"Venus and Cupid" by Lorenzo Lotto, late 1520s
Well, you can say it in this way: after these fields, especially the first one, have been contaminated by an ideological pseudoscience, the only way to proceed is to reinvent the disciplines.
Unfortunately, the flooding of the disciplines by poorly verified and "morally driven" myths has already begun in the modern, rather than postmodern, era, and it was initiated by as likable characters as Carl Sagan. He was nice but very far from infallible.
One must carefully check which insights are legitimate science and which things were politically imported myths - and when it's necessary, you have to start from scratch. But I don't want to degenerate into these moralist rants, so let's jump onto the physics of the problem.
Colose's criticism is simple: he claims that Goddard and I do not realize that the linear functions (of one variable) have two terms (rather than one), the slope term and the intercept:
y = mx + bWe think that there is one term only, we learn. That's a nice hypothesis and it's always nice to learn new things about my own brain :-) but thank you, I understood linear functions when I was 3 years old.
More seriously, Colose agrees that the slope - the lapse rate - is large on Venus - at 8 °C per km, it is comparable to the Earth. But Colose's thesis is that it's the absolute term that would be completely different if the atmosphere of Venus were not dominated by a greenhouse gas (CO2, in this case). If the atmosphere were mostly made out of nitrogen, the surface couldn't be close to 400 °C, he seems to think.
Well, it's not hard to see that Colose's statement is incorrect. We can show that even with a different composition, a very heavy atmosphere would imply a warm surface. (However, we will also see that for an excessively IR-transparent atmosphere, e.g. a pure-nitrogen atmosphere, no stationary state could actually be found at all, so the atmosphere would shrink by various mechanisms.)
Look e.g. at the Wikipedia article about the atmosphere of Venus. The article says a lot of interesting things (besides some out-of-place nonsense inserted by the likes of William Connolley) and I recommend you to read it. But it also contains some hard data such as the following picture:
In the text as well as the chart, you may see that about 50-55 km above the surface of Venus, the temperature as well as pressure are close to the values we know from the Earth's surface: around 1 atmosphere and approximately 0-50 °C. That would be a nice place for (flying) NASA/ESA/RUSA/ChinSA colonies in the future. ;-)
So beneath this Earth-like layer, you still have 50-55 km of extra "air". Because the basic laws of adiabatic heating (without heat transfer) - whose origin will be debated later - imply that the temperature gradient is around 8 °C per kilometer in average, what a shock that the Venus' surface will be found to be 400 °C warmer than what humans like to experience on the Earth. Recall that 50 times 8 equals 400.
The graph above also shows that the temperature keeps on decreasing up to the altitude 100 km where the pressure is just a few Pascal and the temperature is -112 °C or 160 Kelvin or so.
Why is the temperature decreasing so nicely - but it stops decreasing above some point? Well, it's because of circulation that drives the "air" in various directions. And the circulation exists everywhere below the 100-km altitude, but not above it. As a ton of "air" is going up where it can occupy more space, it expands, does work, loses energy, and therefore cools itself. That's why the air ends up cooler at higher altitudes.
Note that this adiabatic mechanism, which works up to the 100-km altitude on Venus, doesn't depend on the greenhouse effect or infrared radiation: it's a mechanical effect. What it depends upon is the circulation, the freedom of the air to move up and down. The winds are ultimately driven by pressure gradients which are caused by the temperature differences which are induced by the changing solar radiation during the seasons and the "day". They're changing because the Venus is revolving around the Sun and spinning around its axis. And the dependence of the pressure (and therefore temperature) on the altitude is a purely gravitational effect. The infrared radiation is not important here.
(The orbital time of Venus around the Sun is 224 [our] days. Venus is the only planet whose spinning goes in the opposite direction than the spinning of the Earth. The spinning is very slow, however, and the solar day on Venus takes 117 [our] days. The spinning is so slow that some winds are faster than the Venus' spinning and can run in the opposite direction relatively to the cosmic reference frame!)
So the circulation, ultimately driven by the Sun (and, at most, the absorption of the visible and ultraviolet light from the Sun which shouldn't be confused with the infrared radiation), guarantees that the adiabatic lapse rate is applicable in a vast majority of the atmosphere - and because the atmosphere is quite heavy, "a vast majority of the atmosphere" means up to the altitudes of 100 km or so.
