I stumbled upon the following paper

Skrable et al. (2022)

The specific activity of ¹⁴C in the atmosphere gets reduced by a dilution effect when fossil CO₂, which is devoid of ¹⁴C, enters the atmosphere. We have used the results of this effect to quantify the two components. All results covering the period from 1750 through 2018 are listed in a table and plotted in figures. These results negate claims that the increase in C(t) since 1800 has been dominated by the increase of the anthropogenic fossil component. We determined that in 2018, atmospheric anthropogenic fossil CO₂ represented 23% of the total emissions since 1750 with the remaining 77% in the exchange reservoirs. Our results show that the percentage of the total CO₂ due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming.

The paper was published in February 2022. I have not heard about it till today. If true the consequences of this discovery are far reaching. Is it true?

  • 25
    Your first hint that this "paper" is junk science is that it was published in a journal that has nothing to do with atmospheric science.
    – Ian Kemp
    Commented Jun 12, 2023 at 16:38
  • 5
    @IanKemp: That line of reasoning isn't really wrong, but it is dangerous. It's one of those things that if somebody wanting to mess you up knows you hold it too strongly they can build a strategy to mess you up around it.
    – Joshua
    Commented Jun 13, 2023 at 14:12
  • 5
    The link you provide in the Q leads to a publication site that helpfully displays "Readers Of this Article Also Read" - there you can find many of the brutal takedowns of that article
    – bukwyrm
    Commented Jun 14, 2023 at 7:54

3 Answers 3


The paper is deeply flawed

There are a number of problems with this paper and many have pointed them out.

Schwartz et al, sum it up.

  1. Erroneous history of ¹⁴CO₂ in air that is at odds with direct observations
  2. Neglect of the consequences of the large input of ¹⁴CO₂ into the atmosphere from nuclear weapons tests in the 1950s and 1960s
  3. Failure to account for isotope exchanges between the atmosphere, ocean, and land biosphere that occur independent of net change in amount of atmospheric CO₂;
  4. Neglect of multiple independent lines of evidence that CO₂ emitted from fossil-fuel combustion is the principal contributor to the increase of atmospheric CO₂ over the industrial era.

They call for the paper to be retracted.

On the basis of the several arguments presented here, we conclude that the paper of Skrable et al. (2022) should be retracted in its entirety.

The authors responded to Schwartz et al and Andrews and Tan. While they acknowledge some errors, they fail to directly address many of the issues below, or claim they are not relevant.

Wrong journal

Health Physics is a journal about radiation science, not atmospheric science.

Health Physics, first published in 1958, provides the latest research to a wide variety of radiation safety professionals including health physicists, nuclear chemists, medical physicists, and radiation safety officers with interests in nuclear and radiation science.

Many have pointed out this could lead to problems with peer-review. Andrews & Tans...

Health Physics ventured outside its area of expertise when it accepted the paper by Ken Skrable, George Chabot, and Clayton French on atmospheric ¹⁴C... [Health Physics editors] should have included a qualified reviewer from the radiocarbon or atmospheric science community. They clearly did not because any reviewer with previous knowledge of atmospheric ¹⁴C would have found the fatal errors cited below. An extensive peer-reviewed literature exists on studying the carbon cycle with ¹⁴C, but next to none of it is cited by the authors.

The editor-in-chief of Health Physics did respond justifying their acceptance of the paper, but does not address any of the specific concerns, nor the flaw.

No collaboration with atmospheric scientists or radiocarbon specialists

Musolino further points out the lack of reaching out to atmospheric scientists who might have provided better data and helped point out fundamental flaws.

[the authors of the paper] did not appear to attempt a direct engagement with the primary scientific community of atmospheric scientists to whom they posed a widely divergent and controversial opinion. The draft was presented for peer review to experts in health physics but not to scientists who are expert in CO₂ emissions and who study CO₂ and ¹⁴C in the atmosphere.

Their value for ¹⁴CO₂ at 1750 is too high.

Both Andrews and Tam and Schwartz et al point out that the model used in the paper is at odds with existing observations. In the graph below, the smooth brown curve is the model used in the paper, the big spike is multiple papers based on actual observations, and the light blue line is a model if there was no nuclear testing.

enter image description here

The first issue is the paper uses a value 20% too high for its 1750 baseline; in the graph above the paper's line starts at 16 rather than everyone else starting at 14. Andrews and Tans explain...

