Rapid and chaotic urbanization is taking a massive toll on human health and the environment, the Worldwatch Institute said today in its annual report on the state of the world. In 2008, half of the Earth’s population will live in cities, the first time in history that humans can be considered an urban species.

How the world tackles the social and environmental challenges of urbanization, in particular the needs of the urban poor, will determine the future of humanity and the fate of the planet, according to the report by the U.S. research group. "Cities are directly or indirectly responsible for the vast amount of the world's greenhouse gas emissions," said Janet Sawin, director of the Worldwatch Institute Institute's energy and climate change program, "But many cities are now leading the way."

The report calls for a broad effort on the part of cities and nongovernmental organizations to gather and share information on local solutions to urban problems and for policymakers to ensure the urban poor have a voice in development decisions.