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Pete Ridley

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"Another Hockey Stick Illusion"?
« Reply #50 on: 19/04/2011 22:30:48 »
Hi yor_on, I’m delighted that you found that article “Uncertainty in Climate Change” of interest but I’m sure that you can find a source of such information that you feel more comfortable with. There are good reasons to be suspicious of arguments presented by organisations on both sides of the climate change debate as each individual involved has his or her own agenda. It’s all of that uncertainty that leaves most of us in a state of confusion and leaves me so sceptical of anything that I am told, particularly when politicians are involved and especially after “The Hockey Stick Illusion” and Climategate. You
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benefit from looking at its 'founders'
and I “Follow the money”.

I’m afraid that your
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.. but to build the contention on your idea of the difference, without presenting anyone agreeing is a hard thing to do
conveyed nothing to me.

I don’t understand why you keep talking about an experiment in relation to my question here. I’ve already covered that point so won’t dwell on it but I will pick up on your
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Doesn't necessarily mean that your ideas is wrong but you should really try to find some supporting evidence before contending what everyone 'mainstream' think is true

If you have read my previous comments carefully enough you should have learned that my “ideas” that:
a) preferential molecule size dependent fractionation of atmospheric gases occurs in an ice sheet,
b) collision diameter rather than kinetic diameter is used during analysis of air from ice,
c) kinetic diameter is relevant when considering gas molecules moving through nanoporous substances,
are supported by evidence. That evidence has been provided by some of those
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everyone 'mainstream'
scientists themselves.

Let me repeat the reference that I gave here on 17th @ 17:49:08 and again on 18th @ 10:04:48. “Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements” by C. Huber, U. Beyerle, M. Leuenberger, J. Schwander, R. Kipfer, R. Spahni, J.P. Severinghaus and  K. Weiler.

It is clear even just from the title that this paper provides evidence of a). The evidence for b) is provided in that same paper by doing a simple search for “diameter”, the second occurrence of which is in Table 2, which shows
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Collision diameter (Å)
for 8 atmospheric gases. There is no mention of kinetic diameter. Finally, evidence for c) abounds and can be found by simply Googling - “porous” “kinetic diameter” - or – “nanoporous” “kinetic diameter”.

I didn’t expect to have to spell all of that out to The Naked Scientists, considering the university that they attended.

When you say
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we are interested in learning and sharing what we know
I assume that by “we” you mean The Naked Scientists. I share that interest, but for me it is mainly learning because I don’t have all that much to share as far as the numerous scientific disciplines involved in improving our poor understanding of the processes and drivers of the different global climates is concerned. It’s a pity that we all let ourselves get sucked into slinging the mud.

Thanks for trying to help but none of the papers that you referred to helps to answer my specific question here. I wasn’t able to locate “Geology, Palaeontology & Archaeology” which I assume is a book. If you know that it says something about the kinetic diameter of gas molecules or the movement of gas molecules in nanoporous substances then it would be of interest and I’d appreciate more information about it.

BTW, are you one of The Naked Scientists or just a blogger like I am?

Best regards, Pete Ridley




yor_on

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"Another Hockey Stick Illusion"?
« Reply #51 on: 20/04/2011 07:57:06 »
Well, I would suggest you put your question where it belongs. I gave you what I suspect might be appropriate 'forums' here in my former post. I'm not sure it is placed in the right forum if it's just a geology/chemistry or physics question. To place it in 'The Environment' and call it "Another Hockey Stick Illusion" just makes me think I'm answering your questions as good as is possible?

Still, if you find them wrong for your question you probably should try those other threads instead, and ask there, and good luck with that. This sub forum is about the environment.
==

You are quite close to sounding querulous here?

If you find the quality of answers offensive to your sensibilities you really should look for another place. Just find a site of 'better quality' and start a thread there instead. As it is I'm starting to wonder what your real agenda is?
« Last Edit: 20/04/2011 08:04:36 by yor_on »

BenV

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"Another Hockey Stick Illusion"?
« Reply #52 on: 20/04/2011 08:27:17 »
Yor_on is a valued member of this forum, but not a member of Naked Scientists staff.  Please stop whining about us, I have told you I will put your question to a relevant researcher when the opportunity presents itself.

Pete Ridley

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"Another Hockey Stick Illusion"?
« Reply #53 on: 20/04/2011 09:55:13 »
Hi yor_on, I am astounded by your
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I'm not sure it is placed in the right forum if it's just a geology/chemistry or physics question

I’m not the only one who considers that questions about fundamental theories underpinning opinions on the causes of climate change belong here on the Life Sciences, The Environment, forum. Let me give you some random examples but there are plenty more:
- “What is the statistical evidence linking climate change to co2?” (http://www.thenakedscientists.com/forum/index.php?topic=15086.msg352828;boardseen)
- “Is Carbon Dioxide the real cause of an increase in Gobal Warming?” (http://www.thenakedscientists.com/forum/index.php?topic=37534.0)
- How can a small change in CO2 make a large change in climate?” (http://www.thenakedscientists.com/forum/index.php?topic=38247.0)
- Science News says “Greenland ice gives us the best view of the climate so far” (http://www.thenakedscientists.com/HTML/content/news/news/1411/).
- Science Articles says “Britain and China collaborate on climate change studies in the Arctic” (http://www.thenakedscientists.com/HTML/articles/article/internationalpolaryear20079/). 

As I said in my opening post on this thread, I came to this blog because of finding this article “Climate Change and Ice Cores” (http://www.thenakedscientists.com/HTML/content/interviews/interview/643/). These together persuade me that I had every reason to think that I was using the proper forum on the correct blog to elicit an answer.

As for my being
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quite close to sounding querulous here
I first raised my simple question about collision v kinetic diameter (see the very first paragraph of the opening comment on this thread) over a year ago on the “Richard Alley at AGU 2009: The Biggest Control Knob” (http://chriscolose.wordpress.com/2009/12/18/richard-alley-at-agu-2009-the-biggest-control-knob/) blog of science student Chris Colose and have discussed it at numerous blogs since. If you Google - "Pete Ridley" "kinetic diameter" – or "Pete Ridley" "fractionation" you’ll find more than enough examples.

