Contact transfer (collision/friction) of energy to CO2 causes thermal energy (IR radiation) to be emitted that exists momentarily until it meets a receptive molecule. The increase in density of CO2 molecules (by additions) excited by IR stimulation must cause an increase in convection that causes an acceleration in upward air movement. An increase e.g. in incoming solar energy causes a higher level of surface IR emission in the full IR spectrum that warms the surface air and causes air expansion. The resultant greater distance between molecules causes contact produced IR to survive for longer and forms the bulk what is claimed to be an increase in "downwelling" IR due to the increasing density of CO2.
Expanding and clarifying as best I can, in the surface air layer:
More CO2 in the surface air layer has the effect of lowering the height where CO2 absorbed IR is converted to kinetic or potential energy (by contact transfer to different atoms e.g. nitrogen) practically to extinction simply because a higher volume of CO2 absorbs the IR more quickly. The influence on temperature is virtually nil because absorbing existing energy does not add energy to the system and the acceleration of convection offsets any negligible warming influence due to the decrease in absorbtion height.
In terms of CO2's IR, all surface emissions are absorbed almost instantly. In the overlapped bands absorption is by water vapour (that does not emit IR in CO2's range in the surface layer) as well as by CO2 whose absorbed energy is mostly lost to contact transfer. Some of the CO2-absorbed IR is re-emitted as IR. The volume of the absorbed energy (from surface emitted IR and collision) that is re-emitted as IR reduces with height as the energy transferred by contact gets stored by molecules with a higher energy capacity. At e.g. 100 mtrs the IR emitted due to contact transfer is reduced to a background level where CO2's range of energy radiated by the surface has been taken up by different molecules and added to the higher energy flux where any radiation emitted is beyond CO2's capacity to absorb. The net effect of energy absorption at a lower height is to accelerate convectional transfer of energy upwards, the principal mode of surface air cooling.
Yet despite the acceleration in convection the surface layer warmed so inputs of energy must have come from elsewhere. IPCC science postulates recycling of CO2's IR emissions due to a fanciful increase in the downward flow of IR emitted by the atmosphere. This could only happen in the IR ranges that the atmosphere is transparent to, that CO2 does not emit. Accepting a third factor was responsible for warming, what then happens to CO2? Warming causes the atmosphere to expand (measured, accepted and well documented) and that expansion causes the air to be less dense. This has several effects. It offsets the reduction in the height of absorption by distributing the CO2 molecules through a larger volume. As we know the atmosphere gets cooler with height and this is because molecules are further apart due to the reducing influence of gravity, the time taken for energy transfer between them increases so produced radiation exists longer before meeting a receptive molecule. This means the volume of energy existing as radiation increases. Logic says that the downward flow meets increasingly denser air and is intercepted more rapidly (amplifying convection) than the upward flow that meets thinner air so the bias must be towards the upward flux of radiation. This must also apply in the surface layer. A reduction in density causes molecule IR emission resulting from contact energy transfer to have a longer path to travel before meeting a receptive molecule just as in the thinner air above the surface layer. A consequence of this is that the increase in the time energy spends as IR is visible to measuring devices as a higher volume. Another factor is that with an increase in CO2 volume, more radiation is produced from kinetic and potential energy absorbed by CO2 being emitted as IR. This is not an increase in warming as robbing Peter to pay Paul doesn't increase the combined total. For CO2 to have a positive (warming) influence an increase in energy emission by the surface must occur. A further consequence of surface warming by a third is that more IR is emitted by the ground and by bodies of water. As far as CO2's IR is concerned, this has the effect of increasing the height (altitude) of absorption due to the reduction in density causing the same number of CO2 molecules to occupy more space.
Summing up, where does the radiation emitted by CO2 go? If only CO2 was involved, the radiation would pass back and forth as the CO2 molecules were carried upward by convection. But the surface emitted IR practically vanishes within 100 mtrs. The simple answer is that the energy is passed to molecules that don't emit IR in CO2's range by contact (collisional or frictional transfer) and because the energy passed on to a non CO2 molecule is below the threshold where that molecule emits radiation, the energy is stored until that molecule accumulates enough energy to emit outside CO2's range or pass on by contact transfer. Nitrogen and oxygen are the most probable recipients as water vapour is almost certainly at an energy level where it is not capable of accepting an energy transfer from CO2 due to surface emission of IR in its range. Water vapour accepts energy in much of the LW and some of the SW ranges and stores energy while CO2 doesn't.
