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Comments 26 to 50 out of 67:

26. Dikran Marsupial at 00:49 AM on 3 February, 2011
    The argument is about what is observed to have happened, and makes no assumptions about what values U_n and E_n actually have, and does not make any assumptions about the sources or whether they vary. Think of U_n and E_n as being the total natural uptake and emissions from natural sinks and sources that actually ocurred in a particular year. We don't know their individual values, we can't directly observe them, but we don't need to know their values, the key point is that we can infer the difference between them and know if the natural environment is a net source or a net sink. Your definition of indirect anthropogenic emissions is unworkable. Firstly issues such as deforestation are already included in anthropogenic emissions as it comes under "land use change". Secondly, the main way in which our emissions have changed the carbon cycle is that there is now far more *uptake* because the atmospheric concentration has risen. The whole reason the natural environment is currently a net sink is due to its response to our emissions. If you want to increase the anthropogenic emissions by including an "indirect component", it just means that the natural environment must be an even stronger net carbon sink than the basic mass balace argument suggests, in which case it remains the case that man is responsible for the observed rise in CO2 (i.e. we agree). As to your question, to understand the ratio if isotopes that you should expect to be in the atmosphere, there is a more important consideration, namely that vast quantities of carbon are recycled between reservoirs annually. If you look at the figures for the fluxes, you will find that the oceans and terrestial bioshphere exchange about 160GTC (IIRC) with the atmosphere each year. This is about a fifth of the atmospheric reservoir, so the residence time (the amount of time a molecule remains in the atmosphere before being taken up by the oceans/biota etc.) is only about five years. This rapidly replaces carbon with "fossil" isotopic signature with carbon of a "natural" isotopic signature, so the change in 12C is not as great as you might expect. However this has nothing to do with the rise in atmospheric CO2 as it is only an exchange of carbon, that is if anything opposing the rise. Thus even though CO2 has risen by about 40% due to anthropogenic emissions, only about 4% of atmospheric carbon is of directly anthropogenic origin (due to the effects of the large exchange fluxes replacing it with "natural" carbon). The export from upper to deep ocean reservoirs is entirely irrelevant. The mass balance argument only involves fluxes into and out of the atmosphere, and only the difference in total emissions and total uptake matters. As to papers on my second post, I haven't seen any papers that use a model of the carbon cycle that is so rudimentary that the result is easily obtained. Anyone who works on the carbon cycle will find it too obvious to publish a paper on, and instead are working on more complex models that take into account things like upper-deep ocean fluxes. The one paper I have seen that uses such a model is the one by Essenhigh (2009), but in that paper Essenhigh fails to understand the distincion between residence time and adjustment time and hence the conclusion of the paper is incorrect.
27. Dikran Marsupial at 05:39 AM on 4 February, 2011
    Julian, I tried to reply to your question on Dr Spencer's blog, but it wouldn't accept it, so hopefully you will find it here at some point: If you get hold of a copy of the 1990 IPCC WG1 scientific basis report and go to page 14, you will find it gives the mass balance argument there about three quarters of the way down column 2 (only in rather less detail than I provided on skepticalscience). Its says "Second, the observed rate of CO2 increase closely parallels the accumulated emissions trends from fossil fuel combustion and from land use changes. Since the start of almospheric monitoring in 1958, the annual atmospheric increase has been smaller each year than the fossil fuel input [DK the difference is even bigger if you include land use changes]. Thus ocean and biota together must have been a [DK net] global sink rather than a source during all these years" So it is in the litterature, just that it doesn't merit much discussion anymore as it is so well known (I have seen it given a similarly brief mention in a paper or two). If there is one observation where natural variability can be ruled out, this is it. We know for sure that the rise in atmospheric CO2 is anthropogenic, as the theory that it is from natural sources is 100% falsified by the observation that the annual increase is smaller than fossil fuel emissions.
28. KR at 01:49 AM on 5 February, 2011
    Julian, Dikran - Odd thing, that; I tried posting there too, my post apparently did not survive moderation. It showed up as "awaiting moderation", but never made it to the blog comments. I'm saddened by that approach, when Dr. Spencer had issued the challenge in the first place. If he wants to issue such quixotic challenges, he should accept responses too.
