If environmentalists really cared about saving the planet, they would be strong advocates for city living, promoting high-rise development and density in or on the fringes of all major cities. The same goes for those of us faced with challenging questions about the best way to promote rural development, reduce poverty, enhance healthcare and education, and save the planet: Cities are the answer. Good cities are, in fact, the only long-term solution to climate change.

Cities create living spaces of maximum density, with smaller housing using less energy, and much less need for travel by car. With most travel by subway, buses and on foot (and vertically via elevator), city dwellers use far less energy than their rural and suburban counterparts. Dense cities (New York, Mumbai, London, Nairobi) emit far less carbon per person than sprawling cities (New Delhi, Houston, Shanghai, Los Angeles), especially those in hot climates where every indoor space is air-conditioned. The nightmare comes when the booming cities of the developing world achieve the density, but without high-rise buildings, subways and decent city services.