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Does breathing contribute to CO2 buildup in the atmosphere?

What the science says...

Select a level... Basic Intermediate

By breathing out, we are simply returning to the air the same CO2 that was there to begin with.

Climate Myth...

Breathing contributes to CO2 buildup

"Pollution; none of us are supporting putting substances into the atmosphere or the waterways that might be pollutants, but carbon dioxide is not a pollutant. If Senator Wong was really serious about her science she would stop breathing because you inhale air that's got 385 parts per million carbon dioxide in it and you exhale air with about ten times as much, and that extra carbon comes from what you eat. So that is absolute nonsense." (Ian Plimer)

At a glance

We, and almost all of our relatives in the animal kingdom, are aerobic. That means we all depend on this simplified equation in order to function:

glucose + oxygen → carbon dioxide + water + energy

We breathe in oxygen and that oxidises carbohydrates in our body's cells. That chemical reaction gives us the energy required to perform all the varied tasks we do, from blinking to running a marathon. The products of the process are carbon dioxide and water. While the air we breathe in contains just under 420 ppm CO2, what we breathe out contains 40,000-50,000 ppm CO2, a hundredfold increase due to the simplified equation above.

Because we are breathing constantly, this rapid gas-exchange with our surroundings is also constant and, while each of us live, is perpetual. We are part of the fast carbon cycle that involves the movements of carbon through the living world. Of course, the living world also includes plants. Plants take in carbon dioxide to react in the presence of sunlight with the water in their cells. That, in a nutshell, is photosynthesis, the process responsible for the plant-based carbohydrates we eat.

We are vastly outnumbered in terms of carbon biomass by the plant kingdom. Of the estimated nearly 500 billion tonnes of biomass carbon on Earth, the animals account for just 0.4% whilst the plants represent 90%. No wonder that the graphs of measured CO2 levels show an annual fluctuation, forming a symmetrical wobble. The wobble represents the Northern Hemisphere seasons because that's where most of Earth's land masses are found. In the growing season when the plants are busy photosynthesising, CO2 falls, only to rise again in the dormant season. The annual wobble is like the heartbeat of the planet, a regular rhythm along the rising slope that represents our emissions from fossil fuel burning.

Let's imagine a world without fossil fuel-burning. The annual wobble from the seasonal growth and dormancy of plants would be superimposed upon a near-flatline of CO2 levels over human lifetimes. Only occasional events, occurring over tens of thousands to many millions of years, would perturb that near-flatline. That's because there is a second, slow carbon cycle that operates over geological time-scales. In the geologic past, sudden changes in CO2 levels have occurred, primarily due to volcanism on a scale no human, living or dead, has ever witnessed. The fossil record tells us the outcome has never been good.

Fossil fuels are part of the slow carbon cycle. They represent one of several long-term geological reservoirs in which carbon gets locked away. But because we are digging or pumping fossil fuels from the ground and burning them, it is the slow carbon cycle that we are interfering with. No other species has ever intentionally interfered with the slow carbon cycle: this is a first on Planet Earth in its 4.5 billion year long existence. The person quoted in the myth box above is a geologist. He should know better.

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

The very first time you learned about carbon dioxide was probably at school, where you were taught that we breathe in oxygen and breathe out carbon dioxide. The process, known as aerobic respiration, is something the vast majority of animals do. In our cells, the following enzyme-controlled reaction is taking place:

C6H12O6+6O2 → 6CO2+6H2O

It's a bit more complicated than that, but the equation is a representative overview. Carbohydrate is oxidised to carbon dioxide and water. The reaction is exogenic - meaning it releases energy at around 3000 Kilojoules per mole of glucose. And while we breathe in air with almost 420 ppm CO2 (2023 figure), it should come as no surprise that the air we breathe out contains 40,000-50,000 ppm (4-5%) CO2, representing a hundredfold increase. That's the product of aerobic respiration.

When confronted with the challenge of reducing our carbon emissions from the burning of fossil fuels, some people angrily proclaim, "why should we bother? Even breathing out creates carbon emissions!"

If someone makes such a statement, they are missing two crucial points. Firstly, our respiration doesn't matter in the big scheme of things. In terms of carbon biomass, we are dwarfed by the plant kingdom. Animals only account for a paltry 0.4% of the estimated near-500 billion tonnes of biomass carbon on Earth. Plants make up 90%.

Through photosynthesis, plants take in carbon dioxide and release oxygen, in a chemical reaction that is essentially the opposite to our aerobic respiration. Plants do perform some respiration, because they need to metabolise as well, but it is outweighed by the photosynthesis. The carbon they collect from the CO2 in the air, converted by photosynthesis into carbohydrates, forms their tissues - roots, stems, leaves, fruit and so on. Such tissues are eaten by all sorts of animals, which in turn are eaten by other animals. We humans are part of this food chain. All the carbon in our body comes either directly or indirectly from plants, which took it out of the air only recently. When we breathe out, all the carbon dioxide we exhale is simply being returned to the air. We are simply giving back the same carbon that was there to begin with. In doing so, we are actively participating in the fast carbon cycle. But our participation is tiny compared to that of plants.

