So, since apparently conversations in here are cyclical in nature..... here is where we started.
"Greenhouse Effect" requires complex molecules in the atmosphere with their higher heat capacity properties. Why? Because they capture radiation from more light/radiation of every part of the spectrum..... hold it.... warmly.... and slowly radiate it..... some of it back to Earth.
The "heat capacity" idea might be confusing to someone with a textbook definition who does not understand the process, the concept. Yes, technically, capture and radiation of radiation/heat is not defined by the term "heat capacity". But the ability to store the energy is. But "heat capacity" is a made up term as defined in the textbooks, and the definition has no direct application to this concept, except as a descriptor in general terms for the idea of capacity for heat storage.
It is the actual capture and storage, and radiation, of energy that is described as "Greenhouse Effect".
At 400 ppm, the amount of heat stored in CO2 in the atmosphere is significant.
Atomic gases like the noble gases have very low "heat capacity" and correspondingly lower factors in heat capture/storage/radiation. Diatomic gases have higher factors. But water and CO2 make up most of the heat capture/storage/radiation. Methane and other hydrocarbon molecules, and SO2, are also powerful factors relative to their abundance.
