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Sceptical Wombat at 11:06 AM on 22 February 2014Dodgy Diagrams #1 - Misrepresenting IPCC Residence Time Estimates
I have a slightly different analogy. Firstly I half full the bath with cold water (I prefer my thought experiments to be as sustainable as possible), and set the cold water tap so that the level stays constant - so far the same as your analogy. Then I turn on the hot water tap just a little bit. Now the level in the bath will start rising. The amount of hot water in the bath at any time will be very small ("CO2 from fossil fuels only accounts for 0.x% of atmospheric CO2") but only an idiot would claim that the act of turning on the hot water tap was not the cause of the rising level. When the bath is nearly full you turn off the hot water tap. The level in the bath will go down, because of the extra pressure, but much more slowly than it rose and it will only asymtotically approach its original level.
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Sceptical Wombat at 10:54 AM on 22 February 2014A Hack By Any Other Name — Part 1
One thing I think you should stop doing is holding passwords in plain text. A better way is to use a one way encryption algorithm and to only store the encrypted password. That way you never know my password and so no one else can get it from you. If I forget my password you issue a new one and require me to change it.
Moderator Response:[BL] Passwords are not and have never been stored in the database as clear text. They are and always have been encrypted, and they are never decrypted. Rather, the password sent by the user is encrypted, and that encrypted password is compared to the encrypted password stored for the user. If they match, then the password supplied by the user is valid.
[BL] Correction, I just looked at the code, and passwords are decrypted in the "Forgot your password" function -- but that doesn't represent much of a security hole, because it can't be used to breach the system, and it can only be used to steal passwords if you already have the password and so can change a user's e-mail, or otherwise have access to that person's e-mail.
Either way, that particular flaw doesn't represent a pressing issue, at least compared to the effort it would take to correct.
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Rob Honeycutt at 10:28 AM on 22 February 2014How we know the greenhouse effect isn't saturated
This could be a case of "I don't (can't, won't) understand until I get the result that I'm looking for."
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Tom Curtis at 10:19 AM on 22 February 2014How we know the greenhouse effect isn't saturated
One addition to my post @81, mgardner has been quite critical of people above for not answering the questions he purportedly asked. He has acted, in other words, as though they had an obligation an answer him. Well, they do not. They do not, firstly because they are volunteers; secondly, because he is ungrateful; and thirdly because the question he wants to focus on is uninteresting. There are far more scientifically informative questions that could be asked - like for example, "how does modtran work". When provided with answers to those informative questions (ie, informative answers to his questions as posed), mgardner has been at his most ungrateful.
He will now, no doubt, complain that his ingratitude has lead to his questions being ignored. He is welcome to those complaints to. He is just not welcome to anymore of my time.
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Tom Curtis at 10:11 AM on 22 February 2014How we know the greenhouse effect isn't saturated
mgardner @80, you are welcome to your opinion, and to waste your time pursuing it. You are not welcome to waste my time on trivial technicalities. Look it up and work it out for yourself. Then when you have, if you still think it interesting, come and let us know the answer, and why it is interesting. In the meantime, your repeated questioning on a trivial point is just spam. Don't be surprised, therefore, if we put you in our personal spam folders (ie, ignore what you have to say, and ask questions about) in future.
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Rob Honeycutt at 09:29 AM on 22 February 2014A Hack By Any Other Name — Part 1
Looking forward to part two!
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mgardner at 09:28 AM on 22 February 2014How we know the greenhouse effect isn't saturated
Tom Curtis@78
"But the further details for which you seek serve no purpose either scientifically, or in terms of general education."
You are welcome to your opinion, Tom.
With respect to general education, I have always assumed that I was protected by the concept of academic freedom in making those kinds of decisions for myself. I do have some experience in this area, and, unless you plan to fly in for the next holiday, you are not the one who is going to be drawing little pictures for my brother-in-law, right?
With respect to scientific purpose, some of the most fruitful physicists of our time have "gone back to the classroom"-the physics 101 classroom-- because it served to clarify their conceptualizations. At the least, for an interested student, wouldn't these 'purposeless' inquiries give some insight into the thinking of those who developed MODTRAN, to which we refer so often?
And then there's the final question-- what's the harm? If HK wants to exercise his chops, is there some policy that prohibits it? I was accused of being 'critical' but several people seem to want to criticize my curiosity. I have always been delighted (and amazed) when students thought for themselves and asked questions.
If this gets me moderated out, so be it. You seem to be much more welcoming and tolerant of 'skeptics' who take up lots of space to little effect.
Moderator Response:[JH] Please lose the condescending attitude.
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How we know the greenhouse effect isn't saturated
Tom Curtis - Agreed. I believe I stated one of those points before regarding the range of altitudes emitting, "...the sum of that emission adding up to the oft-noted temperature equivalent profiles seen in satellite observations of those band". This makes emission from a single layer at that observed temperature an incorrect way of thinking about the physics, as it is a mean altitude, not a single one.
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Tom Curtis at 08:27 AM on 22 February 2014How we know the greenhouse effect isn't saturated
mgardner @77, your question serves no apparent purpose.
You have asked a series of questions on this topic, and have had a perfectly acceptable response to those questions since at least Dikran Marsupial's responce @37, where his final paragraph stated:
"IIRC the lower atmosphere isn't completely opaque to IR, so it probably isn't best to think too strongly about it in that way, instead there is a band in the atmosphere from which the bulk of IR is radiated. Some may come direct from the surface, but not much as it is absorbed in the trophosphere, most will be emitted from the air higher up in the atmosphere, which is cold. The more CO2 you add, the higher in the atmosphere it needs to be radiated from in order not to be absorbed before it escapes. I suspect there is a probability distribution that shows the density of the height in the atmosphere from which IR photons escape; the mean increases with increasing CO2."
Nothing since then has done any more than flesh out details of this basic picture, and perhaps illustrate it better. One key point here is that talking in terms of layers as hard boundaries defined for x,y, such that below x, at wavelength y, no photons emitted escape to space makes no sense. That is DM's first point in the paragraph above. And yet you return to the assumption that such defined boundaries make sense, that in scientific use they are anything more than an approximate, but sometimes useful convention.
In radiation models, the atmosphere is divided into thin layers. For each layer, l, and for each wave number (or some other conveniently small division of frequency) emissions are calculated. The absorption of the total upward radiation for the layer below, l-1, is calculated. The model then passes to the next upward, l+1, layer the total upward radiation from l, ie, the sum of upward emissions plus (1-absorption) of the total upward radiation from the preceding layer. The same is done for downward radiation in the opposite direction. No attempt it made to track the exact point of origin of radiation in the total upward radiation from each level because it is superfluous information. Such models calculate the actual upward or downward radiation at any level with stunning accuracy.
If asked where the radiation that escapes to space comes from, they modellers indicated that it comes from the "effective altitude of radiation", which is defined as "that altitude that has the same temperature as the brightness temperature of the radiation to space at a given wave number" (or other conveniently small division of frequency). Thus talk of the layer from which radiation comes is just a shorthand way of mentioning the temperature weighted mean altitude from which the radiation comes. Nothing more.
In more popular parlance, we can say (and this is literally true) that increased CO2 increases the mean altitude from which the IR radiation escapes to space, and that if that mean altitude is cooler, then the IR radiation escaping to space will be reduced. But the further details for which you seek serve no purpose either scientifically, or in terms of general education.
