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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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 276 to 300 out of 380:

  1. In terms of identifying MM Co2 emissions, how should the CO2 exhaled by the planet's population be counted?  Should CO2 emissions resulting from farming, crop or livestock, be counted as MM or natural?  Same question for CO2 generated from natural decomposition on our world's landfills.  Human waste, treated in sewage plants and piped into rivers and oceans, generates CO2 - natural or anthropogenic? Should the definition of MM Co2 be limited to only that which exits a tail pipe or smoke stack?    Even if all CO2 emissions from burning fosil fules could be sharply curtaild or eliminated through sequestration,  each year there are more people on the planet, and with each year life expectancey is longer.  We all  need to eat and breath and as a consequence of life need excrete waste.   Surely all sources of MM Co2 should be considered and counted in an appropriate way.


    [TD] See "Does Breathing Contribute to CO2 Buildup in the Atmosphere?"  It has both Basic and Intermediate tabbed panes.

  2. toolate: As the mod's suggested link points out, respiration doesn't really have a net impact. The domesticated ruminant (eg cows, sheep, goats) population is another matter though - entric fermentation of plant matter in their stomachs generates methane, a potent GHG.

  3. The chart at the top tells me that vegetation and land, plus the oceans absorb 17 more gigatons than they emit. Assuming we can't do much about the oceans, all we need to do is increase veg&land absorption by 12 gigatons to balance human production of CO2!

  4. Well mushrumps, I have made a mess of this sort of calculation in past but lets see how I go.  The difference between emissions and absorption of land/vege is 11Gt. Land area of earth is 150,000,000 km2. 1/3 is desert, so non-desert is 100,000,000 or .1Gkm2. So land/vege currently is moping up 110 tonne/km2. To mop up an extra 17Gt at current rate, then need 17G/110 = 150,000,000km. That's current area of planet. Cant plant that much forest. Looks like a challenging problem to me.

  5. One other little gotcha is that turning desert/grassland to forest say reduces the albedo of the planet - it doesnt reflect as much radiation to space but I think that would be a minor concern.

  6. According to the IPCC report Table 1. published in 2001, 98.5% of all CO2 is absorbed, not 40%.  The charlatan IPCC since removed that table.

    CO2 is CO2 whether from man or nature; someone had to lay wake at night, probaly on drugs to say less CO2 from Man gets absorbed.

    Table 1. Global Sources and Absorption of CO2

    Carbon Dioxide:           Natural     Human Made   Total       Absorption

    Annual Million Tonnes 770,000      23,100         793,100     781,400

    % of Total                      97.1%          2.9%            100%           98.5%

    Source: Intergovernmental Panel on Climate Change, Climate Change 2001: The Scientific Basis  (Cambridge, UK Cambridge University Press, 2001), p. 188.)


    [JH] If you continue to lace your comments with snark and absurd accusations, they will be summarily deleted.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  7. Bob Ashworth @281, what appears on page 188 of the IPCC TAR working group 1  is Fig 3.1:

    The units used are Petagrammes of Carbon (= Gigatonnes Carbon), and in none of the four parts of the figure are values matching those you show.  More imporantly, in Fig 3.1 B, the human perturbation is shown to clearly dominate the net natural fluxes, a fact that lead the IPCC to write:

    "Atmospheric CO2 is, however, increasing only at about half the rate of fossil fuel emissions; the rest of the CO2 emitted either dissolves in sea water and mixes into the deep ocean, or is taken up by terrestrial ecosystems. Uptake by terrestrial ecosystems is due to an excess of primary production (photosynthesis) over respiration and other oxidative processes (decomposition or combustion of organic material). Terrestrial systems are also an anthropogenic source of CO2 when land-use changes (particularly deforestation) lead to loss of carbon from plants and soils. Nonetheless, the global balance in terrestrial systems is currently a net uptake of CO2."

    (My emphasis)

    And as you add your own little conspiracy theory to your misrepresentation of the IPCC TAR, here is a direct copy of the original report as published, demonstrating that as published the IPCC TAR agreed with the view presented in the OP above.

