Controversial new climate change results
University of Bristol Press release issued 9 November 2009
New data show that the balance between the airborne and the absorbed fraction of carbon dioxide has stayed approximately constant since 1850, despite emissions of carbon dioxide having risen from about 2 billion tons a year in 1850 to 35 billion tons a year now.
This suggests that terrestrial ecosystems and the oceans have a much greater capacity to absorb CO2 than had been previously expected.
The results run contrary to a significant body of recent research which expects that the capacity of terrestrial ecosystems and the oceans to absorb CO2 should start to diminish as CO2 emissions increase, letting greenhouse gas levels skyrocket. Dr Wolfgang Knorr at the University of Bristol found that in fact the trend in the airborne fraction since 1850 has only been 0.7 ± 1.4% per decade, which is essentially zero.
The strength of the new study, published online in Geophysical Research Letters, is that it rests solely on measurements and statistical data, including historical records extracted from Antarctic ice, and does not rely on computations with complex climate models.
This work is extremely important for climate change policy, because emission targets to be negotiated at the United Nations Climate Change Conference in Copenhagen early next month have been based on projections that have a carbon free sink of already factored in. Some researchers have cautioned against this approach, pointing at evidence that suggests the sink has already started to decrease.
So is this good news for climate negotiations in Copenhagen? “Not necessarily”, says Knorr. “Like all studies of this kind, there are uncertainties in the data, so rather than relying on Nature to provide a free service, soaking up our waste carbon, we need to ascertain why the proportion being absorbed has not changed”.
Another result of the study is that emissions from deforestation might have been overestimated by between 18 and 75 per cent. This would agree with results published last week in Nature Geoscience by a team led by Guido van der Werf from VU University Amsterdam. They re-visited deforestation data and concluded that emissions have been overestimated by at least a factor of two.
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Here is the abstract from GRL:
Several recent studies have highlighted the possibility that the oceans and terrestrial ecosystems have started losing part of their ability to sequester a large proportion of the anthropogenic CO2 emissions. This is an important claim, because so far only about 40% of those emissions have stayed in the atmosphere, which has prevented additional climate change.
This study re-examines the available atmospheric CO2 and emissions data including their uncertainties. It is shown that with those uncertainties, the trend in the airborne fraction since 1850 has been 0.7 ± 1.4% per decade, i.e. close to and not significantly different from zero. The analysis further shows that the statistical model of a constant airborne fraction agrees best with the available data if emissions from land use change are scaled down to 82% or less of their original estimates. Despite the predictions of coupled climate-carbon cycle models, no trend in the airborne fraction can be found.
Knorr, W. (2009), Is the airborne fraction of anthropogenic CO2 emissions increasing?, Geophys. Res. Lett., 36, L21710, doi:10.1029/2009GL040613.
According to Pat Michaels at World Climate Report:
Dr. Knorr carefully analyzed the record of anthropogenic CO2 emissions, atmospheric CO2 concentrations, and anthropogenic land-use changes for the past 150 years. Keeping in mind the various sources of potential errors inherent in these data, he developed several different possible solutions to fitting a trend to the airborne fraction of anthropogenic carbon dioxide emissions. In all cases, he found no significant trend (at the 95% significance level) in airborne fraction since 1850.
(Note: It is not that the total atmospheric burden of CO2 has not been increasing over time, but that of the total CO2 released into the atmosphere each year by human activities, about 45% remains in the atmosphere while the other 55% is taken up by various natural processes—and these percentages have not changed during the past 150 years)
Here is Figure 1 from the Knorr paper:
Figure 1. The annual increase in atmospheric CO2 (as determined from ice cores, thin dotted lines, and direct measurements, thin black line) has remained constantly proportional to the annual amount of CO2 released by human activities (thick black line). The proportion is about 46% (thick dotted line). (Figure source: Knorr, 2009)
The conclusion of the Knorr paper reads:
Given the importance of the [the anthropogenic CO2 airborne fraction] for the degree of future climate change, the question is how to best predict its future course. One pre-requisite is that we gain a thorough understand of why it has stayed approximately constant in the past, another that we improve our ability to detect if and when it changes. The most urgent need seems to exist for more accurate estimates of land use emissions.
