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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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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 76 to 100 out of 160:

  1. One thing to consider in the argument that the biosphere is still in balance with 7 billion humans is that 20% of food consuption is from the oceans, not land. In other words, 20% of the 3Gt CO2 exhaled by humans was not part of the normal terrestrial cycle. It's also true that not all food is derived from a source of photosynthesized CO2. 

    Also, to what extent is balance achieved by the burning of fossil fuels - which increases photosynthesis as a feedback response?

    If the existing balance is only made possible by virtue of 400ppm CO2 in the atmosphere, the current population is obviously not sustainable in the long term.   

    Based purely on the amount of CO2 exhaled by humans it should be possible to calculate a population level that's sustainable with a photosynthesis rate commensurate with around 280 ppm atmospheric concentration.  Based on flux apprximations from the IPCC it would appear that we're already beyond a sustainable population maximum. 

    One last point is that 7 billion humans doesn't actually sequester much in the way of C when compared with plants. There's approx 25kg of carbon per human, so <0.2Gt for the entire population.   

  2. Art Vandelay @72, nearly all, if not all sea food eaten by humans are situated in a food chain with photosynthesis at the base.  Ergo, while the exchange of CO2 for oxygen that drives the process may not take place in the atmosphere, it still occurs.  As pCO2 equilibriates between the atmosphere and surface waters in less than a year, that means most of the marine food eaten by humans has no significant effect.

    I am not aware of any human from non-organic sources, or from archaea, so if you want to claim that "food is derived from a source of photosynthesized CO2" is an appreciable source of human food, you will need to provide references.

    The difference in biomass between humans and plants is accounted for in the Land Use Change (LUC) budget in the global CO2 budget.  It is smaller than you think because the biomass of large herbivores (ie, cattle) has massively increased over the last 160 years.  Identifying just a single component in the changed system and comparing it with the total biomass of the preceding system is misleading, though no doubt unintentionally. 

  3. What a fantastic site, as an interested amateur please correct me if I am wrong, but the way I see it all today:

    When water was first created on Earth the environment centred just under boiling point and eventually became tropical with the creation of plant life. 10,000 years ago humans began to upset the carbon cycle by farming and successfully delayed the next ice age, although ice ages are one way to redistribute minerals leached away by farming Hence the lush forest in pre historic times.

    In the last 50-years farming has changed globally. Look at our fields and you will see that a good proportion of the year they are clear of vegetation. Many of our crops are fed hydroponically in polytunnels with nutrients, and field crops use fossle fuel based fertilisers. Worst of all beneficial soil microbes that consume the plant sugars in order to extract nutrients are killed off with herbicides and pesticides as no longer required. one type of microbe burrows into a plant root in order to feed on the sugars from the 8% of carbon extracted between the night/day CO2/Oxgen cycle These particular microbes increase the water take up area of a plant root by 1000x, just think how much nutrient solution or fertiliser is required to account for the microbes lost. This is huge if considered world wide.

    I have a book that recorded Brinks Manometer readings in 1940 that shows that the sugar levels of ripe tomatoes in 1940 are only 10% of best grown organic today, which is an indication of ripeness and mineral content indicating how we are all so well fed while starved for nutrients. This book is ex-library so goodness knows what today's figures are. As I just retired this year and have bought a manometer I intend to start monitoring and tests on my allotment, this is a good forum to discuss the results.

    There is a growing interest in no till farming, using companion planting, organic methods, and green manures with permanent clover keys to sequester carbon from the atmospher. A great book on this is "The one straw revolution". All those ploughed brown fields would over winter with a green manure made from CO2, which fixes nitrogen, and is then retained within the soil when ploughed in.

    Another change to our climate is being caused, so I read, by desertification. See the Savory Institute web site. They will show you how a desert is formed in just a couple of years when animals are removed from the land, elephants are culled or domestic cattle are wrongly farmed standing around in fields. Carbon sequestration from recovery of a desert using just cattle and mob grazing is equivalent to 6000 car emissions/acre (please check this figure yourself on the Savory website). There is a great movement in the USA and UK towards mob grazing techniques, and when you compare the root size of say a Rye grass lay using mob grazing, soil improvement, with cut and digging in rather than ploughing out, you can see first hand where the CO2 is going, or at the moment not going. Even composted it releases CO2 back into the air along with other far worse greenhouse gases.

