Posted on 02/24/2010 11:52:23 PM PST by neverdem
The whole greenhouse analogy is flawed. Greenhouses get hot because light heats the solid matter inside the greenhouse. Air inside gets warmer by contacting (conduction) the solids. The warm air rises but meets a physical barrier only a few feet away. So, a major element of the earth’s atmosphere, large scale convection, is prevented in greenhouses. How do you cool a greenhouse? Open vents in the top and allow convection to take place. The earth does not have anything approaching a glass ceiling.
Specially at 1:26 AM...
: )
Thank you!
I am not a physicist, but I did have to take a couple semesters thirty years ago. It seems to me that I read the ORIGINAL guy that did the greenhouse effect work discovered that it was the GLASS not the gas that caused the IR trapping. That would make sense to me. This may be simplistic, but I see the earth’s atmosphere as symmetrical in the sense that it would absorb as much IR in one direction as the other. If someone could explain to me how this isn’t so we can stop right there. If it is so then there is no such thing as “greenhouse gas”.
All green plants we use for food require CO2 to live. They starve without carbon dioxide. If we need to reduce greenhouse gasses, lets plant more trees and shrubs and crops (and use Al Gore as a scare-crow (get it?))
Glass absorbs infrared light. That is why the glass bulb of a radiative light source is hot. Please just take our word for it, unless of course you like the sound of sizzling flesh. So the glass panels of greenhouses will heat up from solar infrared and conduct energy in both directions. Since the outside world typically has cooler wind, most of that energy will be transferred to the outside wind. Some will conduct inwards. So the heated glass represents water vapor et. al.. The conduction of that heat to the inner and outer atmosphere represents the general atmospheric gases. The total of the atmospheric gases also determines the important Total Heat metric. All atmospheric gases trap heat and can be considered greenhouse gases, if that term was even accurate. Might be better to call them green planet gases. Perhaps the airheads will be happy with that phrase. Atmospheric gas sounds so boring and clinical. Additionally, the heat capacity of the atmosphere increases with higher density and it will ultimately determine the temperature of the atmosphere at given heat fluxes.
Light of all wavelengths can be absorbed and converted to heat. Red light absorbed by the chloropyll in the plants, most wavelengths absorbed by dark soil,black plastic, etc.. These warm the air, but also radiate in the infrared at wavelengths characteristic of temperature and in proportion to the emissivity of the material. These longer wavlengths often are not well transmitted by the glasses, so their heat energy is trapped in the greenhouse. Transmission of IR wavelengths of 10µ or so require exotic materials like zinc sulfide, salt, etc.
This is very close to what the theory is based on.
Now what could possibly be wrong with that theoritical framework?
Only about 20 key aspects of it, that is.
The worst part of it is when they say the IR photons are “trapped” - like they never make it out of the atmosphere ever. A CO2 molecule only holds onto that IR photon for a few picoseconds to less than a millisecond. If anything the “trapped” IR photons still escape from the atmosphere (perhaps in other wavelengths though) a few seconds or a minute or two later than they would have escaped at 280 ppm.
Because that's the prettiest color. (If you want to be technical about it.)
But consider a “thought experiment” if you will. Suppose I am a moeclue of H20 vapor in the atmosphere. I am “seeing” IR coming primarily from one source, the sun but I radiate what I have received in all directions. I warm up some and through convection I warm the gasses around me. There is my “cousin” who is at a lower altitude than I and he sees somewhat less IR than I because of what I have absorbed before it got to him but what he does receive he raditates and also through convection warms symmetrically in all directions. All these molecules also recieve reflected IR from the surface and all of that is proportionately reduced on the way up as it was on the way down. This process is repeated infinitely (almost) and so as these molecules all radiate and convey heat symmetrically, how is it they “trap” anything? There is a gradient of IR aborption on the way down from the sun and a smaller one in the opposite direction on the way up but just where is the “trapping”?
save for later
You warm the gases around you with collision. The wavelength emitted is longer and of lower energy than the wavelength you absorbed to warm up, and the wavelength you radiated is no longer the peak absorbtion wavelengths. The strong absorbtions are at 2500, 1950 and 1450 nM.
Yes, we do, and it was 2:26 AM here. Thank you for picking up the slack for me.
I just went back to the original link and clicked it and got the ‘doesn’t exist’ message and ‘Okay.’ My usual response is, no, not OK! I hit the back arrow. I just found now that if I had hit the Okay, it would have taken me to the correct link.
Learn something everyday. Great link, BTW.
Oops. No it didn’t. It took my back to this thread. Oh, well.
That is true of the properties of glass but the main source of heating within a greenhouse comes from infrared light that passes through the glass and hits the solid objects below like floor, walls and the plants themselves. Those solid objects then release that energy through conduction to the gases within the greenhouse passing in direct contact over them.
OK, I just tried what you did and I got this thread not the one I intended to link. I see that I cobbled together two FR URLs (don't axe me how)(and don't axe me how they still manage to do anything either).
Everybody realizes that CO2 forms an barrier just like glass on a greenhouse ceiling right?</sarcasm>
Surrounded by the vacuum of space, moreover, the earth can only dissipate this energy by radiation.
Hot or energetic molecules can leave the atmosphere into the vacuum of space, dissipating heat without radiation.
Thanks for the ping!
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