After reading through Milankovitch Cycles (MC) and the genius behind their discovery, its pretty evident that ice-ages (glacials) in the last half million years are mostly influenced by this phenomenon [Fig. 1] ( Ref - http://goo.gl/piVTym ) albeit with some discrepancies [Fig. 2] (Ref - http://goo.gl/VE3htv ).

One of the observations from the past ice-ages is that, at the end of each ice-age, temperatures rise abruptly accompanied by rising CO2 levels and then both of them drop gradually. [Fig .3]

In an interglacial, if the greenhouse gas effect was significant, earth should stay warm and not heed to much weaker insolation variations due to Milankovitch cycles. [Fig. 4] From another perspective, we could attribute the gradual decline in temperatures after each interglacial to slow assimilation / absorption of CO2 by oceans. In which case, green house gases can have a long lasting impact on the climate.

All this calls for a closer examination of the significance of GH gas emissions, exclusion of other factors preventing faster glaciation after each interglacial and further investigation into the forcings behind rapid rise of temperatures at the end of each glacial.

Update: MC crests represent extreme seasonal variations and MC troughs represent moderate or low seasonal variations. Extreme summers melt glaciers away but extreme winters do not cause intense snowing. (Extremely cold air carries little moisture.) On the other hand, moderate summers melt less snow but moderate winters cause more snowing. Hence, glaciation progresses slowly with accumulating snow from successive winters during MC troughs but glaciers melt away fast in progressively extreme summers during MC crests.

Update: The CO2 system seems to act only as a buffer smoothing out short term variations in insolation but not influencing the trend as such at the observed levels of 180 - 280 ppm.