> "Human populations, as with any other animal, grow exponentially"
The "populations grow exponentially" argument was state of the art in 1798 [-1], but modern science has taught us that populations grow roughly logistically [0], not exponentially. It's easy to mistake for an exponential in the lower part of the curve (which is all the data we had in 1798), but once you know what to look for, you can see the difference clearly [1].
Of particular note, "exponential growth" means you'll see the same percentage growth rate every year, and larger and larger absolute growth. But what we actually see in humanity is that the percentage growth rate maxed out in the mid 1960s (about 2.2%; it's presently below 1.1%) and the absolute growth rate was at its peak in the late 1980s (88 million in 1989, down to about 75 million now) [2].
Every credible estimate of peak human population puts the number in the 9-12 billion range [3]. That's a lot of people, and will perhaps require some cutbacks, but it's nowhere near the dire levels you predict.
It's not even very interesting if the growth is logistically or exponentially. The point is: there is significant growth. And it doesn't stop until you reach the limit of what the environment can carry. You say that number is projected to be 9-12 billion.
And then we run out of oil. What happens as the mortality skyrockets and humanity downsizes to the new carrying capacity?
> "It's not even very interesting if the growth is logistically or exponentially."
It very much matters which it is. It's the difference between stabilizing at 20% more population than we currently have and dealing with a little more overcrowding, and getting so crowded that we don't have toilets any more.
Running out of oil is going to change American lifestyles significantly. I'm not convinced it's going to change global carrying capacity by very much, though. Do you have a credible model that says otherwise? I would like to see such a thing (in its fullest form.)
I'm more concerned with rising mean global temperatures rendering areas surrounding the equator uninhabitable, when the average temperature gets up near 40c. You won't be able to grow crops anymore, and it will drive people away. If you move the human habitable zone away from the equator, you have less and less land, and even less flatland for ariable farming. So besides the slash and burn land quality loss, you are potentially losing degrees of latitude of ariable space.
Logistic is effectively the same model as "exponential until pressure from a ceiling is applied". Look at formula for its derivative, it is the exponential multiplied by a factor that goes to zero as the ceiling is approached.
The models are effectively identical, until they're not. In particular, they're not identical for the purposes of this discussion.
"Until pressure from a ceiling is applied" is the difference between stabilizing at 9 billion people (a bit more crowded than right now), and growing to so many billions or trillions that the grandparent poster's "no more toilets" prediction would be realistic.
The "populations grow exponentially" argument was state of the art in 1798 [-1], but modern science has taught us that populations grow roughly logistically [0], not exponentially. It's easy to mistake for an exponential in the lower part of the curve (which is all the data we had in 1798), but once you know what to look for, you can see the difference clearly [1].
Of particular note, "exponential growth" means you'll see the same percentage growth rate every year, and larger and larger absolute growth. But what we actually see in humanity is that the percentage growth rate maxed out in the mid 1960s (about 2.2%; it's presently below 1.1%) and the absolute growth rate was at its peak in the late 1980s (88 million in 1989, down to about 75 million now) [2].
Every credible estimate of peak human population puts the number in the 9-12 billion range [3]. That's a lot of people, and will perhaps require some cutbacks, but it's nowhere near the dire levels you predict.
[-1] http://en.wikipedia.org/wiki/An_Essay_on_the_Principle_of_Po... is the origin of the idea
[0] http://en.wikipedia.org/wiki/Logistic_function#In_ecology:_m...
[1] http://www.growth-dynamics.com/articles/Kurzweil_files/image...
[2] http://en.wikipedia.org/wiki/Population_growth#Human_populat...
[3] http://en.wikipedia.org/wiki/Projections_of_population_growt...