onsdag 2 januari 2013

Lapse Rate by Thermodynamics

In the previous post I asked Roy Spencer about the correct description of the GreenHouse Gas Effect GHGE, which he claims is misunderstood by many people, but got no answer.

It seems that Spencer, WUWT, Lubos and of course all climate alarmists, take the existence of a GHGE for granted, maybe because it has an acronym, while the nature of this effect remains elusive, which makes serious scientific discussion difficult or even meaningless.

Spencer gives the hint that GHGE "is an infrared effect" which connects to the common (mis)conception that the GHGE is an effect of radiation, more precisely, that the lapse rate, or temperature drop with atmospheric altitude, is determined by radiation.

This connects to the question of the lapse rate of a thermally isolated column of air subject to gravitation, to which Loschmidt answered the dry adiabatic lapse rate of 10 C/km, while Maxwell and Boltzmann claimed zero lapse rate or isothermal air, without ever reaching any conclusion. 

The observed lapse rate of the atmosphere is 6.5 C/km which keeps the Earth surface at a comfortable + 15 C, while the temperature at the tropopause at 10 Km is chilling - 50 C. 

The surface temperature is thus determined by the temperature at the tropopause and the lapse rate. What determines then the lapse rate? Thermodynamics or radiation? I argue that it is thermodynamics, while people assuming that the GHGE is real seem to argue that it is radiation. 

In a previous post I gave an argument in favor of thermodynamics, which I here return to. Consider thus the column air discussed by Loschmidt and Maxwell/Boltzmann: 

If the column is isolated without heat supply and the air is still, then heat conduction will equalize the temperature into zero lapse rate in accordance with Maxwell/Boltzmann. However, if there is a (small) heat supply Q at the bottom of the column, then by conduction in still air a linear any lapse rate - dT/dx will be established by the balance equation  
  • - alpha x dT/dx = Q 
where alpha is a (small) coefficient of heat conduction. With alpha sufficiently small, this will make -dT/dx bigger than the dry adiabatic lapse rate of 10 C/km, and convective overturning will be initiated (to eventually give an observed lapse rate of 6.5 C/m).

If the coefficient of heat conduction in still air is small, which is the case, then a small heat source at the bottom will prior to convective overturning establish a lapse rate equal to the dry adiabatic lapse in accordance with Loschmidt, a lapse rate thus determined by thermodynamics and not radiation.

To sum up: Loschmidt was more correct in the setting of the Earth atmosphere, since the Earth surface is heated, and the lapse rate is thus determined by thermodynamics and not by radiation. A GHGE based on a lapse rate determined by radiation, is just an acronym and no a real effect.

With the lapse rate determined by thermodynamics and not radiation, the role of GHG is limited to an effect on the temperature at the tropopause, which may not easily be changed by small perturbations in the radiative properties of the atmosphere, thus suggesting small climate sensitivity as discussed in previous posts.

1 kommentar:

  1. Very good again. But it could be even better by saying that radiation is a part of the thermodynamics and that the parameter determining the amount of heat trapped is likely to be the mass.