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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).

Comments

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Comments 51 to 75 out of 149:

  1. TruthSeeker at 09:11 AM on 21 July, 2010 "If these sinks are essentially non-reversable, and the same mechanizms that produced these fuels are currently going on today." But the mechanisms that deposited oil and coal beneath us are *not* going on today. There wouldn't be a problem if oil and coal were being deposited at the same time and the same rate as we use them. That's why they're called fossil fuels - as against renewable or replenishable fuels like burning wood or animal dung or anything else that will grow or return within a short time or at most, a human lifetime.
  2. adelady #51 "But the mechanisms that deposited oil and coal beneath us are *not* going on today." Not in any way at all meaningful to the human lifespan. On the other hand, I seem to recall that the ABC docco Crude suggested that maybe the processes that deposited all that oil might be beginning again, due to the action of anthropogenic CO2 entering the atmosphere (specifically in the Back to the Future episode I think).
  3. I would contest that the mechanisms that deposit oil and coal are very much going on much as they always have. Peat swamps still grow, benthic black ooze still accumlates - they are just very slow processes that remove very small amounts of carbon from the cycle. The oil and gas we use is result of millions of years of accumulation. The more important removal of carbon is from deposition as CaCO3 but this is also only significant on geological time spans as rate of deposition is ultimately tied to Ca flux from weathering.
  4. #53: scaddenp is correct. Oil and gas form at agonizingly slow rates. There are numerous estimates of the ultimate quantity of oil existing on earth; take 1750 billion Bbl as a guesstimate. From UMichigan GS265. Gb=Billion Bbls The oldest known oil may be about 540 million years in age. That's a ballpark formation rate of about 3500 Bbl/year -- against an average consumption rate of 5+ billion Bbl/year from the late 1800s on. (same source: 761 GBbl cumulative production in 130 years, starting around 1865 thru 1995). So we are indeed taking it out MUCH faster than it gets put in.
  5. Can you answer what I think is a more sophisticated version of the “too small to matter” argument? It is often said that natural sources and sinks are in balance, but human emissions throw this balance out and positive feedback sets in. This is in danger of sounding like Gaia-based woo woo. My question is this; why is there a balance in the first place? In other words, why is the equilibrium stable without human activity but unstable with human activity? And in writing that, I think I might have figured out the answer to my own question, though I have never seen this written down. Is it that for *any* CO2 concentration, there is an equilibrium temperature, which the Earth will reach eventually. Human emissions have shifted that equilibrium position higher. We wiould eventually get to a stable point at current CO2 levels, but it will be much higher than today’s temperature. Is that it? John
  6. Good question, John Ballam. Your last paragraph is part of the answer. But since humans continue to add CO2, that new future equilibrium point keeps moving. The other, more subtle, part of the answer is that there is no one special equilibrium temperature for the Earth. The temperature and climate stability of the last few thousand years has allowed human civilization to flourish, but in previous eras the climate was quite different due to different degrees of the various forcings and feedbacks. Except for sudden events such as meteor and comet impacts, changes in the past mostly have been gradual in terms of human lifetime and even human civilizations. So the climate never really reaches an equilibrium, because some forcing or feedback always is changing. But for humans' practical purposes, slow changes are close enough to equilibrium for coping. The human release of massive amounts of CO2 is so fast that the resulting climate changes will be too fast that coping will be tremendously difficult, expensive, and painful.
  7. John Ballam, I second Tom Dayton's remark that this is a good question. Something to keep in mind is that if natural sources and sinks weren't approximately in balance, Earth would quickly become inhospitable for life as we know it. Thus, the fact that our species and our civilization exist (and we are able to ask questions about these things) necessarily implies that we must live on a planet where natural sinks and sources are more or less balanced. Over the long term, however, sources and sinks do fluctuate slowly, as Tom Dayton points out. Thus, there are time periods when CO2 is higher or lower. Note, e.g., the Pleistocene glacial/interglacial cycle, when CO2 naturally fluctuated by around 100 ppm: Figure 1: CO2 concentration over the past 800,000 years from ice cores at Dome C, Vostok, Taylor Dome, and Law Dome. However, as seen on the far right side of that figure, we're currently raising CO2 much more rapidly, and to much higher levels, than anything seen during those glacial/interglacial cycles.
  8. Thank you for those answers. So, it's the RATE of addition of CO2 that is the problem. A 3% increase over thousands of years would be largely taken up by the various sinks and could indeed be called "tiny", but 3% in a few decades is unprecedented and too much for the system to bear. Getting there?
