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The runaway greenhouse effect on Venus

What the science says...

Venus very likely underwent a runaway or ‘moist’ greenhouse phase earlier in its history, and today is kept hot by a dense CO2 atmosphere.

Climate Myth...

Venus doesn't have a runaway greenhouse effect

Venus is not hot because of a runaway greenhouse.

In keeping with my recent theme of discussing planetary climate, I am revisiting a claim last year made by Steven Goddard at WUWT (here and here, and echoed by him again recently) that “the [runaway greenhouse] theory is beyond absurd,” and that it is pressure, not the greenhouse effect that keeps Venus hot.  My focus in this post is not on his alternative theory (discussed here), but to discuss Venus and the runaway greenhouse in general, as a matter of interest and as an educational opportunity.  In keeping my skepticism fair, I’d also like to address claims (sometimes thrown out by Jim Hansen in passing by) that burning all the coal, tars, and oil could conceivably initiate a runaway on Earth.

It is worth noting that the term runaway greenhouse refers to a specific process when discussed by planetary scientists, and simply having a very hot, high-CO2 atmosphere is not it.  It is best thought of as a process that may have happened in Venus’ past (or a large number of exo-planets being discovered close enough to their host star) rather than a circumstance it is currently in.

A Tutorial of Present-Day Venus

Venus’ orbit is approximately 70% closer to the sun, which means it receives about 1/0.72 ~ 2 times more solar insolation at the top of the atmosphere than Earth.  Venus also has a very high albedo which ends up over-compensating for the distance to the sun, so the absorbed solar energy by Venus is less than that for Earth.  The high albedo can be attributed to a host of gaseous sulfur species, along with what water there is, which provide fodder for several globally encircling sulfuric acid (H2SO4) cloud decks.  SO2 and H2O are the gaseous precursor of the clouds particles; the lower clouds are formed by condensation of H2SO4 vapor, with SO2 created by photochemistry in the upper clouds. Venus’ atmosphere also has a pressure of ~92 bars, nearly equivalent to what you’d feel swimming under a kilometer of ocean.  The dense atmosphere could keep the albedo well above Earth’s even without clouds due to the high Rayleigh scattering (the effect of clouds on Venus and how they could change in time is discussed in Bullock and Grinspoon, 2001). Less than 10% of the incident solar radiation reaches the surface.

Observations of the vapor content in the Venusian atmosphere show an extremely high heavy to light isotopic ratio (D/H) and is best interpreted as a preferential light hydrogen escape to space, while deuterium escapes less rapidly.  A lower limit of at least 100 times its current water content in the past can be inferred (e.g. Selsis et al. 2007 and references therein).

The greenhouse effect on Venus is primarily caused by CO2, although water vapor and SO2 are extremely important as well.  This makes Venus very opaque throughout the spectrum (figure 1a), and since most of the radiation that makes its way out to space comes from only the very topmost parts of the atmosphere, it can look as cold as Mars from IR imagery. In reality, Venus is even hotter than the dayside of Mercury, at an uncomfortable 735 K (or ~860 F). Like Earth, Venusian clouds also generate a greenhouse effect, although they are not as good infrared absorbers/emitters as water clouds.  However, the concentrated sulfuric acid droplets can scatter infrared back to the surface, generating an alternative form of the greenhouse effect that way.  In the dense Venusian CO2 atmosphere, pressure broadening from collisions and the presence of a large number of absorption features unimportant on modern Earth can come into play (figure 1b), which means quick and dirty attempts by Goddard to extrapolate the logarithmic dependence between CO2 and radiative forcing make little sense.  The typical Myhre et al (1998) equation which suggests every doubling of CO2 reduces the outgoing flux at the tropopause by ~4 W/m2, although even for CO2 concentration typical of post-snowball Earth states this can be substantially enhanced.  Figure 1b also shows that CO2 is not saturated, as some skeptics have claimed.


 Figure 1: a) Radiant spectra for the terrestrial planets.  Courtesy of David Grisp (Jet Propulsion Laboratory/CIT), from lecture "Understanding the Remote-Sensing Signatures of Life in Disk-averaged Planetary Spectra: 2" b) Absorption properties for CO2. The horizontal lines represent the absorption coefficient above which the atmosphere is strongly absorbing.  The green (orange) rectangle shows that portion of the spectrum where the atmosphere is optically thick for 300 (1200) ppm.  From Pierrehumbert (2011)

 How to get a Runaway?

