I thought I would quickly highlight this Realclimate post which is intended to be the best description of the Greenhouse effect. It’s written by Ramus Benestad, the author of this paper. The main reason I wanted to highlight it was for the animation, that I’ll include at the end of this post.
The basic idea is, I think, similar to what I was trying to describe in this post. If we had no atmosphere (or it was radiatively inactive) then all the energy radiated from the Earth would come from the surface and the surface temperature would be set by the radiated energy matching the energy received – about 255K if we reflect 30% of the incoming solar radiation (an albedo of 0.3). If there is a raditively active atmosphere (one with greenhouse gases) then these would act to increase the opacity of the atmosphere (making it opaque to some of the radiation coming from the surface) and some of the energy would be radiated from the within atmosphere, rather than all of it from the surface.
This allows us to consider the energy as being radiated from an effective emission height in the atmosphere, with the temperature at this height being essentially the same as the surface temperature in the absence of an atmosphere (about 255K assuming the same albedo). The temperature on the surface would then be set by whatever processes transport energy from the surface to this effective emission height. Since the greenhouse gases have increased the opacity in the atmosphere, this cannot all be via radiation. In the case of the Earth’s atmosphere, the dominant process is convection.
In a dry atmosphere, the temperature gradient to which the lower atmosphere would tend would be around 10K/km. The effective emission height in the Earth’s atmosphere is at around 6-7km, which suggests that if the only transport mechanism were convection, the surface temperature would be 60-70K warmer than it would be in the absence of a greenhouse effect. It clearly is not. The reason is that convection is not the only energy transport mechanism. Another is evporation. Water evaporates at the surface and is carried up into the atmosphere. When it condenses it releases energy and heats the atmosphere. It, however, doesn’t do this uniformly and so it acts to reduce the temperature gradient relative to what it would be in the presence of convection only.
Consequently, the typical temperature gradient in the Earth’s atmosphere is 5-6K/km which, with an effective emission height of 6-7km, gives a surface temperature about 33K warmer than it would be in the absence of the greenhouse effect. I should stress, however, that this is a fairly simple picture. The energy is not actually radiated from a single height in the atmosphere, and the temperature gradient is not always what you would expect from convection and evaporation, but it is quite a nice illustration of the general process.
It also allows one to consider what would happen if we add more greenhouse gases. As we do so, we increase the opacity and raise the effective emission height. The surface temperature then rises because the temperature gradient is largely set by non-radiative energy transport processes (convection and evaporation). An interesting point, though, is that the amount by which the surface warms depends on the relationship between convection and evaporation (which drives the hydrological cycle). The more the hydrological cycle intensifies, the less the surface actually warms. This, however, implies that lower surface warming would be associated with more dramatic changes to rainfall patterns, which – as the Realclimate post suggests – shouldn’t necessarily be interpreted as the climate being less sensitive to changes in external forcings.
In the past when I’ve written about this there have ended up being lengthy discussions in the comments about some of the details. Hopefully I’ve got it roughly right this time, but even the Realclimate post suggests that even among experts there are disagreements about how best to decribes this, so maybe I shouldn’t be surprised if not everyone agrees. Anyway, I think it’s nicely illustrated in the figure below.
...and Then There's Physics 
I too have taken an interest in Rasmus Benestad’s article and paper, albeit from a slightly different perspective. Here’s the part I recently highlighted on the blog of UKIP’s energy spokesman, Roger Helmer!
It is usually an advantage knowing why your explanation makes sense when you try to make an impressions on others. The same can be said for explaining climate change to the general public and informing them about how the greenhouse effect (GHE) is altered by the burning of fossil
fuels. Despite a strong consensus on climate change within the climate research community, the efforts to explain climate change to the society so far can be summed up as having had limited success.
I once had a brief conversation with Gavin Schmidt in the perhaps unlikely location of Exeter University about the perhaps unlikely topic of physics education in the United Kingdom. My thesis being that most people finish their education with no understanding of physics. Especially politicians, and In particular those that represent UKIP!
Another interesting thing about this paper, highlighted at RC in a comment from a certain Nic Lewis which has just emerged from moderation:
Thanks for a most interesting paper and, particularly, for providing computer code enabling the results to be easily replicated and investigated. It is a great pity that so few professional climate scientists make their code available. If more followed your example, I think it would result in increased confidence in their work and results by scientifically and technically minded people who, quite reasonably, want to convince themselves of the validity of results before they will accept them.
Unfortunately, from my perspective at least, the code is in R and in a supplementary PDF rather than a Git repository!
Jim –
The reason being..
https://xkcd.com/1597/
I’m sure that there is a point to Git. One day I’ll work out what it is..
More on topic, I do find that the concept of radiative height important, because without that you have problems explaining why saturation doesn’t limit warming.
Andrew – The point of Git, and SubVersioN before it, is primarily version control.
Back on topic, I also note this recent offering from Tamino:
https://tamino.wordpress.com/2016/02/14/global-warming-basics-greenhouse-gas/
Andrew,
Indeed, and the Realclimate post did make this point.
This is the mechanism for Manabe and Wetherald prediction of stratospheric cooling?
I had thought the same, but I think it is predominantly because an increase in CO2 in the stratosphere increases the stratosphere’s ability to radiate LW to space, but doesn’t increase its ability to absorb energy as that mostly comes from SW absorption by ozone. See this.
“Since the greenhouse gases have increased the opacity in the atmosphere, this cannot all be via radiation. In the case of the Earth’s atmosphere, the dominant process is convection.”
I think that is too easily said. In Trenberth’s budget, convection (thermals) is about 17 W/m2 – it’s actually worked out as a balancing term when everything else has been calculated. There is also 80 W/m2 in latent heat transport, but that is mostly only to rain level. The thing is, the atmosphere is mostly convectively stable, with lapse rate below the DALR, and even allowing for moisture. That means that convection requires work. There is some, and the energy comes from kinetic atmosphere of the wind. The outcome is a degree of heat pumping (down) which maintains the lapse rate gradient.
It’s also too easy to talk of a single emission height. That height varies hugely with frequency. In particular, there is a large chunk from surface at the atmospheric window frequency. With total emission constant, more GHG raises the emission height in their band, and reduces the total flux there. That has to be made up elsewhere, including AW. That means the surface has to warm. Most of the transport compensation for GHG blocked flux is not convection, but radiation in other wavelength bands, boosted by warming.
Linus on Git:
That is all.
Nick,
Yes, I was wondering if someone would point that out. In a sense, though, I think Trenberth’s diagram mainly represents energy flows from the surface into the atmosphere, so even it doesn’t capture all the energy flows (I think – the thermal component in the diagram has rather confused me).
Okay, that is an interesting point.
Yes, I realise and you’re correct that increasing GHGs really changes the emission height in some bands which is then compensated for by increased emission in other bands due to warming.
“The basic idea is, I think, similar to what I was trying to describe in this post. If we had no atmosphere (or it was radiatively inactive) then all the energy radiated from the Earth would come from the surface and the surface temperature would be set by the radiated energy matching the energy received – about 255K if we reflect 30% of the incoming solar radiation (an albedo of 0.3). ”
You cannot be serious about this, or are you?
Without a radiatively active component in the atmosphere why would the Earth surface reflect 30% of the incoming Solar Radiation?
The albedo must be < or = to about 0.1
eg think about water making up 70% of Earth surface area.