    This is such a complex topic, my belief is if every aspect is altered just 5% it will make a vast improvement. We all have to do our bit, everyone is correct in their beliefs.


  4. Correction: Brinks values are today 10% of 1940 figures. Sorry.

  5. @78 MLDonoghue

    Sorry to say, but just about everything you wrote is partly wrong and partly right. It's as if in a carefully constructed Poe of partial understanding but failure to grasp the bigger picture. If it is a Poe, I suggest you try just saying what you really mean and forget the low brow humor. 

    If it is not a Poe, then pick one subject and stick with it alone long enough to get a general understanding of that one single thing before you move to the next. Right now you have a tangled up mess of 1/2 truths like Gordian's knot.


    [PS] I think it is safe to assume this is not a Poe. Please be careful not to make responses that could create unconstructive flamewars. Better to simply point out what you think are some of the bigger errors and let discussion continue from there.

    MLDonoghue - while not  a gish-gallop of our more usual sort, you do cover a lot of territory and RBs advice to stick to one point at a time is sound.

  6. My sincere apologies to the Mods and MLDonoghue. I guess what I can say is context is everything. MLDonoghue, get your context right and I will try and help you best I can. For example the way you got it all out of context, it appears as if you think that ice ages recycle farming runoff.

  7. Tom Curtis @ 77, The difference in biomass between humans and plants is accounted for in the Land Use Change (LUC) budget in the global CO2 budget. It is smaller than you think because the biomass of large herbivores (ie, cattle) has massively increased over the last 160 years. Identifying just a single component in the changed system and comparing it with the total biomass of the preceding system is misleading, though no doubt unintentionally.

    That's true, it was wikipedia sourced, though the ratio of terrestrial plant / animal biomass is supposedly still approx 1000 : 1. 

    I was surprised to learn that large domesticated herbivores do constitute about 6x the biomass of humans, but It would be interesting to know how much biomass has been lost with the extinctions and depletions of various animal species as a consequence of human population growth. Such numbers are hard to come by. 

    From a book titled "Harvesting the biosphere", where the author has researched as best he could the various human impacts dating back to pre agricultural times,  it's stated that roughly 200 Gt C of global phytomass has been lost since about 1800, which is considerable given that it represents as much as 60% of fossil fuels burnt over the same period.

    It's postulated that as much as 40% of (post glacial) phytomass has been removed by humans. 

    If as projected, the global population will rise to 10 or 11 billion before 2100, the task of reassimilating all of that displaced carbon (from land clearing and FF combustion) back into the biosphere will not be a simple one, particularly if future land clearing increases phytomass loss for the purpose of increased agricultural output, human settlement, or even biofuel production.

  8. Art Vandelay @82, it is hard to estimate lost phytomass, and I will not try.  I do know that LUC including deforestation has resulted in anthropogenic emissions of 157 GtC (2015 Global Carbon Budget), and that about 50% of the dry mass of wood is carbon, and about 50% of the wet mass is H2O, so that the total wood lost is on the order of 628 Gigatonnes.  Against that, forest regrowth, increased growth due to moister conditions and the CO2 fertilization effect have increased net fixation of carbon by photosynthesis, so that the net change in carbon flux from vegetation is 0.2 GtC per annum (1.1 GtC/annum from LUC - 0.9 GtC/annum increase in net photosynthesis).  If that ratio was consistent through out the post 1850 era, that means the net change in vegetative biomass is on the order of 114 Gigatonnes (28.5 GtC).  That is a big "if", however, and I do not know of any research showing to what extent it holds or not.  I suspect, but do not know, that the net biomass lost is somewhere in the 200-300 Gigatonnes range.

    With regard to the biomass of mammals, we are no more secure grounds.  It has increased around 1.2 Gigatonnes:

    Assuming the 18% carbon content by mass of humans is typical of mammals, that represents 0.22 GtC, not to far from your humans only estimate.  That amount will be included in the uncertain change in net biomass consequent in the difference between LUC and cumulative net increase in photosynthesis.  Clearly animal biomass changes, human or otherwise are an insigificant fraction of the changes in vegetation, so my drawing attention to the change in large fauna biomass was an unintentional diversion.

