Naked Science Forum
Life Sciences => The Environment => Topic started by: Pete Ridley on 13/04/2011 10:25:00
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I came across this blog while searching for detailed pictures of ice extracted from deep down an ice sheet. I have a question that has been puzzling me for over a year now and remains unanswered despite asking it of experts in the subject. 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”? Here is some background.
The photo shown on your “Climate Change and Ice Cores” thread (http://www.thenakedscientists.com/HTML/content/interviews/interview/643/) is a beauty as a starter because it clearly shows the air pockets which are claimed to hold air having the same composition as when it was captured from the atmosphere thousands of years ago. This sounds like a wonderful natural archive which simply has to be emptied of air which can then be analysed to provide what Professor Richard Alley refers to as “the gold standard” for exposing the ancient atmospheric make-up to – but is it?
Dr Eric Wolff from the British Antarctic Survey thinks so. When discussing the natural global warming that has occurred since the Little Ice Age (it always warms between ice ages, then cools again towards another one) he says “ .. the arguments about whether global warming is real hinge on four aspects. The first one is the physics that tells us to expect that when we get more carbon dioxide in the atmosphere it should get warmer. The second one is whether carbon dioxide has actually increased in the atmosphere, and that's what I'm best at because that's what we can see from ice cores. The third one is whether in the past that's caused climate change. And we can see in the ice cores that at least every time carbon dioxide's changed in the past, then it has warmed. So there's no counter evidence .. ”.
Let’s look at each in turn:
- physics tells us that if everything else that controls the mean global temperature remains unchanged then increasing CO2 will cause an insignificant amount of warming amounting to about 1C for a doubling in concentration from 300 to 600ppm. The present atmospheric CO2 content is estimated (from readings on top of an extinct volcano in the “ .. exhaust plume of massive oceanic outgassing in the Eastern Equatorial Pacific .. ” - http://judithcurry.com/2011/02/26/agreeing/#) to be about 400ppm, having risen from an estimated 300ppm in 1850,
- the ice cores are only able to show us that the concentration of residual CO2 in the air bubbles reduces the lower the bubble is in the ice sheet until a depth is reached when the residual level changes relatively little around a mean value of about 280ppm (Fig 2 in http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/icecore.html)
- an important piece of information about this has been withheld. “ .. On the basis of atmospheric CO2 data obtained from the Antarctic Taylor Dome ice core and temperature data obtained from the Vostok ice core, Indermuhle et al. (2000) studied the relationship between these two parameters over the period 60,000-20,000 years BP (Before Present). One statistical test performed on the data suggested that shifts in the air's CO2 content lagged shifts in air temperature by approximately 900 years, while a second statistical test yielded a mean lag-time of 1200 years. Similarly, in a study of air temperature and CO2 data obtained from Dome Concordia, Antarctica for the period 22,000-9,000 BP -- which time interval includes the most recent glacial-to-interglacial transition -- Monnin et al. (2001) found that the start of the CO2 increase lagged the start of the temperature increase by 800 years. Then, in another study of the 420,000-year Vostok ice-core record, Mudelsee (2001) concluded that variations in atmospheric CO2 concentration lagged variations in air temperature by 1,300 to 5,000 years. .. ” (http://www.co2science.org/articles/V6/N26/EDIT.php).
I have been researching the second of Dr. Wolff’s points for over a year now, exchanging opinions with experts in relevant fields such as Professor Alley, Professor Jeff Severinghaus, Professor Michael Bender, Professor Hartmut Frank, Professor Zbiniew Jaworowski, Dr. William Connolley (you may know him), etc. I think that is quite a balanced selection of experts and my conclusion, after reading lots and lots of relevant papers, is this. Due to its much smaller kinetic diameter, CO2 is preferentially fractionated out of the air pockets when the escape routes have reduced to a size in the lowest levels of the firn that prevents the escape of the larger N2, O2 and CH4 molecules. This results in the residual air “trapped” in pockets after close-off are depleted in CO2 while the air above is enriched. I say “trapped” because even after close-off it is still possible for further depletion in CO2 to take place due to H-bond breaking through the ice crystal lattice.
If you are interested in more of this you’ll find some on the Climate Conversation blog (http://www.climateconversation.wordshine.co.nz/2011/03/fallen-snow/#comment-46211 and http://www.climateconversation.wordshine.co.nz/2011/03/its-not-warming-you-nitwit-its-cooling/#comment-45360.
As I said before, trying to simplify science that is poorly understood is fraught with danger and the processes and drivers of the different global climates. Professor Barry Brook, previously Professor but now Director of Climate Change at Adelaide University said a couple of years ago “ .. There are a lot of uncertainties in science, and it is indeed likely that the current consensus on some points of climate science is wrong, or at least sufficiently uncertain that we don’t know anything much useful about processes or drivers. But EVERYTHING? Or even most things? Take 100 lines of evidence, discard 5 of them, and you’re still left with 95 and large risk management problem .. ” (http://bravenewclimate.com/2009/04/23/ian-plimer-heaven-and-earth/). The significant part of that comment is “we don’t know anything much useful about processes or drivers” (Please read the full comment as Professor Brook gets rather upset when readers are unable to ascertain the full context of what he said.)
It strikes me as being perhaps disingenuous to try to imply that only 5% of the science is uncertain by plucking those 100, 95 and 5 lines of evidence out of the air, but it’s a bit like what the IPCC does when trying to quantify “expert opinion”. Maybe Brook has the same attitude as Professor Stephen Schneider "To capture the public imagination, we have to offer up some scary scenarios, make simplified dramatic statements and little mention of any doubts one might have. Each of us has to decide the right balance between being effective, and being honest" (http://www.john-daly.com/schneidr.htm).
I’d be very interested to know what your opinion is of scientists being what is, in my opinion, simply dishonest. It is scientists like Schneider who make lay people like myself trust scientists even less than we trust politicians and used-car salespersons. Talking about politicians (and other power-hungry individuals), isn’t that where all of this CACC propaganda is coming from?
Best regards, Pete Ridley
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So what's your question here Pete?
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Hi BenV, didn't you read the first paragrapg of my comment? I asked " .. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice? .. " and provided some background to help the scientists here to understand what is behind my question.
Bets regards, Pete Ridley
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Hi BenV, didn't you read the first paragrapg of my comment? I asked " .. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice? .. " and provided some background to help the scientists here to understand what is behind my question.
Bets regards, Pete Ridley
Pete would I be right in thinking that your question is how can we trust the Ice core samples, they use to base the global warming data as, it is not clear that the molecules present have arrived as they claim and think they have?
"Migration of air molecules" implies and actually suggests that Co2 in ice- can move and will move. If true how can you be sure that the Co2 levels in the ice cores are the actual levels present at the times they claim they were, and are not higher or lower for other reasons.
Would that be fair Pete, as an interpretation of what you asked?
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Wiybit, you have summarised reasonably well the basic question that Jaworowski et al. raised back in 1992 in their paper “Do glaciers tell a true atmospheric CO2 story?” but they covered about 20 processes that could distort the composition of residual air extracted from “sealed” pockets within ice cores. My specific question relates to only one, preferential fractionation over decades, centuries or even millennia of CO2 and other gases that have smaller kinetic diameters than do N2, O2, Ar or CH4. The researchers that I mentioned in my first comment ignore kinetic diameter and use collision diameter, which I hypothesise is not appropriate when the diameter of pores within and the channels that link ice air pockets approach the size of those smaller molecules as the ice is reaching the final stages of compression to a state where the air pockets become “closed off”.
BenV(alsler?) I’ve checked up on your background and looked up some of your previous comments. The only comment that I found of interest was your response to a question by one neilep who asked on 31/01/2008 @ 02:05:41 “So, how does a climate model get created ?...do they just use the last few hundred years of weather records and data and average it all out or is it a tad more complicated than that ?...and how accurate are they ?”
I found your response less than inspiring. “Basically, you make a weather simulator (if windspeed=x, direction=y, then Z happens - but about a millionfold more complicated) and then plug real data into it. If the outcome of your 'simulator' consistently matches the observed changes in climate over a given timescale, you have a working climate model. If it fails to predict what you already know to have happened, then you need to tweak your model. When your simulator can accurately predict past changes based on past data, you can assume that it may accurately predict future events based on current data.” (http://www.thenakedscientists.com/forum/index.php?topic=12826.msg352094;boardseen).
If that and your background are anything to go by you probably have nothing substantial to offer regarding migration of molecules through porous media, but I could be wrong. Your training and experience in zoology and science communications probably means that you have little more understanding than I have of molecular dynamics. Don’t take that as an insult as it isn’t meant that way. When I discussed this last June with Professor Zbiniew Jaworowski, whose 1992 paper first drew my attention to this issue, he expressed the opinion that “This is a highly specialized field of science. My impression is that it is a terra incognita for glaciologists”. Subsequently I have asked the same question of Professors Richard Alley, Jeffey Severinghaus and Michael Bender without receiving any worthwhile justification for their use of collision diameter.
One thing that you could probably help me out with is in reference to an experiment presented by the BBC’s Ian Stewart and available on U-tube ( It was linked to by climate science “expert” Professor Mike Palin, Otago University during our exchanges on the issue of CO2 fractionation a month or so ago (http://hot-topic.co.nz/the-twilight-zone/). Stewart’s attempt to persuade us through that demonstration that CO2 traps a lot of IR requires further scrutiny. I am always suspicious of anything that the BBC or its minions (like Stewart) say about climate change because of the fact that there is a possible vested interest n supporting the CACC doctrine – pension scheme investments.
I puzzled over what that demonstration really tells us. On investigation, Wikipedia (http://en.wikipedia.org/wiki/Thermographic_camera) advises that the colour picture from an infrared camera is not true but pseudo colour, where the colours represent intensity. So when Steward shows us that candle turning more and more blue what is he really demonstrating. In my humble opinion (I’m not a scientist but a retired Chartered Electrical Engineer) he may simply have verified that the candle gets colder and colder as the CO2 that he is pouring into the tube replaces the O2 upon which the candle depends to keep burning brightly (highest intensity). As most of us would expect, the O2 in the tube is depleted and the candle glows less and less brightly (getting cooler) until it goes out. Stewart’s presentation was cut short to ensure that we didn’t see it go out. Well, that’s my conspiracy theory anyway. As always I’m open to persuasion that I am wrong, so if you can repeat that experiment but this time use N2 instead of CO2 and show that the change in colour is different then I might accept that the experiment was demonstrating IR absorption by CO2 – but I’m a sceptic so I doubt that you’ll be able to because the colour change will be identical.
Best regards, Pete Ridley
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Pete,
You bring up a lot of issues.
Much like Deuterium (2H or just D) and Oxygen-18 (18O) concentrations (the standard for paleontological temperature proxies), the historic CO2 concentrations have been driven by temperatures...
Essentially, as ocean temperatures increase, the CO2 partial pressure increases, and creates the effect of lowering the CO2 solubility in the ocean, and increasing the CO2 concentration in the atmosphere.
Obviously since the discovery of coal and fossil fuels, we've also been adding previously sequestered CO2 into the mix.
The question is whether there is also a feedback mechanism such that increasing CO2 concentrations cause a temperature feedback loop increasing the temperatures more. This is hard to determine from our paleontological data. Those that follow the Milankovitch theory for glacial/interglacial temperature changes believe that additional feedback mechanisms are necessary to cause the temperature shifts. Those people who believe in solar output fluctuations can attribute the temperature changes to the sun without additional feedback mechanisms.
As far as migration of the bubbles. It is quite possible that there is a local effect of migration and homogenization of the bubbles (both up and down). But, this would be over a finite span of years. This would lead the CO2 (gaseous) to be found at different levels than the Deuterium (DHO) in ice. I believe that the current theories is that the migration/homogenization occurs over a period of less than 100 years or so. Has anybody studied Deuterated Methane or 18O as bound to carbon dioxide (C18O16O) which should have a closer association with the CO2 concentration in the ice. Of course, sample size might be an issue.
One of the problems with the CO2 theories has to do with the delays. A brief delay of CO2 increase following the temperature increases could be easily explained by feedback mechanisms as well as the migration/homogenization of the bubbles. Changes in the evaporation of Deuterated water may also have a quicker response to sea surface temperature changes than the release of CO2, some from deep ocean levels.
However, as the temperature falls, the CO2 often remains high for an additional 1000 or more years. If the CO2 is responsible for maintaining high temperatures, it is difficult to explain how the temperature can fall substantially before the CO2 concentrations fall. I think this is one of the major problems with the theories of CO2 driving paleontological temperatures.
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Hi CliffordK (pardon my ignorance but are you one of the “experts” who responds to questions here or just a blogger like I am?), thanks for spending the time responding to my question/comment. You say “You bring up a lot of issues.” but I thought that my very first paragraph here was explicit about the one issue that I was raising as my main question, i.e. “why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice”?
I am not asking about the causes of changes in atmospheric CO2 concentration over time or how paleoclimatologists guess at these. My interest is in the changes in composition of air that originally was collected in snow flakes from the atmosphere, carried to earth then gradually compressed into ice by falls of further snow until it became “trapped” (or “sealed”) in air pockets when the pores in those pockets and the channels connecting them approached the size of the individual air molecules.
You seem to have missed the point of my specific question completely because you make no mention of the molecular diameter of any of the different gases found in the atmosphere either now or millions of years ago. In my ignorance I was not aware that Deuterium was of interest in paleoclimatology other than as an aid to estimating how temperature changed in the past. Although thermal fractionation is a factor to be taken into consideration when looking at the extent to which the composition of the air in ice is distorted over time, this is no more relevant to my question than is gravitational fractionation.
My question is solely about size-dependent fractionation, not about any positive feedback mechanism, such as assumed by the supporters of the CACC doctrine. I am not talking about local or other “ .. migration of the bubbles .. ” but of migration of the individual molecules of the smaller air components such as CO2 after the pores in the walls of the air pockets and the channels that interconnect them have been compressed to a comparable size, too small for the larger molecules like N2, O2 and CH4 to pass through them. I obviously had not made that clear in my earlier comments or in the articles/comments to which I linked.