The Keeling Curve (fig. 1) is the graph showing rising CO2 levels as measured at Mauna Loa and other observatories. On it, the plant world's participation in the fast carbon cycle can be seen. Due to photosynthesis, CO2 levels show an annual fluctuation, forming a regular wobble. The downward part of the wobble represents the Northern Hemisphere growing season. Since that's where most of Earth's land is distributed, it's where most of the CO2 drawdown takes place. In the Northern Hemisphere winter, when most plants are dormant, you get the upwards part of the wobble. The wobble, like a planetary heartbeat, is a regular rhythm superimposed upon the rising slope that represents our emissions from fossil fuel burning.

 The Keeling Curve

Fig. 1: The Keeling Curve - monthly mean CO2 concentration data (with the occasional volcanic anomaly filtered out), Mauna Loa Observatory, 1958-2022. Inset shows the annual 'wiggle' caused by seasonal plant-growth and dieback in the Northern Hemisphere. Image licensed under the Creative Commons Attribution-Share Alike 4.0 International licence.

Secondly, fossil fuels are the remnants of the fast carbon cycle, fortuitously preserved at various points along the geological time-line. That burial and preservation locked them out of the fast carbon cycle, putting them into the long-term storage part of the slow carbon cycle. Normally the slow carbon cycle operates over geological timescales. Thus, some of the coal we've mined has been more than 300 million years in storage, belonging, appropriately enough, to the Carboniferous period.

Forget about breath. Our carbon emissions from the slow carbon cycle are a) colossal and b) geologically unique. No other species in Earth history has deliberately disturbed the slow carbon cycle. But it has been disturbed - occasionally - by geological processes. Magma has occasionally cooked coal-deposits, as has been observed in Siberia (fig. 2). That rapid release episode, at the end of the Permian period 250 million years ago, didn't work out well. Biodiversity took a massive hit. It recovered – but the recovery took around ten million years.

Masses of coal caught up in basalt. 

Fig. 2: masses of coal caught up in basalt, Siberian Traps Large Igneous Province, from Elkins-Tanton et al. 2020. The rising magma interacted with and thoroughly cooked a major coal-basin, releasing a colossal amount of fossil carbon over a few thousand years. The result was catastrophic with the largest mass-extinction of the entire fossil record. Photo: Scott Simper, courtesy of Lindy Elkins-Tanton.

Weathering, plate tectonics, deformation and metamorphism of rocks have all affected CO2 levels - over millions of years. And that's the point. We are doing to our atmosphere, in a few centuries, what most geological processes could only accomplish over millions of years. Through fossil fuel burning, we are performing a unique, vast and uncontrolled experiment with our home planet – the only one we have.

The animation below was published by Dr. Patrick T. Brown (Carnegie Institution for Science, Stanford University) in September 2018, to explain how human respiration fits in to the overall process.

Last updated on 3 December 2023 by John Mason. View Archives

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Comments 101 to 125 out of 160:

  1. @Dr Bill,
    Could you please link to a written transcript? The computer I currently have access has no sound. I do like a good lecture, probably more than most, but unfortunately can't currently follow your points until I get to a computer with speakers. I would love to see what this fuss is actually all about.
    Regarding your comment above, "if for no other reason than to modify any so-called "forcing" effect, which if it operates at all, does not do so only in response to industrial CO2."
    That seems to be stating the obvious but in a way that is an attempt to obfuscate.
    Of course it matters little the source of the CO2 as to the relative forcing. The source matters when calculating the relative net increase in atmospheric CO2. All fossil fuel CO2 is old carbon added to a roughly balanced system. So even though the biosphere is a self adjusting complex biological system, the quantity of old CO2 being released is greater than the biosphere's capability to adjust currently. The net CO2 concentrations rise. Higher atmospheric CO2 concentrations mean increase solar heat retained in the system. The “greenhouse” effect. The IPCC assessment may not be perfect, but that part they got roughly correct. Rapidly cycling CO2 in the biosphere does not have the same net effect on atmospheric CO2 concentration as slower old cycle carbon that has been out of the system for millions of years.
    When it comes to respiration, that only results in a net increase in CO2 levels when the other side of the carbon cycle (photosynthesis) is simultaneously reduced as respiration increases. As long as we are careful not to reduce photosynthesis by destroying ecosystem function, then respiration can’t cause a net increase in atmospheric CO2 levels beyond a very short term peak usually disappearing in a matter of months. It is self limiting. This is what gives the graph a saw tooth pattern.

