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Comparing CO2 emissions to CO2 levels

What the science says...

When CO2 emissions are compared directly to CO2 levels, there is a strong correlation in the long term trends. This is independently confirmed by carbon isotopes which find the falling ratio of C13/C12 correlates well with fossil fuel emissions.

Climate Myth...

CO2 emissions do not correlate with CO2 concentration

'It is easily demonstrated that there is no correlation between CO2 emissions and atmospheric CO2 concentration. Over the three years from 1979 to 1982 when CO2 emissions were decreasing due to the rapid increase in the price of oil that drastically reduced consumption, there was no change in the rate of increase in atmospheric concentration of CO2 proving that humans were not the primary source for the increase in concentration.' (Laurence Gould)

To directly compare CO2 emissions to atmospheric CO2 levels, both sets of data can be converted to gigatonnes of CO2. The CO2 emissions data is typically expressed in gigatonnes carbon (GtC). One gigatonne is equal to one billion tonnes. This means they've only included the carbon element of the carbon dioxide molecule. The atomic mass of carbon is 12, while the atomic mass of CO2 is 44. Therefore, to convert from gigatonnes carbon to gigatonnes of carbon dioxide, you simply multiply 44 over 12. In other words, 1 gigatonne of carbon equals 3.67 gigatonnes of carbon dioxide.

Atmospheric CO2 levels are expressed in parts per million by volume (ppm). To convert from ppm to gigatonne of carbon, the conversion tables of the Carbon Dioxide Information Analysis Center advise that 1 part per million of atmospheric CO2 is equivalent to 2.13 Gigatonnes Carbon. Using our 44 over 12 rule, this means 1ppm = 7.8 Gigatonnes of Carbon Dioxide in the atmosphere.

[Note that the conversion is different for Gigatonnes of Carbon Dioxide emissions, because natural sinks (ocean and biosphere) absorb approximately 55% of human emissions, so the "airborne fraction" added to the atmosphere is about 45%.  This means 1ppm = 17.3 Gigatonnes of Carbon Dioxide emissions.]

The two time series can both be plotted together expressed as gigatonnes of carbon dioxide:

Figure 1: CO2 levels (Green Line - Law Dome, East Antarctica and Blue line - Mauna Loa, Hawaii) and Cumulative CO2 emissions in gigatonnes of CO2 (Red Line - CDIAC).

So putting it all together, Figure 1 is a plot of the total amount of CO2 in the atmosphere (top) versus the total amount of CO2 humans have emitted into the atmosphere (bottom). Several features jump out. Firstly, the similar shape of the curves (dare I say hockey stick shaped). We have correlation but do we have causality?

It isn't too much of a stretch to imagine the amount of CO2 we put into the atmosphere might have a causality link with the amount of CO2 that remains in the atmosphere. Nevertheless, further confirmation comes by analysing the types of CO2 found in the air. The carbon atom has several different isotopes (eg - different number of neutrons). Carbon 12 has 6 neutrons, carbon 13 has 7 neutrons. Plants have a lower C13/C12 ratio than in the atmosphere. If rising atmospheric CO2 comes fossil fuels, the C13/C12 should be falling. Indeed this is what is occuring (Ghosh 2003) and the trend correlates with the trend in global emissions.

Figure 3: Annual global CO2 emissions from fossil fuel burning and cement manufacture in GtC yr–1 (black), annual averages of the 13C/12C ratio measured in atmospheric CO2 at Mauna Loa from 1981 to 2002 (red). (IPCC AR4)

This rebuttal was updated by Kyle Pressler in September 2021 to replace broken links. The updates are a result of our call for help published in May 2021.

