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Climate Hustle

Climate Change Cluedo: Anthropogenic CO2

Posted on 25 July 2012 by Tom Curtis

Anthropogenic CO2?

The human-caused origin (anthropogenic) of the measured increase in atmospheric concentrations of CO2 is a cornerstone of predictions of future temperature rises.  As such, it has come under frequent attack by people who challenge the science of global warming.  One thing noteworthy about those attacks is that the full range of evidence supporting the anthropogenic nature of the CO2 increase seems to slip from sight.  So what is the full range of supporting evidence?  There are ten main lines of evidence to be considered:

  1. The start of the growth in CO2 concentration coincides with the start of the industrial revolution, hence anthropogenic;
  2. Increase in CO2 concentration over the long term almost exactly correlates with cumulative anthropogenic emissions, hence anthropogenic;
  3. Annual CO2 concentration growth is less than Annual CO2 emissions, hence anthropogenic;
  4. Declining C14 ratio indicates the source is very old, hence fossil fuel or volcanic (ie, not oceanic outgassing or a recent biological source);
  5. Declining C13 ratio indicates a biological source, hence not volcanic;
  6. Declining O2 concentration indicate combustion, hence not volcanic;
  7. Partial pressure of CO2 in the ocean is increasing, hence not oceanic outgassing;
  8. Measured CO2 emissions from all (surface and beneath the sea) volcanoes are one-hundredth of anthropogenic CO2 emissions; hence not volcanic;
  9. Known changes in biomass too small by a factor of 10, hence not deforestation; and
  10. Known changes of CO2 concentration with temperature are too small by a factor of 10, hence not ocean outgassing.

1) The start of the event

Annual emissions of CO2 by human use of fossil fuels rose from 3 million tonnes of Carbon (11 million tonnes of CO2) in 1751 to 54 million tonnes of Carbon (198 million tonnes of CO2) in 1850.  After that fossil fuel use rose sharply so that by 2008, annual emissions (including from cement manufacture) had risen to 8749 million tonnes of Carbon (32 billion tonnes of CO2).  The rise in the atmospheric concentration of CO2 also began around 1750 and has followed the emissions up.  This extraordinary coincidence strongly suggests that anthropogenic emissions are the cause of the rise in CO2 concentration.

(Wolfgang Knorr, 2009)

2) The close correlation

The increase in CO2 concentration over the long term (1850-2005) almost exactly correlates (corr.: 0.997; R^2: 0.993) with cumulative anthropogenic emissions from all sources including Land Use Change (LUC).  The close correlation has continued in recent times, with a correlation of 0.9995 when compared to the Mauna Loa record (r^2: 0.999).  So exact a correlation would be extraordinary if anthropogenic emissions were not the cause of the increase in CO2 concentration.

(Scripps Institute)

3) The mass balance

Over the course of the twentieth century, the increase in CO2 in the atmosphere measured in tonnes has been less than anthropogenic emissions in every year, and has averaged only 44% of anthropogenic emissions over the period from 1850-2005.  Indeed, growth in atmospheric emissions probably has not exceeded anthropogenic emissions since the early 1880s, approximately the time anthropogenic emissions reached the equivalent of 0.45 ppmv of atmospheric concentration.  It is interesting to note that the airbourne fraction, ie, the atmospheric increase divided by total emissions, has increased slightly in recent times.  This means that natural carbon reservoirs have acted as a net sink over the course of the 20th century, and strongly indicates that the source of the increase in CO2 concentration is anthropogenic.


(Adapted from Cawley, 2011; data from CDIAC)

4) Declining C14 ratio

Carbon 14 is formed in the atmosphere by collisions between cosmic rays and Nitrogen.  It has a very short half life (5,730 years), but atmospheric C14 is continuously replenished, maintaining a near constant concentration.  Buried C14 is not replenished, however.  As a result, whether from volcanoes or fossil fuels, CO2 from long-buried sources has effectively no C14.  The addition of large quantities of CO2 from a long-buried source to the atmosphere will result in a significant decline in C14 concentration in the atmosphere, which is what we see.  More recent, high precision measurements show the decline in C14 continued after the end of atmospheric nuclear testing.This is strong evidence that the source of the increased concentration of CO2 is fossil carbon, either from volcanoes or from fossil fuels.


