3. Milankovitch Cycles

Scientists attribute a series of ice ages to variation in the Earth's position relative to the sun, known as Milankovitch cycles. The Earth goes through regular variations in its position relative to the sun:

  1. The shape of Earth's orbit changes slightly. The orbit varies from more circular to more elliptical in a cycle lasting 90,000-100,000 years. When the orbit is more elliptical, there is a greater difference in solar radiation between winter and summer.
  2. The planet wobbles on its axis of rotation. At one extreme of this 27,000 year cycle, the Northern Hemisphere points toward the sun when the Earth is closest to the sun. Summers are much warmer and winters are much colder.
  3. The planet's tilt on its axis of rotation varies between 22.1º and 24.5º. Seasons are caused by the tilt of Earth's axis of rotation, which today is at 23.5º. When the angle of tilt is smaller, summers and winters differ less in temperature. This cycle lasts about 41,000 years. 

When these variations are charted, a climate pattern of 100,000 years emerges. Ice ages correspond closely with MIlankovich cycles.

Source: USOE OER Resources. Retrieved from http://www.slcschools.org/departments/curriculum/science/documents/4-Earth-Science.pdf on August 28, 2013.