SIR Napier Shaw, a onetime director of the British Meteorological Office, remarked on one occasion that "every theory of the course of events in Nature is necessarily based on some process of simplification of the phenomena, and is therefore to some extent a fairy tale."
Thus it is with trying to classify a climate: meteorologists over the years have attempted various ways of devising a simple system of descriptive terms to describe the different climatic regions of the world, but with only limited success.
The ancient Greeks were the first to try their hand. They were familiar with the hot, arid lands of Arabia and North Africa, the warm and relatively moist countries of southern Europe, and the colder northern regions, so it was natural for them to place the emphasis on latitude, and on the inclination of the rays of the noon-day sun.
They divided the world into climatic zones which were horizontal strips on the map, each classified with reference to the angle of the sun at that latitude. Indeed the word climate comes from the Greek word klima, meaning "slope" or "incline". It was an oversimplification, but a good first approximation nonetheless.
The system of climate classification probably most widely used today, albeit with a few modifications, is that of the German climatologist Valdimir Koppen. His method, devised in the 19295, is based on the assumption that vegetation responds to climate, and that plants can therefore be used as meteorological indicators. Koppen identified five main climatic regimes, to each of which he assigned a designating letter:
(A)Tropical rainy, (B) Dry, (C)Rainy with warm winter, (D) Rainy with cold winter, and (E) Polar.
Each of these categories is further sub-divided according to its typical rainfall patterns, giving a total of 11 different classes of climate. Each individual climatic regime is then represented by a combination of letters - like Af for "rain forest", or Et for "tundra".
In more recent times there have been attempts to devise more sophisticated methods of climate classification based on available climatological statistics. Perhaps the best known is that proposed by the American geographer, C. Warren Thornthwaite, which uses values of seasonal rainfall and average temperature, processed according to complex mathematical formulae to arrive at a numerical index for each location.
The magnitude of the index allows each local climate to be placed into one of 32 different classes or alternatively, allows an expert to visualise the local weather very clearly once he is given access to its magic number.