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How reliable are CO2 measurements?

What the science says...

CO2 levels are measured by hundreds of stations scattered across 66 countries which all report the same rising trend.

Climate Myth...

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" (disinter)

The following graph shows atmospheric CO2 levels over the last 10,000 years. It includes ice core data for CO2 levels before 1950. For values after 1950, direct measurements from Mauna Loa, Hawaii were used.


Figure 1: CO2 levels (parts per million) over the past 10,000 years. Blue line from Taylor Dome ice cores (NOAA). Green line from Law Dome ice core (CDIAC). Red line from direct measurements at Mauna Loa, Hawaii (NOAA).

Mauna Loa is often used as an example of rising carbon dioxide levels because its the longest, continuous series of directly measured atmospheric CO2. The reason why it's acceptable to use Mauna Loa as a proxy for global CO2 levels is because CO2 mixes well throughout the atmosphere. Consequently, the trend in Mauna Loa CO2 (1.64 ppm per year) is statistically indistinguishable from the trend in global CO2 levels (1.66 ppm per year). If global CO2 was used in Figure 1 above, the result "hockey stick" shape would be identical.


Figure 2: Global atmospheric CO2 (NOAA) versus Mauna Loa CO2 (NOAA).

The following video is a graphic example of where our data for CO2 levels comes from. It shows surface measurements of CO2 varying over different latitudes from 1979 to 2006. The graph is created by Andy Jacobson from the NOAA and includes a global map displaying where the measurements are coming from, a comparison of Mauna Loa CO2 to South Pole CO2 and the graph expands at the end to include ice core measurements back to the 19th Century.

Satellite data is consistent with surface measurements and present a fuller picture of global CO2 concentration. The next video shows global distribution of mid-tropospheric carbon dioxide. This data comes from the Atmospheric Infrared Sounder (AIRS) on the NASA Aqua spacecraft. Superiposed over the global map is a graph of carbon dioxide observed at the Mauna Loa observatory.

Last updated on 9 July 2010 by John Cook.

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Further viewing

How is CO2 transported throughout the globe? This is displayed in a CarbonTracker visualisation of global transportation of CO2 through 2008 (more on CarbonTracker).

Comments

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Comments 51 to 55 out of 55:

  1. Actually I can. Try Severinghaus & Battle 2006. You can find other interesting papers (eg look for MA Headly) by looking for papers that cite it in google scholar.
  2. The problem with the graph showing the atmospheric CO2 content, with the rapid increase in the 20th century is that it is wrong. CO2 has never followed a level of 250ppmv over the past 10,000 years. That claim is a lie. In 1850's CO2 measurements showed atmospheric CO2 content to be 490ppmv, well above today's level and according to alarmists well over the 'tipping point' level.
  3. John Marshall @52, if you run your car in a closed garage and measure the CO2 concentration in the garage, it will be well above 390 ppmv. It would be obviously foolish to conclude from that that global CO2 concentrations are greater than 390 ppmv. You have a nearby source of CO2 that is contaminating the measurement.

    As it happens, there are many sources of CO2 contamination. Not only are there cars, factories and people in abundance in cities, all busily emitting CO2 in abundance, and consequently contaminating any measurement. Not only that, but trees and grass are net CO2 sinks in daylight, but net emitters of CO2 at night. Consequently measurements in a forest on a still night will show elevated CO2 levels, again the result of contamination.

    In the 1850s, and indeed, even in the 1930s this was not well known, and many measurements of CO2 concentrations were made in areas where contamination would be expected. What is worse, Beck, who should have known better compiled a list of measurements without compensating for local contamination beyond the crudest measure, and simply took an average of measurements to determine the CO2 concentration. Given that CO2 concentrations can vary by 100 ppmv or more on a daily basis due to local contamination, the result significantly overestimates background CO2 levels.

    To determine genuine background levels of CO2, you need to get away from local sources of CO2 emission by getting either very far away from their source vertically, as with these measurements over Colorado:



    Note that near ground concentrations shown can be as high as much as 50 ppmv above the upper altitude levels even at 500 meters altitude (let alone the 2 meter altitude used by Beck), but with gain in altitude, CO2 concentrations drop to background levels.