To get a true runaway greenhouse, you need a conspiracy of solar radiation and the availability of some greenhouse gas in equilibrium with a surface reservoir (whose concentration increases with temperature by the Clausius-Clapeyron relation).  For Earth, or Venus in a runaway greenhouse phase, the condensable substance of interest is water— although one can generalize to other atmospheric agents as well.

The familiar water vapor feedback can be illustrated in Figure 2, whereby an increase in surface temperature increases the water vapor content, which in turn results in increased atmospheric opacity and greenhouse effect.  In a plot of outgoing radiation vs. temperature, this would result in less sensitive change in outgoing flux for a given temperature change (i.e., the outgoing radiation is more linear than one would expect from the σT4 blackbody-relation). 


Figure 2: Graph of the OLR vs. T for different values of the CO2 content and relative humidity.  For a fixed RH, the specific humidity increases with temperature. The horizontal lines are the absorbed shortwave radiation, which can be increased from 260-300 W m-2.  The water vapor feedback manifests itself as the temperature difference between b’-b and a’-a, since water vapor feedback linearizes the OLR curve.  Eventually the OLR asymptotes at the Komabayashi-Ingersoll limit.  Adopted from Pierrehumbert (2002)


One can imagine an extreme case in which the water vapor feedback becomes sufficiently effective, so that eventually the outgoing radiation is decoupled from surface temperature, and asymptotes into a horizontal line (sometimes called the “Komabayashi-Ingersoll” limit following the work of the authors in the 1960’s, although Nakajima et al (1992) expanded upon this limiting OLR in terms of tropospheric and stratospheric limitations).  In order to sustain the runaway, one requires a sufficient supply of absorbed solar radiation, as this prevents the system from reaching radiative equilibrium.  Once the absorbed radiation exceeds the limiting outgoing radiation, then a runaway greenhouse ensues and the radiation to space does not increase until the oceans are depleted, or perhaps the planet begins to get hot enough to radiate in near visible wavelengths.


Figure 3: Qualitative schematic of how the ocean reservoir is depleted in a runaway.  From Ch. 4 of R.T. Pierrehumbert’s Principles of Planetary Climate


On present-day Earth, a “cold trap” limits significant amounts of water vapor from reaching the high atmosphere, so its fate is ultimately to condense and precipitate out.  In a runaway scenario, this “cold trap” is broken and the atmosphere is moist even into the stratosphere.  This allows energetic UV radiation to break up H2O and allow for significant hydrogen loss to space, which explains the loss of water over time on Venus.  An intermediate case is the “moist greenhouse” (Kasting 1988) in which liquid water can remain on the surface, but the stratosphere is still wet so one can lose large quantities of water that way (note Venus may never actually encountered a true runaway, there is still debate over this).  Kasting (1988) explored the nature of the runaway /moist greenhouse, and later in 1993 applied this to understanding habitable zones around main-sequence stars.  He found that a planet with a vapor atmosphere can lose no more than ~310 W/m2, which corresponds to 140% of the modern solar constant (note the albedo of a dense H2O atmosphere is higher than the modern), or about 110% of the modern value for the moist greenhouse.


Earth and the Runaway: Past and Future


Because Earth is well under the absorbed solar radiation threshold for a runaway, water is in a regime where it condenses rather than accumulating indefinitely in the atmosphere.  The opposite is true for CO2, which builds up indefinitely unless checked by silicate weathering or ocean/biosphere removal processes.  In fact, a generalization to the runaway threshold thinking is when the solar radiation is so low, so that CO2 condenses out rather than building up in the atmosphere, as would be the case for very cold Mars-like planets.  Note the traditional runaway greenhouse threshold is largely independent of CO2 (figure 2 & 4; also see Kasting 1988), since the IR opacity is swamped by the water vapor effect.  This makes it very difficult to justify concerns over an anthropogenic-induced runaway.



