Possible climatic agencies in the development of post-Glacial habitats

For the meteorologist the elucidation of the reasons for past climatic fluctuations or changes must be a major scientific objective in order that he may be better placed with regard to the future. But before he can attempt a satisfactory explanation of past climatic events, great or small, he must be provided with quantitative data. He must know the magnitude, the extent and the time of incidence of the phenomena. We are acutely in need of more accurate dating of the events whose effects are brought to our notice by botanical evidence. We need to know their spatial extent because we can readily think of events affecting the sun which would be likely to produce immediate reactions over the whole earth. But we can equally readily think of others, such as the freezing of the Norwegian Sea that would very rapidly affect the climate and the vegetation of the coast of Norway but would, at best, make but a slight impression on that of a distant area such as the plain of north China. Accordingly, the meteorologist finds himself immediately interested in the quite notable changes represented by the recurrence-surfaces in the bogs of north-west Europe. Twenty years have passed since van Post (1944) described the results of the many pollen-analytical investigations up to that time as ‘a kaleidoscopic synthesis of larger and smaller climatic waves’. He was disposed to think that period lengths of approximately 1700 years, 800 to 900 years and about 400 or 200 years might be deduced for the undulations of climate. But he went on to say that ‘if the facts appear to agree approximately, then the theory becomes positively dangerous for it may tempt us to wishful thinking that obscures our vision of the empirical realities’. It is with some of these realities that I propose to deal.