Contemporary climate change may be studied by constructing records of values (daily, monthly and annual) which have been obtained with standard equipment. The instruments must be properly installed in suitable places, carefully maintained and conscientiously observed. The instruments should be exposed in such a manner to ensure that a representative or homogeneous measurement of the climate in question is made (Oldeman, 1987). The concept of homogeneity is discussed further in section 3.2.2. It is not possible to measure the climate per se, but only the individual elements of climate. A climate element is any one of the various properties or conditions of the atmosphere which together specify the physical state of the climate at a given place, for a particular period of time (Linacre, 1992). The most commonly measured element is temperature.