    Finally, for good measure there is a table 3.1 in the IPCC report, appearing on page 190, which reads:

    "Table 3.1: Global CO2 budgets (in PgC/yr) based on intra-decadal trends in atmospheric CO2 and O2. Positive values are fluxes to the atmosphere; negative values represent uptake from the atmosphere. The fossil fuel emissions term for the 1980s (Marland et al., 2000) has been slightly revised downward since the SAR. Error bars denote uncertainty (± 1s), not interannual variability, which is substantially greater.


    Atmosphere increase
    3.3 ± 0.1
    3.2 ± 0.1
    Emissons (fossil fuel, cement)
    5.4 ± 0.3
    6.3 ± 0.4
    Ocean-atmosphere flux
    -1.9 ± 0.6
    -1.7 ± 0.5
    Land atmsphere fluux*

    *partitioned as follows

    Land use change
    1.7 (0.6 to 2.5)
    Residual terrestrial sink
    -1.9 (-3.8 to 0.3)

    * The land-atmosphere flux represents the balance of a positive term due to land-use change and a residual terrestrial sink. The two terms cannot be separated on the basis of current atmospheric measurements. Using independent analyses to estimate the land-use change component for the 1980s based on Houghton (1999), Houghton and Hackler (1999), Houghton et al. (2000), and the CCMLP (McGuire et al., 2001) the residual terrestrial sink can be inferred for the 1980s. Comparable global data on land-use changes through the 1990s are not yet available."

    (Sorry for loss of formatting.)

  8. Bob Ashworth:  I don't see that "Table 1" on page 188 of Chapter 3 ("The Carbon Cycle and Atmospheric Carbon Dioxide") of the IPCC's TAR WG1 "The Scientific Basis."  Nor are there any results from searching for the exact quoted phrase "Global Sources and Absorption of CO2."  Are you claiming that the IPCC does not have that table in its post-2001 reports, or are you claiming that the IPCC removed that table from its 2001 (TAR) report after final publication?  Perhaps instead that table was in only a preliminary draft of the report (which was not published because, um, it was preliminary.  Duh.).

    Where is there any statement by anybody, that less anthropogenic than natural CO2 gets absorbed?

  9. Bob, did you not read the article or were you not able to understand it?

    Yes, much more CO2 is released by natural sources than human industry. We all know that. The article says it.

    However, the 'conclusion' you draw from this is just nonsense. A>B, therefor A+B cannot be greater than C? Natural CO2 emissions (A) and absorption (C) are roughly in balance. Ergo, the addition of CO2 from human industry (B) tips total emissions over total absorption and causes atmospheric CO2 to increase. Put another way: If, as you proudly say, 98.5% of total emissions are being absorbed, then 1.5% aren't being absorbed. Clearly, without the extra 2.9% from human emissions there would not be 1.5% in excess of absorption and atmospheric levels would not be increasing. Ergo, human CO2 emissions are causing atmospheric CO2 levels to go up.

  10. Tom Curtis @ 273, in order to accurately determine whether the co2 leads or lags temperature, should you not be taking the fourier transform of each data set to accurately determine the phase relationship?  It just seems to me looking at your graph (casually eyeballing it), looks like there is a slight phase shift with co2 lagging temp.  


    [PS] Please do not let this discussion of CO2 lags/leads relationships wander off onto topics discussed in detail on "CO2 lags temperature" or "CO2 increase is natural, not human caused". It is very important to note that Tom has detrended the series because he is looking for change in CO2 in response to a temperature change. Ie Co2 is both a forcing and a feedback. As feedback it does of course lag temperature. Note also that the feedback CO2 is small (8ppm) cf forcing (~100ppm). Please take further discussion to a more appropriate place.

  11. this article is very informative showing how humans are contributing to carbon emissions in to our atmosphere. I would be interested in seeing a more complex version of this showing exactly where natural emissions and man made go.