As you are probably aware I have been very disappointed with the level of scientific expertise that has been displayed here with regard to my question. I came here with great hopes that at last I had found a blog where scientists would be able to answer it but after 7 days, 55 replies and 923 views I am no nearer getting an answer.

The impression that I get is that your latest comment was made out of frustration with yourself that so far you have been unable to provide anything that helps to answer my simple question. My suspicion is that it requires expertise that you don’t have. If that is the case then just say so. I understand BenV to have acknowledged that The Naked Scientists cannot answer my question. There is no shame in ignorance and none of us, not even the most brilliant, are in a position where we can scoff at others because of it.

I’ve tried to elicit an answer from scientists at Cambridge, Otago, Wisconsin, Johns Hopkins, Texas, Suffolk County, etc. without success. Now I’ll have to try elsewhere, perhaps University College London’s Environmental Change Research Centre can do better than any of these.

My only agenda is to get an answer to my simple question.

Best regards, Pete Ridley

yor_on

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"Another Hockey Stick Illusion"?
« Reply #54 on: 20/04/2011 11:28:24 »
Sorry, but I honestly start to wonder if you're trolling here. And saying that no scientist can answer your question is a rather big bite to ingest :)

I would say that the evidence regarding the way the ice-cores correlate to other sources make them quite acceptable.  Now it suddenly seem to be a environmental question again, in which case my responses should give you some ideas why I expect it to be so, if you now read them? Before dismissing them? But if it will turn out to become a physics/chemistry/geology question again in your next post, well, then I'm afraid I will continue to point out that this sub-forum is about Environment.

Maybe you should take it up with some university near to you?
Possibly they can help you,  or NOOA?
Otherwise I suggest Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology

They seem to have a very good reputation, and if your question is as important as you seem to feel it to be, I'm sure they too will recognize its importance. Good luck.
==

Peter, I don't know what familiarity you have with chemistry but maybe this book will give you some ideas how to continue your research? Chemistry: The Practical Science.

And maybe you will find this one of interest. It puts some weight to your thoughts. I'm not saying that it has to do with your question, but it might have an importance. And it could be worth checking up..

"The team's calculations are based on a probabilistic analysis of climate variation between the years 1050 and 1800 - that is, before the Industrial Revolution introduced fossil carbon into the atmosphere. Using 200,000 data points, the study - believed by Nature to be the most comprehensive of its kind so far - compared the Antarctic ice core record of trapped CO2 bubbles with so-called proxy data like tree rings, which are used to estimate temperature changes.

The most likely value among their estimates suggests that for every degree Celsius of warming, natural ecosystems tend to release an extra 7.7 parts per million of CO2 to the atmosphere (the full range of their estimate was between 1.7 and 21.4 parts per million). The oceans' ability to absorb CO2 figures strongly into the debate This stands in sharp contrast to the recent estimates of positive feedback models, which suggest a release of 40 parts per million per degree; the team say with 95% certainty that value is an overestimate.

"This is a valuable paper that helps to constrain certain feedback components for the past," said John Schellnhuber, director of the Potsdam Institute for Climate Impact Research. "However, it is probably not suited for extrapolation into the future and it does not cover the really interesting processes like anthropogenic activation of permafrost carbon or methane clathrates." "

The discussion on Realclimate I guess that you might see them as the 'enemy', but they're foremost Climatologists Peter. So take a look and see what they, and you, think.
« Last Edit: 20/04/2011 15:03:47 by yor_on »

Pete Ridley

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"Another Hockey Stick Illusion"?
« Reply #55 on: 20/04/2011 22:38:11 »
Hi Yor_on whether or not anyone here regards me as a troll or anything else is not important. What I see as being important is that scientists can give a convincing answer to a question that is fundamental to the CACC doctrine, i.e. the manner in which atmospheric CO2 content has varied in the past. Scientists like Drs Alley, Severinghaus, Huber, Bender, etc. regard measurements of gas composition in residual air recovered from ice as being the “Gold Standard” but I question whether this is in fact simply “Fools Gold”. I question this as a layman and have every right to do so, however, I have never said, as you claim,
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that no scientist can answer your question
What I have said repeatedly is that no scientist has given me a convincing answer to my question posted here, which is a lot different from can answer.

As I have been unable to get a satisfactory answer to my question here or elsewhere I have indeed today E-mailed several professors at University College London, including
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Dr. Tim Atkinson, Professor of Environmental Geochemistry .. research interests include earth and environmental sciences, centring around the applications of chemistry and physics to problems in hydrology, hydrogeology, Quaternary geology and palaeoclimate, and geomorphology ..
(http://www.ecrc.ucl.ac.uk/index.php/content/view/375/94/).

I also had an interesting chat with
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Dr. Euan Nisbet, Professor of Earth Sciences, Department of Earth Sciences, Royal Holloway, University of London
(http://pure.rhul.ac.uk/portal/en/persons/euan-nisbet%282ff4ba1e-64af-450c-b39d-eb64b7f809d1%29.html). Although he acknowledged that he is not an authority on this subject he has sent me a couple of papers by Etheridge et al. and has recommended that I talk with Dr. Eric Wolff, EPICA. Isn’t that a surprise. That might well be the same Dr. Eric Wolff who chatted with Naked Scientists Dr Chris Smith and Dr Helen Scales on 21st Jan 2007 (just ahead of the publication of the IPCC’s scare-mongering AR4 SPM) about “Alternative Energy, Climate Change and Carbon Capture” (http://www.thenakedscientists.com/HTML/podcasts/show/2007.01.21/). Oh yes, and the same Dr. Eric Wolff who was interviewed by Chris at the same time on the subject of “Climate Change and Ice Cores” (http://www.thenakedscientists.com/HTML/index.php?id=40&tx_naksciinterview_pi1[showUid]=643&cHash=7faa6cce3f&table=tx_naksciinterview_interviews) and attracted me to this blog in the first place.

I have sent a message to Dr. Wolff and look forward to chatting with him.

You may recall that when I was pointing out the differences in collision and kinetic diameter of the molecules of various atmospheric gases on 14th April @ 21:38:13 I said to Wiybit
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Note the difference for CO2. Also note the size of He and think of the He-filled party balloon compared with one that you and I might blow up ourselves – which stays up the longest and why?
He has a smaller kinetic diameter than the molecules of the gases in air coming out of out lungs, which is mainly N2 and O2.