Figure 4: The H2O–CO2 greenhouse. The plot shows the surface temperature as a function of radiated heat for different amounts of atmospheric CO2 (after Abe 1993). The albedo is the fraction of sunlight that is not absorbed (the appropriate albedo to use is the Bond albedo, which refers to all sunlight visible and invisible). Modern Earth has an albedo of 30%. Net insolations for Earth and Venus ca. 4.5 Ga (after the Sun reached the main sequence) are shown at 30% and 40% albedo. Earth entered the runaway greenhouse state only ephemerally after big impacts that generated big pulses of geothermal heat. For example, after the Moon-forming impact the atmosphere would have been in a runaway greenhouse state for ∼2 million years, during which the heat flow would have made up the difference between net insolation and the runaway greenhouse limit. A plausible trajectory takes Earth from ∼100 bars of CO2 and 40% albedo down to 0.1–1 bar and 30% albedo, at which point the oceans ice over and albedo jumps. Note that CO2 does not by itself cause a runaway. Also note that Venus would enter the runaway state when its albedo dropped below 35%.  Se e Zahnle et al 2007


This immunity to a runaway will not be the case in the long-term.  In about a billion years, the sun will brighten enough to push us into a state where hydrogen is lost much more rapidly, and a true runaway greenhouse occurs in several billion years from now, with the large caveat that clouds could increase the albedo and delay this process.

Interesting, some (e.g.. Zahnle et al 2007) have argued that Earth may have been in a transient runaway greenhouse phase within the first few million years, with geothermal heat and the heat flow from the moon-forming impact making up for the difference between the net solar insolation and the runaway greenhouse threshold, although this would last for only a brief period of time.  Because the runaway threshold also represents a maximum heat loss term, it means the planet would take many millions of years to cool off following such magma ocean & steam atmosphere events of the early Hadean, much slower than a no-atmosphere case (figure 5).


Figure 5: Radiative cooling rates from a steam atmosphere over a magma ocean. The radiated heat is equal to the sum of absorbed sunlight (net insolation) and geothermal heat flow. The plot shows the surface temperature as a function of radiated heat for different amounts of atmospheric H2O (adapted from Abe et al. 2000). The radiated heat is the sum of absorbed sunlight (net insolation) and geothermal heat flow. The different curves are labeled by the amount of H2O in the atmosphere (in bars). The runaway greenhouse threshold is indicated. This is the maximum rate that a steam atmosphere can radiate if condensed water is present. If at least 30 bars of water are present (a tenth of an ocean), the runaway greenhouse threshold applies even over a magma ocean. Note that the radiative cooling rate is always much smaller than the σT4 of a planet without an atmosphere


Venus likely underwent a runaway or “moist greenhouse” phase associated with rapid water loss and very high temperatures.  Once water is gone, silicate weathering reactions that draw down CO2 from the atmosphere are insignificant, and CO2 can then build up to very high values.  Today, a dense CO2 atmosphere keeps Venus extremely hot.

Last updated on 11 April 2011 by Chris Colose. View Archives

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Comments 26 to 50 out of 267:

  1. Rosco - try using the search button up top and posting on topic. But first read the articles - you need to learn some science to make sense. If what you post isnt relevant to venus, then I guess it will be deleted. If you want your articles read, then stick to the rules.

    [DB] "But first read the articles"

    I can think of no better advice to give someone who is not yet doing so.  Thank you.

  2. Rosco - you seem to disagree on the possibility that CO2 makes it more difficult for energy entering the climate system to leave that system. These energy forms are at different wavelengths and so CO2 affects one over the other. CO2 doesn't create energy on its own (nobody has ever suggested this), it just reduces the ability of the whole system to shed energy effectively. Since the only way the Earth's (or Venus') climate system can shed energy is by radiation, that is rather important. Please be courteous and read the links you were provided with earlier. Based on your postings I suspect you haven't. What temperature would Earth be, if the atmosphere was unable to trap any of the outgoing longwave radiation?
  3. Watch that word "trap" sky--it's a denialist deviation point. I prefer "lengthen the path" of OLR. Rosco, what power are you assigning to convection? And are you implying radiative transfer has nothing to do with the average temperature of the Venusian atmosphere? Let's see some specifics on Venus, or take your theory over to the Colose article I linked earlier . . . please.
  4. 28, DSL, Rosco, I agree. I just looked around and came up with the same thread. The Planetary Greenhouse Interestingly, there's nothing better. No one else in the history of creative denial ever seems to have tried to argue that the greenhouse effect isn't relevant because convection + conduction does it all. Rosco, if you post a clear and concise argument on that thread (leaving out all of your observations that prove that conduction and convection exist, which is a strawman -- that is to say, an argument against something which no one is really contesting, and so of no value in advancing the discussion) then I will post a clear and reasoned response.
  5. There has never been any demonstrated mechanism of trapping heat - it is the engineer's dream to achieve this and increase efficency of machines. Even the stars have an energy input through gravity and if the assertions about Venus albedo being so reflective that almost no radiation reaches the surface there must be some source of heat that we don't know about. I think Earth's temperature would be about what it is plus or minus a degree or two. We would still have the sun's input and water.

