How reliable are CO2 measurements?

CO2 measurements are suspect

The Keeling curve, which is widely used to show the increase in CO2 emissions, is based on data from the top of Mount Mauna Loa in Hawaii. Mauna Loa is a volcano and it doesn’t seem to me that a volcano is the best place to be taking CO2 measurements (Source: disinter)

Comments 1 to 40:

1. Mizimi at 00:57 AM on 26 August, 2008
   Checking out the site:
   
   http://gaw.kishou.go.jp/wdcgg/wdcgg.html
   
   simply re-inforces in my mind that the data we have collected does not reflect the real situation.
   Firstly, there are 298 stations listed which collect information on various atmospheric gases.
   Only 159 collect data on CO2. The rest sample other gases.
   There is a range of sampling methods from fixed low level to mobile high altitude....
   The distribution of sampling stations is unrepresentative of the global state; there is virtually no coverage of:
   Afica/Australia/ India/ Middle east /Russia /Asia/ China/Nth Canada/ S.America/Greenland.
   Sampling is concentrated in the highly industrialised countries so who is going to be surprised that CO2 levels there appear to be increasing?
   The data cannot represent the global condition.
2. chris at 00:27 AM on 9 October, 2008
   Re #1 That really doesn't make much sense Mizimi. Since the atmosphere is a relatively well-mixed medium, one doesn't need a whole network of sites measuring CO2 to obtain a pretty accurate measure of global atmospheric CO2 concentrations. It's not like a temperature measurement which is a highly local parameter, even if this may be correlated with temperature measurements up to quite a large distance away.
   
   Again this is straightforward to demonstrate. For example if you click on John's link above to the NOAA site you will see that the Manua Loa CO2 measurements and the globally averaged sea surface measures match very closely (within around 1 ppm). Even comparing Northern hemisphere and S hemisphere averages, the numbers are pretty similar, especially when averaged over a year.
   
   
   What's fascinating about your post is that on another thread ("It's the sun"), you promote the awesomely inept analysis of paleo CO2 measures of a German school teacher (Mr Beck), who "finds" historical CO2 measures that jump up and down wildly (100 ppm in a few years!).
   
   Now if one actually examines the original papers from which Beck's weird analysis descends, you find a bunch of wildly unrepresentative CO2 measurements made in cities. We know these give false measures of the globally averaged atmospheric CO2 levels since the scientists who made them point out, for example, that CO2 measures are 40 ppm higher in the afternoon than in the morning, and higher on windless days compared to windy days. These are clear indications of massive contamination of CO2 measures with industrial/human sources (see my post #172 on the "It's the sun" thread).
   
   So on the one hand you are cheerleading for awesomely nonsensical paleoCO2 data massively contaminated with urban/industrial contributions...
   
   ...and on the other (here), asserting that the atmospheric CO2 data "cannot represent the global condition" when in fact it's easy to demonstrate that they do represent the global condition, since data from urban centres isn't used in assessing the atmospheric CO2 concentrations ('though they might have other uses with respect to local conditions).
   
   One needs to decide whether one is being skeptical or is instead pursuing conspiracy theories on behalf of dodgy agendas!
3. Quietman at 10:50 AM on 11 October, 2008
   Re: "relatively well-mixed medium"
   SEE
   Earth's Air Divided by Chemical Equator By Andrea Thompson, Senior Writer
   posted: 30 September 2008 06:53 am ET
4. chris at 23:42 PM on 11 October, 2008
   Re #3:
   
   Sure, the atmosphere is a relatively well-mixed medium. The specific point of interest is the locational variability of atmospheric CO2 levels. It only requires a brief perusal of the CO2 data from different sites around the world to show that CO2 mixes relatively quickly on an annual basis, even if there are very clear hemispheric differences in CO2 production and sequestration and so on.
   
