For decades, we’ve been told that the world’s biggest problem is too many people. From Malthus in the 18th century to The Population Bomb in the 1960s, the warnings were dire: more people would mean more famine, more poverty, more environmental destruction. But something unexpected has happened. The demographic math has changed. And the United Nations, the world’s most cited authority on population forecasts, has taken notice.
Until recently, their models predicted that the number of people on Earth would continue growing throughout the 21st century, topping out near 11 billion by the year 2100. But in its 2022 and 2024 revisions, the U.N. quietly lowered its global population projections. The most recent estimate puts the peak at just 10.3 billion, and it comes nearly two decades earlier around 2084.
Fertility Collapse
The shift in projections isn’t happening because people are dying faster. In fact, life expectancy continues to rise, albeit modestly, in most parts of the world. The big change is that people are having fewer children—much fewer.
Around 1970, the global fertility rate (the average number of children a woman has in her lifetime) was about 5. Today, it's down to 2.25 and falling. In nearly 70% of the world’s countries, fertility rates are already below the so-called “replacement rate”—the level needed to maintain a stable population. In developed countries, that’s typically pegged at around 2.1 children per woman. In higher-mortality countries, it is slightly higher.
This global fertility decline has happened faster than most experts expected. And that’s why the U.N. has revised its models twice in just the last five years. But not everyone thinks the U.N. has gone far enough.
Over the last decade, several independent teams of researchers have developed alternative population projections. Most of them show that fertility will drop faster than the U.N. is predicting. A team at the University of Washington's Institute for Health Metrics and Evaluation (IHME), for example, gained wide attention in 2020, when it projected that the global population would peak around 2064 at just over 9 billion and decline to about 8.8 billion by 2100.
Wolfgang Lutz, one of the world’s most respected demographers, has also published projections showing a lower and earlier population peak. Lutz’s group at the Wittgenstein Centre for Demography and Global Human Capital bases its models on education and urbanization trends, which are closely tied to fertility behavior. In a 2024 analysis of surveys involving over a million women in Sub-Saharan Africa, Lutz and his co-authors concluded that fertility rates there are falling faster than expected, especially as female education improves.
In their 2019 book, Empty Planet, Canadian journalists Darrell Bricker and John Ibbitson summarized the case for the likelihood of the lower projections. While not academic demographers, they conducted extensive interviews and focus groups in about a dozen countries, asking women about their thoughts on family and childbearing. They concluded that the fertility collapse is as much cultural as economic, and that the cultural factors will drive down fertility rates further and faster than in the past.
“Predictions are hard – especially about the future.”
So said that famous American philosopher, Yogi Beara. As a result, all models use probabilistic variations that incorporate a wide range of possible futures. For example, while the U.N.’s median projection sees a peak at 10.3 billion in 2084, their model also includes a low-fertility scenario, in which the population peaks around 2060 at 9.5 billion and declines from there. That lower path aligns more closely with the academic projections. By the way, notice what a dramatic difference changing the fertility rate by only .5 makes as indicated by the blue lines on the chart below.
It is all about Africa
The fertility rate has already fallen to or below the replacement rate in countries where nearly three-quarters of the world’s population live. In another 15%, the rate is only just above the replacement rate and is falling fast.
However, there are about two dozen countries in Sub-Saharan Africa and parts of Southwest Asia where the rate is still very high. Although these countries only account for about 11% of the world’s population, they will contribute nearly all of whatever population growth there is between now and whenever the population peaks. The common denominators in the countries that have kept birth rates high are a blend of suppression of the education of women, religious fundamentalism (particularly fundamentalist Islam), limited international engagement, and weak state capacity.
Nonetheless, the birth rate is falling in these countries, albeit to varying extents. Most of the debate over the trajectory of future global population boils down to how fast and to what extent these countries will follow the same fertility decline seen in the rest of the world over the last fifty years.
Why This Matters
The population projections we rely on shape everything from how we plan cities to how we fund pensions. They inform immigration policy, school construction, military recruitment, and long-term economic growth assumptions. If those projections are off by a billion people or by two decades, that is not just a rounding error. It’s a seismic shift in the underlying math of the future.
However, most institutions continue to operate on autopilot, assuming that a growing population—encompassing more workers, consumers, and taxpayers—is the natural order that will persist indefinitely. However, the data clearly indicates that era is rapidly coming to a close and the age of population growth is ending. Indeed, in some places, it already has. For the past three years, China has reported a decline in its population. What follows, and how we react to it, is one of the most critical and least understood stories of our time.
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Author’s Note:
I am currently working on a book on this topic that we expect to release this fall. Also, I regularly speak to various groups on this topic. I made the presentation at my blog readers' conference in February. The presentation is available on YouTube here. If you are interested in me speaking on this topic to your group, contact me by replying to this email.
