Posted by 
Last week, the UN Department of Economic and Social Affairs released the World Population Prospects, the international body’s annual report on the current and future state of global population.
The headline was clear: We are well past the days of worrying about having more people than the Earth can handle. The UN’s demographers now expect the number of people on the planet to peak at a bit under 10.3 billion in 2084.
That’s two years earlier than the UN was predicting peak population as recently as 2022, and considerably earlier than forecasts from just a few years before, when population wasn’t expected to peak until the 22nd century.
10.3 billion, of course, is some 2 billion more people than the planet currently holds, so population growth isn’t stopping anytime soon, but it is slowing down rapidly. Women on average now have one less child than they did in 1990, and in more than half of all countries and areas, the lifetime fertility rate is less than 2.1 — the number needed for a population to replace itself through birth alone. And as of 2024, total population had already peaked in 63 countries or areas including Russia, Germany, and China, which last year was passed by India as the world’s most populous nation.
It’s impossible to discuss global population without landing in the middle of a culture war, whether it was over supposed overpopulation in the 1970s or now, when the right, very much including new Republican VP candidate J.D. Vance, is increasingly pushing controversial pronatal policies designed to increase family sizes. What you think about population change — whether you welcome it or fear it — will depend on which side you fall in these fights.
The battles over population policy will continue to be fought and they are important, involving reproductive rights, fiscal policy, and cultural values. But when it comes to the sweep of demography in the 21st century, they are largely beyond the point. That’s because of something called “population momentum.”
Given that fertility rates are falling everywhere and pronatal government policy has almost totally failed to alter that fact, population in the future is mostly going to be a function of how many adults of reproductive age a country has, which is already largely fixed. The UN’s demographers may be off by a few years or a few hundred million people, but the changes are generally baked in. “All populations,” John Wilmoth, head of the UN Population Division, told the AP, “are following a similar path.”
Which means the important question we’re facing isn’t how to change a world headed toward peak population in 60 years. It’s how to understand it and respond to it.
Extreme decline
The UN population report is full of startling predictions, but perhaps none so much as this: China, where the fertility rate is now just one child per woman, is forecast to see its population drop from 1.4 billion today to 633 million by 2100. That’s a drop of more than half, and it would see China, a country long synonymous with population size, reaching a level it hasn’t experienced since before 1960.
China is part of the nearly 20 percent of the world that has “ultra-low fertility,” according to the UN report — meaning fewer than 1.4 children per woman. Another country in that group is South Korea, which has the world’s lowest fertility rate at 0.72. By 2100, South Korea’s population is expected to halve, to just 27 million people. Even more surprising: just 800,000 South Koreans by then are forecast to be children under the age of 5, while some 11 million will be 65 or older.
China’s and South Korea’s population declines will be extreme, but other countries will be right behind them. Another 48 countries and territories — including Brazil, Turkey, and Vietnam — are projected to see population peak between 2025 and 2054.
Before they get there — and continuing well after — these countries and much of the rest of the world will get much older. That’s in part a success story — after dipping during the Covid-19 pandemic, global life expectancy is on the rise again, reaching 73.3 years in 2024 and projected to continue to rise to 77.4 years in 2054. The upshot, though, will be global graying: while today children under 18 globally outnumber those 65 and above by a nearly three to one ratio, by the late 2070s, there will be more elderly than children.
The importance of immigration
The US is an exception in the rich world in that its population is projected to keep growing through the 21st century, reaching some 421 million by 2100. But that’s much less a function of fertility — US fertility has been below replacement level for years — than it is of the country’s openness to immigration. Recent census projections show that if immigration to the US stopped tomorrow, the US population would begin to fall immediately and hit just 226 million by 2100.
That fact underscores that while meaningfully shifting fertility rates may be impossible, countries can control immigration, which gives the US more influence over just how big or how small it will be decades into the future. But even that’s a relative change. Unless we start getting off-world immigrants, every new citizen to one country is a population loss to another.
A new world order
Even while population growth in the world as a whole slows down and eventually reverses, some countries with younger populations and relatively higher fertility rates — chiefly in sub-Saharan Africa — will see massive growth.
The result is that by the end of the century, the makeup of the world will look very different. Nigeria is projected to become the world’s second-most populous country after India, with a population that will more than triple to over 700 million. Pakistan’s population is expected to increase by more than 100 million. The Democratic Republic of Congo, which ranks 15th in the world in population now, is forecast to reach seventh place with 388 million people — more than the US has today.
We’re only beginning to grapple with what an older, shrinking world will feel like. Population change is a bit like climate change: a mega-trend that will do much to shape the kind of future we and our declining number of descendants will live in. The difference is that it remains in our control to alter the trajectory of climate change through energy and environmental policy. Despite the culture war rhetoric, that’s largely not the case for demography. All we can do is adapt.
