Holocene Antarctic CO2 Variability or Lack Of

Guest Post by Renee Hannon


This post examines CO2 ice core measurements from Antarctica during the Holocene Epoch. The key CO2 dataset for paleoclimate studies is the EPICA Dome C (EDC) data also known as Dome Charlie or Dome Concordia. Dome C is located on the eastern Antarctic Plateau, one of the coldest places on Earth and our planet’s largest frozen desert. The average air temperature is -54.5 degrees C with little to no precipitation throughout the year. CO2 measurements from the unique conditions at Dome C are compared to other Antarctic ice cores.

CO2 Parallels Antarctic Temperature Trends

Antarctic ice core CO2 data is readily available and has been studied extensively (Bauska, 2015, Ahn, 2012, Siegenthaler, 2005 Marcott, 2014 and Rubino, 2019). Bereiter, 2014, established a CO2 composite that is considered the gold standard and used by IPCC AR6 (although AR6 incorrectly references Bereiter as 2015). This CO2 composite shown in Figure 1 is based on three ice cores over the Holocene: Law Dome, EPICA Dome C and WAIS. Most of the Holocene (2,000 to 11,000 years BP) is covered by Dome C. The Late Holocene (0 to 2000 years BP) is covered by Law Dome and the Early Holocene (>11,000 years) is covered by WAIS which is shifted downward by 4 ppm to match Dome C (Bereiter, 2014).

Also shown on Figure 1 are Dome C proxy temperature anomalies derived from oxygen isotopes. The CO2 data correlates well with Antarctic ice core temperature anomalies as noted by the authors above.

Figure 1: A composite of Antarctic ice core CO2 data over the Holocene after Bereiter, 2014. EPICA Dome C proxy temperature anomaly shown in black from Jouzel, 2007 with a 100-year smoothing filter. Data references for CO2 shown on plot.

Antarctic temperature is not representative of global temperatures or Arctic temperatures. According to Ahn, 2012, Antarctic data represents a specific set of processes in the climate system such as the transport of heat to and from the Southern Hemisphere via oceanic and atmospheric circulation. Local southern insolation also plays a role (WAIS members, 2013). Although Antarctic temperatures are unique to the Southern Hemisphere, CO2 data from Antarctica is considered representative of past global CO2.

What is surprising is that CO2 from Dome C is used as a key dataset for most of the Holocene and past 11,000 years. The Dome C ice core site with the low snow accumulation rates and extremely low temperatures resulting in one of the lowest temporal resolution records.

Antarctic CO2 Records Show Scatter

All public Antarctic CO2 datasets were plotted in Figure 2 to see if higher resolution CO2 data exists during the Holocene. CO2 was measured using the dry extraction technique that minimizes ice core melt and potential chemical reactions. Surprisingly, there is quite a bit of scatter between the different Antarctic datasets. The maximum is nearly 25 ppm and the average is 7 ppm. The largest amount of scatter appears at the end of deglaciation and on the shoulder of the Early Holocene interglacial from 10,500 to 11,500 years BP.

Ahn, 2004, describes key Holocene CO2 trends based on Siple and Taylor Dome data. After the Younger Dryas (YD) event, CO2 rose during the deglaciation reaching up to 284 ppm at the beginning of the Holocene (11,500 years BP). During the mid-Holocene, CO2 concentrations decrease to a local minimum of 260 ppm around 8,000 years BP and then increase to 285 ppm in the late Holocene.

Figure 2: Different Antarctic ice core datasets compiled over the Holocene. Data references shown on graph.

The past 2000 years is documented by detailed sampling done in studies by Ahn, 2012, and Rubino, 2019 and others. In summary, CO2 data show a small bump up to 287 ppm during the Medieval Warm Period (MWP) around 800 BP (1150 AD), a decrease of CO2 during the Little Ice Age (LIA) to almost 270 ppm and the recent modern rapid rise. Ahn, 2014, also conducted a detailed sampling program using Siple Dome over the 8000-year CO2 Antarctic minimum in pursuit of the distinct 8,200-year cooling event that is observed in both Greenland ice core oxygen isotope and methane records. This rapid decrease is absent in Antarctic methane and oxygen isotope data, and instead shows a more gradual decrease labeled the Antarctic CO2 minimum in Figure 2. The Antarctic temperature and CO2 minimum are likely associated with the Arctic 8,200-year event and not coincident.

The CO2 Composite Displays Muted Values

How does the Antarctic global CO2 composite compare to other Antarctic CO2 ice core data? Figure 3 shows the “gold standard” Antarctic CO2 composite highlighted by the red line along with all other Antarctic CO2 records represented by dots. The widely used CO2 composite for the Holocene underrepresents CO2 and has lower CO2 readings than other Antarctic datasets by 2 to 20 ppm.

Vostok is also highlighted by an orange line as it is the other CO2 dataset frequently used for past paleoclimate interglacial comparisons. The Vostok CO2 data is even more muted but does capture long-term underlying trends. The last data point is quite interesting around 2500 years BP, which is the highest Vostok reading of 285 ppm.

Figure 3: Antarctic datasets compared to the Antarctic CO2 composite (red line). Vostok CO2 data highlighted in orange. Note color coding of high resolution in blues and greens, and lower resolution in red, orange and yellows. Dome Fuji wet extraction was added.

Byrd, Siple Dome, and WAIS all show elevated CO2 variations in the early Holocene with differences up to 20 ppm higher than the CO2 composite from 11,500 to 10,500 years BP. CO2 elevated levels are 10 ppm higher than the composite until the CO2 minimum around 8000 years BP. From 8000 years until about 2000 years BP, the scatter is minimal and less than 5 ppm. Increasing differences begin to occur again during the past 2000 years.

Ahn, 2004, also noted similar intervals where the CO2 concentrations in Siple Dome ice are higher than in the Vostok, Taylor Dome and Dome C cores. Multiple causes for the discrepancies are discussed ranging from age scale uncertainty, chemical reactions due to carbonates and organic material, melt layers and fractures. Ahn concluded the cause of these elevated concentrations is not known with certainty.

Figure 3 shows elevated CO2 as the climate transitioned out of the cold Younger-Dryas and this shoulder may represent a period of climate instability which results in more scatter in the Antarctic ice core data. These unstable CO2 conditions lasted for about 1000 years. Relatively stable CO2 climatic conditions occur after the CO2 minimum around 8000 years BP where CO2 scatter between ice cores is minimal. The scatter in CO2 over the past 1000 years suggests a return to less stable climate conditions.

Dome Fiju wet extraction CO2 data points from Kawamura, 2007 are added to Figure 3. They follow general trends but also show higher CO2 by up to 10 ppm, mostly during the early Holocene shoulder excursion and more recently during the RWP and MWP. Kawamura found the higher CO2 concentrations are not related to Ca2+ concentrations which are the indicator for carbonate concentration and potential chemical reaction. He suggested the dry extraction method might not always be suitable for analyzing CO2 concentrations of ice samples containing clathrate hydrates. He also states the wet extracted CO2 data should be regarded as an upper limit of estimation of atmospheric CO2 in Antarctic cores instead of completely ignoring the data.

Temporal Resolution Matters

There are two very different processes that impact CO2 data resolution. One is related to gas smoothing during snow densification and the other is simply sample spacing. There does not appear to be a section in the newly released IPCC AR6 that discusses either of these data resolution issues. Although I have not yet read all 3,949 pages of the document.

Gas smoothing due to the firn to snow transition is site dependent and related to snow accumulation and temperature. Low snow accumulation sites include Dome C and Vostok. High snow accumulation sites include Law Dome, Siple Dome, and WAIS. As atmospheric CO2 passes from firn to ice, it is altered due to gas mixing processes (Ahn, 2012; Rubino, 2019). The gas is younger than the ice age when it is trapped in the bubbles, so scientists calculate an ice-gas age delta. This age delta is very large in low accumulation sites such as in Dome C and Vostok with the delta exceeding thousands of years as shown in Table 1.

Vertical gas diffusion and gradual bubble close-off during the transition from firn to ice also result in gas that is mixed over multiple years. A gas age width or smoothing is calculated or modeled. Frequently, the gas width is estimated to be on the order of 10% of the delta age value. Low accumulation sites in East Antarctic such as Dome C and Vostok show that gas is averaged or smoothed over hundreds of years. This smoothing effect removes high frequency variations from the ice core record.

Table 1: Antarctic ice core site accumulation rates and temperature properties. Numbers in italics use the assumption of 10% of the ice gas age delta for gas width.

Higher snow accumulation sites Siple Dome, Byrd, WAIS and Law Dome have the smallest ice-gas delta and the highest resolution with smoothing over tens of years. These ice core records show higher CO2 variability in the early Holocene and large deviations from the CO2 composite. Unfortunately, CO2 from Law Dome is only measured over the past 2000 years.

Dome C and Vostok have the lowest temporal resolution. Monnin, 2004, states that the time resolution of Dome C and Vostok records are too low to provide a history of CO2 changes that shows the detailed evolution of the atmospheric CO2 record. These records do not capture the elevated CO2 levels in the early Holocene. The Holocene CO2 composite by Bereiter, 2014, which uses mostly Dome C represents the low end or minimum case for CO2 data and does not represent the average from Antarctic cores. Then shifting WAIS down by 4 ppm to match Dome C in the composite reinforces the CO2 minimum case.

Sample spacing resolution is a problem that is frequently overlooked and/or not addressed. Average sample spacing interval in time for CO2 measurements over the Holocene for each core is shown in Figure 4. It should be noted that very little sample spacing is less than 10 years and most samples are spaced 100 years or further apart.

Figure 4: Average sample spacing resolution in Antarctic ice cores for various records and studies. Note several datasets sampled at shorter intervals for CO2 are associated with studies that tend to target “interesting times” such the 8000-year minimum and the last 2000 years.