(Levin and Hesshaimer 2006)

5) Declining C13/C12 ratio

Carbon has two stable varieties (isotopes), C12 an C13.  Because C13 has an extra neutron, it is heavier.  In photosynthesis, most plants find it easier to take up the lighter C12, and do so at a higher rate than they take up C13, with the result that carbon compounds formed from the products of photosynthesis, including plants, animals and fossil fuels have a lower C13 to C12 ratio than does the atmosphere.  Introducing a large quantity of CO2 derived from photosynthesis would cause the  C13/C12 ratio to decline.  In contrast, CO2 introduced from volcanoes or from outgassing from the ocean would not significantly affect the C13/C12 ratio.  In fact the global C13/C12 ratio has declined, which is very strong evidence the source of the CO2 increase has was C12 enriched, ie, derived from photosynthesis.  Therefore it is very strong evidence that it comes from the biosphere or fossil fuels, rather than from volcanoes or oceanic outgassing.

(Bohm et al, 2002)

6) Declining oxygen concentration

Because the change in solubility of O2 in water with change in temperature significantly differs from that of CO2, the change in O2 concentration is not affected by other possible CO2 sinks. That means the decline in CO2 concentration means any large unknown natural sources of CO2 must not come from a source of combustion but must come from a low C14 source generated by photosynthesis. These facts together almost completely preclude the existence of such putative natural sources. Because of the importance of the O2 decline, it is worthwhile looking at the chart below from the IPCC TAR which shows it:


The observed decline in O2 is straightforward. The diagonal arrow from the start point marked "fossil fuel burning" represents the expected change in CO2 and O2 concentrations from known fossil fuel consumption. The arrow marked "ocean uptake" represents the uptake of CO2 by the ocean, which does not affect the O2 level. The arrow marked "land uptake" is the uptake of CO2 and release of O2 by photosynthesis, which also decreases the CO2 concentration and increases the O2 concentration. Finally, the small arrow marked "outgassing" represents outgassing of O2 from the ocean, which does not affect CO2 concentration. That outgassing is partly the result of a warming ocean, and partly a result of the very slight decrease in the partial pressure of oxygen in the atmosphere. These factors are reasonably, but not exactly known. It is important to note that because the fall in O2 concentration is significantly less than that predicted from known combustion of fossil fuels, the uptake of CO2 by photosynthesis must exceed the combustion or decay of modern organic material from either anthropogenic (Land Use Changes) or natural sources.

7) Increasing CO2 concentrations in the ocean 

Simultaneously with the rise in the concentration of CO2 in the atmosphere, the concentration of CO2 (and its equilibrium products) in the ocean has been increasing.  The rise in CO2 in the ocean is referred to as an increase in the "partial pressure" of CO2, and results in a simultaneous decline in the partial pressure of Hydrogen (pH), ie, an increase in the ocean's acidity.  If the amount of CO2 in the ocean was falling, the partial pressure of CO2 would be falling, and the pH rising.  This is very strong evidence that oceanic outgassing is not the cause of the rise in atmospheric CO2.


(Source )

8) Measured volcanic emissions

Scientists have used a variety of methods to determine the CO2 emissions from volcanoes.  A common method is to use a tracer gas, ie, a gas emitted from volcanoes but which does not stay in the atmosphere for long.  Determining the emissions rates of the tracer gas from volcanoes, together with the concentration of those gases in the atmosphere allows the overall level of volcanic activity to be measured.  Once that is measured, measurements determining average rates of CO2 emissions for a given amount of activity can be used to determine the global CO2 emissions from volcanoes.  Other techniques are used to measure CO2 emissions from volcanoes, mid-ocean ridges and subduction zones under the sea.  The emissions, from all volcanoes, both on land and under sea, are about one hundredth of anthropogenic emissions.  While there may be some error in the estimates, it is unlikely that the error would be large enough for volcanoes to be emitting a sizable fraction of anthropogenic emissions.  That strongly suggests volcanic emissions are not the source of the increased CO2 concentration.


