al is that the past 2 to 3*106 years (and more) have been characterised more by change than by constancy. It is equally apparent that climatic change, whether it is a response to natural or cultural stimuli, is complex. It is not yet understood which factors, either singly or in combination, create positive feedback, nor is it understood how they interact. Even further, the indices of climatic and environmental change over the past 2 to 3*106 years have been proxy records, which makes the identification of their underlying causes a formidable task. Having noted these inherent problems, its is possible to objectively evaluate some of the predictions that have been forwarded over time. There are several ways by which climatic change can be recorded and understood. Three of the most well known are quaternary subdivisions based on the terrestrial record, ocean sediment cores, and ice cores. These methods have been used in isolation and also in conjunction with one another. Of particular interest here is the growing body of data that has been collected from ice cores that is contributing to studies of environmental change and aiding correlations between polar, continental and ocean sediment records. The polar ice sheets and those of high tropical mountains are nourished by precipitation from the atmosphere, the composition of which is thus recorded as successive layers of ice accumulate. Such records provide information on environmental change over the past ca. 200K years and base line data from pre-and post-industrial levels for the biogeochemical cycling of metals such as lead. Over the past century, countless theories about climate change have been advanced and tested using the above techniques. First to be highlighted are those that look at climatic change as part of a system of internal adjustments within the climatic system. Several have emphasised changes in the quantity and quality of solar radiation, especially in relati...