Since the point of Benestad’s article is to advance climate change communication, and specifically the GHE, I guess the proof of the pudding is in the customers needing help (those needing to understand the GHE), rather than those who don’t!
I recommend David Archer’s “Global Warming: Understanding the forecast” for those with some science background. While some analogies can ‘dumb down’ the science, Archer uses one that he finds useful (and is analogous to the animated illustration shared in the post):
The blackbody atmospheric layer is not a source of energy, like some humungous heat lamp in the sky. How then does it change the temperature of the ground? I am going to share with you what is perhaps my favorite earth-sciences analogy, that of the equilibrium water level in a steadily filled and continuously draining sink. Water flowing into the sink, residing the in the sink for a while, and draining away is analogous to energy flowing into and out of the planet. Water drains faster as the level in the sink rises, as the pressure from the column of water pushes water down the drain. This is analogous to energy flowing away faster as the temperature of the planet increases, according to ε σ T4. Eventually the water in the sink reaches a level where the outflow of water balances the inflow. That’s the equilibrium value, and is analogous to the equilibrium temperature we calculated for the layer model. We constrict the drain somewhat but putting a penny down on the filter. For a while, the water drains out more slowly, and the water level in the sink rises because the water budget imbalance. The water level rises until the higher water level pushes water down the drain fast enough to balance the faucet again. A greenhouse gas, like the penny in the drain filter, makes it more difficult for the heat to escape the earth. The temperature of the earth rises until the fluxes balance again.
Click to access archer_global_warming.pdf
(Chapter 2, Page 8)
It’s a thought experiment. He’s not planning on actually stripping the Earth of its atmosphere.
Yet.
“The thing is, the atmosphere is mostly convectively stable, with lapse rate below the DALR, and even allowing for moisture.”
My understanding is that this means the mean properties of the atmosphere are convectively stable (the atmosphere, seen as a rather simple fluid, has a vertical density gradient that has to be stable long term). The instantaneous properties are not convectively stable. We have the wind driven no-slip surface boundary layer (representative of the surface temperature proxies). It’s the wind driven convection that maintains the long term mean convectively stable atmosphere.
IMHO, we are seeing that right now. The ENSO has redistributed the heat throughout the Pacific Ocean, thus more heat is currently entering the atmosphere. Where and how it is entering the atmosphere becomes rather important for the net short term (several years) restabilization of the TLT (after ENSO is over).
This is how I’m currently reconciling the satellite TLT measurements, that’s what the TLT measurements show before and after the 1997-8 ENSO, absent the 1997-8 ENSO ‘spike’ there is a step like increase in the satellite TLT temperature proxies. I”m sort of expecting to see another ‘step-like’ increase in the satellite TLT post current ENSO. I could be wrong, as is all too common for someone lime myself, not trained as a climate scientist.
The troposphere warms and the stratosphere cools, or so I’ve been told, for increasing GHG’s. I’m currently of the opinion that global mean energy budgets and whatnot are rather pointless absent direct contributions in those calculations due to wind driven convection and the no-slip surface boundary layer. It does make one wonder what parameterizations are used in the AOGCM’s with respect to the no-slip surface boundary layer (mean properties or mean + perturbations, seems kind of important to me, are we modelling real or make believe inviscid fluids).
Same goes for meridional transport calculations (the lower oceans, the abyss, operates on a time scale of centuries to millennia the surface oceans and atmosphere on a time scale of days-months-years-decades). We are not currently in equilibrium, so stop with the calculations that assume equilibrium. YMMV.
I ‘think’ I’m a fluids person.
There is an apparent paradox here, that is, what does one mean exactly when using the word convection, in my book (at least) ‘convection’ means both heat and wind driven, vertical and horizontal.
A bigger paradox, IMHO, is that the more you all talk about the GHG effect, the less I appear to understand the GHG effect. 😦
So, evaporation cools the surface, a warm moist parcel of air then rises via vertical buoyant convection into the atmosphere, at some point (saturation) it rains and warms that part of the troposphere, say a few km above the evaporation point. So this is one mechanism for vertical heat transport within the troposphere. Beyond that, I’s still trying to understand the dominant pathways for the heat travelling upwards throughout the Earth’s atmosphere.
I’m feeling kind of stoopit right now,
I’m mostly cribbing from two of Isaac Herd’s posts:
52. Warming and reduced vertical mass exchange in the troposphere
http://www.gfdl.noaa.gov/blog/isaac-held/2014/11/15/52-warming-and-reduced-vertical-mass-exchange-in-the-troposphere/
60. The quality of the large-scale flow simulated in GCMs
http://www.gfdl.noaa.gov/blog/isaac-held/2015/06/07/60-the-quality-of-the-large-scale-flow-simulated-in-gcms/
Ethan Allen,
“This is how I’m currently reconciling the satellite TLT measurements, that’s what the TLT measurements show before and after the 1997-8 ENSO, absent the 1997-8 ENSO ‘spike’ there is a step like increase in the satellite TLT temperature proxies. I”m sort of expecting to see another ‘step-like’ increase in the satellite TLT post current ENSO. I could be wrong, as is all too common for someone lime myself, not trained as a climate scientist.”
I think it’s an advantage in not being a climate scientist to think this way. Colleague and I have just had two papers rejected with extreme prejudice that said exactly that for TLT 97-98 and for surface temperature. It was attacked by one reviewer who completely ignored the science because they hated what it was claiming. Because the denialati are trying to use step changes to disprove greenhouse, some within the orthodox community will have none of it. Defend the trend! That’s the second rejection, the first was without review. Am anticipating feelings of schadenfreude sometime in the future, when both sides are proven wrong. I’m happy to be wrong but don’t think so.
The climate science community needs to think more about how the system behaves and fluids is a big clue. While I think Benestad and ATTP’s summary of what happens to heat once it is in the atmosphere and available for convection is good and useful, people need to think about more about where it’s been between the time of forcing and when the atmosphere warms (so this is largely a pre-convection thing). The not currently in equilibrium comment is spot on.
Bryan,
It’s just hypothetical: what would the surface temperature be if the albedo remained the same and the atmosphere was removed?
Anders, Bryan is obviously correct. After all, an Earth with not atmosphere would have no plant life and no rain. Hence the albedo of land surfaces would be that of dry sand or 0.4. Further it would have no liquid water so, the entire surface would be dry sand or ice (albedo 0.8). Clearly the supposition that albedo would remain the same way overestimates the likely albedo. /sarc
I think it is a very topic issue and I certainly don’t think I understand all the processes very well.
Indeed 😉
Maybe another related way to consider this (as was also pointed out in Benestad’s paper) was that we absorb 240W/m^2. In equilibrium, we must radiate 240W/m^2 back into space. As Nick points out, this is not all emitted from a single height; some comes directly from the surface, some from within the troposphere, and some from the stratosphere. Ultimately, the energy transport within the atmosphere will tend towards a state where the energy trasnported to each radiating height matches the energy radiated from that height.
Richard – Thanks for that. I was beginning to think I was the only one in here interested in the “educational” angle in Rasmus’ article/paper.
Would anybody care to weigh in on the pros (and cons?) of including code and/or data in amongst the supplementary material of learned journal articles?
Willard – Over an hour of off-topic video! Whatever next? What do you make of this one?
Is that the sort of thing that will show our lords and masters the light?
Nick posted “Trenberth’s budget” diagram. Every time I see it I think of The Flat Earth Society. Seriously. Just look at it, flat Earth depicted, Sun always on. No horizontal components. No net latitudinal transports shown (tropics net in, poles net out, no horizontal transport). Lots of large numbers (error bars anyone?) with a rather small positive net number.
I think I’m better off looking at the AOGCM numbers. Trying to explain GHG’s to simpletons (like myself) with diagrams that appear too simpleton to begin with in the 1st place, is IMHO, the hallmark of lack of proper communications skills. I would think that one would rather suppress confusion rather than create confusion.
The real irony though is that Benestad states …
“Not all of my colleagues may agree with my description of the greenhouse effect; it was a struggle to get this paper published. To my surprise, I realised that there are scholars with different ideas about it. However, I hope that my description will lead to more discussions and debate about the over-arching principles and our basic understanding of this phenomenon.”
From SNL Weekend Update … Really? Really!
Maybe I should have posted this in the consensus messaging thread?
OK! From “Infrared radiation and planetary temperature” by Pierrehumbert (p. 36 last full paragraph) …
“For atmospheres heated partly from below—either as a consequence of solar absorption at the ground as in the case of Earth, Mars, and Venus, or due to internal absorption and escaping interior heat as with Jupiter and Saturn—the lower layers of the atmosphere are stirred by convection and other fluid motions, and the constant lifting and adiabatic cooling establish a region whose temperature decline with height approximates that of an adiabat. That region is the troposphere. At higher altitudes, heat transfer is dominated by radiative transfer instead of fluid motions; the corresponding region is the stratosphere.”
… and (p. 37 last full paragraph) …
“The same considerations used in the interpretation of spectra also determine the IR cooling rate of a planet and hence its surface temperature. An atmospheric greenhouse gas enables a planet to radiate at a temperature lower than the ground’s, if there is cold air aloft. It therefore causes the surface temperature in balance with a given amount of absorbed solar radiation to be higher than would be the case if the atmosphere were transparent to IR. Adding more greenhouse gas to the atmosphere makes higher, more tenuous, formerly transparent portions of the atmosphere opaque to IR and thus increases the difference between the ground temperature and the radiating temperature. The result, once the system comes into equilibrium, is surface warming.”
Nevermind.
This seems a pretty good explanation.
Jim – I also had Ray Pierrehumbert contribution to the excellent film Thin Ice in mind too. I did a straw poll of people attending the film (which we had as part of our town’s climate awareness day 6 months ago), and they seemed to appreciate it, but the test would be whether they can play it back and handle a Q&A. I think they might struggle because of the underlying subtleties. But I do believe that developing ‘climate fluency’ (or whatever we call it) is crucial, to help empower a wide number of people.
[Btw – on the Git sidebar … I would say configuration management is crucial for ensuring sustainable systems, trusted/ shared/ evolving libraries, etc., particularly when needing variants of systems (the real world), and ability to execute regression testing on these multiple variants. This applies to plane building, and software building! Something this speaker seems to dismiss.
Back in the 1980s I was on a huge s/w project with 10m lines of code and multiple teams building an ASIC chip design system, and the ability to have everyone working independently, but able to merge modules according to different build rules. It worked beautifully. This required awesome configuration management, and the system we used went on to become Rational ClearCase. Version control and sand-boxes are relatively trivial and may be fine for smaller projects. Any project manager wanting control over any design and build (a plane or a s/w system), ought to be ultra pedantic when it comes to configuration management. And that involves the requirements, design, and ‘as built’/ ‘as released’ are mutually consistent, to enable full life-cycle change control.
I suspect Mr Torvalds would disagree].
I don’t get the condemnation of the energy budget cartoons. There are a number of them. None of them are perfect (I prefer the one by Graeme Stephens,) but they represent, ultimately, what is happening.
I am surprised that no one has linked to this excellent exposition of how the atmospheric GHE works. It starts off with a graph of outgoing radiation and shows the emission temperature of the radiation in the absorption/emission spectrum of various GHG’s.
http://acs.org/content/acs/en/climatescience/atmosphericwarming.html
It shows how the height of CO2 which is a well mixed gas in the atmosphere is higher and the temp is lower, that the height of water vapor, which tops out at a lower elevation.
I’ve been thinking about this. Suppose you take a pistol grip infrared thermometer — the kind you can point at a wall in you house to see how well the insulation works and the like — Easily under $20 at Amazon or Banggood.com, and a plastic bag full of air, and a plastic bag full of C02 – doable with a $1 C02 cartridge and a little cleverness to snip the end off with scissors inside a sealed mostly empty bag. I tested and found thin clear plastic is pretty transparent to infrared rays; not so with glass. Measure the temperature of a warm object via infrared rays passing through each bag in turn. Will there be an observable difference? I really don’t know; might be dramatic, or it might be miniscule. If dramatic, the contrast to transparency to sunlight is obvious; otherwise one may have to work harder and bring in more measuring artifacts.
Consider the atmosphere with around 400 ppm Co2 — very little, but the infrared radiation has to travel through miles of atmosphere. Should a mile of 400 ppm Co2 produce as much light trapping as 2 feet of pure Co2?
If the basic principle can be vividly established, the onus is on the deniers (those who deny – not the true skeptics) to argue that the effect is reversed by some combination of water vapor, albedo, etc., and unless it’s reversed *uniformly* across the planet, the basic Co2 + reversal mechanisms will redistribute heat and cold around the planet, and we can observe that it’s happening non-uniformly, and that that is a serious matter. I really wonder that changes over the last decades to temperature at various high latitudes is rarely mentioned in trying to educate the public, though we show animations of changes to arctic ice area — those animations come out of a long sequence of black boxes as far as the public is concerned and might lead to reactions of “I’m really not all that clear what the phenomena being animated are, much less how it is turned into animation, much less what the implications would be”.
eadler2,
Thanks, that does look like a great site. I don’t think I’d seen it before.
Hal,
I think the basics of the greenhouse effect has indeed been illustrated in that kind of way.
Hal,
I think the basics of the greenhouse effect has indeed been illustrated in that kind of way.
What I meant was do it a lot; make it a sort of iconic thing; Say “Try this yourself” on educational blogs, but only if the results would be easily detected, and I imagine you could work out the math.
I think it is quite tricky, but I think Mythbusters have already done it 🙂
Even simpler
http://scienceblogs.com/stoat/2014/02/16/the-idealised-greenhouse-effect-model-and-its-enemies/
Anders, at approx 2:30 on the mythbusters video you can see that the CO2 enhanced greenhouse has two greenhouses to its left. You can then see that the methane enhanced greenhouse has at least one greenhouse to its right. That is consistent with positioning of Control , CH4, CO2, control; or CH4, control, CO2, control. In the first instance, the controls would have received less energy from adjacent experiments (due to only having one adjacent experiment), and consistent with the video, that may be the explanation of the increased temperature in the non-control greenhouses.
Is Tom Curtis muddying the waters with an urban heat-island like claim? The Myth Busters demonstration was interesting, but no one will try it at home, and it’s complicated enough to provide room for doubt. I’m suggesting a very clean and simple approach if only I knew if would work. The only questions, I think, are how big a bag of Co2/Air you need, and how accurate an infrared thermometer. It emphasizes the wave energy in a different frequency range nature of what get’s stopped by Co2 molecules, and is about as simple as can be.