  9. Re: John Ballam (58) Mostly. Consider, though, that we now have CO2 levels approximately 40% higher than "normal" interglacial highs... Something to chew on. The Yooper
  10. Okay, since CO2 is only about 0.0360% of the atmosphere, is it really that big of a deal? Come on now, whatever we do to reduce the CO2 in the atmosphere is so negligible that it won't be seen. People continue to breathe and fart. What goes in, must come out. How about carbonated sodas, beer, and paintball guns? What effect do those have on the atmosphere? "Iceland volcano causes fall in carbon emissions as eruption grounds aircraftCooling effect from volcano ash cloud will be 'very insignificant', but flight ban stops emission of estimated 2.8m tonnes of CO2" but from the same article, "Worldwide, the US Geological Survey says volcanoes produce about 200m tonnes of carbon dioxide every year." I better stop now, turn off my computer and put a gun to my head, so as to not upset the balance of CO2. Oh wait a second, firing a bullet produces CO2!, I better hang myself.
  11. #60: " whatever we do to reduce the CO2 in the atmosphere is so negligible that it won't be seen. " How do you know that? Please cite such a claim with a reputable source. If you can find any to back it up. Consider the flip side: We've done plenty to increase atmospheric CO2 that is not negligible and can easily be observed. So your argument makes no sense. Please look more carefully at the plentiful information on this subject: Fossil fuel burning now emits CO2 on the order of 30 Gigatonnes each year, whereas the number you quote for volcanoes is in Megatonnes. Fossil fuel burning produces about twice the annual rate of atmospheric increase (after converting metric tons to ppm by volume). The remainder is stored in the oceans and/or biosphere. As far as "low" concentrations necessarily not having an effect, try hanging around an environment of 380 ppm H2S for a while.
  12. muoncounter, with H2S being around .0000002% of our atmosphere, I'm not too worried about your 380ppm. The real question is, Is CO2 really causing global warming? Or is it the scapegoat for earth's natural cycle of weather change?
  13. You are asking questions that are well answered on this site. Go to the "arguments" and check them out. However please bother to read the counter-argument before just repeating the assertion. muoncounter's argument is that if 380ppm seems too small to have any effect consider what would happen if you replaced each molecule of CO2 with a molecule of say H2S or HCN. (To save you looking it up, it would annihilate mammalian life on earth at least with a couple of hours). 380ppm does not mean insignificant.
  14. Who is going to replace CO2 with H2S or HCN? That can't and won't happen. CO2 is not poisonious and naturally occurs with our existence. So the population of the world has almost tripled in the past 50 years which will of course increase the CO2 emitted into the atmosphere. What's the solution, global birth control? Genocide? The earth has naturaly cycled through significant temperature changes throughout it's creation. Does our data from the last 200 years really tell us that our incremental affect of CO2 is causing the global warming, or like I said previously, this is a natural cycle of the planet?
  15. #64: "The earth has naturaly cycled through significant temperature changes " Ah, the natural cycles game ... its all happened before. Dealt with extensively here and here and here. Its necessary to substantiate your claims. Please find a reputable source that documents a prior natural cycle with all of the following: increasing global temperatures, accelerating Arctic ice melt, etc (full list here); in the face of decreasing solar output, lower concentrations of atmospheric aerosols, etc (full list here); AND increased CO2, all over a very short period of time. And stop throwing around things like 'global birth control'. Once you come to understand that we have indeed made significant impacts on the environment, look for some practical ideas for creating change.
  16. I'd invite not to point to birth control (let alone genocide) just to frighten people with unacceptable theories never backed (and not allowed on SkS) by anyone here.
  17. People who have convincing evidence and intellectually sound reasoning on their side don't generally have to accuse their rhetorical opponents of advocating genocide. Care to try again?
  18. Skepticalenergyguy-- Yes, CO2 has been higher in the past; yes, global temps have been higher in the past; yes, there are natural cycles that modify the Earth's climate. Modern humans, however, have never had to deal with a relatively very rapid global temperature increase. Our tripled population rests on an infrastructure and political/economic framework that has enjoyed a relatively stable climate. Worse yet, as this incredibly energetic economic mode has developed over the past 150-200 years, absolutely no responsibility was built into the system. Externalizing waste costs has been a matter of course for most of industrialized history, to the extent that when such externalization is pointed out, industrialists like, I assume, yourself are shocked by the gall of someone questioning the integrity of the system ("it's just CO2 -- we've been pumping it out for decades. So what?"). You can't seriously expect a rapid doubling of a gas that re-radiates long-wave radiation to have no effect, can you? You do understand how the process works, yes? Maybe that's the first question skeptics should be asked: how does global warming work, according to climatologists? Well, ESG?