If that isn’t clear enough then please take a look at the animation ( but imagine that the bubble is an air pocket in an ice sheet approaching close-off, with all excepting one pore closed to all molecules (CO2 included). Imagine also that the hole size of that single pore is just larger than 0.33nm (the kinetic diameter of CO2) and that the red balls are CO2 molecules (N2, O2 and CH4 molecules present but not shown because they can’t escape but are still bouncing around inside in far larger quantities than CO2). Also imagine that the pore is not giving access to an empty space as shown but access to an equally small channel linking to another similar air pocket in a chain of such air pockets. Does that very simplified picture of the structure within the ice/firn help to clarify the basis of my main question? Does that very simplified picture of the structure within the firn/ice help to clarify the basis of my main question?
The secondary question that I put to The Naked Scientists about Ian Stewart’s experiment with a candle should be quite straight forward.
Best regards, Pete Ridley
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For some reason it's not letting me quote you so I'll have to do it the old fashioned way:-
Wiybit, you have summarised reasonably well the basic question that Jaworowski et al. raised back in 1992 in their paper “Do glaciers tell a true atmospheric CO2 story?”
Thankyou Pete, I was half dreading someone moaning about asking questions.
but they covered about 20 processes that could distort the composition of residual air extracted from “sealed” pockets within ice cores. My specific question relates to only one, preferential fractionation over decades, centuries or even millennia of CO2 and other gases that have smaller kinetic diameters than do N2, O2, Ar or CH4.
I take it you mean, that over time CO2 moves in a different way to the other elements, potencially distorting the figures even more. Sorry to use a more common language but I find laymans terms are eaier to understand.
The researchers than I mentioned in my first comment ignore kinetic diameter
If that is true, I do not know if it is, but if that is true, potencially all the current thinking is based on incorrect research. Are you sure they do not have a system to try and figure out where the co2 has moved from? and then compensate, although personally thinking about it, if they did that- that appears to me to be an activity in guess work.
and use collision diameter,
So is that the system they use to compensate? The gases movement, a brief search tells me:-
http://dictionary.reference.com/browse/collision+diameter
"collision diameter
–noun Physics .
the distance between the centers of two colliding molecules when at their closest point of approach."
I suppose they are working under the idea that as ice forms the elements like Co2 collide, and therefore move into the pockets they do, in a certain way, that however does not take into consideration of movements after the fact.
I think I see your point.
which I hypothesise is not appropriate when the diameter of pores within and the channels that link ice air pockets approach the size of those smaller molecules as the ice is reaching the final stages of compression to a state where the air pockets become “closed off”.
But what does that really mean that the Co2 levels were highier than they think, as more moved upwards and escaped? or that we just cannot be sure?
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Too long, didn't read
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BenV(alsler?) I’ve checked up on your background and looked up some of your previous comments. The only comment that I found of interest was your response to a question by one neilep who asked on 31/01/2008 @ 02:05:41 “So, how does a climate model get created ?...do they just use the last few hundred years of weather records and data and average it all out or is it a tad more complicated than that ?...and how accurate are they ?”
I found your response less than inspiring. “Basically, you make a weather simulator (if windspeed=x, direction=y, then Z happens - but about a millionfold more complicated) and then plug real data into it. If the outcome of your 'simulator' consistently matches the observed changes in climate over a given timescale, you have a working climate model. If it fails to predict what you already know to have happened, then you need to tweak your model. When your simulator can accurately predict past changes based on past data, you can assume that it may accurately predict future events based on current data.” (http://www.thenakedscientists.com/forum/index.php?topic=12826.msg352094;boardseen).
If that and your background are anything to go by you probably have nothing substantial to offer regarding migration of molecules through porous media, but I could be wrong. Your training and experience in zoology and science communications probably means that you have little more understanding than I have of molecular dynamics. Don’t take that as an insult as it isn’t meant that way.
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One thing that you could probably help me out with is in reference to an experiment presented by the BBC’s Ian Stewart and available on U-tube ( It was linked to by climate science “expert” Professor Mike Palin, Otago University during our exchanges on the issue of CO2 fractionation a month or so ago (http://hot-topic.co.nz/the-twilight-zone/). Stewart’s attempt to persuade us through that demonstration that CO2 traps a lot of IR requires further scrutiny. I am always suspicious of anything that the BBC or its minions (like Stewart) say about climate change because of the fact that there is a possible vested interest n supporting the CACC doctrine – pension scheme investments.
I puzzled over what that demonstration really tells us. On investigation, Wikipedia (http://en.wikipedia.org/wiki/Thermographic_camera) advises that the colour picture from an infrared camera is not true but pseudo colour, where the colours represent intensity. So when Steward shows us that candle turning more and more blue what is he really demonstrating. In my humble opinion (I’m not a scientist but a retired Chartered Electrical Engineer) he may simply have verified that the candle gets colder and colder as the CO2 that he is pouring into the tube replaces the O2 upon which the candle depends to keep burning brightly (highest intensity). As most of us would expect, the O2 in the tube is depleted and the candle glows less and less brightly (getting cooler) until it goes out. Stewart’s presentation was cut short to ensure that we didn’t see it go out. Well, that’s my conspiracy theory anyway. As always I’m open to persuasion that I am wrong, so if you can repeat that experiment but this time use N2 instead of CO2 and show that the change in colour is different then I might accept that the experiment was demonstrating IR absorption by CO2 – but I’m a sceptic so I doubt that you’ll be able to because the colour change will be identical.
Best regards, Pete Ridley
I don't recall claiming any expertise in migration of molecules through any medium, so it's no surprise you find me lacking in that arena. My response to Neil was a general answer to a question from a lay person - not intended to inspire anyone, merely answering the question in broad, accessible terms.
I can't really comment on Ian Stewart's demonstation, as with most TV science there are lots and lots of details left out. But I've had a look for you and have a couple of comments:
It being a false colour image is irrelevant unless someone is changing the colours throughout the experiment, or is set up to give automatically changing contrast. It may make a small change look large, or vice versa - we can't know without the details.
Am I right in assuming that your interpretation involves having the candle inside the tube, exposed to the CO2 he's releasing? As far as I can tell, the tube is sealed off from the candle (there seems to be a membrane of sorts in place, but I don't know where the air is venting out. Had he placed the candle inside the tube it certainly would have been extinguished by the CO2 - but he's showing radiation from a candle traveling through a sealed and separated tube of CO2.
The CO2 conc in that tube may be ridiculously high, so there's every chance that this still doesn't really show us anything useful, but it does seem to be a good demonstration of CO2 being opaque to IR radiation. I think you may be wrong about replicating the experiment with nitrogen - as the vast majority of the air in that tube is nitrogen anyway, the change in the tube would be minimal, and I doubt there would be any colour change.
I don't think you should worry about bias at the BBC, it's a huge organisation and not everyone involved cares about pensions. We broadcast on the BBC and have never had any editorial instruction from above, I suspect there are many other similar teams.
By the way, my original comment about your question was not intended to be rude - I had hoped it would act as a catalyst for you to summarise your ideas, and hopefully avoid responses like this one:
Too long, didn't read
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Wiybit, your comment today at 12:12:30 shows that you pretty well understand my hypothesis. Let me just expand a little on it and clear up a few misunderstandings, but please bear in mind that what I describe is only one of several different process that distort the composition of air “trapped” in ice. According to Professor Hartmut Frank, these processes start from the time that the snow begins collecting air from the atmosphere.
The first point is that collision diameter seems to me to be relevant where the distance travelled by a molecule before a collision with any other molecule can occur is large compared with the size of the molecules involved. This is from the top of the ice sheet covered in highly porous fresh snow down to a level in the firn well before the eventual “close-off” of the air pockets, under which circumstances the laws of Fickian diffusion apply.
As “close-off” is approached (in the Antarctic after many decades of snow build-up) there will come a time when the space available for molecular movement is of the same order as the diameter of the molecules, where collision diameter is irrelevant and kinetic diameter becomes significant. At that level only smaller molecules will be able to move through the ice, hence air pockets will be depleted in those smaller gases. This process is recognised by the paleoclimatologists and their models take it into consideration. What they do not seem to consider is that it is the kinetic not collision diameter that is appropriate at this stage.
For many of the gases that make up the atmosphere there is little difference between collision and kinetic diameter, as seen in the listing below, but for CO2 this is not the case. Consequently, as the ice is compressed and pressure builds up in the pockets the CO2 molecules (and any smaller ones) escape from the pockets and move down the pressure gradient towards the surface, long after the larger gases like N2, O2, Ar and CH4 are trapped. Thus when the air extracted from ice cores is analysed it shows a lower concentration of CO2 than that which existed in the original atmospheric air at the time the falling snow brought it down to the ice sheet surface.
Quickly comparing collision* v kinetic** diameter (in Å) for the molecules of atmospheric gases of interest to paleo-climatologists, N2 (3.8 v 3.6), O2 (3.5 v 3.5), Ne (2.8 v 2.8), CO2 (3.9 v 3.3), CO (3.7 v 3.8), CH4 (3.8 v 3.8) Ar (3.5 v 3.4), He (2.6 v 2.6), Kr (3.7 v 3.6), Xe (4.0 v 4.0).
* From “Fractionation of gases in polar ice during bubble close-off: New constraints from firn air Ne, Kr and Xe observations” by Jeffrey P. Severinghaus and Mark O. Battle, Table 1.
** From “VUV absorbing vapours in n-perfluorocarbons” by E. Albrecht, et al. Table 3.
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?
The researchers like Severinghaus, Huber, Bender, make no mention in their papers of kinetic diameter and have concluded from their research and modelling that there is a “magic” molecular diameter of about 3.6Å above which size-dependent fractionation does not ocurr. Because they only consider collision diameter they do not bother with CO2. I have asked Severinghaus if he has run his model using kinetic diameter but had no response.
Your interpretation “ .. that as ice forms the elements like Co2 collide, and therefore move into the pockets they do, in a certain way .. “ is as I see it incorrect. The air is drawn down to the ice sheet surface within falling snow and diffuses within the firn (along with some atmospheric air from above). As the firn is compressed the air pockets develop around the air already present there.
Finally, yes (in my opinion) as far as the original past atmospheric composition is concerned it does “ .. mean that the Co2 levels were highier than they think, as more moved upwards .. ”, but only to higher levels, not necessarily “ .. and escaped ..”, if by that you meant escaped from the ice sheet into the atmosphere.
BenV, maybe I have misunderstood what The Naked Scientists are trying to do. I was under the impression that the idea was to present proper science in a manner that was understandable to lay people but nonetheless well-informed and accurate. From what I have seen the impression is given that The Naked Scientists understand the science they discuss and they happily discuss climate science. I may be mistaken here but according to your ”About Us” page “The Naked Scientists are a media-savvy group of physicians and researchers from Cambridge University who use radio, live lectures, and the Internet to strip science down to its bare essentials, and promote it to the general public (http://www.thenakedscientists.com/HTML/about-us/).
The Naked Scientists are by no means silent about climate change and I can find no admission that the subject is beyond the group’s competence. On the contrary, the blog gives the impression of fully supporting the CACC doctrine. Here’s an example relevant to the question that I raise about “Another Hockey Stick Illusion?”. In 2007 the blog posted this statement “ .. In the last 800,000 years, carbon dioxide's always ranged between 180 ppm (parts per million) in the cold periods up to 300 ppm in the very warmest times. And at the moment, it's 380 ppm. So that's already 30% higher than it's ever been. And the only possible explanation for that is human activity. There's other evidence too. We can look at the isotopic structure of the carbon and it looks like stuff that's come from fossil fuels rather than from natural systems. Also we know how much stuff we're putting into the atmosphere and all the calculations work. We're contributing to the increase .. ” (http://www.thenakedscientists.com/HTML/content/interviews/interview/643/).
The caption under that beautiful picture of apparently isolated bubbles says “Figure 1: Air bubbles fixed in ice. These can tell us how gas concentrations have changed over thousands of years.” There is no hint of uncertainty there or in the other related statements and no challenge raised about it. BTW, it would be very helpful to have some dimensions on that picture to give a hint as to whether or not there could be tiny channels of about 0.36nm or less linking those bubbles. I have given links to comments that provide much better detail via SEM reconstructions if anyone is interested.
Am I being unreasonable to expect the Naked Scientists to be able to give me a convincing answer to my question? After all, claims that past atmospheric CO2 concentrations can be determined from air “trapped” in ice for millenia are not of recent origin. Am I wrong in thinking that you are one of those Naked Scientists? Can’t the Naked Scientists get an “expert” like Dr Eric Wolff from the British Antarctic Survey to respond to it?
If I come across as being a little irritated then it could be because I have tried very hard for over a year now to get a convincing answer from such “experts” but had no success whatever. Since you were the only Naked Scientist to respond to my question I assumed that you must be the most expert among you, hence my disappointment to find to the contrary when I checked your background. If I was being unfair in my comments then I apologise and hope that you can understand my reaction.
As for Madidus_Scientia’s comment today at 12:57:20, anyone who finds my contributions “Too long, didn't read” obviously has no interest in the subject. I’m pleased to see that at least one reader thought otherwise.
If the question is too hard for The Naked Scientists to answer then just let me know and I’ll take it elsewhere, although I will be very disappointed if “ .. a media-savvy group of physicians and researchers from Cambridge University” are stumped by it.
BTW, I think that the features provided to us commenters on this blog are great – congratulations to the Web designer.
Best regards, Pete Ridley
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Wiybit, your comment today at 12:12:30 shows that you pretty well understand my hypothesis. Let me just expand a little on it and clear up a few misunderstandings, but please bear in mind that what I describe is only one of several different process that distort the composition of air “trapped” in ice. According to Professor Hartmut Frank, these processes start from the time that the snow begins collecting air from the atmosphere.
Does snow collect air? i assume some particals could get trapped inside the snow flake structure, yet every flake is different and all would therefore(in theory) capture air molecules in different ways. Would there even be a way to figure an average amount captured if every snow flake is different? You would be left with possible ranges for each flake, and therefore a possible range for snow fall, I assume.
The first point is that collision diameter seems to me to be relevant where the distance travelled by a molecule before a collision with any other molecule can occur is large compared with the size of the molecules involved.
But how can you even know the starting point of a molecule? I sounds like a lot of guess work to me.
This is from the top of the ice sheet covered in highly porous fresh snow down to a level in the firn well before the eventual “close-off” of the air pockets, under which circumstances the laws of Fickian diffusion apply.