Several ice cores are sampled across the entire Holocene, but with different sample spacing intervals. The higher temporal resolution Byrd and Siple Dome CO2 data have a sparse sample spacing of 200 to 400 years. Ironically, the lowest temporal resolution records of Dome C have the highest sample frequency of about 100 years over the Holocene. Increased sampling of low snow accumulation sites with low temporal resolution won’t increase the data resolution.

In summary, reduced temporal resolution due to firn densification processes and low sample frequency can explain elevated CO2 levels in the early Holocene not captured by Dome C and Vostok but seen in Siple Dome, Bryd and WAIS.

How does the recently increasing CO2 values compare to altered smoothed CO2 in the ice core records? First, the modern record needs to be smoothed to mimic diffusion within the firn, and then re-sampled. To compare to Dome C, the modern record needs to be smoothed or averaged over 210 years and then resampled every 100 years. To compare to the higher resolution records, the modern record needs to be smooth over about 50 years and then resampled every 100 to 200 years. The modern CO2 increase of 100 ppm over the past 100 years will preserve at most 1 to 2 elevated data points in the past ice record. David Middleton did a nice job of demonstrating modern record smoothing (without resampling) in his WUWT post here.

Interestingly, many scientists frequently flag elevated data as suspicious outliers and reject them from the record because they deviate more than 1-2 standard deviations from a spline trend (Mitchell, 2013). Perhaps these outlier data points in ice cores are indicating higher frequency events but is difficult to know since most are deleted and removed from further study. It is likely the modern CO2 increase, after attenuation due to firn smoothing and sample spacing resolution, would be deleted as an outlier that exceeds the 1-2 standard deviation threshold.


Ice cores from the East Antarctic Plateau, Dome C and Vostok, do not capture the full magnitude of Antarctic CO2 variability. They are the lowest temporal resolution datasets for CO2 measurements and represent the minimum CO2 values as well as reduced variability over the Holocene. Yet they are the key past CO2 records used when comparing to modern CO2 data. Recent CO2 increases appear rapid and radical. If the recent CO2 increase over the past 100 years is attenuated to replicate ice core measurements and then resampled to ice core data intervals it will only represent a mere data point or two within the Holocene ice core record.

Exclusion of high temporal resolution records and sparse sampling results in an incomplete picture of CO2 variability. Dome C data underestimates CO2 values during the early Holocene and perhaps the dynamic behavior of CO2. The need to utilize CO2 data that records short-term variability, as well as longer-term trends, is essential to understand the modern centennial increase. Ice core CO2 records are imperfect data and therefore, the CO2 composite should be an average of all ice core values that includes both a maximum and minimum range.

Lastly, Dome C and Vostok are the few ice core records that cover past interglacial periods. This means that CO2 responses on past interglacial periods are CO2 minimums. And higher frequency centennial CO2 variability is not captured.

Acknowledgements: Special thanks to Donald Ince and Andy May for reviewing and editing this article.

References Cited

Ahn J, and J. Brook, Atmospheric CO2 over the last 1000 years: A high-resolution record from the West Antarctic Ice Sheet (WAIS) Divide ice core, Global Biogeochemical Cycles/Volume 26, issue 2, 2012.

Ahn J., Martin Wahlen, Bruce L. Deck, Ed J. Brook, Paul A. Mayewski, Kendrick C. Taylor, James W. C. White, A record of atmospheric CO2 during the last 40,000 years from the Siple Dome, Antarctica ice core. 15 July 2004. AGU. https://doi.org/10.1029/2003JD004415.

Ahn, J., E.J. Brook, and C. Buizert, Response of atmospheric CO2 to the abrupt cooling event 8200 years ago, Geophys. Res. Lett., doi:10.1002/2013GL058177 (2014).

Bauska, T.K.; Joos, F.; Mix, A.C.; Roth, R.; Ahn, J.; Brook, E.J., WAIS Divide Ice Core 1,200 Year Atmospheric CO2 and d13CO2 Data, 2015. ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/wais2015CO2.txt

Bereiter et al. (2014), Revision of the EPICA Dome C CO2 record from 800 to 600 kyr before present, Geophysical Research Letters, doi: 10.1002/2014GL061957. https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/antarctica2015CO2.xls. Note, IPCC AR6 references Bereiter et al (2015), pretty sure its 2014 not 2015.

Indermuhle, A., T. F. Stocker, F. Joos, H. Fischer, H. J. Smith, M. Wahlen, B. Deck, D. Mastroianni, J. Tschumi, T. Blunier, R. Meyer & B. Stauffer, Holocene carbon-cycle dynamics based on CO2 trapped in ice at Taylor Dome, Antarctica. NATURE | VOL 398 | 11 MARCH 1999.

Jouzel, J., et al., Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years. Science, Vol. 317, No. 5839, pp.793-797, 10 August 2007. ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/epica_domec/edc3deuttemp2007.txt

Kaufman D., N. McKay, C. Routson, M. Erb, C. Dätwyler, P.Sommer, O. Heiri & B. Davis, Holocene global mean surface temperature, a multi-method reconstruction approach, Scientific Data volume 7, Article number: 201 (2020).

Kawamura, K., F. Parrenin, L. Lisiecki, R. Uemura, F. Vimeux, J.P. Severinghaus, M. A. Hutterli, T. Nakazawa, S. Aoki, J. Jouzel, M. E. Raymo, K. Matsumoto, H. Nakata, H. Motoyama, S. Fujita, K. Goto-Azuma, Y. Fujii, and O. Watanabe. 2007. Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years. Nature, Vol. 448, pp. 912-916. doi:10.1038/nature06015.

Marcott, S. A., Bauska, T. K., Buizert, C., Steig, E. J., Rosen, J. L., Cuffey, K. M., Fudge, T. J., Severinghaus, J. P., Ahn, J., Kalk, M. L., McConnell, J. R., Sowers, T., Taylor, K. C., White, J. W. C., and Brook, E. J.: Centennial-scale changes in the global carbon cycle during the last deglaciation, Nature, 514, 616–619, https://doi.org/10.1038/nature13799, 2014.

Mitchell, L. E., Brook, E., Lee, J. E., Buizert, C., and Sowers, T.: Constraints on the Late Holocene Atmospheric Methane Budget, Science, 342, 964–967, https://doi.org/10.1126/science.1238920, 2013.

Neftel, A., H. Friedli, E. Moor, H. Lötscher, H. Oeschger, U. Siegenthaler, B. Stauffer: Historical Carbon Dioxide Record from the Siple Station Ice Core. 1994. https://cdiac.ess-dive.lbl.gov/trends/CO2/siple.html

Oyabu, I., Kawamura, K., Kitamura, K., Dallmayr, R., Kitamura, A., Sawada, C., Severinghaus, J. P., Beaudette, R., Sugawara, S., Ishidoya, S., Dahl-Jensen, D., Goto-Azuma, K., Aoki, S., Nakazawa, New technique for high-precision, simultaneous measurements of CH4, N2O and CO2 concentrations; isotopic and elemental ratios of N2, O2 and Ar; and total air content in ice cores by wet extraction. 2020-12-15, https://amt.copernicus.org/articles/13/6703/2020.

Mitchell, L., Ed Brook, James E. Lee, Christo Buizert, Todd Sowers. Supplementary Materials for Constraints on the Late Holocene Anthropogenic Contribution to the Atmospheric Methane Budget. 2013, Science 342, 964 (2013) DOI: 10.1126/science.1238920

NOAA ESRL Global Monitoring Division – Global Greenhouse Gas Reference Network., 2020.

Rubino, M., Etheridge, D. M., Thornton, D. P., Howden, R., Allison, C. E., Francey, R. J., Langenfelds, R. L., Steele, L. P., Trudinger, C. M., Spencer, D. A., Curran, M. A. J., van Ommen, T. D., and Smith, A. M.: Revised records of atmospheric trace gases CO2, CH4, N2O, and δ13C-CO2 over the last 2000 years from Law Dome, Antarctica, Earth Syst. Sci. Data, 11, 473–492, https://doi.org/10.5194/essd-11-473-2019, 2019.

Siegenthaler, U. et. al. EPICA Dronning Maud Land CO2 Data for the Last Millennium, 2005. https://www1.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/maud/edml-CO2-2005.txt

WAIS Divide Project Members. Onset of deglacial warming in West Antarctica driven by local orbital forcing. Nature 500, 440–444 (2013). https://doi.org/10.1038/nature12376.

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AGW is Not Science
August 13, 2021 6:23 am

And yet under the pseudo-science they compare the ice core data to today’s atmospheric measurements like it is an “apples to apples” comparison, when “apples to hockey pucks” is closer to reality.

Atop this scientific incompetence is piled the assumptions of CO2 level changes of today all being down to human CO2 emissions, without a scrap of measurements on the estimated “natural” inflows and outflows of 97% and 100% of the estimated totals, respectively.

In other words, scientifically speaking, nonsense. The climate pseudo-scientists are in love with ice core CO2 data only because it shows a correlation (though they gloss over the inconvenient fact that the correlation runs the wrong way) and it shows small variability, feeding their nonsensical claims that a change from (allegedly) 285ppm to 420ppm is because of us in a system that has seen a range of about 180ppm to 7,000ppm.

Reply to  AGW is Not Science
August 13, 2021 9:14 am

The amount of fossil fuels being burned every year is more than enough to explain the yearly rise in CO2 levels.

Stephen Wilde
Reply to  MarkW
August 13, 2021 10:11 am

Correlation is not causation.

Clyde Spencer
Reply to  Stephen Wilde
August 13, 2021 8:27 pm

Yes, just because something can be used to explain something else doesn’t mean it should be!

