(I think they mean CO2, which doesn't matter either.)
ML/NJ
There is also Methane and Carbon Monoxide which I read in another report. I thought it best to keep it general. I am sure if they look hard enough, they will find some Coke a Cola residue.
Well C02 certainly matters to plants. If the amount in the atmosphere gets too low plants will not grow. Conversly more CO2 will make them grow faster and larger (which is why people will sometimes pump extra CO2 into green houses). The ironic truth is when the "green" movement opposes having more CO2 in our atmosphere, they are opposing having a greener more abundantly alive planet.
I believe carbon in the atmosphere usually combines with the oxygen to take the form of C02...although it might briefly be CO before doing so in some cases. Albeit my knowledge of the chemistry is sketchy at best...I am pretty sure it makes sense to talk about a carbon cycle as opposed to a CO2 cycle.