ABSTRACT
Following the traditional concept of Hann (1908), climate has been considered as the sum of all meteorological phenomena which characterize the mean state of the atmosphere at any point of the Earth’s surface. This classical definition has proven to be useful for climatology, the descriptive view of climate. However, for understanding climate dynamics, i.e. the processes which govern the mean state of the atmosphere, the classical definition appears to be too restrictive since the mean state of the atmosphere is affected by more than just atmospheric phenomena. In modern text books on climate dynamics, therefore, climate is described in a wider sense in terms of state and ensemble statistics of the climate-system (e.g. Peixoto and Oort, 1992). The climate-system, according to the modern concept, consists of the abiotic world, or physical climate-system, and the living world, called the biosphere. The physical climate-system is further subdivided into open systems, namely the atmosphere, the hydrosphere (mainly the oceans but also rivers), the cryosphere (inland ice, sea-ice, permafrost and snow cover), the pedosphere (the soils) and, if long time-scales of many millennia are concerned, the lithosphere (the Earth’s crust and the more flexible upper Earth’s mantle).
