Offset it? It is at its lowest in earth's history. No it's not. The source of the graphic you posted even admits that's not true.
Where did all that CO2 that man is creating go?
Read the source you cited. Follow the source it uses, an October 2000 Department of Energy report.
That report has been updated--in 2006--and guess what...it supports what I was saying. Atmospheric carbon dioxide has increased by about 100 ppmv. Radiative forcing (that is, the difference since AD 1750) is nearly 2 W/m2 through 2005. Nowhere in that report does it say that there are natural sources of CO2 increase three times as high as the man-made ones.
Remember that there are the land mass and oceans to consider when you look at carbon dioxide levels. Since both the oceans and land biomass have increased concentrations of carbon, it can't be coming from there, and the atmonspheric concentration was relatively constant in the recent history before 1750. This confirms that it's mainly from our activities.
BTW, where in the DoE report does it claim that 68.52 ppmv is from "natural sources"?
No it's not. The source of the graphic you posted even admits that's not true.Odd then that the graph says that and the text below it does too. The site I got that graph at does say natural additions to CO2 are 68 ppmv.
Greenhouse Gas Concentrations: Natural vs man-made (anthropogenic)
I would post the graph but it doesn't work with the HTML I know. It is on the page linked above. Below you will find your assertion that CO2 was stable before 1750 only holds true if you limit how much history you take into account. There has been a consistent and steady rise for 18,000 years.
2. CO2 in our atmosphere has been increasing steadily for the last 18,000 years-- long before humans invented smokestacks ( Figure 1). Unless you count campfires and intestinal gas, man played no role in the pre-industrial increases.