    Image source: National Oceanic & Atmospheric Administration

    What gives the graph the smoothed out steady increase is a combination of fossil fuel use and ecosystem degradation, mostly due to agriculture.
    If there is a blind spot in the IPCC assessment, it could be in underestimating the impact of agriculture in degrading ecosystem function. This is a case I have made elsewhere on this forum. However, the assessment is certainly correct in ignoring for the most part the short term biosphere cycle of photosynthesis and respiration as roughly canceling each other. There is no net increase in CO2 due to animals breathing. That’s just the natural carbon cycle signal, nothing to do with AGW.

  2. I still do not understand what point you're trying to make. The net addition of carbon to the atmosphere is the problem, the only problem. 

    The net increase is the only thing that matters; it is not, and can not physically be caused by animals breathing. They get their carbon from the atmosphere, through organisms that have the ability to absorb it and integrate it in their structure. The bulk of these organisms is made of plants. How is the animal activity going to change the balance? Animals just shift the carbon around in short term small cycles. They do not add carbon to the atmosphere that wasn't taken out of it in the first place, so why does that matter when considering the bigger picture?


    [RH] Go to the link for Bill's video lecture and start about at minute 12:00. In a nutshell, he's attempting to say (not joking here) that the change in atmospheric CO2 levels is due to the increase in human population. 

  3. RedBaron  Sorry, I never made a transcript. I had notes, but never typed them up.  I am quite familiar with the summary data of Mauna Loa, thanks.

    That said, it is not the summary data that matters in my analysis, and I suspect others have something of that confusion when they "do not understand what point [I'm] trying to make" {Phillippe}.  The summary data collects all the CO2 from industry and breathing and all sources, less that which returns to biomass, terrestrial and aquatic, or to the oceans directly.  It has many issues of validity, but that's not for here and now.

    What is for here and now is that Mauna Loa is like the old flip-chart 'digital' clock, that flipped over once a minute.  Real CO2 is the sweep hand of a better clock, counting continuously.  The sun does not wait for the report from Mauna Loa, if it does anything, CO2s effect is there all seasons, all times, neither just when the sun's out, nor only when it's summer, nor only when industry is running.  It's not that hard to see: the addition of CO2 by vastly accelerated conversion (as fossil fuel) or much slower accelerated conversion (as digestion/respiration) or still slower conversion (simple rot), leads to some measureable level of CO2 on a moment by moment basis, an increase, by the explanation I've given, that seems to cause much consternation.  Any decrease, by plant growth or subduction in the sea around Antarctic  would do something that made the final totals at monitoring sites change, but until such decrease took place, the CO2 from all sources I've mentioned is still in the air and still doing what CO2 does.

    Moreover, it does not matter which process is faster and which slower, since the production rate is the sum of both industrial production and digestion/exhalation, like the sweep second hand (or if the circularity of the sweep overwhelms is graphic value of smooth and unrelenting, consider a pail with a hole in it, being dripped into by two sources (I actually might like that one better myself).  At the moment we are not concerned by the drip, or even how full the pail might get, but only in the amount of something inherent in the water that might be able to do some harm.  Would it serve to say we've identified the problem because we found a leaking faucet over the pail, while ignoring a smaller leaking faucet?  Since the drip keeps the pail from filling up quickly, are we being good pail-monitors to just evaluate the level monthly and deny the smaller faucet?


    As an OT, on this thread, I would enjoy finding a thread that addresses the process I have heard called "positive feedback loop".  Where might I find it most discussed in terms of its physics?  TIA


    [DB] "I would enjoy finding a thread that addresses the process I have heard called "positive feedback loop""

    Unlike the simple example of positive feedback we learned in high school, the increase from every round of feedback gets smaller and smaller, in the case of the enhanced greenhouse effect. It is a significant factor in the overall warming, but it does NOT lead to a "runaway" trajectory for temperature.

  4. Dr Bill Hoffman @100:

    "[T]he equation I showed, Tom, was directly copied from their 2005 Report that I used ..."

    The IPCC had only two reports in 2005, that on Carbon Capture and Storage and that on Safeguarding the Ozone Layer.  I have skimmed the first of these and found nothing resembling your formula.  Nor, obviously is there anything resembling it in the relevant chapter of the 2001 report (the current assessment report in 2005).  The formula doesn't appear in the 1995 assessment report (SAR) either, although Table 2 (page 17) could be interpreted as supporting such a formula, however Table 2 is explicitly labeled as "...the anthropogenic carbon budget...", and makes no claim to be a complete carbon budget.  With regard to that, it says:

    "The estimate of the 1980s' carbon budget (Table 2) remains essentially unchanged from IPCC (1994). While recent data on anthropogenic emissions are available, there are insufficient analyses of the other fluxes to allow an update of this decadal budget to include the early years of the 1990s."