  9. Tom and Art,

    You could also try to estimate fish biomass changes which would be very difficult.  Reports that there were so many cod that ships were slowed in sailing by the friction on the fishes backs indicate much loss of fish.  During World War II fish mass increased, possibly contributing to the hiatus in in warming in the 1940's.  Whales were also much affected.

  10. I am not sure if this is what you are looking for, but Vaclav Smil has some numbers in his article "Harvesting the Biosphere: The Human impact", 2011.  (a free copy is available on his homepage, but it seems to be offline at the moment;)

    Here are some numbers from Table 1, p 616:

    Year -  Population (million) - Global phytomass stock (Gt C)

    0 - 200  - 1,000
    1000 - 300 - 900
    1800 - 900 - 750
    1900 - 1,600 - 660
    2000 - 6,100 - 550

     The changes in zoomass are quite smal in comparison (p 618f):

    " The total zoomass of wild terrestrial mammals ... yields no more
    than about 50 Mt of live weight (about 10 Mt C) in 1900 and 25 Mt of live
    weight (about 5 Mt C) in 2000, a decline of 50 percent. In contrast, during the same time, the global anthropomass rose from roughly 13 to 55 Mt C."

    His estimate for the biomass of domestic animals is 35 Mt C in 1900 and 120 Mt C in 2000.

  11. michael sweet @84, fish are tricky.  

    Unlike the case with land animals, where we eat herbivores, humans preferentially eat large, predator fish.  The consequence is that while we fish down stocks of our preferred fish, the resulting lack of predators allows an increase in the number of prey fish.  This 2014 study indicates that we have reduced the biomass of predator fish by 66.4 (60.2-71.2)% over the last 100 years, with most of that occuring in the last 40 years.  Over the same time, however, the biomass of prey fish have increased by 130%, ie, more than doubled.  Given the trophic pyramid, the biomass of prey fish in the undisturbed state was likely 10 times that of the predator fish, giving a net change in biomass of 0.9*2.3 + 0.1*0.34 = 2.1, so that overall fish biomass may have approximately doubled.

    Of course, the increase in prey fish will also have resulted in a decrease in the biomass of their prey, ie, plankton.  That is difficult to estimate, however, because:

    1)  The population of prey fish were initially predator limited so that the biomass of planckton would not have been approximately 10 times that of the prey fish as according to the standard trophic pyramid; and

    2)  The prey fish often fed on zooplanckton which fed on phytoplanckton; and to the extent that is the case phytoplanckton would have become more numerous, possibly resulting in an overall increase in ocean biomass.

    To further complicate things, a recent study has suggested that fish numbers in the middle layer of the ocean (mesopelagic fish) have been underestimated.  As mesopelagic fish have not been primary catches in global fisheries until recently, the numbers quoted above may be overestimates by an order of magnitude.  

  12. If we are to assume that humans only recycle Carbon without adding any, and fossil fuels are not part of the cycle anymore, it begs to asks the question "where all the carbon came from before it became fossil fuel".?

    If carbon in CO2 (now stored in fossil fuels) was in the atmosphere to start with, how come the planet cooled down?  Thanks for simple answer, I am not Scientist.

  13. GB... For starters, carbon is the sixth most abundant element in the universe but that's very different than the "carbon cycle" being discussed here. The carbon in fossil fuels was part of an ancient carbon cycle from millions of years ago that has since become sequestered in the earth's crust. Fossil fuels (or "hydrocarbons") are ancient plant and animal life.

  14. GB @87, first, the Sun is gradually getting warmer over time.  The formula that describes its rate of warming is:

    L(t)/L(c) = 1/(1+2*(1-t/t(c))/5)

    Where L(t) is the luminosity at time, t, L(c) is the current luminosity of 3.85 *10^26 Watts, t is the time in Gigayears from the formation of the Sun, and t(c) is the current time since the formation of the Sun, or 4.57 Gigayears.

    Using this formula we can calculate that to maintain the same temperature as we had in the preindustrial, in the Carboniferous (when most coal, and hence most fossil carbon was laid down) we would have required an extra 700 ppmv of CO2 in the atmosphere to maintain preindustrial temperatures.  100 million years ago (the approximate age of most oil (but see also the age of the Tethys sea, were most middle eastern oil was laid down), we would have required an additional 130 ppmv of CO2 in the atmosphere.

