ABSTRACT
The world’s climate is forever changing and such changes impact in a multitude of ways upon humans, organisms and landscapes. The changes range from the minor fluctuations within the period of instrumental record (with durations of a few years or decades) to the major geological periods (with durations of many millions of years). The shorter-term changes (Table 2.1) include such phenomena as the Sahel drought and the warm years of the last two decades. The changes with durations of hundreds of years include such events as ‘The Little Ice Age’, which caused alpine glaciers to expand and upland farming to contract between about AD 1500 and 1850. Within the Pleistocene epoch of the last two or so million years there have been larger duration fluctuations-cold glacial and warm interglacial cycles-which lasted for 10,000 to 100,000 years. At an even larger duration scale ice ages such as those of the Pleistocene appear to have been separated by about 250 million years (Figure 2.1).