Except for molecules close to the surface where contact transfer of energy can happen, I find the transfer of energy back to the surface by radiation in CO2's range highly improbable. This conclusion is supported by physics and logic where the transfer of energy from a cooler object to a warmer object cannot cause the warmer object to be stimulated to a higher level of energy. Except in peculiar circumstances this holds. The peculiar circumstances I can envision is where a molecule of CO2 receives energy and the molecule is moved to an area where the emitting surface is at a lower energy level and is therefore receptive by fast upward air currents on a hillside perhaps.
When water evaporates it absorbs energy. The energy is released when the water vapour condenses to form cloud. Clouds also absorb solar radiation and the residual energy not absorbed by the cloud constituents plus the condensation product is emitted as IR. Emission is biased to the vertical due to the greater breadth to height ratio of clouds. The humidity of the air and the mix of molecules above a cloud regulate the volume of radiation that arrives at the cloud top. The transparency of a cloud dictates the depth of penetration and the volume of absorption. Dense cloud is mostly opaque to UV and visible light (e.g. heavily overcast, dim days) but increasingly transparent as droplet, aerosol and ice crystal density reduces. The brightness of a cloud determines the amount of visible light that is returned to space and that appears to be controlled by ice crystal size. The extinction rate of cloud emitted IR applies as it does to atmospheric CO2 IR emission. IR emitted downwards is more rapidly absorbed and converted to kinetic and potential energy compared to upward emissions.
The tropopause is the next point of interest. The main factors regarding CO2 that come to mind are as follows. Turbulence that is controlled by the direction and speed of air flow in the troposphere versus that of the stratosphere, humidity that makes a large contribution to the energy reserve available to be radiated and CO2 density and the ambient temperature on either side of the pause.
Increasing turbulence increases the probability of molecule collisions while reduced turbulence reduces the probability. Humidity is important because of the energy storage capacity of water vapour, higher humidity means more energy available. Temperature determines how much energy a molecule will release, the lower the temperature the greater the energy amount that can be released, offset by lower molecule density. CO2 volume determines its capacity to emit radiation. Measurements indicate a reduction in outgoing long wave radiation in CO2's IR bands whilst the full spectrum shows an overall increasing volume emitted to space. That is probably due to the reducing humidity of the upper troposphere (also seen in the stratosphere) reducing energy availability at the tropopause. With water vapour volume reducing, it isn't going upwards or sideways so it must be going down, increasing energy availability in the mid to lower troposphere where it would likely cause a temperature increase. At warmer temperatures energy transfer probably favours molecules with a shorter IR wavelength emission than CO2's and so an increase in upward IR in those bands would be expected and is seen. E.g. Harries 2001 Figure 1B, the range ~800-1000 cm-1 shows an increase in outgoing long wave that exceeds the decrease due to GHG's. This observation is also present in Griggs 2004 and Chen 2007. Golovko and Kondranin 2005 state "It was detected (Duvel et al., 2001) that during the past two decades global outgoing longwave radiation increased (considerably energy, emitted from the tropics (Chen, 2002; Wielicki, 2002) and certain region of the northern hemisphere).
As we see in Fig. 1, global LW flux trend was about 4.4 Wm-2 pea decades (Golovko, 2003).
And then the stratosphere. Reducing humidity there could be for the following: cooling due to the Pinatubo eruption causing increased ice crystal formation and crystal enlargement. Cooling reduces stratospheric air current speed and volatility and so tropopause turbulence. Ice crystals would have an easier time passing downwards across the barrier than lighter water vapour. Crystal formation may have been enhanced by GCRs creating conditions for particle formation. Ozone volume has seen recovery and water vapour depletion has likely amplified this (by reducing availability of hydrogen). Ozone's warming ability must be offsetting the cooling amplification due to vapour depletion. Reduced vapour means less stored energy available for transfer by radiation or by contact transfer to emitters such as CO2, much the same as the situation at the the tropopause.
Putting this all together, the negatives versus the positive influences of CO2 are near to balanced, probably around 370 ppm was a point where CO2 changed from a positive warming influence of an insignificant value to a cooling influence of an insignificant value, or neutral. As for CFCs and ozone, and sulphur dioxide as pollution so for CO2 and temperature, mountains from molehills reap rewards disproportionate to the value of the information tendered. Sulphur dioxide reflects visible light back to space, their reduction due to legislation must have been a warming factor. CFCs? Show me where they have significant influence.
(1978-2002 Switzerland and 1978 -2007 NZ) I put the UV (turned upside down) in the ozone graph to show the close relationship. Where is the CFC signature?