It may just be a spurious correlation because so many things are increasing with time.

Fred Middleton
Reply to  MarkW
August 13, 2021 10:54 am

What about WW2 fuel and coal, gun powder materials, buildings, things etc that burned – creating really nasty stuff, and CO2?

Reply to  MarkW
August 13, 2021 5:58 pm

And land use changes

Reply to  MarkW
August 16, 2021 2:38 am

Not really. The CO2-turnover (3000 gigaton atmospheric CO2, the cycle) is ~4-5 years.

You need to look at temperatures. Increasing planet- and ocean temperatures does “something” to the CO2 solubility of said oceans.

You need to increase the temperature with 0.0056 Kelvin to release 100 ppm (Henry, Dalton). Not measurable but certainly easily calculable.


Richard S Courtney
Reply to  AGW is Not Science
August 15, 2021 11:41 am

AGW is Not Science,

The above article says,
Ice cores from the East Antarctic Plateau, Dome C and Vostok, do not capture the full magnitude of Antarctic CO2 variability. They are the lowest temporal resolution datasets for CO2 measurements and represent the minimum CO2 values as well as reduced variability over the Holocene. Yet they are the key past CO2 records used when comparing to modern CO2 data. Recent CO2 increases appear rapid and radical. If the recent CO2 increase over the past 100 years is attenuated to replicate ice core measurements and then resampled to ice core data intervals it will only represent a mere data point or two within the Holocene ice core record.

You rightly say of that,
And yet under the pseudo-science they compare the ice core data to today’s atmospheric measurements like it is an “apples to apples” comparison, when “apples to hockey pucks” is closer to reality.

I observed it and started a discussion of it in the same week as the MBH Hockey Stick was first published. I repeatedly wroye emails that e,g. said,
“People attack the ‘hockey stick’ because it is uses an improper procedure to assess inadequate data as a method to provide a desired result.
I have defended Mann et al. from accusations of scientific “fraud” because I am willing to accept that this was done in naive stupidity, but I am not willing to accept that is good science. As you say, “people like Mann, Briffa, Jones, etc.” have conducted “careful work”, but doing the wrong thing carefully does not make it right.

The ‘hockey stick’ is obtained by splicing two different data sets. Similar data to the earlier data set exists for up to near the present and could have been spliced on, but this would not show the ‘hockey stick’ and was not done.”

Michael Mann was informed of my observation and wrote an email that was released as part of ‘climategate’. His email wrongly claimed my observation was untrue and threatened me. It said,
“This guys email is intentional deceipt. Our method, as you know, doesn’t include any “splicing of two different datasets”-this is a myth perpetuated by Singer and his band of hired guns, who haven’t bothered to read our papers or the captions of the figures they like to mis-represent…”

In 2014 Mann’s email was the subject of this WUWT item

Your comment which I am now replying says,
And yet under the pseudo-science they compare the ice core data to today’s atmospheric measurements like it is an “apples to apples” comparison, when “apples to hockey pucks” is closer to reality.

In the discussion of the matter on WUWT which I have linked I said,
In the same week as MBH98 was published I wrote an email on the ‘ClimateSkeptics’ circulation list. That email objected to the ‘hockeystick’ graph because the graph had an overlay of ‘thermometer’ data over the plotted ‘proxy’ data. This overlay was – I said – misleading because it was an ‘apples and oranges’ comparison: of course, I was not then aware of the ‘hide the decline’ (aka “Mike’s Nature trick”) issue.

You and I don’t like the issue of temporal resolution. In the discussion of the matter on WUWT which I have linked some people (notably Anthony Watts) agreed with our dislike but some others (notably Steve McIntyre) did not.
To date, I have seen nothing which alters my opinion of the matter in any way,


Renee Hannon
Reply to  Richard S Courtney
August 15, 2021 9:51 pm


My statement you quoted from my article pertains to gases in ice cores, specifically CO2. It is well documented that gases are altered and smoothed during the firn densification process via gas diffusion with atmospheric gas over years to decades to centuries. And if you compare the past, say 1000 years, of atmospheric CO2 data to the high resolution Law Dome ice core CO2, the splice may not be too far off. Although it still doesn’t explain Greenland CO2, not shown, or Dome Fuji wet samples with higher CO2 values during the MWP.

With that said, the past 1000 years of high resolution data and yearly sampling increments are certainly not comparable to the low resolution and poorly sampled ice core data over the entire Holocene. Now you are comparing apples to oranges.

From your comments, I believe you are referring to atmospheric instrumental temperature spliced onto temperature proxies from tree rings, corals, and ice core oxygen isotopes. Coral proxy temperatures have very low resolution and tree ring proxies exhibit local influences. Additionally, the global and Mann temperature profiles are heavily influenced by the abundance of Northern Hemisphere data.

I agree splices should be marked and documented. And both the positives and negatives of all data sources should be clearly described.

Richard S Courtney
Reply to  Renee Hannon
August 16, 2021 12:43 am

Renee Hannon.

Thank you for your response to my comment on your article. Your response agrees my comment by saying,
With that said, the past 1000 years of high resolution data and yearly sampling increments are certainly not comparable to the low resolution and poorly sampled ice core data over the entire Holocene. Now you are comparing apples to oranges.

Your comment also says,
My statement you quoted from my article pertains to gases in ice cores, specifically CO2. It is well documented that gases are altered and smoothed during the firn densification process via gas diffusion with atmospheric gas over years to decades to centuries.

Yes, and I add that weather provides changes in atmospheric pressure that force air in and out of the firn. Thus, diffusion is not the only – and is probably not the major – smoothing process.

In 2008 I gave an ‘off-the-cuff’ presentation of Jaworowski’s work on these matters at the first Heartland Climate Conference. A video of me providing that presentation is at

I hope you find my comments to be helpful additions to the above fine article that you have provided.


John Tillman
August 13, 2021 6:50 am

Average CO2 concentration for past 210 years is at most around 325 ppm. Sampling every 100 years, say, in 1850 and 1950, would find about 285 ppm and perhaps 300 ppm, although Keeling Curve in 1958 was around 315 ppm.

If my arithmetic and chart reading be in the ball park.

Stephen Wilde
Reply to  John Tillman
August 13, 2021 10:10 am

Do you have a sample for the peak of the Mediaeval Warm Period?

John Tillman
Reply to  Stephen Wilde
August 13, 2021 1:10 pm

Not all high resolution, but around 290 ppm in Antarctic cores and close to 300 ppm in Greenland. Strong MWP signal in both, yet again showing the global nature of balminess around 1000 years ago.


Low res means that there could have been decades above 300 ppm.

Stephen Wilde
Reply to  John Tillman
August 14, 2021 8:25 am

The point is that ice cores probably do not record short term variability so the MWP could well have had more than 400 ppm.

August 13, 2021 6:59 am

It is likely the modern CO2 increase, after attenuation due to firn smoothing and sample spacing resolution, would be deleted as an outlier that exceeds the 1-2 standard deviation threshold.”

“And higher frequency centennial CO2 variability is not captured.”

Thank you Renee for going through the steps to arrive at this conclusion. Many of us suspected as much; I did.

EPICA data indicates CO2 lags temperature by 400-600 years (residence time).
comment image

Reply to  Bob Weber
August 13, 2021 7:12 am

What does the lead/lag look like when compared to the global temperature?

Reply to  bdgwx
August 13, 2021 8:06 am

It can be determined from sufficient data with adequate resolution, but do we have that fine quality data? Maybe it can be roughly estimated.

In the short term, 12mo changes in ML CO2 follow HadSST3 by ~10 months, but that doesn’t address residence time, the outstanding $64K question.
comment image

M Courtney
August 13, 2021 7:02 am

There are two very different processes that impact CO2 data resolution. One is related to gas smoothing during snow densification and the other is simply sample spacing.

Every time this comes up I point out a third mechanism.

Vibrations (caused by anything; wind, tectonics, meteorites and just thermal expansion and contraction… anything).

Vibrations will cause cracks deep in the ice. Only briefly, but they will occur with liquid water films instead of ice where the vibrations amplify each other. Gases will migrate into the film. Then they freeze up again. Migrating and smoothing the signal. How much migration compared with the resolution of the signal? Well, how big is the resolution of the signal?
You may think this mechanism seems improbable. But who thinks it seems impossible?

Now consider the time-scales we’re talking about. Hundreds even thousands of years. This must happen sometimes.

And this questions the usefulness of the ice cores for any gas that is water soluble.

Last edited 1 year ago by M Courtney
Reply to  M Courtney
August 13, 2021 7:15 am

And Antarctica is also noted for being a volcanic region, complete with earthquakes. I’ve been pointing this out for years

Carbon Bigfoot
Reply to  Sparko
August 13, 2021 1:43 pm

Kamis’ definitive study http://www.plateclimatology.com/ advanced here many moons ago. CO2 up the wazoo.

Reply to  M Courtney
August 13, 2021 10:28 am

All true, and, in addition, though water melt occurring during sample preparation of ice cores for analysis is minimized, it is not eliminated. Apparently, laboratories are able to achieve reproducible results, however, but studies of fit for purpose and bias have not been done.

It would be my educated guess that CO2 is lost due to adsorption/absorption processes resulting in biased low measurements.

M Courtney
Reply to  Scissor
August 14, 2021 2:49 am

That would be my guess too. It would be smoothed and peaks lowered.
But what annoys me is no-one ever takes my idea seriously enough to test it.
At least lab tests are controlled and recorded, not ignored.

It’s almost as though they lack curiosity. As though ice core experts don’t want to know.

Richard S Courtney
Reply to  M Courtney
August 16, 2021 1:09 am

M Courtney,

You say,
It’s almost as though they lack curiosity. As though ice core experts don’t want to know.
My only dispute with that is use of the word “almost”.

