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How do human CO2 emissions compare to natural CO2 emissions?

What the science says...

Select a level... Basic Intermediate

The natural cycle adds and removes CO2 to keep a balance; humans add extra CO2 without removing any.

Climate Myth...

Human CO2 is a tiny % of CO2 emissions

“The oceans contain 37,400 billion tons (GT) of suspended carbon, land biomass has 2000-3000 GT. The atpmosphere contains 720 billion tons of CO2 and humans contribute only 6 GT additional load on this balance. The oceans, land and atpmosphere exchange CO2 continuously so the additional load by humans is incredibly small. A small shift in the balance between oceans and air would cause a CO2 much more severe rise than anything we could produce.” (Jeff Id)

Before the industrial revolution, the CO2 content in the air remained quite steady for thousands of years. Natural CO2 is not static, however. It is generated by natural processes, and absorbed by others.

As you can see in Figure 1, natural land and ocean carbon remains roughly in balance and have done so for a long time – and we know this because we can measure historic levels of CO2 in the atmosphere both directly (in ice cores) and indirectly (through proxies).

Figure 1: Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons (Source: Figure 7.3, IPCC AR4).

But consider what happens when more CO2 is released from outside of the natural carbon cycle – by burning fossil fuels. Although our output of 29 gigatons of CO2 is tiny compared to the 750 gigatons moving through the carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra CO2. About 60% of this additional CO2 is absorbed. The rest remains in the atmosphere, and as a consequence, atmospheric CO2 is at its highest level in 15 to 20 million years (Tripati et al. 2009). (A natural change of 100ppm normally takes 5,000 to 20,000 years. The recent increase of 100ppm has taken just 120 years). [Paragraph updated July 2022, to correct information on % of additional CO2 that is absorbed.]

Human CO2 emissions upset the natural balance of the carbon cycle. Man-made CO2 in the atmosphere has increased by a third since the pre-industrial era, creating an artificial forcing of global temperatures which is warming the planet. While fossil-fuel derived CO2 is a very small component of the global carbon cycle, the extra CO2 is cumulative because the natural carbon exchange cannot absorb all the additional CO2.

The level of atmospheric CO2 is building up, the additional CO2 is being produced by burning fossil fuels, and that build up is accelerating.

Basic rebuttal written by GPWayne

Update July 2015:

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 5 July 2015 by gpwayne. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

Both graphs from this page are taken from Chapter 2 of the IPCC AR4 report.

Real Climate goes in-depth into the science and history of C13/C12 measurements.

The World Resources Institute have posted a useful resource: the World GHG Emissions Flow Chart, a visual summary of what's contributing to manmade CO2 (eg - electricity, cars, planes, deforestation, etc).

UPDATE: Human CO2 emissions in 2008, from fossil fuel burning and cement production, was around 32 gigatoones of CO2 (UEA).


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Comments 326 to 350 out of 352:

  1. I made an account just to post this comment. Nice work, but I have to raise question to the statement made on carbon emmisons being the highest the've been in 15-20 millions years. While I do agree humans have been doing their part to upset the balance, while I don't feel like doing the research, I'm fairly certain major volcanic eruptions and cosmic events such as Toba and the astroid that ended the Younger Dryas period would have launched more gas into the atmosphere. May be wrong, but we always overplay the power we have vs what Earth and space are capable of. 


    [PS] Welcome to SkS. You should do your own research if that is what you believe. It requires a certain hubris to believe that you know more than scientists working their careers in this. For volcanoes, see here. For CO2 at Younger Dryas (asteroid theory is contentious), see here. If you are going to make claims, you must support them with evidence otherwise it just sloganeering. (see the comments policy).

  2. >humans add extra CO2 without removing any.

    But humans do remove co2. It's called farming.

  3. hedron, the crops resulting from farming quickly are consumed by people or animals, and if animals then those animals are consumed by people, and whatever is not consumed decays. The carbon taken up by those crops thereby quickly returns to the atmosphere, minus an inconsequential fraction that gets buried essentially forever. Note that most of what gets buried decomposes and releases carbon back into the atmosphere.

  4. @327 hedron,

    You said, "But humans do remove co2. It's called farming."