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mgardner at 07:06 AM on 22 February 2014How we know the greenhouse effect isn't saturated
HK@76
Thank you. Like your other posts, this is very thorough and well written.
My interest is in the area (nominally 5 km) where we say that 'most of the energy is radiated to space'. And, because my goal is to explain or 'draw a picture' (literally or verbally) at the simplest level, I wish to discuss only one wavelength resulting in somewhere between big x and little x.
So, let's say we define at about 5 km two layers of 100 m thickness (as in that graph @55 we both like). We call the top one A and just below it B. (I use top and bottom "plane" to indicate the boundaries not to confuse with "the" surface of Earth). Also, I will simply use zero rather than negligible for quantities. And, CO2 is the only GHG for this discussion.
A has zero CO2, and B has some. (I say that A is transparent, and B is translucent.) C, which begins at the bottom plane of B and goes down x, is 'opaque' since nothing originating below its bottom plane reaches B.
How do we characterize the radiation flux and the temperature for these layers, first as described, and then after we add CO2 in the equivalent amounts to each?
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How we know the greenhouse effect isn't saturated
mgardner @64 & 73:
You want some examples of how long a path of air must be to reduce the amount of IR radiation passing from one end to the other to a “negligible” level?If a “negligible” fraction of surviving radiation is defined as 1% (my arbitrary choice), it should be possible to calculate some path lengths of air needed to achieve this, assuming that my layman understanding of the Beer-Lambert law is reasonably correct. First a hypothetical example to show the principle:
Suppose that 25% of the radiation at a particular wavelength is absorbed by 1 metre of air. The next metre will absorb 25% of the remaining radiation and the same fraction will be absorbed by each successive metre after that (75% surviving through each metre).
The surviving fraction through 5 metres is 0.755 = 0.237, for 10 metres the fraction is 0.7510 = 0.056 and so on. In this case it takes 16 metres of air to reduce the surviving radiation to a negligible level, since 0.7516 = 0.01 = 1%.
And now some real data:
This graph from this article by Science of Doom shows the fraction of radiation entering one end of a 1 metre path of air at sea level that is transmitted (survives) to the other side. The CO2 concentration is 380 ppm, and the radiation originating within the air itself is ignored. The y-axis goes from 0 (no radiation transmitted) to 1 (all radiation transmitted), and the x-axis covers the wavelength interval from 15.15 micron (left) to 14.88 micron (right), i.e. around the very strongest absorption band of CO2. (10,000 / wavenumber = wavelength in microns)
As you see, 99% of the radiation is transmitted at 662 cm-1, while only 2% is transmitted at 667.5 cm-1, so the radiation at 667.5 cm-1 is already reduced to an almost negligible level by only one metre of air at sea level!
A calculation like the one above shows that it takes 458 metres of air to reduce the radiation at 662 cm-1 to a negligible level (0.99458 = 0.01) while it only takes 1.18 metres (0.021.18 = 0.01) to achieve the same for radiation at 667.5 cm-1. (See the last paragraph in Tom’s comment @67)If we ignore the complexities caused by pressure broadening and so on (I’ll leave that to the experts!), these path lengths are roughly inverse proportional to the atmospheric pressure. If the pressure drops to 0.2 bar (at about 12 km) the number of CO2 molecules per m3 is only 1/5 of that at sea level, so you need a 5 times longer path to get the same absorption as at sea level. That should translate to 2.3 km for radiation at 662 cm-1 but still only 5.9 metres for radiation at 667.5 cm-1. In the middle of the stratosphere (30 km / 0.01 bar) the same path lengths are about 46 km (!) and 118 metre, respectively.
(this approach only works for well-mixed gases like CO2, not for water vapour that is strongly concentrated in the lower troposphere)So, mgardner, the “x” you have been asking for can be anything from a metre to tens of kilometres, depending on wavelength, altitude and other factors, including how you define the term “negligible”.
Did this help?
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One Planet Only Forever at 02:40 AM on 22 February 2014'It's been hot before': faulty logic skews the climate debate
ubrew12,
I postulate that:
"Abbott has only made a statement that sounds like what people who desire to get away with benefiting from the unsustainable and damaging burning of fossil fuels will readily accept. He has claimed what that type of person wishes to hear and prefers to believe. And he does it without any substantial evidence to support his claim, because the evidence actually substantially contradicts such a claim."
It appears that Abbott is one of the many powerful and wicked people who are trying to take advantage of that potential popularity to benefit from unsustainable and damaging attitudes and actions any way they can get away with.
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michael sweet at 02:24 AM on 22 February 2014How we know the greenhouse effect isn't saturated
mgardner,
The people you are posting with are volunteers who have gone to a lot of effort to find graphs and explainations that will answer your questions. They are searching the background data for information outside of their specialties. You have thanked their efforts with criticism. Has it occured to you that the problem may be that your questions have been poorly phrased from the beginning? You appear to have specific needs for your answer that it is difficult for others to understand. Perhaps you need to do your own homework, instead of criticizing others for doing a poor job of it. You could be building your knowledge by searching for the answer yourself.
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Dikran Marsupial at 22:37 PM on 21 February 2014How we know the greenhouse effect isn't saturated
mgardner, as you continue to be ill-mannered and dismissive towards attempts to address your ill-posed questions, even after my appology in post 63, consider my participation in this discussion over.
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mgardner at 21:15 PM on 21 February 2014How we know the greenhouse effect isn't saturated
HK@70
"What if the diagram in @55 had showed radiation from a narrower wavelength interval, say 14.5-15.5 microns in stead of 13-17? I’m sure the radiation within each CO2 concentration would originate from a much narrower altitude interval and look more like a “layer” in the atmosphere (more like what mgardner has claimed). "
HK, please look at the graph @55. Look at the label of the vertical axis.
Now, read carefully what I said @64.
What have I so far claimed about radiation originating in a 'layer' other than what the graph says? Again, my original problem was the original 'layers' language of the explanation-- about 'radiating layers moving up to where it is colder'.
I've now quoted myself so often I guess there is not much point-- I think it is the hammer and nail problem. Whatever question I ask, the answer is going to be the one that everyone has learned to repeat.
Moderator Response:[JH] Ypou are now skating on the thin ice of escessive repetition which is prohibited by the SkS Comments Policy. Please cease and desist.
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michael sweet at 21:09 PM on 21 February 20142014 SkS Weekly News Roundup #7
Many here follow the Arctic Sea Ice. For those who don't, this sea ice map from Feb 20 shows astonishing melting near the North Pole. The North Pole is not imaged since the satalites do not fly directly over it, but it is clear that there are open areas of ocean at the North Pole in the middle of winter! It will be interesting to see what the NSIDC has to say about this in their monthly comment around March 7. Of course the total sea ice extent is near record lows. Another interestng melt season ahead.
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ubrew12 at 20:13 PM on 21 February 2014'It's been hot before': faulty logic skews the climate debate
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Doug Hutcheson at 19:21 PM on 21 February 20142014 SkS Weekly Digest #7
My apologies - I have just seen the repost of The Conversation article here and that is where I should have commented.