    Of course, CO2 pumped straight into the atmosphere does not simply stay there, but over time, achieves equilibrium with the ocean, and with the chemical weathering process.

    That means to achieve a stable eqilibrium the actual amount of CO2 not locked up in fossil fuels would have had to be 4 or more times the 830 ppmv indicated just by considering insolation.  Allowing for the much faster chemical weathering prior to the carboniferous (ie, when there were no land plants to slow weathering) it would have been much more.  And more still again to account for the fact that in the Carboniferous and earlier, the Earth was warmer than it currently is.  Although an exact calculation of the amount of CO2 locked away to balance these factors is not available, these back of the envelope calculations show the magnitudes are in the right range.  

    More exact (but still approximate) calculations using carbon cycle models reproduce the history of Earth's temperature quite well, given known changes in CO2 concentration:

  15. Sorry,  but it seems a rather simplistic approach to assume the result would neccesarly be net neutral in terms of emmissions.  Yes, we've obviously grown more crops in order to consume them.... but that would have to assume the land upon which the crops were grown was absent of vegitation wouldn't it?  

    The assumption seems to be that we've increased the total amount of vegitation exactly enough to offset our increased respiration.... but haven't what we've actually done is CHANGED THE TYPE of vegitation from a form we can't consume to a form we can consume.

    Where is the evidence to suggest that we've actually increased the total mass of vegitation in an amount exactly equal to our respiration?

    Further wouldn't that also assume that all plant mass has exactly the same value in removing carbon from the atmosphere and acting as a carbon sink.  Just the fact that certain plants have longer life cycles and hold onto their mass for longer periods of time.... or have different growing cycles would tend to suggest otherwise wouldn't it?

    Would even a deciduous tree have the same value in removing carbon from the atmosphere and producing O2 as a conifer occupying the same acerage?

    That's even ignoring the role of livestock in the cycle and assuming all our intake comes directly from plants.

    I'm not a scientist but it seems rather like you've made a convenient set of assumptions of net neutrality for something that is not nearly as simplistic.... but maybe I'm completely off base.


    [RH] Note that all caps isn't allowed here. Thanks.

    In terms of your question, first, make sure you've read both the basic and intermediate tabs for this topic. It seems to me that you're trying to make the question more complicated than it is. This topic isn't intended to address land use changes due to population growth. For that you can read this SkS article.

  16. Thanks for your rapid response and I aplogize for the use of capitals. I was just trying to denote emphasis.

    I think the problem I'm running into is simply this.  The claim is that an increase in the numbers of humans engaging in respiration has a zero net effect on the level of CO2 in the atmosphere because that is offset because we produced more crops which themselves take in C from the atmosphere and thus results in net zero change.

    In theory if the only things you were considering were plants consumed and human respiration (and I suppose storage of C in tissues) in isolation... that argument would seem to make sense.

    However,  just as the Carbon we exhale comes from somewhere (consumption of plants) and our respiration should not be looked in isolation from that so too do the crops we produce to eat come from somehere and our production of them has some effect beyond thier simple consumption.

    In other words, I think what you are categorizing as land use change is salient to the topic being discussed and should not be artificially isolated from it.

    That is to say, if we weren't burning any fossil fuels whatsoever but still somehow performing all the other activities we perform in order to produce the food that we consume and which in part we respirate out as CO2 waste would the effect on the composition of the atmosphere be nothing whatsoever? Would the composition of the atmosphere be exactly the same as if there were no humans on the planet doing those things? or if there were only 1 billion. I really don't see how that would be a given.

    I can see the argument that the change might be very small compared to fossil fuel production, maybe even reach some equilibrium but would it be exactly the same equilibrium as were there no humans on the planet. I really don't see how you could make that argument?


    [RH] Again, you're extending the issue into other topics outside whether breathing adds CO2 to the atmosphere. Re-read the myth statement at the top of the article. That is what is being discussed. It's a very common misunderstanding that many non-scientists have regarding climate change and CO2 levels.

  17. Grumpymel @91 and 92, the claim above is a rebutal of denier claims that human respiration is a direct source of the increase of atmospheric CO2, just as is the combustion of fossil fuels.  That claim by deniers is typified by the quote from Ian Plimer, that

    "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."