29. Dikran Marsupial at 02:24 AM on 5 February, 2011
    My posts on that thread have now also started to be "waiting moderation", which is very indeed very dissapointing. If his hypothesis is falsifiable it should be straightforward for him to have answered my question directly. If it is not falsifiable then the challenge is meaningless. My most recent was timestamped "February 4, 2011 at 8:36 AM".
30. Julian Flood at 04:57 AM on 5 February, 2011
    quote The argument is about what is observed to have happened, and makes no assumptions about what values U_n and E_n actually have, and does not make any assumptions about the sources or whether they vary. Think of U_n and E_n as being the total natural uptake and emissions from natural sinks and sources that actually occurred in a particular year. We don't know their individual values, we can't directly observe them, but we don't need to know their values, the key point is that we can infer the difference between them and know if the natural environment is a net source or a net sink. unquote Yes, but this means you have no knowledge of the sizes or even composition of the various sinks and sources. In particular you have no knowledge of the proportion of the atmospheric component which is due to fossil fuel. Without that knowledge you cannot know if decreasing, or even eliminating, fossil fuel emissions will have much impact on atmospheric CO2. quote Your definition of indirect anthropogenic emissions is unworkable. Firstly issues such as deforestation are already included in anthropogenic emissions as it comes under "land use change". Secondly, the main way in which our emissions have changed the carbon cycle is that there is now far more *uptake* because the atmospheric concentration has risen. The whole reason the natural environment is currently a net sink is due to its response to our emissions. If you want to increase the anthropogenic emissions by including an "indirect component", it just means that the natural environment must be an even stronger net carbon sink than the basic mass balace argument suggests, in which case it remains the case that man is responsible for the observed rise in CO2 (i.e. we agree). unquote Where we disagree is in the relative importance of the various components of anthropogenic CO2. They are unquantified and give no guidance on the best course ahead. Lumping any particular flux into 'land use change' or whatever does not improve the situation, it just makes the assertion a tautology. [snip re fluxes] My question was whether isotope changes fit in with the 45% addition to the atmosphere. Perhaps I can ask the question again. Does the isotope change in the atmosphere match that expected from the amount of fossil fuel CO2 produced and not taken up by the enhanced sink? If not, does the discrepancy give us any hint as to the source of other inputs or changed exit fluxes? quote The export from upper to deep ocean reservoirs is entirely irrelevant. The mass balance argument only involves fluxes into and out of the atmosphere, and only the difference in total emissions and total uptake matters. unquote Here we disagree. Deep ocean clathrate deposits are quite capable of belching methane directly into the atmosphere (where they rapidly oxidise) or CO2 from methanophage digestion. In your initial crude equation this does not matter, as everything just gets lumped into the same number. However, in the real world whether the atmospheric CO2 rise is due to a pinch of fossil and a peck of something else matters enormously. The simple mass balance equation gives us no useful knowledge. Is the MWP deep water warming clathrates? A fraction of a degree would do it, and enormous fluxes of light isotope carbon would be released, handily just at the 800 year point which seems to be the lag between warming and CO2 increase in the historical record. quote As to papers on my second post, I haven't seen any papers that use a model of the carbon cycle that is so rudimentary that the result is easily obtained. Anyone who works on the carbon cycle will find it too obvious to publish a paper on, and instead are working on more complex models that take into account things like upper-deep ocean fluxes. The one paper I have seen that uses such a model is the one by Essenhigh (2009), but in that paper Essenhigh fails to understand the distinction between residence time and adjustment time and hence the conclusion of the paper is incorrect. unquote So, as it is elementary, there is a breakdown of the method in a text book? Even so, I'd like something more than a hat tip to increased carbon dioxide automatically keeping the 45% in balance. It seems unlikely. Thanks for the reference to Essenhigh, I've had correspondence with him re his paper on albedo. A gentleman with an engineer's grasp of reality. I'll read that paper with interest and any refutations you can reference. TIA. JF Re your last post: this just reiterates the mass balance argument. It tells us nothing of attribution. Which is why I ask about expected isotope ratios. Ferdinand Englebeen (I think it was in his WUWT posts) mentioned that the ratios are not as expected. Have I remembered that correctly?