    [DB] "There has never been"

    Never?  In over 150 years of scientists researching the greenhouse effect?

    Honestly, you betray your extreme lack of knowledge with comments like this.  You are not doing well, here.

  6. Heard of insulation? Plain ordinary convention physics with 100 of years of experimental evidence has no trouble calculating the temperature on the surface of venus without any mysterious energy source. By contrast, your misunderstanding has a problem. If you look at the energy diagram you see the breakdown, but most importantly, this energy flows are measured. In your understanding, you could not account for these measurements. Do you agree that the test of whether the science is right is measurement? By all means come up with alternative physics but your alternative theory in which the GHE is missing must be able to account for what we actually observe.
  7. DSL - point taken! Word-play is always dangerous ground. #30: Estimates of Earth's temperature without GHG's come in at well below freezing (IIRC ~-18C), mentioned in Chris Colose's article. The Sun does not provide enough energy this far away from it.
  8. 30, Rosco,
    There has never been any demonstrated mechanism of trapping heat
    Even the stars have an energy input through gravity
    Misleading or misunderstood. See Kelvin-Helmholtz timescale. See nuclear reactions, the true source of energy in stars. But in a nutshell, for the potential energy of gravity to be converted to another form, work must be done, meaning the object must compress, which it cannot do indefinitely (for a star, it would "burn out" in mere 18 million years). Otherwise it is a perpetual motion machine that is creating energy and violating the First Law of Thermodynamics.
    ...there must be some source of heat that we don't know about.
    I think...
    Fuzzy thinking of no value. What you think does not make it true. It does not create facts or truths, and is not a valid argument.
    We would still have the sun's input...
    Yes, about 241 W/m2 of solar input, which would bring the planet to 255K, when it is in fact at 288K. The question is how do we get that extra 33K? Answer: The Greenhouse Effect This is all very, very basic science. Please follow the links and read before posting further comments.
  9. Rosco, did you read the paper I linked to? Did you? I recall you saying, "I'm more than open to listen." Reading is "listening" when writing is the primary means of communication. You are not arguing from a physical model. You're arguing from what seems to be right to you. If you accept "seems to be right" as an argument, then we are at an impasse, because then my word becomes as good as yours, and we're all right. If you don't accept "seems to be right" as an argument, then start describing your physical model. Everything you've said so far suggests that you don't believe that CO2 absorbs and emits at specific frequencies (broadened by pressure). That might be a good place to start understanding. What are the emission/absorption spectra of Earth's (or Venus') ten most populous atmospheric gases? If you don't know, then you're not prepared to enter the discussion. While some here might tell you to go away (either directly or in tone), I won't.

    [DB] "While some here might tell you to go away (either directly or in tone), I won't."

    I think you speak for everyone in that our sincerest wish is for Rosco to be able to express himself more ably by addressing the science directly, uncomplicated by feelings and fuzzy thinking.

