The theory that the ice ages are caused by the variation of the ellipse the earth makes as it goes around the sun due to the gravitational attraction of the larger planets is flawed:
1) It is 20,000 years out of phase
2) Their periods are more than 5,000 years different
3) The 100,000 year ice age cycle has been occurring for only 1.5 million years ... the orbital eccentricity has been around for billions of years.
4) For the first 1 million years of the 100,000 year ice age cycle, the ice ages grew progressively colder, but they have been very similar for the last 500,000 years (the last five cycles).
5) The change in solar energy reaching the earth due to the orbital eccentricity is minimal ... it would take tremendous positive feedback for it to have any affect.
Ever heard of the Milankovitch cycles?
http://en.wikipedia.org/wiki/Milankovitch_cycles