The very dry, very adiabatic lapse rate
Over at the real Pielke Sr. web site aka Tony Watts plays scientist, Steven R Goddard misunderstands what the dry adiabatic lapse rate is and tries to claim that the hothouse Venus is strictly a gravitational effect. Nick Stokes and Leonard Weinstein try and set him right. The Bunny got a comment through (after a considerable delay) but Watts is blocking Eli's further words of wisdom over there, and besides the same thing has broken out on moyhu and Real Climate, where Richard Steckis touched it off
The essential argument is that the heating of the Venusian atmosphere occurs through adiabatic processes and not through absorbance of IR by GHGs.and
[Response: Since 'adiabatic' means without input of energy it seems a little unlikely that it is a source of Venusian heating. - gavin
Comment by Richard Steckis — 7 May 2010 @ 12:19 PM
Stephen Baines says:
7 May 2010 at 10:44 PM
“@ RS “As for Gavin’s comment re: pseudo-science, I guess it is only pseudo-science when it disagrees with your pre-conceived ideas about Venusian climate.”
If by preconceived ideas, you mean ideas conceived and tested by scientists over more than a century of prior research, I think he would agree.”
A century of research can be toppled by one experiment. So do no hang your petard on the fallacy that a century of research is an unbreakable bulwark of truth.
[Response: If you think a century of science is going to be toppled by obviously ignorant blog posts on WUWT, you are very mistaken. There is a big difference between coming up with new insights that cause a reevaluation of current paradigms and just getting very basic physics wrong and misapplying completely other bits of physics. Goddard and Motl are engaged in the latter, not the former. - gavin]Comment by Richard Steckis — 8 May 2010 @ 9:22 PM
There is more but you get the feeling, so let Eli have his say.
It's called the dry adiabatic lapse rate, which means that it is an idealization where the energy flow into and out of any packet of air is balanced. That is what Gavin was getting at.
The surface temperature is fixed by a radiation balance between incoming solar and out and incoming IR. The second, colder endpoint is some place up there where something else happens to break the adiabatic condition, for example ozone absorption starting to kick in at the top of the Earth's troposphere. For a planet with an atmosphere and no greenhouse gases, pretty much the temperature of space.
That leaves gas rarification/compression driven by gravitation as the mechanism for setting the atmospheric temperature profile. It is not saying that radiative energy flow is negligible, just that it is balanced.
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There are, of course, a few other things to consider. First, the dry adiabatic lapse rate is not 10 K/km for every atmosphere. For example it is 4.5 K/km on Mars and 2.0 K/km on Jupiter. Better put it is the ratio of the local gravitational constant divided by the specific heat (in J/(kg-K) or g/Cp. For the case of Venus, where the surface and the atmosphere are very hot, we have to account for the contribution of molecular vibrations to the specific heat, which will change with temperature and thus with altitude.
The lapse rate does not set the surface temperature, which is determined by the solar radiation absorbed at the surface and the IR re-emitted by greenhouse gases in the atmosphere.
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