Hal Morris, @ February 16, 5:26 pm, the sort of experiment you are describing has been done graphically by Iain Stewart:
However, the demonstration only shows that CO2 absorbs IR radiation (as would your postulated experiment). It does not demonstrate the greenhouse effect.
If you look at simple experiments “demonstrating” or “refuting” the greenhouse effect, there are a number of attempts, all of which have flaws in the experimental design, or at least in the explanations which leave open the possibility of flaws in the experimental design. That is part of the reason why you get experiments, often of the same design, both purportedly proving, and purportedly disproving the greenhouse effect.
The closest valid simple experiment proving a greenhouse effect is found with de Saussure hotboxes (as discussed here and following). However, there is enough denier misinformation on this case, as demonstrated by Postma on the same thread, to confuse the case sufficiently that such experiments are of dubious rhetorical value. This is particularly the case as they use glass rather than CO2 as the IR absorber, and very substantial quantities of CO2 would be needed for a similar CO2 based demonstration.
I think it would be very interesting to conduct a more rigorous version of the de Saussure hotbox experiment published in the peer reviewed literature to clear away some of the denier deadwood on the subject – but I do not imagine for a moment that it would be simple. It would be even less simple (but probably possible) to do an experiment demonstrating a greenhouse effect based on a temperature gradient in the gas medium (as in the real atmosphere) rather than a series of “grey slabs”.
The figure is a jazzed up version of an old figure from Jim Hansen that Chris Colose used in his description of the greenhouse effect and made its way into our refutation of Gerlich and Gepetto.
I very much appreciate the pointer to the Iain Stewart youtubes. Based on that, unless I’m really missing something approx. 3 feet of pure Co2 is very opaque indeed to infrared light, which encourages me to think my idea can work. My gut feeling could be wrong, but I think this ability to demonstrate strong infrared absorption by Co2 on a kitchen table with a few dollars worth of stuff could become quite a robust meme in the wider population. It will invite people to try something that will be fun and perhaps the strongest demo of a non-obvious scientific principal that most people have ever had a chance to perform.
It is only one side of the greenhouse effect of course. While following the controversy or rather kerfuffle for years, I only just read something that really made it clear for me. Energy as sunlight passes through the atmosphere with hardly any obstruction. Before any of the energy can be reflected back into space, it is transformed to infrared, and the same air that is transparent to light is less so, according to the amount of Co2 to the form of energy that is sent back out.
Anders,
That is not at all clear to me, particularly the first sentence. I elaborate below.
THAT makes perfect sense to me. Perhaps a piece I’m missing is that the latent heat gets there via convection. When condensation occurs, convection gets another boost, lifting dryer air higher until radiative cooling comes into its own. However, under increased radiative forcing, this all happens at a greater altitude on average … but what. I’m not tying it together.
The RealClimate post was worth reading for me if only for this statement:
I knew something had to net to zero at “average emission height”, but it couldn’t be net flux at the given altitude since in an equilibrium atmosphere average net flux at all levels is zero. Next paragraph:
Yes that’s obvious, but I’ve often seen it explained that raising the roof is what causes the warming below which has always seemed too simplistic … almost magical. The way I think about it is that increasing atmospheric density decreases path length for 100% extinction, so there are more layers for outbound photons to fight through to escape. Thus more opportunities for thermalization, and thereby temperature is higher at lower levels to maintain radiative equilibrium.
It then follows that net LW becomes increasingly negative with altitude as shown in this nifty plot:
… taken from Wu and Liu (2010): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2871903/
Interestingly (a) implies that ~240 K not 254 K is the “magic” temperature dictating average emission height at ~6 km. Whether that’s a quirk of this purposefully simplified 1D model, I’m interpreting it wrongly or something else, I cannot say.
Anywho, the shape of the curves in that plot suggest to me that raising the roof is NOT the primary mechanism of near-surface warming. It’s difficult for me to conceive how what photons at 10 km above the surface are doing affect what’s going on at the surface when 15 micron photons at sea level only travel on the order of 10 m before getting gobbled by CO2.
Benestad asserts that a model which does not include convection and goes for the pure radiative mechanism I’ve outlined does not explain observation, “Convection also plays a crucial role.” But the body text of the article does not explain what or why:
I’m afraid the RC post raises more questions than it answers for me. I will dig through the comments and also read Benestad (2016) to see if I can sort it, but input from you and the literati here would be also be welcomed.
Tom,
You may well be right. I did wonder if that experiment was not going to be quite good enough.
Brandon,
I thought this site explained it well. At the end of the day, if you add GHGs, then it prevents radiation from escaping straight from the surface. Some of the energy must therefore be transported by other processes, such as convection, advection, latent heat. Ultimately, those processes set the temperature profile.
Anders,
I’ve read through the link you provided and agree that the explanation is quite clear, nothing surprising or controversial for me in there, but a handy reference. Thanks.
I guess what’s going on here is that the way you stated that isn’t how I think about it. It’s the “must be transported by other processes” that feels like a wrong constraint to me. I think of it as there being more energy available to drive those other processes, and temperature profile is set by where the new equilibrium happens. Perhaps I wouldn’t have been so tripped up by this statement …
The temperature on the surface would then be set by whatever processes transport energy from the surface to this effective emission height. Since the greenhouse gases have increased the opacity in the atmosphere, this cannot all be via radiation. In the case of the Earth’s atmosphere, the dominant process is convection.
… if you had instead written “the dominant non-radiative process is convection”. And this statement …
In a dry atmosphere, the temperature gradient to which the lower atmosphere would tend be around 10K/km. The effective emission height in the Earth’s atmosphere is at around 6-7km, which suggests that if the only transport mechanism were convection, the surface temperature would be 60-70K warmer than it would be in the absence of a greenhouse effect.
… I get the maths, as well as the follow-on about latent heat release at altitude reducing the temperature gradient further than the dry lapse rate would suggest.
I would expect a dry atmosphere with no LW-active species to have a much smaller lapse rate — the LW from the heated surface would pass straight through without sticking around to drive as much convection, and advection would be more a mover both poleward from the equator and from daylight to night side.
Brandon,
Yes, that’s a fair point. I was really just thinking along the lines of if the system is not optically thick, then somehow the rate at which you transport energy to the emission height, has to match the rate at which you’re losing energy from that height. If it can be via radiative transport, then it has to be something else. Of course, you are correct that if the energy is not transported via radiation, it becomes available to drive those other processes.
I think that’s probably true. Again, I think the rate at which you transport energy through the atmosphere has to match the rate at which it is lost from some height within the atmosphere. If most of the energy is radiated directly from the surface, then little will be radiated from within the atmosphere.
Richard, Anders et al.
Nobody else seems to have picked up the ball on all the newly available “educational” material concerning the GHE and run with it, so I have taken the liberty of doing so over at:
http://GreatWhiteCon.info/2016/02/explaining-the-greenhouse-effect/
In the 1820s, the French mathematician Joseph Fourier was trying to understand the various factors that affect Earth’s temperature. But he found a problem – according to his calculations, the Earth should have been a ball of ice.
Please feel free to add your (constructive!) comments.
Brandon,
Convection cools, which even ATTP is implying, if not outright stating. That’s why the surface is cooler than the Wu and Liu (2010) temperatures indicate on those graphs.