31. Dikran Marsupial at 05:08 AM on 5 February, 2011
    Hi Julian, I'll deal with the first bit as it is fundamental "Yes, but this means you have no knowledge of the sizes or even composition of the various sinks and sources." Knowledge of the size or composition of the sinks is not necessary to establish that as a whole, the natural environment is a net sink. This fact is established by the fact that the difference between total environmental emissions and total environmental uptake is equal to the difference between the increase in atmospheric CO2 and anthropogenic emissions. If the natural environment is a net sink, i.e. it takes more CO2 out of the atmosphere each year than it puts in, how can it be the cause of the observed increase? Do you agree that the mass balance argument demonstrates that the natural environment is a net sink? If not, can you explain why?
32. KR at 05:11 AM on 5 February, 2011
    Julian Flood - Isotopic ratios are indeed falling (see here in How do human CO2 emissions compare to natural CO2 emissions). And that rate of change correlates to our emissions. Given the rather massive exchange of the natural carbon cycle, direct attribution is going to be a challenge either way. But the mass balance issue (that we're emitting ~29 GT/year of CO2, and that atmospheric concentrations are rising at 15 GT/year) indicate that we are making a difference in the balance. You've presented no arguments against the total mass balance points other than arguing uncertainties in the natural carbon cycle - we have no such uncertainties about our emissions and the rate of atmospheric increase. Even +/- 50 GT/year uncertainties (balanced) in the natural carbon cycle makes no difference to the fact that we emit 29 GT and only see 15 GT staying in the atmosphere, indicating that nature acts as a sink for the additional 14 GT/year. And that's supported by the ongoing changes in isotope ratios. Your argument against mass balance calculations doesn't hold up. If we were to stop emitting CO2 tomorrow I would expect ~2ppm/year decreases in CO2 for a while, slowing and then halting somewhere above the 280ppm preindustrial level when carbon cycle exchanges balance out with the pulse of CO2 we have contributed over the last 150 or so years.
33. Dikran Marsupial at 05:27 AM on 5 February, 2011
    Hi Julian, "Does the isotope change in the atmosphere match that expected from the amount of fossil fuel CO2 produced and not taken up by the enhanced sink? If not, does the discrepancy give us any hint as to the source of other inputs or changed exit fluxes?" I've not done the calculations myself, but if they didn't match there would be a paper demonstrating that they didn't match, and I'm pretty sure we would have heard about it. "So, as it is elementary, there is a breakdown of the method in a text book? Even so, I'd like something more than a hat tip to increased carbon dioxide automatically keeping the 45% in balance. It seems unlikely." See the paper by Canadell et al in PNAS the bit about the ariborne fraction being 0.45 is about half way down the second column on page 2. The AF is changing slightly but it has been about the 0.45 mark for a long time. "Here we disagree. Deep ocean clathrate deposits are quite capable of belching methane directly into the atmosphere (where they rapidly oxidise) or CO2 from methanophage digestion. In your initial crude equation this does not matter, as everything just gets lumped into the same number." If enough calthrate deposits were released that the natural environment became a net source of CO2 into the atmosphere, the annual rise would be greater than anthropogenic emissions. But we know this is not the case. Prof. Essenhigh is indeed a gentleman, however that particular paper is flat wrong. He makes no distinction between residence time and adjustment time and says there is a confusion in the 1990 IPCC WG1 report. However, if you look at the report, you will find the terms are well defined (Table 1.1, page 7) and in section 1.2.1 there is a paragraph that explains why it is the adjustment time that is relevant to a discussion of the change in atmospheric concentration not the residence time. Prof. Essenhighs calculation of the residence time is essentially correct, it is the corrollory that is incorrect.
34. Dikran Marsupial at 06:20 AM on 5 February, 2011
    Julian, if you want a peer reviewed paper with the mass balance argument, try Raupach et al., it is on section 2.1 on the first column of page 2.
35. Julian Flood at 07:58 AM on 5 February, 2011
    quote If enough calthrate deposits were released that the natural environment became a net source of CO2 into the atmosphere, the annual rise would be greater than anthropogenic emissions. But we know this is not the case. unquote No, you can't assume that. All you can say is that the sources are greater than the sinks by .45 of the fossil fuel emissions: this says nothing about the amounts released by the various sources because you have not quantified the sinks. Which is why the mass balance argument gets you no further than the fact that anthropogenic CO2 is a contributor to atmospheric CO2 rise. The proportion due to fossil fuels is unquantified. The sinks are unquantified. Many of the sources are unquantified. You do not have enough data to say anything other than 'fossil fuel CO2 contributes to atmospheric CO2 rise, proportion unquantified.' quote I've not done the calculations myself, but if they didn't match there would be a paper demonstrating that they didn't match, and I'm pretty sure we would have heard about it. unquote Nice try! Argument from absence is a new one on me. "Raupach et al." Thanks. JF
36. KR at 08:12 AM on 5 February, 2011
    Julian Flood - I think you're being rather disingenuous here. Our well known emissions represent twice the well measured atmospheric increase. Isotope changes correlate with fossil fuel consumption. It is entirely, completely irrelevant what the various sources other than fossil fuel emissions are - our emissions are making the difference in changing CO2 levels, up 115ppm since the beginning of the industrial era. CO2 levels are rising, and without our emissions they would currently be falling. The isotope evidence is no more than a supporting (albeit very interesting) character in this play. Arguing (as you continue to) about attribution, rather than sum effect, is just a pointless distraction.
