[Martin Taylor 2006.08.22.14.49]
[From Bill Powers (2006.08.07.1447 MDT)]
Richard Kennaway (2006.08.07.1720 BST) --
The world changes. Did it become overpopulated when hunting and gathering weren't enough any more, and agriculture had to be invented? Or when cities were founded? How many people is too many? Who decides, and how do we get there?
That's a question I've been trying to answer. What sort of measure could we use to define "overpopulation"? ...
The degrees of freedom criterion is the best way I've seen yet.
Yes, I agree with this approach, but I think that there are probably separable "chunks" of degrees of freedom -- quite apart from the obvious chunking tat goes with levels of perception. One of those "chunks" has to do with degrees of freedom entailed in the land area required to produce the energy we use.
When I think about overpopulation (which has been quite often over the last 60 years since my elementary school geography teacher first discussed it), I now take as a basis an article "Population density and body size in mammals (John Damuth, Science, 290, 699-700, 23 April 1981). This article has a plot of the population densities in favourable habitats for 307 species of mammals. They cluser within an order of magnitude around a pretty good straight line on a log-log plot. If you take a human as being 70 kg, and you take the entire land surface of the earth including Antarctica, Greenland and the Sahara as being good human habitat, the carrying capacity of the Earth is about 70 million people.
Not all the earth is equally suitable for habitation at maximum density. Even allowing for an order of magnitude slop in the estimation, it's hard to push the sustainable population much over a couple of hundred million, if humans are like other mammals. So, how is it that we have two orders of magnitude more people than the simple fit to the plot allows?
The answer has to be that other mammals get their energy from eating other animals and plants, whereas we contribute energy from artificial sources. That energy goes into fertilizers, house heating and cooling, and much else that allows us to reduce our individual ecological footprints.
How does this relate to degrees of freedom? If we did not have coordinated (common reference, common output) energy supplies, we would be conflicting with the perceptual control of our co-habitants of the earth much more than we already do -- and even so we are extinguishing species at a higher rate than has been seen since the catastrophic extinction of most dinosaurs. That's conflict due to loss of habitat degrees of freedom. Availability of energy from concentrated sources reduces that kind of conflict, but only to a certain degree. How many people constitutes "overpopulation" depends on how well we can continue to find energy sources and how well we can reduce the spatial area we each need to control our perceptions effectively.
My guess is that a word population of 70 million people would allow most to live about as well as the richest do now, with little conflict either among humans or between humans and the rest of our co-habitant species. Larger populations than that probably can be sustained to a degree that depends on the land area requirements for sustainable energy supplies roughly equivalent to a couple of orders of magnitude greater than our food requirements, or around 10 kW per person (if I calculated correctly).
Other conflicts pale in comparison with this one, when we consider what is meant by "overpopulation".
Martin