The Astronomical Connection: Milankovitch Theory
Early in the 20th century, a Serbian geophysicist and astronomer name Milutin Milankovitch worked out mathematically the subtle changes in Earth’s orbital cycles, involving cyclic changes in its rotational axis and its revolution around the Sun changes. Three orbital forcing cycles include the eccentricity of Earth's orbit, Earth's axial precession (41,000 years), precession of equinoxes (21,000 years)(illustrated in Figure 9.34). Eccentricity refers to the change of earth's orbit from being round to more elliptical in shape this cycle repeats every 95,000 years. When it is more elliptical the Earth has shorter, warmer summers and longer, colder winters. Axial precession refers to the wobble in the tilt of Earth's axis. The tilt of the axis changes from about 21.5 to 24.5 degrees on a cycle lasting about 41,000 years. The precession of equinoxes refers to which hemisphere is facing the sun when it is closest to the sun. Right now, the earth is closest to the sun during the winter in the Northern Hemisphere. These cycles impact how much incoming solar radiation that the regions of the earth receive over time, most important being where land is exposed in high latitude regions (where continental glaciation has taken place repeatedly). Milankovitch showed that these cycles combine or interfere with each other in the amount of energy the polar regions receive through time. Climate investigations in the last century have shown that Milankovitch Cycles closely correspond with the record of global temperature changes retrieved from ice cores, marine sediments, and other sources.
However, Milankovitch Cycles alone don't explain the onset of the ice ages.