37. Julian Flood at 08:24 AM on 5 February, 2011
    Re KR quote Isotope changes correlate with fossil fuel consumption. unquote At last, some facts that mean something. Where's the reference please? I've been looking for a paper which calculates that the isotope changes are caused by, and only caused by, fossil fuel emissions. Your other assertions.... could you work through the logic for me? I can see no way from the mass balance argument that you can assert anything other than very weak arguments: our emissions have contributed some increase to atmospheric CO2; if we stopped burning fossil fuel there would be some decrease in atmospheric CO2; fossil fuel burning is one contributor of unspecified size to our climate problem. Sum effect is meaningless in this arfgument because without attribution you do not know relative quantities. That's why the isotope measurements and attribution matter. Incidentally, your first post simply restates the mass balance argument which you may have noticed does not contribute anything other than the 'some of the CO2 from fossil fuel burning remains in the atmosphere.' As, of course, does some of the CO2 from all the sources. JF JF
38. KR at 08:42 AM on 5 February, 2011
    Julian Flood - The earlier link I provided to How do human CO2 emissions compare to natural CO2 emissions has that information, specifically references to Ghosh 2002. That's an excellent reference with a good discussion of the isotopic balances of various sources and sinks. As to the mass balance point - we actually know the size of our contribution: 29GT/year to the list of sources. We see 15GT/year increases in the atmosphere, indicating that 14GT/year of our contribution to the CO2 balance are absorbed by natural sinks. How can our contribution possibly be clearer than that?!? How can it not be us causing the increase? If the CO2 increase was larger than our emissions, then there would be plenty room for discussion as to which part of that CO2 rise was due to us. But it's not - it's much less than our emissions. We cause all of the rise in CO2.
39. KR at 08:46 AM on 5 February, 2011
    Julian Flood - It's also well worth looking at IPCC AR4 for a collected discussion of the isotopic data.
40. muoncounter at 08:53 AM on 5 February, 2011
    #25: "The difficulty of applying atmospheric CO2 levels to the export from upper to deep ocean reservoirs ... presumably someone must have overcome this." See Physical Chemistry of CO2 Absorption for a very detailed analysis. #30: "Where we disagree is in the relative importance of the various components of anthropogenic CO2. They are unquantified ... ." This seems to be on the verge of becoming a strawman. Is what you are really questioning the reality of anthropogenic contribution to increasing atmospheric CO2? Or are you searching for a means to quantify its magnitude? In either case, data exist to resolve the questions to a reasonable degree of certainty. We can track local atmospheric CO2 concentrations against seasonal fuel use patterns (several authors have done this at various locations in Europe); we can see weekly and diurnal traffic patterns in urban environments (multiple papers on urban 'CO2 domes') and a prior thread noted that land sources of CO2 can be tracked via CO and black carbon deposits. #37: "Sum effect is meaningless in this arfgument ... ." Perhaps you should spend some time looking through EIA CO2 emissions data before making that claim. But on the whole, I must agree with KR; the sum is greater than any individual part.
41. Dikran Marsupial at 03:20 AM on 6 February, 2011
    Julian@35 wrote "Nice try! Argument from absence is a new one on me." Experience has told me that when genuine attempts to explain the science in a friendly and open manner get a response such as the one given above, it is not worth the bother continuing. This is especially true of those who (a) don't give answers to questions intended to clarify someones position (you did not answer the questions posed in post 31) (b) do not acknowledge when evidence is presented that answers an argument that they have presented (for instance the Canadell paper that demonstrates that the airborne fraction has been pretty constant at about 45%) and (c) do not pay attention to key issues (for instance that the volume of fluxes are irrelevant, whether atmospheric CO2 rises of falls depends only on the difference between total emissions and total uptake). You have done all three of those things in this discussion. If you don't understand the mass balance argument, you may want to consider that perhaps the problem might be at your end of the discussion. BTW, you wrote: "No, you can't assume that." - I didn't assume that, it is a direct (and rather obvious) consequence of the principle of conservation of mass.
