Arguments
How do human CO2 emissions compare to natural CO2 emissions?
What the science says...
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Basic
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Intermediate
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The natural cycle adds and removes CO2 to keep a balance; humans add extra CO2 without removing any. |
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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)
At a glance
Have you heard of Earth's carbon cycle? Not everyone has, but it's one of the most important features of our planet. It involves the movement of carbon through life, the air, the oceans, soils and rocks. The carbon cycle is constant, eternal and everywhere. It's also a vital temperature control-mechanism.
There are two key components to the carbon cycle, a fast part and a slow part. The fast carbon cycle involves the seasonal movement of carbon through the air, life and shallow waters. A significant amount of carbon dioxide is exchanged between the atmosphere and oceans every year, but the fast carbon cycle's most important participants are plants. Many plants take in carbon dioxide for photosynthesis in the growing season then return the CO2 back to the atmosphere during the winter, when foliage dies and decays.
As a consequence of the role of plants, a very noticeable feature of the fast carbon cycle is that it causes carbon dioxide levels to fluctuate in a regular, seasonal pattern. It's like a heartbeat, the pulse of the Northern Hemisphere's growing season. That's where more of Earth's land surface is situated. In the Northern Hemisphere winter, many plants are either dead or dormant and carbon dioxide levels rise. The reverse happens in the spring and early summer when the growing season is at its height.
In this way, despite the vast amounts of carbon involved, a kind of seasonal balance is preserved. Those seasonal plant-based peaks and troughs and air-water exchanges cancel each other out. Well, that used to be the case. Due to that seasonal balance, annual changes in carbon dioxide levels form regular, symmetric wobbles on an upward slope. The upward slope represents our addition of carbon dioxide to the atmosphere through fossil fuel burning.
Fossil fuels are geological carbon reservoirs. As such, they are part of the slow carbon cycle. The slow carbon cycle takes place over geological time-scales so normally it's not noticeable on a day to day basis. In the slow carbon cycle, carbon is released by geological processes such as volcanism. It is also locked up long-term in reservoirs like the oceans, limestone, coal, oil or gas. For example, the "37,400 billion tons of 'suspended' carbon" referred to in the myth at the top of this page is in fact dissolved inorganic carbon in the deep oceans.
Globally, the mixing of the deep ocean waters and those nearer the surface is a slow business. It takes place over many thousands of years. As a consequence, 75% of all carbon attributable to the emissions of the industrial age remains in the upper 1,000 m of the oceans. It has not had time to mix yet.
Fluctuations in Earth's slow carbon cycle are the regulating mechanism of the greenhouse effect. The slow carbon cycle therefore acts as a planetary thermostat, a control-knob that regulates global temperatures over millions of years.
Now, imagine the following scenario. You come across an unfamiliar item of machinery that performs a vital role, for example life support in a hospital. It has a complicated control panel of knobs and dials. Do you think it is a good idea to start randomly turning the knobs this way and that, to see what happens? No. Yet that is precisely what we are doing by burning Earth's fossil fuel reserves. We are tinkering with the controls of Earth's slow carbon cycle, mostly without knowing what the knobs do - and that is despite over a century of science informing us precisely what will happen.
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
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 a range of natural processes, and absorbed by others. The carbon cycle is the cover-all term for these processes. It has both fast and slow components.
In the fast carbon cycle, natural land and ocean carbon remains roughly in balance and has done so for a long time. We know this because we can measure historic levels of CO2 in the atmosphere both directly, in ice cores and indirectly, through proxies. It's a seasonal response to things like plant growth and decay.
In stark contrast to the fast carbon cycle, the slow version operates over geological time-scales. It has affected carbon dioxide levels and therefore temperatures throughout Earth's history. The reason why the slow carbon cycle is so important is because many of the processes that lead to long-term changes in carbon dioxide levels are geological in nature. They take place over very long periods and do so on an erratic basis. The evolution of a species that has deliberately disturbed the slow carbon cycle is another such erratic event.
Annually, up to a few hundred million tonnes of carbon pass through the slow carbon cycle, due to natural processes such as volcanicity. That's small compared to the fast carbon cycle, through which some 600 billion tonnes of CO2 pass to-and-fro annually (fig. 1). However, remember that the fast carbon cycle is a give-and-take seasonal process. The slow carbon cycle instead runs in one direction or another over periods typically measured in millions of years.
Fig. 1: Schematic representation of the overall perturbation of the global carbon cycle caused by anthropogenic activities averaged globally for the decade 2012–2021. See legends for the corresponding arrows and units. The uncertainty in the atmospheric CO2 growth rate is very small (±0.02 GtC yr−1) and is neglected for the figure. The anthropogenic perturbation occurs on top of an active carbon cycle, with fluxes and stocks represented in the background. Adapted from Friedlingstein et al. 2022.
Through a series of chemical and geological processes, carbon typically takes millions of years to move between rocks, soil, ocean, and atmosphere in the slow carbon cycle. Because of these geological time-scales, however, the overall amount of carbon involved is colossal. Now consider what happens when more CO2 is released from the slow carbon cycle – by digging up, extracting and burning carbon from one of its long-term reservoirs, the fossil fuels. Although our emissions of 44.25 billion tons of CO2 (in 2019 - source: IPCC AR6 Working Group 3 Technical Summary 2022) is less than the 600 billion tons moving through the fast carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra emitted CO2: about 40% of it remains free.
Human CO2 emissions therefore upset the natural balance of the carbon cycle. Man-made CO2 in the atmosphere has increased by 50% since the pre-industrial era, creating an artificial forcing of global temperatures which is warming the planet. While fossil-fuel derived CO2 is a small component of the global carbon cycle, the extra CO2 is cumulative because natural carbon exchange cannot absorb all the additional CO2. As a consequence of those emissions, atmospheric CO2 has accumulated to its highest level in as much as 15 to 20 million years (Tripati et al. 2009). This is what happens when the slow carbon cycle gets disturbed.
This look at the slow carbon cycle is by necessity brief, but the key take-home is that we have deeply disturbed it through breaking into one of its important carbon reservoirs. We've additionally clobbered limestones for cement production, too. In doing these things, we have awoken a sleeping giant. What must be done to persuade us that it needs to be put back to sleep?
Cartoon summary to counter the myth
This Cranky Uncle cartoon depicts the "Cherry picking” fallacy for which the climate myth "Human CO2 emissions are small" is a prime example. It involves carefully selecting data that appear to confirm one position while ignoring other data that contradicts that position. Source: Cranky Uncle vs. Climate Change by John Cook. Please note that this cartoon is illustrative in nature and that the numbers shown are a few years old.
Last updated on 17 September 2023 by John Mason. View Archives
Uhhhh.... Thanks for burying me in reading material! :)
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.
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.
John Fornaro @302:
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".
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.
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."
[DB] As others have noted, you will need to furnish a source citation for this claim:
Hotlinked DOI. An openly accessible copy is here.
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.
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:
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.
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
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".
The graph in the "Further reading" section appears to be broken.
Sadly, CAIT doesnt seem to supply anymore. Try here for what it looked like.
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
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.
(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).
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).
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!
[JH] Sloganeeing snipped.
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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.
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.
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?)
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.
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.
@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.
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.
@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.