In this persuasive volume, Young (The Blue Planet, 1983) presents clear arguments for the present dangers of acid rain, ozone destruction, and, maybe, global warming. The ""maybe"" is because Young finds the historical data on global temperatures as complex and confusing as most, what with ice ages, interglacials, and anomalous periods of coolness or warmth. When those data are combined with current speculations about whether the greenhouse effect might not be offset by dirty skies that limit solar heating, who can say what will happen? But on the other counts, Young is firm. To set the stage, she reviews the facts of atmospheric science, including the heroic efforts of the first balloonists. This is familial ground for Young, whose earlier books waxed eloquent on the charms of the earth seen from above. Here, she describes the various ""haloes"" of troposphere and stratosphere that circle the globe and, along with myriad other variables (the inclination of the axis, precession of the pole, etc.), help explain wind and weather. The last chapters delineate precisely how chlorofluorocarbons and other compounds have made holes in the ozone; how the burning of sulfur-rich coal in England, for example, is destroying lakes and evergreen forests in Scandinavia, and even how the burning of African savannahs (to encourage the growth of grasses) is blowing acid rain onto the virgin forests of equatorial Africa. Given the global problem, the cure must also be global. Young argues, calling for international agreements on ozone protection and on control at the plant of emissions from fossil-fuel burning. Reforestation is a must, along with more efficient cars and appliances. Young argues for alternate energy sources as well, such as solar cells, even nuclear fusion. To make all this happen, Young suggests, Americans need to understand that their deceptively small electricity bills are due to subsidies that ultimately come out of taxes. A good point among many in this generally excellent exposition.