    Looking to figure 4 (page 21) of the 1994 report (Radiative forcing of climate change) clearly shows the other fluxes to include global net primary production and respiration.  These are also discussed in the First Assessment Report (1990), as can be seen in Figure 1.1 (Page 8).

    In short, the formula is not justified by any IPCC report prior to 2006, and certainly in none after it.  If you wish to maintain the contrary, you will need a precise citation, ie, the report by full title, together with the page number at which the formula appears.

    "I said 40% more, and you want to argue 33%...tomayto tomahto...they found industrial CO2 and stopped accounting"

    First, you claimed 50% in the video, not 40%.  In otherwords, even at face value you exagerated the effect by 50%.  If you think pointing out a 50% exageration is mere quibbling, you are no scientist.

    Second, as clearly shown by my review of their literature above, the IPCC since day 1 (First Assessment Report 1990), have included "respiration" which includes respiration by animals and plants, along with the emission of CO2 by decay of organic matter and by fires.  Since the fourth assessment report (2007), they have also included volcanic emissions. 

  5. Dr Bill, I don't see any clarification with this addition of words. The issue is the physically nonsensical argument that the CO2 from respiration is of a same non-polluting nature as that which is produced by oxydation of fossil fuels previously sequestered in the crust. The implication of Plimer's quote is that some of the atmospheric CO2 we are experiencing is due to animal respiration.  You seem to concur with that, without clearly stating it, so far as I can recall.

    I see nothing in your contribution here that would actually support this argument. I see no explanation of how animal respiration can cause a net increase in atmospheric CO2, which is the real problem, as I have stated above. I see no possible source for animal generated carbon other than the atmosphere itself, you offer no alternative. 

    You stated yourself at #100 earlier that "No one said it was a net addition to the carbon budget." 

    This suggests that you are trying to hypothesize that the atmosphere can go from 300 to 400 ppm in a very short time without a net addition, only by shuffling carbon around (possibly by way of animals) and loosing sinks, while the ocean is still absorbing enormous amounts of it. If so, you must come up with a loss of sink so gigantic that no geological event in the relevant past could foot the bill, certainly not the known land use changes, subject of abundant litterature.

    Meanwhile of course, the oxydation of fossil fuels is real and ongoing, regardless of any other hypothesis, as are the isotopic signature changes in the atmosphere and multiple other elements consistent with the net addition of fossil carbon. 

    I am not thus far enclined to spend any time on your YouTube vids.

  6. Imagine a model system in which plants are grown in a sealed, airtight compartment.  Suppose conditions are such that the growth of the plants is limited only by energy input (ie, sunlight).  As the plants grow we feed in CO2 until the plants are mature.  We then seal the system so that any further growth of plants can only be achieved by reducing CO2 concentration within the model system.  After a period of time an equilibrium concentration of CO2 will be achieved.  Plant growth will be CO2 limited, in that addition of further CO2 to the system would allow an increase in plant biomass within the system, but as CO2 was fed in until the plants were near maturity, the CO2 limit on further growth will not be much below the energy limit on further growth.

    What happens when we introduce a small population of herbivores, predators, and such other organisms so as to allow a stable ecology in to the system?

    The obvious first effect is that plant biomass will be reduced, and replaced by animal biomass.

    However, there will not be a one-for-one replacement of animal biomass for plant biomass.  That is because of the energy pyramid.  As you proceed up the trophic levels, from plant to herbivore, from herbivore to carnivore etc, each level converts energy to biomass with an efficiency of about 10%.  As an example, suppose in our model system, equilibrium is reached when the herbivores reduce total plant biomass by 10%.  Then of the energy stored in that plant biomass, only about 10% will be converted to herbivore biomass.  Similarly, only about 10% of the energy storage of herbivore biomass consumed will be turned into carnivore biomass. Consequently the total biomass in the model system will be reduced.  

    The difference between the carbon content of the original plant only biomass and the plant plus animal biomass will by stored in other carbon reservoirs.  That may be as soil carbon, but due to the processes of animal respiration and decay, some of it will be as an increased CO2 concentration.

    This is the mechanism explicitly mentioned by Grumpymel @93, and possibly is the mechanism discussed by DrBill @95.  To the extent that it is the mechanism envisioned by DrBill, his claim that increased animal biomass will result in increased atmospheric CO2 is correct, although his calculation of the effect is not necessarilly valid.

    Ignoring for simplicity the potential increase in Soil Organic Carbon, and any uptake by standing water, and other carbon compounds, the increase in atmospheric CO2 in our model system will be:

    (((Final plant biomass - initial plant biomass) x % of carbon by weight in plant biomass) - ((final animal biomass - initial animal biomass) x % of carbon in animal biomass)) x 44/12

    The final factor can be ommitted if you measure the CO2 concentration by mass in units of GtC rather than Gt-CO2.