The problem with all this rationalization about the inappropriately named “greenhouse” effect, is failure to verify the assertion that changes in the observed outgoing LW spectra due to incremental increases in IR active gases translate into additional temperature increases greater than that which results from certain critical concentrations. IOW, the climate system is now sufficiently efficient in removing incoming energy that further increases in CO2 will have little effect, if any, on the average global temperatures.
ATTP
Why do you delete perfectly reasonable ‘on topic’ posts.
You complain when others snip your comments.
Is your grasp of physics so fragile
Others have commented that you cannot cope with constructive questioning of your views.
I guess they must be correct.
Bryan,
They’re not deleted, they’re pending (edit: they were, at least. They’ve been deleted now). It’s where they started, for reasons I don’t quite know. However, I certainly wasn’t planning on posting the first, given that it appears to be linking to a paper that disputes the existence of the greenhouse effect and I certainly can’t be bothered starting one of those discussion again.
I can only think of one case where I said anything that might be regarded as a complaint about having a comment snipped. I tend to feel that people can run their blogs as they see fit.
Nope, pretty happy with my grasp of physics.
You can guess whatever you like. It’s neither here nor there to me.
I’ll add that it’s also sometimes useful to see how people respond to their comments not appearing as fast as they’d like. It’s quite instructive.
Chic,
I’ll post your comment, only because it illustrates the value of this particular way of looking at the greenhouse effect.
Well, no, if you increase GHGs it raises the effective emission height and – given the lapse rate – increases surface temperatures. The movie at the bottom of the post illustrates this nicely.
Of course, you can also consider this slightly differently. As Nick Stokes points out
chic wrote “Convection cools” given that the planet (being in a vacuum) can only gain or loose heat by radiation, convection alone cannot cool the planet. It is the radiation budget that giverns the warming and cooling of the planet, convection can only change the distribution of heat within the planetary system.
Meanwhile global warming deniers will argue about the conveniences, like so;
ATTP,
In spite of the elaborate work that went into the Benestad paper, was there any experimental evidence there indicating an elevation in effective emission height effects the amount of OLR? The paper seemed to describe a model designed to explain, for the nth time, the GHE. Was it a sufficiently realistic model to prove an elevated EEH decreases OLR? Are there any radiative conductive models that do? I’d like to know.
Compared to a cold planet without an atmosphere or planet with an inert atmosphere subject to extreme temperature swings, we now have a relatively static atmosphere that remains relatively cool during the day and warm during the night. My hypothesis is that greater concentrations of IR active gases will not substantially increase average global temperatures above what’s already been observed or assumed over the past few thousand years. Now that we have powerful computer capacity, we should have the ability to develop sufficiently realistic radiative-convective models that will determine whether that hypothesis is true.
Chic,
Good, but you’re almost certainly wrong. Since I try hard to make this a site that promotes credible science, I think I shall not post any more of your comments suggesting that we won’t warm if we continue to add GHGs to the atmosphere.
ATTP,
Fair enough. It’s your site.
If I implied I knew for sure about the precise consequences of increasing IR active gas concentrations, I stand corrected.
Chic,
What you’re hypothesising is at odds with a vast amount of evidence and the views of a vast majority of relevant experts. If you read the paper, it does say
Suggesting that we can add GHGs without warming is a very long way from being a credible position.
The overwhelming problem is that nobody’s been able to come up with a credible mechanism for why this would happen. The best attempt came from Lindzen, vis-a-vis the Iris Hypothesis, but thus far experimental evidence has not been kind to this hypothesis.
And how do we explain > 50 years of ocean warming if adding GHGs doesn’t warm?
Jim … I have been away (a little matter of the day job!). With the GHE I am reminded of that joke of a maths professor giving a class who write something on the board and says “This is simple …”, steps back and screws up his face then disappears out the room for 15 minutes, coming back to declare “Yes I was right, it IS simple!”.
I think that those that criticise ‘simplistic’ explanations, because they do not include all the subtleties of the physics need to be clear about who the audience is: is it a class of 12 year olds? A talk to the local Probus business group? A undergraduate class in climate science? … how much physics do you pile in on conversation #1 ? Certainly, the Planck law would not make an early appearance.
The challenge is to keep it simple without abusing the truth, i.e. dumbing down.
But as Stephen Hawking was advised when writing a Brief History of Time, each equation will halve the number of readers. I think the use of pictures, like the one ATTP posted are really useful in articulating the science without resorting to the equations (yet staying true to the maths).
Ok, so the blanket model is too simple, but isn’t the point of teaching (if that was the original purpose of this post/thread) to take someone from one level of understanding to another, one step at a time? You start with a simple model, then embellish it, then replace it with a more sophisticated one, and so on, until the listener’s appetite (and questions) are sated, which will be different for everyone.
I wonder if anyone has tried used tried and tested dialogues, between the teacher and student, allowing the ‘reveals’ of each layer of understanding, without the need to ‘choose’ between simple and sophisticated. A really useful pedagogic device in my view. May have a go myself!
Student: “So what is the ‘greenhouse effect’?”
Teacher: “…
ATTP,
You quoted from the Benestad paper: “This [23 m/decade upward trend] is consistent with a deepening of the optical depth, as well as a global mean surface warming of 0.12 K/decade over the period 1979–2011.”
But is it consistent with no LT warming and no OLR decrease of late, while CO2 continues to increase?
“And how do we explain > 50 years of ocean warming if adding GHGs doesn’t warm?”
The planet is warmed by the sun. The ocean absorbs most of that energy. I don’t think the details involving lag times, clouds, and so many other things have been thoroughly worked out yet.
Also, Venus.
Thanks to its high albedo, it absorbs about the same amount of solar radiation as earth.
Several hundred degrees hotter. If extra CO2 doesn’t warm the planet – with no limit – this is hard to explain.
Yes, the energy comes from the Sun, but why is it warming now?
What you’re promoting is the epitome of science denial. You’re welcome to do so. Doing it here, however, is discouraged.
Andrew,
Venus actually absorbs a lot less radiation than Earth. NASA’s Venus Fact Sheet gives an effective black-body temperature of 184K. That works at only 65 W/m2. Could CO2 really absorb 65 W/m2 and re-radiate ~17,000 W/m2? Seems amazing to me. Internal heating is always a possibility.
Chic Bowdrie,
Indeed. He also wrote:
Water evaporates at the surface and is carried up into the atmosphere. When it condenses it releases energy and heats the atmosphere. It, however, doesn’t do this uniformly and so it acts to reduce the temperature gradient relative to what it would be in the presence of convection only.
I unequivocally agree that upward convection cools the surface by transporting sensible and latent heat away from it. The T&K energy budget implies that convection is net negative for the surface, net positive for the mid-troposphere, thus reducing the lapse rate.
This further implies that radiative loss must be greater at altitude than at the surface to maintain equilibrium.
If I didn’t already know better, I would say you just tacitly agreed with W&L’s radiative explanation for tropospheric lapse rate. Since that’s a topic Anders obviously discourages here, I’d be willing to host it on my own (rather disused) blog.
It doesn’t have to. 65 W/m^2 in, 65 W/m^2 out, everybody’s happy.
Anders,
Sometimes sleeping on things helps me. This may be one of those times.