    It is true that some kinds of farming remove CO2 from the short carbon cycle, which does indeed offset some emissions. However, as an average, most farming is actually a net source, and those who do offset emissions a decided minority, especially when it comes to cropping.

    We could change that and many have recommended it.

    Why Farmers Are Ideally Positioned to Fight Climate Change

    But it is not the current reality we face today. Right now there just are not enough regenerative organic farmers to counterbalance even the industrial farmers, much less the rest of the industrial world's emissions.

  5. The point being is that it's a false statement.  The average is completely irrelevant.  I assume that that fact simply slipped the authors mind when he wrote that.  But now that, I assume, the author is aware of that error.  I don't know why a website that bases itself on science would leave a false statement up.

  6. Hedron,

    I wouldn't call it false. I would call it ambiguous. 

    We are adding to the short carbon cycle with fossil fuels and habitat biomass losses. We have also reduced the capacity for natural biological systems to mitigate CO2 levels by those same habitat losses with their resulting loss of ecosystem function.

    Yes there are some humans striving to do the opposite, but as noted above, in most countries that % is a very tiny decidedly inconsequential minority.

    We could change that. I am an advocate that we change that. Humans are just as capable of habitat restoration as they are for habitat degradation. Farming in particular does indeed have methods for every crop and food type that can sequester massive carbon in the soils of the world.[1]

    But the approximately <3% doing that sort of farming right now isn't enough to matter. It's like the exception that proves the rule right now.

  7. I wouldn't call it ambiguous.  I'd call it lying.  It's still not explained why a self-descibed scientific publication would knowingly publish a falsehood.  It seems to me, given the deflection tactics used to rebut my observation, that it was intended to deceive, which is the literal definition of a lie.


    [DB]  You are welcome to your opinions.  When those opinions extend to personal attacks/ad hominems, they are unwelcome here (review the Comments Policy for details).  If you are of the opinion that a particular article or point within an article is erroneous, the burden of proof is incumbent on you to cite credible sources as to why the particular points are wrong and what a more accurate text would look like.

    Sloganeering/personal attacks snipped.

  8. Vacnol: volcanoes are like pimples: irrelevant...and that is exactly how the scientists in this field view the matter !

  9. '.. our output of 29 gigatons of CO2 is tiny compared to the 750 gigatons .. it adds up because the land and ocean cannot absorb all of the extra CO2. About 40% of this additional CO2 is absorbed.'

    That CO2 natural sources and sinks are on such a knife edge balance that an additional 4% created by man cannot be fully absorbed strikes me as being either an amazing coincidence, incorrect, or there is some other mechanism creating such a balance that is not described here. 

  10. Kiwironnie @334 , adding a new 30 thousand million tons of CO2 quickly and repetitively (= annually) would seem quite a lot, to many people !   With or without knife edges.

  11. So Eclectic you are describing a compounding, of 750 (in balance) then 30 + 30 + 30 ... and so on per annum. Consequently double the weight in 25 years, less what can be absorbed.  The next question(s) then is at what are the absorbtion feedback mechanisms (such as planetary greening), how quickly can they react and what is their ceiling capacity?

  12. Kiwironnie, for convenience we probably should revert to using GigatonsCarbon (GtC) rather than CO2 mass.  Particularly so, when discussing the biomass which is absorbing (very roughly!) 25% of the fossil CO2 emissions.

    You will find a vast amount of discussion of the topic of atmospheric residual CO2 emissions and of the oceanic absorption of CO2.

    Absorption of CO2 by rock weathering is far too slow to contribute to the short term (a century or two) picture.

    As you say, that leaves [excuse pun] the increase of plants as the third factor.  Can you think of another factor that would absorb or sequester additional carbon?

    Land-based plants are the predominant biomass; bacteria/ fungi/ animals are only a small contributor to biomass, relatively.  (Note that modern agriculture tends to reduce soil fungal mass.)

    Zaichun Zhu et al., 2016  estimates plant biomass in the region of 450~500 GtC . . . which we must compare with 10 Gtc of fossil carbon emissions as an annual output.

    I have not seen a quantification of the (satellite-observed) "greening of Earth".  Area of leaf (as leaf area index) has increased distinctly over the past 30+ years.  But what about plant biomass ~ which would seem beyond the satellites' capabiity?  Example case: rainforest clearing is presumably a carbon "negative" compared with the establishment of pastures or palm oil plantings, which have lower biomass.

