[Right Wing Professor]

2% of the atmosphere is CO2.

In your bong, maybe.:-) 0.035% of the normal atmosphere is CO2.

[ChildOfThe60s]

Dude, I knew that bong would get me into trouble. I stand corrected.

According to:
http://www.uigi.com/air.html
it is .038%, essentially the same as your claim.

I guess that makes this a case of me being right even when I am wrong. Man's output of CO2 is even less of a potential influence than I said. I am incorrect, but accurate (beat that CBS!)