The stationarity of global mean climate

The observed climate exhibits noticeable fluctuations on a range of temporal and spatial scales. Major fluctuations are often attributed to 'external' influences, such as volcanic eruptions or solar perturbations, which obscure climatic fluctuations associated with natural climatic variability generated by internal processes within the climatic system. Although it is difficult to isolate the role of natural climatic variability within the observed climatic system, coupled global climatic models permit such a discrimination to be made in appropriately designed simulations. Thus, the CSIRO coupled global climatic model has been used to determined some basic characteristics of annually averaged global mean climate within a multi-millennial climatic simulation. Some examination of observed climate is also presented. A stationary climatic state was simulated for periods of up to 10000 years using the CSIRO model, with equilibrium usually being maintained to within 1-2% for all climatic variables investigated. The means by which such stationarity is maintained is analysed and the necessity for rapid negative feedback mechanisms is emphasized. The role of topographically induced climatic features is also discussed. Finally, the implications of the present, presumably greenhouse-related, global warming are considered in the context of the present results. Copyright (C) 2004 Royal Meteorological Society.