The Sun and climate

Abstract

Many geologic records of climatic and environmental change based on various proxy variables exhibit distinct cyclicities that have been attributed to extraterrestrial forcing. The best known of these are the changes in Earth’s orbital geometry called Milankovitch Cycles, with periodicities of tens to hundreds of thousands of years. However, many cycles seem to have subMilankovitch periodicities, commonly on decadal and centennial scales, similar to those of known solar cycles. A direct connection between solar irradiance (solar constant) and weather and climate has been suggested for more than 100 years but generally rejected by most scientists, who assume that the effect of solar variations would be small. However, recent satellite radiometer measurements and modeling studies indicate that small changes in total solar irradiance could produce global temperature changes of the magnitude suggested for climatic events such as the Little Ice Age (A.D. 1550–1700).