CO2 is essential to the balance of Nature and to human survival. However, in excess, it disrupts natural systems in many ways, not all evident and understood, that in turn affect human systems with measurable consequences. The emissions of automobiles and coal-fired powerplants, increasing carbon concentrations in the air, have been shown to have serious consequences downwind with destructive impact on forests, lakes and streams, wildlife, and humans. How does the carbon cycle work? What do we know about these changes? What is the current situation and why is it important? If CO2 is a problem, what can we do to solve it?