Even if you assumed that the temperature at those 100 km is 0 Kelvin, which is the lowest allowed temperature, it would still imply that the surface temperature has to be 400 °C or so higher and therefore not hospitable for life (well above 100 °C). However, you can be more accurate than that.
The temperature of the "air" about 80 km above the Venus' surface is higher than 0 Kelvin. At the 80-km altitude, the temperature is actually -76 °C, almost 200 Kelvin, and this value is much higher than 0 Kelvin for a good reason. What is it? Imagine how Venus looks like from a point in the upper atmosphere:
Venus lightning, by a NASA artist
There is a lot of stuff even in the atmosphere that exchanges the incoming and outgoing thermal radiation. In particular, the stuff absorbs a part of the solar radiation. And we don't need to talk about the carbon dioxide at all. The matter of fact is that Venus is covered by sulfuric acid clouds which are opaque (not transparent). That's why we can't see "inside" Venus. A part (2/3) of the solar radiation is reflected, a part of it is absorbed, and very little gets to the surface.
The lower portions of the atmosphere are only heated adiabatically, by convection, as the circulating gas warms up as it drops down and gets compressed, and by heat conduction.
Believe me or not but sulfur that is abundant as much as 80 km above the surface is not made out of carbon dioxide. ;-) Even though the density of CO2 on Venus is something like 300,000 times higher than it is on the Earth, and it constitutes 95 percent of the atmosphere, it is not enough for this gas that we call life to dominate optics on the planet.
And believe me or not, the sulfuric clouds are often at the altitude of 80 km above the surface of Venus (at "night"). They're able to get that high, without any help from the greenhouse effect. Again, mechanics and winds should be credited with getting such material to these places.
And this material is damn able to absorb a notable fraction of the sunlight. So it follows that at these very high altitudes, you may match the outgoing thermal and incoming solar radiation (the solar radiation doesn't get too much deeper to the atmosphere, because of these clouds). When you do so, you may estimate the temperature at those altitudes to be 200 K, well above 0 K, and by extrapolating to the surface using the known slope (lapse rate), you will get to something like 700 K on the surface.
The greenhouse effect is not needed for the qualitative explanation of any of these things, up to a ten-percent accuracy or so. The greenhouse effect still does exist but it is just a relatively small enhancement of the pre-existing lapse rate, and a relatively small lifting of the tropopause (here, defined by the place where the cooling with height stops) to higher altitudes.
In a more detailed discussion, we must be careful about the definitions of the tropopause: on the Earth, several definitions nearly agree. On Venus, they may be at different altitudes. Here, I need the tropopause defined by the point where the cooling-with-height ends. But don't get carried away: the tropopause as defined in the previous sentence is so high because the atmosphere of Venus is so heavy and because the Sun- and mechanically driven "air" circulation mixes most of it, not because of some infrared emission or absorption.
As we have mentioned, the 300,000 times higher CO2 concentration on Venus, relatively to ours, means that they're just 18 CO2 doublings above our levels which only adds 20 °C or so (there are no H2O-related feedbacks over there worth talking about). You know, powers of 2 increase very quickly (2^18 = 262,144), so the logarithms of large numbers are still reasonably small.
The bulk of the surface warmth on Venus - those extra "unwanted" 400 °C - is caused by things that don't depend on CO2's being CO2 or on the greenhouse effect i.e. on the absorption or emission of the infrared radiation. In the same way, the solid interior of the Earth is warming up by 30 °C per kilometer (near the surface, where you can still find some fast enough and adiabatic circulation of the lava etc.) and going up to thousands of degrees (and even millions of degrees according to the leader of the AGW movement) and this fact is gravitational in origin, completely independent on the emissivity of the rocks in the infrared spectrum. There's no important infrared radiation going through the rocks in either direction. ;-)
Much like on Venus, the infrared radiation trying to get through the medium (either rocks on Earth, or the atmosphere of Venus) is almost immediately absorbed - and even a tiny portion of the infrared-absorbing radiation would be enough to absorb it (and to re-emit it). So there is no puzzle why the emissivity is so low (why so small a part of the thermal radiation from the surface gets out). Because the atmosphere is almost completely opaque in the infrared, the radiation everywhere inside the atmosphere is simply in thermal equilibrium with the material around: the properties of this radiation follow the temperature gradients - they're not their cause. The cause of most of the temperature gradients is mechanical (lapse rate) rather than infrared-radiative.
