[lmilcin]

This is not a complex multi variate problem.

There are two flows of carbon to our atmosphere (and oceans).

One flow is cyclic which means carbon involved in the proces is just changing form constantly but the total amount of it stays relatively constant as it is the same carbon just changing form. The only way this process could alter atmospheric CO2 is if amount of biomass drastically changed. It can't cause infinite rise of atmospheric CO2 as the amount of biomass is finite and relatively small. Even if you burned all biomass and converted it to CO2 it would just dissolve in our oceans causing slight acidification as oceans have capability to dissolve more CO2 than our entire biomass in circulation. There is not enough biomass on Earth to cause long term rise in atmospheric CO2 unless another mechanism is present.

The second flow is steady addition of carbon from outside the cycle, from fossilized stores. This carbon has been unavailable for hundreds of millions of years since times when our atmosphere was very different from todays. Every molecule dug out from sequestered stores ends up in the atmosphere as addition, causing steady rise in CO2. Oceans have only limited ability to buffer long term flows of CO2.