What about carbon monoxide as a tailpipe emission? Is this not a GHG? [Alan]

Carbon monoxide is certainly toxic since when we inhale it, the molecule binds with hemoglobin irreversibly and thus prevents oxygen from reach our tissues.  Therefore, sitting in a parked idling car in the closed garage can be lethal.

However, in terms of its impact on global warming visit:  http://www.ghgonline.org/otherco.htm