"Richard Alley tells the history of global climate changes as revealed by reading the annual rings of ice from cores drilled in Greenland. In the 1990s he and his colleagues made headlines with the discovery that the last ice age came to an abrupt end over a period of only three years. Here Alley offers the first popular account of the wildly fluctuating climate that characterized most of prehistory - long deep freezes alternating briefly with mild conditions - and explains that we humans have experienced an unusually temperate climate. But, he warns, our comfortable environment could come to an end in a matter of years. ". "The Two-Mile Time Machine begins with the story behind the extensive research in Greenland in the early 1990s, when scientists were beginning to discover ancient ice as an archive of critical information about the climate. " "Alley explains the discovery process in terms the general reader can understand, while laying out the issues that require further study. "--BOOK JACKET.