Another possible approach is to add more data through the combination of many detailed regional studies such as the ones by Schuster and Watson (2007) and Le Quéré et al. (2007), or using process based models combined with data assimilation approaches (Rayner et al., 2005). If process models are used, however, they need to be carefully constructed in order to answer the question of why the AF has remained constant and not shown more pronounced decadal-scale fluctuations or a stronger secular trend.
Michaels adds:
In other words, like we have repeated over and over, if the models can’t replicate the past (for the right reasons), they can’t be relied on for producing accurate future projections. And as things now stand, the earth is responding to anthropogenic CO2 emissions in a different (and perhaps better) manner than we thought that it would.
Yet here we are, on the brink of economy crippling legislation to tackle a problem we don’t fully understand and the science is most certainly not settled on.
UPDATE: A professional email list I’m on is circulating the paper, read it here: Knorr 2009_CO2_sequestration
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Is it not true that the warming effect of CO2 is very limited? After 200ppm it is saturated, and a doubling or a trebling wouldn’t produce any significant further warming. It doesn’t matter where it came from, or goes to, or gets taken up by, it cannot cause catastrophic warming.
So what is the fuss about? If CO2 can’t produce warming on an alarming scale it can go on increasing, do its own thing, producing excellent plant food for larger crops, and we will all be better off.
Let us assume that someone developed a machine that drew in atmospheric air and separated-out the CO2. It would be fair to say that the operation would make no real difference to the level of CO2 in the atmosphere.
Why? because for every 100 tons of CO2 extracted from the atmosphere, the oceans would outgas 98 tons of CO2 to restore the equilibrium conditions, as Henry’s law suggests.
Now so far, I have not heard any contradiction of the rough man-in-the-pub proposition that, for every 100 tons of anthropic CO2 put into the atmosphere, 98 tons of it will be absorbed by the oceans.
I have heard counter ‘stuff’, but nothing that would alter or refine this rough assertion gto give a rough correction.
Why this is important, is because it is at the man-in-the-pub level that Cap’n Trade policies will need to be sold. And everybody in the pub is well aware of the workings of Henry’s law, because they have a lot of experience of the behaviour of CO2 and liquids. You just have to open a fizzy drink bottle to know what is going on.
So can anyone tell me: if it is not 98 tons of CO2 absorbed in the sea for every 100 tons emitted, what is it?
Bart, I’ll reply if I want to. You needn’t be so defensive.
“What??? I wrote it as a functional variable. Just like “C”. Is C a constant in my equations? ”
In that case, when you went to solve it, you’d have to substitute in some explicit function of t: some slope*t. As soon as you said substituted in “delta_u = 0.03u”, you lost any dependence with time. You made it a constant. You seem to think that is somehow capturing the most it could do, but it doesn’t (at some later t, it will be 0.04u, and then 0.05u): it doesn’t capture the trend with time – which would seem to be important, because the trend with time was the whole point in the first place.
“So, subsume the kC* term into the “u” variable. There is no loss of generality. Are you being willfully obtuse?”
What makes you think C* is a constant with time? That’s why I said you’d need to solve another set of equations for the ocean, too. The amount of CO2 in the oceans changes over time, just as it does in the atmosphere. You’re determined to let the outflow from the atmosphere be changing with time, while forcing the inflows to be constant. I don’t know why. (breaking up the two terms kC and kC* doesn’t have the physical meaning you’re trying to capture, anyway – when we say 90 Gton/year of carbon go from ocean to air, and 90 Gton/year of carbon go from air back to the ocean, those are referring to actual net flows at some time and place).
“I am looking at steady state dynamics and simplifying the model to a level in which general conclusions of typical behavior may be drawn.”
If your model is poorly formulated, then you can’t draw any conclusions from it. When you write a model, the entire solution should make sense: at t=0, the approach to steady state, and the steady state itself. If your model wanders around for no physical reason, you didn’t write it well.
In any case, I don’t know what steady state you’re looking for. If the rate of emissions continues increasing, then the atmospheric concentration will continue increasing. What steady state?
Ferdinand Engelbeen (04:46:04) :
That is a very incorrect model. It is a straight integration, like a sink with no drain.
Indeed it is the result of the integration over time, if the human emissions increase with a relative constant rate over time, which is the case over the past about 1.5 century. Thus the formula is quite adequate over the past 150 years, but may fail if the emissions remain constant or get reduced (as may be now with the economic crisis).
I have a 55% airborne fraction, as I only use direct fuel use (and other industrial processes), not including land use changes, as these are quite uncertain. Knorr includes land use change, therefore his airborne fraction remains lower.
Took me some time to interprete your formula (too long ago that I worked in process engineering…), but I think that Carrot Eater is right. The more that the rate of change is not dependent on the absolute height of the natural emissions, as in equilibrium the natural emissions and the natural sinks are equal and their net result is zero rate of change and zero change.
Only the addition by human emissions matters and any difference in natural balance. The latter is less than halve of the human emissions in variability and (currently) negative. -C/tau should be -(C-Co)/tau where Co is the natural equilibrium CO2 level at the current temperature.
carrot eater (11:03:42) :
dT = Te – Tb, the difference in temperature between start and end of the period, whatever length of period. For short periods (0-2 years) the factor 4 ppmv/K applies, for periods longer than a few centuries (to near a million years), the factor 8 ppmv/K applies. For in between periods, no reliable data are available, but I suppose that the factor would be in between.
“for every 100 tons of CO2 extracted from the atmosphere, the oceans would outgas 98 tons of CO2 to restore the equilibrium conditions, as Henry’s law suggests.”
And that, people, is the way it is, [today’s date].
Mariwarcwm: “After 200ppm it is saturated, and a doubling or a trebling wouldn’t produce any significant further warming.”
No. There are wavelengths where it is still optically thin, but even that is besides the point. When you talk about saturation, you’re only thinking about the transmittance of an IR beam through the atmosphere. You need to think about what happens to the IR that is absorbed – it doesn’t just disappear.
supercritical: “Now so far, I have not heard any contradiction of the rough man-in-the-pub proposition that, for every 100 tons of anthropic CO2 put into the atmosphere, 98 tons of it will be absorbed by the oceans.”
Did you read the paper this thread is about? About 45% of the accumulation is in the atmosphere.
carrot eater,
Are you saying that for every 100 tons of CO2 put up in the atmosphere, roughly 50 tons ( as opposed to roughly 98 tons) gets absorbed by the sea?
Does this mean that the Henry’s law is about 1:50 for fresh water, but for seawater it is about 1:25?
I’d like to know if that is what you are actually saying.
supercritical (12:49:56) :
Ferdinand,
Could you now tell us roughly; at a simple level of circa 1: 50 for fresh water, what is the equivalent for seawater?
I don’t know what you mean with the 1:50, I know that there is about 50 times more CO2 in the oceans than in the atmosphere, but that is not (yet) in equilibrium…
The difference in CO2 (in different forms) content between seawater and fresh water at the same temperature and ambient CO2 levels seems in the order of 200 times, if I have calculated that right (but that was a very long time ago that I have looked up such formula’s…). That doesn’t say anything about what the oceans are capable of absorbing or releasing, as that only depends of the partial pressure difference between CO2 in the oceans surface and in the atmosphere. The former dependent of temperature, pH, DIC, total salt content,…
Finally gotten around to writing a response to this. There are two reasons this study is irrelevant to the consensus on climate change:
First, Knorr’s conclusion makes no claims about FUTURE carbon cycle feedbacks—it simply finds that carbon sinks’ ability to absorb CO2 has not declined in the PRESENT. Claiming that Knorr casts doubt on models predicting accelerating future growth in CO2 concentrations makes the logical fallacy of extrapolating future trends from current results—the same error that led financial firms to conclude that housing prices would always increase.
Second, the studies that Knorr critiques were published AFTER the 2007 IPCC report came out; therefore, if Knorr is correct in proving these studies wrong, his findings cannot logically have any bearing on the accuracy of the IPCC’s conclusions. At worst, Knorr simply returns us to the state of science when the IPCC report was written. In other words, you’re attacking a straw man.
http://akwag.blogspot.com/2009/11/duds-skeptic-bombshell-that-never-went.html
carrot eater (05:24:16)
Summarizing all your hand-waves about the sea’s ability to absorb or emit CO2 you seem to be in effect arguing that whether the oceans are a net source or sink is largely guesswork with large potential error and hence clearly open to much doubt but however, a warming sea being a net source is probably more likely than not.
In any event the annual flux is 400 Gt and apparently we think we can attribute -1% or so to human emissions absorption. Yes I think i can safely impugn anyone in climate science who would hang his hat on such a number, as opposed to an equally reasonably +1% emission, bearing in mind the very large error bars involved.
I notice you didn’t mention the deforestation chaps who, of course were universally wrong with their net deforestation number, since the planet is demonstrably greening. It’s apparently quite easy for an entire collection of group-thinkers to be wrong. Happened with economists too. Your argument, like most arguments about CO2 fractioning consists of starting with the desired result and working backwards to the calculation.
This idea of course that nature exactly takes in what it puts out and the extra 3% of man-made CO2 just sort of hangs around, not really wanting to get involved in the party, may be attractive to alarmists but is totally philosophical in nature and has no actual basis in fact. It’s also quite amusing considering you just lectured me about how complex nature really is. Yes indeed, it’s not really in any form of equilibrium steady state at all is it – either spatially or temporally? So why present a mere dubious philosophy as a fact? An indisputable fact even.
Few people are even measuring the inflows and outflows of the biosphere – they prefer a simpler, imaginary computer world it seems. The few who do bother to measure real sources and sinks always seem to be surprised by their results since it always rocks the dogma. Empirical science is like that: It doesn’t always like to follow our preconceived and overly-simplistic theories. Modeling isn’t science and science isn’t modeling. Models must always be validated against empirical results. There are no doubt more surprises in store for those who bother to look.
supercritical:
Did you read the paper? Empirical data. I thought that was preferable to models? By the way, a chunk goes into the biosphere, too; the ocean isn’t the only other sink.
Beyond all the complications Ferdinand gives (multiple chemical equilibria, biology, etc), remember that the ocean is nowhere near being well mixed; it’s not as if the entire thing is in equilibrium with the atmosphere. The deep ocean isn’t in good contact with the surface, and altogether different things are happening at different latitudes.
I don’t know why you’re trying to back out a Henry’s Law constant from this bit of data alone. It’s not doable.
P Wilson (12:50:30 and following) :
jarowowski goes through 15 processes that occur in ancient ice to alter its capture process of real amount, and you only document two. Solubility in water is certainly one of them. Given that proxies exist that show elevated c02 at various timescales across the hemispheres other than in Vostok or the Law dome then there’s still much doubt that ice at 420,000 years old gives the exact measure of aerial co2 at each year or decade over those 420,000 years.
Solubility in water is not an item at all: Vostok at -40°C has no water at the ice surface and other ice cores (near the coast) with less cold temperatures show the same CO2 levels for the same periods of time. In fact all objections of Jaworowski about (possible) problems with ice cores were answered by the 1996 work of Etheridge e.a.: http://www.agu.org/pubs/crossref/1996/95JD03410.shtml
I have my doubts about Jaworowski as scientist: many of his remarks are simply impossible or should show the opposite result of what he says. And he seems not to understand the difference between the age of the ice in the ice core and the enclosed bubbles (the gas age), while accusing others of deiberate fraud in comparing CO2 levels in an ice core ((Siple Dome) and Mauna Loa. For an ice core specialist, that is quite remarkable.
given that there are 1000gts of c02 at ocean surfaces alone and 38,000gts at intermediate and lower depths, then nature can add .. For the Anthropogenic part, that gets lost in the flux. Its like adding 30ml a day to your 1 litre a day drinking water (and following)
If you eat 2000 kcal/day and burn off 2000 kcal/day, nothing will happen with your weight. Eat some 5 kcal/day more, slowly increasing over the years to 50 kcal/day, without more excersizing, watch what happens with your weight.
