CO2 is irrelevant. There is no greenhouse warming.

I don’t know what you mean by “geophysical factors and convection effects”. The only way that Venus planet-atmosphere system can get rid of heat is to emit it into space radiatively. (I suppose a little bit could be liberated through mass transfer out of the atmosphere into space, but probably not very much.) And, the Venusian surface simply could not be nearly as hot as it is without an IR-absorbing (or reflecting) atmosphere because otherwise it would radiate out into space way more energy than it absorbs.

If by geophysical factors, you mean that the planet itself is generating sufficient heat internally through, e.g., nuclear decay that is then being transported to the surface, I think you would have a real uphill battle in claiming that. As I recall, a paper from way back in the 60s or 70s showed that even if such a process were occurring internally, the amount of heat that could possibly by transferred to the surface of the planet was too small to maintain the high surface temperature.

As for your last question, here is a paper that discusses their hypothesis of where all the CO2 on Venus came from: http://www.ucm.es/info/climast/paco/abstr/venus00.pdf

My prediction is that mature science will conclude that Venus’ temperature is the result of geophysical factors and convection effects, not radiative “trapping”, as per the GH hypothesis.

The first crucial question that needs answering, IMO, is: where did all the CO2 on Venus come from? Its atmosphere is about 100X as dense as Earth’s and CO2 here is 1/3,000 of the atmosphere, so the relative CO2 concentration on Venus is 100×3,000=300,000X that of Earth. That is a whole different scenario than any relevant to our situation.

For some information on Venus and its greenhouse effect, see http://www.realclimate.org/index.php/archives/2008/03/venus-unveiled/ Some facts therein:

(1) “Traces of water vapor, which though tiny, contribute significantly to the greenhouse effect of the atmosphere.”

(2) “Most of the greenhouse effect comes from the carbon dioxide, however, which by itself is sufficient to raise the surface temperature most of the way toward its observed value of around 470C.”

(3) “A key feature of the atmosphere of Venus is the sulfuric acid cloud deck. These clouds account for the high reflectivity of Venus, but because they also reflect infrared back to the surface (unlike water clouds, which absorb and emit), they have a warming effect as well, and constitute the second most important factor in the greenhouse effect of Venus after carbon dioxide. Radiation model calculations demonstrate that the clouds have a pronounced net cooling effect on the planet, when both factors are taken into account.”

See also http://en.wikipedia.org/wiki/Runaway_greenhouse_effect and http://en.wikipedia.org/wiki/Venus and references therein. In terms of a runaway effect, the second link says: “Studies have suggested that several billion years ago Venus’s atmosphere was much more like Earth’s than it is now, and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.[34]” Ref. [34] is available as a PDF file here: http://geosc.psu.edu/~kasting/PersonalPage/Pdf/Icarus_88.pdf This thesis would presumably also be a good source of information: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.75.6539&rep=rep1&type=pdf and here is a recent review of the radiative transfer in the Venusian atmosphere: http://yly-mac.gps.caltech.edu/Z444/Flash4/Venus_greenhouse/RT_in_Venus_Atmosphere_AGU_GM01301CH08.pdf

In any case, since the IR bands CO2 absorbs are such a small fraction of the total thermal radiative EM range, I just don’t see how it could possibly even be the “forcing driver” on Venus (much less Earth).

In order to avoid a lot of misunderstanding, then, here’s the way I see it: a hot lower troposphere would accomplish heat transfer by convection AND radiation to the upper troposphere. In the process of convection, much of the water vapor content is lost, so the heat-trapping is bypassed.

It is true that some of the heat transfer in the atmosphere occurs via convection and specifically evapotranspiration, where water is evaporated at the surface (which absorbs energy) and condenses in the atmosphere releasing the energy as latent heat. (See http://www.windows.ucar.edu/earth/Atmosphere/images/radiation_budget_kiehl_trenberth_2008_big.jpg ) These processes are included in climate models. I’m not sure what you mean when you say, “much of the water vapor content is lost, so the heat-trapping is bypassed”.

I agree with you that for the atmosphere to get anything like Venus, there would have to be significant releases of CO2 from carbonates or other sources because we don’t have nearly enough atmospheric oxygen to produce it simply by oxidizing fossil fuels. I’d be curious to understand more about how the process happened on Venus and whether they have any idea of what the atmosphere was like before runaway occurred. But, this is probably mainly of academic interest.

On Venus we know very clearly the climate history – an earlier Edenic period existed of apple trees and dwarfs and elves, but they lit too many fires so greenhouse warming somehow became runaway in their oddly linear world, and the planet got toasted as punishment for the sin of industry.

We know all this of course from all the spacecraft and astronauts that have landed on Venus, all the cores that have been taken and all those hardy bristlecone pines somehow still surviving to provide rings.

Our own planet earth of course is a different matter – here the history of climate is lost in the mists of time an unavailable to inform the present. The mediaeval warm period, the little ice age, the Roman and Holocene warm periods, Younger Dryas, ice ages, are all now abstract myths which it is blasphemous to mention or even think about. Instead we extrapolate climate confidently backwards from a handful of borehole estimations with exponentials tending to a straight line.

Yeah right!

I actually think I covered much of what you mention here and in the ensuing paragraph, but I’m a little puzzled. It appears that you’re making a point that the connection between lower and upper troposphere is largely radiative. In order to avoid a lot of misunderstanding, then, here’s the way I see it: a hot lower troposphere would accomplish heat transfer by convection AND radiation to the upper troposphere. In the process of convection, much of the water vapor content is lost, so the heat-trapping is bypassed.

Possibly I’ve completely misunderstood, though. Likely, I’m thinking.

As regards a Venus runaway, I want to reemphasize that Venus has such an enormous greenhouse effect for several reasons that are not achievable on Earth, such as nearly a hundred times more atmospheric mass, and nearly all of that mass CO2.

