Milankovich cycle hypothesis is a good one, but there are some major problems with it - not the least of which being that the 23kyr orbital cycle _should_ manifest stronger changes than the 41kyr cycle and that _should_ be stronger than the 100kyr cycle. In reality, the power is reversed. There have been recent solar plasma physics studies that may provide a better explanation for the climate cycles responsible for the Ice Ages than Milankovich. In any event, it is increasingly clear that when looking at CO2, we’re looking at a minor player in climate change.