Guest Submission: CO2 Doesn't Heat The Atmosphere

Below is a comment submitted in regards to the Global Warming Skeptic Challenge. The challenge ended July 31, 2014 (a year ago), so this is not a submission. In fact, it really wasn't even new in that this claim has been made. However, this person's comment had sufficient valid science in it that I felt compelled to address it in detail. It is still invalid (and I will show why below), but there is some valid science in it.

Guest Submission

FreedomClause

I'm not sure what challenge this would fall under, but, i'll give it a go....let's start with the basics; there is no mechanism by which the IR EM radiation absorbed and then re-emitted by co2 can be absorbed and changed into kinetic heat energy that warms the atmosphere. The theory of global warming as I understand it is dependant on the assumption that the IR EM radiation re-emitted by co2 adds additional heating to the atmosphere, so I should be able to knock the whole theory down with the above assertion...... The atmosphere is made of several different gasses, and each has its own electromagnetic (EM)absorption spectrum. The co2 absorption spectrum does not overlap with any of the major gasses that make up the atmosphere. Nitrogen gas (N2) has its own absorption spectrum, as does oxygen (O2), and all three gasses will absorb EM at different frequencies from one another. In other words, the frequency band of EM that can be absorbed by each of the different gasses is unique. If the atmosphere is irradiated with EM at a frequency within the absorption spectrum of say N2, it will not affect co2 or O2, and the N2 will absorb the EM. N2 reacts to absorption of EM energy by vibrating, thus changing EM energy into kinetic energy. It then collides with other molecules in the atmosphere dispersing the kinetic energy into the atmosphere through convection. This KE is measured as heat energy by thermometers. If co2 is irradiated by EM that is at a frequency within the co2 absorption bandwidth, the co2 will absorb some of the EM. but, co2, even though it is a symmetrical molecule will temporarily form a polar molecule. A dipole moment. when it returns to its symmetrical state, it re-emits EM at the same frequency it absorbed. co2 does not convert the EM into KE, so there is no heating effect. Since the EM re-emitted by the co2 must be at the resonant frequency of co2 and thus within the absorption spectrum of co2, it cannot be absorbed by the other gasses in the atmosphere. so, the IR that is emitted by the earth and absorbed by co2 in the atmosphere will cause no heating effect in the co2, and the IR that is re-emitted by the co2 back into the atmosphere will not be absorbed by the other gasses in the atmosphere, and again there will be no heating effect due to any of the IR within the co2 absorption spectrum. no heating effect means no atmospheric global warming caused by co2. The theory is sunk...I think the thing that caught climate scientists off guard was relying on the simple experiment where co2 is put in a jar with a thermometer, and another jar with just air and a thermometer, and both are exposed to the same IR source. The jar with co2 gets warmer than the air only jar.... the problem with that experiment is that glass shares a bsorption spectra with co2. so the IR emissions from the co2 will heat the thermometer directly through radiant heating, and show additional heating compared with the air only jar. The gasses inside the jar did not get warmer due to co2 changing the IR into KE, or because they absorbed any of the IR emitted by the co2, but the thermometer did get warmer because of the increased amount of IR within the absorption spectrum of the glass. the jar and the thermometer were incorrectly assumed to be isolated from the interactions within, but they were not... they were actively changing the results of the test, giving a false positive... ok, so that's my country bumpkin attempt, did I even come close? lol, I don't even check the e-mail on this account, so i'll probably never find out :)

Response

FreedomClause is correct on several points. But, he is incorrect on others and, most importantly, he is incomplete.