    From all this, it would seem that we should not expect an exponential "absorption feedback" from plant biomass increase.  We will be fortunate if there is a linear biomass increase!  ( I haven't found the source, but I recall a recent report that the observed "rate of greening" is slowing down ~ so I don't know if that was a reliable observation, despite its plausability, and neither do I know the more important relation to actual biomass.)

    Ceiling capacity for plant biomass is a difficult question.  There was a huge plant biomass back in the Carboniferous era.  However, conditions are vastly different in the modern era, for plant biomass is greatly reduced by the presence of vertebrate herbivores nowadays (plus other human actions . . . including the food consumption by that "megafauna" called humans).

    And judging from the long-term upward trend of the Keeling Curve, we cannot expect that a planetary greening will be of major benefit in reducing the CO2 / Global Warming problem.

  13. The two strong facts here are:

    1/ CO2 concentrations are rising in the atmosphere and the observed increase in surface radiation is precisely as expected from the math.

    2/ The decrease in O2 and the changing isotopic concentration of CO2 in the atmosphere is consistant with the increase being from FF use.

  14. Thanks Eclectic, very much appreciate your taking the time to respond so fully and in such a straightforward manner.  Am not aware of any other obvious absorbtion mechanism.  Photosynthetic 'real estate' (leaf area) is surely more important than biomass. (Rain forest culling is bad news.) Got me seriously thinking!

    Also now need to be looking at relationship between CO2 concentrations and reflection of relevant parts of the spectrum (overlap with water vapour etc).


  15. Scaddenp, thanks. Are you aware of any ongoing monitoring of the ratio of human produced CO2 isotopes vs naturally occuring.   This seems like such a key figure that it is surprising perhaps that there aren't six monthly Internet broadcasts in large neon numbers!!  Clearly though sampling would somehow need to be representative, and I don't understand how that can be achieved.

  16. World Resources Institute "just produced an updated diagram explaining where the world’s greenhouse gas emissions come from and how they are used. This time we have both interactive and static versions."

  17. Gseattle:

    Here is a link to climate Myth 34.


    [BL] Michael Sweet's comment is the result of an increasingly off-topic discussion on this thread:

    2020 SkS Weekly Climate Change & Global Warming News Roundup #35

    Hopefully discussion will continue here, but readers may want to read the other thread for context.

  18. According to figure 1, "The Global Carbon Cycle", vegetation, land and the ocean absorb more carbon than they produce, 17 gigatons more. Where those extra tons come from? They have to come from somewhere, or someone. The answer is fossil fuel burning and land use. Nature is not seletive when it comes to carbon, it will absorb whatever is available. And by the way, part of the 29 gigatons produced by human actions, are absorbed as result of other human actions, technologies and materials. So the figure is misleading because the net result is not 29.

  19. High-Resolution Temperature Variability Reconstructed from Black Pine Tree Ring Densities in Southern Spain This article received in June/2020, revised, accepted and published in July/2020, shows that temperatures are declining.

  20. Luiz @344 , the Spanish regional study you have mentioned, is stating that the temperatures were cooler during 1600 - 1800  and have been warmer since 1800 (approximate date).

    Why do you mention temperatures declining?  Please explain.

  21. Luiz @ 343:

    The 29Gt is misleading? No, it is not. It is not a net flow. None of the arrows in figure 1 represent net flows. That's why there are two arrows in two directions between atmosphere and land, and atmosphere and ocean. One arrow for one flux in one direction.

    There is no flow from atmosphere to fossil fuel, so there is no arrow. Any transfer from atmosphere to vegetation, etc on land is contained in the middle arrow (450 Gt). The "land use" part of the left-most 29 Gt arrow is only that portion of anthropogenic activity that causes carbon flow into the atmosphere.

    There is precious little that humans have been doing that removes carbon from the atmosphere, unless you want to claim credit for crop growth, etc., that largely repsesent a replacement of natural systems, not an addition.

    There are agricultural practices that can potentially increase soil carbon, etc., but on a global scale they are a drop in the bucket at this time. Agricultural practices have tended historically to lead to increased atmospheric CO2.

