Founded in the fourteenth century, Mexico City has been a center for three great civilizations: the Aztecs, the Spanish, and the modern-day Mexicans. But in addition to an imposing political background, its geographical location has assured the city a fascinating ecological and environmental history. Mexico City lies in a basin 7,350 feet (2,240 m) high. It is surrounded by mountain ranges on all sides, and the presence of the extinct volcanoes Ixtacihuatl and Popocatepetl to the east are a reminder that the city lies on an active earthquake fault.

Most of Mexico City's environmental problems are caused by a combination of its geographical location and growing population. In 1900, the population was estimated at 350,000; the rest of the century has seen nothing but rapid growth. Population has leapt from 1,029,000 in 1930 to 4,871,000 by 1960, and then to 12,000,000 in the mid-1970s, and then 15,000,000 by 1981. According to some estimates, Mexico...