As we already know, CH4 has a smaller collision diameter (0.38nm) than CO2 (0.39nm) but a much larger kinetic diameter (still 0.38nm) than has CO2 (now 0.33nm). This would suggest that if collision diameter is relevant with regard to molecule movement through nanopores then there should be little difference between the two gases whereas if kinetic diameter is relevant then CO2 should move more readily than CH4

Professor Nisbet provided me with some anecdotal evidence of the movement of smaller molecules through nanoporous material similar to the party balloon evidence. If you look at the link to his credentials you will see that he has been involved in research with two of the gases, CO2 and CH4. He advised that he has found when transporting the two gases around that CO2 is much more problematic than CH4 and has to be carried in heavy steel containers. He likened CO2 to a needle due to its linear O-C-O molecular structure (http://www.eou.edu/chemweb/molmodel/mmp4d1.html). On the other hand the CH4 molecule has a tetrahedral structure. For anyone interested there is an excellent description and animation of these (and other) structures on the Oklahoma State University’s Department of Chemistry site (http://intro.chem.okstate.edu/1314f00/lecture/chapter10/vsepr.html).

My study of chemistry stopped at A-level 35 years ago so thanks for the heads up about “Chemistry: The Practical Science” (http://books.google.co.uk/books?id=VfcKIManfkUC&printsec=frontcover&dq=chemistry+the+practical+science+media+enhanced+edition&source=bl&ots=CXTSWgDBgd&sig=M1SzmDCo67bprWuJDZXra32cRSY&hl=en&ei=rESvTZTMDsHG8QOXs5yQDw&sa=X&oi=book_result&ct=result&resnum=9&sqi=2&ved=0CFIQ6AEwCA#v=onepage&q&f=false). I have done a search and cannot find any reference to collision or kinetic diameter although it does give a brief mention of zeolites on page 310, describing what appears to be a similar process to what I hypothesise occurs in the deep firn. You may recall that on 18th April @ 10:04:48 I referred Wiybit to a patent that says
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.. separation on size is possible, when the components to be separated are small enough in kinetic diameter to migrate through the zeolite pores and the components from which they have to be separated have a kinetic diameter that is too large ..


Professor Nisbet, who has relevant expertise in this area, recommends “"Mathematics of Diffusion" by John Crank, Professor of mathematics at Brunel University from 1957 to 1981 (http://www-history.mcs.st-and.ac.uk/Biographies/Crank.html) so I’ll try the library for a copy (maybe some kind person will buy me a copy for my birthday).

Thanks for reminding me about that Jan 2010 BBC article “Temperature and CO2 feedback 'weaker than thought'” as I had forgotten about Professor Brian Hoskins, a climate expert from Imperial College London. I’ll drop him an E-mail tomorrow.

Regarding Realclimate and your claim that
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they're foremost Climatologists
there are those who have argued that they are not climate scientists but software engineers helping scientists to construct and tweak their models. Because I am discouraged by their membership of the “Hockey Team” I look for less biased sources.

I have to say that I do appreciate that you are doing what you can to help me find an answer to my question.

Best regards, Pete Ridley

yor_on

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« Reply #56 on: 21/04/2011 00:16:23 »
Good on you Peter. The study I referred you too is somewhat confusing in that it assumes that there will be a reduction of CO2 instead of an addition, at least as they have found statistically. I'm not sure how this fits with how you view it? Maybe it does. It is still a discrepancy and as such worth looking into. When it comes to Realclimate I find them totally professional myself, allowing both sides a fair debate, as far as I've seen.

As we both seem to agree on that TNS can't take you any further for the moment, I will allow myself the liberty of locking this thread, for now. I'm sure that Ben will try his best to search for the specific expertize you hoped for, and finding it we will reopen it. And I'm as sure that you will continue your quest for truth.

Good luck.
==

« Last Edit: 21/04/2011 00:53:57 by yor_on »

ericwolff

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« Reply #57 on: 27/04/2011 13:53:30 »
I admit I did not wade through the entire thread, but as far as I can see the originator of this thread would be content if I can answer one key question: “why do palaeoclimatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice”?  For your information, I am an ice core scientist at the British Antarctic Survey, as mentioned by Pete Ridley in one of his posts above.

The underlying issue is whether we can believe that the air in bubbles in ice cores is an un-fractionated representation of the atmosphere.  In other words, when we crack open a bubble of air, does it contain exactly the relative proportions of different molecules as the air in the atmosphere.  Because some readers of this post will not have done the reading that the questioner has, I will first state some issues that the questioner has already got past in order to get to his more subtle question.

Firstly, of course molecules that are unstable will not be present.  Thus the photochemically produced radical OH is not going to be found in the air bubbles.  Secondly, the air is fully enclosed in ice (ie the ice becomes impermeable) only at a depth, typically 60-100 m depending on the site, and the air is sitting in a slowly diffusing column of firn until it is enclosed (typically taking 1-3 decades to reach the enclosure depth).  In this column, there is a small gravitational fractionation, which is sometimes corrected for (the correction is easily made for a given core by looking at the fractionation of 15N14N compared to 14N2, and is of order 1 ppmv for CO2).

However, from your comments, I think you are more concerned about whether there is a further fractionation at the final stages of enclosure, related to the size of the molecule – do some smaller molecules more easily escape enclosure leading to a fractionation?  Certainly such a fractionation can exist for some atoms and molecules: it is very strong for neon (Ne), noticeable for O2 and Ar (at the permil to 1 percent level) but the literature says that there is no fractionation for CO2 (or CH4) compared to N2.  This is, I think, the issue that is worrying you.