  10. Again, a Climastrology button is needed for Rosco. These sorts of creative science perception discussions need a thread of their own, because they really don't belong anywhere, and hence tend to wander about willy-nilly. Rosco barely met the requirements of this thread by rather randomly throwing the word "Venus" into his post. This sort of Alice-through-the-looking-glass discussion has been happening just far too often in recent months.
  11. I hope you will consider posting this - it is an analysis of energy input to a planet's atmosphere that is surely a starting point for discussion. You wanted a concise analysis well this may meet your requirements. The solar constant TOA Earth is ~1368 W/sq m agreed ? The solar constant TOA Venus is ~1.91 times that ~2612 W/sq m agreed ? I will talk about earth initially because we have better knowledge. The sun's radiation is approximately parallel. When it hits an atmosphere at 90 degrees to the tangent it will be absorbed at the maximum. When it hits at an angle to the tangent some will be reflected and some will pass into the atmosphere. The maximum component of the radiation that enters at 90 degrees to the tangent is the cosine of the latitude of the point - hence at the mid point the angle is 0 cos 0 = 1. Let’s stop the planet rotating - the solar constant is still 1368 W/sq m. The earth presents approximately a hemisphere to the sun's insolation. At the midpoint of the hemisphere the tangent to the atmosphere is at 90 degrees to the insolation and the angle between the incident radiation and the normal is zero - at the poles the tangent to the atmosphere is parallel to the radiation and the angle to the normal is 90 degrees. The tangent to the atmosphere at any point North or South is the cosine of the latitude. The insolation at any point varies as the cosine curve of the latitude. So let’s stop the earth at midday on a point on the equator when the sun is vertical to the equator and consider a line from north to south. At the mid point the insolation is 1368 W/sq m minus the albedo minus absorption by the atmosphere. If not, why not ? If you consider any other point on the hemisphere the angle the sun's parallel rays make to the tangent is the cosine of the latitude. Therefore the factor to reduce the insolation incident on the atmosphere is the cosine of the latitude – that is it varies from 1 at the midpoint to zero at the “pole”. So at the equator the insolation is ~ 684 W /sq m - 1368/2 - additional source is IPCC - Chapter 1 Historical Overview of Climate Change Science P115 -"About half the solar radiation is absorbed by the Earth's surface and warms it." This energy is capable of causing a maximum temperature of 331 K or ~58C which if my memory serves me well is approximately the highest temperature recorded. If the albedo were uniform over the earth - which it isn't - the maximum insolation should vary as a cosine curve from the midpoint north or south. For example consider Baghdad - ~ 33 N (why choose Baghdad ? - A well known desert location with "normal albedo low cloud and a well documented temperature record) - the maximum insolation is cos 33 x 684 = ~573.65 W/sq m. Maximum temperature for this insolation is ~317 K or 44 C. Meterological records show Baghdad's maximum temperatures are ~ 44 C in summer. So how does this even matter ? It demonstrates that maximum is different to average - obvious. It demonstrates that Earth and Venus may possibly receive more radiation and hence have higher temperatures than is calculated by reducing solar insolation to ~240 W/sq m to calculate the average temperature on Earth or to ~132 W/sq m on Venus. Again, I have not denigrated anybody's opinion simply proposed some discussion points.
  12. Oh dear. 'Discussion' here is a bit (not very much, but a bit) like discussing an English or history topic at an educational institution. Reading the material first is an unavoidable requirement of talking or writing on the item in question. You've been given quite a few excellent references. Stop writing, thinking, discussing for a while and do some reading. You only need to choose a couple of those offered to start with. But you do need to get started.
  13. What is wrong with the exchange of ideas and analysis ?
  14. Sphaerica said "false" to my assertion that "There has never been any demonstrated mechanism of trapping heat". OK - what is it ? Sphaerica said "Misleading or misunderstood" to my assertion that "Even the stars have an energy input through gravity" Are you denying it was gravity which initiated all the fusion reactions in the stars through increasing pressure resulting in increasing temperatures which eventually reach the point where fusion reactions can take place ? If you do assert this then I think you will find yourself at odds with every theory about the universe. From what I remember from my studies gravity is credited with the formation of virtually everything after the big bang - our rocky planets are thought to have accreted from the dust and gases of space until they achieved sufficient mass that this accretion process accelerated because gravity exerts a force proportional to mass - F = mass X acceleration. The core of Earth is