According to United Nations estimates, by 2060, for every 100 people of working age, there will be 30 people who are 65 and older. That’s more than double the ratio of old-to-young people today. Because of relatively low birthrates, the age wave is more acute in developed countries, where it will have a larger impact, increasing the cost of social programs and impeding economic growth.

One solution: Allow younger migrants to join the workforce to boost productivity—and chip in taxes to support the elderly along the way.

For more on immigration, read “Germany needs migrants. Do we?”

A version of this article appears in the October 1, 2015 issue of Fortune magazine.

For more on immigration, watch this Fortune video: