What is the Limit to Human Population Growth? | Hacker News Reader

What is the Limit to Human Population Growth?

newyorker.com

45 pointssampsonjs47 comments

Here's a shot at an upper limit (idea ripped off from an Isaac Asimov essay I read a long time ago--late '70s most likely, but I re-did the calculations myself since I couldn't remember his numbers).

Imagine all humanity packed into a very large sphere, with each human allocated a mere 1 cubic meter of space. As the population expands, we have to enlarge the sphere to make room.

Starting with the current population, how long can a 1% growth rate be sustained before the frontier of the human sphere would have to expand faster than the speed of light to make room for the new humans?

That's a pretty good hard upper bound on long 1% growth can be sustained. If my calculations are right, it's about 9000 years from now. (That fits with my recollection of Asimov's result).

I'd say the chances that the speed of light is still infinite, 9000 years from now, are rather slim. After all, Newton's system was radically corrected after 320 years, and even Aristotle's only held sway for about 2000. Einstein's has held well for the past 106 years, but an additional 9000 years of observation, experiment and theorizing will probably improve it a bit.

Speed of light as a limit on speed of information or matter is a universal constant. There is a reason why it is called a universal constant, no amount of observation or experimentation would change this universal fact. Of course, the science and technology would change, we would have better understanding of the universe but I doubt we would find anything that would defy the speed of light.

If there's some neat trick we are going to figure out in 9000 years to get around the speed of light then the galaxy / universe would have been overrun by advanced alien civilizations already. Who knows, we may have "sublimed" or been uploaded, but we won't be tooling around at warp 9 in velour uniforms.

That same argument goes for sub-lightspeed galactic colonization. The time between the disappearance of the dinosaurs and today (65 mil years) is more than enough to colonize the entire galaxy with simple rocket ships.

Good point – some kind of near light speed travel is as magic as FTL for most intents and purposes. So, no star trek.

It's a nice math problem, but it misses one key element: Relativity. If most of the universe's human population is expanding away from earth at a speed approaching c, the population growth rate in the earth's frame of reference would slow down -- people might still be breeding at the same rate in their own reference frames, but from the perspective of the earth all the fast-moving people would be living their lives very slowly.

Fast-moving people will also be Lorentz contracted, so there will be plenty of room... if there's enough energy.

One of the most annoying things things in science fiction is this plot line: the earth is running out of food, so several hundred thousand people get on a big ark ship to the nearest star. They then feed themselves in a few cubic kilometres simply using nuclear energy to power giant greenhouses.

Why couldn't they have done that on earth? Using nuclear power plants to desalinate water and power vertical greenhouses, back of the envelope calculations show the maximum population of the earth at somewhere around 1 TRILLION people.

Sure, that would make food more expensive, but given how dramatically the cost of food has dropped over time, we could deal with it.

For example, the price of a bushel of wheat has been within an order of magnitude of 1 UK pound for the last 1000 years. The price of everything else has increased over time, but wheat hasn't.

I've always wondered why more people don't discuss a future based around the idea of practically unlimited nuclear energy + practically unlimited clean water from desalinization + practically unlimited hydrogen from electrolysis.

It seems that that would solve a vast number of problems, no?

As far as I understand, unless we develop reliable fast breeders, there is hardly enough fuel for that many nuclear plants. I thought the Japanese were on a good way to build an energy economy based on breeders. Now, these efforts might be on halt.

AFAIK, that's entirely a political issue at this point. We have the technology, we just are just skittish to process the fuel thru the bomb-suitable phase, and haven't correlated catastrophic failure with building the facility on a tsunami-and-earthquake-prone site. Psychology, not technology.

Ah, time to crunch the numbers again...

149M sq km total land

15M sq km farmland

7000M people

So by dividing current farmland by population and rounding the result up a bit, each person gets a plot 47x47m for 603 sq ft for living and the rest for farmland. Assuming half the land is rank (unusable) wilderness, that roughs out to an optimistic carrying capacity of 33000M people.

But that’s not taking into account high-efficiency farming or compact housing.

