Causes: Milankovitch Cycles
Earth’s wobbly orbit
Changes to Earth’s climate over long periods are caused by the natural variations in the intensity and distribution of solar radiation that reaches the planet. These variations are due to Earth’s eccentric orbit around the Sun (Fig. 1), it’s tilted axis (Fig. 2), and it’s wobble (Fig. 3). Each of these cycles occur over different time frames so they have different levels of impact across time.
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Fig. 1: Earth’s eccentric orbit around the sun (100,000 year cycle). When Earth is further away from the sun it receives less solar energy and therefore less warmth.
Fig. 2: Earth is slightly tilted (40,000 year cycle). As most of the land mass is now in the Northern Hemisphere (see the link in the menu ‘How to start an ice age’), when less of that hemisphere is facing the sun in winter, it receives less warmth.
Fig. 3: Precession (26,000 year cycle). This wobble can either add to the cooling or warming depending on which phases of the other two cycles that Earth is in (Figures 1 and 2).
The cycles are named after the geophysicist and astronomer Milutin Milanković, who developed James Croll’s theory that these cycles were the main climate forcings (Videos 1 & 2).
When the Milankovitch Cycles are taken into consideration Earth should have been slowly cooling over the past 9,000 years. Instead, the Earth is warming delaying the next glacial epoch by at least 50,000 years (Video 2 & Fig. 5).
The gradual warming offset the cooling because people developed agriculture. So on balance, the climate remained relatively stable until the Industrial Revolution in the 1800s when we started burning huge amounts of fossil fuels. This rapid anthropogenic (man-maded) forcing has rapidly outweighed the gradual cooling effect of the Milankovitch Cycles.
Recent evidence (2024) shows that there is a subtle gravitational effect of the planet Mars on Earth’s multi-million year climate cycle, as the Martian orbit takes its closer to Earth.
The effects of astronomical cycles also impacts oceanic currents that in turn, influence climate change in a feedback effect.
