photosynthetic machinery. If one wants to go by with the simple model of atoms based on positive-negative charge, one might think that the distribution of the nuclear charge in 13C gets polarised more to the one side of the nucleus so the electrons on that side would be on thighter orbits than usual. In the case of CO2, the explanation of 12preference in plants in #42, would mean that the central C in O=C=O rotates horizontally along the long axis of the molecule while the slight excess of negative charge would be located perpendicular to it, making the O=13C=O look a bit fatter than O=12C=O. I'm pretty sure there are better explanations about this within physical chemistry, but I'm not that advanced in that discipline. "1st, I see that Mr.Curtis confirmed my point that lower C13/C12 ratio is NOT unique to burning FFs.("just as the combustion, DECAY, or RESPIRATION of (or by) biomass will add more C12? than C13 to the atmosphere" So he tacitly agrees that the CAGW "unique FF fingerprint" meme is false. He argues that the biosphere cannot be the source of the increased CO2 in the atmos b/c "PHOTOSYSTHESIS WILL TAKE OUT MORE C12 THAN C13 (his bold) by exactly the same amount per tonne of biomass generated"" "While that is true, Curtis's argument fails in his next statement:"Given that the total amount of biomass in the world is stable...". That is a false assumption, similar to the false CAGW assumption that climate is stable except