When unsustainable agriculture began about 10,000 years ago in 8,000 BC the human population of the earth was 5 million. The reason agriculture is unsustainable is because it caused our population to grow beyond a level that can be supported in the long-term. Hunting and gathering is the only sustainable lifestyle for humans on earth because it is the only type of human society with a proven record of limiting their population to a level that can be supported in the long-term.
Since agriculture began, we have degraded the earth's capacity by at least 50%. There's less than half the quantity of forest there used to be, less than half the fish in the ocean, and many species have gone extinct. Therefore, I think the current sustainable world population would be about 2.5 million. To find the sustainable population of your country, find its percentage of the world population and divide by 100 and multiply by 2,500,000.
Overpopulation is easy to reverse on a country-by-country basis using government policy that reduces immigration and reduces the birth rate using a system of taxation-and-bonuses.
Earth has 148,429,000 square kilometers of land and 6.7 billion people. At 247.105381 acres per square kilometer, there is 36,677,604,596 acres of land on earth, which is about 5 acres of land per person. This is not enough land per person for humans to survive sustainably in any lifestyle given that the average land on earth is either too cold, too wet, too dry, too hot, too rocky, too steep, too infertile, or some combination of the above.
I haven't yet looked into who issues the Nobel Prize and what criteria they use to award it, but if it has anything to do with making life better for all living things on earth, they may want to consider the above.
Brishen Hoff, November 23, 2008