My understanding is that at equilibrium the net of ALL fluxes at ALL levels must be zero. I think it’s also proper to say that an equilibrium system will take the most efficient path toward equilibrium. Equilibrium never actually happens of course, but that’s the state the system is everywhere constantly “trying” to achieve.
A higher average emission altitude implies that the system must do more work for upward convection to transport sensible and latent heat to the point where LW losses cause condensation and loss of buoyancy sufficient to induce downward convection.
Same conclusions I think, just different approaches. I hope — I still have more reading to do. Cheers.
Brandon,
I accept your offer to continue at your blog. Should I know where it is?
Brandon,
Yes, I think that’s right.
Chic,
Are you really serious about discussing this? I think we’ve done this before and it’s never really gone anywhere. What are you hoping to achieve?
Chic,
I wouldn’t expect you to know my blog because I don’t promote it:
http://climateconsensarian.blogspot.com/
I’ll create a new post tomorrow with short summary and we can take it from there. Look for it sometime after mid-afternoon.
Anders,
I won’t speak for Chic, but I like talking to him because he mainly sticks to the science and asks me questions I either haven’t thought of, or don’t already have good answers for. Our conversations can get quite lengthy, and it’s probably more appropriate for me to do that in my own space.
Brandon
Do be sure and ask Chic to explain the PETM given his ‘hypothesis’ that:
He needs to address the problem of Cenozoic hyperthermals explicitly, with detailed physical mechanisms describing why they did not and could not have happened 😉
Martin
“It doesn’t have to. 65 W/m2 in and 65 W/m2 out, and everybody’s happy”
Well, yes it does. The CO2 on Venus is absorbing a maximum of 65 W/m2 and we are told CO2 is increasing the atmospheric surface temperature of the planet to 740K which corresponds to a radiance of around 17,000 W/m2. CO2 on Venus is absorbing 65 W/m2 and somehow turning that into 17,000 W/m2. Who know, could be possible, although such amplification seems so remarkable that I can’t help but chuckle incredulously.
Well, no. The surface of Venus is emitting around 17 kW/m^2, CO2 in the lower atmosphere is absorbing 17 kW/m^2. Again, in = out, and everybody’s happy. You’re comparing different flows, that’s all.
“The surface of Venus is emitting 17 KW/m^2”
No Martin, the surface temperature of Venus is 740K and according to the Stefan-Boltzmann law that equates to a radiance of 17,000 W/m2 whereas the incoming energy absorbed by Venus from solar radiation is only 65 W/m2. The standard explanation is that CO2 increases the effective temperature of Venus from 184K (65 W.m2) to 740K (17,000 W/m2). Hence, as I said, there is apparently a huge amplification effect occuring. I have not been talking about the “flow” of solar radiation into and out of Venus, which I agree must be equal. I have been talking about the re-cycled amplification of energy, and that amplification, as stated above, is around 17,000 W/m2.
ATTP,
I see two ways to approach the AGW question. One is to hypothesize that CO2 and water vapor feedback amounts to 3K sensitivity and try to make everything else fit that hypothesis. Another approach is to test the cornerstone assumption that additional CO2 will have any further effect on the global average temperature. I have not found sufficient support for the latter. To my knowledge, the relationship between radiative and convective energy flux through the atmosphere is not characterized well enough. When the subject of a blog post is about those model equations, I drop in to see if there’s been any progress in that area.
Other than that, I don’t expect to achieve anything here other than to have my views challenged. That’s how I learn.
Nathan,
Sorry, but Martin is correct. Venus is essentially in equilibrium. The only way the surface temperature can be 740K is if something is stopping the energy from being radiated directly to space. I’ll leave it as an exercise as to what that something is.
Chic,
Then you’re not looking hard enough.
There is an abundance, from the PETM to deglaciation under orbital forcing. As ATTP says, you aren’t even looking.
“The only way the surface temperature can be 740K is if something is stopping the energy from being radiated directly to space”.
Yes, and this is what I have been saying. I never once said that Venus was not in equilibrium. I have merely said that some people suggest the CO2 in the atmosphere on Venus amplifies the 65 W/m2 from solar radiation to approximately 17,000 W/m2. That is all. Sheesh.
“I have merely said that some people suggest the CO2 in the atmosphere on Venus amplifies the 65 W/m2 from solar radiation to approximately 17,000 W/m2.”
I may have missed something, but isn’t that sort of what the “back-radiation” is doing? I realise back-radiation is basically returning some of the upwelling IR from the surface, but since that energy originally came [indirectly] from solar radiation, isn’t this splitting hairs somewhat?
@ Nathan
See Chris Colose on Venusian GHE.
ATTP, when Chic writes “But is it consistent with no LT warming and no OLR decrease of late, while CO2 continues to increase?” he is just channeling the “no warming since __” nonsense. Don’t let him.
Jim,
Yes, I know.
Nathan,
Hmmm, I’m not sure anyone actually says this. As BBD points out, Venus’s atmosphere is so opaque to outgoing LW that the surface temperatures need to be > 700 K in order for the outgoing flux to balance the incoming flux. You don’t really get to promote what appears to be science denial and go “sheesh”.
@semyorka
If I’m following it right then this picture works for the stratosphere because stratospheric temperature increases with height. Increased greenhouse gases raise the emission level to a warmer level and energy balance then requires cooling.
I think this gives a good rule of thumb: adding greenhouse gases warms areas where it cools with height but cools areas where it warms with height. So long as the temperature profile is largely set by something else, e.g. hydrostatic equilibrium in the troposphere and ozone absorption of sunlight in the stratosphere.
On Venus, those numbers seem in the right ballpark. The split between CO2 and other factors I don’t know – but in terms of total back radiation it seems about right.
Unless there is an enormous downward sensible heat flux or the Stefan-Boltzmann law is wrong.
Richard,
My previous comment wasn’t aimed in your direction. It’s more that the conversations here (with honourable exceptions), Open Mind and RealClimate haven’t discussed the “pedagogical” aspects of Rasmus’ paper much, and papers with supplementary code+data at all.
Would you prefer to pursue the pedagogical pastime you suggest here, or wander over to my place? In the meantime, here’s a topical example of one of the games I play:
Chic Bowdrie,
http://climateconsensarian.blogspot.com/2016/02/on-competing-mechanisms-for-observed.html
Have at me. Regards.
BBD,
Problem there is that I don’t know enough about the PETM to comfortably explain it. I generally only invoke it as a cautionary tale of what happens when climate changes relatively abruptly in either direction. Most compelling causal hypothesis I know of comes from Wikipedia, namely abrupt methane release (which then oxidized to CO2) for mechanisms IIRC not fully understood. A citation from you to primary literature, and/or a reliable secondary source using more lay terms would be helpful.
I have already lobbed Venus at him, for which I can do the basic S-B calcs alluded to elsewhere in this thread. He has declined to take it up, and I have let it go since I believe there’s more than enough theory and Earth-bound evidence to make my own case.
I hold myself to the same duty for my end of things. It’s been an enjoyable challenge for me to dig into it with him even though neither of us have significantly budged from our initial positions — which does get frustrating for me because he’s so obviously wrong. Worse, he’s caught me out for a few errors. Don’t tell anyone. 🙂
Brandon
There’s a good overview in Cronin 2010. The key points for ‘sceptics’ with ‘hypotheses’ like dear Chic is that the carbon release may not even have been a doubling and it still managed to produce a hyperthermal. This suggests that ESS even in a hot climate state with no cryosphere is >4C.
