Falling birth rates, more than longer lives, are what make populations grow old
Ageing societies are usually explained by people living longer, but that is the smaller half of the story. Across the world, declining fertility now drives most population ageing: fewer babies mean fewer young people each generation, pushing the median age steadily upward even where lifespans barely change.
The shift began in developed countries in the late nineteenth century, and by the late twentieth the world as a whole was ageing. The number of people aged 60 and over has tripled since 1950, reaching 600 million in 2000 and passing 700 million in 2006, and is forecast to hit 2.1 billion by 2050. Only 18 countries, labelled demographic outliers by the UN, buck the trend of falling fertility.
Median ages tell the story. In the UN's more developed countries, home to 1.2 billion people in 2005, the median age was 28 in 1950, had climbed to 40 by 2010, and should hit 44 around 2050. For the world it went from 24 to 29 over the same period, heading to 36. Less developed regions are expected to climb from 26 in 2010 to 35 in 2050, and because their fertility is falling faster, they will age more quickly than rich countries did, with less time to adjust.
Asia and Africa hold many countries facing rapid ageing; within two decades their largest age group may be over 65, with average ages nearing 50. Research led by the University of Washington projects 2.4 billion people over 65 by 2100. The Oxford Institute of Population Ageing concluded that ageing has slowed in Europe and will hit Asia hardest. Most developed countries now have fertility below replacement, so their growth depends on immigration and on large older generations living longer.
Remedies are debated. Canada has the world's highest per capita immigration rate, partly to offset ageing, yet the C. D. Howe Institute and other scholars doubt immigration alone can fix it. Nobody knows whether extra years will be healthy; compression of morbidity would mean less disability in old age, while expansion would mean more illness. George Leeson's Global Ageing Survey, covering 44,000 people aged 40 to 80 in 24 countries, found most are well aware of the shift.
Source: Population ageing
