10 February 2014

Why backradiation has no warming effect

We are told by greenhouse theorists that backradiation from the sky warms the ground -- 33C warmer than it would otherwise be without the greenhouse effect. In greenhouse theory, backradiation from the sky is recycled and counted again. For example:
NASA "radiation budget", or as I call it: "how to count energy twice"
Some insist that it's not the backradiation that does the warming, it's that light (EMR) is "slowed down" or "trapped" by the greenhouse layer. But even if EMR is trapped optically by the greenhouse gas layer it continues on its merry way in an energy sense.

Even if EMR is trapped by absorption, every photon that is absorbed by the greenhouse gas layer is matched by one that is emitted. This must be so per Kirchhoff's Law, unless the gas layer is changing in temperature. It will change in temperature from time to time, but not overall, not in a way that energy can be gained.
The backradiation paradox

So let's get straight to the backradiation paradox.

In the mini universe above, object A is a thin square that has an internal heat source. Object A is hot and represents the earth's surface in the analogy. 

Object B is an even thinner square that represents our greenhouse gas laden atmosphere which will "trap" and "slow down" EMR and act like an "EMR blanket". Both and B are opaque to EMR (block light).

B has no heat source of its own, it is "passive" (just like earth's atmosphere). These two objects are surrounded by infinite heat sink C maintained at absolute zero. Curiously, according to greenhouse theory, by introducing object B into this universe, object A is warmed, even though object B has no energy source of its own.

First, we take object A by itself emitting heat into a cold universe, and it receives no backradiation:
Situation 1

Next, object B, which starts at absolute zero, and represents the greenhouse gas layer, is introduced. According to greenhouse theory B "blocks" the EMR of A; it "traps" the EMR; B "slows down" the EMR of A; object A now gets warmer because B forms a "greenhouse blanket" on object A.
In the first few moments after B is introduced, because B is cold, there is no change in the EMR received by A.  At first object B absorbs all the EMR it receives and just warms.
Situation 2

As object B warms it starts to emit EMR.  By greenhouse theory object A will now warm up due to the extra backradiation from B, which, according to some, must have some effect.
After a while B equilibrates to its top temperature, which is almost as high as A, and it emits about as much EMR back to A as it receives from it.

The paradox is: in situation 1, A receives no backradiation, yet in situation 2 it receives lots of backradiation from B and yet gets no warmer. How can this be?!  This extra radiation surely must have some warming effect, right?!  According to greenhouse theorists: yes. Object A must get warmer than it was before B was introduced.

According to real life, however, object A isn't warmed at all by B's backradiation. Some greenhouse theorists will ask: isn't that a violation of the conservation of energy?  How can B's EMR have no warming effect?! Short answer: because mutual EMR cancels, it does not add.
Light as a particle

A lot of this misapprehension is the fault of Einstein, who helped re-popularise regarding light as a particle with the notion of photons. Greenhouse theorists are obsessed with always regarding light as photons.  But while, in its interaction with matter, light can act like a particle in some ways, it is correctly regarded as a wave.

If you strip away light's wave-like properties, and represent it as a scalar, such as an arrow, or a moving pool ball, you remove the capacity to see how light can possibly cancel, and why mutual radiation has no warming effect.

Ira Glickstein diagram for greenhouse effect
If you view light as a bunch of pool balls e.g. as Ira Glickstein does in this article, then yes: surely EMR must have some warming effect, in every case! But if you view light correctly, which is as a wave, then it retains its correct properties; waves can cancel, pool balls can not. 
If such mutual EMR didn't cancel, objects would heat without limit, and the universe would end in an infinite heat death. This is the preposterous logical conclusion of the greenhouse effect.

If you represent light as an arrow, as in Trenberth's heat budget diagram above, then yes, it seems as though all EMR must have some warming effect.

It is better to view light via the Poynting Vector. In this way EMR can and does cancel. Light expands as a spherical shell. It expands in all directions equally. Every object in the universe is bathed in a sea of EMR. An simple arrow is far too inadequate to represent this situation.

If you go 1mm below the surface of any object, there is mutual EMR happening everywhere. And yet, surprise surprise, none of it has any warming effect.  All internal fluxes of EMR can have no warming effect. Only the EMR that is emitted (and received) on the outside of an object affect its temperature. And only temperature and emissivity can influence that.

If CO2 could change earth's emissivity, then it could change its temperature. But CO2, being a good absorber, is also a good emitter; if anything, CO2 will increase earth's emissivity and therefore decrease its temperature.

When object B reaches equilibrium temperature it is effectively transparent to the EMR of A. In an optical sense the object is not transparent, but in energy sense it is because the amount of EMR that is absorbed by B is matched by an equal amount of emission.
Similarly, B's EMR has no warming effect on A, just as the earth's sky backradiation has no warming effect upon the ground. Earth's atmosphere is effectively transparent to the ground's EMR in an energy sense, across all wavelengths, even though it is optically opaque at certain wavelengths.
In the thought experiment above let's draw a square around A and B:

If you think inside the square, it seems that backradiation must have some warming effect. The paradox can never be solved until you think outside the square, literally and figuratively, and consider the effect of the infinite heat sink C. 
The infinite heat sink is creating an unrealistic situation, one of no EMR emission, giving rise to the paradox.  Without the magic 0K refrigeration coils in C, it would warm until it emitted as much EMR back to object A as it received.
And even after removing C's cooling coils and C warms to emit as much EMR to A as it receives from it, it still can't warm A. Why? Because EMR from any object which is cooler or the same temperature has no warming effect.

It seems like a paradox that EMR from a cooler/same-temp object has no warming effect, while EMR from a warmer object does. Yet it must be true, if the universe is to avoid an infinite heat death due to mutual radiation. 

This principle is codified in the second law of thermodynamics, where heat can't spontaneously move from cool to hot.
The Tyndall experiment
The thought experiment above is similar to the Tyndall experiment, where the gas target tube is artificially cooled by a water cooling system (V in diagram below).
Heat is removed from the Tyndall experiment and vented to an outside heat pool in a way that can never be replicated by the atmosphere -- earth has no such outside heat pool to vent to, it can only lose heat via EMR to space.
Breakdown of the Tyndall experiment.
In the Tyndall experiment the gas target tube is never allowed to warm, such that it emits as much backradiation to the heat source; so of course it will continue to absorb EMR from it -- more than it emits.
By contrast, the sky could not go on being the unlimited absorber of the ground's outgoing EMR, and not warm. Tyndall's experiment therefore does not, and can not, prove an atmospheric greenhouse effect.

Now, if the Tyndall gas target tube's EMR could warm up the heat source, then you would have something that proves the greenhouse effect. But unfortunately this isn't even tested in the Tyndall experiment, so how can it possibly prove something it was not even designed to measure?


EMR is the universe's great equilibrator of energy. It identifies each object's temperature and transmits that as a signal to the universe. Other objects will respond to the signal and will get warmer according to whether the emitting object is warmer or cooler.  Yet this trivial observation becomes a paradox if you view light as pool balls rather than waves.
The goal of all EMR is to have every object reach the same temperature and emit and absorb EMR in equal amounts. And none of this mutual radiation creates any extra energy or warms the universe as a whole. To think otherwise is to believe in the greenhouse effect.

(Glossary: The terms EMR, electromagnetic radiation, and light are used interchangeably in this post.)

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