hot due to gravity which is ultimately responsible for vulcanism and our magnetic field. Sphaerica accuses me of "Fuzzy thinking of no value". OK - well demolish the arguement posted above. The fact is you cannot unless you reduce the solar insolation to ~342 W/sq m then again by the albedo to achieve ~240 W/sq m. You must justify this by reasoned argument. What you need to demonstrate is why this reduction is valid when at any point in time no matter what the undeniable truth is that at TOA Earth the solar constant is 1368 W/sq m and at any time the insolation on the Earth's surface is the radiation normal to the atmosphere minus the albedo and whatever is absorbed by the atmosphere. All climate scientists agree with the value of the solar constant as 1368 W/sq m. If the earth only receives 240 W /sq m whare did the other 1128 W/sq m go ? The IPCC state ~50% makes it to the surface - this is broken down to 30% reflected (albedo) 20 % absorbed by atmosphere - and don't tell no insolation is absorbed because it is shortwave because there are plenty of bands available to absorb the > 50 % of insolation that isn't visible light - ~ 44% of the insolation is in the infrared wavelebghts while ~ 8% is ultraviolet which is the most energetic. There is indisputable proof that the radiation TOA Earth is capable of raising the temperature much higher than minus 18 C. NASA quotes the maximum temperature on the moon as in excess of 120 C. This explains what a fantastic shield our atmosphere is.
    Response: You continue to refuse to get a basic education. You are derailing this thread. All other readers, I suggest you simply stop responding to him.
  15. PS - I am not arguing from what seems to be right to me. I have a degree in Environmenta health Science and a degree in Engineering Technology. I was a professional Environmental Health Officer whose principal role was to enforce Environmental legislation especially prosecuting individuals or businesses responsible for pollution. I have retired. My last University attendance was in 1994 when I completed the Engineering degree. Basic physics involves breaking down a force into its components for example using the sine and cosine of the incident angle so there is plenty of precedent for the use of this concept.
  16. I've read the response. I've quoted the IPCC. I've made valid calculations using Stefan-Boltzman to arrive at maximum temperatures for different radiation levels and I have provided 2 example that demonstrate actual recorded temperatures correlate almost exactly with what was calculated. I am simply proposing something to think about. I am certainly not uneducated - I achieved honours in nearly every subject I undertook in my 2 degrees.
  17. Rosco @39:
    "Are you denying it was gravity which initiated all the fusion reactions in the stars through increasing pressure resulting in increasing temperatures which eventually reach the point where fusion reactions can take place ?"
    The gravitational force is not consumed by the production of energy in stars. Therefore, regardless of the fact that it is essential for establishing the conditions of fusion, it is not the source of the energy. The energy in fact comes from the conversion of mass to energy by fusion in that the daughter elements in fusion are very slightly lighter than the parent particles.
    "The core of Earth is hot due to gravity which is ultimately responsible for vulcanism and our magnetic field."
    The Earth was heated to a molten state by impacts early in its history, but the heat from those impacts escaped to space in approximately 10 million years of the earths 4,500 million year history. It remains molten because of the energy released by fission of radioactive isotopes (primarily Uranium) in the core, along with a small amount of energy from tidal friction. Again in fission, the combined mass of the daughter isotopes (and particles) is slightly less than that of the parent isotopes, the difference being released as energy. Gravitation is completely irrelevant to this process. These may seem like minor points to you, but what they show to me an others on this site is a casual disregard for accuracy which permeates your posts and turn them into scientific garbage. As others have done, I cannot recommend highly enough that you sit down and read before continuing to post this nonsense online.
  18. Rosco @39:
    "What you need to demonstrate is why this reduction is valid when at any point in time no matter what the undeniable truth is that at TOA Earth the solar constant is 1368 W/sq m and at any time the insolation on the Earth's surface is the radiation normal to the atmosphere minus the albedo and whatever is absorbed by the atmosphere. All climate scientists agree with the value of the solar constant as 1368 W/sq m. If the earth only receives 240 W /sq m whare did the other 1128 W/sq m go ? "
