Alert readers will have noticed the fewer-than-normal postings over the last couple of weeks. This is related mostly to pressures associated with real work (remember that we do have day jobs). In my case, it is because of the preparations for the next IPCC assessment and the need for our group to have a functioning and reasonably realistic climate model with which to start the new round of simulations. These all need to be up and running very quickly if we are going to make the early 2010 deadlines.
But, to be frank, there has been another reason. When we started this blog, there was a lot of ground to cover – how climate models worked, the difference between short term noise and long term signal, how the carbon cycle worked, connections between climate change and air quality, aerosol effects, the relevance of paleo-climate, the nature of rapid climate change etc. These things were/are fun to talk about and it was/is easy for us to share our enthusiasm for the science and, more importantly, the scientific process.
However, recently there has been more of a sense that the issues being discussed (in the media or online) have a bit of a groundhog day quality to them. The same nonsense, the same logical fallacies, the same confusions – all seem to be endlessly repeated. The same strawmen are being constructed and demolished as if they were part of a make-work scheme for the building industry attached to the stimulus proposal. Indeed, the enthusiastic recycling of talking points long thought to have been dead and buried has been given a huge boost by the publication of a new book by Ian Plimer who seems to have been collecting them for years. Given the number of simply made–up ‘facts’ in that tome, one soon realises that the concept of an objective reality against which one should measure claims and judge arguments is not something that is universally shared. This is troubling – and although there is certainly a role for some to point out the incoherence of such arguments (which in that case Tim Lambert and Ian Enting are doing very well), it isn’t something that requires much in the way of physical understanding or scientific background. (As an aside this is a good video description of the now-classic Dunning and Kruger papers on how the people who are most wrong are the least able to perceive it).
The Onion had a great piece last week that encapsulates the trajectory of these discussions very well. This will of course be familiar to anyone who has followed a comment thread too far into the weeds, and is one of the main reasons why people with actual, constructive things to add to a discourse get discouraged from wading into wikipedia, blogs or the media. One has to hope that there is the possibility of progress before one engages.
However there is still cause to engage – not out of the hope that the people who make idiotic statements can be educated – but because bystanders deserve to know where better information can be found. Still, it can sometimes be hard to find the enthusiasm. A case in point is a 100+ comment thread criticising my recent book in which it was clear that not a single critic had read a word of it (you can find the thread easily enough if you need to – it’s too stupid to link to). Not only had no-one read it, none of the commenters even seemed to think they needed to – most found it easier to imagine what was contained within and criticise that instead. It is vaguely amusing in a somewhat uncomfortable way.
Communicating with people who won’t open the book, read the blog post or watch the program because they already ‘know’ what must be in it, is tough and probably not worth one’s time. But communication in general is worthwhile and finding ways to get even a few people to turn the page and allow themselves to be engaged by what is actually a fantastic human and scientific story, is something worth a lot of our time.
Along those lines, Randy Olson (a scientist-turned-filmmaker-and-author) has a new book coming out called “Don’t Be Such a Scientist: Talking Substance in an Age of Style” which could potentially be a useful addition to that discussion. There is a nice post over at Chris Mooney’s blog here, though read Bob Grumbine’s comments as well. (For those of you unfamiliar the Bob’s name, he was one of the stalwarts of the Usenet sci.environment discussions back in the ‘old’ days, along with Michael Tobis, Eli Rabett and our own William Connolley. He too has his own blog now).
All of this is really just an introduction to these questions: What is it that you feel needs more explaining? What interesting bits of the science would you like to know more about? Is there really anything new under the contrarian sun that needs addressing? Let us know in the comments and we’ll take a look. Thanks.
… that’s all assuming V varies over large distances relative to the scale of the crystal lattice (V in this case does not include the small scale V variations set up by atomic nuclei and other electron orbitals/states that shape the E(k) function).
Back to the original subject matter for a moment: Some of my favorite posts are those which explain the physical mechanisms, and I would enjoy hearing more about fluid dynamics, including PV (potential vorticity, not photovoltaic).
BobFJ says (6 July 2009 at 7:06 PM):
“d) Do you believe that it is a common perception of people at large that the sun does NOT have uniform brightness across what appears to be a flat disc?”
Do you know many people who look directly at the sun? http://en.wikipedia.org/wiki/Limb_darkening for an overview, or if you care to see for yourself, pick a somewhat hazy/smoky day when the sun is just setting, so you can look at it, and you should be able to see the limb darkening for yourself.
