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MAURICIO11346 at 00:57 AM on 19 November 2014More Carbon Dioxide is not necessarily good for plants.
The American and German researchers who worked on the Nature study wanted to test out those models in the real world. Using data collected from forests in the northeastern U.S., they found that as carbon concentrations increased by about 5% per decade over the past 20 years, the rates of water-use efficiency increased by about 3% a year. That’s much faster than computer models would have suggested—it means the improvement in water-use efficiency is about six times as large as the corresponding increase in carbon concentrations. As Trevor Keenan of Harvard University, a lead author on the paper, put it in a statement:
This could be considered a beneficial effect of increased atmospheric carbon dioxide. What’s surprising is we didn’t expect the effect to be this big. A large proportion of the ecosystems in the world are limited by water–they don’t have enough water during the year to reach their maximum potential growth. If they become more efficient at using water, they should be able to take more carbon out of the atmosphere due to higher growth rates
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ianw01 at 00:21 AM on 19 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
Figure 1 is extremely suspect. It lacks data points and has no indication of uncertainty. I'll bet the particpants in "From Peru"'s reference did not use that figure in advance to extrapolate to determine their likely blood pH! :-) The result is nonsensical, but nonetheless the figure indicates a horrifically acidic blood pH, which of course did not arise.
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CBDunkerson at 23:17 PM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
Per capita may be the easiest remotely valid method to follow, but it does have many limitations. As OPOF notes, it ignores differences in emissions between individuals / groups within each country. It also ignores the cumulative emissions issue raised by scaddenp. Though, on that, do we need to consider emissions prior to knowledge of the potential harm and/or dangerous atmospheric levels differently than emissions thereafter? Does using a per capita basis discourage wealthy nations from continuing to conduct research on better food crops which have allowed the large populations in some developing nations to survive? Et cetera.
There is no 'perfect' / 'fair' solution. Per capita is a reasonable starting point, but while we structure things to give developing nations a chance to improve their standard of living we should do just as much to allow developed nations to continue improving their standard of living as well. Ultimately, the global targets have to be based on 'units of energy / units of GHG'.
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longjohn119 at 18:11 PM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
Comparing exposure over a 75 years span with exposure over a mere 42 days doesn't really tell us anything about long term exposure. For one the effects could be at least somewhat cumulative like we are now finding out about radiation exposure.
I think they should redo this study with Climate Change Deniers and non-Deniers ..... I have a sneaking suspicion the 'stupidity threshhold" Deniers is closer to 350 ppm ..... Just a hunch and it certainly would explain a lot
Moderator Response:[JH] Please keep it civil.
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From Peru at 15:22 PM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
I recommend this article:
Toxicity of carbon dioxide: a review
I just began to read it, but I quote:
"Volunteers were exposed to 1.5% CO2 over a period of 42 days, and acid base balance and changes in electrolyte metabolism were studied
(...)
although there were some minor modifications of the pH and serum level of the electrolytes, the experimental conditions were well tolerated"
However, it is said also that intermittent high levels of CO2 are much less well tollerated.
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One Planet Only Forever at 13:43 PM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
Regarding the debate about per-capita measures of impact, in my earlier comment I indicated that the problem is not created by the 'number of people' as much as it is created by people who live a high-impact lifestyle. A reduction of the impact of the highest-impacting people is required.
There are many wealthy people in nations with high per-capita impacts who strive to be low-impact. They are not the problem. The people who are high-impact livers in a nation full of very poor low-impact people are as much of a problem as the high-impact livers in a richer nation.
Per-person impact evaluation clearly needs to be the focus, with the sharpest focus being on those whose lifestyle and way of profiting produce the largest impact regardless of the nation they are in.
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One Planet Only Forever at 13:27 PM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
It is unfortunate that the Berkeley experiment did not include a baseline for behaviour with CO2 concentrations of 400 ppm. That may have provided some evidence regarding the potential consequences for long term exposure to elevated concentrations.
However, 600 ppm may be an appropriate baseline for the potential indoor concentrations when the best quality of 'fresh air' to improve indoor air quality is 400 ppm. And it is clear that capability was diminished on a number of measures when the concentration increased.
So, although the claimed long term consequence of 426 ppm is in question there would be less doubt about the potential negative long term consequences of being indoors too much of the time now that the likely indoor air concentration is above 426 ppm and increasing.
