Weight of the Atmosphere, and "Tons' of CO2 "Pollution"

I have been listening to the reports from Copenhagen, and have noticed in general how the reporters love to estimate how many tons of CO2 "pollution" have been generated by certain activities. One estimate had the CO2 footprint of the Copenhagen meetin at 40,000 tons of CO2. What I have never heard is anyone put that in context. I did some conversions, and estimate the total weight of Earth's atmosphere at around 5 quadrillion (or billion billion if you like) tons. Thus the "natural" weight of the total CO2, at 0.038 percent is around? Fifty trillion tons, by my reckoning! - HLG