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How do human CO2 emissions compare to natural CO2 emissions?

What the science says...

Select a level... Basic Intermediate

The natural cycle adds and removes CO2 to keep a balance; humans add extra CO2 without removing any.

Climate Myth...

Human CO2 is a tiny % of CO2 emissions

“The oceans contain 37,400 billion tons (GT) of suspended carbon, land biomass has 2000-3000 GT. The atpmosphere contains 720 billion tons of CO2 and humans contribute only 6 GT additional load on this balance. The oceans, land and atpmosphere exchange CO2 continuously so the additional load by humans is incredibly small. A small shift in the balance between oceans and air would cause a CO2 much more severe rise than anything we could produce.” (Jeff Id)

Before the industrial revolution, the CO2 content in the air remained quite steady for thousands of years. Natural CO2 is not static, however. It is generated by natural processes, and absorbed by others.

As you can see in Figure 1, natural land and ocean carbon remains roughly in balance and have done so for a long time – and we know this because we can measure historic levels of CO2 in the atmosphere both directly (in ice cores) and indirectly (through proxies).

Figure 1: Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons (Source: Figure 7.3, IPCC AR4).

But consider what happens when more CO2 is released from outside of the natural carbon cycle – by burning fossil fuels. Although our output of 29 gigatons of CO2 is tiny compared to the 750 gigatons moving through the carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra CO2. About 40% of this additional CO2 is absorbed. The rest remains in the atmosphere, and as a consequence, atmospheric CO2 is at its highest level in 15 to 20 million years (Tripati 2009). (A natural change of 100ppm normally takes 5,000 to 20,000 years. The recent increase of 100ppm has taken just 120 years).

Human CO2 emissions upset the natural balance of the carbon cycle. Man-made CO2 in the atmosphere has increased by a third since the pre-industrial era, creating an artificial forcing of global temperatures which is warming the planet. While fossil-fuel derived CO2 is a very small component of the global carbon cycle, the extra CO2 is cumulative because the natural carbon exchange cannot absorb all the additional CO2.

The level of atmospheric CO2 is building up, the additional CO2 is being produced by burning fossil fuels, and that build up is accelerating.

Basic rebuttal written by GPWayne


Update July 2015:

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 5 July 2015 by skeptickev. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Further reading

Both graphs from this page are taken from Chapter 2 of the IPCC AR4 report.

Real Climate goes in-depth into the science and history of C13/C12 measurements.

The World Resources Institute have posted a useful resource: the World GHG Emissions Flow Chart, a visual summary of what's contributing to manmade CO2 (eg - electricity, cars, planes, deforestation, etc).

UPDATE: Human CO2 emissions in 2008, from fossil fuel burning and cement production, was around 32 gigatoones of CO2 (UEA).

Comments

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Comments 301 to 346 out of 346:

  1. Uhhhh....  Thanks for burying me in reading material! :)

  2. Tom Dayton @ 297: "Your understanding that "the current warming cycle is releasing more naturally sequestered carbon into the atmo than mankind is emitting" is incorrect."

    There is an argument that warming is forcing carbon release. My understanding of the argument as simply phrased above is correct. That doesn't mean I'm a proponent of that argument.

    Tom Dayton: "The amount we release is enough to outstrip the abilities of the natural sinks to absorb it."

    That is also my understanding of this argument. From the 'intermediate pane':

    "Therefore human emissions upset the natural balance, rising CO2 to levels not seen in at least 800,000 years."

    Obviously, temperatures, ocean levels, and CO2 concentrations have varied over the millenia. Because that was the case then, doesn't mean that humans now are or are not forcing the climate beyond what is thought to have been a natural balance.

    There is no question in my mind that humans have burnt off a lot of fossil fuels that otherwise would have stayed in the ground. The climate will seek a new balance, but that new balance would also include warmer temperatures and different coastlines, among several other effects.

    I looked at:

    https://skepticalscience.com/warming-co2-rise.htm

    "But in today's world, the greatly increased partial pressure of CO2 from fossil fuel emissions causes a flux of CO2 from the atmosphere to the oceans."

