I had always taken it as well established scientifically that the hypothesis that the 100000 year Milankovitch cycle, which is due the eccentricity (variation in shape) in the earth’s orbit, is responsible for the ice ages. Surprisingly, there is evidence that this is not the case, as documented in the following scientific paper:
http://ocean.mit.edu/~cwunsch/papersonline/milankovitchqsr2004.pdf
To paraphrase the abstract:
There is no event in the historical record of which more that 20% can be attributed to orbital eccentricity. Even when the time scale of the temperature record taken from an ice core is tuned to match the Milankovitch cycle, the forcing caused by eccentricity does not not explain the overall behavior in the record. All records are dominantly random, with only a small component forced by eccentricity. The probability that the hypothesis is true is likely indistinguishable from chance.
Jim's Jumbler 