A new study has projected that as countries urbanise, 38 per cent of the world's population will be residing in large cities by 2100. The research, conducted by Andrea Musso, a junior fellow at the Complexity Science Hub in Austria and a PhD student at ETH Zurich, Switzerland, and published in the Proceedings of the National Academy of Sciences, provides a detailed analysis of global urbanisation trends.
Current Urbanisation Levels
According to the study, about 11 per cent of the world's population lived in cities with more than one million inhabitants in 1975. Today, that share has risen to approximately 24 per cent. The researchers note that over the next 25 years, one billion people are expected to move into cities, which is roughly equivalent to adding one New York City every two months. Decisions about infrastructure, housing, transport, energy, and climate adaptation all depend on where people will live.
Projections for 2100
The study's projections indicate that 38 per cent of the world population will be living in cities with more than one million people by 2100. This is a significant increase from current levels but lower than what simple extrapolation of current trends would suggest. Musso explained, "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."
The Urban Life Cycle
The gap in projections is driven by the study's discovery of a life cycle that urban systems follow, which determines how fast large cities grow relative to smaller cities in a country. In countries only beginning to urbanise, large cities grow much faster than smaller ones, as people move to urban centres where jobs, hospitals, universities, and other opportunities and amenities typically concentrate. However, as a country urbanises further, the magnetic pull weakens.
Regional Differences
Between 1975 and 2025, cities with more than one million inhabitants in less urbanised countries, including those in Asia and Africa, grew about 7.3 per cent faster than the average city in the respective country. In highly urbanised countries, including much of Europe and the Americas, cities with more than a million inhabitants grew at roughly the same rate as the national average over the past 50 years, meaning that smaller and larger cities grew at similar speeds.
Data and Methodology
The researchers used satellite and micro-level census data to study urban growth consistently across countries and over time. The study covered 99 countries, representing about 94 per cent of the global population in 2025, and spanned the period from 1975 to 2025. Using satellite imagery, the team tracked cities as they physically expanded across the landscape.
Implications
These findings have important implications for urban planning and policy. Understanding the urban life cycle can help governments and planners anticipate future growth patterns and make informed decisions about infrastructure, housing, and services. The study also highlights the need for sustainable urban development to accommodate the expected influx of people into cities.
