Just to keep this astronomical: CO2 is a small fraction of the Earth's atmosphere. Persuing through my Allen's Astrophysical Quantities_ (2000 4ed), pp. 258-260 and 301, here are some numbers: Total mass of the Earth's atmosphere: 5.136 x 10^18 kg Earth, Venus and Mars Top Seven Earth Atmosphere Gases as a percent of the total atmosphere volume Earth (%) Venus (%) Mars (%) N2 78.08 3.5 2.7 O2 20.95 0.0 0.13 H2O 0.03- 0.002 0.03 0.000002 Ar 0.00934 0.007 1.6 CO2 0.000345 96.5 95.3 Ne 0.000018 0.001 0.00025 He 0.00000524 0.0012 0.0 Volume percents can be directly applied to the mass. The Earth percent by mass is: Earth Top Seven Earth Atmosphere Gases as a percent of the total atmosphere weight Earth (%) N2 75.02 O2 23.14 H2O 0.05- 0.000003 Ar 0.0129 CO2 0.000524 Ne 0.0000127 He 0.000000724 In amateur astronomy, we are used to small variations in gaseous composition of a body changing its properties - in stellar evolution. In stellar physics, an older measure of a star's metallicity is its "Z" characteristic - the fraction of all its gases heavier than helium to the star's total mass. About 2% of the Sun by mass are "metals" other than helium and hydrogen. Relatively miniscule changes of a star's metallicity (relative to its total mass) can greatly change in the evolution of a star by, among other things, increasing its solar wind. - Kurt ____________________________________________________________________________________ Do you Yahoo!? Everyone is raving about the all-new Yahoo! Mail beta. http://new.mail.yahoo.com