  12. Can you be more specific about you want? The gory detail can be found in Chapter 6 of the IPCC AR5 WG1 report.

  13. According to some reports, we didn't emit more Carbon dioxide in 2015 than in 2014.  Perhaps our output has leveled off or may even decrease as more and more energy saving, renewable generation and a flat economy take hold.  I find this frightening.  If you look at the Mana Loa Carbon dioxide site for April, Carbon dioxide went up 4.16ppm despite this lack of increased carbon output.  All things being equal one would have expected, possibly, a 2.5ppm increase.  Apparently all things are not equal.  Is this some effect of the strong El Nino we experienced or have one or more carbon sinks started to shut down. If this continues to the end of 2016 and into 2017, we just may be in a spot of bother.  All things being equal, we would expect the line to revert to the long term increase and should see some quite small increases on into 2017. 

  14. william

    I would think its most likely an effect of El Nino. Even if carbon sinks start to shut down, they wont be that precipitous.

  15. William, 

     Most likely the soil causing it. That's good news and bad news. The good news is that it is reversable. The bad news is that we are fairly unlikely to do so. As although it really is easily reversable, there is a huge institutional resistance to even trying, and actually the trends are to accelorate it rather than mitigate it.

  16. Everyone on the world needs to glow at least 10 tree in his/her life. Assume only half of population can grow the trees for some reasons. The current population is 7.4 billions. Then we have 3.7 billions of people grow the trees, eventually, we have more 37 billions of tree. Each big trees can absorb 1 ton of carbon dioxide a year. Each year, 370 billions of carbon dioxide will be absorbed by trees. And we have schedule to control the tree, say to cut away the old trees, to collect the wood (solid carbon oxide) as recycle, reusable materials. The next thing we need to do is to get rid the dairy farm. As we know, the green effect of the methane is 12 times of CO2. A dairy cow can produce 110kg CH4 a year. Some researchs said that cow milk is not for human. Some countries not rely on the cow milk. I think these two method can improve the green house effect.

  17. mr_alanng - I think it would by a lot simpler to just get off using fossil fuels rather than trying to sequester CO2. Also, while methane is an issue, it is less than 30% of total forcing from CO2 because the emissions are far smaller.

    " Some researchs said that cow milk is not for human."

    I dont think any food is "for human" except breast milk but evolution has equipped us to use it. The gene for lactase persistance is highly selected for since the paleolithic particularly in european populations. Ie once you had settled agricultural, humans with lactase persistance survived and bred better than those without.

  18. Your citation to the IPCC AR4 Figure 7.3 seems to be incorrect. The figure shown is shown here:


    This figure states different numbers from yours. And I cannot find the 29 Gt/yr figure anywhere.


    Any further info or clarification is appreciated.

  19. dcordell @293, I think you will find that the figure above shows the fluxes in Gigatonnes of CO2, whereas the IPCC figure shows it in Gigatonnes of Carbon.  The fluxes from right to left in GtC are:

    7.9, 119.7, 122.7, 90.5 and 92.2

    According to the IPCC AR4 Fig 7.3 they are 8, 119.6, 122.6, 90.6 and 92.2, with the differences being down to rounding.

  20. Hi all. I've posted hardly at all on this site due to time constraints. However, I have read the first page and the last page very carefully.

    My predilection is that AGW is probably happening, but that mankind's affect [effect?] on the climate is not catastrophic.

    I would like to point out that there are, in my opinion, three sides to the AGW question as it pertains to CO2 emitted by humans. There are those who believe in the "consensus" that humans are forcing the climate. There are those who deny that the human influence on the climate is large enough to force it.

    There is a third group, those people who do not know which side of this matter is correct, and who are looking for truth.

    Anyhow... here's the background, followed by my question.

    I first started reading up on a related thread here on SkepSci...

    ...on Page 1 of that thread, back in 2007, is the argument that warming is likely to be causing CO2 release. This argument holds, as I understand it, that mankind, while emitting a lot of CO2, is not the major CO2 emitter on the planet, but that the current warming cycle is releasing more naturally sequestered carbon into the atmo than mankind is emitting.

    I understand the argument that it is thought that the minsiscule amount of CO2 that is emitted by mankind is forcing the warming, becasue of a logarithmic relationship, but the apparent leverage of that warming has not yet been proven. My understanding is that CO2 on forces the water vapor cycle in some fashion. Thus, less and less of a percentage of human emitted CO2 has a greater and greater effect on the climate.

