Telegraph: Cities act like giant contraceptives and could help curb the Earth’s explosive population growth that drives climate change, according to two studies. The United Nations estimates that in the past year the majority of the world’s population will, for the first time in human history, live in town and cities. Cities are now home to half of the world’s 6.6 billion humans and by 2030 that urban fraction will rise to 60 per cent as nearly 5 billion people will live in cities of the …