You are raising an interesting point about the underlying processes occurring at the depth where the air becomes fully enclosed in ice.  However, I must start by being precise about the question.  To my knowledge, no paper bases its declaration that CO2 is unfractionated on theoretical arguments about the diameter of CO2 (whether collision or kinetic).  Rather they base their conclusions on observations of CO2 in the firn just above full enclosure and the bubbles just below it.  Because it has the highest snow accumulation rate of any core where CO2 has been measured, the best core to look at is Law Dome, and in particular the paper by Etheridge et al (1996).  Their most direct evidence is achieved because just around the enclosure depth, the air is “locked-in” (ie no longer significantly diffusing), but some bubbles are closed while some air is still in a partly open space.  Thus it is possible to measure air that should be of identical age that is not yet enclosed (by pumping on the firn air), and that is fully enclosed (by cracking open air bubbles).  In their figure 2, Etheridge et al show samples they have measured in the firn air (circles) and in trapped bubbles at the same depth (triangles): they conclude that the difference is a random 1.3 ppmv, showing that the enclosure process does not affect the concentration.  This is a really direct and elegant measurement which shows that, at least at Law Dome, there is no fractionation of CO2 on enclosure.

One can supplement this direct evidence:
a) For pre-industrial ice, one gets the same concentration at several different sites in Antarctica, so the conclusion of no fractionation for Law Dome must be true of other sites also;
b) One gets an excellent overlap between measurements in the atmosphere at South Pole, and measurements in enclosed bubbles of the same age air at Law Dome (Etheridge et al 1996, Fig 3) - the same concentrations and trends are seen.

I suspect that what you have in mind is the papers by Severinghaus et al (2006) and Huber et al (2006).  In both these papers the authors discuss the fractionation that does occur for O2, Ar and other gases, and they appear to be able to make sense of their data using a model that depends on a size-dependent fractionation in which they use the collision diameter, and find a threshold of 3.6 Angstroms below which fractionation may occur.  I agree that one could imagine constructing a model in which the kinetic diameter is important (and because of it's non-spherical nature, CO2 has a smaller kinetic than collision diameter).  However, in such a model, Ar would be more fractionated than O2, whereas Severinghaus et al's data shows it is only one-third as fractionated; and as you are implying, CO2 would be somewhat more fractionated than either Ar or CO2, which the data of Etheridge shows not to be the case.  But again, I want to be really clear, while you can argue whether their model is right, the conclusion about CO2 is based on the data, and the data are clear that there is no fractionation of CO2 compared to N2 (within the measurement uncertainty, which is of order 1 ppmv).

I hope this is clear and does answer the question. The strict answer is that palaeo-climatologists do not use any diameter to form the conclusion that CO2 is unfractionated - they use the data.  They find that using the collision diameter in a model helps them to understand those data, but the conclusions about what happens do not depend on that, only on the data. I have added the relevant references below.  For more general readers, we (at BAS) recently produced a science briefing about ice cores, which you can read at
http://www.antarctica.ac.uk/press/journalists/resources/science/icecorebriefing.php

References:

Etheridge, D. M., Steele, L. P., Langenfelds, R. L., Francey, R. J., Barnola, J.-M. and Morgan, V. I.: Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn, J. Geophys. Res., 101, 4115-4118, 1996.

Severinghaus, J. P. and Battle, M. O.: Fractionation of gases in polar ice during bubble close-off: New constraints from firn air Ne, Kr and Xe observations, Earth planet. Sci. Lett., 244, 474-500, 2006.

Huber, C., Beyerle, U., Leuenberger, M., Schwander, J., Kipfer, R., Spahni, R., Severinghaus, J. P. and Weiler, K.: Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements, Earth planet. Sci. Lett., 243, 61-73, 2006.

Wolff, E. W.: Greenhouse gases in the Earth system: a palaeoclimate perspective, Philos. Trans. R. Soc. Lond. Ser. A-Math. Phys. Eng. Sci., 369, 2133-2147, 2011.


imatfaal

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« Reply #58 on: 27/04/2011 15:58:10 »
Great post Eric - I will check out your science briefing

yor_on

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« Reply #59 on: 27/04/2011 16:44:45 »
Beautifully put Eric, stringent and clear. We're pleased, both of me. That is, my royal persona as well as my more down to earth peasant, ahem. And yes, that was a joke. I'm only one, although looking in my mirror sometimes (mornings especially) I hardly recognize myself?

Hopefully it won't be the last time you write here, and I will follow that link.

Pete Ridley

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« Reply #60 on: 27/04/2011 21:39:34 »
Hi Professor Wolff, thanks for responding so promptly to my Email of 20th with your detailed explanation. This is just the sort of response that I have been trying to elicit for over a year now. You have given me plenty to think about and I was in the middle of replying to your E-mail of yesterday when I spotted that this thread had been unlocked (thanks moderators) and you had posted here. Your explanation here is very similar to what you E-mailed, apart from the background information that you have provided for those who aren’t so familiar with the issue. I’m sure they’ll appreciate it.

I have several points that I’d like to discuss and will do so one post at a time until you get tired of responding. I had thought of simply exchanging E-mails but I’m sure that there are others who are interested in this, judging by the views this thread is getting.

You say
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.. Secondly, the air is fully enclosed in ice (ie the ice becomes impermeable) only at a depth, typically 60-100 m depending on the site, and the air is sitting in a slowly diffusing column of firn until it is enclosed (typically taking 1-3 decades to reach the enclosure depth) ..
so maybe I’m misunderstanding the ice sheet structure.

Here’s a diagram that might help

I was under the impression that from the top down there is:
- a very small depth (much less than 1m?) of snow, which is affected by surface activity such as wind and others, below which there is
- a significant depth (tens of metres) of increasingly dense firn (see Figs. 2 & 3 of the Goodwin reference below) in which all air components diffuse relatively freely (is this also known as the stagnant zone?), below which there is
- a relatively short depth (10m?) in which the pores and channels interconnecting air pockets gradually reduce to nanometric size, where free diffusion no longer takes place and size-dependent fractionation occurs (is this known as the transition zone?) below which
- all air pockets are sealed to molecular movement other than through the crystal lattice via the breaking of hydrogen bonds.

Consequently, I find your
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.. the air is sitting in a slowly diffusing column of firn until it is enclosed ..
surprising, because I would expect that the air components having the largest molecular size (e.g. CH4, N2, O2, Ar) would be “enclosed” before the smaller molecules like CO2, Ne and He, which will continue to leave the air pockets and move down the pressure gradient towards the surface.

Can we concentrate on that first. Are you saying that this does not happen?

