There are 4 main gases in our atmosphere:
Proof: http://en.wikipedia.org/wiki/Earth's_atmosphere

• Nitrogen - 78%
• Oxygen - 20%
• Argon - 0.9%
• Carbon - 0.04%

Atomic Mass:
Proof: http://www.webelements.com/

• Nitrogen - 14.0067
• Oxygen - 15.9994
• Argon - 39.948
• Carbon - 12.0107

We now see that the Atomic Mass for Carbon is the LIGHTEST. It is also in the LEAST numbers.

Light Gas		Heavy Gas

As we can see; the lighter gases are more spread out, meaning less resistance to photons. With this in mind we should now be able to see how Carbon can NOT be the cause of Greenhouse Effects.

Why are we blaming Carbon? The least amount, the lightest, the most harmless...

If you put this together with other things such as Carbon Tax (a tax on our lifeform, yes; we are Carbon based life forms), things are just getting scary!