[Steve Van Doorn]

"a far greater amount of CO2 is contributed to the atmosphere by human activities each year than by volcanic eruptions. Volcanoes contribute about 110 million tons/year, whereas other sources contribute about 10 billion tons/year.

First Volcanoes contributes from 130 to 230 million tons/year of CO2 not 110 million. Sulfur dioxide is the problem with Volcanoes and warming effects on the earth not CO2. If you factor in what Sulfur Dioxide does, Volcanoes contributes considerably more to global warming then what man does per year.

Second why don't you just say how much man contributes instead of adding in other numbers to what man creates?
Of the 186 billion tons of CO2 that enter earth's atmosphere each year from all sources, only 6 billion tons are from human activity.

again even if the earth doubled the total amount of CO2 we would have a temperature increase of around 1.2 Deg C.

[cogitator]

If you factor in what Sulfur Dioxide does, Volcanoes contributes considerably more to global warming then what man does per year.

Sulfur dioxide (provided it enters the stratosphere in significant quantities) COOLS the global temperature.

Of the 186 billion tons of CO2 that enter earth's atmosphere each year from all sources, only 6 billion tons are from human activity.

The quantities on the left are the anthropogenic contributions. Add up the natural contributions into the atmosphere and out of the atmosphere and see what you get.

The answer indicates why atmospheric CO2 concentrations are increasing.