So methinks the alarm has been prematurely sounded. We’re still a ways from 33 billion occupants, and between technology and nature methinks that issue will be...adjusted.

Plus, regularly-efficient farming can be greatly expanded.

For example, a lot of former cropland in the United States' southern region (think former Confederate states) was purposefully reforested after WWII because agricultural overproduction was one of the causes of the Great Depression. Basically, the United States produced more food than it could sell domestically, sell internationally, and give away.

As another example, the organized high-latitude herding of reindeer is practically non-existent in North America, and I suspect in a similar position in Eurasia. Reindeer literally thrive on moss, breed like bunnies, and taste like filet mignon.

Reversing just these two examples with today's normal farming know-how will produce substantially more food.

although I like people who use facts, please enlighten me, how do they cook their food? And why is there such a huge desertification in countries with an exploding population? And if hunger is so bad for a population, how did Sudan manage to multiply it's population by 20 within the last 100 years?

Sorry if my 6-sentence post failed to provide encyclopedic coverage of the issue. (Snarky start aside...)

I'm a bit confused by the prevalence of the "so how do they cook it?" question in such discussions when I point out that one can live sustainably, if not well, on very little. It's as though many have never gone camping and cooked over a fire. Gas/electric stoves and metal cookware are recent developments which humans got by without for a long time - and many still do. For starters, shish-kabobs come to mind for cooking veggies on a stick.

In a cramped/austerity situation, little actually needs cooking, given that much can be either eaten raw, or just dried and eaten straight or reconstituted as needed. What needs cooking can be over a fire using the dried inedible remainder of the plants. Stir-fry Solar ovens are not hard to build. High-tech solutions, at the other extreme, could provide very efficient heat sources. (We need not abandon high- and future-tech for high-population-density scenarios; to the contrary, there would be great motivation to advance technology to match demands for efficiency.)

Desertification correlating with population growth? Will have to look into it more. Causation is not obvious (which influences which how & more?). Seems people _are_ figuring out how to feed a population with little resources, translating to sustainability with small per-capita footprint.

BTW: Gladwell's "Outliers" spends a lot of time researching how ancient/remote/low-tech/cramped/austerity populations managed to feed themselves with few farming resources. For one, Japanese rice farming was a tour-de-force of squeezing as many calories out of a very limited space per capita. Worth a read.

you didn't get the hint, right? you divide by zero because you neglect all other circumstances and of course, human nature ..

Desertification often results from destroying native trees and grasses so you can find plenty of older instances. EX: The US Dust Bowl in the 1930's all the way back to Egypt the Late Lower Paleolithic due to pigs.

Right, so energy can be substituted for arable land.

But I wonder if the real limit to human population is mineral-based, rather than energy-based. Every person needs a certain portion of different minerals: calcium, iron, potassium, magnesium, phosphorus, zinc, selenium, etc. Maybe we would run out of one of those minerals before we would run out of energy?

This could be a topic for science fiction. We run out of zinc, and then have to send an unmanned spaceship over to some other galaxy to mine some zinc... but there would have to be some other complication, because unmanned spaceflight is boring.

Pot growers manage to substitute energy for arable land.

I once calculated that at a constant doubling rate of every 15 years, the human race would need to use all of the resources of the asteroid belt in about 12,000 years.

There's a lot of stuff out there.

We're not going to run out of minerals. Choose a mineral, any mineral, even a trace mineral. Look on Wikipedia to see what percentage of the earth's crust it makes up. (for example, iron is 5%). Do the math and realize that we've got thousands to millions of years worth of minerals left.

Sure, we can run out of "easy" deposits. We did that for Copper decades ago. Copper mines today are essentially giant processing plants that extract the tiny amount of copper in pretty much ordinary dirt -- "copper ore" these days only has about 10 times as much copper per kg as the stuff in your backyard.

>The price of everything else has increased over time, but wheat hasn't.

By what measure? Over the long run, prices have surely fallen for just about everything.

the earth is running out of food, so several hundred thousand people get on a big ark ship to the nearest star.