    With regard to the IPCC's treatment of this, the first thing to note is that they do report on the change of Carbon due to the change in plant biomass.  Specifically, in IPCC AR5 they report that plant biomass has decreased by 30 +/- 45 GtC.  That means that, unless animal biomass has decreased, they have over estimated the total change in biological carbon reservoirs (ignoring the controversial issue of SOC).  Further, the total change in animal biomass, which has increased; represents a further reduction in CO2 available for other reservoirs including the atmosphere.

    So, if this is what DrBill is drawing attention to, he is right that the mechanism can increase total atmospheric CO2 (by reducing plant biomass); but wrong in assuming it is neglected by the IPCC, who do their best to quantify the positive side of the equation (ie, the loss of plant biomass) even if they neglect the much smaller (by an order of magnitude) negative side from the increase in animal biomass. 

  7. Here's a video from NASA on this topic.

  8. I understand the idea Tom. You expand quite well on what I described a little too quick as "shuffling carbon around." My opinion is that the kind of biomass change that would be required to explain the past 100 years increase in atmospheric carbon is so immense as to preclude a major role in this change, especially while the oceans are still acting as a sink. The idea that all of the increase could be due to biomass changes is simply not believable.

    Perhaps Dr Bill is trying to make the argument that the biomass contribution is underestimated, although the bulk of what he said was innuendo on IPCC intentionally skewing the issue, which was unwarranted, as you showed. My understanding is that there is quite a bit of litterature on the subject and that the range of possible contribution of biomass changes is fairly well constrained. I don't see at first glance that Dr Bill has anything revolutionary to overturn the current state of knowledge on the subject.

    Intesresting discussion here:

  9. As this is your first post, Skeptical Science respectfully reminds you to please follow our comments policy. Thank You! Since  breathing is nessasary to sustaining our life seems like a moot point for discussion. Unless you are proposing extermination on a significant part of the population.  The 34.7 Billion tons from fossil fuel combustion a year however IS something we can change. Old figure 2009.

  10. Nearly 8 yrs elapsed  since the first question on this topic was posted: "Does breathing buildup CO2 in the atmosphere?"

    With the use of many technological advances in research and data analysis over these 8 years, is the answer different? I would appreciate a review and updated opinion presented for both basic and intermediate level readers. Thank you. 


    [TD] Nope, there are no changes in the conclusions.

  11. Update information: The basic version of this rebuttal was updated on September 12, 2018 to swap the graphic showing a - to some - "odd looking cow" with the new animation we happened to notice on Twitter. Thanks to Patrick T. Brown for making it available on YouTube!

  12. As a chemical engineer I feel it's misdirection to talk about the carbon cycle and say that an increase in human resperation does not add to atmospheric CO2. It may turn out to be a trivial amount, I'd have to find some numbers to guage it, but this post is meant to give a little background.

    If all the carbon on earth were solid carbon and suddenly you changed it all to gaseous CO2 (this can't actually happen according to the gas law) and did this back and forth and back and forth according to the "carbon cycle" argument since there's no change in net carbon we are supposed to ignore atmospheric carbon going from nonexistant to "lots" and back again. "Hey - the cabon cycle is balanced." If more CO2 is put into the atmosphere from breathing the "cycle" itself gets bigger, the partial pressure of CO2 increases. Since biomass is a scrubber of CO2 (plants eat CO2) then there could be a net effect if the additional CO2 isn't eaten by plants. That's the issue. So to me, whipping out the carbon cycle doesn't make a whole lot of sense. My quick take is figure the volume of the atmosphere and the CO2 percentage and get that amount (huge # of moles) and then figure the amount in the resperation of 8 billion more people and see if the CO2 exaled from people is of the same order of atmospheric CO2. And keeping in mind that everything is an estimate - we don't know how many moles of carbon or anything else are on Earth. We don't know the exact volume of the atmosphere - they are estimates. 

    It may not factor in, but saying "the carbon cycle accounts for more breathing" is misdirection, it is just saying the net amount of carbon on Earth is staying the same, and that's not what the issue is.  The net amount of gold on Earth is staying the same, too. Everything is - excepting new material from meterites and junk we send away in rockets that reaches outer space.  We should be arguing about the partial pressure of CO2 in the atmosphere. 

    'Ol Wikepedia says this "The oceans of the world have absorbed almost half of the CO2 emitted by humans from the burning of fossil fuels."  It's like soda pop - if the ocean warms slightly, CO2 is released into the atmosphere increasing the partial pressure of CO2. Since the CO2 level seems to be cyclic

    perhaps periodic ocean warming is the culprit. People argue that the older peaks are not as high as the current peaks, but remember the latest data is from direct measurement, the older values are taken from ice core samples and perhaps while the samples show higher CO2 values the peaks are lost from gas loses at the sample boundries, handling issues, etc.

