For some time, it has been clear that a global population imbalance is emerging. High income countries, including nearly all of the Americas, Europe, and most of East and parts of South and Southeast Asia, have seen a dramatic, sustained fall in fertility. Already, this is resulting in shrinking labor forces and the oldest mean age populations seen in history. At the same time, the low income countries and even some lower middle-income countries—mainly in Africa but also in Central America, the Middle East, and parts of South and Southeast Asia—continue to have relatively high fertility. This is now, and even more in the coming decades, producing fast-growing labor forces and relatively young populations.

Today, while Africa has a median age just under 20, all other continents have a median age over 30; in North America and Europe the median age is roughly 40. This divergence will only grow over the next forty years and will be a major driver of the global economy, international migration, and political conflicts through most of the 21^st century.

A lower median age is associated with higher risks of conflict and greater propensities for migration. This combination will likely spread violence and displaced populations across Africa and other relatively young countries and regions for the coming decades.

For those countries experiencing low fertility, a higher median age is strongly associated with less violence and more stable democracy—that would be expected to be good news for most of the world. These favorable tendencies, however, can be counteracted by material and political insecurities that raise support for strongly nationalist and more authoritarian governments. These insecurities are intensified by a combination of demographic and climate trends, in ways that seem likely to increase.

First, as the “baby boom” ages and heads toward retirement, and a smaller cohort strongly affected by the Great Recession of 2007-2009 takes their place, economic growth in richer countries is slowing down. Europe, the US, and China have all seen slower growth for the entire decade since 2009, with many countries just skirting recession. Inflation remains so low that official interest rates have been pushed below zero in many countries. Productivity growth remains low and wage growth is modest, even as labor markets seem saturated. This is largely because older workers form the dominant part of the labor force, limiting opportunities for younger workers.

Such slow growth and negative interest rates are placing terrible strains on national and private pension plans, just as the above-60 population in richer states is soaring. Anxieties about future growth and the ability of governments to keep their promises regarding pensions and health care, especially following the experience of austerity policies following the Great Recession, have led Western populations to put much more emphasis on material security than democracy, and contributed to the success of populist parties.

Second, the regions where population is still fast growing—parts of the Middle East (Yemen, Syria, Iraq, Afghanistan), Central America, and most of Africa—are precisely the parts of the world most impacted by climate change. As the world warms, changes in precipitation are impacting agricultural productivity in many regions, and contributing to increased migration. Combined with weak governments unable to provide fallback options or physical security, such local climate crises are contributing to surges of migration to Europe and the U.S., further exacerbating anxieties and increasing support for populist strong-leader government. We’ve seen this in the Central American migration to the United States and the Syrian migration to Europe, both of which were rooted in a combination of climate and conflict pressures (Goldstone and Diamond forthcoming). This combination promises to become more widespread in the near future.

There is an obvious way out of this maze. If richer countries accept migrants from the younger populations of poorer regions, they will benefit from a larger and more flexible labor force that can help grow their economies. It will also provide a modest pressure relief for the fast-growing countries and remittances to help bolster sending communities. Much as after the wave of population growth and revolutions in the 1830s and 1840s in Europe, migrants to the Americas both enriched North and South America and reduced political pressures in Europe, a new wave of migrants to Europe and the US could have similar win-win effects. 

On its own, this will not be enough. Greater efforts also have to be made to reduce and cope with the effects of climate change; otherwise, further surges of crisis-driven migration will continue to fuel hostility to foreigners and strengthen authoritarian tendencies in receiving countries.

Our very success in increasing energy use and lifespans is now pushing us to a new era—one in which accelerating climate change and global population imbalances will combine in ways we have never yet seen. This new phase of the global population and economy will usher in great challenges for politics and prosperity—challenges that can only be met by global efforts and cooperation. If countries continue with anti-migration and pro-fossil fuel policies, we will almost certainly enter a vicious circle of economic decline and authoritarian resurgence that will look much like the 1930s. As in that decade, perhaps only a Rooseveltian turn to more progressive policies will be able to save the day.