[Sharlin]

You’re confusing net and gross carbon release. In a balanced system, on average 100% of released carbon will be reabsorbed, by rocks, oceans, and (to a fairly small extent) plants, making the net rate of change of atmospheric carbon practically zero. Then humans began to meddle with things, starting to introduce extra carbon to the atmosphere from outside the primary carbon cycles. Carbon fixing rate has also increased to compensate (leading to further problems like acidification of the oceans) but has not been able to keep up, especially because the excess anthropogenic release rate has been growing exponentially. Thus the net release rate has been slightly above zero for the past 200+ years, and it’s starting to show.