    Ai chihuahua. 400 ppm is a "greatly increased partial pressure? As compared to 270 ppm in 1750? The pressure relationship is not defined solely by 400/270. I could use some education on this matter.

    Still, "Hocker begins his analysis by calculating the first derivative of the CO2 data", which doesn't make sense to me either. It seems more like he's hindcasting.

    I also looked at:

    https://skepticalscience.com/co2-coming-from-ocean.htm

    "Caveat: Land use and biomass changes certainly soak up a lot of CO2, some [of] it [is] simply regrowth of forests etc, but the point is that the increasing CO2 in the atmosphere clearly demonstrates that they do not soak up enough." [a small amount of editing for clarity added]

    Woah, in that, the same care in studying carbon sequestration by plant life has not been included in the calculations. My three acres is sequestering more carbon than either an equivalent area in Manhattan or the Sahara. Land based plant life must be included for the sake of accuracy.

  3. John Fornaro: It seems you have overlooked or misunderstood the mass balance evidence of humans being responsible for the rise in CO2. It's just algebra.

  4. John Fornaro @302:

    "400 ppm is a "greatly increased partial pressure? As compared to 270 ppm in 1750?"

    Importantly, the current CO2 concentration is 400 parts per million by volume, ie, ppmv - not parts per million by mass.  That hooks it into a number of important equivalencies.  Specifically:

    1)  pi/p = ni/n where pi is the partial pressure and p the total pressure, and ni the moles of the individual gas and n the total moles of the gas; and also

    2) Vx = Vtot x pi/p = Vtot = ni/n, where Vx is the partial volume and Vtot is the total volume of the gas.

    The second equation is why the ratio of molecules of CO2 to the total number of molecules in dry air is expressed as ppmv.

    It follows from the above that an increase of 42.9% in concentration will result in approximately a 42.9% increase in partial pressure, any slight variation being due to a variation in the total pressure.  That, as the article says, is a "greatly increased partial pressure".

    "Woah, in that, the same care in studying carbon sequestration by plant life has not been included in the calculations."

    The change in plant life is given fairly precisely by the change in C12/C13 ratio once adjustment is made for the contribution of fossil fuels to that change.  It is also given some what less precisely by the change in O2 levels, in that the total change in O2 level, ignoring ocean outgasing, is the original total, minus the amount combusted with fossil fuels, plus the extra amount from CO2 that has been photosynthesized, with the carbon being retained in plant matter.  Detailed local surveys (which have been conducted across a number of ecosystems) are necessary to determine in what form the retained carbon is stored (living plant tissue, or dead plant tissue, or soil organic carbon) but not to determine the total extra amount stored. 

  5. The following study published in Nature, April 5th 2017, shows a 31% ± 5% plant growth since the beginning of the industrial revolution. This would counter the claim that "sinks" are static and cannot process the comparatively tiny increase in carbon emissions due to human activity.

    Large historical growth in global terrestrial gross primary production http://dx.doi.org/10.1038/nature22030

    Large historical growth in global terrestrial gross primary production:  "Growth in terrestrial gross primary production (GPP)—the amount of carbon dioxide that is ‘fixed’ into organic material through the photosynthesis of land plants—may provide a negative feedback for climate change1, 2. It remains uncertain, however, to what extent biogeochemical processes can suppress global GPP growth3. As a consequence, modelling estimates of terrestrial carbon storage, and of feedbacks between the carbon cycle and climate, remain poorly constrained4. Here we present a global, measurement-based estimate of GPP growth during the twentieth century that is based on long-term atmospheric carbonyl sulfide (COS) records, derived from ice-core, firn and ambient air samples5. We interpret these records using a model that simulates changes in COS concentration according to changes in its sources and sinks—including a large sink that is related to GPP. We find that the observation-based COS record is most consistent with simulations of climate and the carbon cycle that assume large GPP growth during the twentieth century (31% ± 5% growth; mean ± 95% confidence interval). Although this COS analysis does not directly constrain models of future GPP growth, it does provide a global-scale benchmark for historical carbon-cycle simulations."

    Response:

    [DB] As others have noted, you will need to furnish a source citation for this claim:

    "This would counter the claim that "sinks" are static"

    Hotlinked DOI.  An openly accessible copy is here.

