Evidence of past weather and climate

In reconstructing the climatic events and regimes of the past, use can be made of an almost limitless variety of kinds of evidence. This chapter will serve as a guide to the main ones. Our aim here is to indicate the potentialities of each, and to illustrate the contributions to knowledge that have come from them, but also to point to some of the precautions that are necessary and the uncertainties of interpretation that remain. ¹ Because nearly all aspects of our environment, and indeed of human affairs, are in some degree or at some points sensitive to weather and climate, the most multifarious traces of past climatic events can be found, given the required insight. Our list of possible sources of evidence therefore cannot be exhaustive. The great variety of the fossil witnesses of the past is important, however, because the often necessarily imaginative interpretations of any one thread of evidence must be treated with reserve until they find support from at least one other, unrelated, field of study and the independent reasoning suggested thereby. Only so can one altogether avoid arguing in a circle, as one may, for example, in conjecturing some climatic event, or sequences of events, in the past to explain a human migration or some change in the composition of the vegetation of a given region and then regarding the hypothesis as proven by its ability to explain all similar happenings around the same time.