Population ageing is, in the first instance, a demographic phenomenon; although its consequences go far beyond demography. But the future trends of ageing are not yet known and many of the consequences of ageing will depend on the future speed and extent of ageing. Here we summarize what is already known and what is not yet known about future ageing trends in different parts of the world. We do this through the means of new probabilistic population forecasts. The section ‘New Regional and Global Probabilistic Population Forecasts’ presents the results of those forecasts. They confirm the earlier finding (Lutz et al., Nature, 412(6846), 543–545, 2001a) that it is highly likely that the world’s population growth will come to the end during this century. The following four sections present results for proportions of populations 60+, old age dependency ratios, proportions 80+ and average ages. In the section ‘New Measures of Ageing’, we analyse a new measure of ageing that takes life expectancy changes into account.
Population ageingProbabilistic population forecastingLife expectancy adjusted ageing measuresUncertainty in ageing measuresPopulation growthMortality uncertainty