Researchers challenge conventional urban forecasts, finding that large cities lose their growth edge as countries become more urbanized. By 2100, just 38% of the global population is projected to live in cities of over 1 million people — far less than trending models predict.
If you’ve ever imagined the future as an endless sprawl of megacities, a new study wants to complicate that picture. Research published in the Proceedings of the National Academy of Sciences by scientists at the Complexity Science Hub (CSH) and ETH Zurich finds that the gravitational pull of large cities weakens as nations urbanize — and that projection changes the math on where billions of people will actually live by the end of this century.
The Forecast Gap
Back in 1975, only about 11% of the global population called a city of more than 1 million home.
“Today, we estimate that share to be about 24%,” lead author Andrea Musso, a junior fellow at the Complexity Science Hub and doctoral student at ETH Zurich, said in a news release.
The pace has been staggering: over the next 25 years alone, roughly 1 billion people are expected to move into cities — the equivalent of building a new New York City every two months.
Yet the new model diverges sharply from what simple trend-line extrapolations would suggest.
“Compared with simply extrapolating current trends, our model projects about 450 million fewer people living in million-plus cities by 2100 – a difference much larger than the current population of the United States,” Musso added.
That single gap — 450 million people — is enough to reshape how governments, planners and investors think about the urban future.
Why Big Cities Stop Dominating
The core finding is that urban systems move through a predictable life cycle. In the early phases of a country’s development, major cities act like magnets, drawing people who are chasing jobs, healthcare, universities and opportunity. Musso’s team quantified this effect precisely.
“We found that between 1975 and 2025, cities with more than one million inhabitants in less urbanized countries, including many countries in Asia and Africa, grew about 7.3% faster than the average city in their respective country,” added Musso.
But that advantage erodes. In highly urbanized nations — much of Europe and the Americas — cities of all sizes have grown at roughly the same rate over the past half century. The megacity premium disappears, and smaller cities catch up.
Frank Neffke, who leads the Transforming Economies research group at CSH and is also a professor at IT:U Interdisciplinary Transformation University Austria, stressed why the timing of that shift matters.
“That pace matters,” Neffke said in the news release. “Decisions about infrastructure, housing, transport, energy, and climate adaptation all depend on where people will live.”
The Hidden Trade-Offs of Urban Scale
The study also surfaces a tension that any student weighing a move to a major metro area might recognize.
“Studies of US cities show that people in a city of one million spend more than twice as much time in traffic and are nearly three times more likely to contract certain diseases compared to those in a town of 10,000,” Musso added. “At the same time, residents of the million-person city are more than three times as innovative and almost twice as productive.”
Neffke framed the economic stakes clearly.
“If moving to a city leads to a doubling in productivity, then the rise of large cities can be a powerful driver of economic growth,” he said. “Our findings show that this driver gradually loses momentum as countries become more urbanized.”
In other words, the economic case for concentrating everything in a handful of megacities weakens as a country’s urban network matures.
A Methodological Overhaul
One of the study’s most significant contributions is methodological.
“Most earlier studies had to rely on administrative city boundaries,” Musso said. “But these boundaries are often misleading. Paris, for example, is much larger than the administrative City of Paris. New York is not just Manhattan – or even the five boroughs.”
To get around that problem, the team built two entirely new datasets from scratch using satellite imagery and granular census records.
“We divided the world into small grid cells, each roughly one square kilometer in size, and then determined, based on population and built-up area, whether a cell was urban or rural,” added Musso. “We then linked clusters of urban cells over time and tracked how their populations changed.”
This “harmonized way of defining city size is crucial to compare not just individual cities but entire urban systems both across space and in time,” Neffke added.
Why It Matters for Students and Young Professionals
For college students deciding where to build a career — or for those studying urban planning, public policy, economics or environmental science — these findings carry direct practical weight. The assumption that global talent and opportunity will keep concentrating in a shrinking number of mega-hubs may simply be wrong. Smaller and mid-size cities could offer increasingly competitive prospects without the congestion and public-health downsides that scale brings.
“Knowing that urban growth follows a predictable life cycle is enormously important for decision-makers,” added Neffke. “It can help guide infrastructure planning, climate adaptation strategies, and forecasts of future economic growth.”
Students entering fields tied to housing, transportation, climate resilience, or economic development are walking into a policy landscape where these recalibrated projections will likely reframe debates for decades.
An interactive data story exploring the study’s findings — including visualizations of how different boundary definitions change the apparent size of cities — is available at megacities.ch.
Source: Complexity Science Hub