   The relatively well-mixed nature of the atmosphere with respect to CO2 can be seen by observing the similarity in atmospheric CO2 levels at Manua Loa or averaged over the marine surface.
   
   i.e. compare the two data sets here:
   
   http://www.esrl.noaa.gov/gmd/ccgg/trends/
   
   or look at an entirely seperate data set. For example the atmospheric CO2 measure at the South Pole:
   
   http://cdiac.ornl.gov/trends/co2/csiro/CSIROCO2SOUTHPOLE.JPG
   
   These differ by very small amounts (less than 1%)
   
   Your link is highlighting something quite different. This is a temporary "equator" that exists only during the monsoon season and that temporarily stops atmospheric mixing with respect to atmospheric pollutants. However if one considers the distribution of the atmosphere on an annually averaged basis as one does when considering atmospheric CO2 levels then the atmospheric is relatively well-mixed.
   
   That's not to say that macroscopic/particulate pollutants may not be concentrated over either their production sources or follow wind patterns. Nothern hemisphere skies are more polluted than Southern hemisphere skies on average. Thus brown clouds and other sulphurous aerosolic clouds may not disperse and mix so quickly.
   
   But if one considers the point of interest for this thread, namely the mixing of atmospheric CO2 with respect to obtaining valid atmospheric CO2 measures for monitoring short and long term changes, the atmosphere is a relatively well-mixed medium.
   
   The proof is in the pudding!
5. Quietman at 11:45 AM on 24 October, 2008
   chris
   May I offer you a little pudding perhaps.
6. chris at 03:40 AM on 25 October, 2008
   Nice pudding Quietman, but it doesn't really go with the main course.
   
   This thread (and my posts) is about the accuracy of global CO2 readings and the mixing of the atmosphere on the annual timescale.
   
   The fact that efforts are being made to measure the concentrations of atmospheric NF3 is a seperate issue and not related at all to the accuracy of atmospheric CO2 measurements. Note that NF3 concentrations are extraordinarily low (I calculate around 42,500,000 times lower that those of atmospheric CO2 based on the info in your link)...no doubt it hasn't been easy to measure these...or perhaps no one has bothered up to now...
7. Mizimi at 08:45 AM on 26 October, 2008
   Well, the World Data Centre for GG's shows more than 1% differences...eg...
   Syowa Station * Japan NOAA/GMD 13CO2 2007 379ppm
   Hegyhatsal * Hungary HMS CO2 2007 405ppm
   Minamitorishima * Japan JMA 2008 380ppm
   Puszcza Borecka/Diabla Gora * Poland 2008 398ppm
   
   A small sample, there are others.
   
   7% differential....5% differential; a bit difficult to accept the idea that there are no significant global variations in CO2 levels. Especially when no-one has bothered to measure the rather large areas mentioned in #1
8. chris at 09:57 AM on 26 October, 2008
   Re #7, Well yes, that's rather the point. If one wants to obtain reliable global estimates of atmospheric CO2 concentrations, it makes sense to sample the atmosphere in isolated locations far from major sources of CO2 production.
   
   So one expects to see a bit of variability of atmospheric CO2 in measurements made in industrialised countries especially in the Northern hemisphere, and of course there is the yearly plant growth/decay cycle dominated again by the N. hemisphere.
   
   However if one examines the yearly average of atmospheric CO2 in isolated locations (there are dozens of these), the variability is low. These locations give a good measure of the global CO2 in the well-mixed atmosphere averaged on a yearly basis.
   
   Obviously local measures of CO2 concentrations can be somewhat higher, especially in or near cities (where they can be locally very much higher). There's masses of data that indicate that rather obvious consequence of measuring near human sources of CO2 (industrial/transport/heating etc.).
   
   Clearly if one wishes to assess the extent to which global atmospheric CO2 concentrations are changing in time, one asesses the global average on the time scale of good atmospheric mixing (e.g. annually) at the wealth of sites in isolated locations far from CO2 sources...
   
