Human and livestock respiration is not s significant contributor to increasing atmospheric CO2

October 1, 2010

A small minority of  skeptics need to simply disabuse themselves of the wrong-headed notions that either CO2 levels aren’t really rising; or if they are, then it is not due to human activity.  

Let’s be clear about this:
1. CO2 has been increasing for a hundred years, and that increase is due primarily to the burning of fossil fuels.
2. Human and livestock respiration is not a contributor to increasing atmospheric CO2.  

I am an anthropogenic catastrophic global warming skeptic.  But I wish that small minority of the skeptics would get their facts straight about those two points. 

I could do a lot of math, which is my habit, to make my point, but in this case a picture says a thousand equations…. 


Plant and animal respiration are part of a cycle in which the biosphere, the atmosphere and the oceans exchange carbon.  This continuous exchange had been in quasi-equilibrium for thousands of years before the industrial revolution.  Most all of the carbon that you, your livestock, and your crops exhale (yes, even plants produce CO2 when they are not photosynthesizing) into the atmosphere came out of the atmosphere in the first place.  And it didn’t come out of the atmosphere very long ago – probably less than a few years ago.  So, respiration does not lead to any real increase in atmospheric CO2. 

But when you burn fossil fuels, you are adding new CO2 to the atmosphere.  Yes, it also was originally removed from the atmosphere, but that was millions of years ago.   The CO2 from fossil fuels changes the current quasi-equilibrium.  The increase in atmospheric CO2 that has occurred over the last century is due almost entirely to human activity (primarily the burning of fossil fuels).  

Others have written long expositions  (or here, here, and here) on these points, but I’m afraid their valiant attempts to bludgeon the point home may result in complicating the obvious for those who will not hear. 

The idea is simple and obvious.  Without human activity (primarily burning fossil fuels) the amount of CO2 in the atmosphere is in quasi-equilibrium, like an old bucket where the water from a faucet flows in at the same rate the water flows out through the holes…

Atmospheric CO2 in quasi-equalibrium.

But when you start dripping a little extra water into the top of the bucket, the level will rise until a new equilibrium is reached.  Burning fossil fuels is like dripping more CO2 into the atmosphere.   This is true even if the CO2 added every year is a drop in the bucket compared the movement of CO2 through the entire complex atmosphere-biosphere-ocean system. Slowly the level rises. 

CO2 from fossil fuels causes atmospheric CO2 to increase.

The details may interest you or bore you, but it is senseless to argue these basic facts.  Anyone who wants to convince others that the catastrophic anthropogenic global warming is exaggerated must be realistic about these fundamentals to be taken seriously.


  1. Clearly an oversimplification which doesn’t show the possibility that the natural sinks may increase (or decrease, for that matter) somewhat in the scenario.

    In past times, atmospheric CO2 levels have decreased at a similar rate to the current increase. If we were burning fossil fuels at the same rate as we are now in one of those downturns, all we would be doing would be possibly slowing down the decrease. In our current situation, all we are doing is very slightly adding to the already increasing CO2 levels.

    Has anyone determined exactly how high the CO2 levels would go due to the natural rise that began over a 100 years ago? Unless or until that “natural” level is surpassed and it can be shown conclusively that it was surpassed by anthropogenic emissions, there isn’t anything of concern, is there?

    In any case, does any of this matter if the slight addition of CO2 in the atmosphere can’t be shown to be having more than an overall minor positive influence to our eco system?

    • JohnWho,

      Yes, you are correct, this is a vast oversimplification. However I careully used the word “quasi-equilibrium” to imply that the natural sources and sinks can and do change. I pointed out that when you start with a quasi-equilibrium and start adding to it…

      But when you start dripping a little extra water into the top of the bucket, the level will rise until a new equilibrium is reached

      If natural sources and sinks could not vary, then no new equilibrium would ever be reached. The links that I provided support the fairly obvious conclusion that the natural sources and sinks are not, and have not, varied nearly as fast at the non-natural sources have increased. The evidence for this fact is overwhelming.

      Your last paragraph is the truly salient point though, and directs us to a more worthwhile debate.


  2. Tom:

    I love your site and agree with almost everything you write. However, in this case I have to respectfully disagree, if not with your general position on the (relatively low) importance of this issue, then at least with the admonition that skeptics should all tow the line and accept the consensus view.

    I have no philosophical problem with the idea that man’s emissions are contributing to, or even causing, the increase in CO2 seen in recent decades. This is because, as you note, even if it is true, there are more significant issues remaining in the CAGW narrative. However, I do not think it is correct to say that no rational individual could question the idea that man’s emissions are the cause of the increase. The issue is much more nuanced than that, and ultimately depends on our ability to fully and completely and accurately (i) identify, (ii) measure, (iii) analyze and (iv) predict the behavior of all natural CO2 sources and sinks. We simply are not able to do that yet.