Skrable et al.’s “educated guess” of 16.33 dpm (gC)−1 for the specific activity of ¹⁴C in the 1750 atmosphere is not bad for a guess, but it is 20% too high. It corresponds to a ∆¹⁴C of 200‰ (parts per thousand, see below). Except during the era of atmospheric nuclear testing, such a value has not been seen for over 10,000 years (Cheng et al. 2018). A 20% specific activity error in ¹⁴C converts to a dating error of over 1,800 years. Carbon-14 (¹⁴C) dating is much better than that because the atmosphere’s specific activity during historical times is accurately known. It is meticulously calibrated from materials of known age such as tree rings. There was no need to guess its starting point in 1750 or its trajectory since. There was no need for the authors to limit themselves to only the recent data from Niwot Ridge.

Skrable et al replied they knew their value might be too high, and there are errors, but believe their methodology has value.

We also recognized the likelihood of the excessive value of the specific activity, S(0), of ¹⁴C in 1750, and noted our rationale for maintaining a high value. We realize that the values we have determined for the anthropogenic fossil component, CF(t), and non-fossil component, CNF(t), may include some errors, but we do believe there is value to our methodology.

They fail to account for the effects of nuclear bomb testing

There's a huge spike in observed ¹⁴CO₂ which the paper completely ignores. This spike is due to nuclear bomb testing. The paper claims they can ignore this effect citing [checks notes] Wikipedia. :facepalm:

A Wikipedia link for ¹⁴C describes the increase in the concentration of ¹⁴CO₂ in the atmosphere that resulted from high altitude nuclear bomb tests, circa 1955–1963. Based on the figure in the Wikipedia link, ¹⁴CO₂ from the atmospheric bomb tests during this period would be significant in 1955 to about 2005.

As can be seen in the graph above, when nuclear testing is omitted from modelling the result diverges significantly from observations. They misinterpreted the data, nuclear testing remains significant and cannot be omitted.

Schwartz et al explains...

The contribution of bomb ¹⁴CO₂ to atmospheric ¹⁴CO₂ was explicitly examined in a modeling study (Graven et al. 2020) in which the source of bomb ¹⁴CO₂ was omitted, shown also in Fig. 1; the signal of bomb ¹⁴CO₂ is given by the difference between the measurements and the model in the absence of the bomb ¹⁴CO₂ source. This difference shows that residual bomb ¹⁴CO₂ cannot be dismissed over the years 2004–2012 used by Skrable et al. in their analysis. Failure to include this residual bomb ¹⁴CO₂ in their apportionment of the increase of the increase of atmospheric CO₂ to fossil fuel and non-fossil fuel sources completely vitiates this apportionment.

Skrable et al replied...

Exchange among the reservoirs was inconsequential for our work, except for the possible residual effects of bomb ¹⁴CO₂, which we admittedly assumed were not significant. Information provided by Schwartz et al. and others indicate that there likely was current feedback of bomb ¹⁴CO₂ from reservoirs to the atmosphere, and the claim is being made that this invalidated our findings.

Failure to account for isotope exchanges between the atmosphere, ocean, and land biosphere

Schwartz et al list a host of issues with their assumptions about how carbon flows between various parts of the Earth.

The Skrable et al. (2022) framework assumes that carbon in the environment can be divided into two categories: (1) preindustrial carbon, which is taken as uniform in the ¹⁴C/¹²C ratio, and (2) fossil carbon, which is devoid of radiocarbon. They further assume that these categories maintain their identities as carbon is exchanged between the atmosphere, ocean, and land biosphere. In fact, the flows of different carbon isotopes are not connected as assumed by Skrable et al.... Thus, importantly here, ¹⁴C can be exchanged between the atmosphere and ocean with no net exchange of carbon as a whole. An important consequence of this independence is that impact of emissions of fossil-fuel CO2 on the ¹⁴C/¹²C ratio of atmospheric CO₂ is much greater than the impact of these emissions on atmospheric CO₂ as a whole... These critical aspects were not considered by Skrable et al., causing their calculations to underestimate the input of fossil-fuel CO₂.

Skrable et al responded...

While we do recognize the reality of exchange of CO2 among the atmosphere and reservoirs, it was not our intent to attempt to develop a model that considered these, nor do we believe this was necessary for our purposes.

