Earth’s climate has never been static. It shifts between warm interglacial periods and deep freezes, driven by complex interactions between the atmosphere, oceans, and even Earth’s orbit around the Sun.

Scientists say small changes in the way the Earth orbits the sun hold the key in major global changes in climate, like ice ages.

The Earth's next ice age is expected to begin in about 11,000 years -- unless human-caused global warming disrupts natural cycles.