(Ratio of anthropogenic to volcanic CO2 emissions; source)

9)  Known changes in biomass

Anthropogenic Emissions from Land Use change and deforestation represent 10% of all human emissions (0.9 PgC of 10 PgC). Over the last century, human-caused deforestation and other land use changes have been by far the largest cause of change in land cover, and hence natural changes cannot be significantly larger than that.(Source)  Indeed, as discussed regarding the declining oxygen concentration, that decline together with the land uptake shows that the biosphere is a net sink for CO2.

10) Past changes in CO2 concentration

During past "ice ages" (glacials) CO2 concentrations have correlated with temperature, with approximately a 22 ppmv increase in CO2 for every 1 degree increase in temperature.  In more recent historical times, there was an increase in CO2 concentration during the Medieval Warm Period (MWP) relative to the Little Ice Age (LIA) of about 10 ppmv for approximately a 1 degree C change in temperature.  Given that global temperatures have increased by 0.7 C since 1850, we would expect an increase in CO2 concentration of between 7 and 15 ppmv based on historical precedents.  That CO2 concentrations have increased by approximately 110 ppmv over that period is very strong evidence that the source of the increase was not outgassing from the ocean.



Playing Climate Change Cluedo

As a child I enjoyed playing Cluedo (Clue in the US market).  I soon learned you discovered more from the questions people did not respond to than from those that they did, and developed a matrix from which to plot responses and non-responses.  Filling in the matrix soon honed in on the correct answer, who killed whom, with what and where.  Science is sometimes like that.  The lines of evidence are the questions we put, and if we plot out our matrix, it quickly becomes clear that it is the humans who have caused the rise in CO2 levels, by burning fossil fuels in the twentieth century.  Every other hypothesis makes a host of predictions that do not pass the test of the evidence.


Correction:  The figures in section (2) have been corrected as of 12:45 PM, 29/07/2012.  The nature and reason for the correction explained in my comment of 12:40 PM of that date.

The figure for the airborne fraction in section 3 was corrected at 8:54 AM, 18 th Feb, 2013.


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Comments 51 to 67 out of 67:

  1. Done.
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  2. Rob Honeycutt @46, a typical response for a fake "skeptic". If you recall the story of the blind men and the elephant, the better informed fake "skeptics" are like a blindfolded man, who having felt a trunk insist that elephants are snakes - refusing to either listen to others, or to take of their blindfold and look lest they see any fact that might disturb their opinion.

    In RealOldOne2's case, he has seized on the C13/C12 ratio and refused to even admit or discuss other relevant evidence. In particular he refuses to consider the prediction with regard to other evidence that would result from accepting his favourite theory. Specifically:

    a) As previously discussed, if biomass was the source of just half of the atmospheric increase, the total biomass of the planet (including bacteria) must have halved over the last 150 or so years;

    b) If biomass was the net source of even a significant fraction of the CO2 increase, O2 would have declined by more than the amount required to provide for combustion of known fossil fuel usage, not less;

    c) If biomass was the net source of a significant fraction of the CO2 increase, it would massively dilute the impact of adding fossil carbon to the system, thereby massively reducing the reduction in the C14/C12 ratio;

    d) If non-anthropogenic biomass emissions were the source of a significant fraction of the CO2 increase, the 0.997 correlation between anthropogenic emissions and increases in atmospheric concentration would be almost inexplicable;

    e) If non-anthropogenic biomass emissions were the source of a significant fraction of the CO2 increase, anthropogenic emissions would not have exceeded the increase in mass of atmospheric CO2 by 25% or more in all but nine years since 1850, and every year since 1886;

    and let's not forget that a biomass origin of the CO2 increase does not explain:

    f) The extraordinary coincidence in timing between the start of the rapid increases in atmospheric CO2 and the ramp up in anthropogenic emissions.

