Answer:
The 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. The climate over any given period is an expression of all of these nested mechanisms and cycles operating together
Step-by-step explanation:
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 different seasons (NASA 2000).
In addition to multi-millennial glacial and interglacial cycles, there are shorter cold-warm cycles that occur on approximately 200 to 1,500-year time scales. The mechanisms that cause these cycles are not completely understood, but are thought to be driven by changes in the sun, along with several corresponding changes such as ocean circulation patterns (Bond et al. 2001,