    There are, however, a few things that we do know. Among them:

    – CO2 increased and decreased in times past without man’s emissions. Therefore, other factors can, and indeed do, result in changes in CO2 concentration.
    – Man’s emissions represent a small fraction of what is released naturally.
    – Mauna Loa measurements show an almost-linear increase in CO2, whereas man’s emissions have not always been linear over that time. Therefore, there are two things we can conclude from that observation: (i) other factors are at work to at least partially balance out or offset the variation in man’s emissions (i.e., there is some kind of offsetting or feedback mechanism at work), and (ii) those other factors work relatively quickly (One other possibility is that the variation in man’s emissions only becomes visible after some significant lag time, but if that is the case then it would not be clear that man’s emissions are responsible at all for the increase of CO2 in recent decades. As a result, I don’t see anyone taking that position.).

    Many argue that because man is emitting more than the amount of the increase, man must be either causing the increase or significantly contributing to it. However, what we do know, including the above items, demonstrates that the simple fact that man is emitting more than the amount of the increase does not necessarily mean that man is responsible for such increase. Further, it is not clear that man’s emissions are even contributing to the increase in any meaningful sense. This is true, regardless of whether we are able to measure a greater % of man’s emissions in the atmosphere.

    There are no doubt some skeptics who simply deny the amount of man’s emissions or that CO2 concentration is increasing, but such individuals are probably a minority. There are, however, thoughtful skeptics who are still not convinced on this issue, not because of man’s emissions and the overall CO2 increase, but because of the complex and countervailing forces at work. Specifically, without knowing exactly what all the natural emissions and sinks are, the exact timescales they operate on, and how they react to and what kind of feedbacks result from man’s emissions, we cannot say for certain that man is responsible for the increase, or even that man’s emissions contribute to the increase in any meaningful way.

    Perhaps I can return to your bucket analogy to make the point. In your bucket analogy the input pipe and output holes do not vary (thus giving the impression that man’s input is the key variable), but we know for a fact that they do vary. The graphic should actually be a bucket into which man is dripping a few drops (as you show), but in which the size of the natural input pipe is constantly varying and the holes in the bottom are also constantly varying in size. Without knowing exactly how the input pipe and the holes in the bottom behave, in terms of both quantity and time, and without knowing the precise operation of the feedback parameters which potentially vary the size of the pipe or the holes in response to man’s drips, we cannot in fact say that man’s drips are the cause of the rise in the level of the water. Indeed we cannot even say that man’s drips meaningfully contribute to the rise in the level of the water.

    I would be happy to agree with you that the question of man’s contribution to the rise in CO2 concentration in the atmosphere is not the skeptics’ strongest point and that debating energy might be better spent elsewhere, because even if it is true that man is the cause of the increase in CO2 concentrations, more significant issues remain. However, I do not think it is scientifically correct or tactically correct to proclaim that this particular issue is settled and that skeptics must abandon their skepticism in this particular issue: an issue that is still quite opaque in terms of real-world understanding and observations and that is still subject to many open questions – open questions about which reasonable minds can differ.

  3. Another thing overlooked is the gas laws. if a liquid heats up it out gases. So the ocean warmed up due to increased solar irradiance insolence will out gas CO2.

    That explains past CO2 increases. Climate change is cyclic and complicated with anomalies.

    • True, the solubility of CO2 in the water goes down with increasing temperature. But the CO2 content of the oceans has increased, not decreased. This is simply more evidence that the increasing CO2 content of the atmosphere is man-made.


  4. It is fantastic to see people discussing this issue in a reasonable manner, using data and logic rather than hysterical emotion and name calling!
    I am a public school teacher, I teach chemistry, biology, and ecology. I have taught high school and middle school. Many times, students minds are totally made up on this issue based completely on their parents political affiliations and nothing more.
    Personally, I have a BS and MSc in Marine biology, and know a little bit about the issue. I feel that the issue is incredibly complicated- at this point we have far, far more questions than answers, and that characters like Al Gore do absolutely nothing to advance our pursuit of the truth when they try to incite hysteria.
    I tell all the young people that I teach the same thing- That we have seen global warming and cooling on this planet for millions of years- long before the internal combustion engine came along- But, to me at least, it makes sense that if you bring huge quantities of fossil fuels to the Earth’s surface and burn them, that it could potentially cause an increase in the global temperature- However, I do not understand at all how the Earth’s capacity to absorb that CO2 may vary depending on CO2 concentrations.
    At the end of the day- I tell my students that they must pursue the truth without the influence of politics,based on real data from the real world (As opposed to Hollywood!), and a logical mind that is determined to find the truth.
    Thank you all for being reasonable- You all are the ones who will uncover the truth eventually!!!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: