My curiosity has been aroused by climate change debates, but my physics is inadequate. Perhaps I can get some help. My question is simply: As viewed from the earth surface, what percentage of the area of the visible sky is occupied by CO2 molecules? This could be expressed in simple terms of x% per square metre. I take as basic data: Effective height of atmosphere 10,000 m. CO2 molecules 400 parts per million in volume. (0.04%) Diameter of Co2 molecule approx 3.23 angstroms. So consider a shaft of atmosphere, 1 m x 1m x 10 km high. How many CO2 molecules are in the shaft? What is their average spacing? As viewed upwards from the earth surface, what is the effective area of all the CO2 molecules? The answer is not 0.04% of 1 sq m! And from this, pro rata, if Co2 molecules were considered as perfectly reflecting mirrors, what proportion of heat radiation emitted from the earth (240 W/sm) would be reflected back? I dont think the IPCC will be taking this sort of calculation on board, :) but it would be interesting to know.