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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)

The very first time you learned about carbon dioxide was probably in grade school: We breathe in oxygen and breathe out carbon dioxide. Any eight-year-old can rattle off this fact.

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. 

This new animation published by Dr. Patrick T. Brown (Carnegie Institution for Science, Stanford University) in September 2018 explains the process:

Therefore, when we breathe out, all the carbon dioxide we exhale has already been accounted for. We are simply returning to the air the same carbon that was there to begin with. Remember, it's a carbon cycle, not a straight line - and a good thing, too!

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

Last updated on 13 September 2018 by BaerbelW . View Archives

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Comments 51 to 75 out of 159:

  1. Hi Tom, thanks for the explanation and clearing up the definition of biomass. 

    My background is in engineering, not geology, so I'm by no means an expert on atmospheric CO2 exchange.

    There's is however one part of your explanation that doesn't make sense to me: -   

    "So, we add the human carbon input, which comes from food and all of which comes initially from the atmosphere. You then have a cycle in which the ouput (human respiration) is very slightly less than the input (human consumption of CO2 indirectly drawn from the atmosphere). 

     

    I don't understand why CO2 initially comes from the atmosphere. I would have thought it correct to say that CO2 in the atmosphere initially comes from biomass (respiration) or an external input such as vulcanism, and that the atmosphere is the transport media in the system.  

    Rather than take the thread OT I'll consult with a geologist friend of mine in the next day of so to get a better understanding of why the atmosphere is regarded as the starting point in the cycle. 

  2. Art Vandelay @51, there a couple of reasons to treat photosynthesis as the primary process (so that the CO2 is treated as initially coming from the atmosphere).  First, historically that is what happened.  Ie, before there were multicellular animals, there was photosynthesis, and indeed multicellular animals only became possible because of the existence of photosynthetic plants (or microbes) on which to feed.  Second, food consumption can be treated as a flow of energy from low entropy to high entropy.  As such the conversion from the lowest entropy energy supply generally available on Earth (sunlight) to the next lowest entropy source of energy generally available (sugars in plants) is the primary process.  So, thermodynamically photosynthesis (and hence extraction of CO2 from the atmosphere) is primary.

    However, these are not reasons directly related to the accounting of carbon flows.  For that purpose we can take several approaches.  The simplest approach, and the one in fact used by climate scientists, is to ignore churning.  That is, to only take account of change of carbon in biomass reservoirs.  If we account for carbon in that way, the human respiration is closely balanced by photosynthesis absorbing almost the same amount of Carbon.  As this is just churning, it is ignored, and the only thing that is accounted for is the slight increase in carbon storage in humans due to increasing population and obesity.

    Alternatively, you could consider human respiration as a relevant emission, but only if you consider all photosynthesis a relevant sequestration.  

    Looking at the IPCC graph I posted @42, we can either consider net land flux (=4.3 GtC per annum sequestered), or we can consider the two fluxes seperately, and say there are 118.7 GtC per annum emitted and 123 GtC per annum sequestered.  It makes no difference in the end.  What you cannot do is consider treat the total respiration as emissions, but consider only excess photosynthesis as sequestration, which is what the denier argument rebutted above tries to do.  That is similar to their similar dishonesty in suggesting anthropogenic emissions are very small because they are only 4.3% of total emissions because they are only 4.3% of total CO2 flux into the atmosphere while ignoring that the natural components of that flux are almost exactly balanced by natural fluxes from the atmosphere so that the net increase is entirely due to anthropogenic emissions.

    These figures are for the entire terrestial biosphere, but the same point applies to human respiration and the photsynthesis of the carbon content of human food.  Further, because that photosynthesis is a continuous process (as is the respiration), the two components almost exactly balance at any point of time, and certainly the time averaged processes do.  

  3. Tom Curtis@52

    Thanks for that detailed explanation, and particularly the explanation of accounting methods employed. It all makes much more sense to me now.

    My Geologist friend had a slightly different take on it, and not unexpectedly employed a different accounting method. Although he deemed the assertion that "human breathing causes atmospheric CO2" to be largely spurious, he also added that it's more relevant to examine changes to the biomass itself, and specifically the ratio of photosynthetic to non-photosynthetic biomass due to human population over a given timeframe. He thought that human activities such as deforestation through logging and burning were likely to be more influential on changes to atmospheric CO2 than human respiration itself - leaving aside the impacts of fossil fuel burning.

