greenhouse effect radiative transfer

[2dye4]

Most of us were taught that it's the long wave radiation emitted by warmed objects in the greenhouse that is reflected by the glass that causes the heat to be trapped.

A number of qualified people appear to reject this interpretation of the heat trapping.

http://www.wmconnolley.org.uk/sci/wood_rw.1909.html

They claim it all about preventing convective heat loss and an IR transparent roof would do the same thing.

Of course the genesis of this discussion is global warming but i am really only interested in other opinions about the physics of actual greenhouse heat entrapment.

IF this is true what about an experiment with two boxes identically constructed one has a floor with emissivity = e and a glass roof, the other has an roof with the same emissivity and does not transfer visible light. Would they be the same temp??

 

[electricpete]

Wikipedia is probably a good starting point

http://en.wikipedia.org/wiki/Greenhouse_effect

Greenhouse effect
...The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.[2][3][4]

Just reading the few references, it seems to me safe to say regarding the warming effect created by adding a greenhouse:
[*]preventing convection is the primary effect
[*]"greenhouse effect" is a smaller effect



=====================================
(2B)+(2B)' ?

 

[IRstuff]

However, one can do the math.

A perfect blackbody at 330K radiates ~213 W/m^2 into a 300K ambient, of which, only ~14.7mW/m^2 can pass through standard window glass.

Convection from the same 330K blackbody into a 300K ambient amounts to about 150W/m^2

So, infrared wins by a nose. The article is unclear as to all the details of the experiment, so who knows what really happened? The "professor" is not identified as to his area of expertise, and there is no published data as to the exact setup of his experiment, resulting in a possibly irreproducible result. Note that hothouses are constructed with angled roofs, and there is much internal reflection going on, so even with an IR transparent covering, the index of refraction might be high enough to reflect all the IR energy internally. Again, ill-posed experiment with zero data may mean zip.

The math, on the other hand, is relatively straightforward, but obviously, more verisimilitude might skew the results in a different direction.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Compositepro]

The importance of the "greenhouse effect" in a greenhouse will depend on the "sky temperature". If the atmosphere is cold and dry the radiative heat loss is much greater than when it is warm and humid. When the atmosphere itself is the greenhouse you will not see the effect of the glass on radiative heat loss.

 

[davefitz]

well, the modeling of the atmosphere to include the "greenhouse effect" is allegedly more complicated than the above. Among other things, the simple models of a "participating media" usually use CO2 radiation parameters that are derived from equilibrium data, while the processes in the atmosphere are not necccesarily best modeled with equilibrium data. For example , the value of the CO2 emmissivity or absorbtivity from equilibrium data masks the effect of the cooling of the CO2 molecule that occurs as it strikes a colder molecule during the significant time period between wehn it absorbs an IR photon and the time it re-emits a photon.

But , it is likely more prudent to stay outt of that catfight.