    Concentrating on the one line of evidence which is compatible with a biomass origin of the increase in atmospheric CO2 while ignoring the six lines that absolutely rule it out represents a massive cognitive dissonance.

    It sort of gives a new meaning to the old saw:

    In the land of the (willfully) blind, the one-eyed (ie, biased) man is king.
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  3. The reason I ended up on this post was because RealOldOne2 was claiming that there is no empirical evidence that humans are causing catastrophic warming. I wanted to start with this post as evidence, first, that humans are causing the dramatic rise in CO2 concentrations. From there I was going to go through radiative forcing and then climate sensitivity.

    But of course, the whole track, which I think he knows would lead to the answer he doesn't want to hear, ends up derailed on one small point while ignoring all the rest.
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  4. Ahh. You could have started off asserting that water is wet, and you would never have got past that argument.

    Nice post though. Very thorough.
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  5. By searching on "RealOldOne2's" nick, the GoobleBox turns up a devoid-of-any-videos video feed. Hmmmm.....

    RealOldOne2's UT account

    Now, this *could* be a different RealOldOne2, but given the other ~10K denier/contrarian refs Google turns up, I highly doubt it. Golly, to know the real reason why all those videos are now gone...;)
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  6. Thanks for a very good summary of the topic. However, I think it takes a very geological mind to describe 14C as having a " very short half life (5,730 years)". Our perspectives are different in this matter.

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  7. Mattias Ö true, but a "very geological mind" is exactly the sort that is needed in working out how much 14C we should expect to see in fossil feuls (i.e. practically none). ;o)

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  8. Elsewhere gac73 has linked to some pseudoscientific drivel as an example of "common sense" science.  An example of the author (Timothy Casey) of the drivel style is shown by his table of emmissions per annum from various volcanoes.  Unfortunately for him, one of his sources (Shinohara, 2008) is available free online.  Consulting that work we find that Shinohara lists total emissions for an erruption event, not emissions per annum (see table 3, and discussion in text).  While erruptions typically take less than a year to occur, they do not represent ongoing emissions and presenting them as such distorts his source.

    One further misrepresentation (among a host) is Casey's is in his discussion of C13 where he suggests volcanic CO2 could account for the the modern rise in CO2.  In fact, volcanic CO2 is C13 depleted relative to the Vienna Pee Dee Belemnite Standard having a d13C of -4 in most cases, but up to -12 at convergent plate boundaries.  For comparison, fossil fuels have a d13C of -27, and the atmosphere has a d13C of -8.  That is right.  The atmosphere is C13 depleted relative to the standard, and the vast majority of volcanoes are not depleted relative to the atmosphere, ie, volcanic eruptions typically enrich the atmosphere with C13.  Casey creates the opposite impression by only noting the C13 depletion relative to the standard reference case, but leaving that technical detail unclear.

    (Sources of data for the C13 discussion are noted at my Notes for the OP here, found on my blog.)

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  9. Hi,

    let me please start a discussion on the source of CO2(atm) based on the 18O isotope composition. This reply comes from this posting

    Let me please continue, the 18O isotope composition in atm CO2 is key to understand the sources.

    The lack of any significant trend in d18O reveals there's one main source of CO2 Oxygen atoms. The seasonal variation gives clues on the two alternating sources.

    If the Oxygen comes from atmospheric O2 by combustion, there are two main sources of photosynthetic O2, terrestrial and marine organisms.

    In this posting, I have already discussed with more detail the reactions involved.

    Photosynthetic O2, has the isotopic signature of the water the organisms use in their metabolism.

    As convention, the 18O isotope composition of sea water is taken as zero, although, deep and surface ocean waters show important diferences.

    Terrestrial waters, come from precipitation waters that have markedly depleted delta18O and deltaD values.

