Next week's United Nations conference in Cairo on population and development will evoke some hand wringing about the inability of governments to act quickly enough to avert demographic and environmental crises. Gloomy predictions have been made since at least the time of Malthus, who at the end of the 18th century foresaw geometric increases in population outstripping arithmetic increases in food production.1 Largely because of unforeseen technological advances in agriculture, major disaster has not occurred - although current per capita production trends are not reassuring.2 So, as life expectancies edge up in most populations, sceptics might ask if there is any new reason for concern over today's rapid population growth.

Yes, there is a reason - and it has clear implications for public health. Today there is a new type of writing on the wall; it concerns the worldwide environmental impact of the size of the human population, energy intensive technology, and consumerism. Globally, we are now seeing anthropogenic changes in atmospheric composition, the degradation of fertile lands and ocean fisheries, the depletion of fresh water, …