the greenhouse effect and the principle of re-radiation
August 11, 2011 in climate change
Quote from Wikipedia (on the interpretation of the greenhouse effect);
“The Earth’s surface and the clouds absorb visible and invisible radiation from the sun and re-emit much of the energy as infrared back to the atmosphere. Certain substances in the atmosphere, chiefly cloud droplets and water vapor, but also carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, and chlorofluorocarbons, absorb this infrared, and re-radiate it in all directions including back to Earth.”
I am watching with some amusement a lot of scholar discussions on the green house effect as I realised again that the people that I encounter on most scientific blogs don’t understand the chemistry principle of absorption and subsequent re-radiation. In fact very few people do understand it because if they did they would have raised the alarm bells ringing long time ago. But they all got stuck at Tyndall and Svante Arrhenius. … They know that CO2 (carbon dioxide) “absorbs” in the 14-16 um region. Most people think that what it means is that the molecules absorbs photons here which then subsequently get transferred as heat to neighbouring molecules. Then it absorbs again, and so on, and so on…and all the absorbed light is continuously transferred to heat…Although this may happen up to a certain saturation point as soon as the light or radiation hits on the gas, that is in fact not what is causing the heat entrapment.
I happen to be familiar with spectrophotometry. You have to understand what actually happens when we put a beam of light of certain wavelength on a sample of liquid or gas. We have various spectrophotometers that can measure the various ranges of UV-visible -IR etc. Usually you have the option to vary the wavelength of the beam of light, either manually or automatically. If the gas or liquid is completely transparent, we will measure 100% of the light that we put through the sample coming through on the other side. If there is “absorption” of light at that specific wavelength that we put through the sample, we only measure a certain % on the other side. The term “extinction” was originally used but later “absorption” was used to describe this phenomenon, meaning the light that we put on was somehow “absorbed”. I think this was a rather unfortunate description as it has caused a lot of confusion since. Many people think that what it means is that the light of that wavelength is continually “absorbed” by the molecules in the sample and converted to heat. If that were true, you would not be able to stop the meter at a certain wavelength without over-heating the sample, and eventually it should explode, if the sample is contained in a sealed container. Of the many measurements that I performed, this has never ever happened. Note that in the case of CO2, when measuring concentrations, we leave the wavelength always at 4.26 um. Because the “absorption” is so strong here, we can use it to compare and evaluate concentrations of CO2.
The best way to experience re-radiation for yourself is to stand in a dark forest just before dawn on a cloudless night. Humidity must be high. Note that water vapour also absorbs in the visible region of the spectrum. So as the first light of sun hits on the water vapour you can see the light coming from every direction. Left, right, bottom up, top down. You can see this for yourself until of course the sun’s light becomes too bright in the darkness for you to observe the re-radiated light from the water vapour. This is also the reason why you will quickly grab for your sun glasses when humidity is high, because even with the sun shining for you from your back and driving in your car, you can feel on your eyes that the light from the sun is re-radiated by the water vapor in the atmosphere.A third way to experience how re-radiation works is to measure the humidity in the air and the temperature on a certain exposed plate, again on a cloudless day, at a certain time of day for a certain amount of time. Note that as the humidity goes up, and all else is being kept equal, the temperature effected by the sun on the plate is lower. This is because, like carbon dioxide, water vapour has absorption in the infra red part of the spectrum.
We can conclude from all these experiments that what actually happens is this:
in the wavelength areas where absorption takes place, the molecule starts acting like a little spherical mirror, the strength of which depends on the amount of absorption taking place inside the molecule. We may assume that at least 50% of a certain amount of radiation is sent back in a radius of 180 degrees in the direction where it came from. (However, because the molecule is very small and therefore might behave more or less like a sphere, it could be up to ca. 62,5% ). This re-radiation in the sun’s spectrum and in the earth’s spectrum is the cooling effect, or warming effect, respectively, of a gas hit by radiation. An effect that is very similar to this, is also observed when car lights are put on bright in humid, moist and misty conditions: your light is returned to you!!
