No precedent exists for protecting the environment from the pollution and resource consumption required by such multitudes. Urban regions, entire countries, and ultimately the entire earth could be affected by cities improperly managed. Within cities, poor citizens face the worst environmental consequences. But cities can not be blamed for global environmental deterioration, despite the magnitude of their environmental and population problems. In reality, dense settlement patterns are necessary to preserve open spaces for other uses.
Cities cause environmental problems, but also hold the key to their reduction and ultimate solution.
Rather, they are ideas, experiments and experiences that evolve into successes over years, sometimes decades. But the critical environmental problems threatening health and well-being for so many urban dwellers around the world compel us to speed the process by which successful innovations are recognized and imitated by other cities. The three case studies that follow reveal the transformative potential of local solutions. Two experiences have been extremely successful and have been replicated many times over, while a third had mixed results. They each contain valuable lessons about the promise and pitfalls of implementing environmental innovations and the factors that contribute to their success or failure.