    Of course, if Ian Plimer was at all honest in his science (on global warming) he would have noted that the carbon in what we eat comes from CO2 in the atmosphere, and consequently Senator Penny Wong's, and our respiration causes no direct increase in CO2 concentration.

    That is a seperate question as to whether or not human agricultural activity has changed atmospheric content.  It has, and in complex ways.  Of these the most important have been the increase in CO2 from deforestation, and the increase in CH4 from rice farming and cattle production.  Nothing above denies this, and there is extensive discussion of this in comments above.  Further, the IPCC takes account of CO2 and CH4 production from these scources.

    For what it is worth, CO2 emissions due to Land Use Change (the title given to those emissions) represents about 10% of emissions from fossil fuel use and cement manufacture (another important source).

  18. I've been reconsidering this for a bit now and I think Plimer actually has a point about exhalation contributing to GW in a minor way. Hear this out. I know that carbon is a cycle but at only one point in that cycle is it acting as a GHG in the atmosphere. What actually determines how much warming GHG contributes to at any point is how much is in the atmosphere at that point, correct?

    If something happaned to increase the percentage of time that carbon spent in the atmospheric portion of it's cycle then that would increase the amount of carbon in the atmosphere at any given time and if the factor that caused that change were persistant rather then transient, the amount of carbon in the atmosphere at any given time would be consistantly higher as well, correct?

    For example, if hypothetically, at base line carbon spent 50 percent of it's cycle in the atmosphere and 50 percent in the non-atmospheric portion and some factor came along to change that ratio to 90 percent of it's time in atmosphere and 10 percent out, we'd have significantly more GHG in our atmosphere, correct?

    So the question, it seems to me, is "Does human consumption of carbon increase the amount of time it spends in the atmosphere?" or perhaps more directly "Does eating an apple return it's carbon to the atmosphere more rapidly then had we not picked it, let it fall to the ground, decay and rot"? Given what human consumption does to an apple compared to what would happen via natural decay...I'd have to say the answer was likely yes. We significantly decrease the amount of time it takes for carbon to return to the atmosphere.

    That doesn't mean that exhalation is a major factor in climate change but I'd have to say that yes, more humans on the planet consuming food and exhaling carbon back into the atmosphere probably does result in a consistantly larger amount of carbon in the atmosphere then if we weren't engaged in such activity.

  19. Grumpymel @93.

    Your argument only works if you assume that an apple (or other plant-matter that would grow and decay in its stead) somehow does not emit CO2 when it decays. An apple contains carbon and oxygen so as it decays, what happens to the carbon and oxygen? Is it only humanity that by eating apples and other food breath out CO2?

  20. Since I addressed this very topic at length in my YouTube video  I will only spend a couple of moments addressing the main subject of this thread.

    1.  As we breathe in 400 ppm CO2, we do not exhale "about ten times that amount", so the premise is incorrect.  We exhale some 100 times that amount, about 40,000 ppm (4% CO2).

    2.  It is not a few cows that have CO2 (and I didn't even consider the trivial issue of flatulence that so fascinates the AGW humorists), but all the herds of animals, and all terrestrial animals, including rodents and insects, that contribute CO2 to the atmosphere.  Indeed the mass of all other living things on land far exceed and far exceed in CO2 production, human exhalation.  I had no basis for calculating marine sources, and for that matter did not include the direct release of CO2 by oceans, springs, grottoes or even volcanoes.

    3.  The CO2 production that I found in my meta study as shown in the video was growing, and growing at the same rate as the CO2 reports put out by IPCC showed (what a surprise as the curve is the same shape for human population growth), but *they focused entirely on industrial production* in intentionally misleading people imo, and my data showed that the total terrestrial animal production was 40% as large as that produced by industry.  It's a sum because the industrial production data is well developed and not dependent on measuring Mauna Loa, and the other calculations are straightforward as well, so there's no confusion of what's a total produced (with my limitations as shown) and what's reported by measurement at 13000 feet.

    4.  Nor is it to be fobbed off as just part of the carbon cycle...ALL carbon comes from other carbon...but if the CO2 is being ascribed a causative action  (a la Anthropogenic Global Warming theory by IPCC), then ALL the sources need to be accounted for, not just some summary presumption (I say presumptuous, tendentious, presumption), 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.


