Atmospheric absorption spectra?

Question

Absorption spectra are the charachteristic "lines" which are absorbed (or emitted, if gas is heated) by a gas. Each type of molecule (like CO2 or H2O) absorbs specific portions of the infrared spectrum. This chart shows how much of each portion of the infrared spectrum is absorbed, and by which gas in the atmosphere
http://www.globalwarmingart.com/wiki/Image:Atmospheric_Transmission_png
Notice that :
- the bands affected by CO2 are already ~100% absorbed
- The band where the outgoing infrared is allowed, is weakly affected by water vapor
- The smaller chart at the side shows 40 watts directly radiated back to space, 195 watts of thermal radiation - this would be due to conduction and convection transferring heat to upper atmosphere.

Now , nobody seriously suggests that increasing CO2 will directly increase the greenhouse effect. The hypothesis is that increased CO2 will cause increased water vapor and that will increase the effect. But :
- Gases rise as they warm (convection). Water vapor is 18/28ths (by mole wt.) of the other gases, so it rises well - until it reaches an altitude cool enough to condense it (which releases heat)
-Water vapor content varies (humidity). areas with low hunidity are that way for reasons. The bitter cold of the upper atmosphere or the arctic. The heat of the deserts ( causes increased convection of H2O)
- Although water vapor only reaches to 25000 feet (the highest clouds) , 2/3rd of the atmosphere is below 25000 feet - barometric pressure decreases rapidly. So is 2/3rds of whatever greenhouse effect
is due to other gases.
- increased water vapor means an increase in the evaporation/ convection/ condensation cycle - a very effective negative feedback. If it's cold out, the wator vapor ends up being snow over wider areas- ( has anyone noticed? )increased albedo is another negative feedback. And increased albedo from more cloud cover.

Nobody seriously questions that CO2 is a greenhouse gas, or that there's a greenhouse effect. Nor that global warming has been occuring since the little ice age ended ~1860. Statements that "scientists don't question greenhouse effect or global warming" are misleading.

The questions :
- Is all that beyond the understanding of voters?
- shouldn't the media and schools be talking about the facts of the matter, rather than scary speculations about inundated cities & such?
- Since the energy policies needed to fight AGW would make 4$ gasoline look like a warning shot, shouldn't there be serious debate, including educating the public?
- If 4$ gas was a warning shot, wouldn't cap & trade be like having the green gang ( or gang green, if you prefer) shoot us in the foot, after the warning shot?
- Since gas prices began receding immediately after pres. Bush forced discussion of the idea of talking about increased oil drilling in the USA, shouldn't we send him a thank you note, every time we buy gas for 1.50?

Answer 1

I have been trying to get to the bottom of the greenhouse effect aswell recently, some call it simple physics but even an article on Realclimate.org stated it was complex to explain with simple physics or even climate models, hence it is simulated with simplified equations designed to represent climate but not based literally physics (due to the complexity that would be required in the model) and complex radiative convection is ignored etc...many explantions are contradictory of each other and are often simplifications that do not really explain the physics behind it (and the physics are very complex and poorly understood i.e. hypothesised).



Hienz Hug is not the only person to try such practical experiments and tests done with glass also show the same results, i.e. a material that absorbs infrared doesnt warm the air beneath and in some instances causes very slight cooling. Practical tests in science take priority over models on the evidence scale, hence the tests are the most reliable indication of what increased co2 will do, though it doesnt make it correct.



The climate modellers explain it as this: there are "layers" in which infrared is abosrbed, what isnt absorbed in the first one that is already a max absorbtion moves up until it can find a layer that isnt at its max, by adding co2 there will be more co2 higher up to absorb infrared.



Re-emission by definition is caused by a gas that gains no heat.

instead the level at which energy is readiated to space rises and due to it being cooler, its less efficient at loosing the heat, and hence warming occurs. The mechanism that no one seems to explain well is how this extra warmth (which hasnt been observed) makes it then back to the surface against the energy flow to warm surface air below, and what radiative convection would occur due to warmer air and cooler air meeting.



Gerlich 2007 also discusses some of the problems with the greenhouse theory, for example it is in breach of the second law of thermodynamics. See his paper in sources below.



Jelbring, 2003 also demonstrates that the greenhouse effect can be explained in a completely different manner to climate models within the bounds of physics. "Here, using a different approach, it is shown that GE can be explained as mainly being a consequence of known physical laws describing the behaviour of ideal gases in a gravity field" The comment from his paper above suggests the current explanation is not currently explained entirely within known physical laws.



Finally, I read an article recently where something like 50 MIT physicists were given the task of working out what reduction in co2 would be needed to curb disaster, all of them came up with differing answers and none were apparently correct, demonstrating how it is difficult to understand or explain within the laws of physics. This just demonstrates how complex the explanation really is. The there is the issue water vapour or co2 isnt well mixed at the surface (where most absorbtion occurs) as its missing or outgassed from the sea at the equator and re-absorbed at the poles etc...



Greenhouse effect aside, the other issue of course that the co2 lifetime is only around 7.5 years (based on the average of 31 peer reviewed papers) based on c12/c13 isoptope analysis at Mauna Loa, which proves that nearly all the rise in co2 has been predominantly natural due to outgassing from the sea as it warmed (this is backed up by the earths climate history), and why this may add some warming, it is a natural effect and cutting emissions will make no difference unless (I wont go into what has warmed the sea, it certaintly isnt air temps as its drives them).



