Many of the environmental problems with which we still are trying to cope were discovered in the late 20th century. One of the major problems was the degradation of the ozone layer, especially over the poles. Another issue was global climate change; although some CFCs were banned by industrialized countries, other greenhouse gases continued to rise. Although some pesticides such as DDT were eliminated from use in the developed world in response to books like Rachel Carson`s Silent Spring, others continued to be used. Overpopulation put increasing pressure on aquifers and fresh water supplies. The rapid development of countries like China, Brazil, and Russia put increasing pressure on their air and water quality.