  22. The view that an increase from 2 billion to 8 billion people breathing out billions of tons of CO2 is carbon neutral cycle and not a problem is interesting.  Using that logic, we could say that burning fossil fuel and building concrete infrastructure is simply releasing CO2 back into the atmosphere from whence it came is a carbon neutral cycle too - albeit on a longer time frame.


    [TD] The long time needed to recycle the carbon injected into the atmosphere from burning fossil fuels in fact is the problem. Read the post about breathing, and if you want to comment more on that topic do so there not here.

  23. Here’s why IPCC’s core theory is invalid.
    All climate alarmism is based upon the United Nations Intergovernmental Panel on Climate Change (IPCC) invalid core theory of climate change: human CO2 emissions caused all the increase in atmospheric CO2 above 280 ppm and since 1750.
    IPCC claims climate events provide “extensive evidence” that human emissions caused the events. But events cannot prove their cause.
    IPCC assumes its own core theory is true to argue its core theory is true. This is invalid circular reasoning.
    The IPCC says its core theory is “incontrovertible.” But the scientific method says evidence cannot prove a theory is true. Rather, only one error can prove a theory is false.
    IPCC’s core theory says human and natural CO2 act differently, e.g., human CO2 sticks in the atmosphere while natural CO2 flows out of the atmosphere. This is impossible because all CO2 molecules are identical.
    The correlation between annual human CO2 emissions and annual atmospheric CO2 increases is zero, which proves IPCC’s core theory is false.
    Ice core data prove IPCC’s core theory is false.
    Stomata leaf data prove IPCC’s core theory is false.
    IPCC’s human CO2 cycle is not a scientific deduction. It is merely a replication of IPCC’s core theory.
    IPCC’s human CO2 cycle is not compatible with IPCC’s natural CO2 cycle. This proves IPCC’s core theory is false.
    In addition, preliminary data on the small 2020 reduction in atmospheric CO2 caused by the 2020 reduction of human emissions also proves IPCC’s core theory is false.


    [DB] Making things up is unhelpful.  Further, simply asserting something does not make it true.  This is a science and evidence-based venue and substantive sources are required to support hyperbolic statements.  Please adhere to the Comments Policy and refrain from sloganeering.

    Sloganeering snipped.

  24. Lindzenfanone @348 :

    You have quite a laundry list there.  Much of it is wrong, but I guess you don't really care about that ~ since you obviously haven't bothered to educate yourself about climate science.

    My next guess is that you are making a giant leg-pull.  (Only on something like WattsUpWithThat  website could your "ideas" be taken seriously.)

    But I do have a question:  Why your "Lindzen" connection with climate?   For more than 15 years, Prof Lindzen has been moving away from scientific thinking and has been making his religious beliefs an emotional basis for his (largely rhetorical) speeches.

  25. Eclectic @349,

    I think what you call "quite a laundry list" presented by commenter lindzenfanone @348 is less a laundry list and more a nonsensical rant. (The commenter doesn't start well in my book with his chosen nom-de-clavier. For me Dicky Lindzen is today a proven liar who long-ago turned away from the scientific method.)
    The rant begins effectively saying that there is no available ontological truth which of course will make all argument circular. This is followed by some silliness about naturally-emitted CO2 and anthropogenic-emitted CO2 requiring to act differently with AGW science. The non-correlation comment could be presented statistically if it were not so crazy and wrong, this followed by poorly presented statements that try (but fail badly) to set out reason to support a bold (and with the failure, unsupported) assertion that "IPCC's core theory is wrong!!"

    The links appended to the comment lead to a number of dubious published papers that don't bear scrutiny**, Berry (2019) 'Human CO2 Emissions Have Little Effect on Atmospheric CO2' (two links provided), Humlum et al (20130 'The phase relation between atmospheric carbon dioxide and global temperature', Koutsoyiannis & Kundzewicz (2020) 'Atmospheric Temperature and CO2: Hen-Or-Egg Causality?' and Harde (2019) 'What Humans Contribute to Atmospheric CO2: Comparison of Carbon Cycle Models with Observations' (**These 'usual suspects'  have been publishing drivel like this for years. If these particular papers presented anything game-chnging for AGW, indeed anything at all new and worthy of some small consideration, then that 'something' is failing to appear either within the denialist world or in the real world.)

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