Not so long ago, civilization learned that it was no match for just a few degrees drop in temperature. Scientists call it the Little Ice Age--but its impact was anything but small. From 1300 to 1850, a period of cataclysmic cold caused havoc. It froze Viking colonists in Greenland, accelerated the Black Death in Europe, decimated the Spanish Armada, and helped trigger the French Revolution. The Little Ice Age reshaped the world in ways that now seem the stuff of fantasy--New York Harbor froze an...