Also, even if the sun was not variable, the following would cause changes:


1) Astronomical Causes

11 year and 206 year cycles: Cycles of solar variability ( sunspot activity )
21,000 year cycle: Earth's combined tilt and elliptical orbit around the Sun ( precession of the equinoxes )
41,000 year cycle: Cycle of the +/- 1.5° wobble in Earth's orbit ( tilt )
100,000 year cycle: Variations in the shape of Earth's elliptical orbit ( cycle of eccentricity )


from http://mysite.verizon.net/mhieb/WVFossils/ice_ages.html