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Space Forum / Astronomy / July 2008The run-away greenhouse is impossible
The conventional explanation of the run-away greenhouse effect, which produced the conditions we see on Venus today, is that the evaporation of water vapor caused the temperature to rise so high that the atmosphere became unbound. I have seen a journal article that says the temperature would reach 'several thousand degrees' until the surface could 'radiate in the visible'. This is absurd and impossible. In fact I am sure the temperature on Venus has never been significantly hotter than today. First of all, even if the surface did reach such temperatures, it could not 'radiate in the visible' to space, as the H2O atmosphere would be completely opaque at all wavelengths. Even if there were no clouds, it would be nearly opaque in the visible due to Rayleigh scattering. Second, where does the heat come from? No sunlight will reach the surface, so the only source of surface heating is internal heat. On Earth today internal heating of the surface is roughly 1/5,000 of solar heating; on Venus it must be much closer. But regardless of the heat source, convection limits the surface temperature to a value that increases only logarithmically with pressure, and is proportional to the adiabatic lapse rate. In an atmosphere saturated with H2O at high temperatures (> 100 C), the lapse rate is very small; therefore, even though the atmosphere is think, the temperature will surely remain below the critical point of water as long as the atmosphere is mostly water. When, however, the planet has lost most of its water to photo-dissociation, the base of the cloud layer will lift off the ground and the surface temperature rise because of the increase in the lapse rate (the amount of sunlight getting through is irrelevant as long as the atmosphere is in convective equilibrium). This results in the conditions observed on Venus. What happens when the last of the water is lost? The cloud layer then disappears, but the surface temperature won't decrease unless the amount it can now radiate to space exceeds solar input, which seems unlikely unless the CO2 atmosphere is so thick as to be opaque in the visible from Rayleigh scattering (several times Venus). Andrew Usher This wasn't supposed to go to soc.men actually. My point (I didn't quite finish) was that there can be no such thing as a true 'run-away greenhouse', that there can be no abrupt tipping point but only a gradual change. It is nonetheless irreversible, though. Also, this has no effect on projections of man-made global warming, as it can't occur unless solar input is considerably higher than today. Andrew Usher > This wasn't supposed to go to soc.men actually. > [quoted text clipped - 8 lines] > > Andrew Usher And according to the Gaia Hypothesis, life on Earth itself will evolve to absorb and subsume any climate conditions that will lead to runaway greenhouse effects. Yousuf Khan > And according to the Gaia Hypothesis, life on Earth itself will evolve > to absorb and subsume any climate conditions that will lead to runaway > greenhouse effects. The planet is not a living organism. Organism live on the planet. Bob Kolker > > And according to the Gaia Hypothesis, life on Earth itself will evolve > > to absorb and subsume any climate conditions that will lead to runaway > > greenhouse effects. > > The planet is not a living organism. Organism live on the planet. And the way you know this for such a certainty is? Oh that's right. FAITH! I love faith-based science, don't you? I especially love those who have such unquestioned authority that they can simply answer all questions with unshakable assertion that is obviously so authoritative that none dare question it! Love, ya, Bob! >> > And according to the Gaia Hypothesis, life on Earth itself will evolve >> > to absorb and subsume any climate conditions that will lead to runaway [quoted text clipped - 11 lines] > obviously so authoritative that none dare question it! Love, ya, > Bob! Well, unless you know of some life form that can survive without liquid water and can breath "live" steam, I'd say that Bob is right. The runaway greenhouse predicted for Earth would be the result of solar luminosity increase giving rise to extra CO2 and water vapour, hence greenhouse feedback into yet higher temperatures. By the way, the Gaia Hypothesis is just that, a hypothesis, or conjecture, proposed as an explanation of certain observations in the fossil record. It hasn't reached the status of a theory, yet.  