The Concept of a Self-Sustainable
Earth Day in 1970 brought forth a new era in environmental consciousness. Over the last several decades, humans have made significant improvements in restoring some of the Earth's fragile environment. In the United States, the return of pollution-sensitive fish to many freshwater ecosystems, the cleaner air over some urban areas, and the rise from near extinction of the California gray whale and bald eagle are several examples of environmental "progress" since the first Earth Day. However, the world's environmental record leaves ample room for improvement. As indicated in Chapter 2, approximately half of all species are likely to become extinct by the end of the twenty-first century. The principal underlying causes of extinction are the expansion of the human population, trophy hunting, economic harvesting, deforestation, wetland drainage, urbanization, agricultural clearing, and pollutants. Humans are changing the environment and destroying natural habitats too rapidly for most species to adapt.
In addition, environmental disasters, such as the Bhopal gas leak in India ( 1984), the discovery of a growing hole in the stratospheric ozone layer ( 1985), the explosion of the Chernobyl nuclear reactor in the former Soviet Union ( 1986), and the predicted global warming during the twenty-first century, have forced people to recognize that human actions have destructive influences on the environment. All the while, the "four horsemen of the apocalypse" (pestilence, war, famine, and death) run rampant in much of the world. In 1996, one out of every three people worldwide suffered from either hunger, malnutrition, homelessness, or poor health care. Over the last