We're accustomed to thinking of our planet as stable, steady, and solid. In reality, Earth is dynamic. Our climate is changeable. The history of Earth's climate has been marked by many ice ages and warm spells, some measured in millenia and others in centuries. You may be surprised to find that there are some patterns in this changeability, though.
Climate change seems to be cyclical.
A Serbian mathematician named Milutin Milankovitch was intrigued by this puzzle of climate change, and in the 1930s he presented a theory that might explain it. Milankovitch studied climate records, noting differences over time. He theorized that global climate change was brought about by regular changes in Earth's axis, tilt, and orbit that altered the planet's relationship to the Sun, triggering ice ages. Every 22,000 years, Milankovitch calculated, there is a slight change in its wobble. Every 100,000 years, there is a change in Earth's orbit about the Sun.