SignatureMike Dworetsky (Remove pants sp*mbl*ck to reply) > > > And according to the Gaia Hypothesis, life on Earth itself will evolve > > > to absorb and subsume any climate conditions that will lead to runaway [quoted text clipped - 11 lines] > obviously so authoritative that none dare question it! Love, ya, > Bob! Well, faith based science has its merits by avoiding the brain strain that comes as a reult of serious thinking! Hence, without the brain strain, empty headed believers in faith based science tend live longer than those that actually contribute to the physical sciences, but fortunatly for the human race, don't reproduce very often. This is why we see so many 80 year old Bible thumpers, but not very many historically productive sceintist over the age of roughly 70. Harry C. p.s., On a more serious note, during their college years, most physical science majors burn the midnight oil studying, sometimes pulling all-nighters simply to stay ahead, and in other cases, to pay for their education. I've noticed that this takes years off of one's lifespan. I'm 70, and a vast majority of my physics classmates are already dead. Still, the business and theology majors are still going strong! I have to tell you this: Classical and Theoretical Mechanics courses are the real killers, having seen several physics majors taken away the those nice men in the white lab coats, while still muttering bable about Euler's equations and the nunation and precession of a gyroscope. (I only use Euler as as example, because an equal level of brain strain can result when one thinks about the physical implications of any transform, and it is clearly better for your health to simply accept that these devices work on face value alone. Not ponder them. and why they work. This is how faith simplies life.) Harry C. > > > And according to the Gaia Hypothesis, life on Earth itself will evolve > > > to absorb and subsume any climate conditions that will lead to runaway [quoted text clipped - 4 lines] > And the way you know this for such a certainty is? Oh that's right. > FAITH! Science does not deal in "know this for such a certainty." Science deals in valid theories that make predictions and can be falsified. The "Gaia hypothesis" isn't such a thing. The "Gaia hypothesis" is bad poetry. We know that the planet isn't alive because we go out and observe it and it does not have any of the properties of a living thing. > I love faith-based science, don't you? No, I don't. And the "Gaia hypothesis" is one such chunk of trash that we really would be better off putting in the dustbin. It can keep company with alchemy and phlogisten. > I especially love those who have such unquestioned authority that they > can simply answer all questions with unshakable assertion that is > obviously so authoritative that none dare question it! Love, ya, > Bob! Um. Where do you see these unshakable assertions? Other than in the pronouncements of the Gaia enthusiasts that is. Socks > > And according to the Gaia Hypothesis, life on Earth itself will evolve > > to absorb and subsume any climate conditions that will lead to runaway > > greenhouse effects. > > The planet is not a living organism. Organism live on the planet. Not that he said that... I read Yousef's comment as discussing the effect of "life on Earth" collectively. not that the earth itself is alive, nor that he personally endorses the Gaia 'Hypothesis' (really a New-Age neo- religion). The consequence of non-equilibrium thermodynamics (see Prigogene, for example) is that 'dissipative systems' (such as 'organic life') that absorb absorb energy and reduce entropy are almost inevitable wherever a system has a net energy influx, a solvent which can affect the constituents of the system, and a potential for a phase transition in the solvent. The temperature and phase changes will differentiate and segregate the constituents, producing 'organized' structures and reducing entropy locally. > Bob Kolker Tom Davidson Richmond, VA >> The planet is not a living organism. Organism live on the planet. > [quoted text clipped - 4 lines] > personally endorses the Gaia 'Hypothesis' (really a New-Age neo- > religion). Thanks, that's exactly what I meant. I was talking about life on Earth, not the Earth itself as a living thing. Anyways, the Gaia Hypothesis segments into "Weak" and "Strong" versions. The Weak Gaia Theories are completely provable and actually undeniable, as models they fit the planet Earth like nylon. But the Weak Theories are only advocating that which is blatantly obvious: the advent of life on Earth has affected its environment. The Strong Gaia Theories go further and model the Earth like an organism itself. The Strong Gaia Theory may not be provable for a very long time, and it may only be provable through hindsight through history. Regarding the theory as a neo-religion, it was proposed by Dr. James Lovelock, a NASA consultant, with a background in chemistry and medicine. He was studying tests for finding life on Mars at the time. The poetic nature of the theory's name, Gaia, was proposed by Lovelock's friend, novelist William Golding. Although the theory has been taken up by environmentalists, it hasn't taken on religious proportions. It's unfortunate the name turns off so many people, many who haven't even read it, automatically assume things just based on the name alone. Yousuf Khan > >> The planet is not a living organism. Organism live on the planet. > [quoted text clipped - 27 lines] > > Yousuf Khan well, if you look at it objectively, the climate on earth has for most of its existence been hotter, moister, and much more carbon dioxidey; life, in the form of plants, has altered this by sucking up a lot of CO2 during the carboniferous era and burying the carbon, creating an anomalous situation of higher potential energy; humanity and/or human civiliation is just the particular manifestation of the inevitable result of a high potential energy situation, which is that some mechanism eventually emerges to restore the lower energy state. the rock eventually rolls down the hill. unfortunately, for us, once that potential energy is gone, the mechanism