Cities

Nearly half the world's population lives in towns and cities. Over the next quarter-century virtually all population growth will be in urban areas in less-developed countries. The environmental consequences of urban growth are considerable. Cities are prolific users of natural resources and generators of waste. They produce most of the greenhouse gases that are causing global climate change. They often also degrade local water quality, deplete aquifers, pollute the marine environment, foul the air and consume the land. Several movements are being organized today, some sponsored by the United Nations, to change city planning to address these concerns, to create “green cities.”

Cities are places of concentrated human habitation. People live on almost all of the islands and continents of the world except for inhabitable places, ...