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Doug Hutcheson at 18:47 PM on 21 February 20142014 SkS Weekly Digest #7
John, thanks for going in to bat for reason and logic at The Conversation today. The comments were instructive, but cut off all too soon for my liking. Still, it gave the deniers a chance to enjoy a feeding frenzy, so it was also amusing, in a black kind of way.
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meher engineer at 17:25 PM on 21 February 2014Snows of the Nile: The search for vanishing equatorial glaciers
i have just seen the preview. It dii lok interesting, particularly since I have never heard of these African mountains I tried to rent the video from Vimeo but failed.
meher engineer
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One Planet Only Forever at 13:51 PM on 21 February 2014'It's been hot before': faulty logic skews the climate debate
I postulate that:
"Faulty logic is not skewing the climate debate. The desire to benefit from burning fossil fuels is causing many people to readily accept absolute nonsense that sounds like what they wish to hear and prefer to believe. And many powerful and wicked people are trying to take advantage of that potential popularity any way they can get away with."
And to poke at another twisted piece of the pervasive and persistent irrational thought processes of that group:
"I will only change my mind about that when it is conclusively proven with absolute certainty to my satisfaction that what I prefer to believe is not to be believed."
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PhilMorris at 10:02 AM on 21 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
I suppose as a website devoted to the valuable activity of debunking denialist attitudes towards AWG you provide a valuable service, and as such, quoting 'consensus' information that supports AWG makes sense. But I suspect for a growing number of people AGW is all too real with 100% certainty, and for many people it is happening all too fast. Over the last few years there has been a continual stream of research papers that make the IPCC projections clearly conservative insofar as the pace at which climate change is occurring. In the last couple of weeks alone there were two research papers that continue the bad news.
"Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus" by England et. al, Nature Climate Change adequately explains that the so-called surface temperature ‘hiatus’ has been caused by abnormally strong Pacific Trade winds, which have driven heat into the deep Pacific, and that when those abnormal trade winds abate, we're in for a continued and rapid surface temperature rise.
The second is “Observational determination of albedo decrease caused by vanishing Arctic sea ice” by Pistone et. al.,
PNAS, showing that the loss of ice albedo over the last 30 years is equivalent to an additional 25% of global CO2 forcing. I’m betting that isn’t part of any of the climate models, meaning those climate models vastly underestimate the rate at which climate change is happening. Hm, prehaps that's why we may expect a summer ice free Arctic before 2020, some 30 years ahead of the latest IPCC 'projections' (Maslowski et. al, Ann. Rev. Earth Planet. Sci, 2012)I follow the literature rigorously and perhaps I’m simply blind to certain things but I have yet to see a single ‘good news’, peer reviewed research paper that has stood the test of time, and suggests that things are not as bad as they appear to be.
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How we know the greenhouse effect isn't saturated
Agree with your comment about the non-saturation, Tom!
Unlike the MODTRAN graph, the annotations in the diagram were not added by me. They can be found in the original diagram in the article from 2007. -
Tom Curtis at 09:06 AM on 21 February 2014How we know the greenhouse effect isn't saturated
KR @69, thanks for the advise. Oddly, I read "HK", and intended to type "HK", but apparently my fingers didn't get the message.
HK @70, first, apologies for the misattribution. Second, yes I believe we are saying the same thing.
I like the new diagram from RC. It is particularly interesting to pay attention to the logarithmic scale of the absorption factor, which should drive home the very large differences in the width of the emission profile for small changes in wavelength.
One slight point about the diagram, however. It includes the two relatively highly absorbing bands at 13.9 (720 cm-1) and 16.2 microns (620 cm-1)in the region saturated at 1xCO2. From the modtran graph, they are still clearly in the wings, and become deeper (less emissions to space) with higher CO2. The statement that the region is saturated is, therefore, clearly a simplification and should not in fact be understood as saying that there is no further strengthening of the greenhouse effect across that entire band with increased concentration.
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How we know the greenhouse effect isn't saturated
Tom Curtis @67: Your point seems to agree with what I’ve tried to explain below, which was written before I read your last post:
Agree with Dikran that your diagram is very interesting! I’ve included it in my growing collection of climate graphics.
All of you: Regarding the discussion about of “opaque” layers, have you taken into account that the absorption of IR by CO2 is extremely dependent on the radiation’s wavelength, even within a relatively narrow wavelength interval like 13-17 microns in the diagram? I think that explains why the radiating layers of CO2seem to be so diffuse, i.e. spanning over so large altitude ranges.
Take a look at this diagram from the previously mentioned RealClimate article about the saturation argument. (It also demonstrates another important aspect of this, namely the widening of the absorption band.)
As you see, there is a more than 1000-fold increase of the absorption factor from 13 to 15 microns, and at least a 100-fold reduction from 15 to 17 microns. When that is taken into account, my interpretation of the diagram in @55 is the following:
The radiation from the lower troposphere (in the 1000 ppm case) comes from the periphery of the absorption band, say 13-13.5 and 16.5-17 microns. It’s weak despite coming from fairly warm CO2 because the radiation is partly blocked by CO2 higher up.
The radiation from the middle troposphere comes from wavelengths closer to the centre of the absorption band; say 13.5-14.5 and 15.5-16.5 microns. It’s stronger despite coming from colder CO2 because much less of the radiation is blocked by CO2 higher up. The radiation from the lower troposphere on these wavelengths is completely blocked because CO2 absorbs more strongly here.
The radiation from the upper troposphere and lower stratosphere comes from the central part of the absorption band (14.5-15.5 microns), with the radiation closest to 15 microns originating in the upper part of the stratosphere (even above Felix Baumgartner!). This radiation weakens partly because the CO2 here is very cold, and partly because the wavelength interval where CO2 is able to absorb and radiate gets narrower as the altitude increases (you get less radiation from a 1 micron wide interval than a 4 micron wide). And of course, it’s impossible for any photons in the 14.5-15.5 micron interval to escape to space from the lower and middle troposphere because CO2 absorbs so strongly in this part of the spectrum.
The same goes for the curves for lower CO2 concentrations, but the altitude with peak radiation (about 8 km for 1000 ppm) will be lower while the radiation itself is higher in the warmer parts of the atmosphere.
What if the diagram in @55 had showed radiation from a narrower wavelength interval, say 14.5-15.5 microns in stead of 13-17? I’m sure the radiation within each CO2 concentration would originate from a much narrower altitude interval and look more like a “layer” in the atmosphere (more like what mgardner has claimed).
Does all this make sense, or have I missed something crucial here?
Moderator Response:[JH] Unnecessary white space eliminated.
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Phil at 08:44 AM on 21 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
william @5
On the contrary side, there have been numerous cases where the only scientist that was correct was an individual against all the other scientiests.
I wonder whether this is really true. It would be good to have examples, but to pre-empt the usually case quoted, here in Thomas Kuhn from "The Copernican Revolution" (Chapter 6)
Therefore, when in 1616, and more explicitly in 1633, the Church prohibited teaching or believing that the sun was at the centre of the universe and that the earth moved around it, the Church was reversing a position that had been implicit in Catholic practise for centuries. The reversal shocked a number of devout Catholics, because it committed the Church to opposing a physical doctrine for which new evidence was being discovered almost daily ...
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How we know the greenhouse effect isn't saturated
Tom Curtis - Credit for that excellent MODTRAN graph goes to HK, not to me. The handle are unfortunately easily cross-read.