What he says about absorption is correct. When sunlight enters the atmosphere it is eventually either reflected back to space or absorbed by something. Once it is absorbed, it is reradiated back out as IR light. Infrared radiation falls under the classification of 'long wave' electromagnetic radiation (Note: 'electromagnetic radiation' is the precise term for light, including the visible light we see with our eyes, but also including things such as gamma rays, x-rays, uv, IR, and radio). These long waves are too big to be absorbed by O2 and N2 molecules, so they pass right by them. If our atmosphere was nothing but nitrogen and oxygen then we would be like the Moon - blazing hot in the daylight and freezing cold at night. This is because there would be nothing to retain the heat and it would all go straight back out into space. But, we do have other gases in our atmosphere and these gases can absorb IR. These are the gases we refer to as 'greenhouse gases.' The term is a misnomer, but we're stuck with it.

The two principle gases we have in our atmosphere that act this way are CO2 and water vapor. Water vapor is much more efficient than CO2 at absorbing IR than CO2, but it is temperature dependent. Cold air loses its water vapor. That means something must work to warm the atmosphere independently of the amount of water vapor. CO2 fits the job very nicely. It would take a very cold atmosphere in order to lose the CO2 so we have the greenhouse effect present even when the temperature drops.

A good demonstration of the efficiency of these gases can be seen in a dry desert. The temperatures may get very high during the day (depending on the desert - not all deserts are hot), and then experience a very large drop in temperature at night. This is because the air is dry and the heat is not being retained as well.

So far, Mr. FreedomClause is correct. He is also correct when he states gases that absorb IR radiation then reemit it at the same frequency. So, once again, O2 and N2 don't have a chance to absorb any of that heat.

But, we know there is a way to heat the atmosphere because we know it doesn't drop to sub-zero temperatures every time the Sun sets. Somehow, the atmosphere is retaining heat at night and we all know this for a fact. It gets cooler at night, but it doesn't drop 270 degrees C (500 F) as it does on the Moon when the Sun sets. But, if O2 and N2 don't absorb IR, what is that method?

It is actually pretty simple - collisions. Mr. FreedomClause is incorrect when he says CO2 does not convert the IR energy into kinetic energy. In the dense part of the atmosphere where we live, molecules in the air collide with great frequency - typically between 1 and 10 billion times per second. This comes out to an average of about .13 nanoseconds between collisions (a nanosecond is one-billionth of a second). At these high rates, the molecule frequently doesn't have time to reemit the energy as IR and will instead lose the energy to the other molecule via collision. Since the vast majority of molecules in the air (about 99%) are N2 and O2, it is highly likely a molecule of CO2 excited by the absorption of a photon of IR energy will transfer that energy to a molecule of O2 or N2 before it gets a chance to reemit it (many will still have time to reemit before they collide - thank goodness or else we would all have incinerated long ago). This is the process in which IR energy heats up the atmosphere.

A couple of final notes. Remember, when CO2 reemits the photon of energy, half will go generally upward, but half will go generally downward. Meaning, basically half of the reemitted IR radiation is sent back to the surface where it originated and the surface (water, ground, or ice) is very efficient at absorbing IR.

Also, he discusses an experiment consisting of two bottles with thermometers in them. One bottle has a CO2 atmosphere and one has an N2/O2 atmosphere. He critiques that it is the glass bottles that affect the experiment, not the difference in the atmosphere. I would debate that point, but I don't need to. I developed a lab experiment years ago that I used in my astronomy labs. This experiment was pretty similar to what Mr. FreedomClause describes except I used 2-liter, plastic soda bottles. The plastic does not absorb IR well, so this complaint is invalid. The result of having hundreds of students repeat this experiment showed the CO2 bottles consistently warmed up much faster than the N2/O2 bottles.

So, while this was a well-thought out submission, the conclusion is wrong. The fatal flaw is the omission of collisions of greenhouse gas molecules with other molecules once they have absorbed IR radiation. Once that factor is included it is easy to see how the atmosphere is heated.

One final note: None of this is controversial and nowhere did I make reference to manmade greenhouse gases. Everything here is equally valid for the naturally occurring greenhouse effect which makes our planet habitable. But, what happens when you increase the amount of greenhouse gases?