Climate, vegetation and forest limits in early civilized times

After reviewing the basic conditions which govern climate and the distribution of climates over the globe, with particular attention to the large-scale circulation of the atmosphere and the variations which it undergoes, this contribution proceeds to consider the sites of the early centres of civilization (particularly those that flourished between about 3000 and 1000 b.c.) and routes of travel by land and sea, some of which stand in a surprising relationship to the natural environment as it exists today. The sequences of variations of prevailing temperature, of sea level, of forest limits and rainfall, cloudiness, etc., and of the levels of great inland waters are reconstructed and lead to a consistent picture of the broad sequence of climatic regimes: for those regimes which differed most from the present-day northern hemisphere maps can be given. Climatic fluctuations on time scales from a decade or two to a few centuries are then considered: fluctuations tending to repeat at 200 or 400-year intervals seem rather prominent.