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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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Climate Hustle

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).


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Comments 301 to 316 out of 316:

  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:

    "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:

    "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

    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:

    "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?

  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)

  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! 


    [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?)

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