As the earth wobbles, its axis sweeps out an imaginary cone in space. This is known as precession of the earth's axis. It takes 21,000 years to complete a cycle through which the rotational axis departs from and then returns to its original position. The climatic intensity of the precessional cycle varies in complex cycles with the orbital eccentricity, which has a cycle of 100,000 years. The history of glaciation during the ice age as gleaned from studies of deep sea cores support the orbital control theory of climate change.
Ice age sediments record orbital climatic influences.
Biological productivity as recorded by the fossil record, the record of large mud deposits caused by melting of ice during interglacials, and terrigenous glacial deposits reflect orbital cycles. It is believed sunspots that occur periodically on the sun's surface may increase solar output slightly. In addition, the little climatic optimum, a period of significant warming in Europe, which began in the year 1050 and lasted more than 100 years, began with an increase in sunspot activity. Although the effect of sunspot cycles on climatic cycles remains theoretical, we now have satellite instrumentation in space which should eventually verify whether or not the sunspot climate theory is valid.