Please see the video of my opinion of the matter which I provided in 2008 at the first Heartland Climate Conference when I gave an ‘off-the-cuff’ presentation of Jaworowski’s work on these matters .
The video is at


August 13, 2021 7:15 am

Comparing Holocene CO2 (red) and CH4 (blue) records give a most interesting picture:
comment image

Methane only reached early Holocene levels over the past centuries.

Even more important. When models try to reproduce Holocene temperatures using proxy GHGs values, and despite higher 65N insolation, they produce the green curve, while we are pretty sure they must have followed a profile similar to the black curve with higher temperatures during the Holocene Climatic Optimum, and decreasing temperatures during the Neoglaciation. It is called the Holocene Temperature Conundrum.

Unsurprisingly clown-climate scientists explain away the conundrum by saying that it is only apparent because proxies are seasonal, and in reality yearly temperatures have been increasing through the Holocene, so models are right and data is wrong.
Seasonal origin of the thermal maxima.

Of course they don’t explain how come glaciers were growing during the entire neoglaciation all over the world all the way to the LIA despite increasing GHG levels and model temperature increase.

Ron Long
August 13, 2021 7:20 am

Interesting data in this report. The Antarctic is such a hostile environment one has to wonder if we know all of the processes involved in the capture and preservation of CO2. For instance, the temperatures in sectors of Antarctica is low enough to convert CO2 in gas phase to CO2 liquid phase. Any data from ice cores in this environment should be taken with some caution.

August 13, 2021 7:20 am

It is likely the modern CO2 increase, after attenuation due to firn smoothing and sample spacing resolution, would be deleted as an outlier that exceeds the 1-2 standard deviation threshold.

It is very unlikely. Modern CO2 increase is artificial in origin and has a different 13C signature. CO2 levels will remain elevated for at least a few centuries even if we stop emitting, so more points coming.

Richard Page
Reply to  Javier
August 13, 2021 8:51 am

Modern fossil fuel CO2 increase does not have enough of a different C13 signature to identify it and separate it from modern natural CO2. This is the huge problem in climate science – since fossil fuel CO2 cannot be identified, it cannot be ascribed an exact value and cannot be traced through the carbon cycle. Every report that ascribes a value to fossil fuel CO2 is a guesstimate with varying degrees of accuracy and relevance.

Reply to  Richard Page
August 13, 2021 9:54 am

No problem at all. Our emissions are twice the measured increase in the atmosphere. And we know our emissions quite well since we tax the energy use.

Stephen Wilde
Reply to  Javier
August 13, 2021 10:15 am

The CO2 emanating from the oceans could well involve biological processes from algae and other micro organisms in the water.
Thus the isotope based assumption would be invalid.

Reply to  Stephen Wilde
August 13, 2021 1:03 pm

The CO2 emanating from the oceans could well involve biological processes from algae and other micro organisms in the water.

But that is not the case, Stephen.



Ferdinand is a long time contributor of WUWT and a well respected skeptic with a very good knowledge of CO2 matters.

Clyde Spencer
Reply to  Javier
August 13, 2021 8:44 pm

But as far as I can tell from reviewing his website, like everyone else, he has not looked into the isotope fractionation that occurs when CO2 outgasses. There should be a preference for the lighter isotope carbon because it will take less energy. Thus, it is going to look more like the CO2 derived from coal and petroleum.

Besides that, most of the ramp up of atmospheric CO2 in the Winter is from bacteria decomposing 12C-rich detritus, again mimicking fossil fuels.

I don’t think that this as been adequately studied!

Jim Ross
Reply to  Clyde Spencer
August 14, 2021 12:04 am

Fractionation effects are incorporated in recent models (though not necessarily well defined). See, for example:
Keeling et al (2017) “Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis”.

Clyde Spencer
Reply to  Jim Ross
August 14, 2021 9:01 am

This article addresses the impact of photosynthesis on isotope discrimination, something that has been known about for a long time. It does not speak to the point that I raised which is that the isotopic composition of CO2 dissolved in sea water almost certainly differs from that of CO2 outgassed at the surface because of the difference in weight between 12C and 13C molecules.

While CO2 is conventionally referred to as a “well-mixed” gas, the OCO-2 satellite observations have shown that it varies measurably with altitude. What is needed is a sampling program in the tropics with collections near the water surface and at weather balloon heights.

Jim Ross
Reply to  Clyde Spencer
August 14, 2021 10:33 am

It would appear that you did not read the paper. The model used by Keeling et al incorporated fractionation effects at the air-sea boundary (in both directions). Indeed, there is an explicit reference to “air–sea isotopic fractionation” on page 2 of the paper.

If you want to understand the level of sophistication of their model, please refer to Table S1 in the supporting information, which can be linked directly from the version of the paper I provided. You will find the actual values used in the model for air-to-sea kinetic fractionation and for sea-to-air kinetic fractionation. It also includes terms for the ocean biological pump including marine photosynthetic discrimination and equilibrium fractionation. See also the footnotes to this table.

Of course, sophistication doesn’t make it right (and I do have significant reservations about their conclusions), but I just wanted to make you aware that isotopic fractionation at the air-sea boundary (in both directions) is most certainly incorporated in this and earlier models.

Clyde Spencer
Reply to  Jim Ross
August 14, 2021 1:12 pm

I did read it, although quickly. I was left with the idea that the fractionation at air-sea boundary was that induced by photosynthetic organisms. I will re-read to confirm.

Clyde Spencer
Reply to  Clyde Spencer
August 14, 2021 1:56 pm


I stand corrected. Keeling does address my concern about thermokinetic isotopic fractionation:

Air-to-sea kinetic fractionation3 εoa −0.7 ‰ + anomaly

Sea-to-air kinetic fractionation3 εao −2.1 ‰ + anomaly

It should probably be noted that Keeling says,

The atmospheric δ13C trend is nevertheless fairly sensitive to the air-sea exchange coefficient kam. as shown in Figure S3 (right panel). The times scale for the ocean mixed layer to equilibrate isotopically with atmospheric CO2 is much longer than for (total) CO2 partial pressure. As a consequence, air-sea exchange is a rate limiting step for the uptake of isotopic anomalies by the ocean even though [it] is not strongly rate limiting for the ocean CO2 sink as a whole.

Last edited 1 year ago by Clyde Spencer
Jim Ross
Reply to  Clyde Spencer
August 15, 2021 1:54 am


Thank you for the acknowledgement. There is much that is, in my view, problematic about the Keeling et al analysis, but that is too far off-topic for further comment here.

I’ll leave it with this quote from the paper: “A further difficulty is that the global δ13C budget does not balance convincingly”. Indeed!

Jim Ross
Reply to  Javier
August 13, 2021 11:49 pm

I do like the sponges plot as it supports my interpretation of a 13C/12C ratio of the additional atmospheric CO2 of -13 per mil (as demonstrated by the Keeling plot of the Law Dome ice core data, referenced below). This can be confirmed from the two scales:

(-7.57*345 + 6.48*286)/(345-286) = -12.9 per mil
(CO2 values of 345 and 286 ppmv are derived from the reciprocals of 0.0029 and 0.0035 respectively and the equivalent δ13C values of -7.57 per mil and -6.48 per mil are those on the far left scale that align with these reciprocal points).

Stephen Wilde
Reply to  Javier
August 14, 2021 8:27 am

I have made the same point to Ferdinand but he has not dealt with it.

Geoff Sherrington
Reply to  Stephen Wilde
August 13, 2021 9:52 pm

Further, it has long worried me that emission of CO2 from a concentrated source like a power station might be captured and immobilized long before it can travel to Mauna Loa. Geoff S

Reply to  Javier
August 13, 2021 10:40 am

Yes, we know what our emissions are via energy use, but a lot of climate data is like the PCR testing and SARS-CoV-2, often misapplied and abused to create a narrative for control.

M Courtney
Reply to  Javier
August 13, 2021 12:40 pm

Javier, Your views do not agree with the IPCC AR6. You should read the report.

TS.3.3.3 Relating Different Forcing Agents TS-67 Page110

COVID-19 restrictions led to detectable reductions in global anthropogenic NOx (about 35% in April 2020) and fossil CO2 (7%, with estimates ranging from 5.8% to 13.0%) emissions, driven largely by reduced emissions from the transportation sector (medium confidence). There is high confidence that, with the exception of surface ozone, reductions in pollutant precursors contributed to temporarily improved air quality in most regions of the world. However, these reductions were lower than that would be expected from sustained implementation of policies addressing air quality and climate change (medium confidence). Overall, the net global ERF from COVID-19 containment was likely small and positive for 2020 (with a temporary peak value less than 0.2 W m–2 26 ), thus temporarily adding to the total anthropogenic climate influence, with positive forcing (warming influence) from aerosol changes dominating over negative forcings (cooling influence) from CO2, NOx and contrail cirrus changes. Consistent with this small net radiative forcing, and against a large component of internal variability, Earth system models show no detectable effect on global or regional surface temperature or precipitation (high confidence).

So the IPCC explains why we could not affect the climate by locking down for climate.
It’s because particulates seeding clouds is so warming that their exclusion counters all the CO2, NOx, Methane etc.

There was no drop in atmospheric CO2 as measured by Mauna Loa. So if emissions dropped 7% (5.8% to 13%) then the anthropogenic proportion of atmospheric CO2 emissions is so small that at least 5.8% cannot be spotted. A 20th of man’s emissions is nothing compared to the natural emissions. That’s the IPCC’s conclusion.

By the way, from a policy perspective, this finding of the IPCC absolves CO2 mitigation from any urgent concern.

Reply to  M Courtney
August 13, 2021 1:11 pm

M Courtney, that has nothing to do with what I said.

