For thousands of years, the human race existed in a fairly stable relationship with the earth. There are renowned examples of populations expanding beyond the resources available in the niche they were inhabiting (Sale, 2006a), and of warfare between small-scale human populations over local resources. However, the situation facing the human race now is of a different order of magnitude, because the size of the human population, its rate of increase and its level of consumption mean that we have run up against the limits of all resources available on the earth. This, at least in the view of many environmentalists, is the cause of many of the prevailing social and economic crises. Why human population began to increase so rapidly is a question that has preoccupied economists with a concern for the environment. The response to this population expansion, and the increasingly sophisticated lifestyle and consumption pattern that have accompanied it, has been a constant and accelerating rate of growth in economic activity. As shown in Figure 9.1, following a long period of a more-or-less steady level of population, in the past 200 years both population and economic activity have mushroomed, and this growth increased markedly following the discovery and exploitation of fossil fuels.