"Global warming is hardly new; in fact, the very long-term trend began about 12,000 years ago with the end of the Ice Age. Anthropologist Fagan (The Little Ice Age) focuses on the medieval warming period (ca. 800-1300), which helped Europe produce larger harvests; the surpluses helped fund the great cathedrals. But in many other parts of the world, says Fagan, changing water and air currents led to drought and malnutrition, for instance among the Native Americans of Northern California, whose key acorn harvests largely failed. Long-term drought contributed to the collapse of the Mayan civilization, and fluctuations in temperature contributed to, and inhibited, Mongol incursions into Europe. Fagan reveals how new research methods like ice borings, satellite observations and computer modeling have sharpened our understanding of meteorological trends in prehistorical times and preliterate cultures. Finally, he notes how times of intense, sustained global warming can have particularly dire consequences; for example, 'by 2025, an estimated 2.8 billion of us will live in areas with increasingly scarce water resources.' Looking backward, Fagan presents a well-documented warning to those who choose to look forward. Illus., maps." Publishers Weekly (Copyright Reed Business Information, Inc.)