It doesn’t matter how much carbon is in the (deep) oceans, it doesn’t matter how much is exchanged between oceans/biosphere and atmosphere back and forth. All what matters is the balance at the end of the year: the difference between ins and outs of the atmosphere. For nature that is 4 GtC/year more out than in. For humans that is 8 GtC/year only in…
Oh silly me I’ve gone to WAG’s blog and discovered that the carbon cycle is just like an overflowing bath tub. How could i not have seen that one before? It’s all so obvious. Jeez if i had a penny for the number of people who think a crap analogy explains things. It sure explains his confused lawyerly post above though. Ooh so we can’t say what the future will hold. Well quite, no we can’t. So why pretend we can? What we can say is that people who were wrong with past guesswork shouldn’t be trusted to be any better this time around. What we should do is allow some quality time for skepticism because it’s clear just how much sheer guesswork is inherent in this whole IPCC effort.
JamesG: My handwaving is to serve a simple purpose: to demonstrate that your huge natural flows are part of the carbon cycle. That big natural flow into the atmosphere isn’t all staying there. I don’t know why this is lost on people. After all, the concentration of CO2 in the atmosphere had been fairly stable for most of the current interglacial, bouncing around within a band of +/- 10 ppm or so.
If you take carbon that is currently outside the cycle, and stick it in, it simply has to accumulate somewhere; it won’t just disappear. As it happens, it shows up in many places – the air, water and land/biosphere. Yes, if you wait long enough, it’ll eventually end up in the deep ocean and finally exit out as rocks and such, but that takes quite a while.
Question:
Is the annual uptake of CO2 by “something” increasing
Answer: Yes by 0.11ppm per year
for Point Barrow see:
http://img509.imageshack.us/img509/9348/ptbarrowco2diff.jpg
The annual carbon dioxide sink is absorbing more CO2 over ther period considered
Is this caused by warmer conditions promoting more growth or by an increased greening caused by more CO2 or increased greening caused by CO2 and temperature?
It would appear it is not simply CO2 – As can be seen the annual difference has dropped since 2004. CO2 is in a continuous rising cycle. Temperature has stalled and dropped since 2003.
It would therefore appear to be mainly temperature.
JamesG: Forget bathtubs. You don’t need an analogy to understand the carbon cycle. You only need to look at the carbon cycle itself.
http://en.wikipedia.org/wiki/File:Carbon_cycle-cute_diagram.svg
Pause a moment before you start saying that the numbers on there are made up or uncertain or whatever – because that was not the original basis of your disagreement. The basis of your disagreement was conceptual – how can human emissions cause an accumulation anywhere if they’re only 3% of the inflow to the atmosphere. Turns out, it’s not that hard.
Ferdinand – I have doubts about Jarowelski’s interspersion of political comments, although what I don’t doubt is the idea that c02 dissolved in ice at temperatures of -20 or -40c could be representative of aerial global average c02 at all latitudes and locations. I’m not sure about the trend of c02 following temperature, as the time lag even when looked at in close detail decade on decade – the correlation between c02 and temperature becomes more uneven, although there is no discernable point at which c02 leads a temperature change. Its almost impossible to accept the theory that carbon exchanges are fixed by a natural variation limited to 280ppm to 190ppm, simply because that is what ice core measurements infer from frozen ice in environments which are subzero all year round.
heavily compressed ice can contain liquified water in ice air bubbles, and over thousands to hundreds of thousands of years, there is no way of knowing how isotope ratios change
i mean, they are recognised as proxies and not as actual measurements, but are used as actual measurements for the present purpose of maintaining the c02 has increased due to Anthropogenic emissions, and disregarding Henry’s law. Even if 200ppm 0r 220ppm of c02 were bound in ice 200,000 years ago, that is no indication that the air above didn’t contain 400ppm – just that 300ppm became trapped in ice. Ice doesn’t absorb c02 well. Oceans abosorb it quite dramatically – and sea ice acts as a barrier to gas exchange.
Someone may have stated this, but the residence time of CO2 being 4 to 5 years come from a simple reasoning understandable to even schoolboys.
