The power of the federal government to impose regulations based on environmental concerns dates in large part to the Endangered Species Act signed into law by President Richard Nixon in 1973. That action came shortly after the government banned the use of the pesticide DDT, the broad use of which had been shown to harm animal and human health. By then the population of the bald eagle was in serious decline, and the whooping crane was nearly extinct. The modern environment movement then grew into a diversity of groups focused on air and water quality, wilderness, farmland preservation, energy production, public transit and chemical uses, among others. In many areas industries and user groups responded to urge a balance between environmental concerns and the preservation of jobs and businesses. In recent years the environmental movement joined the international political debate over evidence human activity--especially the production of carbon-based greenhouse gases--has so altered the world as to change the climate. The United States rejected the 1997 international Kyoto Protocol intended to reduce greenhouse gases, and the policy debate in Washington has recently focused on what is known as a cap-and-trade system. That would set a limit on greenhouse gases while creating a market for cleaner industries to sell pollution credits to dirtier ones. Critics call the plan a hidden tax that would drive up costs, and attempts to move the legislation forward have stalled.