I cannot think of a story with that plot. But I am not the world's biggest fan: what story is that?

Why couldn't they have done that on earth?

Because 'people stay home and grow food' is not a very exciting story.

One example is The Hitchhiker's Guide to the Galaxy, but there are many more examples of "generation ships" on tvtropes.org:

http://tvtropes.org/pmwiki/pmwiki.php/Main/GenerationShips

My favorite generation ship story is Heinlein's 'Orphans of the Sky'.

I was asking the poster about the specific plot point he mentioned: running out of food.

Even assuming a limit exists, without hard numbers this discussion is a waste of time. There is a huge practical difference between a limit of 8 billion and one of 20 billion; especially as these same UN population models, which the author mentions, predict that world population may stabilize, or even start declining, by 2050 (http://www.un.org/esa/population/publications/popnews/Newslt...)

All developed nations are either right at replacement rates (USA) or well below (Japan, former Soviet nations etc). The developing nations (Thailand, Brazil, etc) are approaching replacement quickly. That leaves Africa and the poorer parts of large heterogeneous nations like India.

Some of us demographers think that as we continue to develop, population growth rates will go to under replacement and then sort of bounce around replacement after that due to social reasons.

Population will almost certainly run into hard limits before mid-century. The author points out resource limits in passing, but it's worse than he admits.

We run our civilization off of stored solar energy. That's what oil, natural gas and coal are. In a century we've used millions of years worth of stored solar energy. That's the energy that's powered the green revolution (along with non-renewable aquifers).

Nuclear and our small sources of renewable are the only exceptions. The rest of our power comes from stored energy. And nuclear/renewables are generally built using stored fossil energy.

Effectively, we're burning through capital, beyond a sustainable rate. If anyone has thought of a way out, please let me know.

Meanwhile, if you've been looking for something meaningful to build that will be in demand, this is it.

Have you taken a look at the estimates of how many years worth of coal, oil & natural gas we have left? In the 70's they said we had 20-30 years of oil left. They were right: we've basically run out of $10-20 oil, although Saudi Arabia still has some of that. But $100 oil? We've got enough of that to last this century, at least. Heck, the Canadian oil sands alone could probably power the world for most of this century.

And we'll run out of oil before we run out of shale gas or coal -- we've probably got multiple centuries of that, at peak prices.

You're right, there's more left. But as it gets harder to extract, prices will rise. We're already reduced to blowing up mountaintops in Virginia to get coal, or melting the soil of Alberta to get tar. The energy return on investment (EROI) of those sources is much lower than the old Saudi oil.

Optimistically, those sources might help ease a transition. We'd still have energy to power things, and the higher prices would encourage switching.

But there are still dangers. We only have a limited amount of carbon we can still afford to put in the atmosphere. And it will be difficult to run all of our current activities and invest in new energy sources and do so as the price of energy rises.

The question remains: if we switch, what are we switching to?We're currently using energy that was stored for us over millions of years. It's highly concentrated. Renewables must make do with incoming solar energy.

Maybe people will warm to nuclear, but that has its own issues.

EROI for blowing up mountaintops in Virginia is significantly better than 1970's saudi Oil. It's also better than directly minding the stuff. Which is why the cost of coal is so 1/10th the price of Oil per unit energy.

PS: People talk about Oil like it's the single most important energy source out there, but it's only important because it used to be so cheap.

The EROI for blowing up mountaintops ignores the externalized costs of the activity: water pollution, habitat destruction (and the loss of associated ecosystem services), damage from explosive concussions, and ultimately a locality that sacrifices its long-term health for a handful of temporary jobs.

And this argument even yields to the HN party line that states that the value of undeveloped natural spaces is zero.

It's a bit cynical to call that "the HN party line". There's surely a bunch of hardcore libertarians out here who would hold that opinion (by which I won't implicate that any libertarian would) but I doubt it's a majority.

When it comes to energy, I am vary pro wind power and feel solar/fusion are both going to be viable in my lifetime. However, EROI is a measure of the amount of energy it costs to develop an energy source which is both a simple measurement and poorly understood by a lot of people.

