However, the absorption of energy by trace gases is a rather complicated process, as we shall see. We will be using a state of the art radiation model for the earth's atmosphere. We will use the model to calculate the properties of upward shining IR light in the atmosphere as it gets absorbed, scattered, and emitted by atmospheric greenhouse gases and clouds.
Infrared light shines upward from the surface of the earth, brighter if the ground is warmer.
Starting from there, some light in some bands will be absorbed in the next layer up of the air, which will probably be a bit colder than the ground. The layer of air above the ground will also emit IR light according to its temperature and the emissivity of the trace gases in that air parcel. According to Kirchoff's Law, CO 2 will also emit IR light in those bands, and those bands only, stronger when the gas is warmer. Moving upward, the next layer of air will be colder yet, and will have different total pressure and different concentrations of some of the IR active gases, in particular the concentration of water vapor will decrease. Each time you deploy a model run, it will take a minute or so to get your output back on your screen.