Earth has become an urban planet. More than half of the world’s people now live in cities, and the proportion is growing. By 2050, nearly two out of three of us will live in a city.
The interactive map below highlights changes in urbanization from 1950 to 2030. The orange circles represent the world’s 200 largest cities. The bigger the circle, the bigger the population. Select the “countries” button to view the portion of each nation’s population that lives in cities.
Changes in urbanization: 1950–2030
World Urbanization Prospects, the 2014 revision/United Nations; Adapted by J. You/Science
Different regions are urbanizing at different rates, as the chart below illustrates. A few decades ago, most of the world’s city dwellers lived in Europe and North America. But by 2030, most urbanites will live in Asia and Africa. Just three nations—China, India and Nigeria—are expected to add 1 billion city residents in coming decades, with most of the growth occurring in cities of less than 1 million.
Urbanization by region: 1950–2030
Map adapted by J. You/Science
The implications of urbanization are sobering. Cities consume vast amounts of food, energy, water, and materials. The land area needed to provide these essentials is immense: A city’s “ecological footprint” is often 200 times greater than the area of a city itself (or more).
Many urban areas are sprawling outward even faster than they are adding people, swallowing up both farm- and wildlands. And because people often like to live in the same areas favored by wild plants and animals—such as river valleys and coastal lowlands—cities are encroaching on many of the world’s biodiversity hotspots. This competition for prime real estate is highlighted by the map below, which shows where major cities (blue dots) are expanding in areas with high biodiversity (orange).
Where the wild things were (1950 and 2025)
Conservation Synthesis, Center for Applied Biodiversity Science at Conservation International
Cities alter the environment in many ways, from creating air and water pollution to producing extra noise and artificial light. One dramatic change is that cities can become “heat islands” that are warmer than surrounding rural suburban areas. Tons of concrete and asphalt soak up and then radiate heat, making city centers hotter by day—and by night.
City centers become heat islands
Another dramatic ecological change is caused by the spread of impervious surfaces, such as paved roads and roofs. The hardening prevents water from soaking into the soil, promoting flash floods and polluted runoff. A study of nine U.S. cities found that as cities grow, so does the portion of land covered by impervious surfaces (left graph, below). That hardening, in turn, harms aquatic ecosystems, such as by reducing the diversity of insects (right graph).
Urbanization's hard truth
The rise of cities is not all doom and gloom. Packing a lot of people into relatively small areas offers an unprecedented opportunity to improve efficiency. For instance, city dwellers can use less energy, per person, than rural residents, if the right policies and infrastructure are in place. But the image of Vancouver, Canada, below—a combination of a photograph and a thermal scan—illustrates one challenge facing many cities: improving the energy efficiency of buildings. Use the slider to look for the red glow that identifies poorly insulated buildings that leak heat.
Visible light by Ben Nelms; False color thermal image by INO
Whether cities are seen as a problem or as part of the solution, one thing is clear: Our urban planet is here to stay, and the decisions we make today about how we build and live in cities will affect generations to come.
This collection of Reviews, Perspectives, and News features delves deeper into how we came to live in cities and what urbanization means for the future of our planet and ourselves.
More on our Urban Planet special package
- "Leave no city behind" editorial by M. Acuto and S. Parnell
- "In Brazil, a plague of rats signals what may come in a more urban world" feature article
- Podcast interview with author Warren Cornwall on "A plague of rats" news feature
- "Welcome to our urban planet": Video produced and narrated by Science
- Science's previous editorial and news coverage on urbanization