42. JMurphy at 03:45 AM on 6 February, 2011
    Julian Flood wrote : "Argument from absence is a new one on me." I haven't come across any papers that demonstrate that the Theory of Evolution is false : is that an "argument from absence" or a demonstration of the facts ?
43. Julian Flood at 23:47 PM on 23 February, 2011
    Sorry for the long pause, I got rather busy and dropped the ball. At one stage I thought the mass balance argument would allow us to say something about changes in sources and sinks, but further thought led to more doubts. quote Do you agree that the mass balance argument demonstrates that the natural environment is a net sink? If not, can you explain why? unquote The mass balance argument demonstrates that sources are greater than sinks. However, because it does not attribute any numbers to any of the many sinks and sources, it is unable to distinguish between a change in either: for example, see my painstaking plod through the equations above. If you take any source X larger than 14 Gt out of the equations and lump all other sources together as 'natural plus human' then the proponents of the mass balance argument say that all the extra CO2 must be caused by X. This seems to be an error. If sources are in balance and then two sources, X and anthropogenic, increase then all you can say is that some of the increase is caused by fossil fuel burning. If you have no size for X then all you can say is that X+anthropogenic is greater than the sinks by at least 14 Gt. The sinks have increased by enough to absorb (X+anthropogenic) - 14Gt. quote If the CO2 increase was larger than our emissions, then there would be plenty room for discussion as to which part of that CO2 rise was due to us. But it's not - it's much less than our emissions. We cause all of the rise in CO2. unquote No, we cause some of it, that is all the mass balance argument allows you to say. quote Julian Flood wrote : "Argument from absence is a new one on me." I haven't come across any papers that demonstrate that the Theory of Evolution is false : is that an "argument from absence" or a demonstration of the facts ? unquote I have seen elsewhere the conflation of those who ask questions about aspects of climate science with those who e.g. deny evolution, tobacco causes cancer, round Earth etc. It has never, in my experience, been helpful That's my best shot -- we are obviously talking past each other and I am missing some hidden subtlety in your posts which makes things clear to others but not to me. I have seen a post by Lubos Motl where he states that he is sure that the CO2 increase is anthropogenic. I think I'll go and ask him. Thank you all for an illuminating discussion.
44. Dikran Marsupial at 00:37 AM on 24 February, 2011
    Julian@43, Can you explain why it would be informative to exclude some natural source and lump the remainder of the natural carbon cycle together with anthropogenic emissions? We all know that some parts of the carbon cycle are sources and some sinks. WHat is important is whether CO2 levels would be rising if not for anthropogenic emissions, and the answer is quite clearly "no, they would be falling" (which we know because the net effect of the natural environment as a whole is to absorb about half our emissions). Given that CO2 levels would now be falling if we were to cut our emissions to zero, it seems odd to suggest we are not 100% responsible for the current rise. Try giving a specific example, giving values for all natural and anthropogenic sources and sinks, where the annual rise is less than anthropogenic emissions and where the natural environment is a net source. You will find that you are unable to do so, but the attempt will probably demonstrate to you why the mass balance argument is correct. "No, we cause some of it, that is all the mass balance argument allows you to say." It should be obvious that you are missing something here, given that we don't actually need the mass balance argument (or the assumption of conservation of mass) to know that we are the cause of at least some of the observed increase; we already know that simply because our emissions vastly exceed our uptake. It should be no surprise then that the addtion of a constraint (conservation of mass) allows us to make a stronger argument. I have repeatedly explained that you don't need to know the value of individual fluxes to know that the natural environment as a whole is a net sink. If you shared a bank account with your partner and always put in $100 a month more than you spent, but observed your monthly balance only increased by $50 a month, you would know your partner was a net sink (to the tune of $50 a month) without needing to know where he/she spent the money, or how much he/she spent in total or how much he/she deposited each month. The mass balance argument is essententially analogeous.
