Lena and Saheed have never met; they probably never will. Lena lives in 2050 Leipzig, a placid and historic German city of middle-aged professionals. At 51, she is midway through a career as a pharmacist, with retirement more than two decades away. She and her husband no longer have to support their only child, a daughter who has graduated from college, but they worry about caring for their aging parents, who are in fairly good health in their 80s and 90s. Saheed, unattached and unemployed at 22, lives in a marginalized, low-income settlement on the outskirts of 2050 Lagos, Nigeria. He and his three siblings face a very different kind of struggle: finding jobs in a tight labor market overrun with young workers, along with obtaining housing and clean water.

Lena worries about chronic diseases. Saheed is more likely to contract malaria. Germany scrambles to adapt its pension, health care and utility systems to a shrinking population that is living longer than ever before. Nigeria struggles to build roads, schools and sanitation facilities as its cities grow.

Lena's and Saheed's lives could hardly be more different. But these two divergent fictional figures embody many challenges that lie ahead. The distribution of the human population stands to change in unprecedented ways over the next few decades, forcing governments and the international community to rethink what it takes to protect the health and well-being of people around the globe. The decisions they make today will determine whether people like Lena and Saheed have a bright, or a bleak, future.

Population Momentum

Roughly half a century ago popular attention fixed on just one global population trend: sheer size. In his 1968 best seller The Population Bomb, Stanford University entomologist Paul R. Ehrlich warned that rapid population growth would outstrip production of food and other resources, with hundreds of millions dying of famine. Ehrlich's fears were not realized, however. The green revolution soon improved food security, and a mixture of economic development and access to education and family planning brought down birth rates in much of the world. By 1970 annual population growth had begun to decline from its 1960s peak of 2 percent.

And yet population growth is like a moving train—even as it slows, it possesses great momentum. Today the global growth rate continues to decline, but billions more will still be added to the human population over the next few decades. The United Nations estimates that by 2050, it will reach 9.7 billion. The chance that the train will finally come to a stop and world population will stabilize or begin declining before 2100 is only 27 percent.

Large group of women and children sitting on the floor.
Some African nations will undergo rapid population growth by 2050, putting pressure on food supplies and possibly leading to shortages. These mothers brought their children to be screened for malnutrition in Denjuok village, Akobo East County, South Sudan, during the 2014 hunger crisis. Credit: Edwina Pickles Getty Images

If we focus on such big-picture projections alone, though, we miss important nuances. Half of the population growth between now and 2050 will occur in nine countries, five of which are in Africa. Across the industrial world, meanwhile, birth rates are falling and life spans increasing. The number of people aged 65 and older in the world will more than double in the next 29 years, according to the U.N. The number aged 80 and older will almost triple. Many of those elderly will live in Europe, where by 2050 the 65 and over demographic is projected to account for more than a quarter of the population. Jack A. Goldstone, a political scientist at George Mason University and a global fellow of the Wilson Center in Washington, D.C., has called this disruption of the world order as we know it “the new population bomb.”

Germany and Nigeria represent opposite extremes of this changing global dynamic. On one end is a wealthy but rapidly aging country where cities are shrinking and governments are facing ballooning pension costs. On the other is a youthful nation that will need to accommodate both more urban migrants and more babies—trends that could compound existing problems such as climate change and infectious diseases. Particularly in Nigeria, says Hans Groth, chair of the World Demographic and Ageing Forum in Saint Gall, Switzerland, history is no guide for what lies ahead: “We are not prepared as human beings to manage or accept such big changes.”

Growing Pains

By 2050 Nigeria is expected to overtake the U.S. to become the third most populous country in the world. Its population will nearly double, to 401.3 million, according to the U.N. Over the course of Saheed's young adult years, then, he will watch as Nigeria's already thin resources spread even thinner. “Think about it,” says John Bongaarts of the Population Council in New York City. “Everything man-made in the country has to be duplicated. Every school, every clinic, every bridge.”

In 2015 the U.N. Population Division revised upward its estimates for population growth in Africa. To some extent, the change reflected positive news. Thanks to advances in public health, including measures that reduced infant mortality and death from AIDS, life expectancy in sub-Saharan Africa had risen.

But the other half of the story is that although birth rates have declined, changes have not been as dramatic or rapid as many had hoped, and levels remain high compared with those in other countries. In sub-Saharan Africa, the total fertility rate—the average number of children a woman has over a lifetime—hovers at 4.7. In Nigeria, it is 5.4. The country could, in theory, gain from what is called a demographic transition—a phase during which fertility falls and a nation has a large number of working-age adults with few elderly and children to support. Countries that successfully complete a demographic transition, by lowering both birth rates and mortality while boosting education, employment and other drivers of economic development, can experience a “demographic dividend” that catapults them into the next level of development.

