

To put that number in perspective, take it like this : when every human alive today breeds into a population the size of today's entire human population, then we'd be near the "pure solar" carrying capacity of just the planet itself. If we were to beam power from space to the planet, we wouldn't run into the next limit until 1e50 at least.

So we are very, very, very far away, even on an exponential population curve, from the carrying capacity of the planet. When fitting an exponential curve to some sample data (very inaccurate, but good enough for a ballpark figure), I get that if the growth since WWII (1.36% per year, starting at 2000 with 6 billion people), then we'd get to 1e18 a little after the year 3400.

we broke those limits by displacing a lot of other life

Only for a few measurements. There are a lot of problematic measurements of life that are inaccurate and therefore full of noise, and can be outright deceptive. Some of those measurements look bad : number of species, for instance. But how relevant is that number ? Sure, if it keeps dropping our zoos will become boring, but what will actually happen ? The truth is nobody knows, and there doesn't seem to be a reason, aside from nostalgia, to assume it's bad. One "real metric" that is at least measurable and I believe is meaningful : the total amount of life is total biomass, and it is pretty well known that humans have increased that by a lot.

at some point however that fact will effect us unpredictably

It seems to me to be pretty much a given that lots of things can affect the human race unpredictably, and given how many such factors there are, it seems a safe bet that a few are indeed going to affect us (though the vast majority won't). Malthusianism and global warming are such factors, malthusianism has been proven false 3-4 times at least, and many limits to growth theories both before and after have been (I like the economic "debt limit" ones, stating that we can never have an economy larger than the value of all gold, then we passed that, then money became "loaned gold", and the next theory was that there was some factor that limits how big the economy can be n * total_gold, n was to be 10, then 100, now it's at least 100 million, and they're still at it), I wonder what the fate of global warming will be.

If you believe in Darwin and evolution, this is a positive. We will adapt to whatever effect, predictable or unpredictable, starts affecting us.

[1] https://en.wikipedia.org/wiki/Solar_energy [2] http://www.webmd.com/diet/estimated-calorie-requirement

eru3• 11 years ago

Let's say we can recover 99% of energy that we put into humans back out, that's another factor of 100 right there.

Thermodynamics doesn't work that way.

schoen• 11 years ago

Nutritional "calories" are actually kilocalories (kcal), which leads to occasional confusion when trying to do calculations that relate food energetic content to other things. For example, I had a book relating someone's calculation that you should be able to diet by drinking scotch and soda because "the body must furnish 7400 calories" to raise the drink from 0°C to body temperature, which would presumably dwarf the energy input from the liquor and indeed from whatever else the drinker consumed all day. (The author agreed that this "didn't work" but didn't understand why not.)

The problem turned out to be that, while the body does indeed furnish around 7000 calories to heat up an ice-cold beverage, the drinker is consuming 2000 or more kilocalories daily, including around 100 from the drink itself.

So, you should lose a factor of 1000 for the definition of nutritional calories. But the numbers in your calculation are so staggering that this barely affects your point, which is that human population isn't close to being fundamentally physically limited by energy inputs from the Sun.

I think you're basically right conceptually, but should give more weight to the difficulty of adapting to some kinds of environmental change. There's no guarantee that human beings can invent everything we need when we need it, and some changes are difficult or impossible to reverse. So even if some limits aren't at all theoretically insurmountable, humanity could fail to surmount them because things that would need to be done can't be done in practice in the required timeframe.

mike-cardwell• 11 years ago

Other than "nostalgia", there's also the fact that life in general is more likely to survive a changing environment if there is more variation. If there is only one species, life is much, much more likely to die out, even in the short term. I personally don't think that's important, but a lot of people do seem to have strongly held positions that the continuation of life is important for some reason.

x5n12• 11 years ago

One question that I have if there is so much energy then why is life not using more of it? I guess there are a bunch of other constraints on life other than the sun's energy so my point is off.

cataflam• 11 years ago

A couple of flaws in your back of the envelope calculations, but it doesn't change the major conclusions.

