Milankovitch cycles


Milankovitch Theory describes the collective effects of changes in the Earth’s movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. Milanković mathematically theorised that variations in eccentricity, axial tilt, and precession of the Earth’s orbit determined climatic patterns on Earth, resulting in 100,000-year ice age cycles of the Quaternary glaciation over the last few million years. The Earth’s axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates, more slowly, leading to a 23,000-year cycle between the seasons and the orbit. In addition, the angle between Earth’s rotational axis and the normal to the plane of its orbit moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle. Currently, this angle is 23.44 degrees and is decreasing.

As the Earth spins around its axis and orbits around the Sun, several quasi-periodic variations occur. Milankovitch studied changes in the orbital eccentricity, obliquity, and precession of Earth’s movements. Such changes in movement and orientation change the amount and location of solar radiation reaching the Earth. This is known as solar forcing. Changes near the north polar area are considered important due to the large amount of land, which reacts to such changes more quickly than the oceans do.

Orbital forcing is the effect on climate of slow changes in the tilt of the Earth’s axis and shape of the orbit. These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes. In this context, the term “forcing” signifies a physical process that affects the Earth’s climate.

This mechanism is believed to be responsible for the timing of the ice age cycles.

Today, northern hemisphere summer is 4.66 days longer than winter and spring is 2.9 days longer than autumn. As axial precession changes the place in the Earth’s orbit where the solstices and equinoxes occur, Northern hemisphere winters will get longer and summers will get shorter, eventually creating conditions believed to be favorable for triggering the next glacial period.

Precession is the change in the direction of the Earth’s axis of rotation relative to the fixed stars, with a period of roughly 26,000 years. This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the solid Earth, associated with the fact that the Earth is an oblate spheroid shape and not a perfect sphere.

The arrangements of land masses on the Earth’s surface are believed to reinforce the orbital forcing effects. Comparisons of plate tectonic continent reconstructions and paleoclimatic studies show that the Milankovitch cycles have the greatest effect during geologic eras when landmasses have been concentrated in polar regions, as is the case today. Greenland, Antarctica, and the northern portions of Europe, Asia, and North America are situated such that a minor change in solar energy will tip the balance between year-round snow/ice preservation and complete summer melting.


Leave a reply

Your email address will not be published. Required fields are marked *