R.E. Newell President, International Commission on Climate International Association of Meteorology and Atmospheric Physics Water is the active ingredient in the global climatic system, its physical properties ensuring that it plays a major role. Its high thermal capacity provides a mechanism for moderating mid latitude winter temperatures; solar energy is absorbed by the surface layers of the middle latitude oceans in summer and is released to the atmosphere in winter as the ocean cools. The variation of saturation vapour pressure with temperature is the factor which causes oceanic surface...