    Of course, industrial CO2 factors in.  Let's run some real numbers!


    [DB] "the CO2 level seems to be cyclic"

    CO2 levels in the past were driven by known natural factors.  None of those factors are in play during the recent increase in atmospheric concentration of CO2.  The human forcing is now the largest forcing, dwarfing all natural forcings, including that from the sun itself.

    NCA4 2017 Radiative Forcing

    "perhaps periodic ocean warming is the culprit"

    Not so.  Please read this post.  The oceans are a net sink of CO2 released by human activities, which is why they are still acidifying.

    The 18-part 'OA is NOT OK' series, written by subject matter experts in that field, as summarized in Parts 1 and Part 2 is a worthy study.

  13. Lasterday @112,

    As a "chemical engineer" you should have had no problem quickly sourcing those "real numbers" to "run" but as you have not returned with your findings, may I take up the challenge.

    The CO2 expelled in human respiration has been calculated as equivalent to 6% or 9% of the anthropogenic emissions from fossil-fuel-use (although the emissions values cannot include emissions from land-use-change and still appear out-dated relative to the world population figures used). Using more up-to-date (all for 2016) figures (latest Global Carbon Project figures are for 2016) drops the results to to 4% to 6%.

    However, such analysis does lead to the question - Where does the 55kg/head/yr or 90kg/head/yr of carbon required for such breathed CO2 come from? Of course, the source is our food which has, as a primary source of carbon, that obtained through vegitable photosynthesis, which in turn gains carbon from atmospheric CO2.

    The one remaining question relating to human respiration as a contributor to atmospheric CO2 levels would be whether there are carbon pools that have diminished because of that increased cycling of carbon (atmosphere > plants > food > humans > atmosphere). There are more humans with an 18½% carbon content (or 11½kg per head). That would suggest that the rise in human population over recent years (80M/yr) would be sequestering carbon equal to 0.008% of our global FF+LUC CO2 emissions. There is also more plants/food within the cycle but this increase probably sequesters far less carbon than the releases from the land being 'cleared' for agriculture which is responsible for 11% of our CO2 emissions.

    I thus can find no dimishing pool of carbon that is not being accounted within the calculations of human CO2 emissions, or for that matter any significant increasing pool of carbon.

  14. "It should come as no surprise that, when confronted with the challenge of reducing our carbon emissions from the burning of fossil fuels, some people angrily proclaim, "Why should we bother? Even breathing out creates carbon emissions!"

    This statement fails to take into account the other half of the carbon cycle. As you also learned in grade school, plants are the opposite to animals in this respect: Through photosynthesis, they take in carbon dioxide and release oxygen, in a chemical equation opposite to the one above. (They also perform some respiration, because they need to eat as well, but it is outweighed by the photosynthesis.) The carbon they collect from the CO2 in the air forms their tissues - roots, stems, leaves, and fruit.

    These tissues form the base of the food chain, as they are eaten by animals, which are eaten by other animals, and so on. As humans, we are part of this food chain. All the carbon in our body comes either directly or indirectly from plants, which took it out of the air only recently"

    Only one problem, not all plant life is cycled through animal or human consumption. And, although you talk about plant respiration and proclaim that it is a very small contributor of carbon dioxide, it seems you forget that plants release carbon through decay which, when mixed with oxygen, then becomes carbon dioxide. Also, seems the issues of "carbon" and "carbon dioxide" are being confused here. Although humans may consume carbon, they produce carbon dioxide when they exhale. So, to suggest human respiration is carbon neutral is not true and to suggest plants make up for what carbon dioxide it is humans exhale doesn't seem viable either. Plants are only carbon neutral in that they take in the CO2 of which they themselves produce and convert it to O2. However, C (carbon) is produced in the form of waste, or decay. And, when that C (carbon) is exposed to oxygen, it then becomes carbon dioxide of which the plants, again, recycle and turn into oxygen and, again, into carbon in the form of waste/decay. And, the cycle goes on, and on, and on, and on. As I type this, it is autumn and I am watching the leaves fall off the trees. These leaves will decompose and, although some animal and insect life will consume some of these leaves, they will not consume all of these leaves and these leaves will decay and produce carbon. And, when said carbon is mixed with oxygen? It will become carbon dioxide. Of which, of course, these trees will use to produce new leaves when spring time arrives and will also use to continue to live throughout the rest of autumn and through winter.