  6. Pattio,

    Can you provide a reference for your claim that someone says sinks are static?  I am underthe impression that most of the sinks and sources of carbon respond to changes in the environment around them.

    While you article is interesting, it is clear from the measured increase in CO2 in the atmosphere that natural sinks have not been able to absorb all the CO2 humans release.  That may change in the future although it is not clear if the sinks will increase or decrease.

  7. Pattio: as Michael says, please do provide a reference to support your claim that others hold the position that sinks are static.

    The sources that I am familar with (e.g., the IPCC) pretty clearly recognize that about half of what is emitted to the atmosphere (by burning fossil fuels) is abosrbed by the oceans and biosphere (the "sinks"), which directly contradicts two of the claims you made in your opening paragraph:

    1. ...that others claim the sinks are static (unsupported because others feel that sinks have increased to absorb half of what is emitted)
    2. ...that your argument counters the claim that the sinks cannot process the increase in emissions (they can't, as evidenced by the fact that they can only process half, with the other half still residing in the atmosphere).
  8. Pattio: The airborne fraction of CO2 has been fairly constant, despite the growth in the rate of anthropogenic CO2 emissions. Therefore the natural sinks are not static. That determination has been made by scientists who, therefore, do not in reality believe the sinks are static.

  9. Please reconcile your statement in the first paragraph, "Before the industrial revolution, the CO2 content in the air remained quite steady for thousands of years." with the graph in the article entitled "CO2 lags temperature - what does it mean?" Figure 1: Vostok ice core records for carbon dioxide concentration and temperature change.

    Figure 1's CO2 concentrations don't look quite steady for thousands of years at all. Not even close. Am I missing something?

    https://skepticalscience.com/images/Milankovitch_Cycles_400000.gif

  10. Danilushka @309, the most recent plateau in temperature and CO2 level shown in the graph of the Vostock ice core data (which is called the Holocene), has lasted over 10 thousand years.  Over that period, CO2 levels have increased from about 260 ppmv to about 280 ppmv just before the industrial revolution, ie, an average increase of 0.002 ppmv per annum.  Since the industrial revolution, CO2 concentrations have increased by 120 ppmv over approx 270 years, or 0.444 ppmv per year, or 222 times as fast.

    Needless to say, over 10 thousand years is "thousands of years".

  11. The graph in the "Further reading" section appears to be broken.

  12. Sadly, CAIT doesnt seem to supply anymore. Try here for what it looked like.

  13. Any rebuttles to this (which I believe attempts to refute this page)

    http://sacredgeometryinternational.com/ask-randall-response-to-remarks-posted-by-david-camacho-to-redemption-of-the-beast

  14. dkoli:

    It appears that the OP refutes your link without any support needed.  The simple fact that in 1850 CO2 was about 270 ppm and now it is about 410 ppm indicates that humans have significantly increased the concentration of CO2.  In your link they agree that the CO2 concentration has increased.

  15. (314) But he goes on to say "this does not mean that CO2 is driving climate change" and gives reasoning. 

    I have listened to Randall on JRE podcasts before and he seems quite legit, but Ive never seen him debated or debunked so I figure the people here may have good insight into how hes wrong (if hes wrong). 

  16. Dkoli . . . sorry, but Mr Randall Carlson is a very ordinary science-denier when it comes to climate.  Nothing intelligent or original.

    No new points from him, at all.  All his points are old stuff, debunked long ago.   Dkoli, pick any three of the points he raises, and then read through the relevant sections of SkepticalScience and you will see that he hasn't a leg to stand on.  Then pick another three, and you will find the same results.  And so on.

    Dkoli, you are wastiing your time reading any of the "Randall" commentary.  He clearly has a closed mind, and is years/decades out of date with his understanding of climate matters.  Very sad case . . . made even worse by his hubris (of the Dunning-Kruger type).

  17. Well he seems open minded to me. Between his work and that seen on Adapt 2030 it seems to me like the grand solar min, the dalton min, the magnetosphere and the galactic cross correlate with the earths climate far better than an tiny increase in a trace gas. But if me being open minded to that hypothesis makes me a closed minded shill perhaps this isn't the site for me. The comments seem very one sided. I don't feel this is the place for a truly unbiased debate. 