The IPCC of course use an un-validated model to show all the increase was man made, and are left with a mysterious co2 sink that absorbs 50% of co2 that no one can find (i.e the model fails validation). That makes much more sense than using actual observations!

Answer 2

Absorption band saturation doesn't necessarily mean that increasing the amount of CO2 won't increase the greenhouse effect.



It should decrease the distance before light of the correct wavelength is almost entirely absorbed. The CO2 will then release this energy, a proportion via stimulated emission. On average, half leaving an area will go up, half down.



The trick is that a higher concentration of CO2 means a decreased distance for absorption. This means that there are effectively more 'layers' in the troposphere that (effectively) completely absorb the radiation passing through them.



The temperature at the surface can be shown to be approximately[1]:

Tn = T*(n+1)^(1/4)



Where Tn is the temperature of the surface after 'n' completely absorbing layers.



Therefore, even in regions of complete saturation, increased CO2 concentration should increase the temperature of the Earth.

Answer 3

(a) You'd still get an increase in greenhouse warming even if the atmosphere were saturated, because it's the absorption in the thin upper atmosphere (which is unsaturated) that counts (b) It's not even true that the atmosphere is actually saturated with respect to absorption by CO2, (c) Water vapor doesn't overwhelm the effects of CO2 because there's little water vapor in the high, cold regions from which infrared escapes, and at the low pressures there water vapor absorption is like a leaky sieve, which would let a lot more radiation through were it not for CO2, and (d) These issues were satisfactorily addressed by physicists 50 years ago, and the necessary physics is included in all climate models.

Answer 4

It does seem that the scientific basis for AGW has been blown out of proportion. We know that the "enhanced greenhouse effect" is very minor for the reasons you outlined and theories about other warming mechanisms like radiative transfer and some complicated dynamic occuring in the upper layer of the atmosphere are speculative and incomplete.



I've seen the research from Heinz Hug which shows that the atmosphere is virtually completely opaque to the absobtion bands of CO2 implying that additional CO2 will have a negligible effect on climate, while other skeptics suggest that CO2 doubling may be enough to cause a measurable effect.



With so many careers being built on climate change, it's hard to separate fact from fiction these days.



(edit) Benjamin - of course there will be an increase in opacity of the atmosphere by adding CO2, that's not a contraversial thing to say. The question is will this be significant or negligible.



d/dx - I've read some criticisms of Heinz Hug and they don't seem to have any valid arguments. What you and others have said is the very obvious which is a test rig in a laboratory is going to differ from the real world in some respects. This applies for every experiment ever done in a laboratory in the history of science and obviously in itself, doesn't invalidate the experiment. What Hug has done is to fill a glass vessel with CO2 such that radiation passing through the vessel passes throught the same amount of CO2 as is in the atmosphere. What he's measured is that doubling of CO2 has a negligible effect on radiation transmission which is consistant with the greenhouse effect of CO2 being real and the enhanced greenhouse effect of CO2 doubling being negligible.



Your comments seem to imply that there is some fundamental problem with using a high temperature emmiter and an ambient temperature absorber. What if the emmitter was ambient temperature and the absorber was 3 Kelvins? I expect you would find virtually the same thing, doubling CO2 would have the same minor effect on absorption characteristics.



(edit)

Thanks for that MTRstudent. I've given you thumbs up even though I don't agree with everything you are saying - but you are providing constructive input.



I have read your last question and the mathematics is quite interesting, but I'm not sure it's a definitive proof of significant AGW. You will appreciate that with any mathematical analog of a real world phenomon, there will always be assumptions. In practice mathematical analogs tend to work over a certain range of conditions. If we do a thought experiment with a planet with an atmosphere which absorbes 50% of a narrow band of radiation (lets say 10% of the spectrum emitted by the planets surface) - some warming will occur due to the greenhouse effect of the atmosphere. If the atmosphere were altered such that the same 10% of the spectrum was almost 100% absorbed (ie atmosphere becomes completely opaque), then from your equations, Tn becomes infinite (or very large) and the theory you quoted predicts that the planet will warm by infinity (or an arbitrarily large number). If we look at the radiation balance of the planet, it is only possible to warm the surface by approx 2% because then the emissions from the surface will increase by 10% (in accordance with Plancs law) and 90% of the radiation goes straight out without being absorbed.



I think the formula you quoted might work fine for a certain conditions, but breaks down for large numbers of layers with narrow bands.



Tn = (n+1)^(1/4)*T

Answer 5

Thank you for your interest in spectroscopy. The spectra that your link goes to is very low resolution. May I suggest that you look at the HITRAN database for better quality data. The question of saturation was resolved long ago. Molecules both absorb and emit radiation and for a gas in thermal equilibrium the rates are equal. A globar at 1200 K (although the vendors don't state is, this is a typical temperature in FTIR spectrometer) will emit a lot more radiation than a gas at 300 K. A novice may not realize that the difference in emission rates rather than absolute absorption is being measured. Heinz Hug makes this error in the paper cited above. At least at low altitudes, radiative transport is best thought of as a diffusive process in which an infrared photon is absorbed and emitted many times before reaching higher altitudes with a large mean free path and escaping to space. The conclusions outlined by Benjamin above are correct.

Answer 6

Your theory would have validity if the atmosphere was homogeneous. It is not. As pointed out above the lines would not be saturated in the upper atmosphere.