Milankovitch Cycles
Milankovitch cycles are slow, regular changes in the shape of Earth's orbit and the tilt and wobble of its axis that alter the distribution of sunlight over the planet. They pace the advance and retreat of the great ice sheets over the last few million years.
Milankovitch cycles are slow, regular changes in the shape of Earth's orbit and the tilt and wobble of its axis that alter the distribution of sunlight over the planet. They pace the advance and retreat of the great ice sheets over the last few million years.
The Three Cycles: What Changes?
Eccentricity, the stretching of the orbit from nearly circular to slightly oval, varies on cycles of about 100,000 and 400,000 years. Obliquity, the tilt of the axis, ranges from about 22.1 to 24.5 degrees on a cycle of about 41,000 years, and strengthens the seasons at high latitudes. Precession, the wobble of the axis, shifts the season at which Earth is nearest the Sun on cycles of about 19,000 to 23,000 years.
Ice Ages: How Do Small Changes Matter?
The cycles change little in total sunlight, but they alter its seasonal and latitudinal pattern. Milutin Milankoviฤ proposed that cool northern summers allow winter snow to survive and build up into ice sheets. Evidence from deep-sea sediments, published by Hays, Imbrie and Shackleton in 1976, showed the same periods in oxygen isotope records.
Feedbacks: Why Is the Response So Large?
The orbital forcing is modest, so the large swings of the glacial cycles require amplification by feedbacks, including the ice-albedo feedback and changes in atmospheric carbon dioxide. The cycles are central to paleoclimatology and help explain the Holocene interglacial, and they are very slow compared with present climate change.
Milankovitch Cycles at a Glance
| Property | Value |
|---|---|
| Eccentricity | About 100,000 and 400,000 years |
| Obliquity | About 41,000 years |
| Precession | About 19,000-23,000 years |