Astronomical climate factors

The theory of the Milankovitch cycles explains long-term cyclic changes in Earth’s orbit, axial tilt, and direction of Earth’s axis. The Milankovitch cycles also influence Earth’s climate.

Obliquity (axial tilt)

The Earth’s axis is tilted at an angle as it travels around the Sun. Within 41,000 years (one obliquity cycle) this tilt angle changes. It can range from 22.1 to 24.5°. Today, the Earth’s tilt angle is at around 23.4°. The Earth’s tilt angle directly influences how extreme our seasons are. The tilt angle changes how much incoming solar radiation arrives in polar regions. A smaller tilt angle causes milder seasons, so larger ice sheets can form.

Eccentricity (orbit shape)

Earth takes 365 days to orbit the sun. However, the shape of the Earth’s orbit is changing from almost circular to slightly elliptic. Over very long timescales, this changes Earth’s distance from the sun. The closer the Earth is to the sun, the more solar radiation reaches Earth. One eccentricity cycle takes 100,000 years to complete.

Precession (wobble)

The Earth’s axis drifts slightly (or wobbles) as it rotates. This also happens in a cycle which is known as precession. It takes around 26,000 years to complete. The Earth’s wobble is responsible for the timing of seasons and the seasonal contrasts between hemispheres.

Figure 1: The Milankovitch cycles are long-term changes in Earth’s orbit, axial tilt, and direction of Earth’s axis. These cyclic changes impact global climate on timescales of several ten thousand years.