From the tenth to the fifteenth centuries the earth experienced a rise in surface temperature that changed climate worldwide-a preview of today's global warming. In some areas, including Western Europe, longer summers brought bountiful harvests and population growth that led to cultural flowering. In the Arctic, Inuit and Norse sailors made cultural connections across thousands of miles as they traded precious iron goods. Polynesian sailors, riding new wind patterns, were able to settle the remotest islands on earth. But in many parts of the world, the warm centuries brought drought and famine. In his new book "The Great Warming," anthropologist and historian Brian Fagan reveals how subtle changes in the environment had far-reaching effects on human life and how the power of climate change may disrupt our lives today.