Synoptic and dynamic aspects of climatic change

Abstract The changing pattern of world climate during the last hundred years is compared with the inferred pattern of the Pleistocene. Relatively cool climates at high latitudes appear to have been associated much of the time with reduced tropical sea‐surface temperatures, a lower snow‐line on tropical mountains, reduced aridity on the desert fringes and increased storm activity along continental east coasts in middle latitudes. Relatively warm climates at high latitudes tend to be associated with the opposite complex of conditions. Considerations of the water balance suggest that a small temperature decrease would be necessary and sufficient for the re‐establishment of glacial conditions in many regions. Increased snowfall would help but is not essential. Synoptic considerations indicate that glaciation was associated necessarily with strong upper westerlies at relatively low latitudes over the continents and probably with vigorous anticyclones over the subtropical oceans. An increased infra‐red cooling rate in the upper air, particularly over the tropics, could produce all the necessary conditions for the establishment of a glacial/pluvial phase. Possible causes for changes in the infra‐red cooling rate are discussed.