    Basic Education: Area of a circle = pi r^2 Area of a sphere = 4 pi r^2 Ratio of the area of a sphere to the area of a circle of identical radius = 4 Total energy flux from sunlight intercepted by the Earth = 1368 W/m^2 * pi RE^2, where RE is the radius of the Earth. Total area energy flux is distributed over = 4 * pi RE^2, where RE is the radius of the Earth. Therefore, average energy flux of sunlight intercepted per square meter of the Earh's surface equals 1368/4 = 342 W/m^2. And the average energy flux of sunlight intercepted after albedo on the Earth's surface equals 342 * 0.7 = 239.4 W/m^2. What is the value of an education if you just assume any time that you disagree with a climate scientist that the PhD heavily published climate scientists have simply forgotten basic facts of geometry, and not one of the thousands of climate scientists world wide have managed to notice? Because that is what you have done. Your automatic assumption that because you have a bachelors degree in engineering, the PhDs in physics must have got it wrong would be hilariously funny if it where not so sad, and the issue serious.
  19. 43, Tom Curtis, You're wasting your breath. Look at his comment here, where he says:
    Why is it valid to reduce solar insolation by a factor of 4 to calculate the "effective blackbody temperature" of a planet - especially Venus with it 200 odd earth day long day ? I get the geometry I just think it isn't relevant for a dynamic system.
    It's really hopeless, and pointless.
  20. Rosco: "PS - I am not arguing from what seems to be right to me." Rosco: "I get the geometry I just think it isn't relevant for a dynamic system." Eh?
  21. Sphaerica @44, I get that he won't get it. But perhaps some reader will not be familiar with spherical geometry, and will now see for themselves that Rosco is spouting complete and utter tripe.
  22. You still have not demonstrated how the solar constant is reduced from 1368 to 342. How do you explain the temperature on the moon ?
  23. Rosco @47, I have explained it in steps so small a grade 9 education is sufficient to follow, as proved by my explaining it to my daughter (who will no doubt have a good laugh if I show her this conversation). If you have not understood it, read again with care. It is not too hard. You have not raised any interesting questions about the moon. You have merely cited a vaguely remembered maximum temperature. Apparently you base all your reasoning on the assumption that the maximum temperature is the only relevant temperature, but I am disinclined to follow you in that absurdity.
  24. You still have not demonstrated how the solar constant is reduced from 1368 to 342
    Rosco, this is very, very, very simple. The amount of energy that strikes the earth is 1.748310 x 1017 W. [1368 W/m2 times the area of the earth that intercepts the sunlight, or 1.2780049 x 1014 km2]. Because the earth is rotating, this energy is distributed over the entire surface, not just one hemisphere. [Due to the geometry of a sphere versus the relatively linear approach of the sunlight the energy is not distributed evenly, but that issue is not yet a factor and is addressed later, we're only looking for the average energy per square meter. Note that your lengthy previous discussion of cosines and angles was wrong, and should be abandoned.] Albedo is not yet a factor. That is also considered later. We are simply looking for an average W/m2 to use for trivial calculations. The surface area of the earth is 5.1120196 x 1014 square meters. So we can compute the W/m2 as total energy received divided by total area receiving that energy, or 1.748310 x 1017 W / 5.1120196 x 1014 m2 = 341.99986 W/m2. It has now been explained to you. If you are incapable of following this simple logic, then you should simply stop posting. If you feel that you can dismiss this simple logic, merely because you want to but without a valid reason, then you are in serious denial and should perhaps apply some introspection to evaluate the cognitive dissonance that prevents you from rationally using your faculties to solve the very simplest aspects of the problem at hand, the foundation of which is accepted by every single actual climate scientist on the planet, including those who are also in serious denial about the final conclusions.
  25. That arguement is simply wrong. It takes 24 hours to distribute the energy over the earth and during that time the earth has completed one rotation and the whole of the earth is irradiated. Therefore reducing the insolation by a factor of four is not valid. Remember, a watt is a joule/sec so considering any point on earth at a single point in time is valid. If a watt did not involve time the geometric analysis, though simplistic, may have some validity. Tom Curtis @ 48 says "You have not raised any interesting questions about the moon. You have merely cited a vaguely remembered maximum temperature. Apparently you base all your reasoning on the assumption that the maximum temperature is the only relevant temperature, but I am disinclined to follow you in that absurdity." I think we can agree that 342 W/sq m results in ~278.7 K or about ~5.5 C. Obviously you insist the geometrical analysis is the correct analysis. The moon has no atmosphere and is obviously about the same distance from the sun therefore exposed to the same radiation level. The moon's temperature during the day is not ~278.7 K or about ~5.5 C. Obviously we have an anomaly that I find very interesting.

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