There is some academic research on how much population does (or doesn't) matter. The website:
is home to one line of this research.
Other important pieces include:
Entwistle, Barbara and Paul C Stern. 2005. "Population, Land Use and Environment: Research Directions." Washington, D.C.: National Academy Press. (www.nap.edu)
Liu, Jianguo, Gretchen C Daily, Paul R Ehrlich, and Gary W Luck. 2003. "Effects of household dynamics on resource consumption and biodiversity." Nature 421:530-533.
(Jack is the Rachel Carson Professor at MSU.)
Cohen, Joel E. 1995. How Many People Can the Earth Support? New York: W.W. Norton & Company.
This is a meticulous overview of work on carrying capacity. Cohen also has a recent paper in Scientific American's special issue on environment and natural resources.
Hope this may be of some of you following this thread.
Director of the Environmental Science and Policy Program
Michigan State University