    In this link we see how isotopes distribute over the continents

    for example this one shows the distribution of annual mean18O values.

    Seasonal variation is significant.

    According to this map we should expect significant isotope diferences depending on the source of Photosynthetic O2. Basically from higher latitudes of the Northern Hemisphere CO2 would acquire more depleted of negative d18O values. Which is not observed in the Scripps d18O figure above.

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  10. Continuation of 59 jlfam,

    Yes we can see slightly more negative values in the higher latitude d18O values from the figure above, but only during seasonal minima of CO2 production, notice how maximum seasonal CO2 values coincide with more positive or eriched 18O values. This discards mainland as the source or seasonal CO2 production peaks. Mainland CO2 18O are more depleted in the heavy isotope 18O due to isotope fractionation processes that carry water from the ocean surface to the land.

    I have prepared a table comparing the seasonal variation of the different parameters measured in the Scripps Station at Mauna Loa, since it's the classic to compare atmospheric CO2 values.

    CO2 concentration [{CO2], d8O, d13C, D14C and O2 concentration [O2].

    The background value to which seasonal variations are added or subtracted is indicated by an equal sign (=).

    A plus sign (+) means the value increases seasonally (either concentration [CO2] or [O2], or the isotope values become more enriched in the heavy isotope (for example d18O,+, increases 18O/16O ratio)

    A minus sign (-) means the opposite, a seasonal decrease in concentration or an isotope depletion, the light isotope 12C, 16O becomes more abundant in the ratio 13C/12C, 18O/16O, or the D14C suggests older values, lower 14C/12C ratio values.

    Question mark (?), means its open for discussion with specialists.

    The Peclet effect is related to plant metabolism, its inclusion in the table has been suggested by a well known plant metabolism and isotope specialist.

    The possible sources list is not complete, new suggestions are welcome.

    For example, at mloa, an increase in CO2 concentration shows that the CO2 18O isotope ratio is simultaneously more enriched, delta13C takes more depleted values, D14C shows more negative or older values and the [O2] also decreases. This is seen by comparing one by one the plots and data available from here. About [O2], a decrease in concentration when the CO2 concentration increases fits perfectly with water upwelling from the deepest ocean regions which are obviously depleted in oxygen due to microbial respiration. Take a look at this figure from Scripps station.

    Dole means, the d18O value depends on the Dole effect, that is the isotope fractionation of photosynthetic O2, which includes a background value from metabolic water.

    I prefer each one of the readers to do the work, to avoid any alledged manipulation of the data from this writer.

    As you may see the only source that fulfills the same conditions shown by Mloa station is the ocean upwelling.

    I will be glad to discuss any details and accept any correction.

    To illustrate why the upwelling may be the main source of CO2 at mloa, please take a look at Takahashi's team arduous task represented in this map of CO2 sources from the ocean. Notice how close are the Hawaii Islands from the bicarbonate, CO2 rich waters of the Tropical Pacific.

    On this page it's shown how the concentrations of ocean surface CO2 change seasonally, (figures can be expanded indiviually in separate browser tabs)

    Thanks for letting me post this and comments and for the constructive replies.



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  11. Sorry,

    I forgot pasting the map of ocean surface CO2 concentration,

    Notice how close is the Mauna Loa station (Hawaii, filled black Circle) to the ocean CO2 rich waters

    And just one more plot, please take a look at the "good" correlation (I would say, one of the best I could find from independent measurements of natural phenomena) between the Mauna Loa CO2 18O isotope composition, right end plot in 59-jlfqam posting above, and the NINO3 ocean surface temperature series.

    Data sources


    My question is, how is it possible the surface ocean temperature over the equatorial pacific affects the isotopic composition of the CO2(atm) produced by independent sources such as fossil fuel burning anywhere on the Planet?

    An alternative, and very simple explanation, could be the CO2 measured at Mauna Loa station emanates from the CO2-rich ocean waters of the tropical Pacific Ocean.