1. The total amount of CO2 in the atmosphere is roughly 3000 million tons.
2. Photosynthesis by plants draws about 400 million tons yearly, and the same amount goes back to the atmosphere via respiration and biomaterial decay.
3. The atmosphere – ocean exchange of CO2 amounts to roughly 200 million tons yearly.
Both exchange processes do not care whether the CO2 is of biological or non-biological origin. Hence the average residence time is 4 – 5 years. Q.E.D.
Assming a residence time ot 50, 100, 200 years or more is utter nonsense.
carrot eater (11:39:03)
maksimovich: I don’t see how Marinov’s modeling results (2006) show that that Le Quéré’s (2007) work is incorrect, but in any case, I’ve been using very weak language with Le Quéré’s results for a reason. They’re very preliminary results, and have drawn critical responses. Also, my apologies: I see I described Le Quéré’s work as empirical, but it uses models heavily as well.
Asymmetry was a reducible quantification (synthesis) as Marinov et al suggest in the last paragraph.
The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human
intervention to modify one of these without greatly altering the other.
The Le Quere paper questioned in science eg Law et al
Unlike Le Quéré et al. (Reports, 22 June 2007, p. 1735), we do not find a saturating Southern Ocean carbon sink due to recent climate change. In our ocean model, observed wind forcing causes reduced carbon uptake, but heat and freshwater flux forcing cause increased uptake. Our inversions of atmospheric carbon dioxide show that the Southern Ocean sink trend is dependent on network choice.
Le Quere respond
We estimated a weakening of the Southern Ocean carbon dioxide (CO2) sink since 1981 relative to the trend expected from the large increase in atmospheric CO2. We agree with Law et al. that network choice increases the uncertainty of trend estimates but argue that their network of five locations is too small to be reliable..
Probably not the best of papers to state ones case.
CO2 forecast SEE: http://sites.google.com/site/earthquakepredictionbyjac/Home/greenhouse-effect/CO2forecast.pdf?attredirects=0
P Wilson (09:37:49) :
We’re at al natural high point historically of c02. However, there are resolution problems associated with ice core measurements outlined by here:
Ice core measurments are relatively consistent. If there were genuine problems the readings would be all over the place – a bit like the Beck observations.
is also illogical to claim that the 3% of CO2 which humans put into the atmosphere accumulates over time to 30%, while the 97% of CO2 which nature adds to the atmosphere does not accumulate and in fact shrinks to 70% of the total.
This is not what is being said. No-one is suggesting that the oceans and biosphere are selecting which CO2 molecules it absorbs. Read carrot eater (12:21:45) : where he has already responded to this same comment. I’ll try an explain again using carrot eater’s analogy (Anthony – please request a short explanatory post on this issue from carrot eater or
someone).
Lets imagine, in pre-industrial times, a stable concentration of CO2 of 500 units. Each year 100 units is emitted from the earth and each year 100 units is absorbed. This is the natural carbon cycle. (As an aside note that the average residence time for a unit is 5 years).
Now let’s say humans start burning fossil fuels which produces an extra 4 units per year. What happens now? Does the natural carbon cycle continue to emit and absorb 100 units only? If so then the concentration in the atmosphere will begin to increase. It will be 504 units after Year 1, 508 units after Year 2 etc. This doesn’t mean that the extra 4 units are all from human production, it just means that 104 (100 + 4) is emitted but only 100 is being absorbed.
This, though, is not what is happening. It seems as though the earth (oceans and biosphere) is taking up the equivalent of an extra 2 units, so 102 units is now being absorbed, i.e. ~50% of the increase due to human emissions is being removed. However this still means CO2 will accumulate in the atmosphere because 104 units is being emitted, so afeer Year 1 there will be 502 units, after Year 2 there will be 504 units and so on. The source of the emissions is irrelevant. What’s important is the the fact that emissions have increased.
I’m not sure this is any clearer.
P Wilson (19:00:48) :
Ferdinand – I have doubts about Jarowelski’s interspersion of political comments, although what I don’t doubt is the idea that c02 dissolved in ice at temperatures of -20 or -40c could be representative of aerial global average c02 at all latitudes and locations.
