As Paul Valery said, "In the physical world, one cannot increase the size or quantity of anything without changing its quality." Let's face it, even in the unlikely event that both the Northern and Southern hemispheres adopt an ecocentric manufacturing system of zero waste, the Earth's limited supply of water, air, food, and greenery will only be able to sustain a few billion humans by 2100.
The bad news is that the world already feeds 5.8 billion. And what's more, of the projected 3.4 billion addition to world population before 2025, 98% will occur in Africa, Asia, and Latin America. In Jaques-Yves Cousteau's ominous words, "Every 10 years, there is a new China born in the poorest regions of the Earth."
Disappearing stocks of fertile land, fresh water, fossil fuel energy, plants and animal life will control human population the old-fashioned way - through starvation, warfare, and disease - if we cannot reduce our numbers voluntarily. Read Tim Gillman's collection of forecasts as well as Al's Population Archive