I maybe wrong here and over simplifying but don't volcanos emit more into the atmosphere then we ever could? Did we not learn that when the dino's roamed the planet that most all the land was "tropical" (evidence from coal fields today), then we got hit with an ice age and started to thaw from that. If all was tropical at that time we have not reached the original temps of the earth from that time period. They used to shout global cooling but could not get government funding so they shout global warming and pour tons of our money into it.