The CYCLES submodel describes the long-term dynamics of the global biogeochemical cycles of carbon (C), nitrogen (N), phosphorus (P) and sulphur (S), their interactions and their impacts on climate change. The model analysis balances past carbon and nitrogen budgets – emphasising the importance of the N fertilisation feedback – and supports the future projections of the fate of anthropogenic emissions of both carbon and nitrogen compounds in the global environment presented in Chapter 16. This chapter focuses on the link between the global cycles of C and N and their feedbacks, providing calculations of global flows of these basic elements and their related compounds within and between the major reservoirs.
Carbon, hydrogen and oxygen, together with the basic nutrient elements nitrogen, phosphorus and sulphur, are essential for life on Earth. The term ‘global biogeochemical cycles’ is used to describe the transport and transformation of these substances in the global environment. In recent decades detailed studies have been carried out on the global biogeochemical cycles of the basic elements, in particular carbon (C), nitrogen (N), phosphorus (P) and sulphur (S) (Bolin et al., 1979; Bolin and Cook, 1983; Schlesinger, 1991; Butcher et al., 1992; Wollast et al., 1993). Figure 8.1 depicts how anthropogenic disturbances of the global cycles of the basic elements of C, N, P and S lead to a variety of global environmental consequences.