Climatic change in Chile at around 2700 BP and global evidence for solar forcing: a hypothesis

Abstract

Palaeoecological and geological evidence for changing atmospheric circulation patterns in Chile indicates that equatorward and poleward shifts of the Southern Westerlies (Pacific precipitation source) were an important factor during Weichselian and Holocene climate change. We focus on the evidence and possible causes of considerable climate change in the Holocene at around 2700 BP, which was associated with a steep rise in atmospheric radiocarbon content, indicating an abrupt decrease in solar activity. Climate change may have been caused by the lowering of solar irradiation through two amplifying factors, namely (1) increased cosmic ray intensity, stimulating cloud formation and precipitation, and (2) reduced solar UV intensity, causing a decline of stratospheric ozone production and cooling as a result of less absorption of sunlight. A decrease in the latitudinal extent of Hadley Cell circulation may have occurred with concomitant equatorward relocation of mid-latitude storm tracks, which brought about northward movement of vegetation belts and advance of glaciers.