The Earth System consists of the solid planet, its atmosphere, oceans, ice and biota. These are coupled via a myriad of complex physical, chemical and biological processes, which occur over a vast range of scales of time and space. Natural variability and evolution are intrinsic to the system’s behaviour. However, recent dramatic surges in human population and economic activity have resulted in mankind becoming a new and potent agent of global-scale changes. For example, after 10000 years of relative stability, there is mounting evidence that human activities are causing global climatic change.