A light dawns (and the sun sets)
G. Kramm over at dotearth.com #717 finally makes clear to Eli what Gerlich and Tscheuschner were trying to express in their Arxiv manuscript Falsifiation Of The Atmospheric CO2 Greenhouse Effects within The Frame Of Physics,. It remains wrong.
“Please explain, for instance, in which way the tropopause region for which the so-called anthropogenic radiative forcing was estimated can warm the earth’s surface which has a temperature of about 65 K higher than the tropopause region. This is not possible without any kind of compensating changes. If it would be then we would be able to build a perpetual motion machine of second kind.”
Actually he wrote this a few times # 457
(4) Do you believe that the tropopause region for which the anthropogenic radiative forcing is calculated can warm the nearly 65 K warmer Earth’s surface without any compensating changes?
(5) Is it true that a perpetual motion machine of second kind can exist?
(6) Give the various citations of greenhouse effect explanations listed by Gerlich and Tscheuschner evidence that this greenhouse effect really exist?
(7) Is the current explanation of the greenhouse effect physically correct?
before the curtain fell from Eli's eyes. Eli also had the usual kindly personal missive from Tscheuschner. Needless to say the greenhouse effect does not require a perpetual motion machine of any kind, but as we will see the terminology used to describe the greenhouse effect can mislead the willing.
At equilibrium the Earth (including the atmosphere) must radiate the same amount of energy as it absorbs from the sun. If the amount of absorption is greater than the emission then something has to change so that the emission increases. As a general rule this means something has to warm up. Remember that radiation from the Earth in this context includes the atmosphere.
Without greenhouse gases the surface temperature would be about -20 C ON AVERAGE (right now the temperature in Barrow Alaska). Greenhouse gases absorb energy radiated from the surface, blocking a portion of the radiation that is emitted from the surface so it can’t escape to space directly. A further portion of the atmospherically absorbed radiation is later radiated to space, a portion is radiated down to the ground and absorbed there. GT&K object that this contradicts the second law of thermodynamics.
It does not. The net energy flow from the warmer surface flowing into the colder atmosphere is positive. There is no violation of the second law. We can see this using a detailed illustration of the energy balance
So, how do greenhouse gases “warm” the surface. Note the scare quotes. One can formulate the process as the back radiation from the greenhouse gases warming the surface, but on net, radiation from the surface is larger than the back radiation. Greenhouse gases don't so much warm the surface as slow the NET energy flow from the surface to the atmosphere and from the surface and atmosphere to space. If you turned the sun off, the ground would cool because the NET energy flow is from the surface to the atmosphere and to space. But the sun rises and pours energy onto the ground. In that case the NET energy flow onto the ground is positive, composed of a solar and a back radiation component. This requires the surface to warm until radiative balance is achieved.
The point that GT&K miss is that what is warming the ground is solar radiation + the back radiation from the atmosphere.
Let us just look at the radiation part of the problem and ignore latent heat and convection (the numbers are not accurate but indicative. See the figure for more accurate numbers). If the intensity of the sun at the surface was 300 W/m2 without greenhouse gases the surface would warm until 300 W/m2 were radiated to space from the surface. With greenhouse gases (for arguments sake) 200 are radiated to space and 100 to the atmosphere, of which 50 are radiated back to the surface and 50 to space. The sunlight is still pouring in at 300 W/m2 so the energy flow to the surface is 350 (300+50) in and 300 out (200+100) of which 250 make it to space. The net energy input to the surface which includes both the solar and the back radiation is +50. This will warm the surface beyond what it was at without the greenhouse gases until enough emission is generated that the radiation to space equals the radiation from the sun. The effect is a combination of solar radiative heating and the fact that the greenhouse gases block a portion of the long wavelength radiation to space and return it to the surface.
If one increases the amount of greenhouse gas, the absorption surface longwave radiation will increase, the amount of back radiation will increase, less radiation will escape to space until the surface and the atmosphere warm enough to restore the balance.
UPDATE: Flavius Collium has a better way of putting this (see comments)
I'd summarize it that the greenhouse gases "hinder the cooling of earth's surface".Eli also corrected some minor misspeaks (see comments)
Same if you use a resistor to heat a less insulated object vs a more insulated one - the insulation in both cases will always be colder than the object but the better insulated one will reach a warmer steady state.