    Thanks for your attention





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    Moderator Response:

    [PS] Perhaps see the article here . (and dont forget isotopic signature of atmospheric CO2 is consistent with FF not ocean). What is your "simple" explanation for where the FF we have burnt is gone if magically not increasing CO2 in atmosphere? You can use the "Arguments" menu item above to find responses to common myths. You seem to be engaged in a effort to find anything except CO2 (which is by the simplest explanation). Perhaps time to ask yourself where this bias comes from?

    [RH] Shortened link.

  12. 61 jlfqam:
    "An alternative, and very simple explanation, could be the CO2 measured at Mauna Loa station emanates from the CO2-rich ocean waters of the tropical Pacific Ocean."

    Short answer: No!
    If you are suggesting that much of the CO2 measured at Mauna Loa is a result of oceanic out gassing, then you are wrong. CO2 is measured all over the world, and once you get away from large local sources or sinks, the background concentrations and trends are almost identical.

    CO2 worldwide

    This graph is based on direct measurements, with the seasonal variations removed. If you find it hard to distinguish the curves, it should be obvious that there isn’t anything special about the atmosphere around Mauna Loa. CO2 really is a well-mixed gas, far more so than gases like water vapour, ozone or even methane.

    And BTW, your first map does not show ocean surface CO2 concentration, but the net CO2 exchange between the atmosphere and ocean. Red is oceanic uptake, while violet shows oceanic out gassing.

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  13. jlfqam @61, in addition to HK's fine response, I will note that at the location of Mauna Loa, the CO2 air-sea flux is slightly negative, according to the map you show.  Further, it is no closer to the strong positive flux in the tropical east pacific than it is to the strong negative flux at about 40 degrees north in the west pacific.  That directly contradicts your claim that "upwelling may be the main source of CO2 at mloa".

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  14. Answer to HK 62

    the color scale in the ocean surface CO2 fluxes is related to the flux of CO2 from the ocean to the atmosphere.

    This figure shows the pCO2, that is the pressure of dissolved CO2 in the ocean

    This paper shows clearly the pacific ocean being the largest source of CO2 of the planet

    Gruber et al

    Oceanic sources, sinks, and transport of atmospheric CO2

    Figure 2. Comparison of the ocean inversion estimate of the contemporary sea-to-air CO2 flux with that based on the pCO2 climatology of Takahashi et al. [2008] for each of the 23 regions resolved by the ocean inversion. The zero-line crossing of each flux estimate indicates the region that this flux belongs to. Small gray numbers indicate the region number (see Table S1 for the region name). Positive fluxes indicate outgassing.

    Rgarding Tom Curtis 63,

    If you take a look at the seasonal variations of pCO2

    you may see how the Hawaii Islands are bathed by waters with variable CO2 concentrations, which I would say fits the seasonality of the CO2 curve.

    Thanks for continuing the discussion, it helps me think about new ways to reinforce the arguments in favour of a natural source for atmospheric CO2.

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  15. jlfqam,

    You need to read why Mauna Loa (SkS link)was chosen by experienced scientists to measure CO2.  The volcano is so high that it touches the bottom of the upper atmosphere.  The CO2 is well mixed from around the world and is only slightly affected by any outgassing of the ocean.  Your claim that ocean outgassing affects their measurements is incorrect.  Read more, conclude less.  You are reviewig very well explored material. 

    The entire ocean is a CO2  sink. Every year the ocean absorbs more CO2 from the atmosphere than it releases to the atmosphere.  Your claim that the ocean is a source of CO2 to the atmosphere is incorrect.  Perhaps you mean that the ocean flux affects the isotopic composition of the CO2 in the atmosphere but you need to be more clear what you are claiming.  Read your sources more carefully.

    You would be much better off if you asked questios about what you do not understand.  Instead you make incorrect claims based on your own reasoning.  This material has been very closely studied by others with much more experiece.  You are more likely to reach an incorrect conclusion (like the two above) because you do not know as much as the experienced scientists than you are to find  a mistake that they have made.  If you ask questions you will be better received here than if you make incorrect claims based on your own reasoning.   People are happy to help you understand the science.

