fredag 6 augusti 2010

Global Climate = Thermodynamics + Radiation

A basic model of global climate may take the form of the Earth E as a blackbody surrounded by 
an atmosphere A as another blackbody. Observation gives the following data (cf. Atmosphere as Refrigerator):
  • Temperature of E = T_E = + 15 C
  • Temperature of A = T_A = - 18 C
  • Radiative forcing of E by insolation = 240 W/m2
  • Radiation from A to outer space = 240 W/m2.  
We assume that the forcing 240 W/m2 is given, which by Stefan Boltzmann sets T_A = -18 C in accordance with observation. 

We want to find out what sets T_E to + 15 C.

Heat is transferred from E to A by thermodynamics (convection and latent heat) and radiation.

According to Stefan-Boltzmann a temperature drop 0f 33 C from E to A corresponds to roughly
120 W/m2. The heat transfer from E to A is thus roughly divided equally:
  • thermodynamics = 120 W/m2
  • radiation = 120 W/m2. 
In this model A is a blackbody, that is A is assumed to be fully opaque to infrared radiation from E. We cannot make A more black but possibly less black. 

If A is made fully transparent to radiation, or if A is simply removed, then the Earth could directly emit whatever is absorbed at T_E = -18 C.  The presence of an atmosphere absorbing outgoing radiation from the Earth combined with thermodynamics, thus increases T_E from -18 C to + 15 C. This is a "greenhouse effect" of combined thermodynamics-radiation, which has nothing to do with (non-existing) "backradiation"

If A is made fully opaque to also incoming radiation, then A and E both would have a temperature of T_E = T_A = - 18 C (without thermodynamics).

We know turn to the real case somewhere in between a fully transparent and fully opaque 
atmosphere, in which case T_E = + 15 C according to observation, as a result of 
thermodynamics and radiation.

Suppose now that from this present situation, the property of the atmosphere is changed a little (say 1%) by doubling the concentration of the trace gas CO2. Climate sensitivity S is defined as the corresponding change in T_E. The basic question in AGW is the size of S.

If A is already a blackbody, then S = 0.

If A is not black then the present equal partition 120/120 between thermodynamics and radiation will have to shift in the direction of thermodynamics. But it is not clear if that will
cause warming; maybe the thermodynamics simply gets a little bit more vigorous without 
change of the temperature profile. Like a boiling pot on the stove under increased heating.

In any case, it seems that the thermodynamics determines the lapse rate and thus the temperature profile anchored at -18 C at the (top of the) atmosphere. Radiation operates on this profile, passively as it seems. In order to determine climate sensitivity S, it is thus necessary to study the coupled thermodynamics-radiation system. 

No conclusion derived from radiation only, can be scientifically meaningful. In particular not the basic axiom of climate alarmism that S = 1.2 C as a start to feed-back to inflate. 

If anything, it seems more reasonable to set as a start S = 0, and then feed-back has nothing to eat.
In the above model there is no need to introduce the basic concepts of IPCC's CO2 alarmism: "backradiation", "radiative forcing" and "effective radiation into space from a higher altitude at a lower temperature". Using Ockham's razor we find that these concepts belong to fiction and not science.

Concerning radiation, see Computational Blackbody Radiation. For thermodynamics, see Computational Thermodynamics.

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