Just one more number: 90 km above the Venus' surface, the CO2 concentration (in molecules per unit volume) matches the concentration near Earth's surface. And you know that CO2 in a few km above the Earth's surface manages to absorb a big part of the IR radiation. So the lower 60 km of the atmosphere may be thought of as "as IR-opaque as a rock".
By the way, even if you believed that the height of the tropopause (where the adiabatic cooling-with-height stops) is linked to a value of the CO2 concentration more accurately than to a value of the total density of the atmosphere, you should notice (see the Wikipedia table below the graph I included) that above 50 km of the altitude, the pressure decreases 10 times for each 10 km. So even if you kept 10% of the CO2 only, "your relevant tropopause" would be just about 10 km lower and the temperature of the surface would only be by 8 x 10 = 80 °C lower.
(The real figure is smaller than that, about 20-40 °C, because the height of Venus' tropopause is linked to all the gases, not just greenhouse gases, and this difference may be attributed to the greenhouse effect from 18 CO2 doublings "above the Earth". But the bulk of the 400 °C extra warmth on the surface has a gravitational origin so it is independent on whether the greenhouse gases dominate the atmosphere.)
Rabbit and Pig
Pig and Rabbit, animals of the year 2009. Do you know who is who?
If you enjoy alarmists' texts about Venus, try also the essays by Pig and Rabbit. If I understand the Rabbit well, he has just penetrated deeply into Goddard's article, namely the second line with the name of the author: Rabbit just realized that Goddard's first name is Steve, not Richard. 100 more years and Rabbit may get to the second sentence.
Rabbit also reveals that "scientist" Gavin Schmidt thinks that the adiabatic lapse rate is impossible due to the energy conservation. ;-) Moreover, proposing a blasphemy such as a temperature gradient that is induced adiabatically would "topple a century of science". Gavin Schmidt clearly has a nuclear weapon against me and Goddard. Ouch. It gotta hurt. For a Planck time; well, I am willing to topple billions of years of such shoddy "science". I choose not to comment on this opinion because the understanding that the adiabatic lapse rate follows from energy conservation, rather than contradicts it, is probably essential to earn a paragraph of response on this blog. Schmidt is a crackpot.
(Hint for Gavin: "adiabatic" means that there is no heat transfer from a hotter object to a warmer object, and "adiabatic" is therefore "reversible". However, "adiabatic" doesn't prevent a body of gas from doing work, and losing kinetic energy and temperature in this way, or regaining it when it compresses back. The temperature therefore depends on the density or pressure and there's no contradiction with the energy conservation.)
Concerning Pig, I do agree that the effective emissivity is (220/735)^4 = 0.008 in the self-explaining sense. But the correct way to calculate this figure is to calculate the numerator, the denominator, and the fourth power: notice that the emissivity comes out very low despite the fact that the atmosphere is "flooded" with a highly-emitting carbon dioxide. The emissivity comes out so tiny because the atmosphere is so heavy, not because it contains a lot of high-emitting CO2! ;-)
Also note that Pig doesn't propose his own alternative of the temperature profile, "T(z)", for the "nitrogen-filled" Venusian atmosphere because he probably realizes that every significantly different alternative would be manifestly absurd. Such an alternative temperature would either violate the adiabatic rules for the lapse rate in corners where this approximation has to work, due to the circulation; or it would have to go below 0 K - or to otherwise crazy low temperatures - at higher altitudes.
Pig also seems to misunderstand that Goddard's thought experiment (and mine) was to replace CO2 by a non-greenhouse gas with similar mechanical and thermal properties. He replaced CO2 by an equally opaque and equally heavy gas which is why he shouldn't expect too much change.