Looking it up fickian law relates to Mass Diffusivity or diffusion coefficient,
http://en.wikipedia.org/wiki/Mass_diffusivity
http://www.answers.com/topic/diffusion-coefficient
"The weight of a material, in grams, diffusing across an area of 1 square centimeter in 1 second in a unit concentration gradient. Also known as diffusivity."
looks to relate more to solids then gases.
As “close-off” is approached (in the Antarctic after many decades of snow build-up) there will come a time when the space available for molecular movement is of the same order as the diameter of the molecules, where collision diameter is irrelevant and kinetic diameter becomes significant.
I think you mean it's a multi-layered process.
At that level only smaller molecules will be able to move through the ice, hence air pockets will be depleted in those smaller gases.
Ice is a solid isn't it, I kinda think it's like as ice forms and compacts the gases are squezzed out, and if as you are suggesting gases can move through smaller gaps, then I suppose more would be squezzed out.
Going back to the part just before this: "a multi layered process", Ice is solid and gases are gases, two different actions.
This process is recognised by the paleoclimatologists and their models take it into consideration. What they do not seem to consider is that it is the kinetic not collision diameter that is appropriate at this stage.
but why do they ignore it? They either are ignorant of it, or for some reason feel it has no bearing, or plays to insignifcant a role to need to be accounted for. I assume again, but it sounds a bit strage for scientists to just ignore, a kinetic factor for no reason. What is the justifaction for ignoring it?
For many of the gases that make up the atmosphere there is little difference between collision and kinetic diameter, as seen in the listing below, but for CO2 this is not the case.
what is it about Co2 that makes it so different? Personally I think much of the man made co2 we have in the atmospere is comming from CO cabon monoxide, which when realesed from burning fuels etc grabs an oxygen and so forms Co2.
Consequently, as the ice is compressed and pressure builds up in the pockets the CO2 molecules (and any smaller ones) escape from the pockets and move down the pressure gradient towards the surface, long after the larger gases like N2, O2, Ar and CH4 are trapped.
Implies Co2 is a smaller molecule, yet surely it's bigger then 02? What missing?
Thus when the air extracted from ice cores is analysed it shows a lower concentration of CO2 than that which existed in the original atmospheric air at the time the falling snow brought it down to the ice sheet surface.
Thankyou, your saying the Co2 is/was highier then they think. Yet could it not also be the case that the cores have trapped Co2 from the ice below them? Can we trust the findings at all really?
Quickly comparing collision* v kinetic** diameter (in Å) for the molecules of atmospheric gases of interest to paleo-climatologists, N2 (3.8 v 3.6), O2 (3.5 v 3.5), Ne (2.8 v 2.8), CO2 (3.9 v 3.3), CO (3.7 v 3.8), CH4 (3.8 v 3.8) Ar (3.5 v 3.4), He (2.6 v 2.6), Kr (3.7 v 3.6), Xe (4.0 v 4.0).
* From “Fractionation of gases in polar ice during bubble close-off: New constraints from firn air Ne, Kr and Xe observations” by Jeffrey P. Severinghaus and Mark O. Battle, Table 1.
** From “VUV absorbing vapours in n-perfluorocarbons” by E. Albrecht, et al. Table 3.
Note the difference for CO2.
It's .6 compared to 0, 0.2 or 0.1 with the others, why does it have such variation?
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?
Strange he is lighter than Co2, yet Co2 moves more in ice, because it's smaller- fairly clear. So then why does o2 move less then Co2? O2 is O bonded with another O, so maybe the bond structure causes the 02 molecule to take up more space compared to the two double bonds of C02- what do think, that would make sense to me?(I have looked into that area a little Methanes etc)
The researchers like Severinghaus, Huber, Bender, make no mention in their papers of kinetic diameter and have concluded from their research and modelling that there is a “magic” molecular diameter of about 3.6Å above which size-dependent fractionation does not ocurr. Because they only consider collision diameter they do not bother with CO2. I have asked Severinghaus if he has run his model using kinetic diameter but had no response.
Maybe it's too complicated, and add too many varibles.
Your interpretation “ .. that as ice forms the elements like Co2 collide, and therefore move into the pockets they do, in a certain way .. “ is as I see it incorrect. The air is drawn down to the ice sheet surface within falling snow and diffuses within the firn (along with some atmospheric air from above). As the firn is compressed the air pockets develop around the air already present there.
Finally, yes (in my opinion) as far as the original past atmospheric composition is concerned it does “ .. mean that the Co2 levels were highier than they think, as more moved upwards .. ”, but only to higher levels, not necessarily “ .. and escaped ..”, if by that you meant escaped from the ice sheet into the atmosphere.
Yes, I meant escaped into the atmosphere. From what you have said I'm not sure if you could really say either way.
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BenV, thanks for acknowledging that you aren’t competent to give an answer to that very significant but rather scientific “ .. topic in hand .. ”, the validity of attempts to reconstruct past atmospheric CO2 content from air allegedly trapped in ice. Thanks also for trying to give an answer to the other relatively simple question that I slipped in here regarding what is demonstrated by that CO2 experiment carried out by Iain Stewart. The answer you gave to that question, like my air-in-ice one, also gives a fair indication of how competent The Naked Scientists are with regard to the very important scientific debate raging presently around the Catastrophic Anthropogenic Climate Change (CACC) doctrine.
I repeat that simple “What does Iain Stewart's "CO2 experiment" Demonstrate ” question in a new post (http://www.thenakedscientists.com/forum/index.php?topic=38723.new#new) because I do not wish to distract people from the much more important scientific issue I am querying here, but wonder if The Naked Scientists up to the task. Maybe someone among your associated “ .. media-savvy group of physicians and researchers from Cambridge University .. ” can respond to this "Another Hockey Stick Illusion"? question here.
I have tried to simplify the Ian Stewart experiment question for the benefit of people like Madidus_Scientia, although I suspect that once again it may be long for him/her and that he/she won’t be bothered reading it or my response to your answer (propagandists find it easy to persuade the gullible that black is white because many adopt a similar attitude).
Wiybit, I'll get back to you on the ponts that you raised.
Best regards, Pete Ridley
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Just to assit you a bit Pete with Questions to individual posters, Using the quote opition makes it easier to see, BenV will have to read half of your last post before he'll notice the part for him.
If you use the quote option it helps to show what you are replying to. It can be a hassel multi quoting in the same post, and it is easier to just write it all out, just to say if you do put everything in one post, using something to show a change of recipient, makes it easier for others to follow.
Thanks for the reply by the way, and I agree the forum set up is pretty good.
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Wiybit, I'll get back to you on the ponts that you raised.
Yeah cool, You posted while I was writing the last post I made to you.
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BenV, thanks for acknowledging that you aren’t competent to give an answer to that very significant but rather scientific “ .. topic in hand .. ”, the validity of attempts to reconstruct past atmospheric CO2 content from air allegedly trapped in ice. Thanks also for trying to give an answer to the other relatively simple question that I slipped in here regarding what is demonstrated by that CO2 experiment carried out by Iain Stewart. The answer you gave to that question, like my air-in-ice one, also gives a fair indication of how competent The Naked Scientists are with regard to the very important scientific debate raging presently around the Catastrophic Anthropogenic Climate Change (CACC) doctrine.
My answer to that secondary question was perfectly valid and highlighted your clear misinterpretation of the demonstration. It would seem to suggest that I am more competent, and less biased, than yourself in the interpretation of television science demonstrations, would it not?
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I would also like to draw question to your motives for posting in this forum - you seem far more keen to make implications about the Naked Scientists competence than to actually discuss the science in question. You also seem keen to attack people - I personally feel attacked by your language, and your implication about Madidas can easily be seen as, at the least, impolite.
I appreciate that you may have not received an adequate answer to a question you have put to many scientists, and am pleased and honoured that you would come here to discuss it. I'm also very sorry if no-one here can answer the question to your satisfaction either. Perhaps if you were to email it in to the show we would have an opportunity to put it to an expert in our next climate themed show?
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Hi Wiybit, as I have just said to rosy on my “What does Iain Stewart's "CO2 experiment" Demonstrate” post (http://www.thenakedscientists.com/forum/index.php?topic=38723.new#new), I prepare comments using Word so if you can advise me how I embed quotes from here into my word document so that when I copy it all into these blog pages they appear in the way you’d like than I’ll try to accommodate you.
In you comment today at 16:21:39 you ask “ .. Does snow collect air? .. ”. As I understand it fallen snow has a density of anything between roughly 10% and 30% that of water, so falling snow takes a lot of atmospheric air down to the top of an ice sheet. At the simplest level, that falling snow forms a very porous blanket on the ice sheet and is gradually compressed to what is referred to as firn by the paleoclimatologists, which is granular but still porous. Eventually the firn is compressed to become “solid” ice which still contains isolated pockets of air. There is a good description in Wikipedia (http://en.wikipedia.org/wiki/Snow) and there are some good SEM reconstructions at. Fig 3 of http://www.igsoc.org/journal/56/195/j09j041.pdf.
You may find it worthwhile taking a closer look at the comments and links provided during my exchanges with Richard Cumming on the Climate Conversation “Fallen Snow” thread (http://www.climateconversation.wordshine.co.nz/2011/03/fallen-snow/). In my comment of March 26, 2011 at 7:34 am I link to some excellent sets of images at http://itia.ntua.gr/hsj/45/hysj_45_03_0357.pdf which are well worth spending time on.
You ask “ .. how can you even know the starting point of a molecule? I sounds like a lot of guess work to me .. ” and I can’t argue with that. The experts call it probabilities.
Must dash as the boss is calling. This should keep you going for a little while
Best regards, Pete Ridley
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Hi BenV, thanks for the suggestion about using (quote) and (/quote) in Word. I’ll try it now.
BenV, 15/04/2011 23:21:30 Pete, I think you should be able to put (quote) and (/quote) into your word document, but replace those brackets with square brackets. It won't say who the quote is from or when, but should at least appear...
Hi Madidus_Scientia, BenV asked .. What do Madidus' activities on other fora have to do with the topic in hand?
so let me just explain that I have this aversion to the use of false names. It comes from having seen too many CACC disciples and followers hiding behind them and hurling insults at us deniers. I always try to find out who I am exchanging opinions with. We all have our peculiarities, don’t we.
Hi Wiybit, regarding your 15/04/2011 16:21:39 .. I think you mean it's a multi-layered process.
I see the size-dependent fractionation and close-off processes as being “multi-layered” in space and time.
Your … Ice is a solid isn't it, I kinda think it's like as ice forms and compacts the gases are squezzed out, and if as you are suggesting gases can move through smaller, gaps then I suppose more would be squezzed out.
is getting there. Put simply, snow is also ice but, as I said before, has a density of as low as 0.2 that of water. As it is compacted it approaches a density of about 0.9 that of water. The remaining 0.1 is air, hence 10% of an ice berg is above water.
Regarding kinetic diameter you asked .. but why do they ignore it? They either are ignorant of it or some some reason feel it has no bearing, or plays to insignifcant a role to be accounted for. I assume, but it sounds a bit strage for scientists to just ignore, a kinetic factor for no reason. What is the justifaction for ignoring it?
. You are repeating the question that I have been putting to the paleoclimatologists for more than a year now and The Naked Scientists three days ago in my first post above. None have answered it yet. It is worth noting that experts in the field of gas purification, such as in the energy and pollutant extraction industries use kinetic, not collision, diameter. I have made this point on numerous occasions to the “experts” and none have explained why they choose to ignore the smaller kinetic diameter of CO2 compared with N2, O2 CH4 and Ar. That’s odd, don’t you think?
.. what is it about Co2 that makes it so different? Personally I think much of the man made co2 we have in the atmospere is comming from CO cabon monoxide, which when realesed from burning fuels etc grabs an oxygen and so forms Co2 ..
. I’m would expect that this “ .. media-savvy group of physicians and researchers from Cambridge University .. ” (http://www.thenakedscientists.com/HTML/about-us/) called The Naked Scientists should be able to offer a valid answer to that question. I think that you may be way off-beam with your hypothesis about CO, considering that when hydro-carbon fossil fuels are burnt the main products are H2O and CO2, with CO being comparatively minor.
.. Implies Co2 is a smaller molecule, yet surely it's bigger then 02? What missing? ..
. In this context we are talking about size in terms of volume not weight (think of a balloon).
.. could it not also be the case that the cores have trapped Co2 from the ice below them? Can we trust the findings at all really? ..
. My hyp[othesis says “Yes” to part 1 and “No” to part 2.
Regarding the difference in collision and kinetic diamter .. Note the difference for CO2. It's .6 compared to 0, 0.2 or 0.1 with the others, why does it have such variation? ..
, again, there should be at least one of The Naked Scientists who can answer that question.
You seem to have completely missed the point of my mention of the He balloon by saying ..
Strange he is lighter than Co2, so Co2 moves more in because it's smaller fairly clear ..
. I was hoping that you’d realise that the reason the He-filled balloon collapses relatively quickly is because the balloon is a bit like those air pockets in firn – it has lots of tiny pores that are so small that He (0.26nm kinetic diameter) can escape more readily that the larger N2, O2 and Co2 molecules of the expelled air we puff into a balloon.
In saying of the scientists that I mentioned .. Maybe it's too complicated, and add too many varibles ..
you are effectively agreeing with Professor Jaworowski, who, as I’ve already told you, said “This is a highly specialized field of science. My impression is that it is a terra incognita for glaciologists”.
Finally you said of that CO2 that escapes from the air pockets and heads down the pressure gradient towards the surface .. Yes, I meant escaped into the atmosphere. From what you have said I'm not sure if you could really say either way .. [/quote. I ’m inclined to agree with that.
(I know, I still haven’t responded on Fickian diffusion. I need more time for that one, after all, I’m only a retired engineer).
May I just say how enjoyable it is exchanging opinions with you in the spirit of improving understanding rather than scoring points or pushing a particular doctrine. It’s a great shame that on most blogs that I get involved with it ends up simply being a battle by both sides to win an argument.
Best regards, Pete Ridley
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.. BenV 15/04/2011 22:32:12: .. I appreciate that you may have not received an adequate answer to a question you have put to many scientists, and am pleased and honoured that you would come here to discuss it. I'm also very sorry if no-one here can answer the question to your satisfaction either. Perhaps if you were to email it in to the show we would have an opportunity to put it to an expert in our next climate themed show? ..
.
I am not familiar with protocol at The Naked Scientists so please can you explain why I have to raise my question about “Another Hockey Stick Illusion?” separately by E-mail in order that The Naked Scientists .. would have an opportunity to put it to an expert in our next climate themed show? ..