Hank Roberts 1047, you wrote to me:
I have absolutely no dispute with the facts of what you tend other than it is irrelevant to the context of my comments to Kevin that you and others apparently nit-pick-on. In particular, but with some bold emphasis added to the original text to Kevin, in part from my 972:
“Here is a simple thought exercise for you [Kevin] to try and understand EMR better; in this case sunlight; using eye protection;
Take a look at the sun, and you may notice that it appears to be a disc of uniform brightness. However, it is a sphere, which means that only the surface right in the centre is pointing straight at you. (in normal presentation). However, on the circumference, the presentation is 90 degrees away from normal, or pointing away from you. And yet it is just as bright. Why?”
Please note, that the ask of Kevin was posed within the normal human capability of looking at the sun through some form of eye protection…. With limited perception…. Nothing sophisticated; No telescopes, cameras or exposure metres!
I was responding to a series of naïve statements that he had made, trying for simplicity, given the apparent poor scope of his understanding of some very basic physics. However, you 1047, Martin Vermeer 1023, Rod B 981 and Patrick 978 seek to interfere, thus making it inappropriately more difficult for my intended respondent.
Of course, if everyone is terribly upset at discussing the fundamentals at 90 degrees, (which by definition are imperfect), would you be happier to do it at say 45 degrees? However, would that make it easier for Kevin to understand?
Give me a break!
Martin Vermeer, further to my 1046, I see somewhat trivially that you also scolded me in 1023, terminating with a triumphant smiley, thus:
That is addressed to me, not the “Royal We”?
Well, anyway, regardless, I’ll have you know that indeed I have previously heard of limb darkening pertaining to the periphary of stars. For confirmable evidence of some of my prior knowledge, please see the intelligence previously offered in Patrick 027, # 978.
“There is no such thing as a stupid question! There may be a stupid answer and you now probably realise that you’ve given one. You’ve got Max agreeing with you”
Please don’t confuse with “That was a stupid question” with “You are stupid”.
With that out the way, yes, there ARE stupid questions.
And yours was one example.
“(BTW. MSc in Electronics to your question. Does that make a difference? Is that enough to gain entrance to the club?)”
It isn’t an entrance exam.
If you don’t have the maths to manage the quantum theories, some answers will be beyond you.
If you have done Physical Geography, some answers will already be known by you.
Your lack of background means that you can use the same thinking that you have for the charging or discharging of a capacitor.
Or backEMF with charging.
In both cases, the rate depends on how much is left to go. Does this mean that your capacitor isn’t ever charged, since it can never get to fully charged?
Or do you drop the last little bit because your maths doesn’t work at the extremes and you need a different answer there?
It’s a log relationship because that is what is observed.
Just like capacitance charging.
It’s a log relationship because except at extremes and the definition of extremes is known to some degree and the most pessimistic reading of extreme is well beyond our current regime.
Just like capacitors don’t charge if coronal discharge is in effect, but then the coronal discharge voltage is fairly well known.
Patrick 027
Having read several of your very interesting longer posts, which described in great detail different aspects relating to AGW, in particular your post 764, which discussed line broadenning, spectral overlap between CO2 and water, etc., I am very much impressed with the depth and breadth of your knowledge.
I am not questioning this at all in my last post.
I am simply asking you to consider the premise that “what you do not know” may be more important in making a long-term prediction of what is likely to happen that “what you do know”.
And I really believe you would enjoy Nassim Taleb’s book, “The Black Swan”. It is an interesting and enjoyable book to read.
Max
Is this:
“Well, anyway, regardless, I’ll have you know that indeed I have previously heard of limb darkening pertaining to the periphary of stars. ”
The same person who said this:
“d) Do you believe that it is a common perception of people at large that the sun does NOT have uniform brightness across what appears to be a flat disc?”
Because I’m pretty darn sure that
a) people know that the sun is a star, just a lot closer
b) people who think the sun is a uniformly bright disk think that stars are points in the sky, not even disks.
But I guess he is chameleoning his argument for all he’s worth.
Where’s RodB to set him straight…?
“I am simply asking you to consider the premise that “what you do not know” may be more important”
But that “may” is a much (MUCH) lower probability than “probably won’t”.
Which is Patrick’s point.
After all, at the moment, you do not know that CO2 is the problem. Maybe it’s more important to think that CO2 *is* a problem…
> b) Why do you think I included the word ‘appears’, rather than ‘is‘?
“It depends on what the meaning of the word ‘is’ is.” (W.J. Clinton)
> Give me a break!
Get a blog, and you can use lots more colors, fonts, text sizes, and codes like “blink” to improve people’s comprehension.
I think I’d better go drink some coffee and wake up. I’m feeling overly sheepish about what things this morning.
