Rivers of melting ice form on the Sermeq Kujalleq Glacier in Ilulissat, Greenland, pictured in October 2007 You can't see climate change in action, much to the disappointment of photographers and magazine art directors. Warming is a function of time, and we see it only as time passes. Years go by, we add more carbon dioxide to the atmosphere, temperatures rise, glaciers retreat and deserts expand. One of the essential facts about climate science is that unlike, say, weather forecasting, the farther ahead we look into the future, the more confident we can be of our predictions. So we know that burning enough fossil fuel to raise the concentration of CO2 in the atmosphere to 550 parts per million