Natural variations in global temperatures may occur in roughly 500-year cycles:
The primary cause of variations in global temperature is the cycles of the sun and Earth’s orbit about the sun. In addition to 40-year cycles and 500-year cycles, other temperature cycles include:
- 21,000 – year cycle: Elliptical orbit of the Earth around the Sun (precession of the equinoxes)
- 41,000 – year cycle: Cycle of the +/- 1.5 degree wobble in Earth’s orbit
- 100,000 – year cycle: Variations in the shape of Earth’s elliptical orbit (cycle of eccentricity)
