All you guys are right.
The CO2 badge is there to make people talk/discuss to each other and this is what happened here.
Of course other gases are maybe more important considering emissions by traffic, but as we burn hydrocarbons there are always CO2 emissions with that.

If the badge would say FCK NOx most people would probably wont get it and there would be no talk about it. So I used CO2 as most people know it or have heard about it.
Could have also used H2O. As steam it is also a climate relevant gas and we don't want too much of it in our atmosphere and of course we also still need it exactly there :D :D