45. Eric (skeptic) at 01:57 AM on 24 February, 2011
    Currently all of the annual rise in CO2 is caused by man. Since nature absorbs about 1/2 of our annual emissions, one can stretch the word "cause" to say that the rise is caused by the lack of nature's ability to absorb all of our emissions. Part of the lack is due to warming oceans. But our current CO2 causes that warming (averaged over decades to smooth natural variations). A footnote: natural warming following the LIA is the cause of a small part of the historical rise in CO2 (e.g. from 280 to 285 or something similar). But using the common meaning of "cause", man currently causes all of the annual rise in CO2.
46. KR at 02:10 AM on 24 February, 2011
    Julian Flood - Having read and puzzled over your post, I have a question for you. When you state "No, we cause some of it, that is all the mass balance argument allows you to say", is that because not all of the CO2 molecules come from our emissions? Certainly there is continuing exchange of CO2 with the biosphere, with the ocean, etc. If so, yes - lots of the atmospheric CO2 comes/goes without our interaction, even though that's irrelevant to the current discussion. Or (as we have been emphasizing), are you stating that the atmospheric CO2 would be rising without our (well known) contributions? That would be an error. Without our emissions CO2 levels would be dropping - we are wholly responsible for the current increases in atmospheric CO2 levels, which equal half our emissions. The rest is being absorbed by nature. Without our emissions, which without other sources or sinks would cause a >4ppm/year increase? CO2 levels would drop from current values, as CO2 worth ~2ppm/year of our emissions is currently being absorbed by natural sinks. With our emissions? Rising at >2ppm/year. While we are not responsible for every molecule of CO2 out there, we are completely responsible for the current rise in CO2 levels, the change. It doesn't matter if the sum of sources and sinks is 5x our throughput, 10x, or 100x - we're responsible for the current difference between the source/sink levels.
47. Julian Flood at 22:32 PM on 25 February, 2011
    quote Can you explain why it would be informative to exclude some natural source and lump the remainder of the natural carbon cycle together with anthropogenic emissions? unquote Because that highlights the logic of the argument. Any increase outside the lumped-together sources can be pointed to as the cause of all of an increase. If one postulates e.g. an increase in metabolised methane from the permafrost (this is, IMHO, uncontentious as the suppression of methane efflux by acid rain is documented), or perhaps warmer deep water is increasing CO2 emissions from metabolised clathrates, then one can by the same line of reasoning say 'it's all coming from the permafrost'. This would of course be wrong, one needs to add up all the changes and then -- in this case -- one can say 'it's X Gt from permafrost and 27 Gt from fossil fuel. The proportions are X:27 and, since we don't know the absolute size of the sinks, we do not know what eliminating fossil fuel emissions will do to the rate of sink, but it will remove the CO2 in proportion to the contribution, i.e. X:27.' If we cut all of the fossil fuel emissions then we might find that the CO2 levels continue to increase because X from permafrost is bigger than the enhancement of the sink. Because we do not know the actual size of the permafrost contribution, we do not know the actual size of the sink which is taking up all but 14 Gt of the enhanced (fossil emissions + permafrost contribution). We do not know enough to make a meaningful statement. quote What is important is whether CO2 levels would be rising if not for anthropogenic emissions, and the answer is quite clearly "no, they would be falling" (which we know because the net effect of the natural environment as a whole is to absorb about half our emissions). unquote No, that is not the case. We know only that all sinks add up to more than the sum of all the sources. We do not know that CO2 levels would be falling because we have not measured the sinks and sources. See above. quote Given that CO2 levels would now be falling if we were to cut our emissions to zero, it seems odd to suggest we are not 100% responsible for the current rise. unquote No, you cannot truthfully make that assertion -- I could say 'if we cut our emissions to zero then the rate of increase of atmospheric Co2 would only diminish by 10%' and I would be talking equal nonsense. See above. This is just assertion of what we are discussing and brings us no further forward. It does point up one of the problems I'm trying to understand: if we cut to zero, would the increase in atmospheric CO2 entirely cease? My contention -- perhaps too strong a word -- my fear is that it would not. quote I have repeatedly explained that you don't need to know the value of individual fluxes to know that the natural environment as a whole is a net sink. If you shared a bank account with your partner and always put in $100 a month more than you spent, but observed your monthly balance only increased by $50 a month, you would know your partner was a net sink (to the tune of $50 a month) without needing to know where he/she spent the money, or how much he/she spent in total or how much he/she deposited each month. The