Last updated on 19 February 2020 by John Cook. View Archives

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Comments 1 to 12:

  1. The rate of increase of CO2 levels had changed of course even in 1979 to 1982. It fluctuates a lot all the time, as visible from Mauna Loa or global data. This is due to due to the changing fluxes between atmosphere and other pools. A minor signal of yearly variability of human-emitted CO2 is scarcely detectable. A historic discussion of variability of concentration rise is within the Charles D. Keeling autobiography Rewards and penalties of monitoring the Earth from 1998. Excellent images on CO2, fossil fuels and the influences onto CO2 rise anomalies are within his 2005 Tyler Prize Presentation. A minor correction: Law Dome data have 2455 in its URL (the link within the text pointed to Tayler Dome, 2419).
    Response: Thanks for the heads-up, have fixed the link.
  2. Is this particular myth and its answer saying: "The Keeling curve has not yet reflected the economic activity rise of China yet?"


    * No, I wasn't quite sure how to punctutate that!!

  3. I find this one bit hard.  While I can accept what is written above, I come unstuck when comparing it all with what is written at:

    Is there any simple answer or is the complexity muddying the waters?

  4. Patrickjl @3 , your chiefio.wordpress reference = a waste of time.

    It is a 2009 article, containing one or two thinly specious arguments [e.g. that recent forest clearing favoring C4-metabolism grasses which deal with carbon-13 slightly differently from C3 plants . . . thus contaminating/invalidating the standard C12/C13 ratio conclusions].

    Worse, the arguments are not quantified (i.e. are little more than handwaving).

    Worse still, they are accompanied by the Usual Suspects -— a grabbag of run-of-the-mill anti-science nonsense arguments, all long-debunked but living a zombie-like undead existence on Denialist websites.

    [ The author himself claims to be a frequent contributing author at WUWT.   My apologies, if that is taken as an Ad Hominem !   ;-)    ]

    All in all, chiefio-wordpress is a waste of readers' time.

    Sorry for the harsh review, Patrick.  "Chiefio" was a waste of your time, too.

  5. Patrickjl,

    What Eclectic said x2.

    Chiefio restates questions as problems when the answers are well knows.  For example, he questions wether we know the ratio of C12/13 at midocean ridges.  Seems like a good question since the mid-ocean ridges are underwater.  Except Iceland is a midocean ridge with many active volcanoes so this ratio has been measured.  Undoubtedly scientists have also measured this ratio for other mid-ocean ridges.  

    This is not an issue of scientists not knowing the answers but Chiefio has made no effort to find the answers to the questions he asks.  There is probably a lot of Chiefio ignoring the answers when they are provided to him.

    It is easy to make any problem look hard if you ignore the answers scientists have found.

  6. Can you please explain more about the airborne fraction of CO2? The models of CO2's atmospheric lifetime show that half the original CO2 emission is taken up by the oceans and vegetation in about 30 years. But according to the global carbon budget and the airborne fraction, 55% or so is removed from the atmosphere each year.

    So for emission scenarios of different sectors or gases, how is the airborne fraction factored in? GWP calculations, for example, rely on the AGWP or each gas compared to the AGWP of CO2, so is CO2's AGWP devalued by the airborne fraction when compared to, say, methane from fugitive emissions (leaks).

    This would not be an issue for climate models I imagine (because they work on the CO2 in the atmosphere), but for any analysis of sectors or gases it must make a difference.

  7. Gerard Bisshop @5,

    The time for half a CO2 pulse to be drawn-down out of the atmosphere into oceans & biosphere is dependent on the size of the pulse. The graph you link to (from Joos et al 2013) showing 30yr is for a 100Gt(C) pulse, so a pulse equal to a decade's worth of anthropogenic emissions. Anthropogenic emissions are approaching 700Gt(C) and models for a 1,000Gt(C) pulse or 5,000Gt(C) pulse show it takes much longer to reach that 50%-of-pulse level, perhaps 150y & 450y respectively (eg Archer et al 2009), thus making the draw-down numbers more at odds with Af=45% (which means 55% is removed within the year).

    The 'circle' is squared because Af is a measure of the annual draw-down compared with a single year's emissions. Draw-down value is of course dependent on far more than a single year's emissions, indeed dependent on the emissions accumulated over the previous decades. So that 55% comprises, say, 2% of Y(0), 1.5% of Y(-1), 1.25% of Y(-2), 1% Y(-3), etc, these all adding up to 55% of Y(0). If we did manage to zero emissions in 2021, draw-down would continue, the atmospheric CO2 would thus drop and the calculation of Af would require a division by zero.

