The global economy is currently exceeding ecological limits, and producing a variety of destruc tive impacts, including climate change, desertification, deforestation, degradation of arable land, freshwater shortages, depletion of fish stocks, unprecedented species extinction, and widespread chemical contamination of air, land, and water.1 The United Nations Millennium Ecosystem Assessment concluded that human economic activity during the last half-century has produced more rapid and severe ecosystem degradation than in any comparable era ofht1man history.