   ..it ain't rocket science!
9. Mizimi at 07:01 AM on 27 October, 2008
   Most of the stations are located in the N hemisphere, very few in the southern, and the ocean is covered by a few ships. I would be a lot more comfortable with the idea that CO2 is rapidly homogenised if we had some hard data from the areas not currently monitored, especially since most of them are not industrialised.
   For example: we might well find that the CO2 levels west of the Brazilian rainforest are higher than 'average' or that Saharan levels are markedly below.
   The point is we don't know and we should.
10. chris at 21:05 PM on 28 October, 2008
    Re #9
    
    The ocean isn't really "covered by a few ships". The oceans have a scattering of data stations in isolated islands (see map in the World Data Centre For Greenhouse Gases in John Cook's top article).
    
    It's pretty hard to see what your difficulty is. If we can measure CO2 in the atmosphere from a whole slew of data stations in isolated positions around the world situated away from urban centres, and these give rather similar atmospheric CO2 measures (yearly averaged), then we can be pretty confident that we are obtaining accurate and valid measures of the atmospheric CO2 concentration, particularly if we have extended time series that allows us to determine year on year variations in the level from individual sites. That's rather consistent with what we understand about the nature of atmospheric gases that are highly diffusive, and so are pretty well mixed on the annual basis. Of course it's important to monitor yearly averages if we wish to determine the year on year variation in atmospheric CO2 levels, since there are significant intraannual (cyclic) variations, especially in relation to the yearly cycle of plant growth and decay that is dominated by the N. hemisphere seasonal growing/decay cycle.
    
    And we do know what the CO2 levels west of the Brazilian rainforest are. We have data from Huancayo in Peru from various periods in the 1980's. These are within a few ppm of the global average from the ocean surface stations (or the Mauna Loa observatory). We have data from Easter Island that lies to the west of the Brazilian rainforest. Likewise these data are within a few ppm of the rest of the globally averaged data.
    
    I expect you can find more data from sites west of the Brazilian rainforest if you try (it really depends how interested you are in finding out this stuff).
    
    We do know what the atmospheric CO2 levels are in the Sahara. We have extensive data from Assekrem in Algeria in the N. Sahara, for example. The data are rather close to the atmospheric CO2 levels measured from the globally averaged data (or the Mauna Loa data).
    
    In other words wherever we look, we find a rather consistent set of atmospheric CO2 concentrations throughout the world, so long as these are measured in isolated sites unperturbed by major sources of atmospheric CO2.
11. Mizimi at 05:58 AM on 5 February, 2009
    Mauna Loa, sitting on a volcano in the middle of a large CO2 source ( warm tropical ocean), affected by updrafts from local plantations is, of course, unperturbed.
12. Mizimi at 04:42 AM on 14 March, 2009
    Here is a comparison of geochem vs satellite (AIRS) data on CO2 levels :
    
    http://www.agu.org/journals/gl/gl0817/2008GL035022/2008gl035022-op03.jpg
13. chris at 00:20 AM on 16 April, 2009
    re #11,
    
    Well yes, we can either establish the accuracy and precision of atmospheric CO2 measurements by careful calibrations, duplicate independent determinations at specific sites (as is the case with Mauna Loa), comparison with a multitude of monitoring sites all around the world......
    
    ..or we can throw out the science and fall back on arch insinuations (as in your post #11).
14. chris at 00:55 AM on 16 April, 2009
    re #12
    
    For anyone that is interested in knowing what Mizimi's picture actually means, it is Figure 3 of:
    
    M. T. Chahine et al. (2008) Satellite remote sounding of mid-tropospheric CO2 Geophys. Res. Lett. 35, L17807, doi:10.1029/2008GL035022.
    
    The figure compares the July 2003 satellite-determined CO2 distribution (top panel) with a particular model for CO2 circulation (bottom panel).
    
    Not surprisingly there are variations in CO2 concentrations in different regions of the world on a monthly time scale, and this is the reason that the measures of atmospheric CO2 concentrations used to assess the relationshps between emissions and atmospheric concentrations, or atmospheric concentrations and temperature trends, and so on, are yearly-averaged.
    