    See the video. Ask questions there or here as you see fit.  Just one more thing. [snip]  I am not the first person on this thread to doubt some (or all) of the not-so-skeptical-science of the blog, but I see that they have disregarded those comments and not changed a thing. Is it characteristic of "skeptics" to be hardened in their skepticism, or is it that they call themselves skeptics as a false-flag clickbait hewing to the AGW belief system?  FWIW, I will be keeping a copy of this post in my file in the (unlikely) event that it somehow violates the Comments Policy, by its contradiction of skepsci's assertions.


    [RH] I would suggest that you re-read the comments policy. Pre-complaining about moderation is still a moderation complaint.

    This issue has been thoroughly addressed and you're not adding any new relevant material. The carbon you exhale comes from carbon in the current active carbon cycle. It's not adding any new carbon to the carbon cycle. 

    When we burn fossil fuels we are extracting ancient sequestered carbon from the earth's geology and, through combustion, are reintroducing that carbon to the modern carbon cycle.

    This is a very simple concept which is accepted across the board. For you to dispute it clearly puts you outside of any rational scientific debate. 

  21. +RH  It's nice to see the comment has not been removed on the basis that "it clearly puts you outside of any rational scientific debate".  Seems to me pretty close to argumentum ad hominem, but maybe that's just me.  Frankly I resent the implication that contradiction is "clearly" outside of anything.

    First, the level exhaled you led with was completely erroneous, and you did not dispute that, so you make your entire argument that the C was always there and we just recycle it, and disregard your first error.

    And I already answered that "recycle" argument.  The CO2 exhaled by all animals (and their number is growing, along with their exhalation) is in addition to the CO2 created by industry for any given year, and, while isotope analysis can identify that produced by burning fossil fuels (less and less distinctively as exhalation goes on), any warming effect claimed cannot discriminate between that which has increased due to industry and that which is exhaled by increased population of terrestrial animals.  

    Thus, it is not enough to conclude that the world's industry it causing anything (the idea of CO2's effect is not for this thread), while any official body (such as IPCC) simply dismisses it, and your counterargument seems to support such dismissal.  

    I put it to you that if your bank were to say that it paid 0.5% on your average current balance, and then excluded 30% of your balance because it was too recent, you would not bank with them any more.

    More significantly, imo, if any bank tried that, you would report them to the state banking commission.  IPCC is that bank, and their accounting is that faulty.

    RH, I'll ask you to keep the condescension down to a low roar.  I am a serious scientist.  I hope skeptical science has a few whose skepticism doubts the received wisdom of AGW alarmists and not somehow only that from "deniers".  Doubt is the basis for advancement in the sciences.  It should not preselect.  That's just prejudice, not skepticism.


    [JH] Sloaganeering and moderation complaint deleted.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

    [RH] Bill, while your original post was worthy of a complete deletion, it is sometimes instructive for other readers to leave such egregious examples where people think they know more than the entire rest of the global scientific community. That said, your tone and approach to this conversation are rapidly headed toward you being banned.

    We encourage open dialogue here at SkS with caveat that people stick to the science. Drop the aggressive rhetoric and you might have a productive learning experience here.

  22. DrBill, I watched the first half of your 30 minute Youtube presentation (from 2006).

    Frankly, the arguments put forward were appallingly poor.   So appallingly poor, that it woud be impossible for the second half of the talk to redeem the whole 30 minute venture and pull the fat out of the fire.   The arguments put forward were so fundamentally wrong in science, as to make your presentation a nonsense.   So much so, that it would be tiresome to enumerate & discuss all the errors.

    You said you presented your ideas to Science magazine — and were rejected (as being "not of general interest").    DrBill, the Science editors were being polite to you.   They should simply have posted your submission back to you, marked with a one-word red-pencil comment: "Nonsense".

    Your youtube video is a complete waste of viewers' time.

  23. Yes it is just you. "Ad hominem" means that an argument is attacked on the basis of the character  of the one who  makes it. An example would consist of saying that someone is a sleaze ball and therefore what they say is wrong or invalid. That is a logical fallacy, as the character of an individual has no bearing on the validity of the argument, which is to be judged on its own merit. I am surpised that a "serious scientist" could be confused on that point. If an argument is indeed removed from rational thought, it has no merit.