    Endeavouring to research further for myself, I found a paper that calculated atmospheric CO2 from human activities alone to represent 25% of total emissions; mostly the result of biomass depletion through deforestation, which depletes the photosynthetic pool. This highlights the fact that population itself will be a hindrance to efforts to remove excess carbon from the atmosphere in the coming decades, regardless of the emission scenario we eventually achieve, and future radical geo-engineering solutions are perhaps not out of the question.

    As an aside, CO2 from human respiration can be estimated with simple math, and works out to account for about 9% of global emissions – which admittedly looks like a big number in isolation.

    Which brings us back to the original skeptic’s assertion that “breathing causes CO2 accumulation in the atmosphere”.

    Rather than dismiss it as a myth, I regard it as an interesting claim that’s worthy of some examination, even if irrelevant in the discussion of (CAGW) climate change.

    Personally, if I was going to take a skeptic ’s position, I would assert that the current human population, and associated activities required to sustain it, will add CO2 to the atmosphere, with or without fossil fuel combustion.

  4. Humans sink Carbon through waste, Humans are producers by means of the increment in aricultural productivity per hectar which we have developed. Fossil fuel burning recycles sunk carbon like volcanoes do every so often. Humans are part of the biosphere increments in our population do increase co2 in the atmosphere through breathing alone. We do not produce all the food we eat, non farmed fish consumed by humans per year amounts to 70 million tons. the question of how much of the CO2 in the atmosphere comes from breathing is a valid one. in the end it is not just how much goes up and how much is sunk because we can't expect to keep earth on a permanent temperature indefinately as that would be imposible ue to prescesion of the earths axis. In fact trying to do o would probably harm the biosphere much more than fossil fuel burning. the adecuat balance of CO2 at any given moment in the atmosphere should be monitored as a percetage of total mas of living biosphere and in relation to the amount of C escaping the atmosphere aswell.

  5. I wonder... How much of the CO2 in the atmosphere comes from soft drink bubbles?

  6. juan vicini @54 & 55:

    1)  The CO2 in soft drinks is obtained by capturing CO2 from power station exhaust, and then forcing it into the water under high pressure.  Because the CO2 is captured from power station exhaust, the amount of CO2 in that exhaust is reduced by the same amount as the CO2 "emitted" by soft drinks.  In consequence, soft drinks emit no CO2 that was not going to be emitted anyway.  It causes no increase in total CO2 emissions, other than that due to the energy of manufacture.

    2) All human food is either plant life, or processed from plant life (meats).  As such, the CO2 in all human food is obtained from the atmosphere by photosynthesis.  Further, once respired, new food is grown by again taking CO2 from the atmosphere by photosynthesis.  As such, the respired CO2 from humans does not increase overall atmospheric CO2 levels.  It is only possible to imagine that it does by ignoring the photosynthetic half of the equation.  This is all explained very clearly in the original post above, and in the comments afterwards.

  7. 1. isn't most of the swallowed CO2 plus the amount of CO2 produced from digestive processes, absorbed by the intestine, therefore by swallowing power plant co2 through cola arnt we sinking CO2 into fat, is all CO2 in human food obtained from organic sources through photosynthesis, if not how much mineral carbon is in our food?

     

    2. If over all human population growth and the resulting increment in food intake translates into a net depletion of the top of the food chain (excluding whales who eat plancton directly) live biosphere in the oceans, wouldnt that translate into an overall increase in CO2 in the atmosphere resulting from incremental of human respiration? pound per pound does human respiration more eficient than fish respiration in terms of oxygen intake vs CO2 outflow?

    3. Humans are getting very close to applying C as a material to very "usefull" purposes, and more that any other technology out there CO2 recapture tech. will be most responsible for it given that it isnt just regular C laying about that is most useful, but rather the one that is excited to very high temperatures. Hopefully we wont depleate the atmosphere of CO2 then. 

