In 2006 Gerard Roe published a paper “In defense of Milankovitz”  which showed a good qualitative agreement between the rate of change in ice volume with Arctic summer melting as measured by maximum insolation at 65N. The ice volume (temperature proxy) as measured by the Benthic DO16 stack is not correlated directly with insolation but instead interglacials are better correlated with the eccentricity cycle.
I have re-anlaysed data from a previous analysis to look for a correlation with the differential of Bentic DO16 data . I use an orbital calculation of maximum insolation at the North pole to look for correlations. The result if shown in Figure 1.
Ruddimen  argues that CO2 changes induced by Ocean temperatures should be seen as a feedback on Ice Volume rather than a cause direct cause. The 41,000 year changes in tilt effect the latitude range insolation. Interglacials seem to occur at multiples 41,000 years. For 2 million years until 900,000 years ago interglacials were in phase with obliquity. Then as the climate continued to cool they switched first to 2 obliquity cycles and then to 3 cycles from 600,000 years ago. Ruddimen argues that the current saw tooth oscillations are caused by non-linear CO2 feedbacks. – see Figure 2.
There is a clear tendency that with Milankowitz increases in summer insolation at the North pole induces decreases in Ice volume. However it can’t explain why 100,000 year interglacial periods have prevailed for the last 600,000 years.
CO2 is therefore not a cause of glaciations, but instead acts as a feedback on the primary cause which is Milankowitz orbital variations in insolation. Summer insolation reduces Ice volume and ocean temperatures rise. This increases CO2 levels in the atmosphere. Any enhanced greenhouse effect is a logarithmic response to solar forcing depending on temperature. It seems to need 3 tilt cycles before the induced CO2 response is large enough to trigger an interglacial.
1) Gerard Roe, In defense of Milankovitch, Geophysical Research Letters, Vol 33, L24703, 2006
2) Lisiecki, L. E., and M. E. Raymo (2005), A Pliocene-Pleistocene stack of 57 globally distributed benthic d18O records, Paleoceanography, 20, PA1003
3) W.F Ruddiman, Ice-Driven CO2 feedback on ice volume, Climates of the Past Discussions, 2 43-78, 2006