mass balance argument is essentially analogous. unquote But if you have a beneficent uncle who is adding untold amounts to your account, or not, depending on how his ulcer feels, you can then say nothing about what's going on. Your daughter, meanwhile, has found a way of silently tapping off an increased allowance, and a direct debit, which you have had running so long that you'd forgotten it, has ceased. Now you do not know who is doing what because there are too many unknowns, as I have repeatedly pointed out. Unless you know the details about what's going on, you don't know what's going on and you cannot make any meaningful statement about what's going on. I agree that the mass balance argument is analogous. It is, however, incomplete in your presentation. Perhaps here we have an insight into our disagreement -- you believe that the sources and sinks are all accounted for and the only things to be considered are one input and one output, while I am not sure they are, which is why I ask these questions. My own guess is that we have screwed up one or more biological sinks, the pull down of 12C has decreased, leaving more 12C in the atmosphere, and we're misinterpreting that as part of the fossil fuel signal. But that is just a guess -- it might even be MWP deep water at last reaching the deep ocean clathrates. Or something else. However, we'll have to wait for more measurements -- only then, to continue the analogy, will we be able to look at a bank statement and see what everyone's up to. Only then will we be able to truthfully say thngs like 'if we stop emitting fossil fuel CO2 then atmospheric CO2 levels will begin to fall.'
48. Dikran Marsupial at 23:18 PM on 25 February, 2011
    Julian: I note that you have failed to attempt to engage with the challenge I suggested, namely: "Try giving a specific example, giving values for all natural and anthropogenic sources and sinks, where the annual rise is less than anthropogenic emissions and where the natural environment is a net source. You will find that you are unable to do so, but the attempt will probably demonstrate to you why the mass balance argument is correct." Can you explain why you responded to every part of my post, except that one? Regarding the analogy regarding bank balances, it seems I will have to spell it out. The partner represents the natural carbon cycle, all of it, so there is no benificent uncle (unless you think aliens are coming here in flying saucers and taking carbon from the atmosphere). As I said, we don't need to know anything about the transactions performed by the partner to know that he/she is a net sink. [S]He could be putting in and taking out millions of dollars a month, or hundreds, and it wouldn't make any difference to the argument at all. The change in bank balance only depends on the difference between income and outgoings, not on the volume of transactions. You say I that I believe all sources and sinks are accounted for. That is not correct, and the mass balance argument does not depend on knowledge of the sources and sinks, I have said that repeatedly, so you ought to know that by now. The mass balance argument is a means of inferring the difference between total natural emissions and total natural sources. That is all you need to know to be sure that nature is a net sink and hence CO2 levels would be falling if not for our emissions. Now, please try an address the challenge repeated above, can you give a counter-example, using any values you like for the fluxes, even if they are not realistic (as long as they are positive real numbers). If you are not willing to try, or not willing to admit that you can't find a counter example, what would that imply?
49. KR at 01:09 AM on 26 February, 2011
    Julian Flood - Your "beneficent uncle" and "unscrupulous daughter" are variations of the LGM hypothesis - Little Green Men, unknown and unpredictable. You're essentially stating that although we are adding CO2 twice the level seen as atmospheric rises (and hence sources exceed sinks by the amount of atmospheric rise), if we were to change behavior we would not see the expected decrease in atmospheric CO2 (as sinks would then exceed sources by ~2ppm/year). Because according to you LGM would change the source/sink balance. Complete nonsense, Julian. We're responsible for the current rise, no matter how much you try to invoke LGM to dodge it.
50. KR at 01:18 AM on 26 February, 2011
    Julian Flood - One last attempt, Julian. We are putting an amount "A" into the carbon cycle, a well known amount taken from our fossil fuel use. We're seeing a rise in atmospheric CO2 of "1/2 A", indicating that sources currently exceed sinks by that amount. If we remove an amount "A" from the sources, sinks should then exceed sources by "1/2 A", causing a drop in atmospheric CO2. And as we are responsible for amount "A", we are responsible for the "1/2 A" rise. We are responsible for sources currently exceeding sinks. The only way that CO2 would not drop if we stopped emitting would be if the carbon cycle responded in a non-linear fashion (the LGM of the previous post) - and since the carbon cycle is an order of magnitude larger than our contribution, that would be unreasonable unless you have a testable hypothesis of why it would be different, and some evidence to show it.

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