At least this isn't as bad as when there were three different 'Hank's actively commenting...
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Dikran Marsupial at 08:15 AM on 21 February 2014How we know the greenhouse effect isn't saturated
Cheers Tom, that is very interesting, it makes the shapes of scaddenp's plot a little less surprising (but still interesting), and hopefully helps answer mgardners question.
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Tom Curtis at 07:58 AM on 21 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
Prufocks @7, you have touched on a point which is a slight weakness of the paper. One of the strengths of Oreskes' original study is that she identified papers that did not include direct assessment of anthropogenic contribution to global warming, and did not include them in those that affirm global warming. This did not prevent her study being attacked by "skeptics" with the argument from irrelevent denominator (ie, the claim that she overstated support for the concensus because x papers did not support the concensus because they never directly address the issue). In formulating the categories for Cook et al, Cook et al did not include a category for those papers that explicitly address attribution. Consequently "attribution papers" tend to get sorted into "impacts", "methods", and occassionally "mitigation". The problem is that we cannot, from the paper, directly address the propotion of attribution papers support consensus.
Having said that, Dana has said on a couple of times that 100% of recent attribution papers support >50% anthropogenic contribution to recent warming. I suspect his definition of an attribution paper in that comment may be a bit tighter than one that would have been used in the survey; but cannot be sure without conducting a mini survey of my own.
It should be noted that the "obvious" problem with extending the analysis beyond attribution papers to those that merely accept AGW and go on from there is not a problem at all. Scientists do not simply accept claims. If they adopt AGW as a working hypothesis, it is because they have read a significant number of relevant papers, or at least review papers, and been convinced by the evidence. I am sure there are exceptions, but not enough to distort the result. That means that a general survey like Cook et al will pick up on whether or not controversy about a theory is general, or restricted to a small group unconvinced - and clearly the later is the case.
It should be noted that the criticism of the concensus paper is coming from people who, in general, accept the OISM petition as evidence that there is no concensus, ie, they accept that the signing of an internet petition by bachelors or vetinary science, is evidence that there is no concensus of climate science; but they do not accept that detailed discussion of the consequences of anthropogenic warming by climate scientists is evidence, if those climate scientists assume global warming in that study rather than prove it from first principles.
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Prufrocks at 07:31 AM on 21 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
This will undoubtable mark me as a troll of some type (I'm only vaguely familiar with the myriad sub-types)... but I'm not, I'm a lay-person trying to keep up. I'm pretty strongly (~95%) on board with AGW and find no denialist or fake-skeptic credible. I'm somewhat confident to rebut many of their debunked claims and make the case for AGW. Though not diligent enough, my main sources are SS, RC, Tamino, Crock.
But, I'm finally spending some time with "Quantifying the consensus on anthropogenic global warming in the scientific literature" (John Cook et al 2013 Environ. Res. Lett. 8 024024 doi:10.1088/1748-9326/8/2/024024). I've downloaded the datafile.txt and randomly searching citations and going to the original articles online and, where possible, full article not just abstract.
I'm somewhat surprised to see how many of those who "endorse" AGW without quantifying it (groups 2 & 3) seem mostly to be "accepting" it as a premise for their paper rather than forming a conclusion of AGW based on their paper. Which I'm guessing is perfectly fine, appropriate & expected and the little suprise may only reflect my own naïveté. Ever since Oreskes' study – which I accept as being very strong and persuasive – and based on my own observations of the lit, without thinking I had just assumed that 'active climate researchers actively peer-review publishing,' and not rejecting AGW, were most often supporting their conclusion with more or less new data or new analysis (I recognize this does frequently apply).
Am I mischaracterizing? Am I wrong in wondering or wrong in even remarking on it? I have to believe the denialists are squawking about it.
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Tom Curtis at 06:57 AM on 21 February 2014How we know the greenhouse effect isn't saturated
Dikran Marsupial @65, it is important to interpret scaddenp's graph in the light of KR's excellent annotated MODTRAN graph:
For context, Scaddenp's graph is for transmission of 13-17 micron radiation. That is radiation with a Wavenumber of 590-770 cm-1. As such it includes the full width of the notch shown in the graph above, not just the central values. A graph showing just 15 micron radiation (=666.7 cm-1) would show a much narrower effective emission profile for each concentration, and indeed, would show an altitude such that below that altitude, emitted IR radiation is nearly completely absorbed. In contrast, a graph of just 13 or 17 micron radiation would more closely resemble something like the 100 ppmv profile (I also do not have the chops to calculate it, and would need to do so to be sure).
Looking carefully at Scaddenp's graph, you will show that all curves have a right skew, so their mean value of emission is higher than their modal value. That makes things slightly awkward in that we need to guesstimate (if we cannot calculate) that mean value in relating it to the atmospheric profile shown by KR. However, in general the curve of a particular wave number in the 590-770 band will have an effective emission profile with a mean altitude of emission equivalent to the 1000 x (300- brightness temperature)/6.5. As such, even the emission profile of CO2 with a wave number equivalent to the bottom of the trough is not shown on Scaddenp's graph.
Quoting mgardner, he wrote:
"For some altitude h (e.g. 5 km), and for some wavelength (lambda), I think there is an altitude h-x such that the number of such (lambda) photons emitted from a plane at that level (h-k) which reach h is negligible."
(My emphasis)
As I have noted, at 15 microns (666.7 cm-1), that is correct. Indeed, at 15 microns absorption is so strong that I have seen a 15 micron spike in atmospheric spectra recorded in an aircraft from the amount of warmed, cabin air between the window and the instrument (much less than a meter). It is probably also true for the plateau in emissions on either side of 15 micron spike (which has a mean altitude of emission in the tropopause). However, it is not a usefull formulation for CO2 emission in general, because of necessity it will neglect the wings were the important action is occuring with respect to increases in CO2 concentration. On the other hand, in simplified models and discussions, climate scientists treat all emissions as coming from the mean altitude of emission - a simplification that is surprisingly accurate (I am told).
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Rob Honeycutt at 05:44 AM on 21 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
William... Definitely, consensus is not how science progresses. But consensus is how we can evaluate relative risk for things we can never have perfect knowledge of.
What surveys like this give us is a method by which to make value judgements required in order for action to take place.
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william5331 at 05:23 AM on 21 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
I'm still uncomfortable with surveys of scientists to see how many believe in one thing or another. On the contrary side, there have been numerous cases where the only scientist that was correct was an individual against all the other scientiests. I'm not suggesting that that is the case here. The evidence for climate change and it's likely effects are pretty overwhelming and, I think, grossly underestimated but consenses is not part of science.
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How we know the greenhouse effect isn't saturated
mgardner - I'm afraid you're mischaracterizing my posts (and perhaps mixing them with others, as I have not referenced Beers law). I've found your requests for 'opaque' layers quite difficult to decipher, in part as (a) there has been no definition of 'negligible' stated, (b) path length increases as a continuum with decreasing GHG concentration/pressure, and (c) you've kept asking about 'opaque layers' while stating that you think layers are not a proper way to think about the matter - the combination of those factors making it impossible to suggest any dividing lines. Or, quite frankly, for me to follow what you have been asking for. I have not intended to be rude - just trying to answer the questions as I understood them.
The discussion appears to be progressing now that there is sufficient understanding of terms and of your queries - I will leave you to that.