Daily human caloric intake is 2500 calories... 12500 calories per human daily. 12500 calories is about 50k joules.

kilocalories not calories, so 50 MJ not 50 kJ.

20% efficiency (...) recover 99% of energy that we put into humans back out, that's another factor of 100 right there

Not sure how you can recover 99% of the energy while 20% was actually used efficiently, pretty much meaning with non-heat output. And you're not making new energy here, you're just reusing the 80% that was inefficient. If you want to do that, just consider the initial process was efficient.

If we cover the planet in solar panels, why couldn't we recover most of that human-generated heat ?

Surely you mean cover the clouds with bottom-looking "solar" panels sensitive to infrared.

Anyway, this just changes things by a factor of 100000 or so, down to about 10^14 with some inevitable inefficiency before considering other energy sources, which is 100000 billion.

Finally, the current absorption by photosynthesis, that then goes into biomass is only 3000 EJ/year. If we consider 2000kcal per individual (there are about 50% women after all...), a gross estimation of what is currently extracted by the biomass would be enough for 10^12 humans, so 1000 billion.

thaumasiotes3• 11 years ago

So we are very, very, very far away, even on an exponential population curve, from the carrying capacity of the planet.

It's worth distinguishing between the theoretical maximum carrying capacity of the planet, and the current carrying capacity, which is lower.

petercooper• 11 years ago

Less than 0.0000001% of the Sun's energy output ever reaches the limits of our atmosphere, simply due to our size and distance away from the Sun.

Long-term, energy is not the key absolute problem, but actually being able to get the technology, materials, short-term energy, and political will together to be able to harness the mind-boggling amounts of space and energy that's out there.

jkot• 11 years ago

I lived in Ireland and Greece. Many regions there had population peak centuries ago and now are in decline for several decades.

wongarsu• 11 years ago

Most developed nations currently have declining populations. For now it seems like we can simply stop population growth by bringing the rest of the world to our level of wealth. Then again there's the question whether earth has enough resources to make that even possible.

eru3• 11 years ago

Then again there's the question whether earth has enough resources to make that even possible.

In terms of energy: definitely. Nuclear or now solar suffices.

thaumasiotes3• 11 years ago

I saw someone once refer to the great potato famine as a disaster from which Ireland never recovered. From an evolutionary perspective, this is far from obvious; the famine prompted a lot of emigration to the US, with the result that the world Irish population now dwarfs the old peak Irish population, even though the population of Irish in Ireland is smaller. With large ongoing emigration flows, it's hard to say that the smaller population in Ireland reflects hard times in Ireland... it could just as easily reflect good times!

wavefunction3• 11 years ago

A quarter of my ancestry is from Ireland but I don't consider myself Irish. I find your post weird, how are you considering "world Irish population?"

The famine was a political issue anyways, the English oppressors could have released the abundant stores of wheat to feed the starving Irish but didn't want to depress the commodity price of wheat and were also content to let the Irish die. The Irish potato famine happened during an abundance of food withheld, which is the real tragedy.

shoo2• 11 years ago

Humans don’t just extract from a fixed set of resources, but can create new resources through invention.

Perhaps I am being pedantic, but that sounds like nonsense. Sure, humans invent stuff, but they don't invent the resources. They invent new ways to access previously inaccessible resources, or extract accessible resources more efficiently. But they don't magic more resources into being.

Confusion2• 11 years ago

Nothing is intrinsically a 'resource'. Something becomes a resource when it can be used to further some human activity. Iron wasn't a resource until iron forging was invented. Without humans, no resources exist.

jacquesm6• 11 years ago

But the iron was already there before we declared it something useful. Ants use 'resources', so do bacteria so without humans resources definitely do exist and are being used actively, whether we declare something to be a resource to us or not does not change the fact that it was a resource before our wandering eye fell on it.

Asteroids are a nice example. They're 'untapped resources', objects we one day may use as resources but which for now just sit there because we haven't found a way to make tapping that resource cost efficient.

personjerry• 11 years ago

Is there any practical difference?

