Cities contain many people, but it is not just numbers that put strain on resources, it is the way we consume also (Image: Duncan McKenzie/Getty)

GLOBAL population growth has slowed significantly, but it hasn’t stopped. By 2050 there may be about 35 per cent more people on Earth than there are today. We are already seeing increasing shortages of food, water and other resources and growing numbers of hungry people.

Yet to embark on any discussion about limiting our numbers is to enter sensitive and controversial territory. Perhaps this is not surprising, as in the 1960s, when population growth became an issue of widespread concern, the discussions often had a racist undertone, in which the “well-off” focused on the exploding populations of “underdeveloped nations”.

Nowadays it is understood that the key population-related issue is the destructive pressure human activity is exerting on our life-support systems, posing a growing threat to the sustainability of civilisation. Of course, this is not all because of human numbers; it also has to do with how much each of us consumes. That’s why, in our view, the US with its population of over 300 million and high per capita consumption should be seen as Earth’s most overpopulated nation. It is also why the emergence of “new consumers” constitutes a major additional assault on global life-support systems. Moreover, the 2.3 billion people likely to be added to the human population by 2050 will undermine those systems much more seriously than did the previous 2.3 billion, as each additional person will, on average, have to be supported by scarcer, lower-quality resources imposing ever greater environmental costs. …