So, while I dislike coal for a number of reasons, I do feel the need to bring it up when people get all doom and gloom over Oil.

You can make oil out of natural gas, coal, wood, hemp oil, cane sugar. Anything that has carbohydrates can, with an energy investment, be turned into a different carbohydrate.

Gas and coal would be first because they're closer to petroleum and massively abundant, but there's no chemical reason why other substitutes can't be used in the very long term.

Exactly. The price of oil reflects not so much its rarity as the difficulty in extraction. As the difficulty increases, companies like Solyndra will have a much easier time selling substitute products, and will stop going bankrupt despite heavy governmental assistance.

As The Futurist discusses in depth[1], annual world oil consumption has been hovering around 32 billion barrels since about 1982. That means oil consumption, at $100/barrel, is $3.2 trillion, or 5% of nominal world GDP.

My take away from that is technology has made the oil supply a non-issue. And, it will continue not being a problem for the foreseeable future. It is not a hard resource limit.

[1] http://www.singularity2050.com/2011/07/the-end-of-petrotyran...

The practical limits are much more esoteric than Malthus imagined.

First limit: that population limit that some group of people with the power for force their beliefs on everyone else, thinks is ideal. Not like some group, of, oh, let's call them Elites, might decide the limit was radically less than the present population, and plan to use multiple means including mass contagion, war and economic collapse to force depopulation or anything. See: Georgia Guide Stones.

Second limit: The number of people alive at the point when some technological singularity occurs, making 'population' a moot concept. For example: http://everist.org/texts/Fermis_Urbex_Paradox.txt

I just read your scifi short in that folder. Nice writing, and interesting ideas in there.

This is bogus. Hate all this overpopulation nonsense. Every developed country in the world other than the US has a negative replacement rate (births - deaths). The developing world is rapidly slowly as well. If I remember right the world only has another 50 years or so of positive growth. Not only that but the demographic skew in the developing world in male-female will likely cause it to slow even faster. The slowing growth and shrinking populations will be the huge problem of this century because our social structure in its current form can't survive a shrinking population.

if to look at civilization development through energy harnessed/controlled, our civilization has been through the following stages:

1. at human body energy level by gathering/hunting (ie. what nature provided)

2. at human body energy level, managed/renewable. I.e. agriculture.

3. at industrial energy level by gathering - fossil fuels, nuclear fission.

we're at the end of the stage 3. with stage 4. "managed/renewable industrial level" (solar/wind and nuclear fusion) appearing on the horizon.

Increasing available energy levels allows for increased population growth. There is no limit in sight. The Moon and Mars are waiting :)

The only hard limits for human-style organisms on an earth-type planet are thermodynamic. Using 1970s technology, the earth could support hundreds of billions. e.g.:

http://www.acceleratingfuture.com/michael/blog/2006/09/overp...

When you look at the simple figures that show that to be true, it somewhat puts the ridiculous debates over billions into context. i.e. they're not really debates over capacity and resources, they're debates over organization and (lack of) understanding the nature of progress and achievement.

The linked article misses or glosses over a crucial part of sustaining the population. As the New Yorker article touches on, the real rate limiting factor in growing food is not sunlight, or even water, but really phosphorous, nitrogen, and other fertilizers nutrients. The only way to have a long term sustainable food system is to have one where the majority of these nutrients are redirected from human waste back into growing food.

That is merely a matter of attitude. Right now post-processed sewerage isn't used for food production in most First World countries, but it could be. It is often used on golf courses, and there have been experiments in bagging it and selling it to landscape gardeners as a replacement for bagged cow manure. In the DC area, there was Com-Pro in the 1990s, for example, though I heard it was taken off the market for lack of sales even though it was less than half the price of bagged cow manure. If there was serious need for fertilizer, it could easily be satisfied.

If you take the title of this article at face value, why are we limiting ourselves to Earth? Seems like the limit of human population growth is likely at least a quadrillion based on current sky surveys and likely transportation mechanisms.

The limit is right about what we have now.

Reply on news.ycombinator.com