Milankovitch cycles are long-term, repeating changes in Earth's orbit and axial orientation. They alter the amount and geographical or seasonal distribution of incoming solar radiation, contributing to long-term climate changes such as glacial and interglacial periods.
This is HL-only content in IB ESS subtopic 6.1 Introduction to the atmosphere, specifically understanding 6.1.7.
How the cycles work
Earth's movement around the Sun varies through three main cycles:
| Cycle | What changes | Effect on solar radiation |
|---|---|---|
| Eccentricity | Earth's orbit changes from more circular to slightly more elliptical, mainly over about 100,000 years. | Changes the difference between Earth's closest and furthest distances from the Sun, affecting the solar radiation received through the year. |
| Obliquity | Earth's axial tilt varies between approximately and over about 41,000 years. | A greater tilt produces stronger seasonal contrasts, especially at high latitudes; a smaller tilt produces milder seasons. |
| Precession | Earth's axis slowly changes the direction in which it points, like a wobbling top, over cycles of roughly 19,000 to 23,000 years. | Changes which hemisphere is tilted toward the Sun when Earth is closest to or furthest from it, altering seasonal intensity. |
The combined cycles change insolation, meaning incoming solar radiation. Summer insolation at high northern latitudes is particularly important: cooler summers allow winter snow to persist, promoting ice-sheet growth. Warmer summers encourage melting.
A common misconception is that Milankovitch cycles alone fully explain glacial cycles. They provide the initial orbital forcing, but feedback mechanisms amplify the climate response. For example, expanding ice increases Earth's albedo, causing more radiation to be reflected and producing further cooling.
Exam technique
For an IB explain question, identify all three cycles, state what physically changes, and connect each change to the distribution or seasonality of solar radiation. Do not claim that Milankovitch cycles explain present rapid warming: current warming is primarily driven by the anthropogenic enhancement of the greenhouse effect.