Only 55 million years ago, our planet had no polar ice caps; in fact, it nearly became a steamy, runaway greenhouse world, with CO2 levels exceeding 2,500 ppm. Then, all of a sudden, something intervened, causing a shift. Atmospheric carbon dioxide began to drop, steadily generating today's world, with ice caps at both poles. But why did this happen? And better yet, could whatever triggered this drastic switch be used to temper today's climate?