(third post in a series dedicated to the planet Venus as “example” of runaway greenhouse warming)
Venus post #1: Venus: Cool Greenhouse?
Venus post #2: Venus Warming Revisited
Venus post #3: Venus Missing Greenhouse Warming
Venus post #4: Venus and a Thicker-Atmosphere Earth
In reply to Dr. John W. Nielsen-Gammon‘s comment published at Eric Berger’s SciGuy blog entry “Is the global temperature now falling?”
I am the author of the Venus blog originally pointed out in a comment by Jim Mayeu.
I am all for understanding the behavior of atmospheres and the reasoning behind current scientific theories. Chances are, I have not discovered anything major, or nothing at all. But do allow me to probe this further.
(1) First question that springs to mind is, if the terrestrial and venusian atmospheres behave so differently, how could any “greenhouse effect” act similarly in both? Wouldn’t moist convection for example drastically change the consequences of an increase in atmospheric CO2?
Is it a matter then of asking people that mention Venus when talking of anthropogenic global warming, to please shut up in the name of Science?
(2) Also, the “albedo” as a single number for a whole planet is a good approximation to start from, but once again the differences between those atmospheres will surely reflect in different albedo/radiation frequency curves (not to mention how solar radiation diminishes the nearer it gets to the planetary surface).
(3) But let’s go back to the whole adiabatic business.
Lapse rates depend on gravity, and the heat capacity of the atmosphere. Gravity is similar between Venus and Earth, and CO2 responds to compression in a manner similar to air. Is that not enough to expect a similar lapse rate?
In fact, or at least in theory, the “dry” values are:
Venus: 10.468 K/km
In practice, the Pioneer-Venus descent probes actually measured a lapse rate of 8K/km between 60 and 10km above the venusian (or shall I say, Cytherean) surface, and of around 2 between 120 and 60km.
“Under normal conditions” on Earth the lapse rate is assumed to be around 6.38, with a maximum for “dry” air of 10 and a minimum for 100% saturated air of 5.46.
(4) The “energy balance” computation you mention simply assumes a specific “greenhouse effect”. But we cannot use the thesis to demonstrate the hypothesis, so to speak.
All we know is that in terms of flux at the surface, there are 500K left to be explained.
For example, has anybody tried to compute the Earth’s surface temperature with 90-100 times more atmospheric pressure than it has, or better yet, Venus’s with 90-100 times less? (chances are, somebody has done that already). Any “greenhouse effect” would be on top, not instead of that.
The elegance of the Fred Singer’s “explanation” recently partially revisited by John Huw Davies, a geodynamicist at Cardiff University in the UK, is after all the fact that it considers all of the Venus’ peculiarities.
Otherwise, we must imply it’s only by chance that the hottest temperatures belong to the youngest surface, in the one planet with an almost perfectly retrograde rotation (Uranus’ axial tilt is 98deg, Venus’ 177.36deg).
That’s 2.64deg away from the planet’s orbital plane’s vertical. If such a “coincidence” doesn’t scream for an explanation, I don’t know what does.