After giving support to "backradiation" as the physics behind "global warming" Roy Spencer now follows up by giving praise to the basic idea of climate alarmism of a "greenhouse effect" capable of warming the Earth surface to 30 C, if it was not curbed by convective effects reducing it to 15 C, an idea also propagated by Richard Lindzen.
The idea is thus that a lapse rate of about 10 C connecting the Earth surface at 30 C to the top of the atmosphere TOA at -18 C (at the height of 5 km) is determined by radiation alone, which then by convection is reduced to the observed 6.5 C.
The Earth surface is thus supposed to radiate 390 W/m2 of which 240 is radiated to outer space from TOA and 150 are absorbed by the atmosphere and then "backradiated" to the Earth surface contributing to global warming.
I have questioned the physics of "backradiation" as non-existing, and I argued that the lapse rate is not primarily determined by radiation, but by thermodynamics, with radiative heat transfer from the Earth surface to TOA acting passively on the thermodynamic lapse rate.
In this setting there is no "backradiation": Out of the total incoming 180 W/m2 to the Earth surface, 120 is transferred to TOA by convection and 60 by radiation acting on a lapse rate of 6.5 C/km (with 60 absorbed by the atmosphere out of total 240).
It is strange to see leading climate scientists, appearing as skeptics to climate alarmism, still propagating basic misconceptions of climate alarmism such as a powerful "greenhouse effect"
based on radiation alone.
Cannot Lindzen and Spencer understand that the lapse rate primarily must be determined by thermodynamics and not radiation? Why buy the basic argument of climate alarmism,
without subjecting it to scientific scrutiny? Why not scientific skepticism instead of confusion?
Inlägg
Good comment. I have for a long time thought about the "double book-keeping" that seems to occur in the formulations of the greenhouse effect which I will try to explain. First of all, simplicity:
SvaraRaderaThe natural tendency of any thermodynamic system is to approach equilibrium which by definition means that the temperature is the same everywhere. There are a number of heat transfer mechanisms that contribute to this process:
1. conduction
2. convection
3. radiation
When any of these are OFFSET, for example when convection is offset in a real greenhouse, the cooling becomes slower and the temperature rises. However, ALLOWING the atmosphere to radiate more should speed up the process, right? Therefore, adding greenhouse gases should result in a flatter temperature gradient.
This is also what is predicted by the adiabatic lapse rate formula
dT/dh = -g/C_v
By adding greenhouse gases we increase C_v and the gradient gets flatter. This formula actually occurs in climatology and it is amazing why this supposedly "double" effect does not raise the eyebrows of a few more people.
Similarly, GRAVITY seems to be something of a mädschen für alles. Its action is amazingly complicated:
1. It warms the surface by not allowing the atmosphere to escape into space (remember, simplicity)
2. It cools the surface by beeing the CAUSE of convection. (See Rayleigh coefficient)
3. It again heats the surface by OBSTRUCTING ITS OWN CONVECTION, which is expressed by the lapse rate "neutrally stable to convection", expressed by, yes
dT/dh = -g/C_v
Quite remarkable, higher gravity steeper lapse rate, or was it flatter, I'm getting confused....
Anders, there is a fourth form of heat transfer which is possibly the most important for conditions in the atmosphere ie phase change see section 5 of Perry's Chemical Engineers Handbook. For the atmosphere this applies to evaporation of water at the surface (oceans, lakes rivers etc make up about 70% of the earth surface, then condensation and freezing in the troposphere.
SvaraRaderaConduction occurs in solids. Generally, it is regarded that the heat conduction from the earth centre and storage of heat from in coming radiation is small.
Convection occurs in fluids. Convection is enhanced by movement of the fluids (called forced convection). The Reynolds number is one of the factors in determining the heat transfer. My own experience is that when temperatures are below 100C that forced convection is more important in heat loss calculations/measurements than radiation.
I agree with Claes that there is no back radiation which increases the source temperature. If there are are two plates, or for example the earth surface and a low cloud inversion layer, at the same temperature there will no heat transfer by radiation. However, if there is some wind bringing in cooler air then there can be convective heat transfer from both surfaces.
The main point is that climate is complex and that the assumptions concerning radiation in AGW are simplistic.
regards
Cementafriend
I find this point of none back radiation puzzling. And I don't find Claes Johnsons arguments convincing, as there is of course something in them i don't understand. Could anyone please explain why the temperature under a cloudy sky is warmer than under a clear sky? Spencer has an home made example of experiencing this effect by means of an infrared thermometer, bought in "any store".
SvaraRaderaI tried it out my self in september 2010. Turning the thermometer to the blue clear sky it showed minus 20C. Pointed to the ground it read +20C. Directed against clouds it said about minus 5.
Doesn't this mean that the earth recieves IR radiation that prevents heat loss under a cloudy sky?
It is the same with an insulating winter coat, which takes on a temp of - 5 C
SvaraRaderasay when the outside temp is - 20 C, while your skin is at 20 C say, which prevents your skin to directly meet -20 C. What is so strange about that?
Why do think you have to believe that your coat "backradiates" to your body? Isn't it enough to say that the coat is a "mediator", rather than a
"backradiatior"?
one question about your no-back-radiation model: how does heat leaves the earth+atmosphere system?
SvaraRaderaBy radiation to outer space, in the same way as your winter coat delivers
SvaraRaderaheat to your outside by a combination of conduction, convection and radiation.
i do not understand why you're not publishing my question. i'd like to understand your model.
SvaraRaderayou're saying that there's loss of energy in the atmosphere by radiation outwards but there's no radiation back to the earth?
i do not understand this and i suspect you've got a much cleverer idea than that.
i'd be grateful if you would explain that idea to me.
Heat energy can be transferred by radiation (or conduction) from a warm body to a cold. This is forward radiation (or conduction). In backradiation (or backconduction) heat energy would be transferred from cold to warm,
SvaraRaderawhich is unphysical because it is an unstable physical process which cannot be realized.
now i am really confused!
SvaraRaderaeither the atmosphere is radiating because of its temperature (and in that case it will radiate isotropically in all directions) or it is not radiating (nor towards the colder outer space or towards the warmer earth).
what in you model make it possible for the atmosphere to /know/ the colder from the warmer side?
This is described in my book Slaying the Sky Dragon: Death of the Greenhouse Gas Effect, on Amazon.
SvaraRaderawell, believe it or not i had understood that you wrote a book on the subject ;-)
SvaraRaderai was just hoping that you could explain in few words the basic idea(s) behind your model.
as i understand it the greenhouse gas effect does not imply net transfer of heat from a colder to a warmer body, it only observes that the atmosphere -like everything else- is more transparent for higher than lower frequencies of EM-radiation. this is a well established experimental fact, which i do not believe you're questioning.
so my question is still, what is the basic mechanism you're proposing?