Concept of Back-Radiation
There are two diagrams purported to show the Earth’s Energy Budget, one by NASA, and another by Kiehl and Trenberth, both erroneously showing essentially the same information. The following discussion is based on the NASA diagram, although it applies equally to the Kiehl and Trenberth diagram as well, the numbers being only slightly different. It can easily be shown that both diagrams are internally inconsistent. It is easy to argue that there are fundamental violations of physics, particularly Thermodynamics.
Shown below is the NASA diagram for the Earth’s Energy Budget:
The first problem is with the incoming solar radiation, which is based on a “Flat-Disk” model of the Earth. While this in itself is a problem, it is dealt with elsewhere in the website, will not be pursued further here. So for the following discussion the incident solar radiation, 340.4 Watts/m2, yellow arrow on the left, will just be “accepted” to keep the rest of the discussion more focused on the other internal problems and inconsistencies. Of that incident 340.4 Watts/m2, only 163.3 Watts/m2 are absorbed by the surface of the Earth.
Now the problems begin. The left-most orange arrow in the diagram shows that 398.2 Watts/m2 are radiated away from the surface of the Earth up into the atmosphere. This is more than double what is arriving from the Sun! Obviously this is a fundamental problem, as there would have to be another energy source somewhere for this to occur. But there is none. The diagram does show “back-radiation” directed downward from the atmosphere towards the Earth’s surface. It is argued that the “back-radiation” is supplying the extra energy! Once again, however, this “back-radiated” energy from the atmosphere is still more than is coming in from the Sun. This is not possible, as the atmosphere is passive and does not have an energy source with which to supply heat. The atmosphere cannot warm the Earth’s surface, as discussed in more detail below.
The diagram also shows that the atmosphere is radiating 239.9 Watts/m2 to outer space, and in addition, “back-radiating” 340.3 Watts/m2 to the surface of the Earth for a total of 580.2 Watts/m2. This is well more than 3 times that incident from the Sun, and again, not possible!
There are many more problems with this diagram, discussed extensively in an extremely detailed manner by Charles Anderson: Objectivist Article Link
Just for comparison purposes, below is the Kiehl and Trenberth Diagram, basically the same information with slightly different numbers but still with similar problems:
Both the NASA and Kiehl and Trenberth diagrams of the previous section lead directly to a discussion of “back-radiation”, which has fundamental physics problems. “Back-radiation” describes a belief that IR-Active Gases in the atmosphere absorb long-wavelength IR radiation coming from the warmed surface of the Earth, and then re-radiate, or “back-radiate” this energy back to Earth, further warming the Earth’s surface. There are multiple, fundamental reasons why this belief is incorrect.
The first problem, as mentioned earlier, is that the temperature in the atmosphere decreases with increasing altitude (except for temperature inversions which are not common and needlessly complicate the discussion as very special cases, and will not be pursued here), making the atmosphere at any distance above the Earth’s surface, colder than the surface itself. Thermodynamics will not permit a net transfer of heat from a colder region to a warmer region, without the expenditure of energy. This is common sense, although many, including “lukewarmers”, and skeptics have tried to find ways to wiggle out of this violation.
A pertinent quote from Albert Einstein is appropriate here:
“A theory is the more impressive the greater the simplicity of its premises is, the more different kinds of things it relates, and the more extended is its area of applicability. Therefore the deep impression which classical thermodynamics made upon me. It is the only physical theory of universal content concerning which I am convinced that within the framework of the applicability of its basic concepts, it will never be overthrown.”
As an example common to everyone’s experience, the inside of a refrigerator is cooled by transferring heat from the cold interior to the warmer room. This cannot happen without the expenditure of electrical energy by a compressor to do the required work. Spontaneous transfer of heat from the colder interior to the warmer room is otherwise not possible, as dictated by Thermodynamics.
There is no such similar mechanism, like a “compressor”, of transferring heat from the colder atmosphere back to the warmer Earth’s surface. This is a devastating, and fatal flaw for a belief that “back-radiation” could possibly heat the Earth’s surface.
Problems with Details of IR-Active Gases Producing Warming from “Back-Radiation” (For the reader, this section contains a more detailed science discussion, and could be omitted without too much loss of understanding.)
There are more problems with the concept of “back-radiation” warming the surface of the Earth. It is true that IR-Active gases will absorb long-wavelength IR radiation from the warmed surface of the Earth. But the time for re-emission of absorbed IR radiation is very long relative to the time between collisions with other molecules. Collisions with the more dominant N2 and O2 molecules are very likely to dump the added energy from an absorbed IR photon, mechanically, in billiard ball-like collisions. In the process, these non-IR active gas molecules, primarily Nitrogen and Oxygen, will be heated, but these molecules cannot radiate IR significantly. Thus IR-Active Gases will mechanically lose most of their absorbed energy, and not much energy will remain to be re-radiated.*
For any small amount of re-radiation that might still occur, the direction of re-radiation will be essentially random, with less than 50% being directed back down toward the Earth’s surface. Of that directed downward, some is going to be re-absorbed, and then again be subjected to mechanical losses as described above. Some photons might still end up being re-radiated back down towards the Earth’s surface, and actually reach it, but in diminishing amounts.
Any “back-radiated” long-wavelength IR actually reaching the Earth’s surface still cannot be considered as being absorbed and heating the Earth’s surface, as this would violate Thermodynamics. The physics of this issue is very complicated, and is beyond the scope of the discussion here, but in addition to the Thermodynamics violation, a thorough discussion can be found at: Objectivist Article Linkl. A further discussion of this issue that is common to everyone’s experience follows later – example of a coffee thermos.
*There are many articles detailing measurements of downward IR radiation fluxes, that are claimed to be evidence of “back-radiation”, but these measurements are typically made with Thermopiles, and there are a number of papers critical of the validity of these measurements. At worst case, these measurements should be considered as controversial. In any case, people believing that these measurements are valid, would still have to be able to refute the other fundamental violations of physics “back-radiation” entails, notably the violation of Thermodynamics.
Another issue that might be raised is that it would seem the IR-Active Gases are still heating the other non-IR Active Gases, Nitrogen and Oxygen. This does occur, but with these gases absorbing increased energy, they become more buoyant and float upwards. Their effective density would be lower (as in the bedroom experiment described above), and would thus be carrying the excess energy upwards and away from the Earth’s surface for a net cooling influence, not warming.
We should revisit occasionally what the proper role of government is. As the constitution was a good sense of direction, we need a core set of principles to add in order to deal with the future.
So many want to engineer society, remove risk, assist certain groups, rather than let individuals thrive and raise communities. Why?
Is Democracy where we all "get it good and hard" or is it the best means to a free society?
Should we roll with the special interests, or make the government achieve its proper role, what is that role, and how to do this?
When do deficits and governments become too large?
Government is becoming more elitist while trying to sell corrections to problems it created, what makes this possible?
