# Variations in the Earthâ€™s Orbit

As you all know, the earth revolves around the sun along its orbit. Also, it rotates about its own axis. Earthâ€™s axis of rotation is tilted away from the perpendicular to the plane of its orbit around the sun. At present, the tilt away from the perpendicular is about 23.5Â°.

The Milankovitch Theory

Named after the Yugoslav mathematician who first proposed it, the Milankovitch theory is the astronomical or orbital theory of climate variations. The original Milankovitch theory identifies three types of variations in the earth's orbit around the Sun which could act as mechanisms to change the global climate.

The changes include the following.

• Changes in the tilt of the earthâ€™s axis (obliquity)
• Changes in the shape of earth's orbit (eccentricity)
• The shifting of the equinoxes (precession)

The three orbital variations together affect the total amount of sunlight received by the earth, and distribution of that sunlight at different latitudes and at different times.

The following graph shows climatic changes due to orbital variations.

 Changes in climate due to earth's orbit around the sun Source: ace.mmu.ac.uk

It is expected that changes in climate as a result of orbital variations would occur in tens of thousands of years. Indeed, the Milankovitch theory of climate change has been used to explain the global climate of the last 2 million years, with changes between warmer interglacial periods and colder Ice Ages occurring over a 10,000 year cycle (EAE, 2000).

Archaeological records prove that changes in climate patterns influence the distribution of civilizations. One good example is that of the Vikings. About 1000â€“1100 years ago, the Vikings migrated from Scandinavia and moved as far as Greenland. The temperature there was then higher than it is now, enabling them to farm in the region.

They also used it as a passage to North America. Some say that Greenland was actually â€˜greenâ€™ when the Vikings moved in, which is how it got its name. After a few centuries, the temperature began falling, leading to the Little Ice Age (about 1400â€“1850). This caused a decline in agricultural activities, due to which, the Vikings were compelled to move further south to Europe. Thus, the colonies in Greenland ended.

 What if the earthâ€™s axis were not tilted? If the earthâ€™s axis were not tilted in this way, there would be no change of seasons at all. This will lead to continuous summer in one region and continuous winter in another region.