The writer is professor of globalisation and development at Oxford university and the author of ‘Rescue: From Global Crisis to a Better World’. He tweets @ian_goldin

For the first time in history there are more people over 65 than under 5. Pensioners outnumber children in a growing number of countries, including the UK, much of Europe and Japan. By 2030 there will be over 1bn people over 65 and more than 200mn over 80, with the number of elderly doubling over 20 years.

Improvements in public health and medicine account for increased longevity, a long-term trend of about two years per postwar decade (notwithstanding the recent reversals which are primarily due to the pandemic and inequalities in healthcare). More surprising is how quickly fertility is falling. More than half the countries in the world are now below the level of fertility required to keep the population the same from generation to generation.