    Thankfully we'll know in a short time won't we. If 2024 is record colds we know CO2 is less important than cosmic rays. If it's hot again we know CO2 outweighs the suns  But thankfully it will be seled! 

    Response:

    [JH] Sloganeeing snipped. 

    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.

  18. What "seems" to you, would appear to be a reflection of your biases if you cant back it with evidence. Take Eclectic's advice. Pick what you think is his most compelling argument and check it against our rebuttals. Just stating your biases without any evidence to support is what is called "sloganeering" here. if you want to dispute the science, then put up the evidence. Make sure you understand what the science actually does say (read it from source or the IPCC summary), as opposed to how some denialist misrepresents it. Dealing with strawman arguements is tiresome.

  19. CO2 is .04% of the atmosphere, humans are 3.5% of that which comes out to be .0014% of CO2 is man made.  CO2 lags temperature change in ice core samples by 800 years.  Yet it is believed that man can emit a .0014% of CO2 for a mere 150 years and cause a 1.5+ degree change in climate temperature.  

    The weather cannot be predicted beyond several days with any accuracy, due to the complexity of the atmosphere. But we are told to believe that climate modeling can predictions 50+ years into the future is science fact.   

  20. lonegull @319,

    The atmosphere comprises 400ppm by volume of CO2 which is roughly 600ppm by weight. This is a small portion of the atmosphere but given the physical characteristics of CO2, it is significant enough.

    It isn't clear where you come by the 3.5% of atmospheric CO2 is man-made. The usual understanding is that perhaps 45% of atmospheric CO2 is there because of anthropogeing emissions. (That's 400ppm/275ppm.)

    Given the physical characteristics of CO2, that is probably enough to add +1.5ºC to global temperatures in 150 years. But as such levels of additional CO2 has not been in the atmosphere that long, it has only raise global temperatures by some +1.0ºC.

    Concerning the weather being unpredicatable, this is indeed so. Yet the weather has the characteristic of not shoot off to places it hasn't been before. For instance, summer is warmer than winter in the higher latitudes with winters generally getting progressively colder as the latitude increases. By similar considerations, it is possible to identify climatical norms. And when something like CO2 is increased by 45% in the atmosphere, the resulting warming can be identified withi those climatical norms.

    So the one thing not understood about your comment is the "humans are 3.5%" bit. Perhaps you would care to explain.

    (By the by. Is the 'gull' part of your pseudonym based on the noun or the verb?)

  21. If I understood your answer correctly, you said our 29 GT Co2 is small compared to the 750 GT exchanged each year, and that ours is about half absorbed. Question: 29 GT times 25 is 725 GT. It looks to me as if there was plenty of room for ALL of our CO2 to have been absorbed.

  22. chromedome49 @321,

    You appear to be asking a question by beginning a sentence "Question:" but this isn't followed by a question. So I will assume you are asking something like: 'Why, if anthropogenic emissions are but a small fraction of natural emissions (using the numbers in the OP, actually 3.7%); why then can't such a small extra amount be taken up and absorbed by the much larger natural mechanisms?'

    The problem with such a proposition is that the natural cycle was in balance prior to our emissions. Today, the reason the natural cycle is out-of-balance and takes more CO2  than it emits is simply because the atmospheric CO2 levels have gone up. Without such an increase, the balanced natural cycle would fail to take any of our emissions. But as there is now an extra 1,055Gt(CO2) in the atmosphere, there is extra space in the natural absorption part of the cycle for some of our CO2 to be absorbed in that cycle. While we continue to emit at increasing rates the proportion of our CO2 emissions absorbed by the natural cycle will continue to be large, roughly 50%. Were we to stop emitting, the natural cycle would continue absorbing extra CO2 and reducing the anthrpogenic burden in the atmosphere, initially quite quickly over a few decades, then more slowly in successive centuries until in a thousand years 75% or 80% of our emissions will have been drawn out of the atmosphere. After that, the process becomes so slow that it will take many tens of thousands of years to reduce the remainder to insignificance.

