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Earth's Carrying Capacity



 
 
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  #11  
Old August 16th 04, 02:23 PM
Ian Stirling
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In sci.space.policy Ian Stirling wrote:
In sci.space.policy Gactimus wrote:
How many people can the earth support?

snip
This naive calculation indicates that you need around 150 tonnes of crust
to build a human, or around 300 tonnes for an american
Assuming that the crust goes down 10Km, and has a density of 4, that's
around 270 people per square meter of crust, that's about 4*10^17 people,
or the equivalent of the population of the UK, for every person alive now,
neglecting the earths core.

If you want a conventional biosphere feeding them, rather than direct
energy-food converters of some sort, you'r probably going to need
a fair bit more nitrogen, which might limit you to 4*10^15 people or so.


Making possibly incorrect assumptions, you can probably scrape up
4 or 5 earths worth of rocky matter in the solar system.
Assuming that these have some shortfalls, equivalent to needing 1500 tonnes
per person of mass, and using the whole of their mass takes the "people only"
figure to around 10^20.

Assuming it's not possible to get at gas-giant cores, but is possible to
mine their atmospheres for the needed N/C/H, it seems reasonable that
the first bottleneck is phosphourus.
This would take the "people only" totals up to around 10^22, or 10^23.

You can maybe get another order of magnitude or two, by synthesising
Cl and P, but for much more you have to dismantle the gas giants to get
at their cores.
Maybe another couple of orders of magnitude.
So, 10^26 people might be a reasonable guess at an upper limit, or 10^24
eating a largish fraction of naturally grown food.

10^26 people is about one human for each one of every current humans
intestinal bacteria.

To get any more, you need to start on either mining the sun, energy-matter
conversion, or redefining what you mean by a human.

  #12  
Old August 16th 04, 02:25 PM
Al Jackson
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Gactimus wrote in message ...
How many people can the earth support?


Assume exponential growth.
If you assume all humans stay on earth and imagine that there is a
'super science' of progress
solving all social, political, economic and logistics problems. Then
in an article in:

"Population, Evolution, and Birth Control, A Collage of Controversial
Ideas, Ed. Garret Hardin; W.H. Freeman, 1964, ISBN 0716706709, (381p).
"

(I don't have my copy at hand.)

I believe the upper limit is roughly 20 people per square meter! Or
about 2E15 people! The reason for this limit is that the earth would
consist of a single metal sphere and which would start
to melt due to the inability of the sphere to radiate all combined
body heat (by black body radiation) of that many people. This happens
around the year 9000 or so?
I can't remember who wrote this article.

Issac Asimov has an essay somewhere about population exponential
growth , but he lets humans expand into space , limit there seems to
about the year 13,000 (I think?) when human expansion by space ship
fleet would be a sphere expanding at the speed of light.
  #13  
Old August 16th 04, 02:28 PM
John Savard
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On Mon, 16 Aug 2004 05:46:15 -0400, "Ian St. John" wrote, in
part:

The original flax seed ( and oil ) for example, is
equally rich in Omega 3 compared to fish oil.


That reminds me.

Flax is what linen is made from.

I remember an article, by an agriculture student, in a local student newspaper
which was a rebuttal to the propaganda of how allowing hemp to be grown would
solve the world's problems, because it was a wonder plant.

He noted that flax can do anything hemp can do - except make you high - and do it
better.

John Savard
http://home.ecn.ab.ca/~jsavard/index.html
  #15  
Old August 16th 04, 02:34 PM
Steve Craig
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Gactimus wrote in message ...
How many people can the earth support?


I've heard the figure 10 million thrown around before, but I can, in
no way, remember where I heard that, or the justification thereof.
That would make this post quite pointless now that I think about
it....

hmmm...

Steve
  #16  
Old August 16th 04, 03:51 PM
Rand Simberg
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Robert Carnegie wrote:

Six billion so far and we have yet to even start farming the oceans, 70%
of the surface of the planet.



My impression is we've halfway farmed them to death.


We don't farm them, we still hunt them.
  #17  
Old August 16th 04, 03:58 PM
Thomas Palm
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Ian Stirling wrote in
:

In sci.space.policy Gactimus wrote:
How many people can the earth support?


Multiply the population density of Biosphere II, which could probably
work at that population density, with the area of the earth, and you
get 200 billion.


Biosphere II was never self-sufficient but relied heavily on energy import,
and against the rules had to replace the atmosphere when CO2 levels got too
high.
  #18  
Old August 16th 04, 04:10 PM
Rand Simberg
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Thomas Palm wrote:

Multiply the population density of Biosphere II, which could probably
work at that population density, with the area of the earth, and you
get 200 billion.



Biosphere II was never self-sufficient but relied heavily on energy import,
and against the rules had to replace the atmosphere when CO2 levels got too
high.


There's nothing wrong with energy import. The earth wouldn't survive
for long without energy import.
  #19  
Old August 16th 04, 04:12 PM
Ian St. John
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John Savard wrote:
On Mon, 16 Aug 2004 05:46:15 -0400, "Ian St. John"
wrote, in part:

The original flax seed ( and oil ) for example, is
equally rich in Omega 3 compared to fish oil.


That reminds me.

Flax is what linen is made from.


Yes. Fine linen table cloths for example. Highly prized and expensive. They
first soak the stalks under water to rot the surrounding pulp...


I remember an article, by an agriculture student, in a local student
newspaper which was a rebuttal to the propaganda of how allowing hemp
to be grown would solve the world's problems, because it was a wonder
plant.


To a degree, it is, somewhat. Mainly it is cheap and available and with some
binders can be made into nearly indestructable and lightweight panels and
moulded forms for developing world projects.


He noted that flax can do anything hemp can do - except make you high
- and do it better.


For ten times the price and without the wide range of distribution of the
hemp plant which grows much faster and makes larger harvest of a rough fiber
that is suitable for many projects that are just not economical to do with
fine linen. And the hemp they are talking about does not have significant
levels of THC. It also cannot get you high unless you smoke a tons or so all
at once which would be a bit of a stretch.


John Savard
http://home.ecn.ab.ca/~jsavard/index.html



  #20  
Old August 16th 04, 04:21 PM
Ian St. John
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Rand Simberg wrote:
Robert Carnegie wrote:

Six billion so far and we have yet to even start farming the
oceans, 70% of the surface of the planet.



My impression is we've halfway farmed them to death.


We don't farm them, we still hunt them.


We do farm them also. This is really the only way to get salmon these days
as the stocks dwindle due to destruction of their streams and their
genetics.
http://www.worldwatch.org/pubs/mag/2003/165/mos/
"Estimated amount of farmed fish produced in 2002 = 52,700,000 metric
tons.
http://www.st.nmfs.gov/st1/fus/current/hilite2002.pdf
"WORLD FISHERIES (Live weight, 2001)
Total catch 287.0 billion pounds (130.2 million metric tons)"

so we farm about (52/(52+130)) * 100 = 28.57 percent of the total fish
production.


 




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