Demographers cite a range of possible factors for the slow changes in fertility in this region, from the lingering cultural expectations to a longer window during which women customarily have children. Says Akinrinola Bankole, a demographer at the Guttmacher Institute in New York City: “People are still thinking in terms of old-age security”—having a large number of children to care for them as they age. “They think less about the need to invest in the children who will provide that security.”

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High fertility rates will compound the daunting array of threats already facing Nigeria: poverty, hunger, the prevalence of communicable diseases and the effects of climate change. More than 260 million people in sub-Saharan Africa, or one in four, lack adequate food, and more than 30 percent of African children show signs of stunted growth, according to the U.N. Food and Agriculture Organization. As Saheed and his siblings age, the region will add hundreds of millions more mouths to feed. Among those now working to improve food security is the Alliance for a Green Revolution in Africa. Founded in 2006 and led for more than six years by former U.N. secretary-general Kofi Annan (Annan died in 2018), the organization lobbies for changes in agriculture policy and helps smallholder farmers obtain improved seeds, organic fertilizers and basic equipment. “The concentration of population growth in the poorest countries could make it harder for some countries to eradicate poverty, combat hunger and malnutrition, expand services in the area of education and health systems, and improve the provision of basic services and infrastructure,” says François Pelletier of the U.N. Population Division.

Within countries such as Nigeria, moreover, population growth will not be evenly distributed. Birth rates are currently much higher in the north, which is largely resource-poor. As a consequence, growing numbers of northerners are moving toward Lagos—a change that is part of a larger global trend. Urbanization and overall growth are expected to add more than 2.5 billion people to the world's urban population by 2050, with around 90 percent of the increase happening in Asia and Africa.

Urbanization is often a positive phenomenon, accompanied by an increase in education, a decrease in the birth rate and steady economic growth. Well-planned cities reduce land use and boost energy efficiency. Henrik Urdal, a political scientist at the Peace Research Institute Oslo in Norway, and his colleagues have found that urbanization may even decrease the risk of conflict.

But the fact that countries like Nigeria are urbanizing at a much lower level of economic development than they once did means that by 2050 much of the world's population will be concentrated in cities unequipped to provide adequate health care, sanitation and other services. That could increase Saheed's exposure to infectious diseases, which can thrive in densely populated areas with large numbers of migrants. Urbanization is believed to have been a major contributing factor to the early spread of HIV/AIDS in Africa. By 2050 the heavily populated neighborhoods of Lagos could become hotbeds for tuberculosis and malaria.

As Nigeria moves up the economic ladder and more people buy cars and consume electricity, air pollution could pose another health threat. The rapid growth of megacities in Asia over the past few decades provides some guide of what could happen in Africa. Recent data from the Global Burden of Disease Study suggest that air pollution contributed to 1.85 million deaths in 2019 in China alone.

Ironically, if Nigeria manages to lower its birth rate, the shift could produce an unfortunate side effect. As the birth rate falls, the proportion of the total population composed of teenagers and young adults will increase. If the economy cannot provide enough jobs, Bongaarts says, “you have unemployed and underemployed young men who are unhappy. They are readily exploited, and they contribute to crime and lack of security.”

To succeed in coming years, countries like Nigeria will need to simultaneously boost education, youth employment and access to family planning—a mammoth undertaking but one that is not impossible. Fifty years ago few foresaw the rapid decreases in fertility that have occurred in Bangladesh, Indonesia and Iran. If Saheed finds a job and gets married, he may decide to have fewer children than his parents so that he can afford their schooling costs. As more and more people like him do the same, Nigeria has a shot at turning a potential liability into an advantage and achieving a demographic dividend. Such population changes have been crucial to the economic ascent of other countries, including Brazil, China and South Korea.

Flooded slum.
Lagos, Nigeria, is one of the fastest-growing cities in Africa, with its population poised to double in the next 25 years. This will make it the third-largest city in the world but without the infrastructure or resources of other cities. Credit: Frans Lemmens Alamy

In the Old Country

A very different sort of shift is under way in Germany. Lena was born in 1999, when the German economy was the engine for European economic growth and workers abounded. By 2050 the population is projected to fall from 83.8 million to 80.1 million. About 37 percent of Germans will then be 60 and older, whereas people aged 15 to 59, who make up most of the working-age individuals, will account for 50 percent, a 13 percent decrease from today. Parts of Germany already offer a preview of what is to come. In 2015 the septuagenarian mayor of Ottenstein, a community in the northwest of the country, announced that he would give away land to couples with young children. The goal: to keep the village's school open.