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PhilippeChantreau at 13:25 PM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
I also have to voice skepticism on the Robertson paper. What kind of journal exactly is "current science"?
It seems to me that, on severl;a occasions, he starts from a plausible premise but then draw conclusions formulated in drastic language when we are still only in the realm of possibility. I know quite well the effects of a high partial pressure of CO2 in the body, which I have to watch for routinely in my job with various kinds of patients in respiratory failure. However, I do not see that he truly has the data to support some of his assertions.
Nonetheless, it is true that forcing the entire terrestrial biome to endure a spike of 200 ppm in a couple of centuries is one heck of an experiment. I find it extremely irresponsible but that's another debate.
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Rob Honeycutt at 10:21 AM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
I'm afraid I'm going to have to side with Russ here. Lifetime toxicity at 426ppm sounds like a bit of a stretch. I just browsed through the paper by Robertson and it doesn't look to me like the research supports such a claim. The paper states:
Such a situation is unlikely to be tolerable for a lifetime by humans (and other mam- mals with the possible exception of seals) without dete- rioration in general health along with serious curtailing of physical activity presently taken as normal.
But I don't see how Robertson can possibly quantify that based on the information he's presenting.
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uprightsquire at 09:55 AM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
"man's"?
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Russ R. at 09:48 AM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
"Some research suggest toxic effects of carbon dioxide at a constant (lifelong) exposure of only 426 ppm (D. Robertson, 2006).
Even under the most optimistic possible scenarios of emission reductions CO2 concentration in the atmosphere reaches 550 ppm, which is above the safe threshold."
CO2 toxic at 426 ppm? Really? That's a pretty extraordinary claim.
I'm sure you've got some actual evidence to back that up... as opposed to mere speculation, or assertion.
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John Hartz at 09:03 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
[JH] Moderation Comments
Scaddemp & Tom Curtis: Please let Rob Honeycutt do the repsonding to joeygoz from here on out.
Joeygoz: The SkS Comments Policy also prohibits excessive repitition.
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Rob Honeycutt at 08:39 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
...and yes, this is very much a discussion on per capita vs national level emissions. I'm a little surprised that you can't see how this is related.
Let's take another example. If you seem to think that nations should cut equally, how is Bangladesh to tell their citizenry that they must cut their emissions? They certainly can't cut their emissions proportionate the US on a total volume basis since our emissions exceed their's many times over. Even on a proportional basis, can you ask people who are barely living subsistence lifestyles to cut their emissions 50%?
You have to look at this question on a per capita basis. Action has to occur on a govermental level but you have to balance agreements on a per capita measure. And, as I pointed out earlier, even that is complex because maybe China's answer to that will be, "Okay western nations, you can make your own stuff from now on because we don't want your carbon emissions from manufacturing to mucking up our emissions targets."
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Rob Honeycutt at 08:13 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze... That's a deflection of a blatantly obvious and essentially rhetorical question. The answer is, no, the US would never agree to such a strategy.
But you're right, this is verging on dogpiling.
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joeygoze9259 at 07:43 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
@ Rob - have no idea what the U.S. gov't would agree, thought we were having a discussion on the merits of determining reductions based on per capita emissions versus quantitative CO2 emissions per country?
@Curtis - If it is the case that "neither the China nor India are sufficiently gullible or virtuous that they will take a policy which will entrench a lower per capita income for their people for at least the next half century just so the US can maintain a higher standard of living by not tackling seriously the problem the US has primarilly caused." - then in my view, no way the U.S. gets on board as there is no incentive to lower the per capita income for Americans as well.
@scaddenp - do not believe anyone is in a position to determine what is an "undue" hardship for another individual. Can not say what U.S., UK, or Chinese citizens can absorb with respect to emissions reductions.
Moderator - how is this not a "dogpile" as outlines in your Updated Comments Policy?
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Tom Curtis at 07:11 AM on 18 November 20142014 SkS Weekly Digest #45
SteveFunk @2, as best I understand it, John L Casey's theory is that:
1) Solar forcing is much larger than the actual observed solar forcing because.
2) His theory can be trusted because "He is one of America’s most successful climate change researchers and climate prediction experts", the later based on his Master of Arts in administration and his complete lack of peer reviewed publications on climate.