. I have already put the question to The Naked Scientists so why do I need to put it again?
Best regard, Pete Ridley
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"The remaining 0.1 is air, hence 10% of an ice berg is above water. "
Nope.
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Hi Bored Chemist, come on, help out a poor layman with more than simply "nope".
How about using you superior knowledge to expand on your “Nope” something along these lines
.. water is one of the few substances that is slightly denser as a liquid than as a solid. This is why ice cubes float in water. .. Most icebergs actually contain a lot of air. Far from being the solid blocks of ice many people imagine, icebergs are riddled with billions of tiny, trapped air bubbles, giving the huge bergs their white appearance. .. icebergs are made from fresh water. Because of the dissolved salts in ocean water, it is denser than freshwater, adding bouyancy to the icebergs
(http://www.lifeslittlemysteries.com/why-do-icebergs-float-0261/).
Perhaps you’d like to put some figures to the contribution each of those makes towards lifting 10% of an ice berg out of the water. I don’t want to spend my time researching that as it is not really significant with regard to my main question here, but since you can’t respond to that one (too hard for you I guess) perhaps you can help Wiybit out a little. How’s about having a go at that question he has about Fickian diffusion?
Best regards, Pete Ridley
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Oh good grief!
Density of freshwater ice (such as that made from snow): 0.92 (without taking into account any airbubbles)
Density of surface seawater: 1.02-1.03
Expected proportion of iceberg above water level based on these figures: 1.02/0.92 = 1.11
So without considering the effect of the small air bubbles present in the ice, about 10-11 % of the iceberg is expected to float above the water. Elementary arithmetic, and a little bit of looking up numbers (I used wikipedia, other data sources are available).
Do you think a lump of ice composed of 10 % air bubbles by volume would be strong enough to withstand being pulled out of the ground with an ice-core drill? Seems rather unlikely to me. Ice is brittle stuff.
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You ask “ .. how can you even know the starting point of a molecule? I sounds like a lot of guess work to me .. ” and I can’t argue with that. The experts call it probabilities.
Most likly with a certain range, it's "slightly" better than guess work.
Hi Wiybit, regarding your 15/04/2011 16:21:39 .. I think you mean it's a multi-layered process.
I see the size-dependent fractionation and close-off processes as being “multi-layered” in space and time.
I see the complication your refereing to, but at the same time are not all psyical processes, both temperal and spacial?
Your … Ice is a solid isn't it, I kinda think it's like as ice forms and compacts the gases are squezzed out, and if as you are suggesting gases can move through smaller, gaps then I suppose more would be squezzed out.
is getting there. Put simply, snow is also ice but, as I said before, has a density of as low as 0.2 that of water. As it is compacted it approaches a density of about 0.9 that of water. The remaining 0.1 is air, hence 10% of an ice berg is above water.
Well if those figures are correct and 0.1 of 1 is air then 10% is air in the form of pockets sandwiched between the ice. But I think there might be a mix up, at 0.2 what is the air make of of a flake?
I mean your saying that as ice compacts it gains a density of 0.9 compared to 1 of water, but why is the 0.1 difference made up by air? Could it not be 0.9 and 0,2 air? Or are you saying that as a liquid cannot be condensed, proportionally one for one, the water to ice is 0.9 ice and so 0.1 gas to 1 water centermeter cubed(for example)?
Regarding kinetic diameter you asked .. but why do they ignore it? They either are ignorant of it or some some reason feel it has no bearing, or plays to insignifcant a role to be accounted for. I assume, but it sounds a bit strage for scientists to just ignore, a kinetic factor for no reason. What is the justifaction for ignoring it?
. You are repeating the question that I have been putting to the paleoclimatologists for more than a year now and The Naked Scientists three days ago in my first post above. None have answered it yet. It is worth noting that experts in the field of gas purification, such as in the energy and pollutant extraction industries use kinetic, not collision, diameter. I have made this point on numerous occasions to the “experts” and none have explained why they choose to ignore the smaller kinetic diameter of CO2 compared with N2, O2 CH4 and Ar. That’s odd, don’t you think?
Yes it is odd but atleast we get to the crux of your question.
.. what is it about Co2 that makes it so different? Personally I think much of the man made co2 we have in the atmospere is comming from CO cabon monoxide, which when realesed from burning fuels etc grabs an oxygen and so forms Co2 ..
. I’m would expect that this “ .. media-savvy group of physicians and researchers from Cambridge University .. ” (http://www.thenakedscientists.com/HTML/about-us/) called The Naked Scientists should be able to offer a valid answer to that question. I think that you may be way off-beam with your hypothesis about CO, considering that when hydro-carbon fossil fuels are burnt the main products are H2O and CO2, with CO being comparatively minor.
I possibly am but at the same time CO is released from every car, even if it is minor per individual car, it will not be for all of them.
.. Implies Co2 is a smaller molecule, yet surely it's bigger then 02? What missing? ..
. In this context we are talking about size in terms of volume not weight (think of a balloon).
.. could it not also be the case that the cores have trapped Co2 from the ice below them? Can we trust the findings at all really? ..
. My hyp[othesis says “Yes” to part 1 and “No” to part 2.
Regarding the difference in collision and kinetic diamter .. Note the difference for CO2. It's .6 compared to 0, 0.2 or 0.1 with the others, why does it have such variation? ..
, again, there should be at least one of The Naked Scientists who can answer that question.
You seem to have completely missed the point of my mention of the He balloon by saying ..
Strange he is lighter than Co2, so Co2 moves more in because it's smaller fairly clear ..
. I was hoping that you’d realise that the reason the He-filled balloon collapses relatively quickly is because the balloon is a bit like those air pockets in firn – it has lots of tiny pores that are so small that He (0.26nm kinetic diameter) can escape more readily that the larger N2, O2 and Co2 molecules of the expelled air we puff into a balloon.
But then that is contradictory, if Co2 moves more readily than He, He is smaller and lighter, so why would Co2 be under a greater kinetic effect in ice than He as you have suggested?
In saying of the scientists that I mentioned .. Maybe it's too complicated, and add too many varibles ..
you are effectively agreeing with Professor Jaworowski, who, as I’ve already told you, said “This is a highly specialized field of science. My impression is that it is a terra incognita for glaciologists”.
Finally you said of that CO2 that escapes from the air pockets and heads down the pressure gradient towards the surface .. Yes, I meant escaped into the atmosphere. From what you have said I'm not sure if you could really say either way .. [/quote. I ’m inclined to agree with that.
(I know, I still haven’t responded on Fickian diffusion. I need more time for that one, after all, I’m only a retired engineer).
May I just say how enjoyable it is exchanging opinions with you in the spirit of improving understanding rather than scoring points or pushing a particular doctrine. It’s a great shame that on most blogs that I get involved with it ends up simply being a battle by both sides to win an argument.
Best regards, Pete Ridley
Yeah, I know that situation well.
Peace
P.S. As a last point there is the "quote" Box in the top right corner of each post a person makes.
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I confess I'm not much of a scientist, but I have to admit I find it interesting that anyone who is unaware of why ice cubes float in water might think they are qualified to call into question the scientific credentials of anyone else.
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Hi rosy, thanks for applying your mathematical and “Google” talents to the question of how much air there might be in an iceberg, although you stopped before you arrived at an answer. How about developing your analysis a little further by taking into consideration the difference between the “ .. average density of seawater at the ocean surface .. ” offered by Wikipedia (http://en.wikipedia.org/wiki/Seawater) and the actual density of seawater surrounding an iceberg. That will be much more useful in aiding our understanding of how “solid” the ice in an iceberg really is.
Your Do you think a lump of ice composed of 10 % air bubbles by volume would be strong enough to withstand being pulled out of the ground with an ice-core drill? Seems rather unlikely to me. Ice is brittle stuff
suggests that you haven’t spent much time researching ice cores or much time trying to understand my question about “Another Hockey Stick Illusion?”. As you may not have realised, my question here relates mainly to the process of size-dependent fractionation occurring in the firn, not in the “solid” ice (although there is further fractionation there too). According to your speculative comment it should not be possible to remove ice cores from firn but I am not aware that there is a problem there. Maybe you can provide a link to evidence supporting your opinion on this.
A Google search will take you to some interesting papers, including pictures, which should clarify this for you. Yes, those cores a brittle and need very careful handling, but those ice core experts are able to extract long cores even from the much less dense firn above that solid ice. They are so clever at it .. Using the PICO (Polar Ice Coring Office) lightweight auger, a 31 m long firn core was drilled adjacent to the cane farm at GD03. The GD03 core represents 55 years of annual snow-accumulation increments which were interpreted from the combined stratigraphic analyses of density, oxygen-isotope and visible layering. A vertical profile of density .. shown in Figure 2 ..
, (http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/henry.html Page 385 of the source document). Perhaps you should have a good look at the density graph in Fig. 2 before responding.
Hi Wiybit, I was disappointed that none of this “ .. media-savvy group of physicians and researchers from Cambridge University .. ” have tried to help you out on your .. fickian law .. looks to relate more to solids then gases ..
. I’d love some help on the relevant laws of diffusion too and since none of The Naked Scientists seems to be able to help I took the opportunity of chatting about that (and my question about “Another Hockey Stick Illusion?”) with Professor Andrew White who was visiting us this weekend.
Dr. White is Professor and Director, Center for High Energy Physics Research and Technology, Department of Physics, The University of Texas at Arlington and has been a Professor of Physics there for 20 years (http://www.uta.edu/physics/main/faculty/). During that time he has been involved in research at CERN so I thought that he could perhaps save me some time digging up an answer for you. As Bored chemist might say “Nope”. His response was “I’m not up on diffusion” so I had to try elsewhere. Does this help Fick's Law: The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane and inversely proportional to the thickness of the membrane. Combined with the diffusion rate determined from Graham's law, this law provides the means for calculating exchange rates of gases across membranes
(http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/henry.html)?
Geezer, I hope that you were able to spot the point I was making about Dr. White's response to my question. I’ll also mention that I discussed your .. I find it interesting that anyone who is unaware of why ice cubes float in water might think they are qualified to call into question the scientific credentials of anyone else ..
and you’ll also find it interesting that he does not share you implied opinion. His appears to be completely opposite to yours. Why not drop him an E-mail (awhite@uta.edu) and ask him. After all unlike either of us (and many of those who support the CACC doctrine), he is a highly respected scientist.
Best regards, Pete Ridley
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Hi Wiybit, I was disappointed that none of this “ .. media-savvy group of physicians and researchers from Cambridge University .. ” have tried to help you out on your .. fickian law .. looks to relate more to solids then gases ..
.
Seriuosly you shouldn't encourage them(if you get me). [:)]
I’d love some help on the relevant laws of diffusion too and since none of The Naked Scientists seems to be able to help I took the opportunity of chatting about that (and my question about “Another Hockey Stick Illusion?”) with Professor Andrew White who was visiting us this weekend.
Andrew is Professor and Director, Center for High Energy Physics Research and Technology, Department of Physics, The University of Texas at Arlington and has been a Professor of Physics there for 20 years (http://www.uta.edu/physics/main/faculty/). During that time he has been involved in research at CERN so I thought that he could perhaps save me some time digging up an answer for you. As Bored chemist might say “Nope”.
Yeah BC can be slightly funny at times, but generally he's ok, when not going on about dance routines and stuff, and trying to catch you out(so he can laugh at you) [:)] Completly said it light hearted jest BC so don't start.
His response was “I’m not up on diffusion” so I had to try elsewhere. Does this help Fick's Law: The net diffusion rate of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane and inversely proportional to the thickness of the membrane. Combined with the diffusion rate determined from Graham's law, this law provides the means for calculating exchange rates of gases across membranes
(http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/henry.html)?
Thanks, I'll check it out. Yet you still haven't said what it is about Co2 that causes it to act so differently to the other elements, surely HE should move more, in ice if it's smaller and lighter?
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suggests that you haven't spent much time researching ice cores or much time trying to understand my question about “Another Hockey Stick Illusion?”.
Wrong, I've spent no time at all researching ice cores or trying to understand your question. I'm not an expert, and I certainly don't have sufficient free time to do the necessary research, so I leave it to other people.
I'm going to be rude, now. I usually try not to be too rude online, but on this occasion I am completely out of patience, both with your approach to science and with your personal demeanour.
Moreover, I certainly would not trouble to put in all that legwork to answer a question from you, Pete, because although your initial ignorance of what causes ice to float is (just about) understandable, although surprising in someone who claims to have been taking an interest in climate change issues for some time, your apparent failure to make even a token effort to understand what's actually going on by making a few back-of-the-envelope calculations of your own leads me to believe that even if I understood, and explained, it wouldn't improve your understanding because you are more interested in a quasi-religious fight against "the climate change establishment" than in obtaining any level of personal understanding of the field in order to be able to make an intelligent contribution. This is for exactly the same reason I don't bother to argue with creationists about evolution.
Now, if anyone is actually interested (and I acknowledge this isn't rocket science...), the densities of water at different temperatures are given here:
http://www.sfu.ca/physics/ugrad/courses/teaching_resources/demoindex/fluids/fl2b/density.html
The density of pure water is, at least, 0.998 (density at 0 oC, density at 4 oC is a little higher. If the ice (at 0.92) were floating entirely on its own (pure) melt-water, it would float with 8.5 % of its volume above the water. But the water is not pure, it is mixing all the time with salt sea-water, so it might be fractionally less dense than the average surface water density (1.02-1.03), but the absolute lower limit is that 8.5 % will float above the surface, in reality it will be more, and that's entirely without considering the effects of air bubbles.
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Now, if anyone is actually interested (and I acknowledge this isn't rocket science...), the densities of water at different temperatures are given here:
http://www.sfu.ca/physics/ugrad/courses/teaching_resources/demoindex/fluids/fl2b/density.html
The density of pure water is, at least, 0.998 (density at 0 oC, density at 4 oC is a little higher. If the ice (at 0.92) were floating entirely on its own (pure) melt-water, it would float with 8.5 % of its volume above the water. But the water is not pure, it is mixing all the time with salt sea-water, so it might be fractionally less dense than the average surface water density (1.02-1.03), but the absolute lower limit is that 8.5 % will float above the surface, in reality it will be more, and that's entirely without considering the effects of air bubbles.