However, we emit about 4 ppm of CO2 every year, of which 2 ppm remain in the atmosphere. A 7% reduction means we emitted about 3.72 ppm in 2020, of which 1.86 remained in the atmosphere. That’s a 0.14 ppm reduction which is a lot less than the annual variation so it cannot be detected.

It doesn’t mean what you think it means. If we want to make a detectable dent in atmospheric levels we need to make a 10xCOVID reduction one year or repeat the COVID reduction in emissions during 10 years.

M Courtney
Reply to  Javier
August 13, 2021 4:11 pm

Well that’s just madness.

10 x harder lockdown than Covid for not one year but a decade?
No wonder the Summary for Policy Makers disagrees with you. If it agreed with you they would be laughed out of court.

We are never doing anything tougher than Covid in any year ever. Let alone 10 times tougher for 10 times as long.
That’s politically impossible.

If you believe your own science then you need to accept what that would mean. No more mitigation.
Meaningful mitigation is not possible.

However, mainstream science does disagree with you.
Mauna Loa shows the natural sinks vary in re-absorption with the seasons by more than the entire anthropogenic emissions. The build-up of excess emissions required to eventually become detectable could only emerge if the sinks are unchanging – or the AGW is swamped for ever. Yet the heat going onto the oceans must come out again or AGW is not a problem. And if the heat content changes, so does the CO2 absorption ability of the oceans.

Clyde Spencer
Reply to  Javier
August 13, 2021 9:00 pm

You are assuming that 2PPMV of anthropogenic CO2 remains in the atmosphere. In actuality, the only thing that can be said is that all the sinks are acquiring CO2 from all the sources, and an amount equivalent to about half the human production increases the atmospheric concentration.

What logic leads you to conclude that if a 10+% reduction in anthropogenic CO2 cannot be measured even as a change in the slope of the seasonal ramp-up phase, that a more draconian reduction will suddenly appear? It seems to that is a leap of faith.


Reply to  Clyde Spencer
August 13, 2021 11:01 pm

It is always a discussion about fluxes that are very large and very variable, and net change, that interannually is small and varies less. Since anthro emissions are larger (2x) than net change it is obvious that net change is due to us.

Seasonal changes are part of the flux, so not due to us and very large and variable. We won’t see changes there.

We could only see a change to our emissions reduction in the net change, because sinks are not going to change quickly if we change our emissions.

To see a reduction in the net change we need to reduce our emissions a lot or reduce them for a long time.

I am not advocating that we reduce our emissions, I am just explaining why we don’t see a change after COVID-induced reductions, why we shouldn’t expect to see one, and what it would take to see it.

Clyde Spencer
Reply to  Javier
August 14, 2021 9:07 am

To see a reduction in the net change we need to reduce our emissions a lot or reduce them for a long time.

The point being is that your rationalizations are theoretical and not supported by empirical measurements.

Out of curiosity, have you read my article provided at the link?

Clyde Spencer
Reply to  M Courtney
August 13, 2021 8:51 pm

(7%, with estimates ranging from 5.8% to 13.0%) emissions, driven largely by reduced emissions from the transportation sector.

One estimate has the monthly reduction as high as 18% during April 2020, when the seasonal ramp-up was approaching the annual high in May.

M Courtney
Reply to  Clyde Spencer
August 14, 2021 2:39 am

That makes sense but I am sticking to the mainstream science of the IPCC.
It has more authority when disputing the ‘fringe’ ideas of Javier.

Clyde Spencer
Reply to  M Courtney
August 14, 2021 9:10 am

… I am sticking to the mainstream science of the IPCC.

Despite its reputation for pushing an agenda by cherry picking?

“Better the Devil I know, than the one I don’t.”

Jim Ross
Reply to  Javier
August 13, 2021 12:57 pm

I shall be off-line for a while, so I look forward to your explanations of the following plot. The observations are the monthly data from Scripps for Mauna Loa, while the trends are super-imposed by me.

comment image

Reply to  Jim Ross
August 13, 2021 2:06 pm

A short period oscillation and a long term trend. The oscillation is natural, the trend is not.

Jim Ross
Reply to  Javier
August 13, 2021 11:56 pm

The long term trend has a 13C/12C ratio of -13 per mil (intercept of line). Fossil fuels are estimated to have a ratio of -28 per mil. This is best seen after removal of the seasonal cycle (by Scripps):

comment image

Last edited 1 year ago by Jim Ross
Richard Page
Reply to  Javier
August 13, 2021 1:34 pm

Javier – have you included the recent reports that state that the amount of CO2 absorbed by plants has been UNDER estimated by quite a large factor? When you add the amount by which the planet has been greening, increasing year on year, it’s no longer a simple calculation. Your numbers don’t add up.

Reply to  Richard Page
August 13, 2021 2:10 pm

It doesn’t matter, Richard, if CO2 goes to plants on land or algae in the ocean. Those are net sinks. The only net source since the 1950s is us. The airborne fraction separates the part of our emissions that goes to the atmosphere from the part that goes to sinks.

Richard S Courtney
Reply to  Javier
August 16, 2021 10:49 am

You say,
The only net source since the 1950s is us. 
Really? You know that? How?

Many sinks and sources are much larger than the anthropogenic emission and their variability is not known so how could one know
the recent rise in atmospheric CO2 concentration is not entirely a result of natural variability?
Rorsch, Courtney & Thoenes assessed that question in one of our 2005 peer reviewed publications. In 2008 I expanded on it in a presentation to the first Heartland Climate Conference.

Ed Berry has posted a copy of my 2008 paper on his blog at
because, importantly, Ed Berry builds on a finding in my paper by making a breakthrough in understanding (which I and all others failed to make). This has enabled him to assess the data in a way that quantifies the natural and anthropogenic contributions to the cause.

Berry provides a preprint of his paper on his blog at
His paper has been accepted for publication and it reports he finds that the anthropogenic contribution to the rise is only 25% of the total rise.


Jim Ross
Reply to  Richard Page
August 13, 2021 11:35 pm

Yes, it is a problem. The observed decline in atmospheric 13C/12C ratio is much less than expected from the addition of fossil fuel derived CO2. In δ13C terms, the decline reflects a net 13C/12C ratio of the extra atmospheric CO2 of -13 per mil, as distinct from fossil fuels at around -28 per mil.

It is also interesting to note that the Law Dome ice core data shows that the incremental CO2 since the start of the industrial revolution has had a consistent net 13C/12C ratio of -13 per mil. See figure 1 here: Kőhler et al (2006), “On the application and interpretation of Keeling plots in paleoclimate research—Deciphering δ13C of atmospheric CO2 measured in ice cores.”

William Astley
Reply to  Javier
August 13, 2021 1:39 pm

avier … What caused the past step increases in temperature on the Greenland ice sheet. We just experienced a step increase in temperature … The Greenland Ice sheet warmed this time just like it did in the paleo record.

Greenland ice temperature, last 11,000 years determined from ice core analysis, Richard Alley’s paper. William: As this graph indicates the Greenland Ice data shows that have been 9 warming and cooling periods in the last 11,000 years.


Javier…. Obviously you have never looked at the C12/C13 ratio. And you have never looked and tried to explain the cyclic D-O warming. (See below for details.)

The fake atmospheric C12/C13 analysis shows a smoothed curved that hides the fast, paradox killing observational changes in the C12/C13.

If humans were the cause of the recent CO2 rise. The C12/C13 ratio would gradually change tracking human CO2 emissions. It does not.

The fast and large changes in the C12/C13 ratio is a fundamental observation, that physical disproves the CAGW theory.

We are now living at the end of Dansgaard-Oeschger warming period. The D-O warming periods end abruptly. (The Greenland Ice Sheet proxy smoothes the fast D-O cyclic temperature changes. The D-O cyclic short warming periods, see link below, correlate with a fast solar changes.

It is known… it is a fact… that there is a fast weird, solar change, correlating in time with each unexplained short, 20 or 30 years D-O warming event….

That is known because there is large and long duration change in the amount of cosmogenic produced isotopes are deposited on the earth’s surface. The isotope changes… deposited all over the planet, can physically only be explained by a change in the geomagnetic field.

A detailed look at the C13/C12 isotope changes shows that the C13/C12 ratio of atmospheric CO2 has unexplainably, repeatedly, made large step changes up and down.

What is physically causing large step changes in C13/C12 ratio in the atmosphere?
The sudden C13/C12 changes should not be physically possible with CAGW/AGW assumptions.
To suddenly change C13/C13 requires a large missing source of CO2, that is low C13 (primordial CH4) that is entering the biosphere.
Tom Quirk in the SOURCES AND SINKS OF CARBON DIOXIDE shows that C13/C12 ratio changes when there is an ENSO event. (i.e. Anthropogenic CO2 emissions do not increase or decrease when there is ENSO events.)

Sources and sinks of CO2 Tom Quirk
The yearly increases of atmospheric CO2 concentrations have been nearly two orders of magnitude greater than the change to seasonal variation which implies that the fossil fuel derived CO2 is almost totally absorbed locally in the year that it is emitted.
A time comparison of the SIO measurements of CO2 at Mauna Loa with the South Pole shows a lack of time delay for CO2 variations between the hemispheres that suggests a global or equatorial source of increasing CO2. The time comparison of 13C measurements suggest the Southern Hemisphere is the source.
This does not favour the fossil fuel emissions of the Northern Hemisphere being responsible for their observed increases. All three approaches suggest that the increase of CO2 in the atmosphere may not be from the CO2 derived from fossil fuels. The 13C data is the most striking result and the other two approaches simply support the conclusion of the first approach.