    With respect to the odd attempts to insinuate significant problems with the Mauna Loa data, it's worth pointing out that the July 2003 atmospheric CO2 concentration measured at Mauna Loa was 376.7 ppm:
    
    ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt
    
    and although the position of the Hawaiian islands are not easy to identify on the map Mizimi linked to (see top map showing the mid-tropospheric satellite-determined (AIRS) atmospheric CO2 for July 2003), the region of the Hawaiian islands has a CO2 concentration in the range >373 and <377.5.
    
    So the evidence that Mizimi presents us with (it's not clear what his point was) rather supports the large amount of independent evidence that the Mauna Loa CO2 measurements are reliable determinations of regional atmospheric CO2 concetrations, and when yearly averaged, are reliable measures of globally averaged atmospheric CO2 concentrations.
    
    If you want to try to pinpoint the location of the Hawaiian islands and Maun Loa on the AIRS satellite CO2 map for July 2003, here's a picture of a world "globe" with Mauna Loa highlighted:
    
    http://www.eoearth.org/article/Mauna_Loa_curve
15. gruntled at 13:58 PM on 14 June, 2009
    I was looking for some information on the reliability of ice cores. A common argument I'm hearing lately is that chemical effect in ice cores breaks down CO2, making them unreliable proxies.
16. Berry at 03:19 AM on 22 December, 2009
    Isn't strange that similar data are reported, whereas NASA reported recently:
    
    "Chahine said previous AIRS research data have led to some key findings about mid-tropospheric carbon dioxide. For example, the data have shown that, contrary to prior assumptions, carbon dioxide is not well mixed in the troposphere, but is rather "lumpy." Until now, models of carbon dioxide transport have assumed its distribution was uniform."
    
    http://www.jpl.nasa.gov/news/news.cfm?release=2009-196
    Response: Note that AIRS measures mid-tropospheric CO2 levels, some 5 to 12 kilometres above the Earth's surface, as opposed to direct measurements of CO2 which are made on the surface.
17. Tom Dayton at 18:10 PM on 3 January, 2010
    An AIRS press release noted that the AIRS data "complement existing and planned ground and aircraft measurements of carbon dioxide." Complement, not replace, because different tools measure CO2 in different vertical locations. More info on AIRS is available on the AIRS web site.
    
    The AIRS data for a recent two weeks can be seen on an interactive, rotating globe on JPL's "Eyes on the Earth 3D" web site. (On my Mac, it works properly in the Safari browser but not in Firefox; but my installation of Firefox doesn't work quite right, so it might be fine on your computer.) At the top left of the page, click the "AQUA" button. Then on the right side of the page, click the "CO2" button to show CO2 levels in the mid-troposphere as colors on the globe. The dates shown are above and to the left of the globe. Now drag the globe to rotate it. Click on the AQUA satellite to see the AIRS instrument.
    
    Discussion of CO2 being well mixed is on page 79 of Ray Pierrehumbert's book Principles of Planetary Climate, which is available free on line (and will be published in paper in 2010).
18. Theo Goodwin at 13:31 PM on 4 January, 2010
    Chris, Mizimi, and Tom Dayton, Thanks for a really interesting discussion of airborne CO2 concentrations.
    
    As a philosopher and not a scientist, I am more interested in assumptions that are made when measurements are taken. Chris' remarks seem to assume that CO2 is well-mixed in the atmosphere and that, for that reason, the fact that the measurement stations are located on the surface will provide an accurate picture of airborne CO2 concentrations. Now, I wonder if there are airborne measurement stations and if they are distributed throughout the atmosphere in a way that would make them as effective as the ground based stations. I doubt that they are because they would be very expensive. Satelites are very expensive too and they would use a different technique of measurement. So, my tentative conclusion is this: it seems that there is not a regime of measurement in the atmosphere (all the way up) that could serve to confirm the hypothesis that CO2 is well-mixed throughout the atmosphere. Am I right?
19. Theo Goodwin at 13:44 PM on 4 January, 2010
    Tom Dayton, Thanks much for the reference to Pierrehumbert's book.
20. Tom Dayton at 13:54 PM on 4 January, 2010
    Theo, see my 13:49 PM on 4 January comment on the Is the airborne fraction of anthropogenic CO2 emissions increasing? thread. See also dhogaza's comments in that thread. "Well mixed" is not an assumption, it is a longstanding observation.
21. Tom Dayton at 14:00 PM on 4 January, 2010
    Theo, a "single regime of measurement in the atmosphere (all the way up)" is not needed.
    
    Measurements from spacecraft are calibrated against measurements from aircraft and ground stations. Routinely. And different methods of measuring even at ground stations are calibrated against each other. Ditto for aircraft measurements. New spacecraft often are launched while the spacecraft they are replacing are still in service, so that the new spacecraft's measurements can be calibrated against the old spacecraft's measurements. You don't read about such things in the newspaper or even on blogs, because it's part of the mundane, routine, standard, detail of empirical science.
22. James Wight at 18:57 PM on 9 April, 2010
    There's a mistake on this page. The video shown in the “Further viewing box” is identical to the first of the two above. Is this box supposed to contain a third video or is it just left over from a previous version of this page?
    Response: Left over from a previous version. I've replaced the 3rd video with a different one - thanks for pointing it out.
    
23. Johno at 23:28 PM on 17 May, 2010
    Satellites are beginning to debunk the idea that CO2 is "well-mixed" in the atmosphere. More data is needed, but the early indications prove Chris is out on a limb when assuming such an unfounded idea.
    
    In addition, the argument against taking CO2 readings in cities is clearly specious. Long term CO2 trends should be as readily apparent as long term temperature trends. Of course, the data from cities will be as polluted by urban growth as are temperature records, but the results would still be useful.
24. Ned at 01:38 AM on 18 May, 2010
    Johno writes: Satellites are beginning to debunk the idea that CO2 is "well-mixed" in the atmosphere. More data is needed, but the early indications prove Chris is out on a limb when assuming such an unfounded idea.
    
    Did you see the video linked above, which shows a year of satellite data? Note the scale at the bottom. Over the entire year and the entire globe, CO2 ranges from ~375 to ~390 ppmv. That's pretty well mixed, IMHO.
25. johnd at 03:39 AM on 18 May, 2010
    What would be the means that allows CO2 to be well mixed in the atmosphere whereas heat is not. Heat content varies from one extreme to the other not only with altitude but across all the regions of the world. One would expect that whatever mechanism controls the transportation of CO2 would also be involved in the transportation of heat.
    Given that the amount of CO2 that is pumped into the atmosphere by the combustion of fossil fuels is very small compared to the quantity of CO2 that is in constant exchange between the atmosphere and the surface, about 1/60th, either the concentration of CO2 will be higher right at the surface where the exchange takes place or there are very violent forces in place that if able to transport and distribute the CO2 given up by the plants, soil and oceans has to be matched by perhaps even greater violent forces that has to search the entire atmosphere and gather the CO2 up to concentrate it and physically transport it back to the surface, all without doing the same to the heat contained in the environments that well mixed CO2 would find itself. Either that or the CO2 exchanged through natural processes stays very close to the surface.
    