    My question is this: Is this the proper page/thread to discuss the 'Warming is Releasing' argument?


    BTW, I did notice one comment on page one, even though the comments were made back in 2008.

    Mizimi #30: "It's a complex subject, [fraught] with difficulties - but ... deal with overpopoulation and the 'global warming problem' will fade away."


    [TD] I turned your link into a link; in future please do that yourself with the link tool when you write your comment.

  21. #291 mr_alanng

    "Each big tree can absorb 1 ton of carbon dioxide a year."

    Very few people would disagree that planting trees is a good idea to ameliorate the effects of burning fossil fuels. Here's a popular telling of the carbon sequestration available in a forest:

    "'An approximate value for a 50-year-old oak forest would be 30,000 pounds of carbon dioxide sequestered per acre,' said Timothy J. Fahey, professor of ecology in the department of natural resources at Cornell University. 'The forest would be emitting about 22,000 pounds of oxygen.'"

    30,000 pounds is 15 short tons. 15 short tons is 13.6 metric tonnes.

    Information on forest density is here:

    I'm afraid that your figure is way too high.

  22. JohnFornaro: Your understanding that "the current warming cycle is releasing more naturally sequestered carbon into the atmo than mankind is emitting" is incorrect. As is explained by the post we are commenting on right now, the naturally sequestered carbon (sequestered as "fossilized" substances that we use as fuels) is being released by humans burning those fossil fuels, thereby putting carbon dioxide and other greenhouse gasses into the atmosphere. 

    The amount we thereby release is not "miniscule" in the context that matters for warming. The amount we release is enough to outstrip the abilities of the natural sinks to absorb it. Consequently, humans are responsible for 100% of the increase in CO2 over at least the past 60 years, and nearly that percent since about 1850.

    Please read the Basic tabbed pane at the top of this page, then flip to the Intermediate tabbed pane and read that.

  23. JohnFornaro, for more details, please also read these posts:

  24. JohnFornaro, the claim you read that "the minsiscule amount of CO2 that is emitted by mankind is forcing the warming, becasue of a logarithmic relationship... Thus, less and less of a percentage of human emitted CO2 has a greater and greater effect on the climate" is incorrect.

    First: As I explained in my previous two replies to you, the CO2 emitted by mankind is not "miniscule," because what matters for warming is that humans are responsible for 100% of the rise in atmospheric total CO2, and the rise in that total has been more than 30% since 1850. CO2 emissions do correlate well with total atmospheric level, and the causal link is provided by the evidence described in the original post at the top of the page you are reading right now. (CO2 measurements are indeed reliable.) It is the increase in the amount of CO2 in the atmosphere that matters, not the  proportion of CO2 in the atmosphere relative to other gases.

    Second: The argument you cited has the logarithmic effect backward. An increase in the absolute amount (number of molecules) of CO2 in the atmosphere has less, not more, of an effect the more CO2 already is in the atmosphere. But scientists always take that into account, by referring to the (nearly) identical amount of warming from the absolute amount of CO2 doubling, regardless of whether the initial (pre-doubling) amount was large or small.

  25. JohnFornaro @, if you look at the increase of atmospheric CO2 concentration during past warming events and use those increases to predict the modern CO2 increase, the maximum increase expected for the current warming is about 10-20 ppmv.  This is most obvious in the change between glacial and interglacial shows a change in atmospheric CO2 of 15.8 +/- 0.6 ppmv/oC (Epica Dome C, 2 StDev confidence interval).  Given the current increase of about 1oC over the preindustrial average, that would lead to an expectation of a 16 ppmv increase in atmospheric CO2.

    That is likely an overestimate given that the long intervals involved allow time for slow processes (such as much of the tropical forest turning into open savannah and vice versa) to take place.  Comparison with the CO2 increase over the MWP which, globally, was nearly as hot as the 1990s, shows that short term processes such as would have had an influence on 20th century CO2 levels result in even smaller relative increases in CO2 concentration:

    That's not the only evidence against the idea that the modern CO2 increase is driven by the temperature increase, but it should be sufficient.

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