Milankovitch cycles are quasi-periodic variations in Earth's orbital and axial geometry that modulate the amount and distribution of solar radiation the planet receives over timescales of tens to hundreds of thousands of years. They are the primary drivers of the alternation between glacial and interglacial periods during the Quaternary.
The three cycles
- Eccentricity (~100,000 and ~400,000 years): Earth's orbit varies between nearly circular and slightly elliptical, changing the mean distance to the Sun and affecting total radiation received by ~0.2 %.
- Obliquity (~41,000 years): Earth's axial tilt oscillates between 22.1° and 24.5° (currently 23.44°), modulating seasonal intensity. Greater tilt = warmer summers and colder winters.
- Precession (~26,000 years): Earth's axis "wobbles" like a spinning top, changing which point in the orbit each season falls on. Currently, perihelion coincides with Northern Hemisphere winter.
The key factor is summer insolation at high northern latitudes: when it is low, winter snow fails to melt completely, accumulating year after year to form continental glaciers. Ice-albedo feedback and changes in oceanic CO₂ amplify the orbital signal.
Although Milankovitch cycles operate on timescales of thousands of years, they demonstrate the extreme sensitivity of climate to relatively small changes in radiation. The current warming is far more rapid than any orbital change. See also: climate change.