Incorrectly attributes the ocean as a source of CO₂

The paper claims the world's oceans have been a net source of CO₂ since 1950...

This DCNF(t) value of 31.07 ppm in 1950 results from the annual redistribution of CO₂ among its reservoirs, primarily a net release of CO₂ from the oceans due to increases in temperatures from solar insolation in 1950 and afterwards.

Schwartz et al points out this is incorrect, the oceans absorb CO₂.

From the well quantified rates at which CO₂ is building up in the atmosphere and rates of CO₂ release from fossil-fuel burning, it is clear that around 50% of the emitted carbon remains in the atmosphere, with the balance absorbed by other reservoirs, of which the oceans and the land biosphere are the most important. The ocean and land biosphere are thus together acting as a major sink not a source of CO₂. The excess CO₂ in the ocean is now also well measured, and the uptake rate is consistent with a wide body of other evidence on rates of mixing and carbon chemical properties of seawater. This understanding of the rate at which excess carbon is being redistributed into the ocean and land is independently supported by measurements of trends in atmospheric O₂ and ¹³C/¹²C ratio in addition to radiocarbon

Neglect of multiple independent lines of evidence

Schwartz et al point out that radiocarbon is not the sole piece of information about the present increase of atmospheric CO₂.

Finally, the present understanding of the controls on atmospheric CO₂ buildup importantly rests on many convergent strands of evidence in addition to radiocarbon. From the well quantified rates at which CO₂ is building up in the atmosphere and rates of CO₂ release from fossil-fuel burning, it is clear that around 50% of the emitted carbon remains in the atmosphere...

The paper cannot draw such sweeping conclusions about climate change without also addressing other evidence to the contrary.

  • 20
    @CuriousIndeed The first argument of their rebuttal says 'No specific critique of our assumptions is given in the letter.' If I look at the letter Schwern posted it is a long list of critiques of their assumptions. A lot of them are just plain wrong and the letter says so.
    – quarague
    Commented Jun 12, 2023 at 6:41
  • 2
    @quarague It's worth noting that the answer quotes 4 different critical letters, and that link is a response to only one of them. There are responses to each, and a couple do claim specific misunderstandings by their critics, although the main defence seems to be of "the value of our methodology", rather than their exact figures and conclusions.
    – IMSoP
    Commented Jun 12, 2023 at 6:54
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    "Based on the figure in the Wikipedia link" "Wikipedia is incorrect" It appears that Wikipedia is not incorrect here, the paper authors have eyeballed from a figure that the levels would have returned to original 1955 level by 2005 - completely ignoring that CO2 emissions would have otherwise caused an even lower level. Wikipedia doesn't appear to make any claim about nuclear testing effects to stop mattering, either in current or past versions of the article.
    – jpa
    Commented Jun 12, 2023 at 9:20
  • 2
    @jpa What would you suggest changing?
    – Schwern
    Commented Jun 12, 2023 at 17:26
  • 22
    @Schwern I would suggest replacing "Wikipedia is incorrect" to "This is an misinterpretation of the graph on Wikipedia".
    – jpa
    Commented Jun 12, 2023 at 17:43

Skrable et al (2022) does not claim to show that global warming is not at all due to fossil fuels. It shows that part of the measured increases in CO₂ (numbers include the 12% of total CO₂ highlighted in the question) are likely to be attributable to this source and correlate with an increase in atmospheric CO₂.

The paper is very specific : it looks at "The assumption that the increase in CO₂ since 1800 is dominated by or equal to the increase in the anthropogenic component" (Conclusion 10). Relevant words, as well as "fossil" and "anthropogenic" include "dominated" and "equal". Even though it restricts the conclusions to man made sources involving fossil fuels, it is seeking to show that not all ("equal"), and possibly less than 50% ("dominated"), of the observed effects are due to that particular human activity.

In showing that amounts are not "dominated" by anthropogenic fossil fuel effects, Skrable et al (2022) shows variations in effects (Conclusion 5 lists 23% of total CO₂ emissions) which look like they could be significant.