     

  8. The notion that there is an eco balance to cancel respirated co2 and only co2 emissions from other sources should be considered is rediculous. There is no proof that the crops that replaced other disiduous plants that were growning on the ground before the crops were planted were or are any more efficient at converting co2 to o2. The real fact is that the yield of crops have largley been increased by improved germination, resistance to disease, irragation, and the control of pests as much as the number of acres dedicated to agriculture over the last 50 years. Those changes do little or nothing to affect the co2 consumption by crops. In the US farmland was allowed to remain unplanted in order to reduce food surplus and increase crop futures. The reason that we contiune to hear the bable from environmentalist groups about carbon emmissions is that they are more about self preservation. The notion that population control is the real answer to all these issues is unthinkable to them because for many of the leaders of this cause, that is where there power base comes from. The earth has a finite capacity for filtering out co2 strictly based on vegetation. Maybe we should be building co2 converters instead or shutting down coal if favor of nuclear power or trying to convert to wind which can only work if it was a globally connected power grid. That is decades or centuries away.

    Response:

    Thank you for taking the time to share with us.  Skeptical Science is a user forum wherein the science of climate change can be discussed from the standpoint of the science itself.  Ideology and politics get checked at the keyboard.

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

    In particular, please note the "No inflammatory statement and accusations of fraud".

  9. hydman1 @58, in all photosynthesis in plants, molecules of CO2 combine with molecules of water to produce sugar and oxygen.  This is the general formula:

    There are different pathways to achieve this reaction, but the initial and final reaction products are the same for all pathways.  Therefore there is no difference in the efficiency of plants in converting CO2 (plus H2O) to O2 (plus C6H12O6).

    What there is is a difference in is the biomass of different ecosystemts and/or crops per hectare; and hence a difference in the amount of carbon stored per hectare.  That difference, however, is accounted for under the rubric of Land Use Change (LUC).

    Building CO2 converters, ie, machinery that takes CO2 and seperates the oxygen from the carbon cannot (due to conservation of energy) use less energy than is produced by burning coal, and due to inefficiencies, will likely use substantially more.  Any such solution, therefore, cannot work without the majority of the economy being sustained by non-fossil fuel energy.  At that point, it would be simpler, and much cheaper to simply substitute the non-fossil fuel energy for the current fossil fuel energy use.

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

    As biological engines we consume energy and produce waste, given we live on a planet that has finite mass of elements with the only addition to the total mass coming from stellar objects the I think it's safe to say in it's simplest terms the statement is correct.

    CO2 measurements have been taken for many years and have been rising in concert with rising global temps with records extend back to 1850 showing a dramatic increase. Taking those temp records and using quadratic equation to extrapilate the curve of incidence, it shows that temp increases began before 1850, although incremently slower the trend was upward and this is before fossil fuels became popular, increasing trend can be attributed to increasing carbon based energy usage, which is directly related to and attributed to the increase in population.

    Dramatic increases in modern CO2 levels are directly or indirectly linked to man and his actions in most cases.

    A reducing biomass that converts CO2 to stored carbon coupled with mankind's increased CO2 producing enviroment and life suggest's the balances that we assumed as constants no longer apply.

    If we are producing more CO2 than the global environment can absorb then the outcome is obvious, if the environments that can absorb CO2 keeps reducing or slow's down uptake due to excess CO2 then problem further compounds global impact.

    If we were to compare increasing CO2 levels with global population increases we see much the same trend and increases as we see with fossil fuel usage if looked at solely.

    An increasing population does by breathing incrementaly contribute more CO2 gas to the atmosphere, which does contribute to global warming and rising temps, by the time CO2 is converted and stored as carbon it will added it's own impact which add's to rising temps. 

    CO2 is as a gas, a pollutant, we breath out more than we take in so we add to the combined total of CO2 increase, it is posionous or hazardous depending on it's concentrations to most living organism.......

  11. I dont see how we can "breath out more than we take in". We take C in via our food, and emit in breathing. While we live, we are carbon sink.

    The contribution of changes in biomass since 1750 is detailed in the AR5 WG1, p486, table 6.1.  The total land to atmosphere change is estimated at 30 PgC +/- 45. Compare that fossil fuel contribution of 375 PgC +/- 30.

  12. It doesn't look like DailySledge has read all the comments to this article. The comment that "An increasing population does by breathing incrementaly contribute more CO2 gas to the atmosphere" has already been addressed (e.g. here).

    Long story short, as scaddenp points out: more people store more carbon, so an increasing population has to be a carbon sink, not a source.