Rosy, doesn't water compact as it frezzes? shouldn't the density be highier at 0, as the atoms are more compacted, than at 4 oC?
If it is a little higher density at 4 oC than at 0oC that suggests the water compacts as it warms. Doesnt it? Or is it that as the ice melts or starts to, air is realesed and the water comes closer together? That would work from Ice to water but not the other way round.
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Rosy, doesn't water compact as it frezzes? shouldn't the density be highier at 0, as the atoms are more compacted than at density at 4 oC?
No. Water doesn't compact as it freezes, and the maximum density of water occurs at 4 oC. Water's funny stuff. I'm not going to try to explain in any detail here, because it needs diagrams, but there's lots of information on the internet about this. For example this page: http://kentsimmons.uwinnipeg.ca/cm1504/water.htm
On a more hands-on level, consider an ice cube made in your freezer to cool a drink. Not being made from snow, it doesn't contain (a significant number of) bubbles, and yet it floats. If you think about it, I'm pretty sure this is something you know and understand! The density of ice is, inherently, less than that of water at the same temperature. Equally, if you close up a bottle full to the top with water at room temperature (using a plastic bottle is important for safetly..), and freezing the water, the bottle will split as the water expands on forming ice... which shows you that the same mass of water takes up more space (is less dense) when frozen than as a liquid.
Incidentally, if ice didn't float, and if the coldest water didn't float on top of water at 4 oC, then the coldest water would sink to the bottom of lakes and rivers, and they'd freeze from the bottom up. That would mean that instead of a layer of ice over liquid water the whole of the lake would freeze, which would kill the fish and other animals living in the water whereas in reality they can hide in the relatively warm water at the bottom until spring.
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Hi Wiybit, sorry that I didn’t have time to respond straight away to the points you raised on 16/04/2011 @ 20:48:50 and today @ 13:40:20. I don’t want to get distracted from the focus of my question about “Another Hockey Stick Illusion?”, i.e. why the “experts” ignore kinetic in favour of collision diameter. If it’s OK with you I’ll leave it to the Naked Scientists to respond to any that I see as a side-issue. You may have to raise such questions separately in order to attract their attention.
.. Seriuosly you shouldn't encourage them(if you get me) ..
is not the reason that I joined this blog. I will do my utmost to encourage The Naked Scientists to offer their expertise where it relates to my question. I’m very disappointed that I’ve had nothing from them yet and the appropriate laws of molecular dynamics covering the movement of atmospheric gases in firn are certainly relevant.
.. BC can be slightly funny at times, but generally he's ok, when not .. trying to catch you out(so he can laugh at you) ..
is fine for anyone who has come here to be amused but I’m not in that category. I’m here to learn as much as I can about the science relevant to my question. So far the only person on this blog to help improve my understanding is you through your questions.
Regarding .. you still haven't said what it is about Co2 that causes it to act so differently to the other elements, surely HE should move more, in ice if it's smaller and lighter? ..
one day I may be able to fully answer the first part with confidence. All that I can say for the moment is that it is something to do with the bonding between the one C and two O atoms that make up a molecule and the interaction of each molecule with other molecules (N2, O2, Ar, CH4, H2O, etc. Why not put that question to The Naked Scientists.
As for the second part, He, being smaller even than CO2, does experience size-dependent fractionation, as described in the paper “Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements” by Huber et al (http://icebubbles.ucsd.edu/Publications/Huber_closeoff_EPSL2006.pdf).
It is worthwhile looking more closely at that paper, because as well as answering your question about He directly, it expands on my earlier comment (on 14/04/2011 21:38:13) about Huber, Severinghaus (one of the co-arthors) and that magic 0.36nm molecule diameter Abstract .. For smaller gas species (mainly He and Ne) the fractionation factors are linearly correlated to the molecule size, whereas for diameters greater than about 3.6 Å the fractionation seems to be significantly smaller or even negligible ..
Note that Table 2 presents the molecular diameters used in their model and the close-off fractionation factor it produced for 8 of the atmospheric gases, including CO2 and He, but also note that those diameters are collision, not kinetic. Fig. 8 presents a useful graph of 7 of those computer-modelled close-off fractionation factors, with He down at the bottom of the curve, but note which one is missing, dear old CO2. I mentioned in that earlier comment that I had asked Severinghaus why he used collision rather than kinetic diameter and if he had tried his model using CO2’s 0.33nm kinetic diameter instead of its 0.39nm collision diameter. As I said, he chose not to respond directly to those questions. Have a guess where CO2 would have been if he had used kinetic diameter, which I hypothesise is the appropriate measure.
That is why I challenge the conclusion that .. Close-off fractionation factors for different gases depend strongly on the diameter. The mass of the molecule is less important, since the effect on isotope ratios is very low. The critical size of about 3.6 Å seems to be an upper limit up to which molecules fractionate during the close-off process in the firn. A possible explanation for this could be the diffusion of molecules through channels in the ice lattice. From our findings we believe that the effect of close-off fractionation is nonexistent or at least very small for isotope ratios and for large molecules, like Xe, Kr, N2, CO2, CH4, and N2O. This is an important confirmation for the integrity of polar ice cores as a climate archive of the ancient atmospheric composition of these gases ..
But I’m only a retired Chartered Electrical Engineer and Geezer reasonably says .. I find it interesting that anyone who is unaware of why ice cubes float in water might think they are qualified to call into question the scientific credentials of anyone else ..
That is why during the past year I have requested help from “experts” like Severinghaus, Alley, Bender, etc. etc. etc. and now from this “ .. media-savvy group of physicians and researchers from Cambridge University .. ”, but I’m still not getting an answer.
BTW, that paper also gives figures for .. Firn density at surface [g/cm3] 0.40 0.32 .. Firn density at close off [g/cm3] 0.838 0.811 ..
which you (and others here) should find helpful.
Best regards, Pete Ridley.
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On a more hands-on level, consider an ice cube made in your freezer to cool a drink. Not being made from snow, it doesn't contain (a significant number of) bubbles, and yet it floats. If you think about it, I'm pretty sure this is something you know and understand! The density of ice is, inherently, less than that of water at the same temperature. Equally, if you close up a bottle full to the top with water at room temperature (using a plastic bottle is important for safetly..), and freezing the water, the bottle will split as the water expands on forming ice... which shows you that the same mass of water takes up more space (is less dense) when frozen than as a liquid.
Another common demonstration of this phenomenon, well known to scientists and plumbers, is a burst pipe caused when the water in the pipe freezes. The expansion of the ice quite literally rips the pipe apart.
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Rosy, doesn't water compact as it frezzes? shouldn't the density be highier at 0, as the atoms are more compacted than at density at 4 oC?
No. Water doesn't compact as it freezes, and the maximum density of water occurs at 4 oC. Water's funny stuff. I'm not going to try to explain in any detail here, because it needs diagrams, but there's lots of information on the internet about this. For example this page: http://kentsimmons.uwinnipeg.ca/cm1504/water.htm
On a more hands-on level, consider an ice cube made in your freezer to cool a drink. Not being made from snow, it doesn't contain (a significant number of) bubbles, and yet it floats. If you think about it, I'm pretty sure this is something you know and understand! The density of ice is, inherently, less than that of water at the same temperature. Equally, if you close up a bottle full to the top with water at room temperature (using a plastic bottle is important for safetly..), and freezing the water, the bottle will split as the water expands on forming ice... which shows you that the same mass of water takes up more space (is less dense) when frozen than as a liquid.
Incidentally, if ice didn't float, and if the coldest water didn't float on top of water at 4 oC, then the coldest water would sink to the bottom of lakes and rivers, and they'd freeze from the bottom up. That would mean that instead of a layer of ice over liquid water the whole of the lake would freeze, which would kill the fish and other animals living in the water whereas in reality they can hide in the relatively warm water at the bottom until spring.
Like ice in your drink, it floats. I also saw somewhere that water holds it's temperture, which I suppose is why, water in a bottle placed in the frezzer, frezzes around the outside first then moves inward, strange tho I always saw it as cold compresses and heat expands.
As a stab in the dark could it not be a molecular brake down? what I mean is, does the water gives off atoms as it freezes? Meaining you get pockets of oxegen and hydorgen with-in a compressed H2O ice? Expansion comming from having three things H, O and H2o ice, not just h2o water? The atoms individually take up more space then they do binded as water.
So it does compact but breaks down as it does so becomming slightly smaller as ice, but bigger in overall volume beacuse of trapped gases?
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Hi Wiybit, sorry that I didn’t have time to respond straight away to the points you raised on 16/04/2011 @ 20:48:50 and today @ 13:40:20. I don’t want to get distracted from the focus of my question about “Another Hockey Stick Illusion?”, i.e. why the “experts” ignore kinetic in favour of collision diameter. If it’s OK with you I’ll leave it to the Naked Scientists to respond to any that I see as a side-issue. You may have to raise such questions separately in order to attract their attention.
.. Seriuosly you shouldn't encourage them(if you get me) ..
is not the reason that I joined this blog. I will do my utmost to encourage The Naked Scientists to offer their expertise where it relates to my question. I’m very disappointed that I’ve had nothing from them yet and the appropriate laws of molecular dynamics covering the movement of atmospheric gases in firn are certainly relevant.
You didn't get me, I meant encourage them to argue, Ref: your past complaint.
.. BC can be slightly funny at times, but generally he's ok, when not .. trying to catch you out(so he can laugh at you) ..
is fine for anyone who has come here to be amused but I’m not in that category. I’m here to learn as much as I can about the science relevant to my question. So far the only person on this blog to help improve my understanding is you through your questions.
They(the others that have replied to you) would probably argue that they have tried to help you, but that you have not understood their answers, I will say having some experience of this type of issue, that both side often have a part to play in better communication.
You jumped in quiet early and accused BenV of knowing nothing, he could have just not had time to check in, not to say that others couldn't have responded, but at the same time this is a public family educational forum and there are not so many scientists among the many posters on here, there are many people with a general interest in science but as a percentage I think you'll find the majority of posters on here are interested in science but not actually scientists, I'm not actually sure of the actual numbers of actual scientists on here, not forgetting that most of the scientists on here are specialised in certain fields.
But I am sure they are always looking for more scientists to join, I tried to get a girl studying biotechnology to join the other day.
Also not forgetting the time issues, scientists that do post on here are doing so in their spare time generally.
Regarding .. you still haven't said what it is about Co2 that causes it to act so differently to the other elements, surely HE should move more, in ice if it's smaller and lighter? ..
one day I may be able to fully answer the first part with confidence. All that I can say for the moment is that it is something to do with the bonding between the one C and two O atoms that make up a molecule and the interaction of each molecule with other molecules (N2, O2, Ar, CH4, H2O, etc. Why not put that question to The Naked Scientists.
But it relates to your general question, and is only an issue "if" kinetics of Co2 in ice are true, and as far as I can tell that is still part of your main question and so not answered either. Surely first we find out if the kinetic factors are real then ask why does the Co2 move. I asked you because I believed you understood the kinetic science but didn't understand why they ignored it.
As for the second part, He, being smaller even than CO2, does experience size-dependent fractionation, as described in the paper “Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements” by Huber et al (http://icebubbles.ucsd.edu/Publications/Huber_closeoff_EPSL2006.pdf).
It is worthwhile looking more closely at that paper, because as well as answering your question about He directly, it expands on my earlier comment (on 14/04/2011 21:38:13) about Huber, Severinghaus (one of the co-arthors) and that magic 0.36nm molecule diameter Abstract .. For smaller gas species (mainly He and Ne) the fractionation factors are linearly correlated to the molecule size, whereas for diameters greater than about 3.6 Å the fractionation seems to be significantly smaller or even negligible ..
Note that Table 2 presents the molecular diameters used in their model and the close-off fractionation factor it produced for 8 of the atmospheric gases, including CO2 and He, but also note that those diameters are collision, not kinetic. Fig. 8 presents a useful graph of 7 of those computer-modelled close-off fractionation factors, with He down at the bottom of the curve, but note which one is missing, dear old CO2. I mentioned in that earlier comment that I had asked Severinghaus why he used collision rather than kinetic diameter and if he had tried his model using CO2’s 0.33nm kinetic diameter instead of its 0.39nm collision diameter. As I said, he chose not to respond directly to those questions. Have a guess where CO2 would have been if he had used kinetic diameter, which I hypothesise is the appropriate measure.
It's never a good sign if a scientist ignores your question relating to their research, it's either an unknown variables or maybe he felt he need time to formulate a responce and so felt it was too much hassle. Under the law apparently the see silence as agreement, so a non reply could be seen as an acknowledgement that the research wasn't so good; But I cannot speak for him.
That is why I challenge the conclusion that .. Close-off fractionation factors for different gases depend strongly on the diameter. The mass of the molecule is less important, since the effect on isotope ratios is very low. The critical size of about 3.6 Å seems to be an upper limit up to which molecules fractionate during the close-off process in the firn. A possible explanation for this could be the diffusion of molecules through channels in the ice lattice. From our findings we believe that the effect of close-off fractionation is nonexistent or at least very small for isotope ratios and for large molecules, like Xe, Kr, N2, CO2, CH4, and N2O. This is an important confirmation for the integrity of polar ice cores as a climate archive of the ancient atmospheric composition of these gases ..
You know if you keep this up you could publish your own findings, you might need some assistance in generating a scientific paper, but why not?
That is how a lot of science moves and works today.
But I’m only a retired Chartered Electrical Engineer and Geezer reasonably says .. I find it interesting that anyone who is unaware of why ice cubes float in water might think they are qualified to call into question the scientific credentials of anyone else ..
That is why during the past year I have requested help from “experts” like Severinghaus, Alley, Bender, etc. etc. etc.
Well it is a rather meany thing to say, and surely depending on fields lots of scientists do not understand different areas of science, not understanding certain processes even simple ones like why ice floats hardly makes a person stupid, or incapable to see a bad decision made by a doctor and so seek a second opinion as a simple example.
Could be seen as a elitist statement but Geezer isn't that bad, even if the old stick waving git animaton gives that appearence. I know you pain tho.
It's weird how just comming from different places and ways of thinking about subjects causes terms and there meanings to be interprited differently. What I will say is that it appears you have been asking about this for a while in many different places and become a bit "battle hardened", reactions come from actions and all sides are often guilty of over reacting to some degree at times, just chill, getting upset does nothing to futher investigation and often will draw coversations to a close(and there are some that like to cause conflict to achieve that end).
and now from this “ .. media-savvy group of physicians and researchers from Cambridge University .. ”, but I’m still not getting an answer.
