Many believe that, with contraception spreading among developing nations, overpopulation has been solved. In fact, we’re just beginning to experience the worst effects as it peaks. In the New York Times, Somini Sengupta explains:

At no point in recorded history has our world been so demographically lopsided, with old people concentrated in rich countries and the young in not-so-rich countries.

Much has been made of the challenges of aging societies. But it’s the youth bulge that stands to put greater pressure on the global economy, sow political unrest, spur mass migration and have profound consequences for everything from marriage to Internet access to the growth of cities.

That’s especially true of the developing world.

Already, the number of Indians between the ages of 15 and 34 — 422 million — is roughly the same as the combined populations of the United States, Canada and Britain.

Many of them, of course, without job. But

Youth unemployment is especially striking in richer countries.

As for those in developing countries, a solution could lie in migration.

The worldwide age divide makes migration — along with job creation in the global south — critical to balancing the world demographically, according to Rainer Münz, head of research and development at the Erste Group Bank in Brussels. Mr. Münz proposes what he calls a system of “demographic arbitrage,” with industrialized countries competing for talent from elsewhere. Even China, he maintains, will have to enter that race.

“A demographic arbitrage between aging societies with a shrinking work force and youthful societies would be good thing, if the whole thing could be managed,” he said.

Of course, resistance to immigration in the West, due to the unrest in the Middle East, makes that a non-starter at this time. But should the emergency diaspora from Syria, Iraq, and Libya slow, Münz’s idea might become workable. Aging states with a shrinking work force could benefit from the overflow of youth from developing states.