For anyone who is interested, one description of the typical ice sheet structure is given in “Snow-accumulation variability from seasonal surface observations and firn-core stratigraphy, eastern Wilkes Land, Antarctica” by Ian D. Goodwin in 1991 (http://www.igsoc.org/journal/37/127/igs_journal_vol37_issue127_pg383-387.pdf). Another paper “Polar ice structure and the integrity of ice-core paleoclimate records” by Faria et al. in 2009 (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-4XT2CSW-1&_user=10&_coverDate=01%2F31%2F2010&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_searchStrId=1733120326&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=a1695e258504733d23512b27bd34e36c&searchtype=a) provides a helpful diagram in
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.. Fig. 3. Basic outline of the multi-scale structure of the EPICA-DML ..
plus some excellent images, mostly of deep ice but
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.. Fig. 11. Microstructure-mapping mosaic images of two firn sections from 60 m to 85 m depth ..
relates to this discussion.
There are also some excellent SEM images of ice structure in “Snow crystal imaging using scanning electron microscopy: III. Glacier ice, snow and biota” by Rango et al. (http://itia.ntua.gr/hsj/45/hysj_45_03_0357.pdf).

Best regards, Pete Ridley
« Last Edit: 27/04/2011 21:52:45 by Pete Ridley »

ericwolff

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« Reply #61 on: 28/04/2011 07:45:37 »
Pete,
I will respond (though not endlessly, as I am not a natural blogger!).

Yes, your descriptions is generally fine, and not in contradiction with the one-sentence summary I gave. But just to summarise in my own words:
1. At the top of the firn (the name for the whole column of material that is between loose snow and solid, impermeable ice) there is a convective zone in which the air exchanges relatively freely with the atmosphere.  At most sites today, this is very shallow (less than a couple of metres).
2. Most of the firn column is what is called the "diffusive zone".  It is in this zone that gravitational fractionation can occur.
3. Then there are a few metres in which diffusion with the overlying column appears not to take place, but which still has some permeability (this is the non-diffusive zone).  At any depth in this zone, it is likely that some bubbles are closed off and some are not (this is the most obvious way in which the enclosure is "gradual", and the main reason why gas profiles in ice cores have an inherent limit in their time resolution).
4. Finally one reaches solid ice where all the bubbles are enclosed.

Again maybe for the general reader, I should say how we know this, and what we don't know.  While people probably know that we can sample the air bubbles by crushing a core to release the air, they probably don't know that we can also sample the firn.  This is done by drilling a hole, and lowering a pumping device, that has a bladder above the sampling entries, to the bottom of the hole.  By inflating the bladder, one can make sure that the device pumps air only laterally from the firn surrounding the depth the inlets are at.  With such a device it is easy to know when one has reached zone 4: it becomes impossible to pump any air (but obviously this is easily verified when the core is drilled as the air bubbles are intact).  Zone 3 is characterised by the fact that the 15N14N/14N14N ratio, which increases slightly (by a few tenths of a part per thousand) with depth in the diffusive zone (zone 2 in my description), stops increasing.

The question in this thread is entirely about what happens in zone 3.  The answer is of course that we don't fully know what mechanism is taking place because we cannot reasonably observe or reproduce the very slow enclosure process in the lab.  All that scientists can do is observe the results of the process, and hypothesise about the cause.  The data show that there is a fractionation of some atoms/molecules relative to others in this zone, meaning that (using nitrogen as the standardiser) the bubbles are slightly depleted for some "smaller" molecules compared to the air above.  One should not exaggerate this effect, which is of order 0.3% for oxygen.  People have hypothesised that this effect is controlled by a process where smaller molecules are slightly more likely to escape during the final stages of enclosure, but we frankly do not know the exact mechanism.

I cannot emphasise enough though that the exploration of the mechanism (in the papers I cited yesterday) is only a way of explaining the data, which clearly show that CO2 is NOT fractionated during enclosure, at least within the analytical resolution.  I understand your point that, if the process was just physical permeation through a small gap, then we would expect the kinetic diameter to be relevant.  But the data are not consistent with that, so the molecular level process must be somewhat different to that.  What Severinghaus and others note is that there seems to be no fractionation for molecules with a collision diameter more than 3.6 Angstroms.  If this leads someone to a better description of the mechanism, that would be great: but the data are the data.

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« Reply #62 on: 28/04/2011 08:02:12 »

as I am not a natural blogger!.


You could have fooled me! Many thanks for the post.

Bored chemist

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« Reply #63 on: 28/04/2011 09:15:48 »
OK, To summarise the thread .
Pete asked " My question in a nut shell to the scientists here is “why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice”? "
And the answer is

"the data, which clearly show that CO2 is NOT fractionated during enclosure, at least within the analytical resolution.  I understand your point that, if the process was just physical permeation through a small gap, then we would expect the kinetic diameter to be relevant.  But the data are not consistent with that, so the molecular level process must be somewhat different to that.  What Severinghaus and others note is that there seems to be no fractionation for molecules with a collision diameter more than 3.6 Angstroms.  If this leads someone to a better description of the mechanism, that would be great: but the data are the data."


We can stop now, and go out to play.

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« Reply #64 on: 28/04/2011 19:34:11 »
Hi Professor Wolff, I think that Geezer’s comment will reflect what many of the silent viewers of this thread will be thinking. I’ll be most surprised if others do not start jumping in with comments. Thanks for another excellent, helpful response which, as far as the main question in this thread is concerned, seems to be covered in Para. 3
Quote
.. The data show that there is a fractionation of some atoms/molecules relative to others in this zone, meaning that .. the bubbles are slightly depleted for some "smaller" molecules compared to the air above  ..  People have hypothesised that this effect is controlled by a process where smaller molecules are slightly more likely to escape during the final stages of enclosure, but we frankly do not know the exact mechanism ..
In other words, this type of fractionation is evidenced by the data and could be due to size-dependent fractionation as I have described it but this has not been properly researched and we just do not know. My understanding of the work of Severinghaus and Huber, which is the basis for many other papers on the subject and specifically addresses this type of fractionation, is that they rely upon models which use the wrong measure of molecular size, collision rather than the appropriate measure, kinetic diameter.

Let me leave that for a moment to ask about ice sheet structure. Am I correct in thinking that what you refer to in 2. of your summary as the “diffusion zone” is also called by others the “stagnant zone” or is this what you call in 3. the “non-diffusive zone” or is this zone also referred to as the close-off zone? (pause for breath).

