Global Warming?

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.

Earth doesn't rotate perfectly like a wheel about an axis; it spins like a wobbling top. 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. Its almost circular orbit becomes more elliptical, taking Earth farther from the Sun. And finally, Milankovitch discovered, every 41,000 years there is a change in the tilt of the planet's axis, moving either the Northern or Southern Hemisphere farther from the Sun. 

These cycles mean that at certain times there is less sunshine hitting Earth, so there is less melting of snow and ice. Instead of melting, these cold expanses of frozen water grow. The snow and ice last longer and, over many seasons, begin to accumulate. Snow reflects some sunlight back into space, which also contributes to cooling. Temperatures drop, and glaciers begin to advance.