The world’s population now exceeds 6700 million, and humankind’s consumption of fossil fuels, fresh water, crops, fish, and forests exceeds supply.1 These facts are connected. The annual increase in population of about 79 million means that every week an extra 1.5 million people need food and somewhere to live. This amounts to a huge new city each week, somewhere, which destroys wildlife habitats and augments world fossil fuel consumption. Every person born adds to greenhouse gas emissions, and escaping poverty is impossible without these emissions increasing. Resourcing contraception therefore helps to combat climate change, although it is not a substitute for high emitters reducing their per capita emissions. In 1798 Malthus predicted that as the population increased exponentially, shortfalls in food supply would be unavoidable.2 A sevenfold increase in the population has led, 210 years later, to unprecedented food shortages, escalating prices, and riots. Until these events Borlaug’s “green revolution”3 had seemingly proved Malthus wrong. Yet fertilisers, pesticides, tractors, and transport are dependent on fossil fuels, which apart from being in short supply, exacerbate climate change.4 …