Glaciers & Ice Ages

Glacial advance and retreat driven by Milankovitch cycles

Ice ages are driven by Milankovitch cycles — periodic variations in Earth's orbit that alter the distribution and intensity of solar radiation. Three cycles interact: (1) Eccentricity (~100,000 yr): Earth's orbit stretches from nearly circular to slightly elliptical, changing total insolation by ~0.2%. This correlates most strongly with glacial-interglacial transitions. (2) Obliquity (~41,000 yr): Earth's axial tilt varies between 22.1° and 24.5°, affecting seasonal contrast — low tilt means milder summers that fail to melt winter snow, allowing ice sheets to grow. (3) Precession (~26,000 yr): Earth's axis wobbles, shifting when perihelion occurs relative to seasons. When Northern Hemisphere summer coincides with aphelion (farthest from Sun), summers are cooler, favoring ice growth. Ice sheet growth involves positive feedbacks: more ice → higher albedo → less absorption → more cooling → more ice. Glacial periods last ~90,000 years; interglacials ~10,000 years. Ice core records (Vostok, EPICA) show temperature and CO₂ are tightly correlated over 800,000 years.