During the twentieth century we humans doubled our average life expectancy, quadrupled the size of our population, increased the global food yield sixfold, water consumption sixfold, the production of carbon dioxide twelvefold and the overall level of economic activity twentyfold. In so doing we had, by the turn of the century, exceeded the planet's carrying capacity by approximately 30%. That is, we are now operating in ecological deficit. These rates of change in human demography, economic activity and environmental conditions are unprecedented in history. This is why there is a need to seek an understanding, in ecological terms, of the underlying determinants of human population health. This is Big Picture stuff.

There are now serious questions about how we can reorient our social and economic priorities so that we conserve and reuse, rather than consume and despoil.