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Dikran Marsupial at 04:03 AM on 21 February 2014How we know the greenhouse effect isn't saturated
mgardner wrote "For some altitude h (e.g. 5 km), and for some wavelength (lambda), I think there is an altitude h-x such that the number of such (lambda) photons emitted from a plane at that level (h-k) which reach h is negligible."
My reading of scaddenp's graph suggests that for 400ppmv, the maximum power of photons in this band is emitted from about 4km in altitude (about 0.44 watts m^-2), but there is about 0.24 watts m^-2 of photons in this band that reach space directly from the surface, which is far from negligible. Thus there is no truely opaque layer (in this sense) from which the radiation of IR photons from the surface is negligible, at least for current atmospheric CO2 concentrations. Or to put it another way, whatever the values of h and x are, they are too large to fit within the Earths actual atmosphere.
I suspect you really need to use something like MODTRAN to get a definitive answer to this question, however the realclimate article I mentioned earlier in the thread provides this diagram:
Apparently at 300ppm, the CO2 in a column of the Earths atmosphere is equivalent to a 2.5m tube of pure CO2 (at sea level pressure and 20C). The graph shows the proportion of light transmitted through the tube as a function of length. In this case the transmission is still falling appreciably from tube lengths corresponding to 1xCO2 to 4XCO2, which suggests that there isn't a truely opaque layer within the tube in this thought experiment either. Note that this is not really realistic (as the article points out because not all of the atmosphere is at 20C or sea level pressure).
I'd say it was a mixture of (1) and (3), I don't (currently) have the chops to perform the calculations, but hopefully I can help in getting into the ball-park and help to better formulate the problem (you do have the required security clearance though ;o).
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mgardner at 03:24 AM on 21 February 2014How we know the greenhouse effect isn't saturated
DM@63
That pesky "real world" is intruding on our fun little universe here, so I will try to briefly give you something to think about while I take a little time to attend to it. I don't think we're quite communicating yet...
Here's what I mean when talking about an opaque layer. And please remember, I am setting up a simplified, idealized case to further my understanding-- I'm gathering up elements from which I can synthesize an accurate model that works for me, not anyone else. Once I do that, you are free to tell me that I am wrong or that yours is better.
Scaddenp's graph refers to emissions "from a hundred meter layer".
I treat that as a plane.
In my earlier reply to KR, I said something like:
"For some altitude h (e.g. 5 km), and for some wavelength (lambda), I think there is an altitude h-x such that the number of such (lambda) photons emitted from a plane at that level (h-k) which reach h is negligible."
and
"I don't know what x is, or how many subsequent such layers descending from h-x there may be."
To my mind, there are three legitimate ways to answer that:
1) "You're wrong, there's only one (or no such) layer and it goes to the surface. Here's the calculation using this wavelength and Beer's law." (KR's response, sans the calculation, which to me is obviously wrong.)
2) "You are correct, I come up with (n) such layers, and the thicknesses vary thusly as we descend."
3) "Sorry, I don't have the chops to provide you with the numbers you are looking for." or maybe "Sorry, you don't have the required security clearance?"
This can also be applied to the question of how the amount of radiant energy embodied in those photons is attenuated, as measured by radiant energy arriving at h.
Hope that's clearer. I will be back and try to discuss the more general case.
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DSL at 02:50 AM on 21 February 20142014 SkS Weekly News Roundup #7
Not engaging in the conversation directly; just tossing in a few recent and relevant references to supplement Tom's points:
Zhou et. al 2013 - "An Analysis of the Short-Term Cloud Feedback Using MODIS Data."
Evan & Norris 2012 - "On global changes in effective cloud height."
Keep in mind that ENSO plays a significant role in triopical cloud top height and that the measurements discussed in Evan & Norris cover slightly more than the last decade, a decidedly La Nina-ish period. Nevertheless, after accounting for a systematic error in sampling, a positive trend in CHT is found for the period.
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jeff_from_ky at 00:48 AM on 21 February 2014Arctic sea ice has recovered
Just wondering how the dismissives will fit this news into their "60% recovery" meme. Nah, they won't, they'll just quit talking about it.
Arctic Sea Ice Sits at Record Low for Mid-February - Climate Central
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Tom Curtis at 00:42 AM on 21 February 20142014 SkS Weekly News Roundup #7
Russ R @74, before discussing your points, I think we need a point of clarrification about feedbacks. Specifically, feedbacks are responses to changes in temperature. As such, any feedback response produces a further response, which in turn produces a further response and so on. In principle this reiteration proceds for ever, but in practise, after a few repetitions the feedback response is swamped by normal variability and it gets washed out of the system.
The final temperature response to a given initial change of temperature is given by the formula:
ΔT = T0/(1-Σg)
where ΔT is the final change in temperature, T0 is the initial change in temperature, and Σg is the sum of gains for each individual feedback, ie, gwv, glr, gcl, galb etc.
If gxx is positive, then it reduces the denominator, and increases the final temperature response. Ergo, it is a positive feedback. Conversely, if gxx is negative, then it increases the denominator, and hence decreases the final response. It should be obvious from this that so long as Σg < 1, then ΔT is finite, and the total feedback response will eventually lead to a stable condition. Consequently, there is no need for a positive feedback that some negative feedback should overwhelm it to stop it running away. That is only necessay if the sum of the feedback gains is greater than 1. In simpler terms, if each iteration of the feedback response results in a further temperature increase less than the preceding temperature increase, the response will self damp even though the net feedbacks are positive.
Turning now to the details of your post:
Ice Albedo: The IA feedback involves not just the change in albedo, but the actual advance of the ice. Between approximately 80 and 20 degrees of latitude, the surface temperature rises by approximately 1 degree C per 145 km advance towards the tropics, requiring a 1 C fall in temperature for the ice to advance that distance. The IA feedback will be determined by the balance that allows the fall in temperature to result in a sufficient advance in the ice, and consequent increase in albedo to account for it. Among the complexities are that ice sheets do not advance significantly over water (which limits their advance to the NH), and that polar amplification will make the temperature/latitude slope steeper with a cooling climate, thereby dropping temperatures at the poles and making the initial advances easier, but also requiring a greater decrease in temperature for each km of ice advance. That later effect weakens the IA feedback effect, which in turns means your BOE calculations are over calculations of the strength of the effect.
Water Vapour: You mount several counter arguments against the possibility of any significant increase in the strength of the water vapour feedback. The first is based on geometry. It incorrectly assumes that:
1) The greenhouse effect due to water vapour in the tropics is saturated, such that in increase in the strength of the WV feedback can only occur by an advance to the poles. But, in fact, the strength of the greenhouse effect of a substance depends on the altitude of effective emission to space of that subtance. In the tropics that altitude for WV is about 4-5 km, but the tropopause is about 18 km, allowing a considerable increase in height, and hence strenght of the WV greenhouse effect.
2) The brightness of OLR is a function of solar incident angle (effectively the pink line), whereas it is a function of temperature at the effective altitude of emission (effectively the green line), which is much more even between tropics and polar regions:
Consequently your calculation of the upper limit of the WV feedback is completely in error. There is in fact no practical upper limit on the strenght of the WV feedback.
You further argue that the formation of clouds, and a purported limit on sea surface tempertures at about 30 C forms '... an effective "wall" ' to increasing WV feedback strength.
