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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 151 to 175 out of 380:

  1. To Dikran: So what? It was your idea with steps. Will you do the step #3 finally? I agreed long with your Step 2, just written it in an accurate form (your is too sloppy).
  2. bugai agree to step #2 (or demonstrate that it is incorrect) and you will find out. The ball is in your court.
  3. To Dikran: you guy have a problem. I write you: I agreed with your Step 2 long ago.
    Response: [muoncounter] Please avoid any form of ad hominem. Refer to the Comments Policy; such statements as these are usually cause for comment deletion.
  4. bugai O.K., step #3 we can rearrange the equation to get ΔC - E_a = E_n - U_n Do you agree? Note I have change dC to ΔC to make it clear we are talking about the change in C, which is completely conventional notation used in physics.
  5. To Dikran: 1st class school math. Could you increase your steps?
  6. bugai wrote "1st class school math. Could you increase your steps?" I would happily do so if you were more cooperative, while you are obfuscating at each step it make sense to go in as small steps as possible to give you as little room to obfuscate as possible. So, do you agree, if so, say so explicitly.
  7. 156, bugai, [I won't interfere, but you accused me of being argumentative. You are demonstrating the same behavior with Dikran. With small, axiomatic steps this discussion with him will proceed very smoothly and quickly if you are less argumentative. All you need to do at each point is to respond "Yes, I agree" -- unless you truly don't at some point, but as you've pointed out, these steps are fairly trivial and should not involve any side discussion. If you let the steps flow, the answer will arise incontrovertibly.]
  8. bugai @148, For this to be true globally you would require a similar reduction in terrestrial primary productivity. However this doesn't appear to be the case. According to this paper Net Primary Productivity (NPP) has been increasing by 0.52%/yr between 1980 and 2000.
  9. To Hyperactive Hydrologist: terrestrial productivity is not really relevant, because it is CO2 neutral. CO2 binding in oceans is significant, because the phytoplankton is beeing eaten by zooplankton and carbon is bound in the shells. The shells sink to the ocean deep for good.
  10. To Dirkan: I agreed long with your Step 3. Are you going any further?
  11. To Dirkan: to shorten the discussion, just put all your steps in a row. Then I will point, at which step I start to disagree with you.
  12. @ bugai @ 161 "Then I will point, at which step I start to disagree with you." So you have already decided to disagree with Dikran without actually evaluating the full argument, but are merely looking for the proper point in the discussion to insert it? How "skeptical" of you.
  13. bugai sorry, experience tells me that step-by-step, with agreement at each point is the only way to differentiate between truth-seekers and trolls. As Sphaerica points out, if you want the discussion to proceed quickly and smoothly, then co-operate by simply replying "I agree" where you agree, rather than waste time obfuscating. I'm glad you agree with step #3 ΔC - E_a = E_n - U_n Step #4 is as follows, if the left hand side is negative, then we know the right hand side must also be negative, i.e. if E_a > ΔC then U_n > E_n Do you agree (if you state that you agree explicitly and unambiguously, and make no attempt to obfuscate or irritate, then I will have the confidence to proceed in larger steps).
  14. Gosh Daniel. Dikran disagreed with me in posting #130. You've missed that? Now we are just figuring out what is the reason for the disagreement. You want to participate [it] contructively [/it], or just snorking around?
  15. bugai, "terrestrial productivity is not really relevant, because it is CO2 neutral." Again do you have a reference for this? From my understanding terrestrial productivity can also act as a carbon sink.
  16. Sorry, Dikran. Somehow I understand why other "skeptics" did not withstand you. Apparently, I went three steps further then they did, and I have enough. I have no time to discuss the elementary math with you. You have to put all the chain of your arguments at once if you wish any further discussion. Sorry for that!
  17. Daniel, I suspect it may be a second language issue, it is possible that bugai's comment was not quite what was intended. bugai, the difference is that I disagreed after you had stated your argument, where as you have stated that you will disagree before I have stated my argument. This is possibly not what you meant. However, I would suggest that you drop the abrasive tone, it doesn't tend to go down to well here, calm rational discussion is better appreciated.
  18. bugai, I presented the fourth step, had you behaved better it would have taken us a total of seven posts to get to that point, four from me, three from you. Now if you have found the discussion tiring, perhaps you should ask youself why there were more than seven posts and why you didn't simply write "I agree" each time if each step were merely "elementary maths". The fact that you have left the discussion at this point, when you were very nearly at the conclusion, speaks volumes.
  19. bugai, Your withdrawal at this point will be viewed as a tacit admission that you have realized that your position is untenable, and that a very simple and painless, step by step walk through the mathematics that demonstrates this will force you to admit your error. Rather than do so, you bristle, obfuscate, and then retreat in a huff.
  20. I should just add, nobody would be more pleased that I if bugai were able to identify a flaw in the argument.
  21. Indeed, it is interesting that Bugai bails at step 4... as acceptance of that "elementary math" combined with his own previous statements the natural sources and sinks are not in balance and that the increase in concentration can be no more than the human emissions would perforce lead to the conclusion that human emissions are entirely responsible for the increase in concentration.
  22. @ Dikran Perhaps, Dikran, perhaps. But then, given the proper usage of the colloquial express "Gosh" by bugai in 164 above, perhaps we have something else entirely.
  23. Dirkan, as I said, no further discussion until you put all your seven (?) arguments. It's your call.
    Response: The proper spelling is "Dikran".  Please take note of that.
  24. Speaking of "terrestrial productivity," here's the summary of a new study that bears on this topic. Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming. Michael W. I. Schmidt, Margaret S. Torn, Samuel Abiven, Thorsten Dittmar, Georg Guggenberger, Ivan A. Janssens, Markus Kleber, Ingrid Kögel-Knabner, Johannes Lehmann, David A. C. Manning, Paolo Nannipieri, Daniel P. Rasse, Steve Weiner & Susan E. Trumbore: Persistence of soil organic matter as an ecosystem property, in: Nature, 6 October, 2011, DOI: 10.1038/nature10386
  25. bugai wrote: "Dirkan, as I said, no further discussion until you put all your seven (?) arguments. It's your call. " Sorry, bulgai, as I said, a truth-seeker would just co-operate in the discussion. All you are achieving with this pointless posturing is highlighting the fact that you do not think you can refute the argument if it is presented step by step. Yet again you are just spinning it out a bit more by responding in a way that does not allow progress, as I said if you are finding the discussion slow and tiring, the solution is simple; just stop impeding it.

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