Indeed, according to these projections, in some Asian and European countries such as Japan, Korea, Spain and Italy, there will be just 3 working-age individuals for every 2 people over 65 in the year 2050, compared to an average of 11 working-age individuals for every person over 65 in 1950. Even African countries, home to the youngest populations in the world, will see a moderate increase in the dependency ratio in the years to come. I mentioned earlier that net migration inflows can help sustain the current workforce levels in Europe. However, the obvious fact that migrants become part of the retired population once they reach the retirement age implies that the benefits in terms of old-age dependency ratios are less evident. Its effect will last only to the extent that immigrant flows increase further in future. Hence, we may conclude that the role of migration, when it comes to addressing population ageing as measured by dependency ratios, is probably limited. 4  Certainly, we must bear in mind that there is considerable uncertainty over how fertility, mortality and migration flows will evolve in the coming decades. Accordingly, the point estimates of future population levels and dependency ratios must be viewed with some caution. In fact, when the analyses explicitly account for this uncertainty, the results show there is a high degree of variation in the intensity of future population ageing.
Specifically, the central scenario of the UN assumes that, in net terms, around 25 million people will come to Europe over the 2020-2050 period. Therefore, a back-of-the-envelope calculation shows that holding the working age population constant would require at least three times the net migration flow assumed in the baseline scenario. Put another way, if Europe were to offset the projected decrease in the working-age population by receiving more migrants, it would need a net influx of around 2.6 million people each year over the next 3 decades, roughly twice the net migration flow Europe has received in the recent past. We cannot overstate the challenges these magnitudes pose from an economic, social and political perspective. 3  It is worth stressing that population ageing has become a global phenomenon. A closer look at the cross-country evolution of the old-age dependency ratio, that is, the ratio of the over65s to the working-age population, is illustrative of this trend. While in 1950 no country in the world featured an old-age dependency ratio above 20%, nowadays 59 countries surpass this level, including all but one European country. In 2050, according to the UN Population Projections, the group of countries with an old-age dependency ratio above 20% will double to 118, comprising most nations in Europe, North America and Asia.