On limb darkening, one can observe the limb darkening of the Sun using a strong filter such as welding glass. It is true that emission and absorption processes are largely isotropic so that along an opaque sight-line one should see essentially the same surface brightness regardless of the position on the physically spherical surface. That would be true if the plasma which contributes to the opacity were the same temperature on every sight-line. But, at the limb of the Sun, one is seeing a cooler opaque surface than at the center of the disk because more outer layers of the photosphere are contributing to the opacity at the limb than at the center of the disk. It is the temperature gradient (and lower emissivity at lower temperature) that is mainly responsible for limb darkening.
“But, at the limb of the Sun, one is seeing a cooler opaque surface than at the center of the disk because more outer layers of the photosphere are contributing to the opacity at the limb than at the center of the disk.”
Somethingthat has been said here many times before when people were talking about how the CO2 could be causing warming when it’s saturated: The optical depth at which our atmosphere lets go of its energy gets higher up. And our atmosphere is likewise stratified in temperature with height.
BobFJ – “However, you 1047, Martin Vermeer 1023, Rod B 981 and Patrick 978 seek to interfere.”
I was not trying to interfere, but just wanted to add additional information. Which is also applicable to the Earth’s atmosphere – to a person at the tropopause, looking at various wavelengths, the visual space would generally appear brighter straight downward than to the sides; at wavelengths where the stratosphere is optically thick (the CO2 peak near 15 microns), it would also appear brighter straight upwards (but not generally as much or more so than straight downwards), but at most wavelengths, enough of what is visible looking upward is the dark of space, so that it would appear dimmer straight upward than sideways.
In understanding thermal radiation transfer in which scattering is a minor issue, it helps (you might know this) to think of what a fog would look like if the water droplets were actually little bits of red-hot carbon – and then imagine how it would look if there were temperature variations and/or fog thickness variations.
Others – I think BobFJ’s point was just that if one approximates the photosphere as being isothermal over a path of sufficient opacity, one can use that to illustrate blackbody radiation’s isotropic nature.
Mark – “Somethingthat has been said here many times before when people were talking about how the CO2 could be causing warming when it’s saturated: The optical depth at which our atmosphere lets go of its energy gets higher up. And our atmosphere is likewise stratified in temperature with height.”
Yes – however, regarding tropopause level forcing, CO2 is saturated in the central portion of the band centered at 15 microns, and it is important that significant opacity increases occur outside the central saturated portion with increasing CO2. The tropopause does rise in response to increased greenhouse forcing (and I think also to increased solar forcing, but maybe not as much ? since solar forcing does not cool the stratosphere), but I don’t think it rises enough to keep the CO2 opacity above the tropopause constant as CO2 increases, so the width of the saturated portion would increase, but the width of the interval surpassing any set level of opacity between the surface (and/or humidity and clouds) and tropopause also increases, so there is still additional forcing from additional CO2.
Max – see Mark 1059
Mark,
I’d say that Electronics involves at least as much QMs as climate science. Electron doping in semiconductors, allowed energy bands, electron tunnelling through energy barriers. But, I digress.
Why does the log relationship matter? It is important to be able to have some idea of how much CO2 contributes to the natural GHE. When we tell contrarians they are wrong to say that 95%, or whatever figure they claim, of the GHE is caused by water vapour, we might well expect them to ask in return what we say should be the correct figure. It would be good if we didn’t have to say something like “Er, well it depends on how you measure it. Somewhere between 9% and 25% according to the guys at RealClimate”.
Of course they, or some of them, also read Realclimate and they may well have picked up on the 1ppmv that has been mentioned for the lower limit of the logarithmic range. So they may well say “OK if you are saying that a doubling of CO2 produces a 3 degree warming and that the logarithmic relationship holds down to 1ppmv aren’t you really saying that CO2 contributes at least 73% of the natural GHE of 33degs? Alternatively, if we take your higher figure of 25% isn’t that much more consistent with that nice Prof Lindzen’s figure of 1 degC for climate sensitivity ”
Don’t you see the problem?
