What are 'Milankovitch cycles'?

Over the past 2 million years, climate has oscillated between periods of warm climate (glacials) and periods of cooler climate (interglacials). Changes in the shape of earth's orbit help explain these changes. These are known as 'Milankovitch cycles'. 

There are three such ‘Milankovitch cycles’:

1. Axial precession

The angle of tilt on earth's axis changes over a 41,000 year cycle. This causes more or less sunlight to reach the ice caps at the poles.

2. Eccentricity 

Earth's orbit around the sun varies between being a perfect sphere and an ellipse. When this orbit is an ellipse, less sunlight reaches the earth at certain points in its orbit, cooling the climate. 

3. Precession of the equinoxes

Earth does not stay entirely still when it orbits the sun, but rather 'wobbles' slowly on its axis, much like a child’s spinning top. This causes the amount of sunlight hitting the earth to vary.

Combined, these three ‘Milankovitch cycles’ cause the amount of sunlight hitting the earth to change in complex ways over long timescales. They can be seen as the ‘trigger’ for glacials and interglacials operating over the Quaternary period.