    Alternatively you can rely on strong winds to dilute the contamination to determine the background by plotting CO2 levels against wind speed:



    Again, notice when wind velocities are low, local contamination (mostly from forests in this case) can result in CO2 concentrations as high as 600 ppmv, but that the background level is clearly around 390 ppmv.

    Or you can get as far away geographically from any contamination as you can, by going to the South Pole:



    Citing measurements that do not take these precautions to ensure they are measuring the genuine background concentrations, rather than a contaminated sample are, of course of no interest.
  4. 52, John Marshall,

    Please note how easily and completely you fell for what is actually a well understood "lie". You read at a denial site about how CO2 levels were way higher in the 1800s and there's a paper to prove it. Except it turns out that everyone who cares to actually be skeptical and look at the science knows that's nonsense. Scientists go to great lengths to properly, accurately measure CO2, and they aren't stupid about it. At the same time, the paper cited by deniers to trumpet this issue was literally stupid about it.

    They know this. This information is readily available, and it's pretty obvious if you take just a little while to think about it. So why do denial sites keep feeding people this nonsense?

    The point is that you were tricked, and you came in here all full of anger because you thought the ones who tricked you were the scientists. But it wasn't, it was the deniers.

    [Fortunately, this site exists exactly because of those sorts of situations. Every time you have one of these "ah ha, got them" moments by reading something at a nonsense denier site, come here to SkS, use the search button, read and learn. After you've done it enough, you'll start to realize that there is no science or truth to the denial arguments. None.]

    So how do you feel now? Is your anger redirected at a more appropriate target? Or are you instead simply more firmly invested in finding something to justify your anger at "alarmists?"

    And if the latter is the case... doesn't that say something even more important about the "debate."
  5. John Marshall.

    Take the hint from Tom Curtis and Sphaerica - you are, to put it nicely, profoundly in error.

    If the conversation here is too technical for you, there was a more colloquial one on Deltoid, that should make you blush with embarrassment once you've read through it.
  6. wsugaimd, how do you explain the Keeling Curve? The steady rise of atmospheric CO2 cannot be explained by a nearby volcano. Also, the Hawaiian measurements are corroborated by independent measurements. Read the article above.
  7. danielc's comment of 6:14 AM, April 11th, 2012:

    "@wsugaimd:

    Go here: Movie showing CO2 levels measured over the last 50 years it includes information from ice cores, and there are MANY data points, not just at hawaii.

    Go here: impact of eruptions on global CO2 levels - essentially unmeasurable.

    and go here: satellite measurements of CO2 compared to Mauna Loa

    Being skeptical of measurements taken at one point, using one method is reasonable, but CO2 measurements have been made at many, many points using many, many methods...


    Jim Eager's comment of 6:21 AM, April 11th 2012:

    Wsugaimd @38, your skepticism seems highly selective, since Mauna Loa is not the only location where atmospheric CO2 is monitored. Similarly, ocean pH is monitored at many locations around the globe. If you are truly skeptical then you should be noting what those locations also show, not just those in Hawaii.

    As for comparing human CO2 emissions to total CO2 content of the atmosphere, your 1% figure suggests that you are no skeptic, but rather that you are using the trace gas argument distraction (see the "Argument" button in the top bar).

    Consider that every single natural source of CO2 is offset by a natural absorption of CO2. The ocean continuously exchanges CO2 with the atmosphere, making it both a source and a sink for CO2. However, it is currently a net sink, meaning it absorbs more CO2 than it emits, which is why ocean pH is decreasing.

    Similarly, the terrestrial biosphere both emits and absorbs CO2, and it, too is currently a net absorber, although that may well change. Even volcanic emissions of CO2 are offset by geologic sequestration of CO2 via silicate rock weathering and calcium carbonate shell deposition on the sea floor.

    However, there is no human absorption of CO2. Zero. There is only human emission of CO2. Every gram of CO2 we emit must either be absorbed by a natural sink or remain in the atmosphere.