    It is very clear how the local CO2 levels vary considerably during the plant growing seasons around the world which generally coincide with more stable and benign weather systems, and also from the experiences of decades of CO2 enrichment experience in the greenhouse industry producing plants and food, where CO2 levels can vary considerably within each greenhouse itself requiring forced circulation that not only ensures that the required levels of CO2 are evenly distributed to the plants, but also the heat, and one cannot be redistributed without the other.
26. doug_bostrom at 03:47 AM on 18 May, 2010
    Johnd, what about other gases? Forgetting C02 for a moment, how about molecular oxygen? Well mixed? Not well mixed?
27. johnd at 04:04 AM on 18 May, 2010
    doug_bostrom at 03:47 AM, I don't have the appropriate data available, perhaps you will have, what is the proportion of atmospheric oxygen that is involved in exchange processes at the surface, or elsewhere for that matter?
28. doug_bostrom at 05:01 AM on 18 May, 2010
    Johnd, surely the same processes you hypothesize in your #25 would apply for 02 as well?
29. johnd at 07:27 AM on 18 May, 2010
    doug_bostrom at 05:01 AM, since when has the sequestration and liberation of carbon between the atmosphere and the plants, soil and ocean been returned to being a mere hypothesis.
    Perhaps the data on what proportion of atmospheric oxygen is involved in similar exchange processes at the surface as CO2 would provide a clue. What does that tell you?
    The carbon cycle requires CO2 to be sequestered at the very surface of the planet from where it is also liberated. On an annual basis about 200Gt of C is sequestered and 200Gt liberated by processes that occur at the surface. This is out of a total of 750Gt of C present in the air giving an equivalent total turnover time of 3.5 years.
    If a similarly high proportion of oxygen does turnover within a similar time frame than surely you would agree that heat distribution throughout the atmosphere would also be well mixed, oxygen being such a high proportion of the atmosphere rather than a trace gas?
30. doug_bostrom at 09:04 AM on 18 May, 2010
    Johnd, just so we're clear, I understand you to hypothesize that some concentration of C02 is required at the surface in order for the carbon cycle to work?
    
    Or are you saying that we -ought- to see a concentration of C02 at the surface -if- there is a carbon cycle?
    
    Your original explanation is leaving me scratching my head. What does heat have to do with it?
31. johnd at 09:41 AM on 18 May, 2010
    doug_bostrom at 09:04 AM, please correct me if I am wrong, but the carbon cycle and the sequestration and liberation of CO2 at the earths surface by plants, soil and oceans has been established as a fact, and gone beyond being a hypothesis. Yes or no?
    
    With regards to heat, perhaps if you provided some data regarding the processes that you feel surely would apply to the mixing of O2 as they do to CO2, then we will have some basis to examine as to whether they do or not.
    Given oxygen makes up over 20% of the atmosphere whereas CO2 is a minor trace gas, the means that would have to be applied so that such a minor trace gas will become evenly distributed could be expected to apply to all other elements present in the atmosphere, including heat which always seeks to find equilibrium.
32. doug_bostrom at 09:49 AM on 18 May, 2010
    Sorry johnd, you've lost me, I don't understand what you're driving at. I think you're saying that heat has something to do with the carbon cycle, and that unless CO2 is "stirred" up somehow and driven into contact with the surface the carbon cycle can't work?
    
    That's what I take from your post here, anyway. I don't know why you're asking me whether I think there's a carbon cycle in operation. Something to do with my question about mixing of other gases, I suppose.
33. Ned at 11:21 AM on 18 May, 2010
    I agree with Doug that johnd needs to be more clear about what specifically he's claiming. Looking back up-thread to johnd's comment here, I see the question "What would be the means that allows CO2 to be well mixed in the atmosphere whereas heat is not."
    
    The main answer to that is "residence time." The residence time of CO2 in the atmosphere is very long (on the order of a century or so). The residence time of heat in the atmosphere is very short. (Water vapor, one of the vehicles for heat in the atmosphere, has a residence time of about nine or ten days).
    
    Thus, CO2 sticks around long enough to become well-mixed, while heat does not.
34. Tom Dayton at 12:26 PM on 18 May, 2010
    johnd, maybe this article by Parazoo et al. has the kind of info you're looking for.
35. Tom Dayton at 13:46 PM on 18 May, 2010
    johnd, a less technical and much shorter explanation of CO2's thorough mixing in the atmosphere is given on page 8 of the EPA's Response to Public Comments, Volume 2, in the section "Response 2-8":

    "...turbulent mixing (e.g., through wind and convection) dominates the distribution of gases throughout the atmosphere (below 100 kilometers in altitude). The mixing of substances in a gas or fluid is only dependent on mass when the gas or fluid is perfectly still, or when the pressure of the gas is low enough that there is not much interaction between the molecules. Therefore, all long-lived gases become well-mixed at large distances from their sources or sinks over a period of one to two years...."