Possibly we have enough carbonates that, if they were somehow converted to CO2, they’d be able to form a massive atmosphere like that of Venus. But converting them is something you don’t want to hand-wave. Just burning fossil fuels isn’t going to do it, I don’t think, because you’ve got to oxidize the fossil fuels using atmospheric oxygen. And there’s only so much of that. If you could somehow burn ALL of atmospheric oxygen and form CO2, it’d only increase atmospheric mass by something like 28%, as I’ve said.

Thanks for the response, and thanks for the link. I’ll be reading that in a bit.

I was kinda keeping up with you until, “And, it is also important to remember that we are observing Venus’s atmosphere after a runaway greenhouse effect occurred.”

Could you explain this, before I make any assumptions about what you meant?!

Thanks a lot,
MS.

There are a few things that I don’t understand, though. For instance, CO2 and H20 don’t entrap ALL of outgoing energy in their absorption bands, because the mean free path to the next photon interaction with one of those molecules is relatively long (because of the relatively low concentration of CO2 and H20 vapor), and eventually an N2 or O2 or other molecule will simply radiate photons of those wavelengths to space. Given that the atmosphere is 99+% N2 and O2, and about 0.25% H20 and CO2, the CO2 is going to simply slow down reradiation to space, and not present retention per se. That’s my guess, anyway. CO2 and H2O aren’t simply going to refrain from colliding with N2 and O2 molecules, once they’ve picked up some extra energy.

There is an aspect that you are missing here and it involves the fact that the greenhouse effect is actually subtler than the simple explanations of the greenhouse gases absorbing infrared radiation and re-radiating some of it back to Earth. At the end of the day, what turns out to be most important in determining the radiative balance is how much radiation gets emitted back to space. And, the way that greenhouse gases change that is that as you increase their amounts, the average level in the troposphere from which the radiation escapes into space rises. (You can imagine that a plot showing the number of IR “photons” that escape vs the level in the atmosphere will have a peak at some level because for IR emission low in the atmosphere, there is a large probability that the photon will be re-absorbed before it escapes into space and for IR emission very high in the atmosphere the radiative emission is lower because the temperature is colder. In between, there is a “sweet spot”, although obviously it is not that all photons that escape to space come from this level but just that the distribution has a maximum value at this level.) When the average level from which the emission into space occurs rises, that means the emission is occurring at a level at which the atmosphere is colder and hence, by the Stefan-Boltzmann Law, the power emitted is lower (because it is proportional to T^4).

See here for a historical discussion of how the understanding of this evolved during the mid-20th century: http://www.aip.org/history/climate/simple.htm#L_0623

You are right that the process is complicated because you have to consider the details of the spectra of emission and absorption and so forth. So, there is really no substitute to doing detailed atmospheric radiative transfer calculations to determine what the actual numerical value for the radiative forcing due to a given change in CO2 levels is. However, I don’t think that there is any serious disagreement in the scientific community in regards to what this value is (to within about 10-15% precision), as even “skeptic” scientists like Roy Spencer and Richard Lindzen don’t dispute this value, but instead dispute how the various atmospheric feedbacks then translate this into a certain temperature rise.

As for the danger of Earth becoming more Venus-like, well, our atmospheres (in terms of composition and pressure) and insolation levels are so different that comparison is meaningless.

Well, I won’t argue with your basic point that Earth and Venus are quite different. However, that doesn’t mean that we can’t learn anything from looking at what happened on Venus. And, it is also important to remember that we are observing Venus’s atmosphere after a runaway greenhouse effect occurred. I don’t know how much is known about the likely makeup of its atmosphere before this occurred.

But yes, Venus and Earth are quite different and most climate scientists seem to believe that a runaway effect on the Earth is not in-the-cards (at least for the sun at around its current luminosity). Jim Hansen does seem to believe that a runaway would be possible if we really aggressively use most of our fossil fuels but I haven’t seen him spell out his thinking in the scientific literature. (It seems to vaguely involve a notion that what has prevented this from ever occurring in the past were negative feedbacks in the carbon cycle due to geophysical processes [e.g., the drawing down of CO2 levels by chemical reactions that incorporate it into rocks] that occur on timescales that are too long to save us on the much shorter timescale over which we are releasing these stores of carbon back into the atmosphere.)

Of course the other approach is looking for a “signature”. What is diagnostic of non-equilibrium pattern? A key feature of such systems is fractal character, measured by making the log-log plot and looking for linearity.

For example, take the Petit 1999 deuterium temperature reconstruction from the Vostok core going back 420,000 years. You can look at the difference (change) measured between neighboring core data points going back (or forward) in time. Then plot the nat log of point to point deg C change with nat log of frequency. What you get is:

Change between consecutive data points deg C,Frequency,NatLog of change,NatLog of frequency

0.1,2074,-2.30258,7.63723
0.2,322,-1.60944,5.77455
0.3,285,-1.20397,5.65249
0.4,198,-0.91629,5.28827
0.5,162,-0.69315,5.08760
0.6,82,-0.51083,4.40672
0.7,54,-0.35667,3.98898
0.8,49,-0.22314,3.89182
0.9,37,-0.10536,3.61092
1,19,0,2.94444
1.1,8,0.09531,2.07944
1.2,8,0.18232,2.07944
1.3,9,0.26236,2.19722

y = -2.1052x + 3.0077
R2 = 0.9305

x: nat log of change
y: nat log of frequency

So with an R2 of 0.93 we have what is effectively the fractal dimension of Vostok temperature change of 2.105. The temporal changes in temperature do appear to show fractal character thus evidence that global temperatures are controlled by processes which possess non-linear / non-equilibrium emergent pattern.