Intractable limits to a sustainable human population.

The pressing need for a much smaller world population arises for two reasons. Humans are emitting about two and a half times as much carbon as the maximum permissible to achieve stabilisation of carbon in the atmosphere. Today's six billion humans, in striving to enjoy at least a basic quality of life, are damaging many vital ecological systems and causing a major extinction of other forms of life. Within the next half century, a new and compelling reason for a smaller human population is likely to arise through the fact that we cannot be at all sure that a suitable replacement to fossil fuel energy is going to be found. Analysis of all these aspects indicates the need for a world population of about 2000 million (2 billion).

Population and the demise of cheap energy.

Standard of living is determined in part by the availability of ecological resources, and in part by the availability of "cheap energy." The demise of cheap energy is likely to occur during the twenty-first century. Gradually, over this time, humans will be restricted to using renewable natural capital. Reliance on renewable energy sources will require a reduction in population to within the range of 1.5 to 3 billion people in order to maintain what most of us would regard as an adequate lifestyle. Attention is drawn to the need for nations to exercise sovereign responsibility.