Matt Hooper said:
1. Human activity produces less than 3% of the total volume of CO2. More than 97% is naturally occurring.
2. CO2 is less than 5% of the total volume of greenhouse gases world wide.
First - carefully read my 2 previous posts in this thread.
According to the book I referenced, the following are reservoirs of carbon on earth:
- Oceans - 40,000 Gt (gigtons or 1 billion tons), most of that in deep water, not close to the surface
- Soil and living things - 2,100 Gt
- fossil fuels still underground - 5,000-10,000 Gt
- atmosphere - 850 Gt (almost all as CO2)
The vast majority of carbon is locked up deep in the earth's crust - like 1.9 billion Gt
There is a seasonal flow of carbon from the atmosphere to plants and back to the atmosphere again as decaying organic matter. Since the northern hemisphere contains the greatest land mass, we see that seasonal flow as a decrease in CO2 in the atmosphere in the north's spring/summer as plants take CO2 from the atmosphere, and an increase in the north's fall / winter as vegetation loses leaves and decay, etc..
This seasonal flow is about 25% of the atmospheric total average CO2 - or about 200 Gt. The amount that fossil fuels currently adds to this annual flow is about 4-5% - like 10 Gt annually (so you are not far off).
About half of that fossil fuel added CO2 is taken up by oceans and increased vegetation - increased CO2 has increased the total balance of vegetation. The remaining stays in the atmosphere, increasing CO2 levels which have risen by about 2.3 ppm per year over the last 50 yrs - from about 300 ppm to about 400 ppm in that time.
This explanation is somewhat simplified. There are other slower processes that also take CO2 out of the atmosphere.