Why Do Ice Ages Happen?
The answer is written in the shape of Earth's orbit.
You'll learn about 3 slow changes in Earth's orbit
Each one takes thousands of years
Together, they cause ice ages
Earth & Sun
Earth orbits the Sun once a year. But that orbit isn't a perfect circle — and it changes over thousands of years.
These slow changes in Earth's orbit affect how much sunlight different parts of our planet receive. Over time, this can trigger — or end — entire ice ages.
👆 The 3D view above shows Earth orbiting the Sun. Keep scrolling to learn about the three orbital changes.
The Stretch
Scientists call this: EccentricityEarth's orbit slowly stretches from almost circular to more oval-shaped, and back again. This happens over about 100,000 years.
Think of it like stretching a rubber band — when the orbit is more oval, Earth sometimes gets closer to the Sun, and sometimes farther away.
↑ Watch the orbit shape change above
The Lean
Scientists call this: Obliquity / Axial TiltEarth does not spin straight up. Its axis leans, and that lean shifts between 22.1° and 24.5° over about 41,000 years.
More lean makes summers and winters more intense. Less lean softens the seasons. Today, Earth sits near 23.4°.
↑ Watch the white axis line lean farther from vertical
The Wobble
Scientists call this: Axial PrecessionEarth's tilt doesn't just lean — the direction of that lean slowly traces a circle, like a spinning top winding down. One full cycle takes about 26,000 years.
Watch the dashed circle in the 3D view — that's the path the axis traces. This wobble changes which season happens when Earth is closest to the Sun. Right now, northern winters happen near the closest point. In 13,000 years, northern summers will instead.
↑ Watch the axis tip move along the dashed circle above
When All Three Align
Each of these changes is small on its own. But when they line up in just the right way, they can push Earth into an ice age — or pull it back out.
The key is summer sunlight at 65° north. When summers there are cool enough that winter snow doesn't fully melt, ice builds up year after year. Eventually, massive ice sheets cover much of North America and Europe.
Conduct the Climate
Move one dial at a time to feel its fingerprint on Earth's climate — then play them together.
Current orbital configuration.
Orbit shape — how much closer vs. farther Earth swings from the Sun.
Sun is about 3% closer in January than in July.
Axis tilt — the gap between summer and winter.
Summer sun at 65°N: 177 W/m² (0% vs. today).
When summer lines up with closest approach to the Sun.
N. hemisphere winter near closest Sun — mild winters, cooler summers.
You now understand the 3 orbital cycles that drive ice ages
"The purpose of the theory is to explain the alternation of ice ages and warm periods — not by invoking catastrophes, but through the slow, relentless changes in Earth's orbit."
— Milutin Milankovic, who figured this out in the 1920s with just a pencil, paper, and years of calculations.
Built by Filip van Harreveld — great-grandson of Milutin Milankovic