Pure nitrogen atmosphere
Let me mention that I, and apparently also Steve Goddard, agree that the warm surface of Venus couldn't be sustained if the atmosphere were made out of pure nitrogen. The huge thermal radiation of the surface would escape into space without any suppression because the atmosphere would be completely transparent. Because this would be much bigger output than the fixed incoming solar energy, the whole atmosphere would be cooling: it couldn't stay in any "nearby" stationary state.
Eventually, the temperature at some point of the atmosphere would approach the boiling point of nitrogen (very low) and the dry adiabatic lapse rate would be replaced by the "wet" adiabatic lapse rate which is much slower because the work from expansion/contraction is mostly spent to the latent heat of condensation/evaporation of the liquid/gas that moves up/down the atmosphere.
Because the lapse rate would drop, that would also reduce the predicted "hot" temperature of the surface, assuming a fixed thickness of the atmosphere. If a temperature calculated/obtained after these processes would be enough to match the outgoing thermal and incoming solar energy, fine: a stationary state would be found. If it were not enough, the cooling would continue so that the temperatures below the liquid point would ultimately reach the surface (from above). A part of the atmosphere would condense into nitrogen oceans. The remaining atmosphere would be thinner and it would therefore lead to a less dramatic surface-troposphere temperature difference. If there were other gases left that would cause troubles, they could eventually condense, too. After a few steps like that, a stationary state would inevitably be found.
So even for a pure-nitrogen very heavy atmosphere, it's correct to say that the large mass transparent atmosphere would imply a hot surface. However, it's also true that for a pure-nitrogen transparent atmosphere, no nearby stationary state could be found. The atmosphere itself would cool down and/or condense and eventually we would find a different state either with a colder surface and a smaller atmosphere, or a similarly warm atmosphere with IR-absorbing materials in the atmosphere that would develop - where the energy budget would be restored.
On the real Venus, however, there's more than enough stuff to absorb those 99.2% of the surface's thermal radiation. The atmosphere is opaque. There's a lot of CO2 but there is other opaque sulfur-related dirty stuff, too. For example, the Galileo probe showed that the sulfuric clouds appear black at 2.3 microns:
Even so, the high temperatures on Venus are only partially caused by carbon dioxide; a major contributor is the thick bank of clouds containing sulfuric acid . Although these clouds give Venus a high reflectivity in the visible region, the Galileo probe showed that the clouds appear black at infrared wavelengths of 2.3 microns due to strong infrared absorption . Thus, Venus's high temperature might be entirely explainable by direct absorption of incident light, rather than by any greenhouse effect. The infrared absorption lines by carbon dioxide are also broadened by the high pressure on Venus , making any comparison with Earth invalid.The detailed profile is always controlled by the lapse rate - while the overall one-number energy balance does depend on the transparency of the atmosphere.
The importance of the lapse rate is similar to the solid Earth which absorbs infrared radiation so perfectly that the "optical thickness" would be de facto infinite - and predict an infinite rate of geothermal warming as a function of depth.
In reality, the warmth in the geothermal holes is limited and controlled by the adiabatic rate calculated from thermal expansion rather than by the absorption of the thermal radiation (which is de facto perfect).
Rabbit and Pig may join their forces but it doesn't guarantee success.
An off-topic discussion at RealClimate, under the article "Solar", contains the word "Motl" 56 times so far, so the word even beats "Goddard", 56 to 19. If you like to read positive or negative texts with this word, help yourself. :-) I don't like reading texts about myself at all.
See also older articles, Hyperventilating on Venus and Tamino vs Goddard, on The Reference Frame.
Hansen about the climate dice
AFP (click) brings us news about Rev James Hansen who says that the climate dice is now dangerously loaded, much like the Flash applet above. If you throw it 10 times, you will get a higher-than-average result (4,5,6) either 7 times or 6 times or 5 times or 4 times or 3 times.
It's very likely, about 90% odds, try it by clicking at the dice above. ;-) Isn't it impressive? That must be a signal from God, Rev James Hansen tells us. If you happened to get 4,5,6 in fewer than 3 attempts, it was just weather and there's no reason why your weather should ever be repeated. In the asymptotic future, you will only be getting 6,6,6. Try it. If you're sufficiently patient so that the short-term variability goes away, you will only be getting 6,6,6 all the time.
You have heard the word of Devil. Amen.