We can't create matter, if that's what you're saying. But we can learn to transform or interpret previously useless things as very useful resources. For example, flint was just another valueless stone before we realized we could make fire with it, or uranium might've just been another stone before we discovered nuclear sciences. In that sense, we can indeed "create" new resources.

Mz• 11 years ago

Well, we don't create matter. But, for example, new farming techniques do increase actual food supplies. Food is an essential resource. How much of it exists is not arbitrary and can be significantly influenced by human behavior, but we have to have additional resources, such as ideas and tools, to leverage the existing resources, such as soil and stuff that might enhance it, into something more.

hellofunk2• 11 years ago

I suspect that at 7 billion now, if the world population rose to even 100 billion, we'd find a way to survive. It would be a very different life experience, but it would still be life.

jacquesm6• 11 years ago

I highly doubt we'd be able to feed and house 100 billion people.

pflanze2• 11 years ago

Able yes, but at very high risk of deadly instability through destroying most of nature and accordingly higher dependence on technology, and smoothly working social structures?

3pt14159• 11 years ago

Really? Food and housing is fairly easy to solve. Canvas or wood housing and green houses and we could do it with today's technology. Even education is getting way more environmentally friendly with advances in online education resources.

The problem isn't feeding and housing people, it's flying them to Greece for a weekend vacation, buying an endless supply of electronic and motorized consumer products, and a race-to-the-bottom attitude with power generation in the developing world.

hellofunk2• 11 years ago

I don't think it is impossible. And humans have a way of doing things that really seem impossible at first. I'm sure a hundred years ago no one would have thought it possible to walk on the moon. We now have workable methods to turn the dirtiest of water into pure drinking water. Agriculture is a long, long way from being as efficient as it could be; we find ways all the time to quadruple the food output of a plot of land, and there will continue to be innovation in this area. Our diets are largely wasteful around the world as well, it is possible to live on much less food than the typical American eats, for example. And as for space, the world average population density per land is actually not that high; certain places are, but when spread out, there is tremendous room for physically placing more people. So I'd say it is well within possibility to make 100 billion people stay alive. But, a lot would change to do so.

weddpros• 11 years ago

Population growth is exclusively cultural. See how it's declining in Europe, still growing fast in Africa, etc.

Science could change that very fast: birth control isn't available to everyone on earth... yet. But religion could change that fast too.

So I guess estimates for the earth population will depend on both science and religion more than anything.

shoo2• 11 years ago

also helpful in reducing birth rates: education and the available economic opportunities for young women

danbruc10• 11 years ago

Why is this issue getting so much attention? It is a problem that will solve itself, wherever the limit is. The only reason to worry about where the limit is, is if you want to avoid it with birth control so that some nicer forces than famines or resource wars keep the population stable. But even that seems unnecessary, at least in the developed world, because the population growth rates or even the populations are already declining. Which of course is a good thing, why would you prefer a more densely populated world over the status quo? Why would you want to raise child after child if two and a half are enough to sustain the population?

facepalm2• 11 years ago

It will solve itself, but billions of people might die as part of the solution. Mankind will survive, but for the individual some worrying might make sense.

danbruc10• 11 years ago

The people that can prevent overpopulation don't suffer from it, the people that suffer from it can't prevent it. So it's more of worrying for once children's children.

anbu32• 11 years ago

"because the population growth rates or even the populations are already declining."

The population of both the us and w.europe is growing. (Immigration)

danbruc10• 11 years ago

But migration and the normal population growth are qualitatively different - normal population growth is an exponential phenomenon given a constant growth rate, migration is a linear phenomenon given a constant migration rate. And at least in developed countries I see now real issues controlling both forms of growth, limiting the number of immigrants as well as establishing a two children policy if required.

jzwinck2• 11 years ago

Why would you want to raise child after child if two and a half are enough to sustain the population?

