The title of this book implies two questionswhat do we mean by ‘weather’ and ‘climate’, and how do we account for them? As regards definitions, ‘weather’ concerns the conditions prevailing during a particular few hours over a specified area which is perhaps 30 km across, whilst ‘climate’ is the atmospheric character of such an area, shown by records over thirty years or so. We are especially interested in the weather and climate near the surface, i.e. temperature, radiation, humidity, rainfall and wind. The difference between weather and climate is that the latter is the aggregate or composite of the weather. It involves the extremes and variability of the weather as well as average values: floods and droughts at a place do not create a good climate overall. However, any brief definition of climate needs to be greatly expanded to be satisfactory.