You need to look up the literature (especially the work of Etheridge e.a.). There is no liquid water in ice below -30°C, except when impurities are present, which is very low at Vostok and other inland ice fields. Even for other more seaside cores, some layer of less structured water molecules (a few layers thick) are present at the ice/air surface, but less unstructured in between the ice crystals.
A nice presentation of the (small) changes in (isotopic) composition during buildup of the ice layers can be read here:
http://www.pnas.org/content/94/16/8343.full
But once the ice bubbles are closed there is no change in (isotopic) composition anymore in the bubbles. All CO2 is contained in the bubbles, ice doesn’t contain CO2.
One realistic test of CO2 migration was done onder the same pressure and temperature circumstances as for the Vostok ice core at depth. They found a small migration calculated over 100,000 years against ambient pressure. But as the pressure difference between 2 km and 2.001 km is negligible, vertical migration is negligible too. The more that such migration would be measurable as a smoothing out of the variability of the glacial/interglacial transitions against temperature, which is not the case over the past 800,000 years.
In all cases, CO2 and a lot of other gases are measured by NDIR, GC, mass spectrometers, in the gas bubbles. These are not proxies but real measurements, but need to be (and are) corrected for the small changes in (isotopic) composition which happen before bubble closing.
Finally, as Etheridge showed, the CO2 level in already closed bubbles from the ice core (sampled with the normal routine: coring, relaxation, transport, crushing of the ice under vacuum, measurement after a cold trap) and the still open cores in firn (sampled in situ, measured by the same GC equipment above) at the same depth have the same CO2 content ánd these overlap with the South Pole direct air measurements. See:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/law_dome_overlap.jpg
tokyoboy (20:57:32) :
It seems very difficult to grasp the difference between the residence time of a single CO2 molecule (whatever the origin) in the atmosphere and the decay time of an injection of mass (whatever the origin) of CO2 to go back to the original concentration.
Let us suppose that all human caused CO2 was red coloured. At a certain moment we inject 100 GtC (as red CO2) into the atmosphere above the 700 GtC of natural CO2 already there. Thus at the end of year 1, we measure 800 GtC in the atmosphere, of which 12.5% is red. I think we may agree that the increase is 100% of human origin in this case.
Now, during year 2, the seasonal and permanent exchanges of CO2 replace 150 GtC of what is in the atmosphere with colourless CO2 from the (deep) oceans (we forget the exchanges with vegetation for the moment to keep it simple). Thus the red CO2 in the atmosphere decreases with about 20% in a year, leading to a half life time of “human” red CO2 of about 5 years. That is your residence time.
But what happens to the total amount of (partially colored) CO2? The exchanges of CO2 between atmosphere and oceans(/vegetation) don’t change the amounts in the atmosphere, as long as the inputs and outputs are equal. But as we have increased the CO2 content of the atmosphere from 700 to 800 GtC, there will be less natural ins (less pressure difference for the tropic ocean outgassing) and more outs (more pressure difference at the polar sinks), the difference: about 4 GtC more natural sink than source.
Thus of the 800 GtC in the atmosphere, only 4 GtC is removed in the first year. You see the difference? 150/800 GtC is exchanged each year, 4/800 GtC is removed the first year. It is the latter which is important for the greenhouse effect, as quantities matter, not the origin (the color)… The excess decay rate is about 38 years half life time, far higher than the 5 years you mentioned (which is the exchange rate, not the excess decay rate), but far less than the hundred(s) of years supposed by the IPCC.
As the amount of red coloured CO2 dwindles fast with 20% per year, there is practically none left after say 50 years. Even then the total quantity still is 50 GtC above the original level. Thus while the compostion after 50 years is near 100% natural, the cause of the excess quantity still is 100% from the original injection…
In graph form:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/fract_level_pulse.jpg
where FA is the fraction of “anthro” CO2 in the atmosphere, FL in the upper oceans, tCA total carbon in the atmosphere, nCA natural carbon in the atmosphere and anthro carbon is the difference between the two. All based on a pre-industrial level of 580 GtC in the atmosphere and realistic exchange rates.