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).