CLIMATE IS NOT a static set of weather conditions, constant over eons; rather it varies, sometimes in dramatic ways, over time. The hot climate of the newly-formed Earth gave way to glaciers in a little more than a billion years, an immense time by human reckoning, but not nearly so long by geological standards. Earths climate has alternated many times between hot and cold periods of varying magnitudes. Radiation from the Sun, the ocean currents, rainfall, wind, continental drift, the concentration of greenhouse gases in the atmosphere, volcanic activity, radioactivity in the Earths core, the eccentricity of Earth's orbit around the sun, the tilt of Earth s axis, and photosynthesis all affect climate. Climate has not one, but, rather, myriad causes. Disentangling these causes is ...