4. Global Material Cycles

This chapter discusses prominent examples of global material cycles. This is of major significance in order to understand potential perturbations of the natural material cycles caused by man’s production or use of energy. As selected examples, carbon, water, nitrogen, and oxygen cycles will be treated, and in addition aspects of some other material cycles (sulfur, phosphorus, chlorine) as well as interactions of these cycles. The Earth as a closed system is represented by a selection of several open (sub-)systems which exchange material and energy by various processes. Human activities, in many cases, have already had a strong impact on the natural material cycles, often with deleterious impact on ecosystems. In particular the global carbon system with its relatively small natural atmospheric reservoir is under severe threat through anthropogenic carbon dioxide emissions. It is evident that there is a strong incentive to decouple future energy supply from fossil organic material combustion.