The phase relation between atmospheric carbon dioxide and global temperature
Summing up, our analysis suggests that changes in atmospheric CO2 appear to occur largely independently of changes in anthropogene

emissions. A similar conclusion was reached by Bacastow (1976), suggesting a coupling between atmospheric CO2 and the Southern Oscillation. However, by this we have not demonstrated that CO2 released by burning fossil fuels is without influence on the amount of
atmospheric CO2, but merely that the effect is small compared to the effect of other processes. Our previous analyses suggest that such other more important effects are related to temperature, and with ocean surface temperature near or south of the Equator pointing itself out as being of special importance for changes in the global amount of atmospheric CO2.

Reply to  William Astley
August 13, 2021 2:05 pm

Javier…. Obviously you have never looked at the C12/C13 ratio. And you have never looked and tried to explain the cyclic D-O warming.

William, you have no clue what I have looked at or not. You also have no clue what a D-O event is. If you want to learn about Dansgaard-Oeschger events why don’t you start by reading my article about them?
Nature Unbound II: The Dansgaard- Oeschger Cycle
Dansgaard-Oeschger events cannot take place during an interglacial.

William Astley
Reply to  Javier
August 13, 2021 3:29 pm


Javier. Your answer is what the warming did not happen?

Greenland Ice Sheet 2 core analysis. That data shows fast cyclic warming on the Greenland Ice Sheet.

The CAGW did not tell us that this exact warming has happened in the past. i.e. The Greenland Ice Sheet suddenly warms.

And some funny happens to the Sun. Just like it is happening now.

You need glasses. This is D-O warming.

The warming that did happen and is shown in Richard Alley’s paper which is linked to again.


William Astley
Reply to  Javier
August 13, 2021 3:38 pm

The cyclic warming and cooling also occurs in the interglacial period.

Davis and Taylor: “Does the current global warming signal reflect a natural cycle”

…We found 342 natural warming events (NWEs) corresponding to this definition, distributed over the past 250,000 years …. …. The 342 NWEs contained in the Vostok ice core record are divided into low-rate warming events (LRWEs; < 0.74oC/century) and high rate warming events (HRWEs; ≥ 0.74oC /century) (Figure). … …. “Recent Antarctic Peninsula warming relative to Holocene climate and ice – shelf history” and authored by Robert Mulvaney and colleagues of the British  Antarctic Survey ( Nature , 2012, doi:10.1038/nature11391),reports two recent natural warming cycles,  one around 1500 AD and another around 400 AD, measured from isotope (deuterium) concentrations in ice cores bored adjacent to recent breaks in the ice shelf in northeast Antarctica. ….
Public media in the U.S., including National Public Radio (NPR), were quick to recognize the significance of this discovery. The past natural warming events reported by Mulvaney et al. are similar in amplitude and duration to the present global warming signal, and yet the past warmings occurred before the industrial revolution and therefore were not caused by anthropogenic greenhouse gases.”


Timing of abrupt climate change: A precise clock by Stefan Rahmstorf
Many paleoclimatic data reveal a approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.

Reply to  William Astley
August 13, 2021 11:26 pm

William, I am not saying that there is no cyclic warming and cooling throught the Holocene. There are in fact several cycles acting, a 1500-yr tidal cycle and a 100-yr solar cycle among others.

I am just saying that you need to study a lot more, because most of what you are saying is wrong.

D-O events cannot take place during interglacials. They are the result of ocean heat-storage under the sea-ice over the centuries and they require low sea-levels and a lot of permanent sea ice in regions that are currently sea-ice free.

Stefan Rahmstorf is one of the worst warmunists in the world and the worst in Germany. That paper you cite was demonstrated wrong, and the 1470-year periodicity turned out to be non-real, an artifact of an incorrect chronology. That happened after I wrote my article.

There appears to be a real 1500-year cycle, but it is quite misunderstood on its phases and effects. A lot of the bibliography on the 1500-year cycle is wrong.

Again, if you want to learn paleoclimatology I encourage you to learn my articles.

Nature Unbound V – The elusive 1500-year Holocene cycle

Jim Ross
Reply to  William Astley
August 15, 2021 1:59 am

I agree with Tom Quirk, the rapid variations in the atmospheric 13C/12C ratio are directly related to ENSO (and Pinatubo).

Richard Page
August 13, 2021 7:31 am

It’s a little o/t but I’m quite interested in what was happening 1500 years ago – the end of the RWP and the beginning of the Dark Age solar minimum. There was a news item on my feed that mentioned that archaeologists were ‘scrambling’ to comb areas where ice was melting as they were revealing deposits that had been buried under the ice. In particular it discussed the Mongolian Altai mountains where artefacts dating to 1500 years ago are turning up as the ice melts. So the ice on the Altai mountains was deposited around 500-550 CE trapping these artefacts beneath layers of ice – presumably the RWP warmth caused whatever ice that was there before to melt as well. Puts a different perspective on the climate enthusiasts claims when you realise even glaciers and high altitude ice come and go in cycles.

Richard Page
Reply to  Richard Page
August 13, 2021 7:54 am

As a postscript, what I find interesting is what is being revealed as the ice melts – some areas like the Altai must have had a continuous layer of ice since after the RWP (meaning it didn’t melt during the Medieval WP) whilst other areas, such as where Otzi was found, had a continuous layer of ice since the bronze age – Minoan WP? (meaning it didn’t melt during either the RWP or Medieval WP). Still others, like southern Greenland, were ice free during the Medieval WP. This, to my mind, completely undermines the climate enthusiasts notions of global warming but raises the idea of regional weather event’s – different areas experiencing different patterns of warming and cooling at different times.

Reply to  Richard Page
August 13, 2021 8:48 am

Richard, your time period included long duration, (200yr) low solar activity, perfect for ice growth, following a 50+ year period of high solar activity:
comment image

It could happen again…

Richard Page
Reply to  Bob Weber
August 13, 2021 9:42 am

Bob – it happened before that period as well so will happen again, just don’t know the exact time scale.

Smart Rock
August 13, 2021 9:52 am

Thanks to Renee for a concise compilation.

I find it intriguing that the long dip in post-glacial CO2, with a minimum at 7,000 years BP, corresponds fairly closely to the Holocene thermal optimum, when global mean temperatures were perhaps 3 to 4 degrees C higher than today. And sea levels were perhaps 3 metres higher than today.

It’s not logically possible for low CO2 (“a well mixed gas”) to be a local phenomenon restricted to Antarctica, and to be sustained for thousands of years. Unlike temperature, which is always local. No wonder the cartel keeps trying to make the Holocene thermal optimum disappear.

Smart Rock
Reply to  Smart Rock
August 13, 2021 12:25 pm

I took the first holocene global temperature record I could lay my hands on, Andy May’s 2017 multi-proxy reconstruction (https://wattsupwiththat.com/2017/06/09/a-holocene-temperature-reconstruction-part-4-the-global-reconstruction/) and overlaid it on Renee Hannon’s figure 2 from the headpost. The result was very illuminating. So CO2 controls climate, eh? Negative ECS during the Holocene, perhaps?

For some reason, you have to click on the image to see it at full size.

Holocene CO2 & Global temp.jpg
Last edited 1 year ago by Smart Rock
Renee Hannon
Reply to  Smart Rock
August 15, 2021 6:50 pm

Smart Rock,
The global temperature record tends to be dominated by the abundance of Northern Hemisphere proxy records and often reflects their profile. Also, past interglacials are only covered by Antarctic ice core records. Which means both temperatures and GHGs of past interglacial periods only reflect Antarctic data and NOT global conditions.

Stephen Wilde
August 13, 2021 10:01 am

Good, some evidence to support the proposition that ice cores fail to capture the large scale of natural CO2 variability in the atmosphere.
If it is natural then it is due to changes in the balance of oceanic absorption or emission.
Humans not guilty.

August 13, 2021 10:21 am

There is a hockystick problem with these charts. It has to do with the horizontal resolution of each dot. On the left (in the past) each dot represents a mean of a couple of decades but on the right ( more resent) each dot represents one year. So in order to get this graph right you need to keep the resolution of each dot the same.

Len Werner
Reply to  Fulco
August 13, 2021 12:27 pm

An excellent point; this seems to be a clear Mannurism. As the ice gets squished with depth, the sample interval must become equally squished.

I still see no consideration of the potential contributions of bacteria. I’ve worked extensively at high altitudes in Canada’s north and always seen pink algae on the surface of snow in late summer. Where’s there’s algae there will be bacteria to eat it. Where there’s bacteria there will be a contribution of CO2.

I’m not sure this contribution is quantifiable for the past; if present and not quantifiable all usefulness of ice-core CO2 measurements vanishes. It contains an unknown component generated in-ice.

I’d welcome reference to a detailed analysis of the possibility or not of bacterial contamination of atmospheric-sourced CO2 in ice cores so I can correct myself if wrong.

Gary Pearse
August 13, 2021 12:40 pm

Renee, as a geologist, I immediately recognize the importance of using the entire record in sampling a a medium like ice cores. The ‘spurious high’ may be a ‘lucky hit’ of a 100yr elevated CO2 period (as you pointed out re our 100yr modern high) that might correlate with a major volcanic event or effect of a bolide impact (which information may also be indicated by more concentrated dust in the interval). There should be closer spaced sampling done where a ‘spurious high’ occurs to test it.

Also, closer spaced sampling in general can be expected to reveal scattering that might be interpretable. We have no difficulty in interpreting less smoothed data. Weren’t there wide-spread fires in grass and dry scrub at the end of the glacial max? That should give upticks.

Renee Hannon
Reply to  Gary Pearse
August 13, 2021 2:14 pm

The CO2 data variability has definitely peaked my interest in these shoulder transitions from deglaciation to interglacial periods. Need to do more digging around to better understand them.