  23. @321 chromedome49

    You are correct. There is actually room for all emissions to be absorbed by natural systems. But of course we humans have significantly degraded that side of the carbon cycle as well. 

    Farming Claims Almost Half Earth's Land, New Maps Show

    Land Degradation: An overview

    So even though there is room, particularly in the soils, in reality agriculture has turned that sink potential into the second leading cause of AGW behind fossil fuels.

  24. RedBaron @323,

    Your assertion that there is "room for all emissions to be absorbed by natural systems" (by this meaning the biosphere) is a little off-topic here.

    However, a few facts (numbers sourced mainly from the Global Carbon Project).

    About one third of our CO2 emissions since 1750 have resulted from Land-Use-Change (or in simple terms cutting down trees). And as a result of these LUC emissions, the biosphere only became a net absorber of our emissions from the 1970s-on (when FF emissions became the 'bulk' of the total).

    Today (ie the last 40 years) the biosphere absorbs significantly more of our emissions than do the oceans. But when we manage to stop boosting atmospheric CO2 levels (hopefully soon), the oceans will become the major absorber, eventually taking the vast majority of our emissions and in doing so, reversing the biosphere absorption of today (and since 1990 when CO2 was ~350ppm).

    The absorption of CO2 on man-managed lands can be improved and the carbon then 'sequestrated' (ie out of reach of the natural carbon cycle) to somewhere safe (rather than relying on natural 'sequestration' processes). But without such 'sequestration,' added reabsorption relies on either reversing the LUC (so simplistically able to reverse that third of our emissions that came from LUC) or a continued presence of an elevated atmospheric CO2 level, which logically implies not "all emissions" can be absorbed by this route.

  25. @324 MA Rodger,

    "room" in this case refers to the size of the sink potential, not the size of the pool or the rate at which carbon moves from one pool to another.

    Clearly because this is a complex system the rate will vary quite a bit due to many factors, but the size of the sink is far more than large enough to handle all the excess carbon in the atmosphere easily. That would not even get soil carbon levels to pre-industrial, much less pre-agriculture.

    Keep in mind though, I have stated multiple times here with evidence that LUC as you depect here for example is about emissions and completely inadequate at resolving the whole stable soil carbon cycle including lost sequestration capacity. It's a labile or biomass state. ie short term carbon cycle and labile carbon pools. Apples and oranges.

    Because you are about oranges instead of apples I can see where you might think this is off topic. But instead of going off topic, go back on topic, and you'll see more clearly my point. I am not talking about LUC in the biomass and labile carbon pools, I am talking about saturation capacity in the long term stable carbon soil sink.

  26. I made an account just to post this comment. Nice work, but I have to raise question to the statement made on carbon emmisons being the highest the've been in 15-20 millions years. While I do agree humans have been doing their part to upset the balance, while I don't feel like doing the research, I'm fairly certain major volcanic eruptions and cosmic events such as Toba and the astroid that ended the Younger Dryas period would have launched more gas into the atmosphere. May be wrong, but we always overplay the power we have vs what Earth and space are capable of. 

    Response:

    [PS] Welcome to SkS. You should do your own research if that is what you believe. It requires a certain hubris to believe that you know more than scientists working their careers in this. For volcanoes, see here. For CO2 at Younger Dryas (asteroid theory is contentious), see here. If you are going to make claims, you must support them with evidence otherwise it just sloganeering. (see the comments policy).

  27. >humans add extra CO2 without removing any.

    But humans do remove co2. It's called farming.

  28. hedron, the crops resulting from farming quickly are consumed by people or animals, and if animals then those animals are consumed by people, and whatever is not consumed decays. The carbon taken up by those crops thereby quickly returns to the atmosphere, minus an inconsequential fraction that gets buried essentially forever. Note that most of what gets buried decomposes and releases carbon back into the atmosphere.

  29. @327 hedron,

    You said, "But humans do remove co2. It's called farming."

    It is true that some kinds of farming remove CO2 from the short carbon cycle, which does indeed offset some emissions. However, as an average, most farming is actually a net source, and those who do offset emissions a decided minority, especially when it comes to cropping.

    We could change that and many have recommended it.

