So the fact that CO2 levels may have lagged temperature changes in the past is indicative of nothing in and of itself. Nor does the fact that it lagged in the past say anything with respect it the current situation.
The causes of warming and CO2 changes 100,000 years ago are not what is driving the warming engine today.
Two thoughts -
1st - a few posts ago you stated that we did not know what caused interglacial periods, and used that as justification to declare CO2 lagging temperature "irrelevant". Now you state that the causes of past warming and today's warming are totally different (which obviously infers that we understand the causes of both current and historical). Which is it?
2nd ? I'll buy the argument that past CO2 lags aren't relevant to understanding the current warming (although they very well may be if the warming is natural), if you agree that the past CO2/temperature correlation aren't relevant either. After all, the sword cuts both ways.
It all comes down, very simply, to the laws of chemistry and physics that can not be violated. If CO2 levels go up the temperature must too unless counteracted by some other matter of chemistry or physics of which none is known to exist as a factor.
Except you forgot the all important quantification (which is sort of critical here). As I said before, the critical question isn't whether CO2 is a GHG (we know it is). The critical question is how effective CO2 is (at the concentrations we see, or are reasonably expected) at raising temperature. We simply don?t know the answer to that ? if you are aware of some study on this, please pass it along.