[Response: But if that was what you wanted to know, then the answer is 20% (once you attribute overlaps etc.). Water vapour is about 50%, clouds about 25% and ozone makes up most of the rest. – gavin]
“OK if you are saying that a doubling of CO2 produces a 3 degree warming and that the logarithmic relationship holds down to 1ppmv aren’t you really saying that CO2 contributes at least 73% of the natural GHE of 33degs”
Careful about mixing the contribution of CO2 direct forcing and CO2 + feedback temperature change. A doubling of CO2 only produces a 3 degree warming if you include water vapor and other feedbacks. And indeed, if you were to magically remove all CO2 from the atmosphere, I, for one, would not be surprised if _all_ the natural GHE effect were to disappear as the planet cools enough for most of the water to condense out of the atmosphere (leaving a bit of ozone, methane, N2O, and the flourinated gases to hold down the fort). Then, of course, the ice sheets would grow, increasing albedo, and snowball earth would follow soon after. But that 100+% is different than the direct forcing, which is about 20% as answered above by Gavin.
Peter Martin – The ~ 3 deg warming per doubling includes feedbacks, which includes at least much of the rest of the natural greenhouse effect (water vapor, clouds) in going from 0 CO2 to ~ 300 ppm, along with some non-greenhouse feedbacks (including whatever happens to cloud albedo). See my 1048-1049 above. At global average temperatures somewhere below most ice ages, climate sensivity to radiative forcing gets rather larger, and may go to infinity at some point, beyond which the equilibrium is unstable until the ice line reaches the equator, limiting further ice abledo feedback. However, the non-greenhouse feedbacks, indluding that responsible for this behavior, are not included in the ~ 33 deg C natural greenhouse effect figure, so even assuming a constant climate sensitivity to radiative forcing, using the 33 deg C to find the climate sensitivity excludes the cloud albedo and ice albedo feedbacks.
In re solar charging car parks …
Ask anyone who’s ever worked on a solar powered car (pick me) and they (pick me) will tell you that the projected area of a parking space (or top of a solar powered car) isn’t enough for the mass and kinds of driving done as with a typical passenger car. A parking space is about 130 to 160 square feet. Properly aligning and spacing for latitude takes away a LOT of that space (yes, really, unless you solve the spacing problem, and spacing is a HUGE problem the further north one goes).
Patrick 027, your #1063:
Thankyou for your comments, which included:
Firstly, I’d like to echo Max’s 1057 to you, being in part:
“Having read several of your very interesting longer posts, which described in great detail different aspects relating to AGW, in particular your post 764, which discussed line broadenning, spectral overlap between CO2 and water, etc., I am very much impressed with the depth and breadth of your knowledge.
In the context of the original issues I’ve raised with Kevin McKinney, I was trying to keep it simple, given that he does not appear to understand some basics in energy transfer and conversion, and especially that HEAT is a different form of energy than EMR. (e.g. my 972)
At that level of debate, although your second point above is correctly and cleverly expressed, and in a scientific manner, I doubt if it would be understood by Kevin.
In that regard, I chose in the example of the sun, what was hoped to have a dramatic impact in demonstration of the physics, at an elementary level. Of course, it was imperfect, which is not at all unusual in many processes. For instance, if I wanted to be nit-picky, I could point out that photo’s of the sun clearly show a granular image, meaning that the surface temperature is strongly cellular in distribution, oh, and of course, don’t forget those sunspots. Thus, in comparing location A with location B on the apparent surface, it is necessary to be more definitive. But would that not be getting a bit silly and distracting in lesson #1?
Then I started getting unhelpful (some offensive) comments that were irritating because in many cases it was purely semantic, where for instance, the meaning of key words (e.g. ’fundamental’ and ’appears’) were not accepted as being definitive of an imperfect process.
I even see now that where I have increasingly added bold emphasis because critics repeatedly do not want to accept the definitive nature of some key words, that I’m being scolded by Hank for doing just that. Ho hum!
Sorry that I got short with you!
Patrick , Marcus and Gavin,
” And indeed, if you were to magically remove all CO2 from the atmosphere, I, for one, would not be surprised if _all_ the natural GHE effect were to disappear as the planet cools enough for most of the water to condense out of the atmosphere (leaving a bit of ozone, methane, N2O, and the flourinated gases to hold down the fort).”
I was including the feedbacks for CO2 when making my previous comments. And the above statement is what I’m questioning. The average temperature at the equatorial regions is about 27degC. Even without CO2 wouldn’t there be enough partial pressure from water vapour at the tropics for the GHE to be still significant?
I know that this is a difficult question. Mark would say, a ‘stupid question’. However, and as we all know, there is a lot of scepticsm out there, just shrugging our shoulders, and saying we don’t know, is exactly what the sceptics like.