3) There is very strong evidence in support of his theory, and he just needs you to send him some money to explain it.
Is a review of the book of every two bit con artist realy needed?
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Steve L at 07:06 AM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
This astounds me! But I'm going put some plants near my desk and try reading it again....
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scaddenp at 06:47 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
I think there are two point to consider here.
1/ The extra CO2 in the atmosphere is the accumulated result from years of emissions. If you look at historical responsibility for total emissions by country, (for instance the table here) then you see US,Europe far exceed China and so should take the responsibility for reducing output first
2/ Countries with very emissions per capita are far better positioned to make big cuts than countries with low emissions per capita. The US energy consumption (at 250kWh per person per day) is around double that of say UK. It seems entirely reasonable that US citizens could manage with a lot less without undue hardship. It's a lot tougher asking for cuts from people (eg Chinese) using only 50 kWh/per person/per day.
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Tom Curtis at 06:34 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze @15, it is the total CO2 output that is damaging the climate but:
1) The total CO2 output is reduced whether we set equal %reductions by nation or equal per capita targets with the same % reduction of the total. As either method results in the same overall reduction, pointing out that it is the total CO2 output that is damaging the climate is irrelevant to the discussion.
2) In general, fossil fuel use (and hence CO2 emissions) per capita correlates with per capita wealth. Allowing unequal per capita targets therefor entrenches unequal wealth as a precondition for tackling AGW. It is as though the US (and Australia) were to say to the world that they will refuse to tackle the problem they have primarilly created unless they are subsidized by the rest of the world to do so.
3) Emissions of CO2 are a problem. That means all emissions of CO2 harm everybody to some small extent. Entrenching unequal per capita emissions entrenches a right for US citizens to harm the rest of the world more than they are harmed in perpetuity, so that they can recieve a larger benefit than is available for non-US citizens.
4) As a simple pragmatic matter, neither the China nor India are sufficiently gullible or virtuous that they will take a policy which will entrench a lower per capita income for their people for at least the next half century just so the US can maintain a higher standard of living by not tackling seriously the problem the US has primarilly caused. An effective global agreement to cut back emissions can only go forward based on a reduction program that results in equal per capita emissions in the medium term (or something closely approximating it).
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Composer99 at 06:31 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze:
You write:
Think I am suggesting more what @Curtis is saying, in order to reduce emissions on a per country basis each country should reduce "from historical levels at the same rate"
But Tom Curtis then went on to point out why that is not such a good policy.
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Rob Honeycutt at 06:14 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze... So, if the tables were turned, would the US agree to such a strategy?
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joeygoze9259 at 05:35 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
Think I am suggesting more what @Curtis is saying, in order to reduce emissions on a per country basis each country should reduce "from historical levels at the same rate" Believe this drives to the heart of lowering total global CO2 emissions. Not reasonable to suggest that Belgium could or would emit the same as the U.S. but all can reduce by some percentage and if the country is really small like Belgium or Bahamas, let them remain at the status quo since there emissions are negligable versus ROW.
It is not clear how the per capita argument is more "realistic" to determine how any one nation can decarbonize. A country like China whose raw CO2 output is double that of the U.S., how do we give them a pass just because on a per capita basis, they come out lower. It is the total CO2 output that is damaging to the climate.
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michael sweet at 05:33 AM on 18 November 20142014 SkS Weekly Digest #45
Steve,
The deniers are trying to get in the news before the final yearly data comes out. 2014 will be the warmest year ever. Perhaps the cooling will start immediately after the January data showing warming is released!
It is amazing that these guys can make these claims with a straight face.
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SteveFunk at 05:25 AM on 18 November 20142014 SkS Weekly Digest #45
http://www.newsmax.com/newswidget/dark-winter-cold-global-cooling/2014/11/16/id/607672/ Has anyone reviewed this book or tied it specifically to the skeptic arguments page. I suspect I will be hearing about it from my more skeptical friends or from Fox News.
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Rob Honeycutt at 04:55 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze... That's absurd, though. Ignoring per capita would suggest the smallest nations in the world can increase their output many times over. Collectively, that would be an unmitigated disaster. Do you really think that Belgium should have the same opportunity to emit carbon on a national level as the United States?
