• Orbit eccentricity: the shape of Earth's orbit varies between round and elliptical every 100,000 years.

  The current rounder orbit yields less variation in solar radiation as the Earth moves around the Sun; the Northern Hemisphere is closer to the Sun during winter.

• Axial tilt: the angle of the tilt as the Earth spins on its axis varies between 22.1° and 24.5° every 41,000 years.

  Larger tilt results in greater extremes between seasons - hotter summers and colder winters.

• Axial precession: the tilt of the Earth's axis of rotation "wobbles" in 360° cycles of 20,000 years.

  Our current tilt toward the North Star points the Northern Hemisphere toward the Sun during calendar summer to receive greater solar radiation.

These alterations of solar radiation affect climate on Earth over geologic time, triggering periods of cold glaciation and warm interglacial times.

The current global warming is not part of any of these cycles.