  19. I agree that we need to be more environmentally responsible, no I'm not an industrialist, I am an engineer. My job is to reduce energy usage for my clients, increase energy awareness, promote environmental stewadardship, and develop creative ways for my clients to do all of these things economically. Thank you all for your input, it gives me stuff to think about.
  20. @64 Having just asked the question myself - about population and CO2 emmissions - I would direct you to the 'does breathing contribute to CO2 buildup in the atmosphere' argument.
  21. The level of atmospheric CO2 is building up, the additional CO2 is being produced by burning fossil fuels, and that build up is accelerating.
    Yes, the atmospheric level is rising. To say it is "building up" could be an emotive way of saying the same thing. It's certainly a slow rise, at an average over 51 years of about 1.43 ppmv per year. It's incorrect to assert that the whole increase comes from fossil fuel use. For there are other sources, too, such as outgassing from warming oceans and variable (unknown) outputs from various sources, such as wetlands. It's also incorrect to assert that the increase in atmospheric concentration is accelerating. The Mauna Loa record shows no sign of that. In fact, graphing the yearly change (the data given at the Mauna Loa site) shows that since about 1998, the rate of increase has actually slowed. So would you cite your source for the acceleration, please? Cheers, Richard Treadgold, Convenor, Climate Conversation Group.
    Response: See the post CO2 is not increasing
  22. Richard, I believe the assertion is that the cause of CO2 rise is anthropogenic. That's fossil fuel and land use change. Temperature-induced rises in CO2 are feedbacks, not forcings. Now can you please supply a reference for the relative percentage of CO2e (not CO2 as that doesnt tell the whole story) that comes from fossil use, agriculture, and feedbacks? I would be very surprised if feedbacks are much of a issue yet.
  23. Richard Treadgold writes: It's incorrect to assert that the whole increase comes from fossil fuel use. For there are other sources, too, such as outgassing from warming oceans Richard, there are two problems with this. First of all, the oceans are a net sink of CO2. That is, the net flux of CO2 is from the atmosphere to the ocean, not the reverse. See lots of papers on the subject, including Takahashi 2009 and Sabine 2004. Secondly, we know the total fossil fuel flux to the atmosphere quite well, and it's clearly larger than the annual increase in atmospheric CO2. In other words, fossil fuels account for more than 100% of the atmospheric increase (with the excess being taken up by oceans and the biosphere). Richard also writes: It's also incorrect to assert that the increase in atmospheric concentration is accelerating. The Mauna Loa record shows no sign of that. In fact, graphing the yearly change (the data given at the Mauna Loa site) shows that since about 1998, the rate of increase has actually slowed. So would you cite your source for the acceleration, please? From the Mauna Loa data, the linear trend in CO2 for each of the past decades is as follows: 1960-1969: +0.8 ppmv/year 1970-1979: +1.2 1980-1989: +1.6 1990-1999: +1.6 2000-2009: +2.0 That is a very clear acceleration. It's a bit disturbing that someone acting as "Convenor, Climate Conversation Group" would be so seriously mistaken on multiple basic facts about CO2 in the Earth system. What kind of "climate conversations" are you having, and who are you having them with? Somehow, you seem to have picked up a lot of misinformation.
  24. scaddenp, The assertion was straightforward, as I quoted it:
    the additional CO2 is being produced by burning fossil fuels
    Land use change wasn't mentioned. No, I can't supply a reference for what you ask. But I didn't mention it either. You forgot my question: What is the evidence for an acceleration in the rising atmospheric level of CO2? When you say "temperature-induced rises in CO2 are feedbacks, not forcings", does that mean they don't form part of the increased amount in the atmosphere? But of course they do, and they are not anthropogenic, so they ought to be deducted from the anthro emissions budget. That's all I meant. Cheers.
  25. Richard Treadgold at 16:05 PM, regarding land change use, in particular deforestation which has been ongoing for centuries. From 1100 to 1500 significant deforestation took place in Western Europe, global deforestation accelerating from the mid 1800's with the result that only about half of the Earth's original mature tropical forests remain. It is also clear how seasonal plant growth causes significant variation in CO2 levels globally, with dramatic annual variations regionally. The question that needs to be answered, is, is that CO2 that would have been sequestered by the now missing forests being considered as a forcing, and has it been adequately accounted for given that considerable deforestation took place before 1750, particularly in the northern hemisphere, 1750 being the base from which the effects of anthropogenic CO2 are referred back to.

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