Earth's Orbital Clockwork
Earth's orbit is not a fixed ellipse — it breathes. Three overlapping cycles reshape our path around the Sun: eccentricity stretches and rounds the orbit over ~100,000 years, obliquity tilts Earth's axis between 22.1° and 24.5° over ~41,000 years, and precession wobbles the axis like a spinning top every ~23,000 years. Together, these Milankovitch cycles redistribute sunlight across latitudes and seasons, setting the tempo for ice ages.
The Insolation Key
Milutin Milankovitch spent decades hand-calculating how orbital variations change solar radiation at each latitude. His key insight: what matters is not total annual sunlight but summer insolation at high northern latitudes. When northern summers are cool enough that winter snow survives year-round, ice sheets nucleate and grow. The albedo feedback — ice reflects sunlight, cooling the surface further — amplifies the orbital signal into continental glaciation.
Spectral Proof
The theory languished for decades until deep-sea sediment cores provided a climate record spanning millions of years. In 1976, Hays, Imbrie, and Shackleton performed spectral analysis on oxygen isotope data (a proxy for ice volume) and found unmistakable peaks at 100, 41, and 23 thousand years — precisely the Milankovitch frequencies. This was the smoking gun linking orbital mechanics to climate change.
The 100 kyr Problem
Despite the theory's success, a puzzle remains: the dominant ice-age rhythm is ~100,000 years (matching eccentricity), yet eccentricity produces the weakest insolation change. How does a feeble forcing dominate the climate response? Proposed explanations include nonlinear ice-sheet dynamics, CO2 feedbacks, and stochastic resonance. This simulation lets you explore the orbital parameters and see how subtle insolation changes at 65°N trigger the dramatic glacial-interglacial swings recorded in the geological record.