which it drove generally dies off. so, once the earth is restored to 1500 ppm of co2 in the air, high humidity, and temps 10 degrees higher than today, we will be redundant and obsolete. but the good news is that there's no real reason to expect that the "runaway greenhouse" will continue to make the earth a lake of melted solder, given that the closest thing to a stable state the climate has shown is that 10 degrees warmer. might be some overshoot, of course, for a few million years or so. >> And according to the Gaia Hypothesis, life on Earth itself will evolve >> to absorb and subsume any climate conditions that will lead to runaway >> greenhouse effects. > > The planet is not a living organism. Organism live on the planet. Okay, and so what's this got to do with whether or not "life on Earth" will evolve to rectify the climate? Yousuf Khan > >> And according to the Gaia Hypothesis, life on Earth itself will evolve > >> to absorb and subsume any climate conditions that will lead to runaway [quoted text clipped - 6 lines] > > Yousuf Khan well, it's always an error to think that evolution is purpose driven. mutations are random, and wherever there's a niche, presumably one of those random mutations will be such that it can exploit that niche. that's one trouble with "intelligent design" theories; intelligence is limited, compared to randomness. >> Okay, and so what's this got to do with whether or not "life on Earth" >> will evolve to rectify the climate? [quoted text clipped - 6 lines] > that's one trouble with "intelligent design" theories; intelligence is > limited, compared to randomness. "Intelligent Design" is another word for Creationism, isn't it? They don't believe in any kind of evolution. Everything on Earth was put there fully formed by one major intelligence up in the sky or something? Hasn't got anything to do with organisms evolving to rectify the climate. One of the misconceptions of evolution is that something has to evolve after a change in the climate or whatever. But in actual fact what's really happening is that these organisms have already existed prior to the change, and the change makes them far more successful than they were before. So if the environment changes, the organisms that will re-regulate the environment will already exist, and now will simply be more successful. Yousuf Khan | >> Okay, and so what's this got to do with whether or not "life on Earth" | >> will evolve to rectify the climate? [quoted text clipped - 8 lines] | | "Intelligent Design" is another word for Creationism, isn't it? "Design" implies planning. Only idiots attach "intelligent" to it, if a god created us it is a pretty dumb god to run a toxic waste pipe through a recreational area. | They | don't believe in any kind of evolution. Everything on Earth was put | there fully formed by one major intelligence up in the sky or something? That's the general idea. | Hasn't got anything to do with organisms evolving to rectify the | climate. One of the misconceptions of evolution is that something has to [quoted text clipped - 6 lines] | | Yousuf Khan Actually you've given an optimistic bias to the situation. All species survive until killed, success has nothing to do with it. It is not survival of the fittest but destruction of the weakest that drives evolution. That's also called "luck". > | Hasn't got anything to do with organisms evolving to rectify the > | climate. One of the misconceptions of evolution is that something has to [quoted text clipped - 11 lines] > It is not survival of the fittest but destruction of the weakest that > drives evolution. That's also called "luck". Whatever, works out to the same effect. Yousuf Khan | > | Hasn't got anything to do with organisms evolving to rectify the | > | climate. One of the misconceptions of evolution is that something has to [quoted text clipped - 15 lines] | | Yousuf Khan This is not so. "Survival of the fittest" evolution means that individuals within the species compete with each other - for example the antelope chased by a lion escapes and passes on it genes at the expense of the slower antelope that is caught. That didn't help the dodo, they were all wiped out by man. The effects are very different, on the optimistic side the species improves itself gradually, on the pessimistic side the species becomes extinct. An extinct species cannot have one individual more fit than another when neither exist. > | > | Hasn't got anything to do with organisms evolving to rectify the > | > | climate. One of the misconceptions of evolution is that something [quoted text clipped - 31 lines] > the species becomes extinct. An extinct species cannot > have one individual more fit than another when neither exist. There are... what... about a trillion or more different species of life on and in this world at any one time? Many of those species just now popped into existence as beginning life (as if with them, life is just now in its beginning upon the Earth). And many of those just now popped out existence....gone extinct (reminds me of flash occurrences in a particle accelerator). Now evolutionary, or revolutionary, variations in a specific species, that has been around for a while, pop into existence all the time...and just as often as not, really more often that not, pop out of existence, gone extinct, just about as quickly as they (variation) came. Then there are the frozen seed spores of life -- very, very, hard to kill -- that arrive upon the Earth from anywhere and everywhere in the universe at large. No matter how hard to kill, many of these immigrants do not survive the trip or the environment of space. But there are so many of them at all times, neverendingly arriving. Now to go back to "beginning life." For some reason it comes into existence wisely fully equipped immediately to eat, divide, and fight savagely for species' multiplication / prosperity...thus species' survival. Even a base building block creature of life [just now] coming seemingly from up out of nowhere is fully a world, even a universe, of life all in itself since it knows so much of what it needs to know so instantaneously with its appearance. It may even know it [previous] to its appearance here...or its coalescence or spark here. It is a frontier, a frontiering, creature: a Space Age [life-chance] like the others; something the Dark Age Utopian (the not any longer to multiply, prosper, or survive, walking extinct) so [flatly / equally] obviously is not. GLB >> This wasn't supposed to go to soc.men actually. >> [quoted text clipped - 14 lines] > > Yousuf Khan It would have to have life develop into a very different set of species than we now have. Most or intolerant of high temperatures as this tends to cause proteins to degenerate. And protein specificity and moderate temperatures allows this. With very high temperatures there might continue to be unicellular life forms that can tolerate such but not multicellular and highly specialized life forms. Besides such radical evolutionary changes would take tens if not hundreds of millions of years. By then higher life forms might very well have succumbed to more quickly destructive catastrophes. FK >>> This wasn't supposed to go to soc.men actually. >>> [quoted text clipped - 25 lines] > quickly destructive catastrophes. > FK Look, we're only talking about an average temp increase of 10 degC. There's more than that between equatorial and mid lattitudes. SignatureDirk http://www.transcendence.me.uk/ - Transcendence UK Remote Viewing classes in London >>>> This wasn't supposed to go to soc.men actually. >>>> [quoted text clipped - 28 lines] > Look, we're only talking about an average temp increase of 10 degC. > There's more than that between equatorial and mid lattitudes. What about the non-poikiothermic life forms. They would find their chemical reaction rates approximately doubled with such an increase in temperature. FK >>>>> This wasn't supposed to go to soc.men actually. >>>>> [quoted text clipped - 33 lines] > temperature. > FK Emigrate. SignatureDirk http://www.transcendence.me.uk/ - Transcendence UK Remote Viewing classes in London > It would have to have life develop into a very different set of species > than we now have. Most or intolerant of high temperatures as this tends [quoted text clipped - 5 lines] > years. By then higher life forms might very well have succumbed to more > quickly destructive catastrophes. Hardly! Most of the species needed to rectify the climate probably already exist now. Really, if you look at the history of evolution, it's not a matter of developing new species to take advantage of a new condition. The species already existed at the time of the change in condition, and something that was just getting along before, will all of a sudden shoot to prominence in the new regime. So that's what's going to happen now too. Some species will go extinct, while others will begin to flourish. Yousuf Khan > And according to the Gaia Hypothesis, life on Earth itself will evolve > to absorb and subsume any climate conditions that will lead to runaway > greenhouse effects. > > Yousuf Khan Yes, and it won't include human beings. The extremophile bacteria will have the run of the place. I mean, you as an individual have white blood cells. Do you care it they all die? As long as you don't get an infection, you are happy. You have no concern over the life and well being of individual cells in your body. They could be suffering the agonies of hell, but as long as your brain is happy you will not be concerned. The same for this supposed Gaia (which I don't really believe exists). An organism doesn't pay attention to its own components. If Gaia can remain healthy with just a few unintelligent, extremophile bacteria, she will be happy. Without human beings, she may be even happier. I don't think Gaia is a useful hypothesis for anything. In effect, it merely says that some organisms will survive no matter what. And that they will probably affect the geology of the earth somewhere down the line. Most of us are concerned with only with human beings, or maybe with the inclusion of a few animal relatives. I definitely would like to see dolphins and chimpanzees survive with us. But most cultures can't even see other human beings as worth the skin. I will not trust any deity, least of all Gaia, to protect our interests. All and all, I think it would be best if we reduce our carbon footprint. Let the deities take care of themselves. If we can't control ourselves, then maybe human beings would be better off extinct. > Yes, and it won't include human beings. The extremophile bacteria > will have the run of the place. [quoted text clipped - 3 lines] > in your body. They could be suffering