The Milankovitch cycles are named after the Serbian mathematician Milutin Milankovitch who observed/developed/published this in the 1930s. The observation is that the Earth wobbles around it's own axis, and the orbit is not concentric around the Sun (we get closer and further, at different times of the year). These are measured in:
- eccentricity: whether the Earth is orbiting nearly circular or elongated/elliptical. This cycle is affected by other planets in the solar system and has a period of around 100,000 years.
- obliquity: Rotational tilt of the Earth. A greater tilt makes the seasons more extreme. The angle of tilt of the earth’s axis changes from 22.1° to 24.5°. This cycle has a period of 41,000 years.
- The direction of the tilt of the axis changes (precession) on a cycle of 26,000 years.
- axial precession: the direction in the fixed stars pointed to by the Earth's axis, does change over time (axial precession)
- apsidal precession: the Earth's elliptical orbit around the Sun rotates.
The combined effect is that proximity to the Sun occurs during different astronomical seasons. Each of these factors has it's own timeline, and together they can combine to cause magnifying or nullifying effects on climate. This cycle has a far, FAR bigger impact to the Climate than CO2.