    GWP numbers by definition yield GWP(CO2)=1 and use the forcing resulting over a specified period (eg 100y) from 1t(CO2) released into the atmosphere after draw-down is factored in, a draw-down which is dependent on expected accumulative totals of CO2 emissions. The level of draw-down is not considered set in stone and still subject to research. For instance CarbonBrief have coverage of a recent paper reassessing the ocean drawdown. So far, the GCMs do not model the carbon cycle (and of course have to assume future anthropogenic emissions fo all GHGs) so the level of CO2 (and other GHG levels) are inputs assumed for each GCM run.

  8. Thankyou MA Rodger for your time responding to this query, it's greatly appreciated.

    I have a follow on question. Regarding the influence of size of emission on the CO2 response function, it appears from Figure 7 of Joos et al 2013 that a pulse equivalent to one year's emissions follows a very similar path to the 10 year equivalent pulse above (at least for the first decade or so), indicating that the remaining fraction from the pulse is close to 100% (maybe 90%) in the first year after emission.

    As time goes by, the CO2 pulse removal from the atmosphere slows. So in the initial decade, almost 40% is removed, and in the 9th decade, only a few % are removed. So a cumulative removal curve of all previous years would be more heavily influenced by removal of recent emissions.

    Which brings me to my question - given that Joos et al 2013 shows removal of recent emissions to be less than 10% in the first year, and in subsequent years removal drops at a lesser rate, I can only conclude that all the CO2 response functions start with the pulse already-discounted by the airborne fraction.

    Obviously, this is not an issue for climate models, that deal only in atmospheric concentrations, and from what I can make out, the IPCC representative pathways that link emissions with future warming also use response function equations something like Joos et al 2013, that do not seem to discount emissions, but deal in atmospheric concentrations.

    I'm sorry to labour this, and there may be a simple explanation, but I am struggling to find it, and it seems critical to my understanding the relationship between CO2 and other gases.

  9. Sorry MA Rodger, I just did the sums on the remaining fraction loss for this and previous years and it is as you said in your earlier post - the remaining fraction adds up to be (1-) the sum of losses in all previous emission years - problem solved!

    thanks for your help.

  10. I have tried comparing ghg emissions and atmospheric CO2 (yearly figures) in an x-y diagram to get a picture of the degree of coupling, time lag between emission and atmospheric concentration and the effects of economic- politic- and distributioncrises. But the data I have used is not the same as you. And I also find interesting differences between the period before the oil-crisis in the 1970-ies and aftewards. I think the storing and later use of oil and coal can have an impact. As well as strategic planning. Can you recommend any continous sources of data for lets say the period from 1900 up until today, for (anthropogenic) GHG emissions and atmospheric CO2?

  11. Fred Torssander @10,

    Unless looking at the latitudinal trends (so looking at the annual wobble is disappeared at the south pole or the year-plus time lag between northern and southern hemisphere CO2 values), I haven't found the identification of time-lags possible due to the effect of ENSO and volcanic erruptions. So identifying levels of stored FF through a less-than vigorous rise in CO2 does sound a step too far. So best of luck with that.

    If you are asking for annual data back to 1900, you evidently aren't yet using the Global Carbon Project data. The GCP's 'historic' data sheet gives values for FF emissions and atmospheric 'growth' back to1750 and Land Use net emissions back to 1850.

  12. Thanks for your encouragement. I wrote to NOAA and got their table for the diagram on LINK

    It goes back to 1751 and is unbroken series. I will try to fix the change back and forth at the oil crisis by moving the time lag. The reason for my scepticism towards emission data is that there is a trade war on, and statistics is a rather cheap and efficient way to confuse the enemy. LINK


    [DB]  Shortened and hyperlinked URLS breaking Recent Comments thread formatting.  Inserted image.

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