the agonies of hell, but as long > as your brain is happy you will not be concerned. Yeah, of course I would care if all of my white blood cells died, so would you, because that would mean that you have some kind of immunological disease such as AIDS, and you're gonna die. I wouldn't care about individual white blood cells, but as long as there were enough of them around to keep me functioning, I'd be happy. Same goes for my heart cells, and lung cells, etc., etc. Our bodies maintain an average temperature of 37°C (98.6°F), not for the sake of our comfort, but for the sake of keeping our individual cells alive. If one group of my cells died, then chances are that other groups of my cells would die too, if they depended on them. And then my whole body would die. A dead body would initially look the same as a living body, but not for long, and eventually it'll just be a skeleton. A skeleton is an immensely less desirable state for a body to be in, than a living one. > The same for this supposed Gaia (which I don't really believe > exists). An organism doesn't pay attention to its own components. If > Gaia can remain healthy with just a few unintelligent, extremophile > bacteria, she will be happy. Without human beings, she may be even > happier. You're subscribing to the same self-loathing philosophy that most environmentalists have lifetime memberships in. As far as the environmentalists are concerned, all of the ills of the world are caused by humans, and only the humans. All species extinctions are always man's fault; if they could blame us for the asteroid that killed the dinosaurs 65 million years before man even existed, then they would. And of course, global warming can't be a natural thing, it must always be man's fault. If Gaia is alive, then how do you know that man isn't exactly the evolution that Gaia needs to go through to keep living? Everything was leading upto this point where a type of cell evolved that could leave Gaia and inhabit other planets (much like plant spores) and take Gaia's legacy with it. The "unintelligent extremophile bacteria" can't take Gaia into space. > I don't think Gaia is a useful hypothesis for anything. In > effect, it merely says that some organisms will survive no matter [quoted text clipped - 8 lines] > footprint. Let the deities take care of themselves. If we can't > control ourselves, then maybe human beings would be better off extinct. Depends on which version of the Gaia Theory you subscribe to. The Weak Gaia Theories simply state that organisms have changed the environment of the planet they inhabit. Pretty undeniable stuff, but not very useful. Strong Gaia Theories, which are the hardest to prove, believe the Earth itself is the ultimate living organism on Earth. All of the biota and the abiota living inside it were just the individual cells of this organism. The Strongest of the Gaia Theories even believe that Earth is just one of many Gaias in the Universe, and that the entire Universe is just a giant hive of evolving organisms. Yousuf Khan >If one group of my cells died, then chances are that other groups of my >cells would die too, if they depended on them. And then my whole body >would die. Not necessarily. Cells die in your body all the time. Your hair, which grows all the time, consists mostly of dead cells. The very outermost part of your skin also consists of dead cells, which protects the living cells inside the skin and your body. As a matter of fact, almost all of your body is renewed (= the cells are replaced by other cells) every 5 to 7 years or so (the figure varies depending on which part of the body). As long as this is in equilibrium, your organism remains healthy. But if your body would start to generate new cells in an uncontrolled way, you'll get cancer. And if your body would generate too few new cells, you'll get sick and die too - the latter often happens to old people. Signature---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stjarnhimlen dot se WWW: http://stjarnhimlen.se/ > Not necessarily. Cells die in your body all the time. Your hair, which grows > all the time, consists mostly of dead cells. The very outermost part of > your skin also consists of dead cells, which protects the living cells > inside the skin and your body. As a matter of fact, almost all of your > body is renewed (= the cells are replaced by other cells) every 5 to 7 > years or so (the figure varies depending on which part of the body). and i have little funerals for all of them. it's only right. >> If one group of my cells died, then chances are that other groups of my >> cells would die too, if they depended on them. And then my whole body [quoted text clipped - 10 lines] > get cancer. And if your body would generate too few new cells, you'll get > sick and die too - the latter often happens to old people. Yes, I agree with that, I just didn't say it in so many words. Yousuf Khan > The conventional explanation of the run-away greenhouse effect, > which produced the conditions we see on Venus today, is that [quoted text clipped - 6 lines] > This is absurd and impossible. In fact I am sure the temperature on > Venus has never been significantly hotter than today. [snip cogent analysis] The following sends the wrong message, doesn't it? It's factual. <http://wattsupwiththat.wordpress.com/2008/06/21/a-window-on-water-vapor-and-plan