Unfortunately, in their time, Tyndall and Arrhenius could not see the whole picture of the spectrum of a gas which is why they got stuck on seeing only the warming properties of a gas (i.e. the closed box experiments). If people would understand this principle, they would not singularly identify green house gases (GHG’s) by pointing at the areas in the 5-20 um region (where earth emits pre-dominantly) but they would also look in the area 0-5 um (where the sun emits pre-dominantly) for possible cooling effects. If you really want to understand what happens in the atmosphere, this rough graph / representation (on a cloudless day) is very important:
- never mind the fact that the amounts of radiation heat from the sun’s 5525K and 210-310K from earth displayed, are completely out of proportion -
just see how the absorptions that are apparent in the spectra of the individual components of the atmosphere affect the outgoing radiation of earth and see how they affect the incoming radiation. For example, let us look at the absorption of ozone at between 9-10 um? It makes a dent in earth’s outgoing radiation at 9-10. In other words what happens: Radiation from earth of 9-10 goes up, hits on the ozone, most of which is high up in the sky and which is already absorbed to capacity, and therefore a great percentage (at least 50%, probably more) is sent back to earth, leading to entrapment of heat, leading to delay in cooling, leading to a warming effect. Also look at water vapor and CO2 around 2 um and see how that makes a dent in the incoming solar radiation. Notice that the ozone shields us from a lot of sunlight by absorbing and re-radiating in the UV region. In fact, if you really grasp what you are seeing in this graph/ representation (from a cloudless day), you would realize that without the ozone and CO2 and H2O and other GHG’s you will get a lot more radiation on your head. In fact, you would probably fry.
For comprehensive proof that CO2 is (also) cooling the atmosphere by re-radiating sunshine, see here:
They measured this re-radiation from CO2 as it bounced back to earth from the moon. So the direction was sun-earth (day)-moon(unlit by sun) -earth (night). Follow the green line in fig. 6, bottom. Note that it already starts at 1.2 um, then one peak at 1.4 um, then various peaks at 1.6 um and 3 big peaks at 2 um. You can see that it all comes back to us via the moon in fig. 6 top & fig. 7. Note that even methane cools the atmosphere by re-radiating in the 2.2 to 2.4 um range.
This paper here shows that there is absorption of CO2 at between 0.21 and 0.19 um (close to 202 nm):
There are other papers that I can look for again that will show that there are also absorptions of CO2 at between 0.18 and 0.135 um and between 0.125 and 0.12 um.
We already know from the normal IR spectra that CO2 has big absorption between 4 and 5 um.
So, to sum it up, we know that CO2 has absorption in the 14-16 um range causing some warming (by re-radiating earthshine) but as shown and proved above it also has a number of absorptions in the 0-5 um range causing cooling (by re-radiating sunshine). This cooling happens at all levels where the sunshine hits on the carbon dioxide same as the earthshine. The way from the bottom to the top is the same as from top to the bottom. So, my question is: how much cooling and how much warming is caused by the CO2? How was the experiment done to determine this and where are the test results? (I am afraid that simple heat retention testing might not work here, we have to use real sunshine and real earthshine to determine the effect in W/m2/m/ [0.03%- 0.06%]CO2/time period).
I am doubtful of the analysis of the spectral data. I have not seen any work that convinces me. In the case of CO2, I think the actual heat caused by the sun’s IR at 4-5 could be underestimated, i.e. the radiation of the sun between 4 and 5 may be only 1% of its total energy output, but how many Watts per m2 does it cause on earth? Here in Africa you cannot stand in the sun for longer than 10 minutes, just because of the heat (infra-red) of the sun on your skin.
In all of this we are still looking at pure gases. The discussion on clouds and the deflection of incoming radiation by clouds is still a completely different subject.
CO2 also causes cooling by taking part in the life cycle. Plants and trees need warmth and CO2 to grow – which is why you don’t see trees at high latitudes and – altitudes. It appears no one has any figures on how much this cooling effect might be. There is clear evidence that there has been a big increase in greenery on earth in the past 4 decades.
From all of this, you should have figured out by now that any study implying that the net effect of more CO2 in the atmosphere is that of warming, must exhibit a balance sheet in the right dimensions showing us exactly how much radiative warming and how much radiative cooling is caused by an increase of 0.01% of CO2 that occurred in the past 50 years in the atmosphere. It must also tell us the amount of cooling caused by the increase in photosynthesis that has occurred during the past 50 years.
There are no such results in any study, let alone in the right dimensions. For example, consider the fact that time must be in the dimensions.
For more on why it is considered highly unlikely that CO2 is a contributory cause to global warming, see here: