We stand at the threshold of major changes in the earth's atmosphere, facing serious challenges from acid rain, ozone depletion, and global warming. Continually acted on by natural forces, the atmosphere has always been in a state of flux, but in the last decades the problems of atmospheric change have been gravely exacerbated by pollution resulting from human activities. In this important book, a widely known authority in atmospheric research describes the causes of acid rain, ozone depletion, and global warming and the evidence for each one's recent acceleration, and he provides practical and long-range suggestions for controlling these and other forms of atmospheric deterioration.   In clear and accessible language, John Firor discusses how the emission of sulfur and nitrogen substances into the air leads to acid rain, how the release of chlorine-bearing gases into the air causes destruction of ozone in the high atmosphere, and how the addition of infrared trapping gases to the atmosphere restricts the loss of radiation from the earth and thus leads to a heating of the climate. Firor argues that although it is almost impossible to bring the spread of chemicals into the air to a complete halt, steps to slow air pollution are technically feasible and in many cases economically beneficial. He describes these strategies, cautioning that they must be coordinated with a larger goal of lessening the toal impact human activities have on the earth. According to Firor, we can work toward this goal by attempting to stabilize populations (in the developed as well as the developing world), protect forests, encourage the use of modern energy-efficient technology in Third World countries (and the United States), and reduce poverty worldwide.