  15. 9 billion live people would add about 9 million metric tons of carbon dioxide per day to the earth’s atmosphere. All else remaining the same, the atmospheric change in carbon dioxide would be 9 million metric tons lower every day if every human was not here.
    17.6 living people produce the same amount of CO2 as burning 1 gallon of E10 gasoline.
    Humans every day contribute as much CO2 to the atmosphere as burning about 5 million gallons of E10 gasoline.
    If you don’t consider everything you get distorted and untrue results.
    The world burns about 1 billion gallons of gasoline each day. This contributes about 200 times as much CO2 as 9 billion breathing humans.
    If carbon dioxide causes global warming it doesn’t matter its origin. I am absolutely sure that CO2 is not the cause of all global warming.
    Carbon Dioxide is plant food.


    [PS] Hopefully you are able to think of data that would change your mind rather than being wedded to an ideological argument. Your comment is full of misconceptions readily checked by data. Please see CO2 is plant food and CO2 is from Ocean (because it points to evidence that CO2 rise is from fossil fuel burning) and finally Human CO2 emissions are tiny compared to natural which is where you mostly go wrong.

  16. bsettlem @115,
    You say "If you don’t consider everything you get distorted and untrue results," so are you taking everything ito account?
    Yes, the average person exhales something like 1kg of CO2 per day, comprising 27% carbon and 78% oxygen. So if, as you say "all else remaining the same," this average human (who weighs something like 62kg comprising 18% carbon) would be losing 270g of carbon each day through breathing. So, "all else remaining the same," in six weeks time the human race will have run out of carbon to breathe with, and so will be dead. And with 9 billion humans exhausting all their carbon in this way, the atmospheric concentration of CO2, "all else remaining the same," would have risen by a whole 0.05ppm.
    And I am not just "absolutely sure" about this: I know it.

  17. Bsettlem, your post makes no sense at all. You're acknowledgeing that total contribution from human respiration with a population of 9 billions would be only 0.5% of just gasoline burning emissions, therefore an even smaller fraction of all fossil fuel CO2. And somehow that makes it a bigger problem than fossil fuel? Indeed CO2's radiative properties are independent of its origins, and of anyone's opinion as well. As you stated yourself, human respiration generated CO2 is a tiny fraction of that coming from other sources, so these other sources, over which we have control, are what matters. You being absolutely sure of anything does not make it real. Some people are absolutely sure that the Earth is flat.

  18. Philippe Chantreau, Thank you for your response.
    I humbly respond to your reply. I have sectioned your message and responded in italics

    Bsettlem, your post makes no sense at all. You're acknowledgeing that total contribution from human respiration with a population of 9 billions would be only 0.5% of just gasoline burning emissions, therefore an even smaller fraction of all fossil fuel CO2.
    Yes, I essentially said the above. But the fact that my post makes no sense at all to you IMO tells me you need to read it more closely and reason it without self inflicting more information than I have written
    And somehow that makes it a bigger problem than fossil fuel?
    I never said this!


    Indeed CO2's radiative properties are independent of its origins, and of anyone's opinion as well.
    Yes, I essentially said this but not in these words. CO2 does have an effect on the radiative relationship between the sun and Earth.
    As you stated yourself, human respiration generated CO2 is a tiny fraction of that coming from other sources,
    Yes I said this!
    so these other sources, over which we have control, are what matters.
    This is not something I said in my writing. What I conclude is that all CO2 counts even that discharged by humans exhalations, and I add now, that this quantity is approximately 4X that produced by humans when I was born. But there are other somewhat small sourceses which we do not have control over.
    You being absolutely sure of anything does not make it real.
    There is some evidence that Antarctica was once a paradise of life and during this time the Earths average atmospheric temperature was much warmer than it is now. And during the “ice ages” the atmospheric temperatures were much lower. It is absolutely real that the sun warms the earth and it is absolutely real that some atmospheric conditions create an imbalance to the amount of the suns energy that the earth accepts and rejects. The state of balance is the radiative equilibrium. And I am absolutely sure that human behavior is negatively affecting the probability that humans will survive until the earth will no longer be able to sustain life
    Some people are absolutely sure that the Earth is flat.
    And I am sure that your opinions interfered with what you thought I was writing.

    Can you tell me what is wrong with this statement?  By breathing out, we are simply returning to the air the same CO2 that was there to begin with.


    [DB] Note that in this venue, an overusage of bold font is considered shouting.  Please keep its usage to a minimum.

    Also note that the usual custom when quoting someone is to put their text between quote marks and in italic text.  For additional clarity, you can indent the passage.  Like this:

    "I have sectioned your message and responded"

  19. MA Rodger
    Good numbers math but horrible science
    Humans are similar to engines, fuel them and they burn the fuel. Are you assuming that humans can continue to function without eating until they burn up all their carbon content?


    [DB] Please limit the usage of bold font.

