How can we trace enhanced co2 atmospheric levels back to human activity? site; ?

There is no carbon dioxide balance in biomass output or input. There is no dynamic equilibrium since carbon dioxide is being released at various rates. Geologically carbon dioxide concentration was very high for a long time and high enough to preclude evolving oxygen breathes until when carbon dioxide was locked up in plant life and oxygen levels raised by cyanobacteria and algae.

Oceans release carbon dioxide or it absorbs less carbon dioxide which causes a rise in temperature which feeds back. More heat is lost through evaporation which is lost to upper atmosphere then land biomass starts to pick up.