I will first note that the formation of clouds is not a "wall" to the WV feedback, but an independant feedback. Further, your assumptions about that feedback are simplistic. An increase in WV concentration may, for example, result in more rapid formation of heavy rain drops, so that clouds dissipate by rainfall more rapidly. More certainly, they will result in larger diameter cloud particles, an effect which reduces cloud albedo. Further, much of the additional cloud may simply be in the form of thicker clouds due to stronger updrafts, resulting in no significant increase in albedo at all. In sum, while it is probable that increased WV will result in more cloud and a greater cloud albedo, the strength of that increase is far from certain with an number of known factors complicating the issue.
What is worse, you simply ignore the cloud GreenHouse effect. Again, stronger updrafts created by the condensation of more WV will probably result in higher upper boundaries of clouds, and more high cloud, both of which significantly increase their greenhouse effect. The balance of the change in GHE and change in Albedo from clouds is not known, but likely a small positive forcing. Treating clouds simplisticly to arrive at a conclusion of a strong negative feedback is not science.
Even worse is your treatment of sea surface temperatures. You simply claim as fact, and without evidence that approx 30 C is an upper limit on sea surface temperatures. That is an extraordinary claim, as there is literally no mechanism to drive such a limit. It is the more extraordinary as SST as high as 32 C and above have been observed on the Earth's surface:
(The 32 C regions stand out better at original resolution)
That is 5 C above the average tropical SST, so that no higher temperatures have been observed is easily explained in that 5 C increase above average is huge in a body with the thermal inertia of large stretches of ocean - particularly given that winds cause turbulence to deptths of 100 - 700 meters, mixing surface with cooler below surface waters on an ongoing basis.
Not only are SST above 30 C known today, much higher SSTs were known in the past:
"The middle Cretaceous (125–88 Ma) greenhouse world was characterized by high atmospheric CO2 levels, the general absence of polar ice caps, and much higher global temperatures than at present. Both δ18O-based and model-based temperature reconstructions indicate extremely high sea-surface temperatures (SSTs) at high latitudes. However, there are a number of uncertainties with SST reconstructions based on δ18O isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the δ18O value of Cretaceous seawater, the paleoecology of middle Cretaceous marine organisms and seawater pH. Here we applied a novel SST proxy (i.e., TEX86 [tetraether index of 86 carbon atoms], based on the membrane lipids of marine crenarchaeota) derived from middle Cretaceous sedimentary rocks deposited at low latitudes. The TEX86 proxy indicates that tropical SSTs in the proto–North Atlantic were at 32–36 °C during the early Albian and late Cenomanian–early Turonian. This finding agrees with SST estimates based on δ18O paleothermometry of well-preserved foraminifera as well as global circulation model calculations. The TEX86 proxy indicates cooler SSTs (27–32 °C) for the equatorial Pacific during the early Aptian, which is in agreement with SST estimates based on δ18O paleothermometry."
(My emphasis)
Frankly, I feel as though you are devolving to argument by mere assertion. You have now merely asserted as fact several false claims, including that SST do not exceed approx 30 C, and that cold and warm runaway events do not happen. Your only counter argument to refutation of those points has been an appeal to a false account of positive feedbacks.
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Dikran Marsupial at 00:41 AM on 21 February 2014How we know the greenhouse effect isn't saturated
mgardner I am sorry that my posts have been interpreted as being adversarial or dismissive, they really were not intended that way, the intention was to try and warn that your questions were likely to lead down what appears to me to be a blind alley.
Note back on post 37 I tried to explain that a two layer model wasn't an accurate representation of reality, and by post 39 suggesting that it might be better to think of it in terms of a p.d.f. of the heights at which IR photons are successfully radiated. Note scaddenp's interesting diagram supports the idea that there isn't really an "opaque" layer at all, at least at current CO2 levels (which is why I was suggesting concentrating on the photons that actually escape the atmosphere).
Your use of terminology has not been all that clear, you write:
"... I clearly distinguish between "absorption of all possible photons from the emitting plane" (opacity, which is the essence of the original myth about 'saturation',) and "a reduction of the energy emitted from that plane as it traverses the interval" (attenuation). I don't use words randomly.
however your original question (repeated in that post) was
"And what the attenuation would be for IR radiation in some CO2 band through that 'layer'."
Specifying IR radiation in that band makes the use of attenuation ambiguous as the energy entering that region as IR in those bands that is absorbed is not necessarily transferred to the "translucent layer" as IR in those bands, and the IR that is emitted into space from the "translucent" layer largely comes from the bulk heat energy of the atmosphere at that height, which does not primarily come from IR in the absorption bands, but from convection. This means that the best definition of attenuation that works for this sentence as stated is in terms of attenuation of the photons themselves.
I'd be happy to resume the discussion on a non-adversarial, friendly tone, misunderstandings happen, especially in electronic forums!
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mgardner at 00:21 AM on 21 February 2014How we know the greenhouse effect isn't saturated
Bob Loblaw et al:
First, I'd like to explain why I get testy about some responses.
I'm a Spherical-Cow-Physics kind of guy. In learning, problem solving, and in teaching, I do (did) as I was taught a long time ago and try to build understanding from the ground up. Now, I realize that's my particular style, and there's no obligation for anyone to respect it. However, it is a matter of principle when it comes to teaching practice-- 'setting up the problem' requires figuring out the 'position' of the student before 'applying forces to achieve desired displacement'.
In this case, I'm playing the role of the student, but I'm getting this adversarial and dismissive attitude about my questions. Perhaps it's understandable since you've been dealing with 'skeptics' a lot, but even when I think someone is likely a 'skeptic', I ask questions to pin down where he's coming from, rather than just firing off the standard litany and telling him 'you just don't get it' and 'your questions are irrelevant'.
My original comment was @28. Please note that I was not happy with the 'layer' concept that others used-- it's not my invention. Also, I've said several times that I understand both the underlying physics concepts and the complexity of the problem. But I don't have a MODTRAN in my head, so I'm asking very specific questions to help me construct a model (or analogy) that is both reasonably accurate (for myself) and simple enough to use in conversations with those who are more lay than I am.
Since this is awfully wordy, I'm going to start a couple of new specific comments on the layer concept and the overall picture.
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mgardner at 21:50 PM on 20 February 2014How we know the greenhouse effect isn't saturated
scaddenp@55
Thank you for directly answering my question. I zoomed in on the graph and used an index card on the screen to get ~900 m for the height difference between 280ppm and 400 ppm at .4 W/m2. (Is that about right?) That would make a temp difference around 6 K?.
Holding everything constant.
I'm going to reply to others on this as soon as I get the image insertion thing to work. That will require a bit more coffee.
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Doug Hutcheson at 18:39 PM on 20 February 2014Dodgy Diagrams #1 - Misrepresenting IPCC Residence Time Estimates
"the confusion would have been avoided if time was taken to actually read what was written"
Sounds like the sort of comment I used to see written on my examination papers. I learned the value of this trick (actually reading the question) at school and it continued in my life in the software industry, encapsulaed as the time-honoured answer to most questions: RTFM - read the flamin' manual!
Sadly, it seems reading is one thing and comprehension is quite another, judging by the comments I see in the blogosphere.