PeterMartin,
The greenhouse attribution can only be done in an approximate sense
because of overlapping absorption by the various atmospheric constituents. The magnitude of the greenhouse effect is essentially the difference between the emission from the surface and the emission from the top of the atmosphere (i.e., σTs^4 – σTe^4) or about 150 W m^-2 which amounts to the difference between the surface and effective temperature of roughly 288-255 = 33 K. These are, in principle, well-defined numbers. The individual components for each greenhouse gas is a more difficult problem, something involving line-by-line radiative transfer codes to pin down. It is much like asking what part of the floor is covered by towels or shirts in a pile of dirty laundry. A “laundry pile” experiment with radiation models yields gavin’s numbers of about 50% water vapor, 25% clouds, 20% CO2, and 5% going to the rest of the non-condensible greenhouse gases (ozone, CH4, etc). This is a bit misleading since CO2 and other non-condensible greenhouse gases essentially provide the skeleton upon which the water vapor greenhouse effect acts.
It is not really useful to linearize over the whole greenhouse effect to narrow down the CO2 forcing (for incremental changes after 385 ppmv) or to constrain climate sensitivity. We also don’t really speak of the natural CO2 contribution to the greenhouse effect as being a “forcing” since the effect of various greenhouse gases depends on the current atmospheric context (i.e., background concentration, overlap with other gases, etc); that language is usually reserved for some relatively small change from some basline climate. Doubling CO2 under Earth’s current climate regime produces about 1 degree C of warming, while removing all of it would produce a cooling of about 7 C (both prior to any feedbacks), and this shows that the further effects of CO2 cannot readily be deduced from its natural percent contribution, especially as you bring feedbacks into the picture.
Lindzen and others who argue for a neutral to negative feedback simply cannot explain the magnitude of changes seen in the paleoclimate record, for instance how Earth can go from snowball to greenhouse worlds, or even the strength of glacial-interglacial variations.
One way to crudely see this is to assume that the emission and surface temperature are linearly related, so a simple planck-only feedback model would look like [∂(σTe^4)/∂(Ts)]^-1 = (4σTe^3)^-1. This implies that for each Watt per square meter of forcing, you will get a resultant change of about 0.27 K in temperature (the CO2 forcing per doubling is 3.7 Watts per square meter). That indicates that it would require more than 22 Watts per Square meter change in the solar constant just to produce a 1 K change in global temperature, and obviously much more to get the full range of glacial-interglacial variations, or larger changes seen in deep time geologic records. This would imply a very stable climate because we don’t see forcings in the past record that are suitable to explain the magnitude of past changes with just the blackbody feedback acting. Positive feedbacks then indicate that the terrestrial radiation emitted by a warming planet increases less rapidly.
Unfortunately, there are not really any suitable analogs in the past record (either because the situation was different, or because of uncertanties in forcings and global temperature response) to put really tight constraints on climate sensitivity. Additionally the climate sensitivity paramater which links forcing to temperature anomaly (often called “λ” in the literature) is not a constant but changes as a function of the baseline climate, typically decreasing in a warmer world (driven mostly by albedo-feedback potential), although this only really becomes important under a very broad range of planetary climatic cases. See the 2008 paper by Knutti and Hegerl discussing much of the background behind equilibrium climate sensitivity and the evidence for the range given in the IPCC 2007 report.
BobFJ – Thanks, and good point about the granulation and sunspots (and promenances, etc.).
I haven’t really followed your discussion with Kevin McKinney, but I recall one point he made about the totality of the ‘transactions’ being easily greater than the total amount or net transfer involved – a very good point (that you may have agreed with, I would assume).
But if he doesn’t understand that electromagnetic radiation is not considered heat, I don’t think that alone would preclude him understanding the physics. In fact, I think thermal radiation is considered heat, or at least the net flux between two locations is considered heat. I suspect most people really do not operate with the technically correct definition of heat in the context of physics. It is possible to understand internal energy (related to heat capacity at constant volume), enthalpy (related to heat capacity at constant pressure, wherein some heat transfer is converted to work by expansion at pressure), work, temperature, kinetic energy, potential energy, entropy, Gibbs free energy… even if one doesn’t quite have the definition of ‘heat’ quite right (with sufficient context, you can tell what somebody else is refering to even if you call it by a different name).
(I have read that heat is the transfer of energy (of a non-work form), and not energy held by any object – ie the internal energy an object has is not heat, only the energy flowing in or out of it (aside from work). Something like that.)
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Peter Martin – If the entire greenhouse effect were removed AND the albedo increased from 0.3 to 0.6, the temperature drop (drop about 66 K, down to about 222 K) would be about 2 times that from the greenhouse effect removal alone.
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Correction/clarification – I guess the space charge region (or depletion layer, as it can be called) is responsible for maintaining the built-in potential when materials of different work functions (local vacuum 0 – fermi level) are in contact.