National governments are certainly the mechanism for regulation and control of carbon emissions, but per capita emissions are going to define, in a more realistic way, how much any given nation can decarbonize, as well as their potential for increased emissions.
In the U.S. we are one of the top emitters per capita, along with Australia and Canada. That means that we have the greatest opportunity to take responsibility for our emissions levels, and doing so only acts to encourage other nations to act accordingly.
"With great wealth comes great responsibility."
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Tom Curtis at 04:46 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze @10 &12, the idea that CO2 emission targets should be equal between nations rather than equal per capita is one of those ideas that some people think is a good idea, but only because they never apply it. Taken literally, it means that (for example) the Bahamas (population 319,031) should be permitted to emit the same quantity of CO2 as the United States (population 322,583,006) or China (population 1,393,783,836); or that the Vatican City be permitted the same emissions as Italy. Some people think that the idea that the US and China should be permitted the same emissions, but those people never apply the same logic to the many small nations of the world. They would instantly recognize the disadvantage that would accrue to the US should they do so, not to mention the injustice of any such scheme. However, as they want to apply that logic when it advantages their nation relative to some other, their refusal to do so when it disadvantages their nation relative to some third country demonstrates that they do not accept their own reasoning - that their reasoning is in fact a rhetorical ploy serving a tactical end.
Perhaps that sort of strategy is not what you meant. Perhaps what you meant is that each nation should reduce emissions from historical levels at the same rate. Such a strategy has the convenient (for western nations) property that because they contributed most to the problem of CO2 increase in the past, they should be permitted to contribute most to that problem in the future as well. As reducing emissions may well have an economic cost, it also has the convenient effect of locking in current economic advantages, ie, of requiring China to sign up to their citizens having a lower standard of living than those of the US for the rest of this century because the US has historically contributed more to current CO2 concentrations in the past than has China. No US citizen would accept that argument were the situations reversed - and rightly so. They would percieve it as self serving sophistry in an attempt to avoid tackling the problem properly. And so it is.
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joeygoze9259 at 04:11 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
@Rob
National boundaries define an area where industrial activity is occurring and the governments that function in those areas can regulate that region, it is not an arbitrary definition at all. China gov't can initiate regulations to control CO2 output in their geographic domain. U.S. can regulate its geographic domain. If goal is limiting total CO2 output, what is the issue with this?
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Rob Honeycutt at 03:35 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze... That logic doesn't hold. Why would national boundaries be the proper metric? That's an even more arbitrary measure. And, if you're going to say that per capita doesn't matter, then you also can't claim that the carbon footprint of any individual matters.
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michael sweet at 03:14 AM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
How much more difficult is it to ventilate a building when the incoming air is 450 ppm instead of 350 ppm? It would obviously require more air to keep levels below 600 ppm using 450 ppm to ventilate. Ventilating with 550 ppm? How difficult is this? Any input from building engineers?
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Jose_X at 02:37 AM on 18 November 2014Just how ‘Sapiens’ in the world of high CO2 concentrations?
Wow. Had not heard of anything like this. Wonder what Watt and the rest think about this?
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joeygoze9259 at 02:01 AM on 18 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
@Rob
As CO2 is the driver of atmospheric warming, I think looking at the per capita basis is wrong. The tons of CO2 pumped into the atmosphere is the issue. It does not matter that the tonnage is spread over more people, the issue is the quantity of CO2 being pumped into the atmosphere.
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CBDunkerson at 00:11 AM on 18 November 2014More research confirming large methane leakage from shale boom
Russ, yes. Methane emissions have been lower than assumed in the SRES projections.
Congratulations! You are correct!
Of course, we've covered this a few times now, the IPCC reports discuss it in detail, and it is one of the many reasons the SRES projections have been replaced. The assumption that future (at the time) methane emissions would follow past trends was incorrect. Thanks to the Montreal protocols, various CFCs have also had lower emissions than assumed in the SRES scenarios. Advancements in renewable energy are showing that industrialization and other energy use can be achieved without fossil fuels. Ergo, the links between population/technology growth and emissions, which previously were fairly consistent, are breaking down and different assumptions should be modelled.
That does nothing to change the greenhouse impact of methane or the fact that methane levels are now rising again.
