How is CO2 “layered” in the atmosphere? By temperature? Mass? What is the absorptivity of CO2?

Noting that, with a doubling of CO2 in the atmosphere, there are virtually no changes in the capability of the gas to either transfer heat or diffuse it, how does it become such a ’superinsulator’?

The temperature differential between earth’s surface and the average atmospheric temperature indicates infrared radiation from earth to be, at best, insignificant. Most of the heat carried to the atmosphere is by conduction and convection. It is only at the atmospheric/space boundary where the radiant heat transfer becomes significant because of the lack of atmosphere. How can earth’s radiative heat loss be measured accurately with such a wide variance of surface temperatures throughout the globe?