# Milankovitch Cycles Milankovitch cycles are slow, regular variations in the geometry of Earth's orbit that change how much sunlight reaches different latitudes and seasons. Named for the Serbian scientist Milutin Milanković, who worked out the mathematics in the early twentieth century, they are the leading explanation for the timing of the [[Ice Ages]]. ## The Three Cycles Three orbital parameters vary on different timescales. **Eccentricity** — the shape of Earth's orbit, from nearly circular to more elliptical — varies over roughly 100,000 years. **Obliquity** — the tilt of Earth's axis, between about 22.1° and 24.5° — varies over roughly 41,000 years and governs the strength of the seasons. **Precession** — the wobble of the axis, which changes which hemisphere faces the Sun at closest approach — cycles over roughly 23,000 years. These do not change the *total* annual sunlight Earth receives by much; they redistribute it across latitudes and seasons. The pacing of glacial cycles in the Paleoclimatology and Ice Cores record matches these periods closely, confirming that orbital geometry sets the rhythm of glaciation. ## Why They Cannot Explain Modern Warming Milankovitch cycles are sometimes invoked to argue that current warming is "just natural cycles." The argument fails on both timing and direction. Orbital forcing operates over tens of thousands of years; the current warming has unfolded over about 150 years, far too fast for any orbital cause. And the direction is wrong: the slow orbital trend over the past several thousand years has been toward gradual *cooling*, the long descent toward the next glaciation. Instead the planet is warming sharply, against the orbital grain, on a timescale orbital mechanics cannot produce. Orbital changes are also too weak on their own to drive the full glacial-interglacial temperature swing. They work by triggering feedbacks — chiefly changes in CO2 released from or absorbed by the oceans, and the ice-albedo feedback described on Climate Feedbacks and Tipping Points. This is the deeper point: even in the natural cycles, CO2 was the amplifier that did much of the work. Today humans are pulling that same amplifying lever directly, which is why the orbital framing is not a counterargument to human causation but a confirmation of how powerful CO2 is. ## Connections Milankovitch cycles explain the timing of the [[Ice Ages]] documented in Paleoclimatology and Ice Cores, and they illustrate the Radiative Forcing and Earth's Energy Balance principle that small changes in energy distribution can trigger large responses through feedbacks. For the field overview, see [[Climate Science]].