What causes Climate Change?Although the basic causes of climate change are still not fully understood, many clues have been collected. Possible causes include:
(1) Tectonic CausesLandmass distribution: Shifting continents (continental drift) causing changes in circulatory patterns of ocean currents. It seems that whenever there is a large land mass at one of the Earth's poles, either the north pole or south pole, there are ice ages.
Undersea ridge activity: "Sea floor spreading" (associated with continental drift) causing variations in ocean displacement.
(2) Astronomical Causes21,000 year cycle: Elliptical orbit of the Earth around the Sun (precession of the equinoxes)
41,000 year cycle: Cycle of the +/- 1.5° wobble in Earth's orbit
100,000 year cycle: Variations in solar energy output
(3) Atmospheric CausesHeat retention: Due to gases such as carbon dioxide and methane in Earth's atmosphere-- the "greenhouse effect"
Solar reflectivity: Due to clouds, volcanic dust, polar ice caps
We can also separately consider climate changes over several different time scales:
1) Long term (millions of years);
2) Medium term (thousands of years);
3) Short term (decades to hundreds of years).
http://www.lakepowell.net/sciencecenter/paleoclimate.htm