Some 3.5 billion people—more than half the human race today—live in cities, and that number is growing fast. From the suburbs of Phoenix to the slums of Cairo, 60 million people are moving into urban areas every year.
In some ways, that’s terrible news for the environment. Urban areas consume most of the energy used every year and spew out as much as 70 percent of all greenhouse gas emissions, according to the United Nations. But looked at another way, cities can be more planet-friendly than suburbs or rural communities, thanks to population density and economies of scale. Providing power, water, and goods to large numbers of people is much more efficient when they’re all clustered together, sharing roads, rail networks, and power grids.
All of which means that one of the key questions facing us today is, how can we minimize the environmental costs of urban areas while maximizing their benefits? How, in short, can we make cities sustainable? Click through to see how new ideas, new approaches, and new technologies are transforming everything from the office buildings to the storm drains below, and how these can be interlinked to make cleaner, greener cities with healthier, happier residents.