As far as I now Milankovic cycles are
following CO2 peaks, whatever caused
them. Volcanoes and plate tectonics (Deccan trapps etc.) are usually used for explanation, as well as the rise of plants producing toxic O2 gases for the primoridal anaerobic organisms, thus producing O2 out of CO2 and making CO2 levels fall (and thus decreasing atmospheric temperatures). Still, we know what caused the
recent CO2 rise (century-wise) if we do not put our heads in the sand.
Putting up of monitoring stations gives us exact numbers for detailed dates, but this is not really useful when you want to compare it with more general numbers found in sediments of some million years ago.
On the other hand you have detailed temperature and atmospheric data of a certain day or even hour in the jurassic for example (like a coral calcite piece having been turned around during a storm back then with all kinds of other data), but even this does not give us clues of the overall situation of this particular year. You can only use deep drilling cores for getting a general picture