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Tom Curtis at 14:19 PM on 17 November 2014CO2 effect is saturated
Stephen Baines @372, firstly, thanks. Second, the reason I have persisted so long in the discussion is because of a hope that it would prove instructive to interested readers. I judge that by now, any questions that need to be answered have already been answered (several of them several times). However, if somebody other than Satoh has questions, I would be happy to address them if I am able.
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John Hartz at 14:16 PM on 17 November 2014CO2 effect is saturated
[JH] Moderator's Comment
Satoh: Your "Artful Dodger" schtick has run its course. Any future posts by you will be summarily deleted.
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Stephen Baines at 13:11 PM on 17 November 2014CO2 effect is saturated
TC...lest your get frustrated, I just wanted to say that the only reason I followed this discussion was because I am less familiar with this aspect of atmospheric physics thanI should be (it's off my specialty by quite a ways) and I wanted to learn some more. And I have certainly learned a lot in this exchange, perhaps more than if you had simply been trying to explain things de novo.
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Tom Curtis at 12:30 PM on 17 November 2014CO2 effect is saturated
Satoh @370, you are evidently determined in your decision to be absolutely resistant to evidence. In this case, the modtran graphs shown above the only emissions shown are from CO2. The show emissions from an altitude of 80 km, and a difference of 5 km makes a difference in the emissivity. A difference of 10 km would also make a difference. Ergo, your introduction of Hottel graphs into the discussion, and your insistence that only values for the free path length of photons with a wave length of 14.9 microns with respect to a CO2 gas are shown (respectively) to be a red herring, and a blunder. Further, your insistence that you know more on this subject than the scientists who have spent their career pursuing the topic and wrote textbooks on the subject is simple arrogance of a breath taking quantity.
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Satoh at 12:06 PM on 17 November 2014CO2 effect is saturated
Yes, but emissions just above and below the 15 micron band, that go for kilometers, have nothing to do with CO2. They come from water vapor, cloud, and terrestrial. The ones from right next to 15, along the sides of the band that do come from CO2, are negligible in amplitude compared to the emissions from 15, or more exactly, 14.9, and even they don't go for kilometers.
Your attempt to rationalize a path length of 10,000 feet, in an attempt to rationalize a curve on the graph that shows a CO2 emissivity of 0.3, need to come to an end. Especially since you just said the Hottel charts don't work for atmospheric emissivities. (Correct, they don't. The Hottel charts are industrial charts for short distances in factory settings, under high pressure and very high heat.)
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Tom Curtis at 11:56 AM on 17 November 2014CO2 effect is saturated
A slight correction and clarrification for my preceding post. The emissivities calculated with modtran are for the tropical atmosphere only. Further, as I took the ratio of the integrated emission across the wave lengths shown to the total emissions for a black body with the surface temperature the emissivities are underestimates, within the limits of accuracy of the model, not over estimates as I indicated.
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Tom Curtis at 11:14 AM on 17 November 2014CO2 effect is saturated
Satoh @367, I thought you would take that line. That is why I pre-rebutted it, writing:
"Because the emissivity plotted in Hottel diagrams is total emissivity, it is irrelevant that the emission at 15 microns is absorbed within a very short distance. Emissions just above or just below 15 microns may not be absorbed for meter, or even kilometers and hence make a substantial contribution to mean Beam Length (L). Therefore, in determining the total emissivity of the atmosphere, you cannot assume very short mean beam lengths."
(Emphasis added)
I will illustrate what I mean with an example from Modtran, a Broad Band Model of atmospheric radiation. The example shows the downward IR radiation from CO2 only for a tropical atmosphere with no clouds at 0 and 5 kms:
Because the IR spectra are show the net downward flux from CO2 in the absence of other radiative molecules, it shows the net emission from CO2 (ie, total downward emission by CO2 less total absorption of downward emission by CO2). This is not observed data, for which we cannot obtain H2O (and O3, and CH4 etc) free conditions. The model is of the type that has been shown to be reasonably accurate at predicting emissions from CO2 in furnaces and flames (ie, reasonably approximate to Hottel diagrams), especially near room temperatures. Ergo they will show the correct basic principles.