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Doug Hutcheson at 18:28 PM on 20 February 2014Vision Prize: scientists are worried the IPCC is underestimating sea level rise
"Vision Prize participants may be pessimistic that we'll transition away from a business-as-usual emissions path".
Human nature and greed being what they are, I agree with that pessimism, with the codicil that the possible effects of Peak-Something may damage our ability to consume, thereby imposing a brake upon BAU. Short of Peak-Something, I forsee the world continuing to be ruled by Peak Consumption to fuel the all-powerful 'economic growth' mantra, until such time as adverse climatic effects render our vaunted Western society unviable. The fact that we can see the looming threat does not mean our lords and masters will choose to do anything to mitigate it. Homo Stupidus stupidus.
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Bob Loblaw at 12:51 PM on 20 February 2014How we know the greenhouse effect isn't saturated
Another item that has been asked about: the relative role of convection vs. radiation in the atmosphere. In a (much) earlier comment on another thread, I provided a reference to an old paper by Manabe and Strickler (1964). Figure 1 of that paper is:
The left hand side shows a (modelled) atmosphere with no convection. The right hand side shows the same model with convective adjustment (which basically forces the model lapse rate to the observed tropospheric lapse rate). As you can see, convection in the troposphere is very significant. In the stratosphere, radiation dominates.
(The figure shows how the model converges over time to an equilibrium state as energy fluxes balance out.)
Moderator Response:[BL] External image no longer available replaced with a copy at SkS [2022-08-15]
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chriskoz at 12:50 PM on 20 February 2014Dodgy Diagrams #1 - Misrepresenting IPCC Residence Time Estimates
Dikran, John,
This simple sink analogy debunks the "short CO2 residence time" myth. But the analogy is not realistic with relation to the Crbon Cycle figure from AR4 that you've shown. Some people, like me, may even find the analogy confusing, because they don't know where this CO2 is coming and going (what those "faucet" and "sink" abstracts represent). For those paople, a boxed model is far more attractive.
airscottdenning@2 mentioned David Archer excelling in teaching those models. I want to second that and point to this classic video, IMO the best ever educational piece of its kind:
where David expalains his "artwork". The "tubes" connecting the A O and L boxes represent what you call "adjustment" here. In reality, these are the CO2 flows until the system equilibrates as defined by Henry's law (in case of OA exchange). The CO2 exchanges at the equilibrium stage (not shown on David's graphic but represented, rather vaguely, by your flows from the tap and the sinkhole) are an order of 100 times faster and define the residence time of CO2 molecules in those reservoirs. Finaly, the small opening in David's art is the CaCO3 burial coming from rock weathering (0.2GtC/a on the AR4 graphic).
I've looked at images in Google and couldn't find anything like David's creation in this video. The teaching power of that art is so good that it should realy be put on paper (or electronic media nowadays) and preserved. Any graphic artists there wanting to contribute?
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Bob Loblaw at 12:35 PM on 20 February 2014How we know the greenhouse effect isn't saturated
Gentlepeople:
Clearly, a simple explanation for radiation transfer is not easy. I'll try to explain some basics and help show where Dikran and scaddenp are coming from.
First of all, photons that have been emitted will follow Beer's Law, which states that absorption will follow this differential equation:
dI = -b dz
where I is radiation intensity, z is distance (we'll think height here for now), and b is the absorption coefficient. In the usual calculus form, dI is thus the change in intensity, dz is the change in distance, and the minus sign tells us that the intensity is decreasing as radiation is absorbed.
If b is a constant, it is easy to integrate this equation over a distance, and we get:
I/I_0 = exp(-bz)
where now I is the current I, I_0 is the I we started with at z=0, and z is now the final value of z. This integrated form of Beer's Law is the one most people will be familiar with. If we are thinking in terms of surface-emitted radiation reaching the top of the atmosphere, I_0 is the surface emission, and I is the amount reaching the top of the atmosphere (at height z) directly.
The "saturation" argument looks at I/I_0 and says it's very small for the value of b at normal CO2, and argues that making b larger won't really make I/I_0 significantly smaller. This is the "truthiness" of the argument, but it fails to look at what happens at other altitudes/intervals.
Let's take a crude example, where we go from 0 to 70 for distance, and use b=0.1 and b=0.2. (I pull these numbers out of thin air.)
We get, for I/I_0:
z I/I_0 (b=0.1) I/I_0 (b=0.2)
0 1 1
10 0.368 0.135
20 0.050 0.002
50 0.007 0.00045
70 0.0009 0.00000008
At z=70, the "saturation" argument says "who cares about the difference between 0.0009 and 0.00000008? [b = 0.1 vs. b=0.2]"At z=10, the atmosphere says "I care".
The point is that - even though little surface-emitted IR actually reaches the top of the atmosphere directly, increasing CO2 will have an effect on how much radiation is being absorbed in different parts of the atmosphere. Increasing the absorption rate (b) means that more IR is absorbed at lower heights, and you have to go through more absorption/reemission cycles (gradually moving upwards)before IR is radiated to space. At each reemission, only half is directed upwards (half goes downwards), so the number of absorption/reemission cycles affgects the efficiency with which the atmosphere get energy from the surface to space (more cycles - less efficient).
Now, if that isn't confusing enough, the total amount of IR radiation going upwards at height z is not solely based on how much surface radiation reaches that height. It also depends on:
- how much IR radiation is being emitted at height z in an upward direction. (This depends on temperature, which is not solely a radiation transfer result.)
- how much radiation has reached height z from all the other infinitely-thin layers of the atmosphere below height z, and has not been absorbed by all the layers in between.
The result, at height z, is a probability density function of where in the atmosphere (below z) that the IR radiation originated. Repeat for all values of z from 0 to the top of the atmosphere. Continuing from height z to the top of the atmosphere tells you how likely a given photon will escape directly to space from that height.
Now if that isn't confusing enough, the value of b is not a single value - it depends strongly on wavelength. All the equations must be applied at each individual wavelength, not for all wavelengths in total. After you've done each individual wavelength, you can then sum to get totals for a range of wavelengths (scaddenp's graph at 6:55AM).
This is what programs like MODTRAN will do for you. It will also not assume that b is constant with height, and other marvellous refinements (such as probably not using linear distance in Beer's Law).
And the end result is that I/I_0 for z=top of atmosphere (the "saturation" argument value) just doesn't tell use what we need to know about IR radiation transfer in the atmosphere, and that increasing CO2 will have an effect.
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ranyl at 11:38 AM on 20 February 2014Dodgy Diagrams #1 - Misrepresenting IPCC Residence Time Estimates
Dear DM,
I quite like the shrinking sink hole analogy, quite tight, just need to think how to make it into a tap eventually, and do remember that CO2 has always risen as the world's temperature has risen.And don’t more acidic oceans take up less CO2 eventually? And the partial pressure has already pushed 50% of man’s CO2 into sinks, but the other 50% is hanging around for some time, at least a 100 years and isn’t hat ~60% of total warming, keeping in mind total warming CS is double IPCC range…and what level of CO2e are we at?
Remove the SO2 and what happens to heating forcing?
Just saying let’s not think we actual have a carbon budget, we have a debt and huge one, and what we have to ask how much more CO2 is safe to gamble?
Not much I'd suggest looking at the weather, burn Oz burn, how hot is OZ going to be in the next EL Niño Phew!
