The era of global depopulation is coming, and sooner than we once thought. According to the UN’s latest projections, there is now an 80 per cent probability that the number of people on Earth will peak in this century then begin to decline, compared with a 30 per cent probability a decade ago.

For one in four of us, that future is already here. A quarter of the people in the world live in countries whose populations have already peaked, including China, Germany and Japan. Between now and 2054, the UN expects them to be joined by many others, including Brazil and Vietnam.

There has been a lot of debate about why women are having fewer babies, and whether anything can or should be done about it. But the fact we see this trend in so many different societies, from developed countries like the UK to developing ones like Nepal, from conservative ones like Iran to liberal democracies like Finland, complicates the search for simple explanations or solutions.