In atmospheric conditions pL is ill defined because, as shown in the side graph pressure is not constant with altitude, and nor is temperature. For this reason, Hottel diagrams are useless in determining atmospheric emissivities. However, pL in Hottel diagrams is proportional to the number of molecules in the mean beam length. Obviously, there are fewer molecules from 5 km to the top of the atmosphere (TOA) than there are from the ground to the TOA, so that the 5 km look up corresponds to having a smaller pL in a Hottel diagram.
The crucial difference between the two as seen above is that the emission in weak bands is stronger for 0 km looking up than it is for 5 km looking up. This is partially obscured by the lower base temperature for the 5 km looking up, but is very clear in the 10 micron emission range which is moderately strong for 0 km looking up, but near non-existent for 5 km looking up. That difference results in a reduced total emissivity for the 5 km looking up example than for the 0 km looking up example.
In fact, the model output gives the emission over the wavelengths shown in the graph, and the temperatures for the different levels. From that it can be calculated that the total emissivity of CO2 for the tropical atmosphere from 0 km up is 0.264 and for 5 km looking up it is 0.18. Because the calculation does not include the full spectrum, these will be slight over estimates of the emissivity. However, the total emissivity from 0 km looking up will not drop appreciably below 0.2.
SOD shows that it cannot be below 0.13 from observational evidence by SOD using measurements of back radiation spectra:
But that, is known to be an underestimate, not least because the example used is from an Arctic autumn (a factor not mentioned by SOD). It is possible to constrain the lower limit of total emissivity of CO2 in the atmosphere like this for a given surface temperature because CO2 absorbs so strongly in the 15 micron band, making it easy to distinguish.
So, while your reasoning is approximately valid the 15 micron peak of CO2 emissions, it is not valid for total emissivity. That mean beam length at 15 microns is so constrained is one of the reasons why emissivity does not increase linearly with pL.
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Satoh at 09:56 AM on 17 November 2014CO2 effect is saturated
Here is a thought experiment. If 15-micron photons are streaming up from the surface, being absorbed, re-emitted, absorbed, re-emitted, all the way from the surface for 10,000 feet, how can you consider that 10,000 feet would ever come into any sort of calculation for total emissivity? Do you think anything gets bigger and bigger for 10,000 feet? If photons are absorbed and re-emitted 100 times from the surface to the TOA, that somehow that means there are 100 times more photons than if you only considered the uppermost photon paths? When a photon is absorbed and re-emitted, it's still just one photon? The amount of emissivity at the surface depends ONLY on the number of photons coming from the uppermost path length. That is the reason they say path length, and not total distance that all these have traveled. Only the top photons even REACH the surface, the others were all absorbed!
In a relay race, where 4 runners pass the baton, the emissivity at the end of the race is one baton, not 4.
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Tom Curtis at 09:35 AM on 17 November 2014CO2 effect is saturated
Satoh @347, 348, 349, 350, and 354 criticized my understanding of path length as used as a measure of pressure-length (pL) in Hottel diagrams. This is despite the fact that he responded to my post @340 in which I describe my understanding by saying "excellent work" with no expressed quibble about my understanding of pL or emissivity, both of which he now disputes. In particular, he wrote @349:
"You randomly picked the top line and said "it's 4 foot atmospheres which is .0004 X 10,000 feet" so it would point to the 0.2 mark. That's pretty arbitrary. The mean free path length of 15 micron photons at sea level is definitely not 10,000 feet so you can't use that line.
This paper has been floating around the web which says the mean path length for photons in CO2 at sea level is 32 meters. I don't buy it. They first measured it many years ago and it was in millimeters. I'd like to know what the latest calculations are for that.
Mean path length applies to absorption, and it also applies to emission. They are inverse of the same process."
The first and most crucial point is that L is not defined as "mean free path length", and that "mean free path length" is not the same thing as "mean path length". Indeed, Mehrota et al (1995) (download PDF), define L in pL as "mean Beam width". Further, in a worked example, they calculate estimates of emissivity for a Claus plant (described in Nasato et al, 1994), saying, "A mean beam length of L = 0.9 x diameter = 0.04 m can be used." (The inside diameter of the tube in question was 43.99 mm.)
