We may be due an Ice Age any day now as the earth wobbles through its complex long-term cycles of axial tilt, precession, and eccentricity. Not only are these cycles--on the scale of hundreds of thousands of years--poorly understood, but they intersect with other trends that could have an equally massive effect on our planet. It does not take an Ice Age, however, to change our lives; we are so accustomed to our present-day situation that even shorter term, relatively small changes may create havoc. Such fluctuations, no matter what their size, must be understood at broad scales of analysis...