Simple: because you believe your (religion, parenting skills, values, heritable traits) are the best. Having a dozen kids per family is a leading way to innundate society with whatever you think is awesome.

facepalm2• 11 years ago

There are also cultures that vanished after thousands of years, and crisises in which millions of people died. Human ingenuity and technological progress didn't solve every problem. We just forgot about the dead (classic survivor bias). Collapse by Jared Diamond has some examples of societies that failed - by comparison, our current civilization is very young and hasn't really "played out" yet.

Maybe the estimates of Malthus were wrong, but the underlying concern is still correct. Our current food production is not sustainable because it relies on non-renewable energy sources. I don't claim no solution can be found for that, but there is also no reason to believe there will be a solution.

Another way to look at it makes it very plain: the surface area of earth certainly is limited. So if population would grow forever, we would reach a point where every person would only have one square foot of ground to live on.

Even that might be doable - we could live in a stacked way (skyscrapers), or Matrix-Style in coffins with virtual environment. Nevertheless it doesn't seem like a very desirable future.

thaumasiotes3• 11 years ago

Population limits are certainly a well-documented phenomenon. Chinese history shows excellent conformance to a "punctuated equilibrium" model -- the population is stable nearly all the time, with two obvious sudden increases. (From memory, I believe the increases correspond to (1) the local development of a new, more productive strain of rice, and (2) the introduction of crops from the new world.)

The inference is painfully obvious: for most of history, China has been populated at its own carrying capacity. The fact that the limit was broken (really, raised) a few times doesn't mean the limit isn't a worthy concept.

wavefunction3• 11 years ago

My question is why do we need more people or want to encourage or allow it to occur?

My immodest proposal is to introduce a natural decline in human populations to more easily sustainable levels via the introduction of a reproductive "right": every individual when born is entitled to one child.

A couple, then, could have a family with two children. Those who aren't interested in having children could sell their "right" off on a market to people who want to have more than their one child individually, so a couple could buy the rights to more children and a larger family from those who don't want to have children. The market could even fractionalize/derivatize those rights so that individuals could sell "half" a childbirth right and two of those individuals could have a family with one child.

The best part is, at two children per two parents, it's lower than the replacement rate of "2.1" which means population levels would humanely decrease with no need for wars or murder.

Our current societies are predicated on larger youth populations than parent populations to support us in our old ages, but this strategy combined with robotic technology for the elderly and post-scarcity economics would free us from that pyramid scheme. This helps support a basic-income type scenario for those people who assume that everyone (or 'THOSE PEOPLE') living in our society will just have tons of kids due to boredom. Like the fears trotted out about "welfare queens" having tons of kids because they supposedly get "free stuff."

biztos• 11 years ago

So the rich have large families, and the poor have forced sterilization?

wavefunction3• 11 years ago

It's voluntary. Perhaps you missed the part about the basic-income and right to a child.

qrendel7• 11 years ago

Why is lower or stable population of such an imperative that such a totalitarian invasion of natural rights needs be imposed? There are plenty of advantages to larger populations - more people to take part in the creative processes of production, for one.

The disadvantage is the dubious assumption of inevitable resource scarcity. If resource scarcity has yet to become a major problem, and may not in the foreseeable future, why impose population limits?

thomaslkjeldsen2• 11 years ago

Citing "WORLD POPULATION PROSPECTS: THE 2015 REVISION" page 10:

"Globally, total fertility is expected to fall from 2.5 children per woman in 2010-2015 to 2.25 in 2045-2050 and to 2.0 in 2095-2100 according to the medium-variant projection. However, in Europe and Northern America, total fertility is projected to increase between 2010-2015 and 2045-5050 from 1.6 to 1.8 children per woman in Europe and from 1.86 to 1.9 children per woman in Northern America. In Africa, Asia, Latin America and the Caribbean, and Oceania, fertility is expected to fall between 2010-2015 and 2045-2050, with the largest reductions projected to occur in Africa. Thus, in all major areas of the world, fertility levels are projected to converge to a level at or just below the replacement level by 2095-2100"

http://esa.un.org/unpd/wpp/Publications/Files/Key_Findings_W...