Well Chris is the founder and he is involved in medicine and biology I believe, So I doubt Global warming is his field, I do not know if there are any climatologists actually on here, hence which ever of the scientists answer you, they will all probably be working outside their main fields. It appears you think that all the cambridge scientists are involved with the site but it's a voluntary forum, ergo I think many are not.
I can see what you are looking for, someone that knows their field and can answer the questions you have, this site is connected to Cambridge, so potentially there might be someone that knows someone who get you an answer.
But understand that tho, it was your assumption that whole of cambridge uni science wing posted on here. Rather, the people that do, are doing so to help out and out of their own free time.
that ofcourse is what I believe, I cannot speak for NS, it's just my interpritation having been on here a while. But you know, they do so to help out even if they cannot answer all your questions atleast they try to.
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Actually Pete lets just ask the main crux of your question.
Why Do climatologists ignore the kinetic movement of CO2 in ice, as that could, and probably does effect the ice core Co2 levels?
Anyone?
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Actually Pete lets just ask the main crux of your question.
Why Do climatologists ignore the kinetic movement of CO2 in ice, as that could, and probably does effect the ice core Co2 levels?
Anyone?
I think that's exactly what Ben said he would followup on.
If Pete was less interested in whizzing all over TNS and those in the "Scientific Community" who are obviously conspiring against him, we could have got there a long time ago without all this infernal palaver.
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Hi Wiybit, In your comment of 17/04/2011 @ 21:45:42 you make some fair points that don’t relate directly to my question so I propose to take them over to my other post where I am enquiring into the areas of science where The Naked Scientists are competent to comment on.
I agree with your comment of 17/04/2011 @ 22:40:44 that we concentrate on the question that I asked here initially.
About my suggestion that you put a question to the Naked Scientists of why CO2 acts in the way that it does you said .. But it relates to your general question, and is only an issue "if" kinetics of Co2 in ice are true, and as far as I can tell that is still part of your main question and so not answered either. Surely first we find out if the kinetic factors are real then ask why does the Co2 move. I asked you because I believed you understood the kinetic science but didn't understand why they ignored it ..
I thought that I had made it clear that the “experts” to whom I have put my question are aware of the size-dependent fractionation that occurs (in your terminology “the kinetic factors are real”) but use a different (in my hypothesis an incorrect) measure of the estimated size of molecules when modelling their movement within the porous firn.
Collision Diameter: .. (physical chemistry) The distance between the centers of two molecules taking part in a collision at the time of their closest approach
(http://www.answers.com/topic/collision-diameter#ixzz1Jr9mx600). As I understand it this applies to molecules whizzing about in a space that is large compared to their size, i.e. normal diffusion of gases and in my opinion relevant in the upper levels of an ice sheet.
Kinetic Diameter: .. The kinetic diameter can be understood as the diameter of a pore needed to let that specific molecule pass ..
(http://www.patentstorm.us/patents/7214719/description.html), in my opinion relevant in the lower levels of an ice sheet as it approaches close-off.
As I have repeated ad-nauseam in my exchanges with the “experts”, kinetic diamter is the measure used by gas purification practitioners in their patented and working purification systems. As the patent above says (albeit in relation to .. Separating of water .. in particular with H2, CO, CO2, CH4 and higher alkanes ..
(H2O kinetic diameter 0.27nm) .. 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 ..
If you want to find out more about the difference between the two measures there is an excellent book “Materials science of membranes for gas and vapor separation” (http://books.google.co.uk/books?id=Hc6ioeRc7p8C&pg=PA8&lpg=PA8&dq=H2O+%22collision+diameter%22&source=bl&ots=p1PsILlfsd&sig=sNWlODlE3Y4gmadOscv_BDvoTRg&hl=en&ei=0OarTanCDIeg8QPA-Oy4Ag&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBYQ6AEwAA#v=onepage&q=H2O%20%22collision%20diameter%22&f=false). Pages 7-10 and Table 3.1 “Properties of Gases” on Page 96 are particularly relevant and will give you an idea of the complexity of the subject. If I can’t extract an answer to this fundamental question from the ice core “experts” I may well be forced into buying that book and finding an expert in molecular dynamics who is prepared to spend the time giving me .. some assistance in generating a scientific paper ..
But surely if I have to do that it begs the question “Why haven’t the paleoclimatologists done this already?”. After all, Professor Jaworowski raised this specific fundamental issue of size-dependent fractionation in 1992 and Huber, Severinghaus and their co-authors were researching it at least as long ago as 2004 (http://icebubbles.ucsd.edu/Publications/Huber_closeoff_EPSL2006.pdf).
I agree that .. It's never a good sign if a scientist ignores your question relating to their research, it's either an unknown variables ..
but do not think, under the circumstances, that they should .. need time to formulate a responce and so felt it was too much hassle
You and Geezer, appear to defend The Naked Scientists because they may not have expertise in climate science. I would not be here if they had not given me the impression of having a section within their "Environment" area specifically on Climate Change and having their representatives advising on it. If I don’t have expertise then I admit it. Surely it is not asking too much for a simple statement on their “About” page making it clear in what areas they are competent to speak?
Geezer I did not come here for the purpose of .. whizzing all over TNS and those in the "Scientific Community" who are obviously conspiring ..
As I explained in my opening question I came across this blog while searching for detailed pictures of ice extracted from deep down an ice sheet. I have a question that has been puzzling me for over a year now and remains unanswered despite asking it of experts in the subject ..
The Naked Scientists gave me the impression of having access to experts in this subject because when I Googled - “Ice Cores” climate – I was taken to Climate Change and Ice Cores. Dr Eric Wolff from the British Antarctic Survey
(see that lovely picture of bubbles in ice) and thought “Hey, at last I might make headway.
I then looked at TNS’s “About” page (http://www.thenakedscientists.com/HTML/about-us/) and thought “Yes, this is promising” because The Naked Scientists are a media-savvy group of physicians and researchers from Cambridge University ..
but then I saw the photo and thought “Is this a joke?”. Never mind, I persevered and looked at the Who are we?”
page (http://www.thenakedscientists.com/HTML/about-us/who-are-we/) and thought “OK, that ‘photo is just high-spirited youngsters having a laugh. There are three archaeologists, a zoologist, a couple of astronomers, all apparently from Cambridge University, with contacts with specialists who can answer my question.
What was the outcome? Only one of those Naked Scientist, their kitchen science specialist BenV, responds, first simply asking So what's your question here Pete?
despite my question having been spelled out clearly in my first paragraph .. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice ..
BenV then follows up with I don't recall claiming any expertise in migration of molecules through any medium, so it's no surprise you find me lacking in that arena ..
Is there any wonder that I might be getting somewhat irritated. I asked a straight forward question of a group who I understood from their own promotional material and the content of their blog could find an answer for me and provided background information about it to help elicit a worthwhile response and all I get is “what was your question” and “I can’t answer it”. If I have over-reacted then I sincerely apologise, but I think I have pointed out here already, I arrived here after already getting rather irritated by “experts” refusing to respond to my simple question about kinetic v collision diameter.
Please Naked Scientists can you find someone who is knowledgeable enough to provide a straight answer to my fundamental question.
Best regards, Pete Ridley
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As I said, Pete, I will try to put it to someone relevant when I next have an opportunity.
Also, I explained to you why my first comment was about your specific question - because the huge block of text means some people will not read it, discover your question and engage, and I was subsequently proved to be correct. Might I also suggest that your rather aggressive posts may lead to some people who may be able to help being disinclined to do so, and would rather not get involved?
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Hi BenV, thanks for trying to find someone to whom you can put my question. Hopefully it won’t take you long to find someone who understands the subject and is prepared to spend a little time educating me.
Best regards, Pete Ridley
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About my suggestion that you put a question to the Naked Scientists of why CO2 acts in the way that it does you said .. But it relates to your general question, and is only an issue "if" kinetics of Co2 in ice are true, and as far as I can tell that is still part of your main question and so not answered either. Surely first we find out if the kinetic factors are real then ask why does the Co2 move. I asked you because I believed you understood the kinetic science but didn't understand why they ignored it ..
I thought that I had made it clear that the “experts” to whom I have put my question are aware of the size-dependent fractionation that occurs (in your terminology “the kinetic factors are real”) but use a different (in my hypothesis an incorrect) measure of the estimated size of molecules when modelling their movement within the porous firn.
So you are therefore saying that you know why Co2 moves as it does, and know of a better way to model it?
You and Geezer, appear to defend The Naked Scientists because they may not have expertise in climate science. I would not be here if they had not given me the impression of having a to, section within their "Environment" area specifically on Climate Change and having their representatives advising on it. If I don’t have expertise then I admit it. Surely it is not asking too much for a simple statement on their “About” page making it clear in what areas they are competent to speak?
Except enviroment is a huge area of science, I'll defend anyone where I see a need to, I critic also, I just try to be fair that's all.
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Hi Wiybit, your
So you are therefore saying that you know why Co2 moves as it does, and know of a better way to model it?
is way off beam. I have never said that so please don’t distort what I say. You can check my previous comments and the links to other comments of mine elsewhere to refresh your memory on what I am saying.
Regarding Except enviroment is a huge area of science ..
I am only really interested in talking about climate change and on this thread only in getting an answer to my question about kinetic v collision diameter from someone having the required level of expertise. I thought that I had made this clear in my very first comment here 5 days ago. Here again is what I said .. I have a question that has been puzzling me for over a year now and remains unanswered despite asking it of experts in the subject. 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”?
I can’t see anything ambiguous about that excepting perhaps for someone who doesn't know what firn is or why paleo-climatologists are interested in the movement of air molecules in ice. I don’t recall having commented here on any other aspect of the environment.
Hopefully BenV will soon be able to find someone who has the necessary expertise and inclination to give me a satisfactory answer
Best regards, Pete Ridley
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Hi Wiybit, your So you are therefore saying that you know why Co2 moves as it does, and know of a better way to model it?
is way off beam. I have never said that so please don’t distort what I say. You can check my previous comments and the links to other comments of mine elsewhere to refresh your memory on what I am saying.
That's fine I never intended to distort what you said, I asked a question, knowing that we had discussed that before(generally you say NS people can answer you) you stated that under your hypothesis, that the way they currently model is inncorrect, and the way you believe they should model, would work better.
There is the problem you suggest an understanding of the models and propose what you consider to be a better way, yet you are talking in open Hypothicals. That lead me ask what I did because you failed to clarify your understanding.
I am kinda left to conclude that you have a basic understanding of how they do the maths, you see there are things they ignore and are certain they are wrong, yet at times express yourself with a certainity that you really do not have.
Does that make sense? I am not saying that to have a go at you, I have been trying to help you find an answer to your question and still am, but to express certainity when you are not, is slightly contradictory.
Regarding Except enviroment is a huge area of science ..
I am only really interested in talking about climate change and on this thread
Maybe but that does not chage the reality that enviromental issues and topics are far farer reaching than just climate change, just because there is a enviromental section does not mean you should expect every type of enviromental scientist to be present.
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Hi Wiybit, In my second comment here, on 13/04/2011 @ 21:58:19, I said specifically for your benefit [quote .. The researchers that I mentioned in my first comment ignore kinetic diameter and use collision diameter, which I hypothesise is not appropriate when the diameter of pores within and the channels that link ice air pockets approach the size of those smaller molecules as the ice is reaching the final stages of compression to a state where the air pockets become “closed off”[/quote] Note that phrase “ .. which I hypothesise .. ”.
My definition of hypothesise is pretty close to the following Verb 1. hypothesise - to believe especially on uncertain or tentative grounds;
(http://www.thefreedictionary.com/hypothesise).
If you use a different definition then that could account for why you incorrectly say .. So you are therefore saying that you know why Co2 moves as it does, and know of a better way to model it?
Hypothesising (i.e. speculating) is a long way off knowing therefore your statement was, as I said before .. way off beam ..
I don’t believe that my hypothesis says that .. the way they currently model is inncorrect, and the way .. they should model, would work better
It only says that I speculate that they should use a different measure of molecular diameter in their models.
You say .. There is the problem you suggest an understanding of the models and propose what you consider to be a better way ..
but I don’t think that I have ever claimed to know any details of how their models work. All that I know is that they say they use collision diameter in their modelling and I speculate that they should be using kinetic diameter (and asked Severinghaus if he had run his model using that measure).
It is because I speculate about this that I have repeatedly asked the “experts” to explain why they choose to use collision diameter. In my opinion that is simply proposing the use of a different parameter, not proposing a better way of modelling the process. I’m not qualified to do the latter, but am entitled to speculate about using an alternative measure that I understand is used by gas purification practitioners in their operational systems when considering similar processes. The use of this alternative measure could well overturn the conclusions that the ice core “experts” draw from the results of their modelling about their ability to reconstruct past atmospheric concentration of CO2.
I think that I have provided you with an excellent reference book (“Materials science of membranes for gas and vapor separation”) from which, if you are inclined, you can develop a better understanding of the circumstances under which the different measures of molecular diameter are applied.
I don’t understand how you can conclude that I .. have a basic understanding of how they do the maths, .. see there are things they ignore and are certain they are wrong ..
. I have questioned only one thing, why do they prefer collision over kinetic diameter. If I was “certain they are wrong” I would say loud and clear “you are using the wrong measure of molecular size”. Have I done that? If you think so then please tell me where I said it and I’ll withdraw the comment.
As for your .. enviromental issues and topics are far farer reaching than just climate change, just because there is a enviromental section does not mean you should expect every type of enviromental scientist to be present ..
have you looked at the categories that The Naked Scientists list under the Life Sciences forum heading “The Environment”? They are .. Meteorology, ecology, climate change and conservation
(http://www.thenakedscientists.com/forum/).
Best regards, Pete Ridley
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Wow, this thread should really attract interest :)
It has all the ingredients. A lot of 'learned words' and it's argumentative in the best/worst American definition of a so called high school 'debate'. Furthermore it sounds as if it knows what it discuss :) also effectively telling those that don't agree that they are ignorants :)
I do not expect Ben to be such a person Peter. I expect him to know his limits exquisitely well, and what's even better, acknowledging them too :) which is more than I can say about some. The road to wisdom is to know when you're out of your depth, which won't stop us from making educated guesses though :) You come to the site, telling moderators that they 'don't know what they are talking about', thereby implicating that you do :) (by inference there). A classical debate trick, often used in those society's thriving on 'free debate', throwing verbal manure at each other.