Also, I think that it would be sensible to resolve any uncertainties arising from your first comment here before tackling those in your second. Your structure summary point 3. leads nicely into something that came to mind after I read your E-mailed response of 26th.

In your E-mail you sent me the paper “Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn” (http://www.agu.org/journals/ABS/1996/95JD03410.shtml) by Etheridge et al. (one of the papers that Dr. Nisbet had also sent me). Then (and on the thread here on 27th) you make reference to Fig. 2 on Page 4120. I’m unable to provide a link to the full paper so for anyone who is interested and can’t get a copy of the paper I’ll try to describe what Fig. 2 shows. Alternatively, the CO2 (and CH4) “data and descriptions” are available free from NOAA (http://www.ncdc.noaa.gov/paleo/icecore/antarctica/law/law_data.html).

Fig. 2 is a graph of CO2 on the Y-axis (origin 310-360ppm) and depth in the ice sheet (origin 0-120m). The plotted points start at 10m, 353ppm with an almost linear fall to 70m, 343ppm. a gradient of 0.17ppm/m. Around 70m there is a turning point to a steeper fall from 70m, 343ppm to 115m, 310ppm,  a gradient of about 0.73ppm/m.

Related to Fig. 2 is Table 2 on Page 4119, which says
Quote
.. Depth Where Sealing Occurs - 72m, Age of ice at Sealing Depth – 40years, Mean Age of CO2 in Air at Sealing Depth – 10years, Difference Between Ice Age and Mean Air Age – 30years, Duration of Bubble Close-off Process 8years
The inferences that I draw from Table 2 are:
- ice accumulation rate = 72m/40years = 1.8m’year, but this conflicts with the statement in “Interactive comment on “Post-coring entrapment of modern air in polar ice cores collected near the firn-ice transition: evidence from CFC-12 measurements in Antarctic firn air and shallow ice cores” by M. Aydin et al. 30 March 2010” (http://www.atmos-chem-phys-discuss.net/10/C1119/2010/acpd-10-C1119-2010-print.pdf) that
Quote
.. The accumulation rate at their study site was about .. 1.2 m/y (ice equivalent) .
(any suggestions?)
- the close-off process is very gradual, with fractionation of the smaller molecules taking place over several years (around 10), which I understand to be the period in Fig. 2 during which the CO2/depth gradient of 0.17ppm/m in the firn (the diffusion zone?) is gradually changing (in the non-diffusive zone?) to a gradient of 0.73ppm/m (in the “solid” ice – I use parentheses because of the persistent movement of molecules within that zone due perhaps to H-bond breaking and fractures, another aspect of the fractionation process to be considered later).

The first thing that struck me as odd when I first saw Fig. 2 in 2008 was the discontinuity occurring around 70m. At that time I had come across a related graph (http://maps.grida.no/library/files/historical-trends-in-carbon-dioxide-concentrations-and-temperature-on-a-geological-and-recent-time-scale.jpg) on the site of Norwegian GRID-Arendal, a collaborating centre of the United Nations Environment Programme (UNEP). More recently I found the US EPA’s page “Atmospheric Concentrations of Greenhouse Gases” which presents a graph superimposing data from 6 Antarctic ice cores, spliced with measurements from Mauna Loa and sundry other SH and NH locations (http://cfpub.epa.gov/eroe/index.cfm?fuseaction=detail.viewInd&lv=list.listByAlpha&r=231323&subtop=342). That too displays a puzzling discontinuity for CO2 concentration, but in that case relating to the difference between the “normal” periodic swings between ice ages and interglacials).

Rather than jump to the conclusion that the apparent increase in mean global atmospheric CO2 was a consequence of the industrial revolution and our increasing emissions of CO2 into the atmosphere (not least from using fossil fuels) I considered it worthwhile trying to identify another reason for that discontinuity seen in ice core data from numerous different locations. I was reminded of the concerns expressed by Professor Zbinew Jaworowski about fractionation in the ice (see my opening post on this thread) and that led me to research this issue of size-dependent fractionation in the deep firn.

The inferences that I drew from Fig. 2 of the Etheridge paper were:
- CO2 experiences significant size-dependent fractionation down the pressure gradient towards the surface at depths around the nominal close-off depth of 72m where the larger gas molecules (N2, O2, Ar, CH4, Kr, Xe) are trapped in the air bubbles,
- above the nominal close-off zone CO2 is no longer experiencing size-dependent fractionation but is being mixed by diffusion with younger air within the firn.
 
You said that
Quote
.. In their figure 2, they (Etheridge et al.) show samples they have measured in the firn air .. and in trapped bubbles at the same depth .. : they conclude that the difference is a random 1.3 ppmv, showing that the enclosure process does not affect the concentration.  This is a really direct and elegant measurement which shows that, at least at Law Dome, there is no fractionation of CO2 on enclosure
. I need to look more closely at that and revert. Meanwhile I propose to E-mail the scientists I have been exchanging E-mails with for the past year to see if any of them wish to get involved here. After all, opinions from other specialists, especially some who have the necessary expertise in the movement of different molecules in sub-nano-porous media (such as from those involved in gas purification for the energy industry, e.g. removal of of impurities from mine gas to bring it up to grid standard) could help to remove some of the uncertainties arising from the fact that
Quote
.. we frankly do not know the exact mechanism ..
.

If anyone viewing this thread who has such expertise or knows specialists who have it then I’d appreciate them inviting their involvement.

BTW, for anyone who was/is interested in taking a look at those links to ice sheet structure that I provided at the end of my comment yesterday @ 22:39:34, Dr. Al Rango, the main author of “Snow crystal imaging using scanning electron microscopy: III. Glacier ice, snow and biota” (http://itia.ntua.gr/hsj/45/hysj_45_03_0357.pdf) has expressed an interest in joining the discussion. Dr. Rango has kindly offered to try to get his hands on more of those excellent images and the data used as the basis for that paper. I again recommend a look at those images.