etary-temperature-part-2/> Sunspots and such, Graphics ======== <http://upload.wikimedia.org/wikipedia/commons/2/28/Sunspot_Numbers.png> The most recent minimum, to the right, has averaged about 10 sunspots/month. <http://www.dxlc.com/solar/images/solar.gif> local solar flux is dropping <http://www.skepticalscience.com/images/tsi_composite.gif> local solar flux is dropping <http://www.swpc.noaa.gov/SolarCycle/Ap.gif> local solar flux is dropping to 10-year lows <http://www.swpc.noaa.gov/SolarCycle/sunspot.gif> projected sunspot number. All we need do is wait and see. The third unmentioned red curve would be more interesting - stays flat. COMMENTARY ========== Global Cooling is nothing new. Click on graphics to enlarge. <http://smarteconomy.typepad.com/smart_economy/2006/09/global_warming_.html> <http://www.newrivervalleynews.com/content/view/12742/261/> <http://www.climatescienceinternational.org/index.php?option=com_content&task=vie w&id=31&Itemid=1> <http://ff.org/centers/csspp/library/co2weekly/20060920/20060920_13.html> layman reference <http://www.sciencedaily.com/releases/2004/06/040602061025.htm> slightly better <http://www.grisda.org/origins/10051.htm> data Weather is always extreme compared to climate. One can play the GLOBAL WARNING game with anything, earthquakes to <http://thepoorman.net/2008/06/18/gregg-easterbrook-is-wait-for-it-an-idiot/> Proximity is not causality. More hurricanes than any other time in history were predicted post-Katrina! What does the highly anomalous *absence* of Caribbean hurricanes portend? Extreme hurricane disasters! Eventually a pulse will appear. So? SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > The conventional explanation of the run-away greenhouse effect, > which produced the conditions we see on Venus today, is that > the evaporation of water vapor caused the temperature to rise so > high that the atmosphere became unbound. This is not an explanation I've ever heard of. 1. The explanation I've heard involves 90 bars of carbon dioxide. Is there any water vapor at all in the Venusian atmosphere? 2. For an atmosphere that is alleged to be "unbound," there seems to be quite a lot of it. > I have seen a journal article that says the temperature would reach > 'several thousand degrees' until the surface could 'radiate in the > visible'. Reference? The highest possible temperature is the effective temperature of the Sun divided by the square root of 2. This is just conservation of energy for an imaginary atmosphere that is completely transparent to visible light and completely opaque at longer wavelengths. Of course no real atmosphere will be ideal in this fashion. SignatureSteve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) > In article <cbedbe10-d94c-4ccc-a1b0-35f17b7f5...@w7g2000hsa.googlegroups.com>, > [quoted text clipped - 7 lines] > 1. The explanation I've heard involves 90 bars of carbon dioxide. Is > there any water vapor at all in the Venusian atmosphere? Yes, about 0.005 AM (air masses) at present (which is nearly the same as in our atmosphere). But the D/H ratio tells us that there was once much more, perhaps nearly the same as Earth (650 AM, 3/4 in the oceans). It is thought that the water loss to space currently is nearly balanced by outgassing, and therefore the concentration will fall only slowly. > 2. For an atmosphere that is alleged to be "unbound," there seems to > be quite a lot of it. The theory says that most of the atmosphere escaped hydrodynamically during the 'run-away' phase. It is now quite bound. In any case, the CO2 observed today in the atmosphere I believe mostly outgassed after the loss of the oceans. > > I have seen a journal article that says the temperature would reach > > 'several thousand degrees' until the surface could 'radiate in the > > visible'. > > Reference? I can't find it now. > The highest possible temperature is the effective > temperature of the Sun divided by the square root of 2. This is just > conservation of energy for an imaginary atmosphere that is completely > transparent to visible light and completely opaque at longer > wavelengths. I don't know how you did this calculation, but it can't be right. The temperature also depends on the distance from the Sun. I get, with the Wien's law approximation, log (Ts/T) + E (1/T - 1/Ts) = log 4 + 2 log (R/Rs) Let's compute the temperature if the Earth were replaced with such a body. Since Ts ~ 0.5 ev and R/Rs ~ 210, we'll assume E = 1.75 ev (the cutoff of 'the visible'), log (0.5/T) + 1.75 (1/T - 2) ~ 12 I estimate from that T ~ 0.125 ev or 1,450 K. > Of course no real atmosphere will be ideal in this fashion. No, of course not. What would the Earth's surface temperature be if the oceans evaporated entirely into the air? There's about 500 atm of water in the ocean, which is above the critical point. A saturated H2O atmosphere will follow the vapor-pressure curve up to the critical point, then the adiabatic rate from there - but that's pretty shallow, since Cp > 10 for a large region near critical. The critical point is 218 atm and 647 K, and assuming Cp > 10 above that, the surface temperature can't be more than T = 647 K (500/218)^(1/10) = 703 K . That's slightly cooler than Venus today, and is the maximum temperature we could expect in a greenhouse on Earth. Andrew Usher |
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