Until recently, the world population has been growing faster than exponentially. Although the growth rate has slowed somewhat, there are about 80 million more people each year and about 3 billion more will be added by 2050 (a 50% increase). Population will probably increase more beyond that. Such growth is unprecedented and we cannot predict its long-term effects. The environmental impact of this population increase is bound to be astronomic. Large populations engender two problems: over-consumption in the rich countries which leads to environmental misery, and under-consumption in the poor countries which leads to human misery. People living in abject poverty ($1 per day) don’t limit their fertility. Factory jobs in poor countries pay double that, approximately $2 per day. For population to stabilize, income must rise. If population is to increase by 50%, income needs to double — we are looking at a tripling of the world economy. The environment is currently overstressed. Can it survive a tripling of the economy?