thomaslkjeldsen2• 11 years ago

According to Swedish professor Hans Rosling the fast population growth is coming to an end and the population size is expected to stabilize at 11 billion people by the end of this century. His statistics and predictions are based on data from the UN Population Division.

http://www.gapminder.org/videos/dont-panic-the-facts-about-p...

http://www.gapminder.org/news/world-peak-number-of-children-...

qrendel7• 11 years ago

Yikes. I didn't realize the population density in Mumbai was near 53k people per sq. mile. Apparently Manila is nearly twice that at 111k.[1]

Still, it surprises me overpopulation fears are so commonly expressed. Seems like a greatly overblown meme that will end up doing more harm than good. Much like Malthus opposing projects to feed the poor and hungry, I sometimes hear people going as far as saying we (meaning relatively wealthy, white Americans) should just "let them die" when it comes to impoverished people all over the world. Despite the fact that, if energy consumption and environmental damage is the fear, people in industrialized countries use as many resources as dozens, hundreds, maybe thousands of lives in the "developing" world.

The world could likely support orders of magnitude more people than we give it credit for. We haven't even started harnessing materials from space industry, space-based solar power, or using the oceans and seabed as living space. There's another 70% of the Earth's surface that hasn't even been touched yet, and that percentage grows even more when you consider the vertical spaces available within it. The overpopulation meme seems more dangerous to global welfare than actual overpopulation has ever been thus far.

Kevin Kelly's edge.org response is a good read on the entire overpopulation issue: http://edge.org/response-detail/23722

[1] https://en.wikipedia.org/wiki/List_of_cities_by_population_d...

jzwinck2• 11 years ago

The world probably could support lots more people than it has now. The question is, why? If we believe 30 billion people is possible, should it be a goal? What's better about 30 billion than 6?

hk__2• 11 years ago

You don’t have the choice.

qrendel7• 11 years ago

1) Reproduction is a natural right, and some people would consider having children to be a great fulfillment. The evolutionary basis of this desire would make it all the more powerful, and restricting it would only cause the drive to grow stronger over time (as traits evolved to promote the circumvention of the restrictions).

2) If there's no specific advantage to a lower or stable population, why is any particular number preferable to another?

3) There are lots of advantages of large population: larger communities for people with low-frequency deviations from social norms, a broader spectrum of human social and psychological possibilities represented, increased production and creative capacity, greater base of working-age citizens to support the non-working portion (retired, children), more people at the top of the bell curve to draw from for important positions (better leaders, more geniuses, etc)... This is not an exhaustive list.

4) Likely other advantages as well, which would seem to counter the disadvantages of larger population, judging from past human history (and assuming no weird non-linear relationships). If the world is better with fewer people, would you want to go back and live in a world with only 100,000? 1,000,000? Some other specific number?

legulere• 11 years ago

I'm not so surprised about overpopulation fears. We have a non-sustainable use of non-renewable resources. The problem is that especially in the wealthy countries this is hardly visible. We add 1 hectare of forest and at the same time somewhere else in the world 10 hectares are destroyed.

Basically the argument that Malthus was wrong and thus we shouldn't worry about overpopulation is the same as ignoring upcoming problems and saying that we will solve them when they will come up.

We as humans can solve problems but sometimes we're destroying much in the process, we're not fast enough or it's even just not possible. There have been numerous catastrophes and downfalls in human history and the amount of nature we destructed is extreme.

Maybe we can have orders of magnitude (10 billion, 100 billion) people living on this planet, but the question is whether it would still be livable, especially without nature.

daniel-cussen2• 11 years ago

Same thinking as "housing never goes down." How did that one go?

daniel-cussen2• 11 years ago

Edit: also, remember Easter Island, where the population dropped by over 99% after an ecological disaster last millennium.

We’ve predicted and broken human population limits for centuries

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