Why not try to see if you can shorten your question instead? To something more simple and understandable. That's what Einstein did, and if he could so can you, right?
But as I read you it's a question of if we can prove that the ice samples containing air bubbles can be guaranteed to have the exact same atmosphere (and CO2 concentration?) As there was in the atmosphere when the ice layers came to be historically? I might be wrong as I lost myself in your formulations repeatedly, but if that was what you meant, I think the question is valid, and good.
"Such air is found in bubbles trapped in annual layers of ice in Antarctica, in sealed brass buttons on old uniforms, airtight bottles of wine of known vintage, etc. Additional support comes from well-dated carbon-isotope signatures, for example, in annual tree rings. Estimates of "pre-industrial" CO2 can also be obtained by first calculating the ratio of the recent atmospheric CO2 increases to recent fossil-fuel use, and using past records of fossil-fuel use to extrapolate past atmospheric CO2 concentrations on an annual basis.
Estimates of "pre-industrial" CO2 concentrations obtained in this way are higher than those obtained by more direct measurements; this is believed to be because the effects of widespread land clearing are not accounted for. Ice-core data provide records of earlier concentrations. For concentrations back to about 1775, see A. Neftel et al. (http://cdiac.ornl.gov/trends/co2/siple.html)
The record derived from the DSS Antarctic ice core indicates an average concentration of 280.05 ppm from 1000-1750 C.E. For over 400,000 years of ice-core record from Vostok, see J. M. Barnola et al.. For ice-core records extending over 650,000 years back in time, see Siegenthaler et al. (2005)." From Recent Greenhouse Gas Concentrations (http://cdiac.ornl.gov/pns/current_ghg.html)
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"The latest results from the EPICA core in Antarctica have just been published this week in Science (Siegenthaler et al. and Spahni et al.). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have now been analysed for greenhouse gas concentrations saved in tiny bubbles. The records for CO2, CH4 and N2O both confirm the Vostok records that have been available for a few years now, and extend them over another 4 glacial-interglacial cycles. This is a landmark result and a strong testament to the almost heroic efforts in the field to bring back these samples from over 3km deep in the Antarctica ice. So what do these new data tell us, and where might they lead?
Composite CO2: Click to enlargeFirst of all, the results demonstrate clearly that the relationship between climate and CO2 that had been deduced from the Vostok core appears remarkably robust. This is despite a significant change in the patterns of glacial-interglacial changes prior to 400,000 years ago. The ‘EPICA challenge’ was laid down a few months ago for people working on carbon cycle models to predict whether this would be the case, and mostly the predictions were right on the mark. (Who says climate predictions can’t be verified?).
It should also go almost without saying that lingering doubts about the reproducibility of the ice core gas records should now be completely dispelled.
That a number of different labs, looking at ice from different locations, extracted with different methods all give very similar answers, is a powerful indication that what they are measuring is real. Where there are problems (for instance in N2O in very dusty ice), those problems are clearly found and that data discarded.
Secondly, these results will allow paleoclimatologists to really look in detail at the differences between the different interglacials in the past. The previous 3 before our current era look quite similar to each other and were quite short (around 10,000 years). The one 400,000 years ago (Marine Isotope Stage 11, for those who count that way) was hypotheisied to look more like the Holocene and appears to be significantly longer (around 30,000 years).
Many of the details though weren’t completely clear in the Vostok data, but should now be much better resolved. This may help address some of the ideas put forward by Ruddiman (2003, 2005), and also help assess how long our current warm period is likely to last.
More generally, since the extra interglacials that are now resolved have very different characteristics from the previous ones, they may allow us to test climate theories and models over a whole new suite of test cases. To quote Richard Alley “Whether you’re a physicist, a chemist, a biologist, a geologist, or any other “ist” studying the Earth system, there is something in these data that confirms much of your understanding of the planet and then challenges some piece of your understanding”. It’s all very exciting (for us ‘ists’ at least!)." From 2005. RealClimate. (http://www.realclimate.org/index.php/archives/2005/11/650000-years-of-greenhouse-gas-concentrations/)
And this one might give some insight too. Reliability of ice-core science: historical insights. (http://www.igsoc.org/journal/56/200/j10j201.pdf) As well as this. Atmospheric nitrous oxide during the last 140000 years (.pdf) (http://www.taldice.org/pub/taldice/Schilt_EPSL2010.pdf) That takes up the nitrous oxide question mentioned in RealClimate.
( But the only way to really prove that this isn't another of those mad potconjunctures cooked up by those conspiratorial climatologists, physicists and geologists (et al:) is naturally to do as Methuselah. If we just could find someone like him. Even though he is said to only have lived a measly 1000 y it would still be of interest I think? Providing that he regularly corked those air samples, or Jonah maybe, naah, not him? The flying Dutchman then? And hey, i got it. That roman soldier that was there at the crucifixion, doomed to live forever, then we could, at last, get some good ol'human, down to earth, correlations to test it against :)
As it is we have to make do with what we have, and correlate it to other sources and see if the concentrations agree, and when not, try to find the reasons for the discrepancy.
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Lastly.
"The most direct method of investigating past variations of the atmospheric CO2 concentration before 1958, when continuous direct atmospheric CO2 measurements started, is the analysis of air extracted from suitable ice cores. Here we present a new detailed CO2 record from the Dronning Maud Land (DML) ice core, drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA) and some new measurements on a previously drilled ice core from the South Pole. The DML CO2 record shows an increase from about 278 to 282 parts per million by volume (ppmv) between ad 1000 and ad 1200 and a fairly continuous decrease to a mean value of about 277 ppmv around ad 1700. While the new South Pole measurements agree well with DML at the minimum at ad 1700 they are on average about 2 ppmv lower during the period ad 1000–1500. Published measurements from the coastal high-accumulation site Law Dome are considered as very reliable because of the reproducibility of the measurements, high temporal resolution and an accurate time scale.
Other Antarctic ice cores could not, or only partly, reproduce the pre-industrial measurements from Law Dome. A comparison of the trends of DML and Law Dome shows a general agreement. However we should be able to rule out co-variations caused by the same artefact. Two possible effects are discussed, first production of CO2 by chemical reactions and second diffusion of dissolved air through the ice matrix into the bubbles. While the first effect cannot be totally excluded, comparison of the Law Dome and DML record shows that dissolved air diffusing to bubbles cannot be responsible for the pre-industrial variation. Therefore, the new record is not a proof of the Law Dome results but the first very strong support from an ice core of the Antarctic plateau."
By SIEGENTHALER, U., MONNIN, E., KAWAMURA, K., SPAHNI, R., SCHWANDER, J., STAUFFER, B., STOCKER, T. F., BARNOLA, J.-M. and FISCHER, H. (2005), from 1. Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland 2. CNRS Laboratoire de Glaciologie et de Géophysique de l'Environnement (LGGE), Grenoble, France 3. Alfred Wegener Institut für Polar- und Meeresforschung, Bremerhaven, Germany.
But as that one is 'pay for view' from Wiley Online Library / Wiley InterScience I can't link that pdf, which is a shame. Anyway, you got some references I hope. If that now was your question?
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As for kinetic diameter, versus collision diameter? Well, exactly how should we construct that experiment? over what time period? We have the ice cores from 'human reckoning' to compare to trees, rocks, sediment etc of course. And they do seem to fit/correlate to each other? Although that only should be over a measly ?? Thousand years maybe, or so :) Could that make do for a comparison/verification?
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Hi yor_on, I had wondered if it would be long before you turned up here. I have seen comments of yours relating to questions about both “climate change” and “Physics, Astronomy & Cosmology” topics and the impression that I get is that you have a good understanding of the latter. I expect that you would even be able to make a worthwhile contribution to the work that Professor Andrew White is doing at CERN (my comment on 17th @ 11:36:14).
It seems to me that you express opinions on the former from a position of ignorance comparable to mine, so may have more to learn from the exchanges here than to contribute. Of course I may be wrong so, even though you use a false name, are you prepared to disclose the extent of your scientific expertise in the subject of molecular dynamics beyond that you may be a good runner (http://www.thenakedscientists.com/forum/index.php?action=profile;u=9199)?
Your 1612-word comment quotes from and links to some very interesting stuff about those attempts to reconstruct past atmospheric CO2 content using air “trapped” in ice for decades, centuries and millennia (although I am always suspicious of anything that appears in that “Hockey Team” blog Realclimate) but it does nothing that answers my simple question.
You ask Why not try to see if you can shorten your question instead?
but how much shorter than .. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice ..
do you need? I stated that simple question in my opening comment on The Naked Scientists blog and have repeated it twice on this very page, only yesterday at 10:04:48 then again at 18:59:37. Have you bothered to read this thread before commenting or have you simply jumped in blind? How you can paraphrase that simple question as it's a question of if we can prove that the ice samples containing air bubbles can be guaranteed to have the exact same atmosphere (and CO2 concentration?) As there was in the atmosphere when the ice layers came to be historically?
is beyond me.
So, your Anyway, you got some references I hope. If that now was your question?
is way off beam because you have simply provided quotations and links that contributed to answering your own mistaken interpretation of my question.
Your As for kinetic diameter, versus collision diameter? Well, exactly how should we construct that experiment? over what time period?
again has nothing to do with my simple question. As far as I am aware I have not asked for any experiment about kinetic v collision diameter so please would you point to where you think that I have done so. What I have done is ask Professor Jeff Severinghaus, one of the “experts”, if they have run their model substituting kinetic for collision diameter.
I have already had discussions with Professors Richard Alley, Severinghaus and Bender about the other proxies such as .. trees, rocks, sediment etc of course ..
and my scepticism about the statistical manipulations used to make them .. fit/correlate to each other
You may find the article “Uncertainty in Climate Change (WP)” by A.T. Grove and E. Lopez-Gunn (http://www.realinstitutoelcano.org/wps/portal/rielcano_eng/Content?WCM_GLOBAL_CONTEXT=/elcano/elcano_in/zonas_in/dt25-2010) of interest but that really is another question which I suggest that you raise separately if you wish to learn something about those other proxies.
Best regards, Pete Ridley
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Peter I'm always in a state of confusion :)
It's only when I've finally translated what others say and tell me into my own that I understand what they mean. That's also why I wondered what you meant, you see on TNS we have all kind of expertise, but only a very few of them, if any, believe themselves to be modern Leonardo Da Vinci's. Insulting remarks usually lead to a ban here. We're not really interested in mudslinging, we are interested in learning and sharing what we know though. It can become a difficult balance act to know where one end (learning) and the other takes over (mudslinging) but we try :)
As for your reference I will look at it, but to build the contention on your idea of the difference, without presenting anyone agreeing is a hard thing to do. 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. And that's why I asked you for ideas of how you would like to see a experiment made.
You seem quite skilled in innuendo and debate technique though :)
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As for the 'think tank' you linked me too? Driven by business, for business maybe, with the trustees and corporations being made board members, maybe? See, I can do innuendo too :)
It's been in my sorry experience that when I read about some new, or not so new, 'institution' contending climate science, I always will benefit from looking at its 'founders'. All to often you can find that, although all of those organizations proudly declaring themselves 'independent', that they in deed are influenced by the ideas of their 'financial support'. Which in a way is nothing remarkable, just a human fact. It's very hard to make anything 'independently' outside the academic sphere, if even there(?) nowadays. Not even 'independent investigating journalism' is really independent today, as can be seen in any modern war, and how those journalist finds the opportunity to report 'independent views'?
But yes, I will read it. I always do.
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Well I looked it over. Actually a quite nice article, summarizing what we think us know, staying somewhat on the conservative side, carefully avoiding to discuss man made contributions more than in passing. It's a good one I think, I will have to reread it later. As for now I'm still not fully awake. Take me a lot of coffee to get me working those days :)
And I'm not really making fun of you, even though I found the discussion quite inflamed. I'm interested in how you think you could prove your point, and to me that would need 'experimenting'. Assume that we had climatologists here that research, I doubt that they would get involved in this myself. But if you could present a way to simply test it, and that should mean a long term test of it also as I see it, realistically. Maybe some of them would get ideas from a proposition?
So, if it was you wanting to test it, how would you do it?
Myself I would prefer a 'secluded area', meaning not easily contaminated by human activity, where you could measure the atmospheric conditions continually and then compare the layers of snow/ice to those results you get. That wouldn't exactly answer your 'physics' question, but it would tell us if there was a correlation between the atmosphere and the bubbles formed, and also the isotopes, with what we then would measure continuously.
And that would be the important thing to me. And as I'm guessing this is what your question really discuss too? That is, if we are responsible for the climate changes we observe today, and casting into doubt the foundations on where our climatology builds historically. In this case the ice cores we use for comparison. The real problem with your question is that this is already done, continuously as I see it. And if that ice trapped air would give us the wrong results we should have noticed it by now?
Well, as I see it.
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Here you have a description of some techniques used for differing the time-lines involved and how the measuring is done.
Ice-core evidence of abrupt climate changes. (http://www.pnas.org/content/97/4/1331.full.pdf)
And here is some other indirect evidence for it working.
"We reconstructed the radiocarbon activity of intermediate waters in the eastern North Pacific over the past 38,000 years. Radiocarbon activity paralleled that of the atmosphere, except during deglaciation, when intermediate-water values fell by more than 300 per mil. Such a large decrease requires a deglacial injection of very old waters from a deep-ocean carbon reservoir that was previously well isolated from the atmosphere. The timing of intermediate-water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation." From Marine Radiocarbon Evidence for the Mechanism of Deglacial Atmospheric CO2 Rise. (pay site) (http://www.sciencemag.org/content/316/5830/1456.abstract)
And here you have a geological study studying Firn and 'gas transportation' " This study aims to establish the continuity of the gas record at Mt. Moulton, correlate the MBI#1 record to the Vostok EGT4 timescale through the development of MBI#1 age models, interpret the length of the Eemian period in the MBI#1 record and investigate the link between northern hemisphere insolation and Antarctic temperature as expressed in the MBI#1 isotopic temperature record." It also discuss "gas transport within firn" separating it roughly into convection, diffusion and 'non-diffusion', quite interesting in fact. Thesis. (http://www.geosc.psu.edu/undergrads/documents/documents/StantonCusterthesis.pdf)
As for the pure physics of it?
