Yep, it is. If it wasn't for human activities, CO2 concentrations in the atmosphere would probably be decreasing at a very slow rate. (I.e, according to the current estimates, the natural fluxes are nearly in balance. I'll provide a model diagram below; you can find several by Googling "global carbon cycle". The numbers on the arrows may vary slightly in different model presentations.) It's half-size below; click it for full-size.
Yep, it is.
Thanks for the pic, but I was refering to the DOE agency explanation for the numbers. I don't need help with biology or chemistry. The latter was my undergraduate major.
Human activity was responsible for 14 parts of the 100 ppm increase in CO2. Simultaneous human population gains were quite large since 1850.