  13. DailySledge @60, the industrial revolution started in 1750, not 1850.  As a result, from 1750 to 1849, industrial emissions of CO2 from the burning of coal amounted to 1.25 billion metric tonnes of Carbon.  While only, approximately, a sixth of current annual industrial emissions, it still represents a substantive contribution to global warming.  The contribution from Land Use Change was approximately the same as that from fossil fuel consumption in 1850 (spreadsheet), and is likely to have exceeded it beforehand.  Together, these contribute to an annual increase of 1.3 ppmv in CO2 concentration over the period 1750-1849.  However, probably more significant was the significant reduction in volcanic activity over the period, combined with an increase in solar activity.  So your quadratic fits retrodiction of a positive temperature trend prior to 1850 is accurate as far as that goes, but misleading in that there have been substantial changes in the importance of different forcings over various intervals within the quadratic fit.

  14. It's a bit of rhetorical sleight of hand to appeal to the carbon cycle in order to claim that human breath is neutral, since the factor that should be taken into account is that human consumption negates the collection of carbon performed by those plants that are used for food, in addition to deforestation for conversion into agriculture. The impact of human consumption and breathing is that the sink that would naturally be functioning ceases to operate when human consumers are eating it. That biomass (now negated through its function as food) is precisely the kind of sink that stripped atmospheric carbon long ago and created the fossil fuel deposits, which are currently being liberated through human activity back into the atmosphere.

    Response:

    [PS] Changes/carbon loss from vegetation change is accounted for under "Land Use Change".

  15. For clarity's sake: it appears the role of human respiration ("Does breathing contribute to CO2 buildup in the atmosphere?") wrt CO2 buildup amounts to a zero sum when including photosynthesis. In essence this describes a natural sort of equilibrium.

    I completely agree insofar as the science itself goes (and the provided formulas-thanks)

    Pragmatically -somewhat referring to #64 response (Pointfisha) above- the population of humans is increasing alongside deforestation, excluding deforestation where it is a consequence of industrialization.

    This seems to indicate that mass consumption of meat (specifically beef & lamb) has a significant impact on climate.

    I guess I am asking what an acceptable human population would be, assuming pre-1750 (pre-Industrial Revolution) technology, in keeping with keeping CO2 levels static or reducing them from current levels. Another way of asking this: at what population will human respiration outstrip the capacity of photosynthesis?

    I do realize my query is flawed in that is purely theoretical, and perhaps even dumb: excludes other natural sources of CO2 (vulcanism, animal respiration) but those variables seem outside the scope of this article.

  16. MDMonty @65, IMO it is dubious that a preindustrial revolution technology could sustain population levels at even a quarter of current levels.  Primarily that is because it would not be able to sustain the vast energy inputs into food production; but also because the much slower transport speeds would necessitate the majority of food consumption to be from local or close (over sea) distances.  The UK may be able to source wheat from the US, for instance, but not most vegetables or fruit, and not much in the way of meat; simply due to spoilage.  A sustainable population level at those industrial levels would be in the order of half to a billion people.

    More interesting is the sustainable population at current, or likely near future technologies.  I think the evidence is that we have already exceeded it, though primarilly due to the proportion of land committed to food intake, plus the overfishing of the oceans.  Simply as regards global warming, we can sustain the current population on  greenhouse free energy and transport system, possibly at a higher standard of living than is currently common in Western Countries.  That, however, requires a major effort to transition; as the current population with the current energy mix is clearly unsustainable.

  17. @ 66 Tom Curtis,

     You seem to be mixing science and technology with industrialization. Not all technology is industrial in nature. This is important to remember in agriculture.

    The other important thing to remember is that counter intuitively, biological systems yield more when not overused. For example, a fishery that is overfished, yields fewer tons of fish per year than a fishery that is not overfished. Grassland that is overgrazed yields less meat per acre per year than grassland that is properly grazed. Forests that are over timbered yield less wood per acre per year than forests properly managed. We are so wired into net sum zero thinking that people often miss that.

    So yes, agriculture (including fisheries) could sustain populations much higher than we currently have, even though the current population already exceeds carrying capacity. We simply need to use holistic systems models of production instead of net sum zero industrial models of production.

    Don't get me wrong. Industrial models are very good at some things. But when it comes to biological systems, far from ideal.

  18. RedBaron @67, the current population is approximately 7.4 Billion, so that my estimate of up to a quarter of that sustained using preindustrial (ie, pre 1750) technology represents a population of up to 1.85 billion.  That is 2.64 times the 0.7 billion population in 1750, so I am certainly allowing for some advances in non-industrial technologies.

