Today, the most common human habitat is cities. Far more people in the developed world now live in urban rather than rural areas, and there's a rapid push toward urbanization in developing nations too. But cities displace existing ecosystems and remove habitat for other species. Unplanned or poorly planned growth leads to urban sprawl, increased air and water pollution, loss of farmland and other problems. In the United States between 1982 and 1992, 8.3 million acres of farmland and rangeland and 5.4 million acres of forests were swallowed by sprawling cities.
Some cities are now so large and built-up that they are actually changing the local climate.
For example, in Tokyo, warm, humid air from all the buildings, cars and factories rises to form clouds over the city during the day. In the evening, these clouds cause rain and even thunderstorms. But it's a critical one as more and more people move into ever-expanding cities. The amount of energy needed to provide all the goods and services for a city is tremendous. According to Bill Rees of the University of British Columbia, a city like Vancouver, British Columbia, consumes resources that require a productive land area that is 180 times larger than the city itself.