  20. bsettlem @119,

    The prospect is "horrible" indeed. Golly!! Lucky you spotted that!!!

    So then, from where do humans get their 270g carbon fuel to allow continued breathing out of a kg of CO2 per day? As a human yourself, you should have some idea. Do you chew on a lump of coal for breakfast? Or perhaps you have a bedtime pint of crude oil?

    Biomass of planet

    Of course the problem is not just humans. We are a minor part of the animal kingdom. And bacteria & fungi - they breathe. And even plants breathe when the sun doesn't shine. With all that breathing out of CO2 (the graphic shows biomass, Fig 1 from here), where does all this carbon come from?

  21. Bsettlem, you're not making any more sense than previously, sorry. It seems you may even somewhat contradict yourself. In any case, I don't have that kind of time. It's not that difficult to be clear and concise. Try.

    Thanks for the Chart.
    Humans account for about 36 percent of the biomass of all mammals. Domesticated livestock, mostly cows and pigs, account for 60 percent,
    It wasn’t always this way. Humans are responsible for this.
    A similar situation exists for birds. Poultry biomass is about three times that of wild birds.
    It wasn’t always this way. Humans are responsible for this too.
    Where did all this carbon come from you ask. Best guess, from a cloud of hot gases and other mass that resulted from the explosion of a very large star about five billion years ago.
    It is speculated that this early ball of mass was surrounded with an atmosphere mainly composed of nitrogen, CO2 and water vapor.
    I comment on one part of your message, Plants breathe day and night. During the day they do their photosynthesis thing, and produce oxygen. During the night it’s air in and air out. A very few plants are especially talented and do produce oxygen during the night.


  23. I'm still not sure exactly what your point is. All the yelling and grandstanding certainly doesn't help.

    Human respiration can not cause a net addition to the carbon cycle. That would violate thermodynamics. Extracting carbon from the crust and releasing it in the cycle does, so would intense sustained volcanic activity or a carbon-containing space object impact. Once carbon has been injected in the cycle, it will of course be found throughout the cycle. However, if 9 billion humans were to produce all their energy from carbon neutral sources, inluding producing nitrogen and phosphate rich fertilizers through carbon neutral chemical processes, their respiration would not increase the atmospheric content of CO2. Long term storage of carbon can cause subtraction, that's what happened in the carboniferous. Shifts in biomass do not constitute net addition or subtraction.

    As for warming attribution, if you know of some other forcing, it should be verifiable and its effect should be quantifiable. It should also be discussed on the appropriate thread.

  24. Bottom of carbon cycle is plants. When a plant dies, the carbon in it is eventually oxidized and returns to the atmosphere. If it is eaten by anything, then that carbon is going back into atmosphere via respiration somewhere down the track. It doesnt change the amount of carbon in atmosphere whatever the relative no. of human to other organisms is.

    Fortunately, we can test the truth of hypothesis. All carbon in the normal cycle contains the C14 isotope. Carbon in fossil fuels has no C14. If the increase in CO2 in atmosphere was due to humans, the atmospheric concentration of C14 wouldnt change. If the increase in CO2 in the atmosphere is due burning CO2, then the C14 would be diluted. Guess what the actual measurements show.

  25. bsettlem @122,

    While you highlight the increase in the biomass of mankind with its domesticated flocks, in your comparison with wildlife you manage to ignore the decrease in the biomass of wildlife that is also a by-product of human activity. This rather makes your grand theory (that there are tons-more animals exhaling CO2 into the human-dominated world) less than the drama you hope. Not that it makes a ha'p'orth of difference as it is the source of the carbon that is the important issue here, this being the fuel "they burn" according to you comment @119.

    So where does this carbon comes from so as to fuel all these humans and noisy old bleating goats that we meet? You answer @122 is rather poor. You say it was ejected from an exploding star 5 billion years ago. (There is probably an "over" missing from within that reply.) Then miraculously the carbon reappears in the Earth's Hadean atmosphere (of course a hypothetical composition) whence we lose track of it again before it magically reappears for a second time within the breath of today's biomass. I think it's safe to say, bsettlem, you will never make it as a detective with such threadbare reasoning. You would be laughed out of court!!

    (It is interesting that your final point is presaged by the words "I comment on one part of your message." It suggests that only in this final point you were not trolling.) As a plant tend to grow in size with passing time, it is thus accumulating carbon. My understanding (which is not great on this particular matter) is that plant respiration is from all parts of the living plant and it obtains its carbon from the glucose produced by photosynthesis. Thus the living plant as a whole will be a net absorber of carbon from the atmosphere during photosynthesis and a net emitter of carbon through respiration during periods without photosynthesis (or diminished photosynthesis). And I think it is very likely there is a wider lesson to be had here about that damned ellusive source of carbon harnessed for human respiration.

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