> The comparison is being made to the Mesozoic. That is, the Mesozoic was much hotter than the Cretaceous.Um, you do know that the Cretaceous is part of the Mesozoic, right? And that our fossil fuels were not formed during any part of the Mesozoic; they were formed during the Carboniferous, which is part of the Paleozoic, right?
> I can not imagine what you mean when you write "Global temperatures don't correlate ... with the amount of carbon sequestered in fossil fuels."
I mean just what I said: global temperatures don't correlate very well with the amount of carbon sequestered in fossil fuels. Even the amount of CO2 in the air, over the last 600 million years or so, does not correlate well with the amount of carbon sequestered in fossil fuels. If that were true, we would expect to see lots of CO2 before the Carboniferous, very little CO2 from then to now, then a lot now. That is not what we see when we look at the record. See, for example, here:
http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atm...
> if we dig up an amount of carbon that was buried over 500 million years and we burn it all during a 200 or 300 year time span, then presumably we end up with more carbon in the air, at one time, than ever occurred before
And if you look up the actual levels of CO2 in the atmosphere over the last 600 million years or so, you will see that this is not even close to being true. CO2 levels have been in the thousands of PPM during the period between the Carboniferous and now, even though all that carbon was buried in fossil fuels. The current epoch is one of very low CO2 concentrations in geologic terms, even counting the recent increase due to our burning fossil fuels.