And wasn't the southern ocean upwelling CO2 release due to southern shift in the polar winds effectively an external source of CO2 to the balanced carbon cycle system during the last ice age?
And when that was turned off effectively during the Bollinger warm period CO2 levels didn't fall much at all.
Also related it is starting to appear the climate sensitivity is probably more like 4C than 3C due to match observations, and more in keeping with geological records. Pliocene-mid most recent 270-/+55ppm, we are 400ppm and everyone knows that this over a 100years is only half the story to equilibrium, last time CO2 400ppm and above was the Miocene.
And yes the sinks have kept up with increasing emissions but please don't forget the fertilizer effects of industrial nitrogen enhancing both and the fact that acidic waters take up less CO2, and re-release it again as ppm in the atmosphere and that sink hole is going to tighten.
Of course CO2 release from permafrost etc, does shrink the hole, keeping CO2around for ages and if the climate sensitivity is 3C in the model CO2 doesn't fall for 200 years and if it is 4.5C is rises despite all the oceanic and plant life uptake, and more and more 4.5C is looking more likely.
MacDougall Nat.Geo 2012
Models are underestimating everything apart from temperature rise and then there is the report in PNAS about the underestimation of the albedo effect in the Arctic and then think of the models used to predict CS and how for RCP2.6 they have more sea ice in summer in 2070 than we do now, that’s all going melt that permafrost maybe quicker???
Now what else shall we add in, old tree die off, deforestation (storms blew done the last tree one Easter Island), the increasing extreme weather which increases CO2 emissions, ever increasing forest and peat fires, pine bark beetle, and not forgetting the SO2 umbrella which will be removed as fossil fuels emissions cease.
So lets go back to the analogy, filling up the bath, with millions of people emptying millions of buckets into it. Luckily the sink hole has increased in size so far, but aided and abetted by the not insignificant industrial nitrogen fertilizer effects and with many sinks now falling, European, Amazon, North Atlantic, Southern Ocean, the hole will shrink soon, especially as th CO2 fertilizer effect is getting to the C4 plant limit (lots of biomass in grasses), and the C3 fertilization effects will be checked by drought and nutrient deficiencies as ecosystem strain. The sink will block all to soon enough and as CO2 falls all that sinked up CO2 will be re-leased will it not?
Anyway.....
How much more CO2?
Don't we need to get 350ppm at least?
Isn't 1.5C looking quite dangerous considering the weather now at 0.7C?
Adaptation is necessary already and to get to 350ppm won't that need a transformational scale of change and a massive enhancement of the earth ecosystem?
??Moderator Response:[PS] fixed as requested; fixed link, removed excessive white space. Please watch this in future.
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Russ R. at 11:29 AM on 20 February 20142014 SkS Weekly News Roundup #7
Tom Curtis @55,
You made several points, so I'll have to address them in batches.
"As global temperature falls, ice sheets creep towards the equator in the NH. As the edge of the ice sheet, and perhaps more importantly, the southern limit of winter snowfall creeps closer to the equator, it must deal with more direct sunlight, with the consequence that the albedo effect becomes greater and you have a stronger climate sensitivity."
Agree entirely. Ice albedo (IA) feedback will gain strength at an increasing rate as the transition zone extends further toward the equator. There should be two effects, more insolation (as you mentioned) and a larger surface area to operate over. Both effects should be proportional to the cosine of latitude. Assuming they're multiplicative, then the strength of IA feedback should increase proportionally to cos2 of latitude, or around 4x if the leading edge advances from 60N&S to near the equator.
But when you play out the scenario in reverse, IA feedback will weaken substantially as ice retreates to the pole. From 60 to 70 degrees the magnitude of feedback would diminish by approximately half. From 60 to 80 degrees it would decline to 1/12 of its magnitude. Which aligns exactly with what I wrote above: "I would make a case that climate sensitivity was both higher and lower at different points in our planet's history, and will diminish if temperatures continue to rise."
You continue:
"Conversely, with rising temperature, humidity rises, and with it the strenght of the water vapour feedback. In fact, water vapour concentration rises with the fourth power of temperature so that in the right conditions, increasing temperature mean that water vapour can force a runaway greenhouse effect. The right conditions include strong enough insolation, and fortunately for the Earth is safe from that outcome - but that does not preclude an increasing climate sensitivity with increased temperature due to a strengthening WV feedback."
There are two fundamental differences I can immediately think of between IA and WV feedbacks.
First, IA starts from a permanently frozen pole, and as it advance, each additional degree has an increasing effect. WV feedback experiences the opposite. It starts from a permanently humid equator, but as it advances poleward, for each incremental degree it has less surface area and less insolation to drive it. If my math is correct, applying the same cos2 approximation, the entire extratropics north and south of 23 degrees latitude would have the same WV feedback effect as the tropics. In other words, if the earth became suddenly "tropical" right to the poles, the entire magnitude of WV feedback would only double.
Second, WV feedback doesn't act alone... it comes part and parcel with a couple of other factors that limit its feedback effect. First, as you add heat to sea areas (or moist land areas) water evaporates, rises and condenses, transporting heat up through the atmosphere (often violently). It also makes for an instant increase in cloud albedo. Both of these effects constitute not just negative feedback, but an effective "wall". Sea surface temperatures never get above ~30C because thunderstorms (or occasionally tropical cyclones) limit further temperature increases and bring temperatures back down.
So, I would agree that WV feedback will increase as temperatures rise, but at a diminishing rate.
Moving on:
"As noted by Dikran Marsupial, your evidence for the convenient ECS plateau we are supposed to occupy also has it wrong. The Earth has in fact experienced at least two, and probably more runaway cooling events."
Since I'm insufficiently familiar with the evidence for or against the "Snowball Earth" theory, no argument here. I'll happily accept that this happened in the planet's distant past.But I'd focus your attention on more geologically "recent" episodes of cooling, which should be more relevant to today's conditions and concerns. In each of the last periodic glacial episodes over the last million or so years, temperatures have fallen, the IA feedback effect you mentioned would have increased, but no runaway cooling resulted. Some other negative feedback mechanism(s), (possibly WV feedback) overwhelmed the increasingly positive IA feedback, slowing the rate of cooling. In other words, net feedback fell, and the temperature ultimately stabilized. Which again, aligns with what I wrote: "...geological evidence points to a planet see-sawing between two relatively stable equilibrium climate conditions, which suggests high sensitivity in the middle of the range, and low sensitivity at either end of the range".
Nonetheless, I think we've established that net feedback (and ultimately climate sensitivity) is not going to be constant across all climactic conditions. It is the sum total of multiple mechanisms (of which we've only discussed a couple), each of which will behave differently under different conditions. Would you agree?
More later.
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How we know the greenhouse effect isn't saturated
scaddenp - I would agree with Dikran; that's a very useful diagram, and that the spread of emission altitudes is rahter larger than I thought.
One of the more frustrating points of this exchange (and I think where some of the confusion and talking past one another has arisen) is the repeated reference to 'opaque' and 'translucent' layers - as I tried to point out above there is varying IR emission from a range of altitudes, not a single transition altitude between two distinct states. IR in GHG bands is emitted to space at a range of different altitudes - with the sum of that emission adding up to the oft-noted temperature equivalent profiles seen in satellite observations of those bands.
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