I believe this video is a good place to start.
It clearly shows if one takes CO2, and pumps it in a tube, it will block infra-red.
If one can't accept the basic premise, there is no point going further; however, there is a caveat to this particular demonstration (which I'll leave to the imagination for now)
Nevertheless, it demonstrates under controlled circumstances what happens.
[video=youtube;SeYfl45X1wo]http://www.youtube.com/watch?v=SeYfl45X1wo[/video]
What do the skeptics say to this? Yea, Nay? It's real, it's bullshit?