What happens as more people move to cities?

Earth has become an urban planet. Cities are growing everywhere. More than half of the world’s people already live in cities. By 2050, 2 out of 3 of us will live in a city. That has sobering implications for the environment. Cities consume vast amounts of food, energy, and materials. This “ecological footprint” can extend far beyond the city’s edge. Indeed, the land area needed to support a city can be 200 times bigger than the area of the city itself. Another challenge is that cities are expanding into areas rich in biodiversity. That’s because we like to live in the same places that are favored by plants and animals. Cities alter the environment in dramatic ways. Tons of concrete store heat... City centers become “heat islands” that are warmer at night and hotter by day. Urban are noisy… and artificial light means it never gets really dark. Paved roads and rooftops prevent water from soaking into the soil. That leads to flash floods and lots of polluted runoff that can harms streams and rivers. But an urban planet is not all gloom and doom. When you put a lot of people in one place, you can improve efficiency. City dwellers can use a lot less energy, per person, than people living in rural areas. Doing it right will require smart planning. And one thing is clear: Cities are here to stay, and the decisions we make today about how we build and live in them will shape generations to come.