    Why Farmers Are Ideally Positioned to Fight Climate Change

    But it is not the current reality we face today. Right now there just are not enough regenerative organic farmers to counterbalance even the industrial farmers, much less the rest of the industrial world's emissions.

  30. The point being is that it's a false statement.  The average is completely irrelevant.  I assume that that fact simply slipped the authors mind when he wrote that.  But now that, I assume, the author is aware of that error.  I don't know why a website that bases itself on science would leave a false statement up.

  31. Hedron,

    I wouldn't call it false. I would call it ambiguous. 

    We are adding to the short carbon cycle with fossil fuels and habitat biomass losses. We have also reduced the capacity for natural biological systems to mitigate CO2 levels by those same habitat losses with their resulting loss of ecosystem function.

    Yes there are some humans striving to do the opposite, but as noted above, in most countries that % is a very tiny decidedly inconsequential minority.

    We could change that. I am an advocate that we change that. Humans are just as capable of habitat restoration as they are for habitat degradation. Farming in particular does indeed have methods for every crop and food type that can sequester massive carbon in the soils of the world.[1]

    But the approximately <3% doing that sort of farming right now isn't enough to matter. It's like the exception that proves the rule right now.

  32. I wouldn't call it ambiguous.  I'd call it lying.  It's still not explained why a self-descibed scientific publication would knowingly publish a falsehood.  It seems to me, given the deflection tactics used to rebut my observation, that it was intended to deceive, which is the literal definition of a lie.

    Response:

    [DB]  You are welcome to your opinions.  When those opinions extend to personal attacks/ad hominems, they are unwelcome here (review the Comments Policy for details).  If you are of the opinion that a particular article or point within an article is erroneous, the burden of proof is incumbent on you to cite credible sources as to why the particular points are wrong and what a more accurate text would look like.

    Sloganeering/personal attacks snipped.

  33. Vacnol: volcanoes are like pimples: irrelevant...and that is exactly how the scientists in this field view the matter !

  34. '.. our output of 29 gigatons of CO2 is tiny compared to the 750 gigatons .. it adds up because the land and ocean cannot absorb all of the extra CO2. About 40% of this additional CO2 is absorbed.'

    That CO2 natural sources and sinks are on such a knife edge balance that an additional 4% created by man cannot be fully absorbed strikes me as being either an amazing coincidence, incorrect, or there is some other mechanism creating such a balance that is not described here. 

  35. Kiwironnie @334 , adding a new 30 thousand million tons of CO2 quickly and repetitively (= annually) would seem quite a lot, to many people !   With or without knife edges.

  36. So Eclectic you are describing a compounding, of 750 (in balance) then 30 + 30 + 30 ... and so on per annum. Consequently double the weight in 25 years, less what can be absorbed.  The next question(s) then is at what are the absorbtion feedback mechanisms (such as planetary greening), how quickly can they react and what is their ceiling capacity?

  37. Kiwironnie, for convenience we probably should revert to using GigatonsCarbon (GtC) rather than CO2 mass.  Particularly so, when discussing the biomass which is absorbing (very roughly!) 25% of the fossil CO2 emissions.

    You will find a vast amount of discussion of the topic of atmospheric residual CO2 emissions and of the oceanic absorption of CO2.

    Absorption of CO2 by rock weathering is far too slow to contribute to the short term (a century or two) picture.

    As you say, that leaves [excuse pun] the increase of plants as the third factor.  Can you think of another factor that would absorb or sequester additional carbon?

    Land-based plants are the predominant biomass; bacteria/ fungi/ animals are only a small contributor to biomass, relatively.  (Note that modern agriculture tends to reduce soil fungal mass.)

    Zaichun Zhu et al., 2016  estimates plant biomass in the region of 450~500 GtC . . . which we must compare with 10 Gtc of fossil carbon emissions as an annual output.

    I have not seen a quantification of the (satellite-observed) "greening of Earth".  Area of leaf (as leaf area index) has increased distinctly over the past 30+ years.  But what about plant biomass ~ which would seem beyond the satellites' capabiity?  Example case: rainforest clearing is presumably a carbon "negative" compared with the establishment of pastures or palm oil plantings, which have lower biomass.