Best regards, Pete Ridley

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« Reply #65 on: 28/04/2011 19:50:10 »
Hi Bored chemist, although you may have lost interest in discussing this size-dependent fractionation issue and want to
Quote
.. stop now, and go out to play ..
you did raise a relevant question on the “What does Iain Stewart's "CO2 experiment" Demonstrate” thread in your comment of 22nd April @ 17:35:55. Rather than your question being followed up there, which is on a separate topic altogether, maybe it should be addressed here or, better still, as a new question related to the validity of the attempts to reconstruct past atmospheric CO2 content from air in ice sheets.

In response to my
Quote
.. I am surprised that you have had nothing scientific to contribute to the question of how the individual molecules of the different atmospheric gases react within nanoporous media like firn ..
you said
Quote
.. Did it occur to you that the fact that no chemical reaction takes place might have some importance there .. Actually I'm an analytical chemist but, as I have pointed out, what you are asking about is physics
.

Perhaps, as an analytical chemist, you can help clear up other significant uncertainties regarding those other air fractionation processes that take place right from the beginning of the process of ice-sheet development. After all, the validity of those attempts to reconstruct past atmosheric CO2 content from air “trapped” in ice is rather fundamental to the argument presented by the IPCC and its supporters.

Let’s start with the very first part of the ice sheet development process, the falling snow. In my list of scientists I mentioned Professor Hartmut Frank, Chair of Environmental Chemistry & Ecotoxicology, University of Bayreuth. Professor Frank wrote a forward to Jaworowski’s 1994 paper “Ancient Atmosphere – Validity of Ice Records” (http://www.springerlink.com/content/284n23943h8g687p/fulltext.pdf?page=1). Professor Frank sent me a slide from one of his presentations last year to graduates at Technical University in Gdansk.

He described it  as “ .. a simplified illustration of the major processes which are leading to changes of gas concentrations in the secondary bubbles (including and especially of carbon dioxide) .. ”. I don’t know how to embed a pdf page into this comment so will have to describe it (if anyone would like a copy then send me a “Personal Message” and I’ll E-mail it).

The slide provides a diagram showing falling snow beneath which is the section of a fully developed ice sheet. It discusses the manner in which atmospheric air collected within the voids of forming snow has already been depleted in CO2 before it even hits the top of the ice sheet. Alongside it says “Assuming a specific weight of 1 dm3 snow as 0.1 kg/L, it consists of 10 Vol-% of snow-ice and 90 Vol-% of air. Thus, a dm3 snow may contain a total carbon dioxide content of which 4 mg is adsorbed and 0.54 mg comes from the air between the snow flakes –explaining the high values found in ice cores by the gas extraction over long time in the molten state”.

It then goes on to summarise the snow/firn/ice compaction stages after “Deposition:
- Compaction to firn, air bubble closure (when?),
- Chlathrate formation (CO2~ 5 atm) [CO2•5 H2O] preferred diffusion of CO2 into the ice matrix
- Chlathrate formation (N2, O2at ~ 20 atm)
- Carbonic acid formation (formulae shown) N2, O2 non-reactive: selective depletion of CO2
- Primary bubbles disappear.
- Upon drilling and horizontal storage of ice cores, expansion and back diffusion of N2, O2 and CO2 (and slow decomposition of carbonic acid) into secondary bubbles occurs, at different rates”.

My question to you at this stage is whether or not that initial adsorption of CO2 in the snow is a chemical or a physical process (http://www.tutorvista.com/content/chemistry/chemistry-iv/surface-chemistry/absorption-types.php). My suspicion is that it is Chemisorption but as I’m not a chemist I’d appreciate your opinion. Following on from that is another question about adsorption in the deep firn, but that can be followed up later. Let’s work our way down the ice sheet looking at the different processes that Professor Zbiniew Jaworowski has been expressing concern about since 1992 and return to deep firn adsorption of CO2 and clathrate formation at a later stage.

I can ask Professor Frank and Professor Jaworowski and other scientists (see my comment of 13th April @ 21:58:19 on this thread) if they are interested in helping on those other processes.

Best regards, Pete Ridley
« Last Edit: 28/04/2011 21:56:24 by Pete Ridley »

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« Reply #66 on: 28/04/2011 19:54:48 »
I see that I managed to attach that pdf without realising I’d done it. What a great blog this is.

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« Reply #67 on: 29/04/2011 10:25:13 »
Pete - it's a forum not a blog. 

A blog tends to be a regular personal piece of writing with potential for others to comment on it.  a forum has a different structure - it is a public discussion arena, a modern agora, where people can meet and debate diverse topics.  It is structured around the threads, which are back and forth conversations between two or more participants.  Any member (or on some fora anyone at all) can start a question or participate in a thread  - whereas on a blog there is an owner who writes the blog and others who comment.  To stop the naked science forum from descending into a free for all, in common with most fora, there are rules of posting and moderators who gently or not so gently enforce those rules.  I have mentioned this to perhaps help explain why previous posters and mods were talking about editorialising;  in a blog one is expected to be editorial and proprietorial - in a forum it is presumed that debate is the key. 

http://en.wikipedia.org/wiki/Internet_forum
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« Reply #68 on: 29/04/2011 16:49:42 »
Hi Imatfaal, I’m at risk of upsetting the moderator of this blog by responding to your off-question comment, but I’ll risk it with a “quickie”.
Quote
Just what is a blog, anyway? Defining this variable form is not easy in the highly opinionated blogosphere ..
(http://www.ojr.org/ojr/stories/050929/) – but at least I’ve learned what an agora is.

Now, what have you to say about collision v kinetic diameter in the close-off zone of deep firn?

Best regards, Pete Ridley

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« Reply #69 on: 29/04/2011 21:43:40 »
Well, I say we better put a stop to this Peter :)

You've got your answers, now you want more, and if Eric answers those, you will find other things to question :) That's perfectly correct in a 'blog' I presume, or in a private correspondence, but not here. We've delivered what I think is above and beyond the 'call of duty' for our head-bofins managing TNS, just for you Peter, and notably without letting your comments about our incompetence, not being 'firn experts', getting to us.

Why not take some of those courses that are available instead, somewhat slower maybe but then you will know what you're talking about. Or maybe you consider yourself to 'know'? Anyway, it's never wrong to study, if one is burning as much as you for a subject. Alternatively, if you consider yourself knowing already, create that final experiment that will put your question to rest, once and for all. As I read Eric that should be quite a challenge to create? And as i see it that's what it comes down to, your question needs a experiment to answer it. As for how to create it I can't say though? It has to to over quite a long time period, and you will need to prove that you've considered all parameters that may have a influence, and isolated those that you're interested of. You're welcome back with some practical results. This discussion though, seems already have gone to on too long to me.