The paper does not do what the headline question suggests - instead it raises arguments about how much would be significant and what other factors could have an effect on CO₂ levels and global warming. Again, it uses words like "primarily" (Conclusion 9). Meanwhile, other authors have published comments on the paper. Schwartz, Keeling, Meijer and Turnbull, writing for the University of Groningen, have produced comments which cover four main points of contention and use words like "erroneous", "neglect", and "failure". They end with "On the basis of the several arguments presented here, we conclude that the paper of Skrable et al. (2022) should be retracted in its entirety."

  • 14
    -1. Right in the abstract they say "CO2 due to the use of fossil fuels [is] much too low to be the cause of global warming."
    – LShaver
    Commented Jun 11, 2023 at 21:11
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    @LShaver - Again, they're saying "the cause". Looking for one thing and ignoring other contributors. It's quite a clever distraction technique - if you're standing in 1.5m of water and along comes 0.5m, that 0.5m won't be "the cause" or the dominant factor. But it'll have an effect. That said, I'll tweak the first paragraph. Commented Jun 11, 2023 at 21:18
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    A general rule of thumb for "why did a paper get published in a weird, small, out of the way journal that's not really related to the topic" is that they needed one specific editor and to be away from normal peer review. I dunno if it's a valid result but I would not call this peer reviewed research as a result.
    – CJR
    Commented Jun 11, 2023 at 21:52
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    I am reminded of a question on Earth Sciences a couple of years back from someone who'd done some data analysis and claimed to have an interesting result in oceanography and wondered what journals he might submit it to -- since he was unfamiliar with the area of research and the journals that covered it. Commented Jun 12, 2023 at 15:30
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    I appreciate the edit, but the language in the paper is still full of "weasel words", and the intent is still clearly to deny the well-established role of fossil fuels in climate change.
    – LShaver
    Commented Jun 13, 2023 at 15:03

The paper, as the current debate, neglects the contribution by water vapour

The paper has different flaws as noted by another answer. But the most important flaw is the same flaw that affects the entire current debate. It neglects the contribution to global warming by water vapour. As many papers used as a source for the answers to this question show, CO2 is not the only greenhouse gas. A mathematical model that excludes the factors that give the highest contribution can only give wrong results.

About the role of water vapour:

I see some comments to this answer that downplay the role of water vapour. I would like to point out an evidence that took little notice.

During the 19th century the global temperatures went up. The amount of fossil fuels burned increased in that period, but not so much as it did at the end of the 20th century. The problem was that not only the steam engines of the era were inefficient, but they by their own nature they produced a lot more steam than current technologies.

In the first half of the 20th century while diesel engines and power from hydroelectric sources replaced a big chunk of the obsolete steam engines global temperatures went down. Only during the '70s, when the volume of fossil fuels burned became so high that they produced enormous amounts of CO2 and water vapour, the temperature begun to rise with steep curve.

  • 7
    This isn't an answer, rather its a separate claim. But while water vapour is certainly a big factor stopping the earth from being 33 C colder, the amount in the atmosphere hasn't (AFAIK) changed significantly over the last century. The increase in the greenhouse effect over the last 100 years is therefore not down to water. Flagged. Commented Jun 12, 2023 at 15:58
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    This is irrelevant. Water vapour might be the most important greenhouse gas, but the atmosphere is mostly saturated with it (which can be seen when it rains). Water acts as an amplifier - all else being equal, a given increase in CO2 will increase the temperature a bit, which increases the water content a bit, which in turn increases the temperature a little, until a new equilibrium is found. The origin of the overall change is still the increase in long-living greenhouse gases like CO2 and methane.
    – Chieron
    Commented Jun 12, 2023 at 15:58
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    This is just not right. All climate models account for water vapor.
    – Mark
    Commented Jun 12, 2023 at 17:47
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    @userFromEU2 that rate is dwarfed by natural evaporation. It doesn't matter at all. The tropospheric concentration of water vapour is multiple percents, not ppm. Even, if we increased that by 1ppm / day, the difference would not be noticeable, because it condenses after a few days, compared to the equivalent increase in CO2, which accumulates. You seem to be intent on just muddling the waters, no point discussing this further.
    – Chieron
    Commented Jun 12, 2023 at 17:55
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    Just for other people to judge the daftness of your answer (later edits): the cooling in the first half of the 20th century was due to sulfur oxide emissions and similar pollutants. Not, because there would be less water vapour produced.
    – Chieron
    Commented Jun 12, 2023 at 17:58

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