
What is the Limit to Human Population Growth? - sampsonjs
http://www.newyorker.com/talk/comment/2011/10/24/111024taco_talk_kolbert
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tzs
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).

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zeteo
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.

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Tloewald
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.

~~~
wlievens
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.

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

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bryanlarsen
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.

~~~
ctdonath
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.

~~~
coldarchon
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?

~~~
ctdonath
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.

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

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zeteo
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...](http://www.un.org/esa/population/publications/popnews/Newsltr_87.pdf))

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forkandwait
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.

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graeme
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.

~~~
bryanlarsen
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.

~~~
graeme
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.

~~~
Retric
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.

~~~
schiffern
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.

~~~
Retric
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.

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TerraHertz
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>

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

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curt
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.

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VladRussian
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 :)

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reasonattlm
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...](http://www.acceleratingfuture.com/michael/blog/2006/09/overpopulation-
no-problem/)

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.

~~~
icegreentea
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.

~~~
billswift
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.

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spullara
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.

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whackberry
The limit is right about what we have now.