    From all this, it would seem that we should not expect an exponential "absorption feedback" from plant biomass increase.  We will be fortunate if there is a linear biomass increase!  ( I haven't found the source, but I recall a recent report that the observed "rate of greening" is slowing down ~ so I don't know if that was a reliable observation, despite its plausability, and neither do I know the more important relation to actual biomass.)

    Ceiling capacity for plant biomass is a difficult question.  There was a huge plant biomass back in the Carboniferous era.  However, conditions are vastly different in the modern era, for plant biomass is greatly reduced by the presence of vertebrate herbivores nowadays (plus other human actions . . . including the food consumption by that "megafauna" called humans).

    And judging from the long-term upward trend of the Keeling Curve, we cannot expect that a planetary greening will be of major benefit in reducing the CO2 / Global Warming problem.

  38. The two strong facts here are:

    1/ CO2 concentrations are rising in the atmosphere and the observed increase in surface radiation is precisely as expected from the math.

    2/ The decrease in O2 and the changing isotopic concentration of CO2 in the atmosphere is consistant with the increase being from FF use.

  39. Thanks Eclectic, very much appreciate your taking the time to respond so fully and in such a straightforward manner.  Am not aware of any other obvious absorbtion mechanism.  Photosynthetic 'real estate' (leaf area) is surely more important than biomass. (Rain forest culling is bad news.) Got me seriously thinking!

    Also now need to be looking at relationship between CO2 concentrations and reflection of relevant parts of the spectrum (overlap with water vapour etc).

     

  40. Scaddenp, thanks. Are you aware of any ongoing monitoring of the ratio of human produced CO2 isotopes vs naturally occuring.   This seems like such a key figure that it is surprising perhaps that there aren't six monthly Internet broadcasts in large neon numbers!!  Clearly though sampling would somehow need to be representative, and I don't understand how that can be achieved.

  41. World Resources Institute "just produced an updated diagram explaining where the world’s greenhouse gas emissions come from and how they are used. This time we have both interactive and static versions."

  42. Gseattle:

    Here is a link to climate Myth 34.

    Response:

    [BL] Michael Sweet's comment is the result of an increasingly off-topic discussion on this thread:

    2020 SkS Weekly Climate Change & Global Warming News Roundup #35

    Hopefully discussion will continue here, but readers may want to read the other thread for context.

  43. According to figure 1, "The Global Carbon Cycle", vegetation, land and the ocean absorb more carbon than they produce, 17 gigatons more. Where those extra tons come from? They have to come from somewhere, or someone. The answer is fossil fuel burning and land use. Nature is not seletive when it comes to carbon, it will absorb whatever is available. And by the way, part of the 29 gigatons produced by human actions, are absorbed as result of other human actions, technologies and materials. So the figure is misleading because the net result is not 29.

  44. High-Resolution Temperature Variability Reconstructed from Black Pine Tree Ring Densities in Southern Spain This article received in June/2020, revised, accepted and published in July/2020, shows that temperatures are declining.

  45. Luiz @344 , the Spanish regional study you have mentioned, is stating that the temperatures were cooler during 1600 - 1800  and have been warmer since 1800 (approximate date).

    Why do you mention temperatures declining?  Please explain.

  46. Luiz @ 343:

    The 29Gt is misleading? No, it is not. It is not a net flow. None of the arrows in figure 1 represent net flows. That's why there are two arrows in two directions between atmosphere and land, and atmosphere and ocean. One arrow for one flux in one direction.

    There is no flow from atmosphere to fossil fuel, so there is no arrow. Any transfer from atmosphere to vegetation, etc on land is contained in the middle arrow (450 Gt). The "land use" part of the left-most 29 Gt arrow is only that portion of anthropogenic activity that causes carbon flow into the atmosphere.

    There is precious little that humans have been doing that removes carbon from the atmosphere, unless you want to claim credit for crop growth, etc., that largely repsesent a replacement of natural systems, not an addition.

    There are agricultural practices that can potentially increase soil carbon, etc., but on a global scale they are a drop in the bucket at this time. Agricultural practices have tended historically to lead to increased atmospheric CO2.

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