This review is devoted to the problem of global carbon cycle. It analyzes the state of the art in understanding the processes responsible for formation of the global carbon cycle; a particular attention is paid to the need of taking into account the dynamics of various global biogeochemical cycles and climate. The latest estimates for components of the carbon cycle, including contributions due to anthropogenic impact, are presented. In particular, it is shown that the anthropogenically caused increase of the CO2 concentration in the atmosphere can hardly be prevented by the increase of compensating natural processes. The urgency of further development of "integral" methods of numerical simulation (system approach) for obtaining reliable estimates of future evolution of the carbon cycle is emphasized.