    Having said that, I do not think you are giving serious consideration to the difficulties involved.  A preindustrial fishing technology is restricted to small (because of limited work force) wooden, sail powered vessels.  Such vessels cannot fish with long lines, nor trawl, nor drift net.  Nor can they fish the deep ocean, and increasingly important source of modern fish.  Further, they cannot operate more than about a weeks distance from port, and typically will operate within a few hourse sailing from port.  Given those limitations, catchable fish will be a very small fraction of currently available, even with a rebound of fish stocks.

    Or consider grain growing, with no combine harvesters; with plows being of wood construction with (at best) a cast iron plate to restrict wear on the blade, and drawn by oxen or (hopefully) horses.  Harvesting will probably be by scythe.  These factors required something in the order 60-80% of the population to be agricultural workers, just to provide enough food for all.

    Or consider that such heating fuel we use will be in the form of charcoal, requiring extensive forests over much that is now agricultural land.

    And that leaves aside questions of spoilage, famine and drought.

    There is often a ridiculous optimism by some people who, urban dwellers nearly all, and with no knowledge of history, suppose that we can get rid of industrialization to advantage.  But life before industrialization was nasty, brutish and short.  In general, excepting the upper middle class and above, hunter gatherers lived better than the vast majority of even 19th century populations, but only by dint of a very low population per unit area.

  19. @ 68 Tom Curtis,

    Exactly correct Tom. Industrialization has improve some things dramatically. No farmer wants to give up his tractor etc..., except maybe a few Amish who do without. Industrialization has given us tools. It's how we use those tools that make all the difference. If when we treat those biological systems on which we use those tools to harvest food and fiber as a net sum zero product, (ignoring how fundamentally different biological systems function), then that's when we have problems with unsustainability. Which is just the flip side of the overpopulation coin.

    At lower population levels we didn't have this problem because we could always move on to new untapped areas when the areas we were harvesting from collapsed, like you mentioned with fishing. The collapsed areas would recover over time and we could come back to them later in many cases.

    However, now we must fundamentally change the production models. We no longer have to option of overuse, abandonment/fallow, and returning decades or centuries later. Instead we must change the production models to methods using holistic systems science and modern technology appropriately applied.

    If we take current productive land/fisheries etc. and change the production models, we can regenerate the ecosystems services on that land/fisheries. We also can return to currently abandoned areas and apply these new system science based regenerative models to them as well, returning them to productivity.

    So actually when you add the current productive land/fisheries to the abandoned land/fisheries that collapsed earlier due to over use, we can actually increase the total population they can support sustainably long into the distant future.

    A great working example of this is China's Loess Plateau Project. This land was destroyed by agriculture and could no longer support much population at all. Since beginning to restore the land, the amount of food and fiber produced has increased every year. The amount of carbon sequestration has increased every year. The runoff water quality has increase every year. The wildlife and biodiversity has increased every year. When you change the production models you see profound differences.

    In the USA a similar revolution in thinking is also being taught and is in its infancy. Best exemplified by this quote from the USDA-NRCS.

    "When farmers view soil health not as an abstract virtue, but as a real asset, it revolutionizes the way they farm and radically reduces their dependence on inputs to produce food and fiber." -USDA (Author Unknown)

    I am an organic research farmer. I am not afraid of change. I am the change.

  20. RedBaron @69, I understand from your comment that it was my second paragraph @66 that you disagreed with, not the first.  In particular you disagreed with my assessment that:

    "More interesting is the sustainable population at current, or likely near future technologies. I think the evidence is that we have already exceeded it, though primarilly due to the proportion of land committed to food intake, plus the overfishing of the oceans."

    That may, in part, be due to a disagreement about what is mean by "sustainable".  I have no doubt that we can increase food production into the future sufficiently to support the most likely peak world population of about 11 billion people:

    (See also this)

    I do not doubt we can do so and maintain ecosystem integrity in the limited sense that O2 production and soil health will not be impared, and a new stable ecosystem will develop.  But it will be a stable ecosystem similar to that of Britain's, in which all of nature is shaped by man, and there is no room left for most of the native mega-fauna - particularly predators (such as the bears and wolves that used to be native to Britain).

    It may be that is what the world population really desires.  It is certainly true that absense make the heart grow fonder when it comes to large predators; and that humans in the end will have no place for lions, tigers etc, except in zoos.  The same is true for large grazers, other than those dedicated for human consumption.  But I hope we have more space for nature than that, and that would require that we produce the food for the 11 billion on less land than we currently have under agriculture, not more.  

