(continuation)
Yes, if you used an insulator you could retain more heat than you would if you had no insulation. But the "balanced" energy budget that you keep referring to requires that those reflectors cause that heater to radiate more than 200 watts, over 100 of which you are not paying the electric company for because you would be creating energy.
Before you begin to try to pass CO2 and the other greenhouse gasses off as insulation, however, perhaps we need to look at what the science dictionary says is and is not an insulator.
insulator - A material or an object that does not easily allow heat, electricity, light, or sound to pass through it. Air, cloth and rubber are good electrical insulators; feathers and wool make good thermal insulators. Compare conductor.
In order to be an insulator, a material must prevent or retard heat (or radiation in this case). CO2 does not retard IR radiation. Of course it absorbs IR in a very narrow wavelength, as indicated by its absorption spectra. Its emission spectra however is precisely the opposite of its absorption spectra which tells us that it emits exactly as much radiation as it absorbs. IR passes through CO2 molecules at or very near the speed of light and is not slowed down in the least. That narrow wavelength of IR that does get absorbed and emitted, however, does get scattered and scattering IR serves to cool, not warm.
Now, lets take a look at what a conductor is:
conductor - A material or an object that conducts heat, electricity, light, or sound. Electrical conductors contain electric charges (usually electrons) that are relatively free to move through the material; a voltage applied across the conductor therefore creates an electric current. Insulators (electrical nonconductors) contain no charges that move when subject to a voltage.
Clearly, CO2 is a conductor. That is, it facilitates the exit of the narrow band of IR that it absorbs on its way out of the atmosphere. CO2 has no capacity to hold or store heat. There is one molecule in the atmosphere that can actually store heat but alas, there is no political advantage to demonizing that gas because we can do nothing about it. That gas is water vapor.
But the atmosphere does not act as an insulator. It is a conductor.
It is supposed to show that you can not get the heater to radiate more than 100 watts no matter how many reflectors or how much insulation you use. You are never going to get energy out of that heater that you don't have to pay the power company for. In the so called "balanced" energy budgets, however, you must create an additional 332 watts of energy by reflecting it from the cooler atmosphere down to the surface of the earth where it is absorbed and re emitted. Your balanced energy budget requires that the surface of the earth radiate more than 300 watts per square meter above and beyond that which it absorbs from the sun. It is balanced at the expense of the laws of physics. The numbers on trenberth's energy budget are the basis for the energy budgets for NASA, GISS, the IPCC, etc. and they are all fraudulent.
Of course, the atmosphere doesn't act as an insulator.
and no, you can'tget more than 100 watts out of a 100 watt heater.
As for the energy balance, both the chart you posted and the NASA site I went to showed that there is such a balance.