'Geology, Palaeontology & Archaeology' ?
Maybe ask in Chemistry?
Or General Science.
It a field where everything goes into everything else it seems.
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I don’t understand how you can conclude that I .. have a basic understanding of how they do the maths, .. see there are things they ignore and are certain they are wrong ..
. I have questioned only one thing, why do they prefer collision over kinetic diameter. If I was “certain they are wrong” I would say loud and clear “you are using the wrong measure of molecular size”. Have I done that? If you think so then please tell me where I said it and I’ll withdraw the comment.
No need to withdraw comments, and I am not going to go back through all the past conversations, but I am sure you expressed a certainy before about the methods they used being wrong. My point relating to hypothesis was simply that they can be at varying degrees also, from a hypothesis you are more sure of as a possible explaination to ones more you are less sure of as a possible explaination, by saying "open hypothesis" I meant in the middle.
As for your .. enviromental issues and topics are far farer reaching than just climate change, just because there is a enviromental section does not mean you should expect every type of enviromental scientist to be present ..
have you looked at the categories that The Naked Scientists list under the Life Sciences forum heading “The Environment”? They are .. Meteorology, ecology, climate change and conservation
That still doesn't really change my point.
Besides I was only trying to help you get an answer and I hope that I have, there is no need for us to go on and on about this as you say 'but it says Climate change' and I say but climate change has different areas also...
Peace
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Assume that we had climatologists here that research, I doubt that they would get involved in this myself. But if you could present a way to simply test it, and that should mean a long term test of it also as I see it, realistically. Maybe some of them would get ideas from a proposition?
So, if it was you wanting to test it, how would you do it?
Rather than going off to the north or south polls could you not use a snow machine? The flakes might be formed slightly differently than in nature but using extraplation it could be a simply way to test it, no?
All snow flakes are different anyway...
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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
benefit from looking at its 'founders'
and I “Follow the money”.
I’m afraid that your .. 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 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 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 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 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
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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.
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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?
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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.
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Hi yor_on, I am astounded by your
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 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
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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? (http://www.noaa.gov/)
Otherwise I suggest Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (http://eapsweb.mit.edu/)
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.
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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. (http://books.google.se/books?id=VfcKIManfkUC&pg=PA438&lpg=PA438&dq=Co2+trapped+in+firn+kinetic+energy&source=bl&ots=CXTSWdKtc8&sig=CKeIFFTQJEVc0y56kKgWv9hKq4Y&hl=sv&ei=4OauTfD-OpDIswaer-XXDA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCQQ6AEwAQ#v=onepage&q&f=false)
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 (http://www.realclimate.org/index.php/archives/2010/02/good-news-for-the-earths-climate-system/) 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.
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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,
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 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 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 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 .. 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 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
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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.
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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.
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Great post Eric - I will check out your science briefing
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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.
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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 .. 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 [ Invalid Attachment ]
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 .. 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 .. Fig. 3. Basic outline of the multi-scale structure of the EPICA-DML ..
plus some excellent images, mostly of deep ice but .. 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
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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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as I am not a natural blogger!.
You could have fooled me! Many thanks for the post.
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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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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
.. 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 .. 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 .. 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 .. 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 .. 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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Hi Bored chemist, although you may have lost interest in discussing this size-dependent fractionation issue and want to
.. 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 .. 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 .. 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. [ Invalid Attachment ]
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
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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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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
http://en.wikipedia.org/wiki/Blog
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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”.
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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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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Hi Yor_on, I do not agree with your
.. You've got your answers ..
Here is my opening question again .. 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 .. 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 .. 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 .. 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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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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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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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 .. it has been answered ..
You are mistaken if you have the impression that I .. 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
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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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And, once again, for those who still don't get it.
Q
"why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice"
A
because it gives the right answer.
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In response to my original question Professor Wolff has provide two excellent overviews of the fundamental issue of how valid are the attempts to reconstruct past atmospheric composition from air recovered from ice sheets. I thank him for making the time to put together those submissions and hope eventually to cover all questions about the validity of those reconstructions. It is sensible to tackle in a structured manner all of the different complex processes that distort the composition of the original atmospheric air, To this end I have asked the founder of this blog/forum, Chris Smith, if it is possible to expand the thread question to read “Another Hockey Stick Illusion?” – “Do glaciers tell a true atmospheric CO2 story?”. That then allows us to follow the relevant processes from the top of the ice sheet down to the depths of the ice beneath.
I first would like to focus on the matter covered in my original question, which is .. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice? ..
I shouldn’t have to keep repeating this but there are several people who have commented here who seem not to have read it properly. Professor Wolff went to a great deal of trouble to explain his understanding of it in his very first comment here (27th April @ 14:53:30) and I can’t improve on that.
Once a convincing answer has been given to my original question I would like to return to those other important points made by Professor Wolff that do not directly address my original question but are relevant to “Do glaciers tell a true atmospheric CO2 story?”.
In that comment Professor Wolff said .. The underlying issue is whether we can believe that the air in bubbles in ice cores is an un-fractionated representation of the atmosphere .. when we crack open a bubble of air, does it contain exactly the relative proportions of different molecules as the air in the atmosphere ..
Note that reference to “air”, , not N2, not O2, not Ar, not CO2, etc. etc. etc. but “air” – all of it.
He then went on to say .. 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? ..
Note this time that Professor Wolff focuses on “the final stages of enclosure”, i.e. the deep firn, which is precisely where my original question is targeted at.
Professor Wolff then said .. 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 ..
The issue in question should by that stage have been reasonably clear to anyone following this thread.
Let’s look now at what “the literature says” about size-dependent fractionation in deep firn as it approaches close-off, using three papers that Professor Wolff made reference to. First let’s see what is said in the 1996 paper “Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn” by Etheridge et el. As I pointed out almost a year ago elsewhere, that paper (and as far as I could find then, no other that Etheridge was involved in) made any reference to size-dependent fractionation of air in the deep firn, the only references to fractionation being to the gravitational type. I propose to return to this paper at the appropriate point in the wider discussion about “Do glaciers tell a true atmospheric CO2 story?”.
The papers that are much more relevant to my original question are the two from 2006 that Professor Wolff makes reference to. First let’s look at what “Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements” by Huber, Severinghaus, et al. (http://icebubbles.ucsd.edu/Publications/Huber_closeoff_EPSL2006.pdf) says about this. I make the assumption that all eight co-authors can reasonably be called paleoclimatologists. The next point to clear up is whether or not their paper is about the migration of air molecules through firn and ice. The title of the paper certainly suggests so, the paper discusses the molecules of all of the different atmospheric air components and their diffusion within the ice sheet and most importantly .. In the present study, however, we are mainly interested at the bottom of the firn air column ..
This is precisely the area on which I am focussing, as Professor Wolff acknowledged when saying in his first comment here .. 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? ..
At the bottom of the firn air column, as close-off is approached, pores on the surface of the closing air bubbles and the channels that link air pockets must at some stage approach molecular size, i.e. the firn becomes a nanoporous medium. Gas purification experts use nanoporous media (e.g. zeolites) in industrial applications and numerous papers and patents can be found that describe the process. All of these refer to molecular kinetic diameter, not collision diameter, e.g. see the 2002 paper “Application of natural zeolites in the purification and separation of gases” by Ackley et al. (http://www.zeolitanatural.com/docs/gasseparation2.pdf) and “Sol-Gel Processing of Inorganic Membranes for Natural Gas Purification” (http://www.netl.doe.gov/kmd/cds/disk28/NG8-3.PDF) which says .. To efficiently separate CO2 (kinetic diameter = 0.33 nm) from CH4 (kinetic diameter = 0.38 nm) or (harder still) N2 (kinetic diameter = 0.364 nm) from methane, it is necessary to accurately control the average pore size between about 0.3 and 0.4 nm and achieve a narrow pore size distribution ..
So, I repeat my original question .. why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice? ..
As I discussed over a month ago on the Climate Conversation Group’s “Fallen snow” thread (which I provided a link to in my first post on this thread) .. Huber et al. .. say “ .. a critical size of 3.6 Å implies diffusion through channels of about the same dimension .. an outlet from a closing bubble .. changes its dimension steadily from open to closed. .. Diffusion coefficients of gases in ice show a size dependence similar to our findings beside for Ar and O2 .. ”. They should have included CO2 along with those two but didn’t because (I believe) they were focussing on the close-off fractionation of other gases and were misled into ignoring CO2 through using collision not kinetic diameter ..
I won’t say much here at this stage about the paper “Fractionation of gases in polar ice during bubble close-off: New constraints from firn air Ne, Kr and Xe observations” by Severinghaus & Battle (http://icebubbles.ucsd.edu/Publications/closeoff_EPSL.pdf). In Section 1.2 and 3.1 of the paper they provide a good description of the process that I am focussing on and they discuss the results of their .. simple model of the bubble close-off fractionation …
They go on to say .. The model presumes that fractionation is caused by selective permeation of gas through the ice lattice from slightly overpressured bubbles. ..
I’m puzzled by that reference to “ice lattice” because there is another process that is thought to take place after close-off. This is a process related to the one that I am focussing on at present and I would like to consider this one later, however, it is noticeable that they again refer to the 0.36nm molecular size. They say .. The large atoms Kr and Xe do not appear to be fractionated by this process, despite the large size difference between the two gases, suggesting a threshold atomic diameter of 3.6Å above which the probability becomes very small that the gas will escape from the bubble. These findings have implications for ice core and firn air studies that use gas ratios to infer paleotemperature, chronology and past atmospheric composition ..
Once again, they ignore kinetic diameter in favour of collision diameter (see Table 1).
If anyone is interested, more comments of mine on this paper can be found on the Climate Conversation blog threads:
- “It’s not warming, you nitwit — it’s cooling” (http://www.climateconversation.wordshine.co.nz/2011/03/its-not-warming-you-nitwit-its-cooling/) in my comment of 21st March @ 11:26 and
- “Fallen snow” (http://www.climateconversation.wordshine.co.nz/2011/03/fallen-snow/) in my comment of 23rd March @ 11:17.
Professor Wolff, are you at liberty to attach a copy of your 2011 paper “Greenhouse gases in the Earth system: a palaeoclimate perspective” so that subsequently we can look at the evidence provided therein supporting your conviction that .. the ice-core record provides a faithful record of changing atmospheric composition. ..
(http://www.ncbi.nlm.nih.gov/pubmed/21502180)? That paper may provide the answer to the question used by Professor Jaworowski et al. as the title to their 1992 paper “Do glaciers tell a true atmospheric CO2 story?” (http://www.co2web.info/stoten92.pdf).
I referred to that paper in my comment of 13th April @ 21:58:19) and as I said then .. When I discussed this last June with Professor Zbiniew Jaworowski, whose 1992 paper first drew my attention to this issue, he expressed the opinion that “This is a highly specialized field of science. My impression is that it is a terra incognita for glaciologists”. Subsequently I have asked the same question of Professors Richard Alley, Jeffey Severinghaus and Michael Bender without receiving any worthwhile justification for their use of collision diameter. ..
Best regards, Pete Ridley
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Pete and other readers,
My first post (353863) was intended to be a very clear and direct answer to your original question; additionally I have since contacted Professors Alley and Severinghaus: although I have not seen their correspondence with you, they both tell me that they felt they had already answered you, in similar terms, in private e-mails in the past. Given this, I am surprised that you are still claiming your question has not been answered. I will therefore make one closing attempt to be absolutely clear. Your specific question was:
"why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice?".
The problem that we are all having is that this is a false or loaded question: the implication elsewhere in your posts is that the idea that CO2 is unfractionated compared to N2 comes from authors making this assumption. In fact it is quite the other way round: the empirical evidence that CO2 is not fractionated on enclosure (as well as the observation that Ar is less fractionated than O2) is what led these authors to hypothesise that collision diameter was the controlling variable. So the specific answer is that they use collision diameter because this is what allows them to rationalise the data they observe.
I think that none of us has a definite molecular-level understanding of the physical process occurring at closeoff, and it would be great if someone can do the experiments in the lab to understand that better. But it won't alter the empirical facts.
Incidentally it may be worth mentioning that, in their expts, Severinghaus and Huber used trace gases (such as Ar and O2) that are understood to have been invariant in concentration over recent decades, precisely so they could look at the diffusion and enclosure processes free from any assumptions about temporal change in concentration.
You raised several other points in different posts, and I simply don't have time to answer them all. Your questions about kinetic diameter imply you have got quite deep into the literature, so I am surprised that you are confused about the kink in firn air profiles, as this is clearly explained in several of the papers. It is the result of moving from the diffusive zone (in which the air is ageing according to diffusive mixing with the air above) into the non-diffusive zone, where the air is ageing with the ice, ie much faster ageing. Just to give a schematic example:
Imagine a site at which the snow accumulation rate is 1 m ice equivalent per year, and the non-diffusive zone starts at 70 m snow depth (which because the firn is much less dense near the surface, might be 50 m in ice equivalent). This is similar to the situation at Law Dome, but I have chosen to use a hypothetical site with round numbers for simplicity. At 70 m, the ice is 50 years old, but the air is about 10 years old. At 80 m, the ice is 60 years old, and the air is 20 years old. Thus the CO2, would change from about 385 ppmv at the surface (2010 concentration, South Pole) to 365 ppmv at 70 m, then 350 ppmv at 80 m. This would of course show a sharp kink if plotted against depth.
Finally, I am surprised you are citing Jaworowski as an expert. His monographs about ice core CO2 have been comprehensively refuted by those who actually work on the topic, most notably some 15 years ago by Professor Hans Oeschger. I myself looked into his work a decade ago, but found it so full of misunderstandings (if I am generous) that I did not bother to formulate any specific refutation, but such material is easily available on the web. The saddest part is that Jaworowski cites as issues aspects of ice core analysis that many of the pioneers of the field were very aware of, and spent decades carefully studying and overcoming. It is therefore galling to see their efforts ignored.
I will be happy to answer other well-formulated questions about ice cores, but I don't think I have any more to add to this thread.
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Thanks Eric. And, you're most welcome back whenever you find the time and inclination. It's been a, ah, interesting journey, with a lot of twists if I may say so, but myself I think your posts have been oasis's of clearness.
I will close this thread now, as I think your post says it all.