Observed warming in the atmosphere has been at a rate that would indicate that the climate’s sensitivity to CO2 is (roughly) 1/6th what is expected by the IPCC, and a doubling of atmospheric CO2 would translate to a 0.6 degree increase in world temperature. Being that humans currently account for (roughly) 1/3 of all atmospheric CO2 we would have to double our current CO2 output to have doubled natural CO2 levels; and we would have to increase current CO2 production to (roughly) 4 times current level to see a 1 degree increase in global temperatures.
To put this in perspective, a realistic timeline for this to happen is well over 150 years. Now, if you went back in time and projected what the world would look like today 150 years ago assuming we would use the same energy technologies you would come to the conclusion that the sun would be completely blocked out of the sky by the dark clouds of soot and smog from all the coal and wood fires.