The PETM – for all the uncertainties – stands as an impressive example of the efficacy of GHGs as climate forcings and disallows nonsense claims such as Chic’s without any need for rabbit-holing. Which is why I am fond of waving it under the noses of those who deny that GHGs are efficacious climate forcings.
I feel I have just stepped into an alternative universe where normal language no longer applies. What you have just described TTP is the greenhouse effect which I am in full agreement with and my above statement that the CO2 on Venus “amplifies” the incoming solar radiation from 65 W/m2 to 17,000 W/m2 is based on the idea that the atmosphere is relatively opaque to outgoing long-wave radiation, i.e. the greenhouse effect. So yeah, sheesh!
Nathan,
Then I’ve have no idea what you’re getting at. It sounds like you’re disputing a runaway Greenhouse effect on Venus, which is bizarre if you are. If you’re not doing so, then maybe you could be a little clearer.
“Well, yes it does. The CO2 on Venus is absorbing a maximum of 65 W/m2 and we are told CO2 is increasing the atmospheric surface temperature of the planet to 740K which corresponds to a radiance of around 17,000 W/m2. CO2 on Venus is absorbing 65 W/m2 and somehow turning that into 17,000 W/m2. Who know, could be possible, although such amplification seems so remarkable that I can’t help but chuckle incredulously.”
The CO2 isn’t absorbing 65W/m2, it is absorbing the pretty much all of the 17,000 W/m2 radiated from the surface, and re-radiates most of it back down to the surface and about 65W/m2 of the IR re-radiated upwards manages to escape back out to space (maintaining the energy balance).
JUst to clarify, it seems to me that Nathan perhaps thinks that CO2 intercepts the inbound visible/UV light from the sun rather than the outbound IR radiation from the surface (and/or cloud-tops in the case of Venus). That confusion would at least be consistent with what he wrote.
Nathan
*If* there is actual confusion about the physics – as opposed to terminology – perhaps this will clear it up.
It’s the best synoptic reference I could find.
“The CO2 isn’t absorbing 65W/m2, it is absorbing the pretty much all of the 17,000 W/m2 radiated from the surface, and re-radiates most of it back down to the surface and about 65W/m2 of the IR re-radiated upwards manages to escape back out to space (maintaining the energy balance)”.
I agree that outgoing solar radiation must equal incoming. It is a fundamental requirement of the First Law of thermodynamics that if a system is in thermodynamic equilibrium its total outgoing energy must equal its total incoming energy regardless of what the energy does inside the system. The atmospheric greenhouse is just a radiation-recycling mechanism, not a primary source, and it is impossible for it to add any W/m2 to the planet’s total outgoing radiation to space. I understand all of this. I also agree that CO2 in the atmosphere would be absorbing 17,000 W/m2. That said, the CO2 on Venus only has a mere 65 W/m2 of energy available in the form of solar radiation. It must ultimately re-cycle that initial 65 W/m2 until temperatures reach 740K, by which point the surface would be radiating at about 17,000 W/m2. My incredulity comes from this massive recycling of energy. I agree there should be significant re-cycling of energy, but 17,000 W/m2 seems an awful lot. Of course, some, such as Steve Goddard on WattsUpWithThat and Stephen Wilde have suggested alternatives, such as adiabatic compression as being a possible contributor. Steven Goddard apparently calculated the total effect of the CO2 greenhouse on Venus with the IPCC’s Arrhenius equation, although I gather these simplistic calculations ignore the effects of pressure broadening.
Nathan,
The link BBD posted (above) contains a rebuttal of “Steve Goddard”‘s pressure argument
“My incredulity comes from this massive recycling of energy. ”
The reason for your incredulity is unclear. Consider the back-radiation due to 400ppmV of a one bar atmosphere, just how much would you expect from a 93 bar atmosphere that is primarily CO2? Doesn’t seem incredible to me. Either way, there is a scientific approach to incredulity, which is to run a sufficiently complex model to get a meaningful quantative estimate.
What do you mean by recycling of energy? The surface both emits 17000 W/m^2 and receives 17000 W/m^2. The basic point is that for the energy leaving the planet to match that it receives, the surface temperature needs to be about 740K. Any lower than this and it would be receiving more than it emitted. Any higher and it would be losing more than it recieved. That there is a large difference between the flux it absorbs from the Sun and the flux emitted from the surface is rather irrelevant.
Ahh, you appear to be getting some of your info from Steven Goddard. That may explain your confusion.
Whilst I’m in pedagogic mode, please feel free to read all about the unreal science (and colourful vocabulary) of “Steven Goddard”:
http://GreatWhiteCon.info/tag/steven-goddard/
It’s hard to know where to begin when it comes to choosing a suitable snippet from his extensive ouevre. How about this as your starter for 10?
“The most brilliant propagandist technique will yield no success unless one fundamental principle is borne in mind constantly and with unflagging attention. It must confine itself to a few points and repeat them over and over. Here, as so often in this world, persistence is the first and most important requirement for success”
– Adolf Hitler
BBD,
Thanks for Cronin. Unfortunately the book preview cuts out just when things got interesting. As what I think I know of paleo comes from plundering NOAA’s ftp data site, I shall perhaps buy the book, it looks quite readable and informative.
Appeals to evidence, and maths done on the basis of evidence, have thus far failed with Chic due to the Uncertainty Monster. I have pointed out that works against him just as much as me, which he said was a good point. Being the curious sort, I want to see where the rabbit den leads from there.
Apropos Venus, Anders previously cited this resource from ACS: http://www.acs.org/content/acs/en/climatescience/atmosphericwarming/multilayermodel.html
One of the sidebars reads:
The atmosphere of Mars, at a total pressure of 0.64 kPa (about 1/160 that of Earth), is 95% CO2. The amount of CO2 in a column of the Martian atmosphere is about 17 times greater than in a similar column of Earth’s atmosphere. However, the collisional broadening of the CO2 absorption and emission lines in the thin Martian atmosphere is much less than on Earth. This factor, together with the lower temperatures on Mars, reduces the absorptivities and emissivities enough to make the CO2 atmospheric warming effect on Mars weaker than that on Earth. (The lack of water on Mars also means that the water vapor feedback that amplifies the CO2 atmospheric warming on Earth is not operative on Mars.)
Exactly the opposite is the case for Venus with an atmosphere that is about 97% CO2 at a total pressure of 9300 kPa (more than 90 times that of Earth). The collisional broadening of the CO2 spectral lines is larger than on Earth and extends high into the Venusian atmosphere. This factor, and the higher temperature on Venus, increases the absorptivities and emissivities so much that Venus is sometimes characterized as having a runaway greenhouse effect that makes the Venusian surface temperature about 500 K higher than it would be without the atmospheric warming.
Emphasis mine because while I did know Mars’ atmosphere was 95% CO2, I had always assumed its lesser density relative to Earth meant fewer CO2 molecules in a given atmospheric column. I had no idea it was 17 times greater in terms of absolute number of molecules and that pressure broadening apparently makes all the difference to CO2’s optical thickness relative to Mars and Earth.
Brandon
If there’s anything specific you want to know, please ask and I’ll do my best – I didn’t want to pepper you with references to paper this and paper that.
