There are many natural processes that can change climate at a local level. The following are processes that affect global climate over periods of no more than a few thousand years:
- Volcanic eruptions can cause short-term climate change by cooling the earth, as the ash blocks out the sun.
- A cycle of precession in the earth's orbit can initiate gradual climate change over a period that lasts 26,000 years. This is too gradual to be perceptible except over the very long term.
- Climate change can also be initiated by the cycle in which the earth's elliptical orbit rotates. Again, this is too gradual to be perceptible except over the very long term.
- The angle between Earth's rotational axis and the normal to the plane of its orbit oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle. This can affect the seasonal variation of climate.
Sun spots have been considered and studied as a possible cause of global climate change, but have since been ruled out as an unlikely cause.
