If current forecasts are accurate, 2064 will be the first year in centuries when fewer babies are born than people die. Birth rates in India will fall to below the level seen in America last year. Even with immigration and successful pro-natal policies, America’s population will only have a little bit of growth left. By 2100 there will be many fewer migrants left to attract. The world’s fertility rate will hit 1.7. Just two Pacific islands and four African countries will manage to reproduce above replacement level.

Sooner or later, therefore, every big economy will collide with a demographic wall. The bill from pensions and hospitals will pile on fiscal pressure. Sapped of workers and ideas, economic growth could collapse while public debt balloons. Just how catastrophic the situation becomes depends on whether policymakers maintain budgetary discipline, withstand pressure from angry older voters and, crucially, are willing to inflict pain on populations now in order to save future generations from more later on.