The 200 Gt of natural CO2 produced per year (mainly fall and winter) is also absorbed for the most part in spring and summer. In the case of the 8Gt or so (4% of 200) that man produces, almost all of it stays. But nature obviously does not know or care about the difference, it is all CO2
What happens is that nature tries to bring the current 400ppm back down to maybe 300ppm which would be short term equilibrium. To do that, nature absorbs a bunch into the ocean. At that point some is sequestered there (precipitates into some form and falls to the bottom). So in a net calculation, the increased CO2 in the atmosphere is all manmade and would be even higher without the ocean absorption.
If man were not around CO2 would have risen naturally due to warming after the Little Ice and prior warming (e.g. Medieval Warm Period) with a lag. But that would amount to a small increase, 5-10 ppm maybe, not the 120 ppm we have seen and not the 2-3 ppm rise per year we measure.
Supposedly the CO2 produced by burning fossil fuels has a lower C13 isotope component than naturally occurring CO2. The argument goes that the ratio of the C13 to C12 isotope has been dropping therefore the increase in the CO2 must be due to anthropogenic sources however that may not be the case Manmade CO2 ?
In addition we know from the ice cores that CO2 increases lag temperature increases by approximately 800 years ( Not vice versa as Gore claimed in his ridiculous movie). Perhaps not co-incidentally the Medieval Warm period was reaching its zenith approximately 800 years ago.
Also there are other views on whether or not all of the CO2 increases are man made. An alternative View of CO2
Hey Palmer, where is the insertion of the consumption variable into the algorithm due to the increase of plant growth and coverage expansion because of the increase of the availability of food (CO2)? Hello McFly!!!!!