Cities offer employment opportunities, entertainment and other amenities, and potential efficiencies not found elsewhere, as well as advantages in the delivery of education, health, and other social services.

The developed world is already largely urbanized. In the developing world, the rapid urbanization now under way will increasingly concentrate both population and economic growth in cities as much as 90 percent of future population growth and a major share of future economic growth intensifying the problems of the urban environment.

• On average, urban dwellers have higher incomes and live healthier, easier lives than their rural counterparts, although all urban inhabitants do often not share these advantages.

• Cities also play a central role in degrading the physical environment and in shaping the social environments in which most of the world's people will soon live.

• Dysfunctional urban environments have high costs, making more difficult the economic growth needed to improve living standards and helping to perpetuate inequities.

Source: World Resources 2000-2001

In The Urban Explosion, explore a major dilemma of the 21st Century: how to sustain the world's exploding urban population without destroying the delicate balance of our environment. Read the full description of this program or watch a video clip.

In On the Brink, examine how severe environmental problems can lead to political crises and increased hostilities around the world. Read the full description of this program or watch a video clip.

In Land Of Plenty, Land Of Want, investigate the fundamental problem facing today's farmers: how to feed the world's growing population without endangering our environment. Read the full description of this program or watch a video clip.

In Future Conditional, investigate the link between environmental change and the future health of our planet, a future conditional on how we cope with the spread of toxic pollution. Read the full description of this program or watch the video clip.

Read Stories of Hope from the Journey to Planet Earth series focusing on this ecosystem category:

• Mexico City, Mexico
• Istanbul, Turkey
• New York City, New York, USA
• Shanghai, China
• Lima, Peru
• Dakha, Bangladesh
• Tijuana, Mexico and San Diego, California, USA