What puzzles me is why uniform sampling across the Holocene is not conducted in addition to detailed studies. For rock cores studies, we always took a sample every foot to establish a baseline. This removes sampling bias. I also plotted ice core CO2 samples in depth, and it is not consistent.

Gary Pearse
Reply to  Renee Hannon
August 13, 2021 4:22 pm

Thanks Renee. Even for splitting rock core for assays, I alternated which half I selected (1 meter assays). Some thought me too fastidious, but when so much is paid for drilling, logging, sampling, assaying, interpretation and mineral deposit modelling, a thorough, unbiased job should be done.

The job done on ice cores may be sufficient for gross changes in CO2 and temperature over millennia, but it certainly doesn’t meet a geological standard embodied in the rule: ‘You should only need to visit an outcrop once! (If you are properly using multiple hypotheses, examine and measure everything.)

Perhaps there is an idea for a grant to to flesh out the the sampling around so-called outliers – sample also for volcanic ash and sulphur, bolide glass, smoke/charcoal dust…

I’m sure a formula can be derived relating overall project costs for drilling and storing ice cores and interpretive work costs. If getting the ice core costs (all-in) 10s of millions and fieldwork costs (only) for sampling at current spacings is 100k or so (prep, travel, logistics for samplers are sunk costs), then to take twice as many samples costs 200k or so, it would be poor economics to not do the latter.

Steve Z
August 13, 2021 1:44 pm

It’s not clear that CO2 trapped in Antarctic ice is indicative of CO2 levels in the atmosphere all over the globe.

Antarctica is mostly surrounded by water from about 40 degrees to 70 degrees South latitude, with the exception of the narrower strait between the Antarctic Peninsula and Tierra del Fuego (southern tip of South America). The major source of CO2 in Antarctic ice would be any CO2 de-gassed from the Southern Ocean, which is later adsorbed onto snow that falls on the coasts of Antarctica.

Anthropogenic CO2 emissions are almost exclusively over land, and most of the Earth’s land area is concentrated between 30 degrees and 65 degrees North latitude, so that CO2 trapped in Greenland ice would be a better proxy for past CO2 levels than Antarctica, which is largely isolated from human CO2 emissions.

In the more distant past, when anthropogenic CO2 emissions were negligible, most “natural” changes in CO2 concentrations were due to animal respiration and photosynthesis, which have greater effect over land areas than over the oceans.

Over the tropical oceans near the Equator, there is the Intertropical Convergence Zone, where winds are generally from the northeast to the north and from the southeast to the south. Although this “Convergence Zone” moves slightly north of the Equator during Northern Hemisphere summer, and south of the Equator during Northern Hemisphere winter, there is generally little air exchange between the two hemispheres, so that the CO2 fluctuations due to life on land in the Northern Hemisphere would not be reflected in Antarctica.

Renee Hannon
Reply to  Steve Z
August 13, 2021 1:59 pm

I absolutely agree with you, that CO2 from Greenland ice cores should be considered. Unfortunately, scientists have disregarded this important dataset because it shows much more variability than the Antarctic CO2 dataset. The entire Greenland CO2 datasets were deemed unreliable due to chemical reactions with impurities in the ice and therefore have not been used in studies since the late 1990’s.

Dave Fair
August 13, 2021 2:16 pm

Marcott? Seriously? He should be banned from publishing due to past scientific misconduct.

Clyde Spencer
August 13, 2021 8:07 pm

First, the modern record needs to be smoothed to mimic diffusion within the firn, and then re-sampled.

Kudos for recognizing and addressing this need! All too often people attempt to compare recent measurements with historical measurements without considering the need for re-sampling.

Renee Hannon
Reply to  Clyde Spencer
August 13, 2021 9:27 pm

I was surprised that sampling over the Holocene was 100+ years and used the lowest resolution dataset, Dome C. Modern instrumental CO2 data from Mauna Loa began in 1958, a mere 60 years ago. This recent rise in CO2 could easily fall in between ice core data sampling increments.

Clyde Spencer
August 13, 2021 8:20 pm

It is likely the modern CO2 increase, after attenuation due to firn smoothing and sample spacing resolution, would be deleted as an outlier that exceeds the 1-2 standard deviation threshold.

I’ve given some thought to this problem in relation to research I have been doing on the complex refractive index of opaque minerals. I’ve come to the conclusion that for isotropic minerals, probably everything up to at least 2 standard deviations should be retained. However, for anisotropic minerals, with random orientations of the crystals, an even greater range should be retained because there are 2 or 3 distinct maximum values for the indexes of refraction and extinction coefficients, depending on the crystal system.

One should be prepared to strongly defend the decision to omit any data in a summary, and it should always be retained in a data archive.

August 13, 2021 8:52 pm

I have read that CO2 in ice is not necessarily conserved because , with enough pressure, clathrates are formed trapping some of the CO2 permanently. I don’t really understand how this works but Jaworowski thought it was important and reduced the CO2 found in cores. It seems to me that this process could partially explain the low variability of the ice core records by removing some of the higher concentrations as they are subjected to higher pressures.

Renee Hannon
Reply to  DMA
August 13, 2021 9:07 pm

Clathrates typically form at deeper depths than the Holocene and therefore, should not have an impact on this timeframe.

Geoff Sherrington
August 13, 2021 11:35 pm

Thank you, Renee, you have a topic close to my heart.
At the start of my scientific education, we the research team would typically have a number of discussions about a new project, leading to a clear elucidation, written down and agreed, that used headers like Aim, Objective, Apparatus, Methods, Interpretation, Results, Summary, References, Appendices.
If the experiment did not finally meet the aim, the experiment was scrapped. If it had been judged promising but flawed, an amended experiment was created if possible.
In this present case of gases in ice core, we might state the Aim to be to determine if ice cores can contain a useful measure of past concentrations of atmospheric carbon dioxide.
We might start with a broad assumption, that ice cores did indeed contain some CO2. We would try various lab methods to separate ice from CO2. We might find that they did contain some CO2. We would study why some methods gave different recoveries to others and select the method with fewest remaining puzzles.
We might next examine the critical step of calibration: that is, does the CO2 now in ice core bear a reproducible relation to the CO2 known to be in air. Being excluded from past times when natural CO2 in air was not measured, we might well start with synthetic samples, whereby we made artificial ice cores in surroundings with different, known concentrations of CO2. We might even include some isotopic work, tagging the CO2 to see if freezing/experimenting partitioned the isotope ratios. Somewhere along the line we would find a discrepancy that would lead us to gas/ice age differences, firn processes and so on.
(It is not necessary for me to continue step by step through this though experiment. You have the picture by now. It is about required prior formalism.)
It is a concern that a number of uncertainties expressed by bloggers here should have been studied and answered before springing into print with scientific papers that have potential impacts on global energy policies. My difficulty is that I have not seen any such preliminary, exploratory papers. I have searched, but searching can often miss critical references. Time gets away.
So, here I ask other bloggers if they are aware of this exploratory type of work having been done, where I can find references, etc. I have a current impression, which could be wrong, that many steps were made on this topic “on a wing and a prayer” and since one aircraft returned safely to base it was early assumed that all of the processes were solid and all of the answers reliable.
Show me proof, please, that this work is solid and the answers reliable.  Note that adjustments wishing for a scientific answer were a sacking offence. Geoff S

Renee Hannon
Reply to  Geoff Sherrington
August 14, 2021 11:29 am

To be fair to the scientists who study ice cores, they have done much of the preliminary work you mention above. I try to include as many references as I can in my posts.

The alteration due to gas diffusion through the uppermost layers of porous, compacting snow, the “firn” were initially described by Schwander et al., 1993. They analyzed the samples for both gas contents as well as the isotopic composition of nitrogen and oxygen.

Schwander, J., Barnola, J.-M., Andrie, C., Leuenberger, M., Ludin, A., Raynaud, D., and Stauffer, B.: The age of air in the firn and ice at Summit, Greenland, J. Geophys. Res., 98, 2831–2838, 1993. 

The dry extraction technique is described in detail in publications (Etheridge et al., 1996; MacFarling Meure et al., 2006), with recent minor alterations to optimise extraction and measurement of δ13C-CO2 analyses (Rubino et al., 2013).

Etheridge, D. M., Steele, L. P., Langenfeld, R. L., Francey, R. J., Barnola, J. M., and Morgan, V. I.: Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn, J. Geophys. Res., 101, 4115–4128, 1996. 

Rubino, M., Etheridge, D. M., Trudinger, C. M., Allison, C. E., Battle, M. O., Langenfelds, R. L., Steele, L. P., Curran, M., Bender, M., White, J. W. C., Jenk, T. M., Blunier, T., and Francey, R. J.: A revised 1000 year atmospheric δ13C-CO2 record from Law Dome and South Pole, Antarctica, J. Geophys. Res.-Atmos., 118, 8482–8499, https://doi.org/10.1002/jgrd.50668, 2013. 

Test samples are run together with real ice samples to calibrate the equipment (blank correction). The test samples are air samples of known composition processed with no ice present or reference air samples injected over ice grown and grated to simulate an actual ice core sample. Gases are measured using a gas chromatograph. They are also corrected for gravitational fractionation.
Rubino, 2019 referenced in my article.

What I am finding out, is that ice cores are not sampled in detail routinely for gases along the entire ice core like is typically done for routine rock core analysis. I assume they don’t have the funding unless it’s for specific studies targeting the deglaciation phase or other interesting periods. Many authors also state that the time resolution of ice core records are too low to provide a history of CO2 changes equivalent to the detailed evolution of the atmospheric CO2 record (Monnin, 2004 referenced in my article.). This observation is never stated by the media nor by NOAA nor by Scripps. Lastly, there are scientists that measure the data and then there are scientists that interpret the data. I find it quite amusing the lack of geoscientists associated with IPCC.

