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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)

At a glance

Have you heard of Earth's carbon cycle? Not everyone has, but it's one of the most important features of our planet. It involves the movement of carbon through life, the air, the oceans, soils and rocks. The carbon cycle is constant, eternal and everywhere. It's also a vital temperature control-mechanism.

There are two key components to the carbon cycle, a fast part and a slow part. The fast carbon cycle involves the seasonal movement of carbon through the air, life and shallow waters. A significant amount of carbon dioxide is exchanged between the atmosphere and oceans every year, but the fast carbon cycle's most important participants are plants. Many plants take in carbon dioxide for photosynthesis in the growing season then return the CO2 back to the atmosphere during the winter, when foliage dies and decays.

As a consequence of the role of plants, a very noticeable feature of the fast carbon cycle is that it causes carbon dioxide levels to fluctuate in a regular, seasonal pattern. It's like a heartbeat, the pulse of the Northern Hemisphere's growing season. That's where more of Earth's land surface is situated. In the Northern Hemisphere winter, many plants are either dead or dormant and carbon dioxide levels rise. The reverse happens in the spring and early summer when the growing season is at its height.

In this way, despite the vast amounts of carbon involved, a kind of seasonal balance is preserved. Those seasonal plant-based peaks and troughs and air-water exchanges cancel each other out. Well, that used to be the case. Due to that seasonal balance, annual changes in carbon dioxide levels form regular, symmetric wobbles on an upward slope. The upward slope represents our addition of carbon dioxide to the atmosphere through fossil fuel burning.

Fossil fuels are geological carbon reservoirs. As such, they are part of the slow carbon cycle. The slow carbon cycle takes place over geological time-scales so normally it's not noticeable on a day to day basis. In the slow carbon cycle, carbon is released by geological processes such as volcanism. It is also locked up long-term in reservoirs like the oceans, limestone, coal, oil or gas. For example, the "37,400 billion tons of 'suspended' carbon" referred to in the myth at the top of this page is in fact dissolved inorganic carbon in the deep oceans.

Globally, the mixing of the deep ocean waters and those nearer the surface is a slow business. It takes place over many thousands of years. As a consequence, 75% of all carbon attributable to the emissions of the industrial age remains in the upper 1,000 m of the oceans. It has not had time to mix yet.

Fluctuations in Earth's slow carbon cycle are the regulating mechanism of the greenhouse effect. The slow carbon cycle therefore acts as a planetary thermostat, a control-knob that regulates global temperatures over millions of years.

Now, imagine the following scenario. You come across an unfamiliar item of machinery that performs a vital role, for example life support in a hospital. It has a complicated control panel of knobs and dials. Do you think it is a good idea to start randomly turning the knobs this way and that, to see what happens? No. Yet that is precisely what we are doing by burning Earth's fossil fuel reserves. We are tinkering with the controls of Earth's slow carbon cycle, mostly without knowing what the knobs do - and that is despite over a century of science informing us precisely what will happen.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

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 a range of natural processes, and absorbed by others. The carbon cycle is the cover-all term for these processes. It has both fast and slow components.

In the fast carbon cycle, natural land and ocean carbon remains roughly in balance and has done so for a long time. We know this because we can measure historic levels of CO2 in the atmosphere both directly, in ice cores and indirectly, through proxies. It's a seasonal response to things like plant growth and decay.

In stark contrast to the fast carbon cycle, the slow version operates over geological time-scales. It has affected carbon dioxide levels and therefore temperatures throughout Earth's history. The reason why the slow carbon cycle is so important is because many of the processes that lead to long-term changes in carbon dioxide levels are geological in nature. They take place over very long periods and do so on an erratic basis. The evolution of a species that has deliberately disturbed the slow carbon cycle is another such erratic event.

Annually, up to a few hundred million tonnes of carbon pass through the slow carbon cycle, due to natural processes such as volcanicity. That's small compared to the fast carbon cycle, through which some 600 billion tonnes of CO2 pass to-and-fro annually (fig. 1). However, remember that the fast carbon cycle is a give-and-take seasonal process. The slow carbon cycle instead runs in one direction or another over periods typically measured in millions of years.

Global carbon budget

Fig. 1: Schematic representation of the overall perturbation of the global carbon cycle caused by anthropogenic activities averaged globally for the decade 2012–2021. See legends for the corresponding arrows and units. The uncertainty in the atmospheric CO2 growth rate is very small (±0.02 GtC yr−1) and is neglected for the figure. The anthropogenic perturbation occurs on top of an active carbon cycle, with fluxes and stocks represented in the background. Adapted from Friedlingstein et al. 2022.

Through a series of chemical and geological processes, carbon typically takes millions of years to move between rocks, soil, ocean, and atmosphere in the slow carbon cycle. Because of these geological time-scales, however, the overall amount of carbon involved is colossal. Now consider what happens when more CO2 is released from the slow carbon cycle – by digging up, extracting and burning carbon from one of its long-term reservoirs, the fossil fuels. Although our emissions of 44.25 billion tons of CO2 (in 2019 - source: IPCC AR6 Working Group 3 Technical Summary 2022) is less than the 600 billion tons moving through the fast carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra emitted CO2: about 40% of it remains free.

Human CO2 emissions therefore upset the natural balance of the carbon cycle. Man-made CO2 in the atmosphere has increased by 50% since the pre-industrial era, creating an artificial forcing of global temperatures which is warming the planet. While fossil-fuel derived CO2 is a small component of the global carbon cycle, the extra CO2 is cumulative because natural carbon exchange cannot absorb all the additional CO2. As a consequence of those emissions, atmospheric CO2 has accumulated to its highest level in as much as 15 to 20 million years (Tripati et al. 2009). This is what happens when the slow carbon cycle gets disturbed.

This look at the slow carbon cycle is by necessity brief, but the key take-home is that we have deeply disturbed it through breaking into one of its important carbon reservoirs. We've additionally clobbered limestones for cement production, too. In doing these things, we have awoken a sleeping giant. What must be done to persuade us that it needs to be put back to sleep? 

Cartoon summary to counter the myth

Cherry picking

This Cranky Uncle cartoon depicts the "Cherry picking” fallacy for which the climate myth "Human CO2 emissions are small" is a prime example. It involves carefully selecting data that appear to confirm one position while ignoring other data that contradicts that position. Source: Cranky Uncle vs. Climate Change by John Cook. Please note that this cartoon is illustrative in nature and that the numbers shown are a few years old.

Last updated on 17 September 2023 by John Mason. View Archives

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Argument Feedback

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

Further reading

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).

Denial101x video

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


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Comments 151 to 175 out of 354:

  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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