Natural Climate Cycles
Natural Climate Cycles Climate varies without human influence, and this natural variation is a backdrop for the human-caused climate change occurring now. These patterns hold important lessons for understanding the magnitude and scope of current and future climate changes. Cyclical variations in the Earth’s climate occur at multiple time scales, from years to decades, centuries, and millennia. Cycles at each scale are caused by a variety of physical mechanisms. Climate over any given period is an expression of all of these nested mechanisms and cycles operating together. Millennial Climate Cycles Major glacial (cold) and interglacial (warm) periods are initiated by changes in the Earth’s orbit around the Sun, called Milankovitch cycles. These cycles have occurred at different intensities on multi-millennial time scales (10,000 – 100,000 year periods). The orbital changes occur slowly over time, influencing where solar radiation is received on the Earth’s surface during...