Very puzzled by the behaviour of the book preview link. This morning it extended all the way to the end of the section. Now, it is truncated as you say. Weird.
I definitely recommend Cronin. I have a copy (bought new!) and recommend it if you are interested in palaeoclimate. There’s a slightly more up-to-date (and cheaper) text which might do as well / instead.
BBD,
I will surely take you up on the offer for help, with preemptive thanks. If you have handy references to open-access or pre-print literature, pepper away. I’m warming to the idea of blogging as my main writing outlet as no small amount of WUWT-weariness has once again set in. That, and it’s just nice for the only fetters on what I say and how I say it to be mine and mine alone. 🙂
Anywho, a small deluge of papers would help me get a references page going, and serve as both ever-continuing education and ideas for future posts.
Nathan Ditum,
“My incredulity comes from this massive recycling of energy. I agree there should be significant re-cycling of energy, but 17,000 W/m2 seems an awful lot.”
I agree it seems a lot, but that doesn’t mean it’s wrong.
“alternatives, such as adiabatic compression as being a possible contributor.”
17 kW m-2 from adiabatic compression would result in the total collapse of Venus’ atmosphere in about 6 months. This is not happening.
“Steven Goddard apparently calculated the total effect of the CO2 greenhouse on Venus with the IPCC’s Arrhenius equation, although I gather these simplistic calculations ignore the effects of pressure broadening.”
It ignores pressure broadening and how the spectrum changes with temperature because of Planck’s law. Radiative transfer calculations give a contribution of about 420 K warming from CO2, see table on p10 here:
Click to access Titov_Et_Al-EVTP.pdf
I’ve not seen anything from Steven Goddard that suggests even the most basic level of competence when it comes to physics so I’d be very cautious about taking anything he says seriously.
MarkR
“It ignores pressure broadening and how the spectrum changes with temperature because of Planck’s law. Radiative transfer calculations give a contribution of about 420 K warming from CO2. I’ve not seen anything from Steven Goddard that suggests even the most basic level of competence when it comes to physics so I’d be very cautious about taking anything he says seriously”.
Thanks, I’ll look over that when I have some time. And I agree that the spectral distribution of radiation changes in accordance with Planck’s law. As it happens, I was reading a post on Steve’s blog a few weeks ago called ‘IR Expert Speaks out after 40 Years of Silence’ arguing that because the peak emission wavelength for CO2 occurs at temperatures at around 200K then the CO2 in Earth’s atmosphere cannot be absorbing radiation as effectively. However he did not seem to understand that as the temperature of a body increases then the more energy it will emit at all wavelengths, albeit not uniformly. For example increasing the temperature from 200K to 288K increases the amount of available radiation for CO2 at 15 micrometres by around 300%. Hence applying the IPCC’s equation to Mars as some have done is probably somewhat over-simplistic. Likewise for Venus I would imagine too.
“What do you mean by recycling of energy? The surface both emits 17000 W/m^2 and receives 17000 W/m^2”
I am taking about the CO2 on Venus recycling the solar energy of 65 W/m2 up to 17,000 W/m2.
I still don’t understand why you think this is a reasonable description for what is happening. Consider if your oven was extremely well insulated. You could get it very hot even if the input power was low. This – in a simple sense – is what is happening on Venus. The atmosphere is extremely opaque to outgoing flux. Hence, in order for the outgoing flux to match the incoming flux, the surface has to have a very high temperature (relative to – for example – the surface temperature on the Earth).
“I still don’t understand why you think this is a reasonable description for what is happening. Consider if your oven was extremely well insulated. You could get it very hot even if the input power was low. This – in a simple sense – is what is happening on Venus. The atmosphere is extremely opaque to outgoing flux. Hence, in order for the outgoing flux to match the incoming flux, the surface has to have a very high temperature (relative to – for example – the surface temperature on the Earth)”.
I agree. But the fundamental issue to my mind which needs to be explained is that of why the Venus’s surface is radiating with a mean intensity of 17,000 W/m2 when it is only receiving about 65 W/m2 from the Sun. Where is the extra 16,935 W/m2 that is needed to make up the shortfall coming from? The standard text-book explanation is that it as power that came from the surface originally and is being recycled back to the surface via the atmospheric CO2. In order to believe this were the case I would need to at see some empirical evidence of this sort of massive amplification of energy via CO2 back-radiation and insulation. I agree there must be some amplification, but there are other possible alternatives and contributors that I think should be considered also. If we try to imagine what alternative sources of that amount of power at the Venus’ surface there might be, what can we think of? The heat emanating from the interior as suggested by the Velikovskian theses? Pressure? (Though I gather that idea has met criticism). The thick Venusian cloud-layer perhaps?
Anyway, I will read the paper as suggested to me by Mark.
@ Brandon
I’ve fly-tipped a large pile of links on your blog 😉
Nathan,
Because it’s not. The surface is NOT radiating 17000 W/m^2 while only receiving 65W/m^2. The surface is both radiating and receiving 17000 W/m^2. I also am not sure where the 65W/m^2 is coming from. I make the average incoming flux on Venus to be 150W/m^2 (2643 x 0.2/4).
BBD, got it, perfect. TYVM.
Anders, I think 65 W/m^2 would be insolation at the surface whereas 150 W/m^2 is at TOA, but I don’t know the provenance of the former.
@ Nathan Ditum
I’d say that “recycled” energy is a fair description although it’s not just CO2. We have measurements of nightside emission (e.g. doi: 10.1029/95JE03567 ) plus spacecraft and landers. In 1980 they calculated that “the greenhouse effect can account for essentially all of Venus’ high surface temperature” (doi: 10.1029/JA085iA13p08223 ) although those calcs are cruder than today’s.
Physics says it’s radiation from the atmosphere even if it sounds like a lot. One way I think of it is that for some wavelengths then on Earth ~complete absorption happens within about 1 hPa of air with 400 ppmv CO2. If this is one “layer”, then each of these layers represents a single recycling of the energy. So Venus gets 200-odd million “recyclings” at this wavelength. The temperature profile and other wavelengths mean this is a wild overestimate of the truth, but the real factor of 200 or 300 no longer sounds impossible. As for other sources:
Volcanism? Venus was recently active (doi: 10.1126/science.1186785 ) but since craters don’t smooth over very quickly (doi: 10.1038/372756a0 ) then we should rule out much more than Earth’s 0.1 W m-2 (doi: 10.5194/se-1-5-2010 ).
Pressure? 17 kW m-2 needs the atmosphere’s centre of mass to fall at 7 metres per hour. If Venus’ atmosphere doesn’t squash to the surface in the next six months then it’s not happening. Or looking backwards: if this is true and Venus has a stable temperature then 2 million years ago the Sun was inside Venus’ atmosphere. I find _this_ completely absurd.
Clouds? They seem to account for a chunk, about 110 K warming (versus >400 K from greenhouse) according to that chapter I linked to. This is “recycled” back radiation too.
Okay, thanks, but the general point still stands. The 65W/m^2 is probably the flux on the surface from the Sun. However, as MarkR points out, there is plenty of backradiation that accounts for the other 1635W/m^2.
Anders,
Indeed, I did not intend to diminish the point. The difference is somewhat staggering … I’m reminded of Rutherford’s reaction to high-energy alpha particles bouncing off ultra-thin gold foil. I wager if I looked hard enough, I could find someone who STILL doesn’t believe those results either.
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