Further, that is consistent with the lecture slides by Dr Prabal Talukdar on Gas Radiation in which he defines "Mean Beam Length":
"• The simple expression for the hemisphere of gas is not
applicable for other geometries
• A concept of mean beam length is introduced for
engineering calculations- This is an equivalent path length L which represents the
average contributions of different beam lengths from the
gas body to the striking surface- In the absence of information available, mean beam
length is approximately calculated as
L =~= 3.5*V/A
Where A=total surface area of the enclosure
and V = total volume of the gas"He then shows a slide of a table of formula for different shapes including a "Circular cylinder of semi-infinite height" radiating to "an element at the center of the base" for which the formula is 0.9 *D. As these formula are not restricted as to the actual volumes enclosed, and as the worked example by Mehrota et al has a Beam Length significantly greater than your estimated Mean Free Path Length, I take this to show how experts in the field interpret L for the pL contours in Hottel diagrams (as opposed to the interpretation of biologists working outside of their field that even Anthony Watts considers to be a pseudo-scientist).
Worse, however, the mean free path length is given by the general formula l=1/(nσ), where l is the mean free path length, n is the number of particles involved, and σ is the effective cross sectional area of collision. (In Nahle's varian he uses "l=m/(nσ)" where m is the mass of the gas, and n is the number of molecules per unit mass which is equivalent.) However, by the ideal gas law,
P=nRT/V, where n is the number of molecules in moles, P is pressure, T is temperature, V volume and R a constant. Ergo, for constant temperature and volume, P is proportional to n. But n is inversely proportional to l (free path length), so that if L in pL is mean free path length, pL is constant for a constant temperature and volume. Ergo, if L were mean free path length, contours of constant pL in Hottel diagrams (which assume constant volume) would by necessity be vertical, ie, have a constant value in the x-axis (Temperature). Therefore it is mathematically impossible that L from pL = mean free path length. (Put another way that may be less obscure, because p is the inverse of l, of L=l then Hottel diagrams should revert to a mapping of Temperature directly onto emissivity, and shoud require no pL contours for that mapping.)
Turning to emissivity, we have the statement of Byun and Chen (2013) that Hottel diagrams model total emissivity, not spectral emissivity. The latter is the emission at a given wavelength or frequency relative to that predicted by the appropriate form of Planck's law for a black body at that wavelength or frequency. The former is the integral of the spectral emissivions as a ratio to the emission predicted by the Steffan-Boltzmann law for the total emission of a black body. Both, or course, are relative to a particular temperature.
Because the emissivity plotted in Hottel diagrams is total emissivity, it is irrelevant that the emission at 15 microns is absorbed within a very short distance. Emissions just above or just below 15 microns may not be absorbed for meter, or even kilometers and hence make a substantial contribution to mean Beam Length (L). Therefore, in determining the total emissivity of the atmosphere, you cannot assume very short mean beam lengths. (Nor should you assume mean beam lengths equivalent to the total height of the atmosphere because of decreasing pressure with altitude.) But looking horizontally, mean beam lengths of multiple kilometers are possible with near constant pressure. Hence my example of 10 horizontal kilometers, which with CO2 and amtospheric concentrations gives a total emissivity of approximately 0.2 (which I know independently to be the approximate total emissivity of CO2 looking vertically in clear sky conditions).
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Andrew Mclaren at 08:39 AM on 17 November 2014It hasn't warmed since 1998
Looks like this handy rebuttal to a commonly expressed "skeptic" argument needs an update... where it states that the warmest 12 consecutive months on record are June 2009 - May 2010, this has just been surpassed according to NOAA, by the October 2013 - September 2014 interval. Time for a quick edit already!
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Stephen Baines at 07:15 AM on 17 November 2014CO2 effect is saturated
"Stephen, the mean free path length is the path length."
Satoh, saying so does not make it so. I linked to the wikipedia definitions for both terms that make the difference in common usage clear. You refused to acknowledge those links. Hottel et al did not mean mean free path when they refer to pathlength, nor does anyone who uses the graphs. Simply saying they mean something different does not change that.
"Stephen, the curve for 4.0 atm ft doesn't tell us anything about the combination. They could be 4 atmosphere with a path of 1 foot, .04 atmospheres with a path of 100 feet, or .000000000004 atmospheres with a path of 100000000000 feet. Like I said, if you increase the partial pressure you decrease the path, and are still on the same curve of the graph and have the same emissivity."