    Good luck.

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  16. jlfqam @64, where you write, "This figure shows the pCO2, that is the pressure of dissolved CO2 in the ocean", you then provide the URL for a series of monthly maps of surface water partial pressure of CO2 such as this one:

    I have chosen this example as it shows the highest monthly pCO2 at Mauna Loa's longitude and latitude.  Never-the-less, at that longitude and latitude, the colour shown is green, verging on light blue  indicating a pCO2 between 350 and 375 ppmv.  In 2005, the atmospheric CO2 concentration was 380 ppmv.  The lower pCO2 at Mauna Loa therefore implies a net atmosphere to ocean flux at that location, consistent with the map you showed @61 and on which I commented @63.

    In your post @61, you introduced the map as indicating the waters around Mauna Loa were particularly CO2 rich.  It is possible you consider the maps of pCO2 (which show highest values in the tropics), as substantiating that claim.  That would be a mistake.  Specifically, pCO2 is a function not only of the total amount of CO2 dissolved, but also of the temperature of the water.  In fact, looking at actual dissolved CO2, we find that those regions with the highest pCO2 also have the lowest total CO2 dissolved; while the highest quantities of total CO2 are to be found in the Antarctic Ocean:

    This paradoxical result is a consequence of the large temperature gradient in surface waters from poles to tropics.

    In any event, not only are you trying to supplant the theories of climate scientists which they derived to explain the data they collected, and which you peruse; but you have shown a consistent pattern in misdescribing that data.  It is hard enough to find a better theory for the data than that held by professional scientists, given their expertise, time, and the many person/years of cooperative research that has gone into any of those theories.  Trying to do so without getting the data right is pointless.

    Finally, yes there are seasonal variations in pCO2 and ocean/atmosphere CO2 flux at Mauna Loa, just as there is at Cape Grim (Tasmania) and in the waters surrounding the Antarctic (where the seasonal variations are exceptionally large).  Yet seasonal variation in CO2 concentration is much reduced in the Southern Hemisphere, and virtually non-existent at the South Pole.  If ocean/atmosphere flux was the cause of the measured seasonal variation at Mauna Loa, it would have the same effect at Cape Grim and the South Pole, resulting in an equally large seasonal variation at Cape Grim, and a larger one at the South Pole. 

    In contrast, the SH has far fewer deciduous plants than the NH, partly due to reduced land mass but also due to a greater preponderance of evergreens.  The South Pole lacks deciduous plants entirely.  That gives the true, primary cause of the seasonal variation on CO2 concentration - the seasonal cycle of deciduous plants.

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  17. jifqam,

    I think it might be useful to to emphasis the point made by michael sweet @65 paragraph 2.

    The graphic from Gruber et al (2009) 'Oceanic sources, sinks, and transport of atmospheric CO2' presented @64 shows various annual CO2 flux for various ocean regions. These are net fluxes per region. Add them up and they total to about 2.2Pg(C) flux into the ocean and 0.5Pg(C) out of the ocean. The paper tells us global net figure includes " an uptake flux of anthropogenic carbon of 2.2 ± 0.3 Pg C/y(inversion) and 1.9 ± 0.7 Pg C/y(pCO2-climatology)."  This represents about a quarter of our anthropogenic CO2 emissions which today total about 10Pg(C)/year and so it is our anthropogenic emissions that are truly "the largest source of CO2 of the planet." Your interpretation of the Gruber et al graphic is based on a flux from the Pacific of just 0.3Pg(C)/year.

    Yet the carbon cycle shows the gross fluxes to be far higher than the net fluxes.  This is not controversial.

    Carbon cycle

    Annually, the gross flux is about 92Pg(C) flux into the ocean and 90Pg(C) out of the ocean. Any discussion of Δ18O must take account of these gross fluxes.

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