    As to the rest of the post above, I am not sure what you are trying to say. CO2 exhaled by animals is not, and can not be, a net addition to the carbon budget. The only way atmospheric carbon can see a net increase is by injecting some that was taken from an otherwise stable reservoir that kept it away from the atmosphere, such as the crust. Animals do not create CO2, nor do they have the possibility of fetching it in such reservoir, only humans have the power to do that. Furthermore, the majority of animals now existing on Earth are dmoestic animals, i.e. the result of human activity, many of them indeed the result of industrial agriculture. Industrial. 

  24. Dr Bill Hoffman @95:

    A)  You say:

    "As we breathe in 400 ppm CO2, we do not exhale "about ten times that amount", so the premise is incorrect. We exhale some 100 times that amount, about 40,000 ppm (4% CO2)."

    That is correct, but it is not a claim made in the Original Post.  Rather, it is an error by the AGW denier, "Ian Plimer" which was merely neglected as being trivial relative to the gross error rebutted in the OP, and which you appear to repeat.

    B)  You further say the IPCC is "...they focused entirely on industrial production...", but that is simply false as shown by the IPCC's summary diagram of the carbon cycle shown below:

    Note that the non industrial elements are determined by in-situ surveys, satellite observations, changes in isotope ratios, all of which are used to validate models.  For example, here is a paper analysing measurements of Dissolved Inorganic Carbon and comparing the result to earlier estimates.  And here is a review of data relating to anthropogenic emissions from LUC.  Your assertion in your video that "LUC" represents simply "a factor to allow adjusting" (8:44), ie, is merely used to balance the books is simply false.  At best it represents an overwhelming ignorance of the topic on which you chose to lecture.  The equation shown at that point in the video is also entirely of your own manufacture, so far as I can tell.  The IPCC TAR (2001), for example, shows the following elements in the carbon cycle:


    (For clear image of each panel, go here.)

    As the IPCC TAR was the report immediately preceding your presentation, your employment of a truncated equation of the carbon cycle that does not even include vulcanism shows you to be, at best, completely ignorant of what the IPCC claims.  Never-the-less, you feel qualified to make repeated false claims about what the IPCC purports to understand, and how they arrived at those conclusions.

    C)  Your model as shown on the video purports to show 100 Gt-CO2/yr (27.3 GtC/yr) emissions from respiration in 2004 (13:35).  You then show an estimate of the increase in CO2 emissions by animals of about 10 Gt-CO2/yr (2.7 GtC/yr) by 2004 relative to 1900(?) (14:36), which you claim (15:54) to be about 50% of anthropogenic industrial emissions.  Anthropogenic industrial emissions in 2004, however, were 7.78 GtC/yr.  Your "accelerated conversion" was, therefore, just over a third of industrial emissions, and less than a third of industrial emissions plus LUC.

    D)  Whether or not that represents a genuine increase in emissions depends on what you calculated, which is very far from clear.  To avoid excess length, I will discuss it in a following post. 

  25. Philippe Chantreau " I am not sure what you are trying to say. CO2 exhaled by animals is not, and can not be, a net addition to the carbon budget."

    No one said it was a net addition to the carbon budget.  And your clarification of what does add to the carbon budget actually helps identify my challenge to IPCC and their inadequate accounting/summarizing. [FWIW, the equation I showed, Tom, was directly copied from their 2005 Report that I used, and their dismissal of any CO2 but industrial has been shown multiple times in many forums, and informed my angry analysis.]

    In any given year, CO2 comes into the atmosphere from industry, transportation and respiration.  Its presence is all it takes to have any putative effect, not where it came from or what source.  If the atmosphere reacts to the presence of CO2, it does so without regard for its history.  The emphasis on its history is the bias in IPCCs conclusions.

    While I'm at it, Tom, your analysis of what I said does little to change my point, as expressed in the paragraph just above.  I said 40% more, and you want to argue 33%...tomayto tomahto...they found industrial CO2 and stopped accounting.  On the other detail (D), I used UN herd records for my animal calculations, added to it some lesser quality estimates of insect population (rounded down not to be too shocking), and worked with the same kind of growth curve you posted earlier in Fig 5.

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