OK. Dogtowner, I will take you up on your suggestion, since Pale responded to my request, but for now, I will respond just to the phrase,
"a trace gas with no capacity to absorb and retain energy within an open atmosphere" part of the question. The other parts of the question are fraught with Pale's emotions and will lead to a quagmire of bickering.
Do not take this post as addressing global warming. It's just to give an intuitive perspective of CO2 in the atmosphere, and how such an "airy" thing can be thermally so important?
If the atmosphere had the same density of water, it would compress down to a height of about 34 feet of liquid, or 10 meters. There would be about 3.5 mm of CO2 in this condensed pile of atmosphere. This is a significant thickness of material for CO2 resonant absorption of infrared, especially when you consider that a fraction of a mm of sunscreen can protect you from UV.
This hypothetical pile of atmosphere has a similar thermal capacity of 34 feet of ocean, or a dozen or so feet of earth. That is not trivial since the earth mantel can have a low thermal conductivity, and there are no convection currents.
So the CO2 does have a large capacity to absorb energy, and since it is in intimate contact with the rest of the atmosphere, that hypothetical 34 foot of N2 and O2 acts as the reservoir to retain the energy.
When we consider the free uncondensed atmosphere, the absorption and retention capability are not changed, but new effects such as resonant absorption and re-radiation must be considered in order to understand the thermal energy flow.
In my example, the condensed pile of atmosphere would have predominantly a conductive and convection contact with the earth. The free atmosphere would also include a significant radiation contact.