    You should also read Response 2-3, regarding lifetime. And some of the nearby Responses.
36. johnd at 13:56 PM on 18 May, 2010
    Tom Dayton at 12:26 PM, thanks for that article, it goes part of the way, the other part being how the variations in CO2 levels interacts with plants that are far closer to CO2 starvation levels than optimum. Do they take in more when the CO2 levels are higher, thus stripping the CO2 out at a higher rate?
    
    What the article indicates firstly is that understanding of the processes is still very limited, and that what occurs in the real world of complex and infinitely variable conditions is vastly different, not only from what is at times studied in laboratories under fixed and tightly controlled conditions, but also from some of the rather simplistic generalisations by which many of the AGW subjects are understood by many.
    This limited understanding of the processes as indicated in the article is perhaps reflected in the differences between some of the modelled and observed data.
    
    What is also clear from the article is that the transportation of CO2 at the near surface occurs as part of the weather system which is all about the redistribution of heat energy.
    
    What is does not address is the relationship between the belief that CO2 has a residence time of a century or more when the movement of CO2 near the surface satisfies the more immediate requirements of the plants, soil and oceans as both a source and a sink for carbon that requires an equivalent amount of the total atmosphere to be turned over every 3.5 years approximately.
    Is it that the CO2 high in the atmosphere plays no part in the surface exchanges and is merely the remainder left over?
    If so does the measurement of this non active participant include or allow for the more variable and highly mobile CO2 at the surface?
    One wonders whether a statistician studying the utilisation of a swimming pool only counts those passive sunbathers lying on the lawn soaking up the solar energy, using them as a convenient indicator, or does he also count those swimmers who are constantly climbing out of the pool onto the edge and shaking off moisture before diving in again. Getting an accurate count of one group would be easy, nigh impossible for the other in a crowded pool.
37. Tom Dayton at 14:22 PM on 18 May, 2010
    johnd, you're now moving on to the topic of CO2 residence time, which has a considerable number of facts and links on a different thread: CO2 has a short residence time. We all can continue this conversation over there, if that's the topic onto which you are moving.
38. Ned at 22:00 PM on 18 May, 2010
    As Tom Dayton suggests, if the question is whether CO2 has a short residence time, that should be discussed in the thread CO2 has a short residence time.
    
    If anyone is still uncertain about how consistent CO2 measurements are globally, please go to the World Data Center for Greenhouse Gases, search for CO2 data from various stations, and look at them yourself.
    
    Here are some examples of graphs. These data haven't been "normalized" or "fixed" to match each other; they're completely independent data sets. Some are from the polar regions, some from the tropics, some from the northern hemisphere, some from the southern, some from ocean sites, and some from inland sites.
    
    
    
    Here's an enlargement showing 1990 to the present:
    
    
    
    Note how consistent the following are: the actual value, the upward trend, and the seasonal cycle.
39. Ned at 22:18 PM on 18 May, 2010
    FYI, here are the linear trends in CO2 concentration, 1990-2008, at the stations shown in the above graph:
    
    
    
    
    
    
    

    Mauna Loa, Hawaii:	+1.79 ppmv/year
    Barrow, Alaska:	+1.78
    Cape Ferguson, Australia:	+1.79
    Halley Bay, Antarctica:	+1.78
    Key Biscayne, Florida:	+1.78
    Ocean Station M, Norway:	+1.78
    Niwot Ridge, Colorado:	+1.79

    
    
    Of course, the trends are actually increasing exponentially, but over short periods of time they don't diverge much from a linear trend.
    
    There are lots of additional stations all over the world that show the same thing. Anyone who still claims that the Keeling Curve is somehow contaminated by proximity to a volcano and unrepresentative of the rest of the world needs to explain why every other non-urban site shows the same pattern.
40. Ned at 22:23 PM on 18 May, 2010
    Okay, one last comment. I wrote "Of course, the trends are actually increasing exponentially, but over short periods of time they don't diverge much from a linear trend."
    
    To be precise, the CO2 curves are actually increasing faster than an exponential trend.

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