    Fortunately the ocean, biosphere and lithosphere absorb 100% of natural emissions, *plus* roughly half of the carbon that humans emit, leaving only half of it to accumulate in the atmosphere. In other words, we humans have been responsible for 200% of the measured 38% increase in atmospheric CO2.

    A true skeptic should be able to tell the difference between a 1% annual emission rate and a 38% cumulative increase, don't you think?"


    danielc's comment of 6:33 AM, April 11th 2012:

    "@Jim Eager #42:

    The argument I like to use is this:

    Say you have 10,000 dollars in the bank (that's 1 million pennies).

    300 of those pennies are red pennies, and they earn triple interest.

    Every day, I am going to add three red pennies to your bank account.

    For every time you earn triple interest, another free red penny is added to your bank account (positive feedback).

    Are you going to refuse? NO!
    Are the red pennies in your account, and the extra red pennies I add year on year (and the triple compound interest they receive going to add significant amounts of money to your account? YES! Esp. over significant amounts of time."
    Response: TC: The three quoted comments above are in response to wsugaimd's of topic comment here, and have been quoted here in lieu of simple deletion.
  8. wusgaimd, would you care to inform us which volcano is contaminating the CO2 measurements at the South Pole (shown @53 above)?

    For comparison, here is the full Keeling Curve from Mauna Loa:

  9. How can we be confident that the CO2 concentration measurements from the ice core samples, which may have been contaminated in some way, either historically through leakage or in the recent withdrawal process, gives a reading comprable to those from Mauna Loa? Has there been a good rebuttal to the work of Zbigniew Jaworowski in this area. I have not done exhaustive research in the area (really just debating amongst non-science friends), but one brought up this line of argument to discredit the top graph here on historical CO2 concentrations. In researching the issue of comparability and the reliability of the CO2 measurements, I found Jaworowski and few folks countering his arguments. I'm genuinely not trolling here, just interested in the topic.

  10. ajc, which of ZJ's claims would you like a response to?  Tamino responded to the "too smooth" concern here.

  11. It's hard to take ZJ seriously, but for detailed look at the ice core CO2 process and validation, see Etheridge 1996.

    and follow cites for more recent work. For a direct rebuttal, see here. The consilience of CO2 levels between ice cores from different location (eg Greenland, Antarctica) would be big hint that the method is fundamentally sound. Furthermore, the idea that AGW is based on icecore data is hopelessly wrong. ZJ would appear to be a classic case of a scientist "gone emeritus"

  12. ajc...  Watch this small section of the Richard Alley lecture and he tells it like it is on this point.  Start at min 12:10.

  13. A good way to check on claims that have been made in journal papers is to use Google Scholar to identify papers that have cited the paper and see if any of them are critical or provide evidence that answers the claims made.  I this case, I found

    T. GüllükF. SlemrB. Stauffer, "Simultaneous measurements of CO2, CH4, and N2O in air extracted by sublimation from Antarctica ice cores: Confirmation of the data obtained using other extraction techniques", Journal of Geophysical Research: Atmospheres (1984–2012)l Volume 103, Issue D13, pages 15971–15978, 20 July 1998

    A sublimation technique has been developed to extract air samples from polar ice cores for subsequent simultaneous measurement of several trace gases by frequency-modulated tunable diode laser absorption spectroscopy. This extraction and analysis technique is shown to be suitable as an extraction method for the determination of concentrations of the greenhouse gases CO2, CH4, and N2O in air samples of ∼1–5 cm3 recovered from ice samples of 10–50 g. Air samples from the Siple ice core have been analyzed covering the period between 1772 and 1973. In addition, a few samples from two different ice cores from Vostok station have been analyzed. Our results are in a good agreement with results obtained by other researchers using melting and crushing extraction techniques. This agreement indicates that processes connected with the formation of clathrates in ice under high pressure at greater depths and their destruction after drilling are not affecting the CO2, CH4, and N2O measurements significantly.

    [emphasis mine]

    Which appears to provide experimental evidence directly refuting one of Jaworowski's arguments (in addition to that provided by Etheridge).  Essentially the scientists that work on ice core data do know what they are doing and do their best to examine possible sources of bias or error and eliminate them, as these two papers demonstrate.

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