Orkney provides the opportunity to examine the control of the earth’s orbit on the global energy budget in two contrasting periods
- the Devonian, between 380 and 360 Myr when the climatic cycles relate to changing lake levels and
- the Quaternary Ice Age, when ice sheets advanced and retreated according to changes in temperature and snowfall
The driver for these variations is the amount of solar radiation (insolation) reaching the surface of the Earth. Insolation changes with the positioning of the Earth and Sun, as well as changes in the orbital parameters of the Earth.
Milankovitch observed three fundamental cycles:
1. The orbital eccentricity
2. The obliquity
3. The precession of the equinoxes
The combined influences produces a complex pattern of insolation, resulting in increased seasonal contrast in one hemisphere of the Earth and reduced contrast in the other.
1. The eccentricity of the orbit of the Earth around the Sun varies from circular to elliptical giving a change in seasonal incoming solar radiation of about 30%. This cycle takes 95,800 years.