So, why are their multiple lines on the Hottel emissivity graph if the meaning of pathlength, as used by the authors, corresponds to what you say? By your definition, there should only be one line, as concentration and pathlength would be perfectly anticorrelated for a given gas, although varying with temperature.
(BTW..I must apologize to everyone for getting issue involving emmisivity and absorptivity mixed up above in discussion of pathlength. Unnecessarily confusing that.)
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Rob Honeycutt at 05:52 AM on 17 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
joeygoze... ubrew12 included a citation. It's a "per person" reference. I would even hold that it is smaller than that since a portion of those emissions are the result of producing products for western markets.
If you've ever spent any time in China you realize how small a single Chinese person's carbon footprint is. Most of the population still lives an agrarian lifestyle. And even those who live in cities spend very little heating or cooling their homes. Most use public transportation. Appliances are small. Most clothing is still hand washed and air dried. So on and so forth...
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michael sweet at 05:41 AM on 17 November 2014CO2 effect is saturated
Satoh,
You cite the paper I referenced at 249 and 250.
Since you now deny what you previously cited I will no longer post responses to you. It is impossible to resolve diferences when one side denys what they previously claimed.
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joeygoze9259 at 05:39 AM on 17 November 2014Fact check: China pledged bigger climate action than the USA; Republican leaders wrong
@ubrew12
Can you source your data, China carbon footprint 1/4 of USA?
Simple search found "EDGAR (database created by European Commission and Netherlands Environmental Assessment Agency) released 2012 estimates. The following table lists the 2012 estimate of annual CO2 emissions estimates (in thousands of CO2 tonnes) from these estimates along with a list of emissions per capita (in tonnes of CO2 per year) from same source."
China is #1 emitter at 9,860,000 (in 1000s of tons CO2)
USA #2 emitter at 5,190,000
http://www.ask.com/wiki/List_of_countries_by_carbon_dioxide_emissions?o=2801&qsrc=999&ad=doubleDown&an=apn&ap=ask.com#cite_note-EDGAR-9
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Satoh at 05:15 AM on 17 November 2014CO2 effect is saturated
Stephen, the curve for 4.0 atm ft doesn't tell us anything about the combination. They could be 4 atmosphere with a path of 1 foot, .04 atmospheres with a path of 100 feet, or .000000000004 atmospheres with a path of 100000000000 feet. Like I said, if you increase the partial pressure you decrease the path, and are still on the same curve of the graph and have the same emissivity.
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Satoh at 05:08 AM on 17 November 2014CO2 effect is saturated
Michael, I am not interested in discussing that Nahle paper. I did not cite it and don't care about it. I didn't even read it. Attacking that paper is a straw man.
Stephen, the mean free path length is the path length. The photon leaves the surface and hits a CO2 molecule. That's the path. After that, the energy converts to kinetic heat when the CO2 molecule bumps into an O2, N2, H2O, Argon, another CO2 molecule, a tree, a drop of rain, or anything else. It another photon gets emitted by the H2O, tree, raindrop or anything else, it's not a continuation of the "path." It's a new path.
Please end that line of argument because your line of argument has already bumped into something and was absorbed.
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Stephen Baines at 05:01 AM on 17 November 2014CO2 effect is saturated
And yes, I accidentally said 10,000 m instead of feet. Mea culpa, but you are completely missing the main point.
TC picked that line because on that graph it best reflects the combination of the real ppmv of CO2 in the atmosphere (~400) and the real thickness of the atmosphere (which is actually thicker than 10,000', but you take what you can get.) Thus, 0.0004atm*10,000' = 4 ft.atmospheres.
The concept is simple...you need to consider the distance over which light traverses as well as the concentration of substances that may absorb light to determine the fraction of IR that is absorbed as it passes along that path. It's the basis of Beer-Lambert law in spectrometry and underlies a lot of quantitative chemistry.
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Stephen Baines at 04:31 AM on 17 November 2014CO2 effect is saturated
"The definition of mean free path is well known and nothing new. You can't call a column of air the path length. "
Satoh, this is getting tiresome. You can't simply refer to mean free path and then call it path length and expect anyone to understand what you are saying. Those are two different concepts. If you conflate them (and others) noone can have a sensible conversation with you.
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