Until then Peter.

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« Reply #70 on: 30/04/2011 10:51:45 »
Hi Yor_on, I do not agree with your
Quote
.. You've got your answers ..

Here is my opening question again
Quote
.. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice? ..

Only one person, Professor Eric Wolff, has tried to respond properly to that question (see 27the April @ 14:53:30 and 28th April @ 08:45:37). He is not one of The Naked Scientists but works with the British Antarctic Survey and is recognised as a specialist in the area relating to part of my question. He has shown that he fully understands my question but even he has not answered it. Others here may think that he has but by reading his penultimate paragraph in his response of 27the April @ 14:53:30 carefully enough and having done whatever background reading is needed to understand it and my original question, it will be realised that the specific question remains unanswered. Proferssor Wolff focussed on CO2 but my question is not specifically about CO2. It refers to “air molecules”, which covers not only CO2 but N2, O2, Ar, CH4, He, Ne, etc.

I expect that Professor Wolff would quite readily accept what I have just said. More exchanges are needed before the question is answered and that is one reason why, after receiving Professor Wolff’s response, I E-mailed specialists like Professor Jeff Severinghaus to take a look at this thread. Professor Severinghaus and his associate Dr. Chris Huber have written papers on this specific issue of size-dependent fractionation of “air molecules” but used collision diameter not kinetic diameter and did not specifically investigate CO2. The reason appears to be because their model led them to conclude that molecules having a diameter larger than 0.36nm are not affected by the size-dependent fractionation process. CO2 has a collision diameter of 0.39nm but a kinetic diameter of 0.33nm.

If they had used the kinetic diameter measure of molecular size then I hypothesise that their conclusion s about CO2 would have been different. As I have said already, expert practitioners in gas purification through nanoporous media do not use collision diameter in their analyses, they use kinetic diameter. That is what gave rise to my still unanswered question.

Professor Wolff acknowledged
Quote
.. I agree that one could imagine constructing a model in which the kinetic diameter is important (and because of it's non-spherical nature, CO2 has a smaller kinetic than collision diameter).  However, in such a model, Ar would be more fractionated than O2, whereas Severinghaus et al's data shows it is only one-third as fractionated; and as you are implying, CO2 would be somewhat more fractionated than either Ar or CO2 ..
(I think that last should be O2). I expect that gas purification specialists had been involved and the research done by Severinghaus and Huber kinetic diameter would have been used in the model.

As Professor Wolff said in his second response on 28th April @ 08:45:37 
Quote
.. I understand your point that, if the process was just physical permeation through a small gap, then we would expect the kinetic diameter to be relevant.  But the data are not consistent with that, so the molecular level process must be somewhat different to that.  What Severinghaus and others note is that there seems to be no fractionation for molecules with a collision diameter more than 3.6 Angstroms ..
Following several E-mail exchanges with Professor Severinghaus I asked on 29th December about the structure of the models that he had used, including
Quote
.. I note that in both papers you have used collision diameter and ignored kinetic diameter, but why?. Have you carried out any research using kinetic diameter instead? If not do you have a feel for what differences this would make? ..
For some reason I didn’t get a response.

The validity of the attempts to reconstruct past atmospheric composition from air recovered from ice is fundamental to the CACC hypothesis. Many questions about this have been raised repeatedly since at least 1992 by others such as Professor Zbiniew Jaworowski and Professor Hartmut Frank. The question that I posted here initially is just the first of a long string of such questions.

Contrary to what has been suggested here, that first question of mine remains unanswered, hence, in my opinion this very popular “Hot Topic” thread, which continues to attract significant views, should remain open.

Best regards, Pete Ridley

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« Reply #71 on: 30/04/2011 13:31:25 »
That's okay with me Peter. Email as many as you like, and keep on searching for those answers. But the question has been answered as I see it. The next step if you want to prove your point is without doubt a experiment, no words in the world can replace that.

May I most respectfully suggest you to use mails if you won't, instead of TNS.

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« Reply #72 on: 30/04/2011 17:08:36 »
Pete,
you seem to have missed something
"If they had used the kinetic diameter measure of molecular size then I hypothesise that their conclusion s about CO2 would have been different. "
Yes, specifically their conclusions would have been wrong.
The results they calculated tally with the data.
Any different result would not agree with the real world.
Scientific results that don't agree with reality are called "wrong".

Also, where you say "Contrary to what has been suggested here, that first question of mine remains unanswered" you are mistaken, it has been answered. You just don't like the answer.
They use the numbers to verify the model.
They observe that "the data, which clearly show that CO2 is NOT fractionated during enclosure, at least within the analytical resolution. "

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« Reply #73 on: 30/04/2011 19:51:06 »
Hi Yor_on, I consider that The Naked Scientists blog/forum is an excellent place to have this issue discussed. The viewing figures tell me that this thread is attracting a lot of attention but maybe you interpret those figures in a different way to what I do. I repeat, my question has not yet been answered so let’s wait for further help from those who have specialist knowledge in the subject. I believe that the only person to contribute to this thread so far who fits that category is Professor Wolff. Hopefully he will continue to give his valued assistance and others with such expertise will join in.

Hi Bored chemist, from your contributions so far am I being fair if I suggest that you do not have the necessary expertise in the subject to state that
Quote
.. it has been answered ..

You are mistaken if you  have the impression that I
Quote
.. have missed something ..
I certainly don’t miss anything that Professor Wolff says and have every intention of following up on all of it. In the mean time I hope that Professor Severinghaus or Dr. Huber will join in because it was they who modelled the process so should be able to give a  satisfactory answer to my original question. It is possible that Professor Wolff will return to it too and others may join in.

Best regards, Pete Ridley
« Last Edit: 30/04/2011 19:57:39 by Pete Ridley »

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« Reply #74 on: 30/04/2011 21:42:57 »
Well Peter, I'll give it the benefit of a doubt :) But if Eric feels he answered your original question, then that's that, as far as I'm concerned. And then we will move on.

 

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