    What is more, with rising economic expectation in the third world, we need to factor in an increase in food consumption per capita by about 30-50%, and an increase in food quality (ie, more protein and fresh fruit and vegetables).  This is particularly the case in Africa where most of the population increase is expected to come.

    All in all, this means we need a increase in food production per hectare by about a factor of two for current populations (assuming 70% loss of agricultural land to allow for a wild nature), and near three for projected future populations. 

  21. @ Tom Curtis # 70

    You said, "All in all, this means we need a increase in food production per hectare by about a factor of two for current populations (assuming 70% loss of agricultural land to allow for a wild nature), and near three for projected future populations."

     

    I am nearly 100% certain we could do exactly that and very likely more on 1/2 the land currently under agriculture. Probably not England. It is an Island. But in the North America, most of Asia and Africa? I would bet my bottom dollar we can. And I am not just saying that without evidence either. The current industrialized models of production in agriculture are that inefficient in land use. The models are designed to be efficient in other things, not quantity food produced sustainably per hectacre. In fact in some things like the CAFO buisness model, it was specifically designed to be inefficient on purpose as a buffer stock scheme. This from Wiki:

    Most buffer stock schemes work along the same rough lines: first, two prices are determined, a floor and a ceiling (minimum and maximum price). When the price drops close to the floor price (after a new rich vein of silver is found, for example), the scheme operator (usually government) will start buying up the stock, ensuring that the price does not fall further. Likewise, when the price rises close to the ceiling, the operator depresses the price by selling off its holding. In the meantime, it must either store the commodity or otherwise keep it out of the market (for example, by destroying it)

    The more inefficient the better. Biofuels has the same purpose. The idea is to purposely over produce grain because although an inefficient use of land, it can be stored. Then unlike many buffer stock schemes, instead of destroying the surplus, you waste it as inefficiently as possible on livestock or biofuels. The system does work in what it was designed to do. But in no way can you estimate the land needed to feed the world's population based on that type of system. The system was designed for a world where land was seen as practically limitless. Now within that system, production is incredibly efficient. But the system itself was designed to be an inefficient use of land, to fit the buffer stock scheme instead.

    The very first thing you could do to  approximately double the food produced per hectare is reintegrate animal production back on the crop farmers land. Then of course they must be properly managed, but there are countless ways to do that without lossing any crop yields at all, and sometimes increasing yields. Remember in industrialised countries like USA over 1/2 the arable cropland goes for producing animal feeds and biofuels. Just by going to a forage based system integrated into the arable cropland you reach that food production goal of "factor of two for current populations" right away. In fact probably would be too fast. Might have to first switch to forage based regenerative systems, to repair the non-arable grazing land first, and gradually remove livestock as wild populations of animals rebuild their numbers in the newly restored habitat. Those removed domestic animals placed gradually into the integrated arable cropland as they are removed from rewilded land. If you took them away too fast the non-arable land would be undergrazed and either recover too slowly or even sometimes degrade even faster.

    It a bit hard to really explain it all on a forum like this. But I can say that IMHO we could do exactly what you asked with our current technology and at the same time actually sequester 5-20 tonnes CO2 per hectare per year into the long term stable soil carbon pool. And there are lots of case studies that show this from all over the world.

  22. RedBaron @71, I will bow to your superior knowledge of farming.

  23. This rebuttal is missing something. It says that people arguing that breathing causes CO2 are missing the other half of the cycle.

    By that very same logic, those who are saying we should cut down on fossil fuel use are missing the other half of the cycle — those plants that created the fossil fuels also took that CO2 out of the atmosphere hundreds of thousands of years ago. This is all a cycle and if it happens, it happens. You can't stop it. 

  24. Mochan

    Nope. More like 100's of millions of years ago. Plants removed vast amounts of carbon over huge timescales and it has been locked away ever since. Plants today work on a carbon cycle that doesn't include that sequestered ancient CO2. So adding this carbon from long ago is disrupting the balance of that system.

  25. Lets not get into handwavy arguments. The relevant diagram is already on this thread here. Long term burial of carbon by plants etc takes place at rate about 0.2Pg C per year. Emissions from fossils fuels and land use change are about 9Pg C per year.

    Not to mention the obvious fact that CO2 levels in the atmosphere are rising, and that the isotopic composition of CO2 in atmosphere is consistent with addition coming from FF.

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