Carbon dioxide cannot possibly play the role assigned to it by the pseudo-scientific “community”. First, because its concentration is so LOW, in relation to the other components of the atmosphere, and second, because the compound cannot behave in any known manner to either retain heat or transfer that heat content to any other medium.
Water Vapor has the necessary quantity and the physical characteristics to effect a great deal of heat transfer, both by absorption of the heat (through something called “heat of fusion” and “heat of vaporization”) and the highly effective transfer of that heat to the radiation OFF the earth at nighttime, while that side of the earth is turned away from the sun.
The sun itself is subject to varying amounts of radiation emitted, of which the earth only catches a VERY small portion, the remainder shooting off into the outer reaches of space, to unimaginable distances.
I believe the theory is CO2 acts like the roof of a greenhouse, "trapping" the heat and holding it in. But as you stated, the concentration is too minimal to have any such effect.