Germany's situation is reflected throughout Asia, Europe and Latin America. The U.N. projects that 26 countries, including Japan and Ukraine, could lose 10 percent or more of their populations by 2050. Media reports already make much of the declining birth rate in Germany and neighboring countries. By 2050 policy makers could be worrying about a sustained economic slowdown caused by a shortage of young workers and taxpayers.

Immigration could relieve some of that shortage. The U.N. predicts that between 2020 and 2050, Germany will be one of the world's top receivers of migrants. The hundreds of thousands of desperate Syrian families who have crossed into Europe to flee civil war, their possessions strapped to their back, have already brought this issue into focus. As the population continues to grow in sub-Saharan Africa—and especially if young adults like Saheed do not find jobs in their home countries—the number of migrants may increase, linking the futures of Germany and Nigeria. Pundits sometimes argue that this trend will help counteract the aging population. But, Goldstone notes, “it would take tens of millions of migrants to offset the shrinking youth cohorts in Germany, Netherlands and other low-growth countries”—and conversely, to relieve population pressure in fast-growing countries in sub-Saharan Africa.

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That means that even with modest rates of immigration, the population of Leipzig might decline. In the process, the city may struggle to adapt its utility system and other services to less use, perhaps by raising fees—a change that would be borne by working-age people like Lena. The shrinking city could be an expensive one.

Germany is also likely to face new health challenges, as improvements in health and longevity shift its disease burden. Lena's parents, for example, are part of an “oldest old” group of people, aged 80 and older, that is projected to include 12.8 percent of Germans in 2050. They will be less likely than previous generations to die of cancer or a heart attack. But they will be more susceptible to dementia, a disease that is becoming more prevalent as life expectancy increases and that will only become more common unless a cure is found. “Before, people simply died before they contracted Alzheimer's,” says Axel Börsch-Supan, director of the Munich Center for the Economics of Aging and project coordinator for the Survey of Health Ageing and Retirement in Europe, a longitudinal study of more than 140,000 Europeans aged 50 and older. “Now that doesn't happen.”

Economically, aging in Western Europe is associated with some benefits. It is not only the result of low birth rates: it has also been brought on by marked jumps in life span and individual health and well-being. People are not merely living longer; they are staying healthy and able to work much longer as well. Over the past two decades life expectancy at birth in Germany increased by nearly four years to just over 81. Health metrics are improving across Europe, Börsch-Supan says: “Longevity is increasing linearly. There's no sign of the curve flattening out.” (In the U.S., in contrast, discussion about the slower aging rate tends to obscure a disappointing trend in life expectancy, which has actually worsened, Börsch-Supan notes.)

In Europe, some say nothing short of a redefinition of what it means to be elderly is now required. Sergei Scherbov, a demographer at the International Institute for Applied Systems Analysis in Laxenburg, Austria, has proposed considering a person to be “aging” during only the last 15 years of life, as measured by a country's life expectancy at birth. Such a measure better reflects ability and health than the U.N.'s definition of aging as 60 and older, he says: “In the 1950s the oldest person to climb Mount Everest was 39 years old. [In 2013] a Japanese guy of 80 climbed it.”

Indeed, pension systems are being overhauled across much of Europe. In Germany, the retirement age, which is now 65 and 10 months, will be gradually increased until it reaches 67 in 2031. But to provide for people like Lena's parents who are living past 80, the country's retirement age ultimately will need to be linked to life expectancy, as has happened in Norway and Sweden—a change that will likely prove unpopular. “The issue in Europe is that people love to retire early,” Börsch-Supan says. “That is not sustainable.

The Gravity of Demography

The fates of Saheed and Lena depend in no small part on what transpires now. By planning well for the future, demographers say, both Nigeria and Germany can tackle coming population changes. Demography, Goldstone says, is like gravity—you have to acknowledge its force and act accordingly. “If you manage to deal with gravity, you can make planes fly,” he says. But you have to design your airplane well and fly it competently. “You can have a stable government and growing economy in the face of population growth or population decline. But you have to invest wisely, manage the economy well, educate the labor force to be more productive and plan for the welfare needs of different age groups as they change over time.”

In a way, Nigeria and Germany can be seen as sitting at two ends of a global continuum. Between these two extremes are dozens of other nations whose role in the world will also shift with changes in population distribution—including the U.S., which will both age and grow in overall population. By acting now on issues such as health care, urban infrastructure, education, and food and pension security, countries across the spectrum can ensure better lives for generations to come.

Comprehensive efforts at maintaining global stability, meanwhile, will need to better involve populous emerging economies, among them Brazil, China, India and Mexico. That means reconfiguring global governing bodies such as the G7 and NATO so that they better reflect the changing face of the world—and ensuring that money flows toward the public health, resource and infrastructure challenges of the entire world, not just those of industrial nations. By thinking creatively and acting early and decisively, humanity might improve the quality of life for everyone, no matter where they are born.