[renormalised (Carl)]

I'm quite well aware of all that you have written there. I did climatology/meteorology as part of my first degree...along with remote sensing. The problem is that this question is too large for any one branch of science to tackle on it's own. I can give you all the lowdown on the astronomical side of things concerning what you have written there (i.e. I've read many of the papers), however, you also need to know it from a geological (my area of specialty), climatological, biological and physical point of view as well. There are just so many factors that come in play it's near impossible to account for them all and that's why this sort of study should be multidisciplinary right from the start.

Actually, the last 2.5-3 million years has been the coldest period in Earth history for the last 680 million years. Even during cold snaps in the Devonian and Permian Periods, the overall global temps were higher than what they are now. The big deterioration occurred about halfway through the Oligocene when there was a massive fall in sea levels and temps declined by more than 15-20 degrees from the Paleocene-Eocene Climatic Maximum.

The correlation between obliquity, eccentricity and precessional drift of the semi-major axis of the Earth's orbit and long term climate is reasonably well documented, but not entirely nailed down, yet. But what ultimately effects the climate is that big heat engine in the sky...in other words the change in solar insolation at the Earth's surface over time. Like I said, there are various lag effects which means any change in solar insolation at the Earth's surface won't necessarily mean an immediate shift in climate, but it is the principle driving force behind the changes which may or may not occur rapidly or slowly.