August 14, 2021 6:56 am

Thanks Renee for some real climate science!

Figures 1-3 show the clear signature of the bipolar seesaw, the tendency for the NH and SH to undergo temperature changes in opposite directions. This results in part from interhemispheric heat piracy 🏴‍☠️.

The whole Antarctic curve of both temperature and CO2 (the former driving the latter) from 11kya till the present is the mirror image, the simple inverse of what NH temperature did over the same interval.

From glacial termination at 11kya till around 8kya, the NH warmed to the Holocene optimum (sharp NH cooling at 8kya was a brief anomaly). Conversely the SH and Antarctica cooled from 11-8kya.

Then about change – from 8kya till the present the NH slowly cooled while the SH slowly warmed.

The global trace of CO2 follows the SH, not the NH, simply because there is more ocean water in the SH. The SH will always “win” a battle of strength between the two hemispheres.

It’s interesting that measured CO2 variability is high in the early Holocene, is very reduced in the mid Holocene but that variability started increasing again about 2000 years ago (well before any anthropogenic effect). It could be that variable CO2 is a signature of instability that naturally occurs at both ends of an interglacial; near its beginning and its end.

Last edited 1 year ago by Hatter Eggburn
Renee Hannon
Reply to  Hatter Eggburn
August 14, 2021 10:29 am


Nice summary. In addition, Holocene polar temperature trends are largely synchronous and in the same direction as their local summer solar insolation. For most of the Holocene, Antarctic and Arctic temperature trends appear out of phase with each other just as Northern and Southern summer insolation are out of phase. The role of local insolation may play a strong influence on the underlying millennium-scale polar temperature trends in the polar regions.

Today, northern, and southern summers are reversed from the Early Holocene. Presently, the southern summer occurs near perihelion when Earth is closest to the sun and northern summer occurs when Earth is farthest from the sun. In the future, northern insolation will continue to decline, and southern insolation which is currently strong will begin to decline.

I concur CO2 variability suggests climate instability particularly on shoulder events like the beginning of the interglacial period. And perhaps we are entering another period of instability due to the high CO2 variability seen today as we slowly exit the current interglacial period. A natural explanation for CO2 increases we are experiencing. It’s always good to have multiple theories.

Last edited 1 year ago by Renee Hannon
Reply to  Renee Hannon
August 14, 2021 11:18 am

Thanks Renee – yes precession is a big factor. Including in how things move forward.

Heat piracy comes from the AMOC pulling warm surface water south to north across the Atlantic equator (in exchange for cold deep water going the opposite way). Classically oceanographers talk of Norwegian Sea deep water formation being the driver of the global THC (Thermohaline circulation) – it is important of course but I suspect that Antarctica is more so.

Renee Hannon
Reply to  Hatter Eggburn
August 15, 2021 10:08 pm

Thanks for the diagram. It would be interesting to put together a hierarchy or flow diagram of the key influences (external astronomical – internal planet core) and subsequent reactions of ocean, land, and atmosphere. By latitude.

Last edited 1 year ago by Renee Hannon
Jim Ross
August 15, 2021 2:09 am


Please accept my apologies for going somewhat OT with some of my responses here about the atmospheric 13C/12C ratio. I know very little about paleoclimate analyses so really appreciate your posts about ice core data. Do you have any views on the paper I referenced about the analysis of Law Dome data (as shown in their figure 1) here: Kőhler et al (2006), “On the application and interpretation of Keeling plots in paleoclimate research—Deciphering δ13C of atmospheric CO2 measured in ice cores”.

Last edited 1 year ago by Jim Ross
Renee Hannon
Reply to  Jim Ross
August 15, 2021 12:40 pm

No worries on the discussion of the 13C/12C ratio. Carbon isotopes are important in trying to quantify the contributing sources to atmospheric CO2; terrestrial, ocean and fossil fuels. I agree that the decline net 13C/12C ratio of -13 per mil tends to favor natural influences over fossil fuels. WAIS and DML show a similar decline as Law Dome.

Rubino, 2019, also has a good discussion on δ13C-CO2, section 3.4. He uses an additional record of carbonyl sulfide (COS) for biogeochemical interpretations. He shows that COS increase during the LIA confirms that the LIA CO2 decline was caused by net terrestrial uptake due to cooling. Using trends of CO2, δ13C-CO2, and COS can provide multiple datasets to interpret the processes influencing atmospheric CO2 variations over the recent past. And I have read several articles which state that terrestrial influences on atmospheric CO2 tend to be underestimated.

I’m surprised nobody brought up the 14C/12C ratio which also shows a steady downward trend. Carbon isotopes are definitely intriguing and worth the discussion.

Sorry for the late response, just saw your comment.

Jim Ross
Reply to  Renee Hannon
August 16, 2021 7:40 am

Thanks very much for the response. When I started looking at the direct measurements of atmospheric δ13C-CO2 using Keeling plots on the data available from Scripps, I was surprised to find that the plots all showed a strong linear relationship between 1/CO2 and δ13C with intercepts as follows:
Point Barrow -13.2 per mil, r squared 0.96
Mauna Loa -13.3 per mil, r squared 0.98
South Pole -13.0 per mil, r squared 0.98
As you will know, a linear relationship on a Keeling plot is reflective of a constant δ13C content of the CO2 being added to the reservoir being analyzed (the atmosphere) and is based on simple mass balance equations. However, we have only had direct δ13C measurements from the atmosphere since the late 1970s. I was initially skeptical that ice core data would be sufficiently robust to add to this, but I was very surprised to find that the Law Dome data also showed a strong linear relationship, as confirmed by Figure 1 in Kőhler et al (2006), with an intercept of -13.1 per mil and r squared of 0.96.
These results indicate that the net δ13C content (on average) of all additional atmospheric CO2 since 1750 or thereabouts has been the same. I say “on average” since it does fluctuate up and down with ENSO events (El Niño events are associated with lower δ13C content values, vice versa for La Niña). In my view, this is extremely important in terms of evaluating δ13C models, such as Keeling et al (2017), but I would assume that it also has some relevance to your work in assessing the reliability of ice core (ice and firn) data.
Happy to discuss further.

Clyde Spencer
Reply to  Jim Ross
August 17, 2021 9:37 pm

I say “on average” since it does fluctuate up and down with ENSO events (El Niño events are associated with lower δ13C content values, vice versa for La Niña).

This is a clue that outgassing is driving the isotopic changes!

Jim Ross
Reply to  Clyde Spencer
August 18, 2021 3:10 am


I agree that it could well be support for that hypothesis. I will respond in more detail, but it may not be for a day or so.

Jim Ross
Reply to  Clyde Spencer
August 19, 2021 6:47 am

First of all, just in case there is anyone still following this discussion who is not familiar with δ13C and Keeling plots (which are not the same as the Keeling curve, though both are attributable to Charles David Keeling) …..
Put simply, the δ13C of a CO2 sample is the difference between the measured 13C/12C ratio and the 13C/12C ratio of a fixed standard, expressed in per mil terms. Thus, a negative δ13C means that the sample has a lower 13C/12C ratio than the standard. The units of ‘per mil’ mean per thousand, so exactly the same as if expressed as a percentage (per hundred) but multiplied by 10. So, for example, a δ13C of -13 per mil means that the sample has a 13C/12C ratio that is 1.3% lower than the 13C/12C ratio of the standard.
Since 13C and 12C are stable isotopes (unlike 14C), there should be an isotopic mass balance just as there should be a mass balance of CO2. A Keeling plot is based on the mass balance equations where plotting pairs of 1/CO2 and δ13C measurements of a single reservoir (e.g. the atmosphere) that are changing over time, will give a linear relationship if, and only if, the net δ13C content of the CO2 being added to that reservoir is a constant (which has the value shown by the intercept of the linear fit to the data). The chances of this happening with a complex mix of sources, sinks and variable disequilibrium fluxes must be extremely small and hence is actual evidence in support of a simpler explanation.
Models (hypotheses) that are able to fully match observations are not evidence that the model is actually correct; models are no more than non-unique, possible, explanations. On the other hand, models that do not match observations are proof that the model is invalid.
And yet there would appear to be no published models that are fully able to provide an explanation for the observed atmospheric δ13C behavior. Think about that – no accepted explanation in climate science despite it being a crucial aspect of understanding atmospheric CO2 observations. Keeling et al (2017) were able to get closer to a match with the observed δ13C trend by adding a new variable to their already-very-complex model, but did not attempt to match the short term fluctuations. Since the model does not match these fluctuations, it lacks credibility in my view.

The most recent paper that I have seen which investigated in detail the short term fluctuations in atmospheric δ13C was van der Velde et al (2013) “Biosphere model simulations of interannual variability in terrestrial 13C/12C exchange”, which concluded that: “Our new terrestrial bottom-up results cannot confirm the suggestion of a closed 13C budget that allows low prescribed ocean net exchange variability”.

One major problem in these considerations is the oft-repeated myth that the atmospheric 13C/12C trend is somehow consistent with the estimated fossil fuel quantities being the primary driver of the trend. If you refer to Table S5 in the supporting information for Keeling et al (2017), you will see that 70% of the huge ‘adjustment’ that is required to derive an isotopic mass balance is from estimated disequilibrium fluxes which do not have any net effect on atmospheric CO2 levels. This is nowhere close to demonstrating that the observed 13C/12C trend is being driven by fossil fuels.
Here are a couple of simple isotopic mass balance examples which, as far as I can see, are being largely ignored by climate scientists. The calculations are based on conservation of 13C and include a non-material approximation that 12C quantities can be taken as total CO2 (12C is 98.9% of CO2; this approximation can easily be checked by conversion back from δ13C to 13C/12C):
1750: CO2 280 ppmv; δ13C -6.4 per mil
1980: CO2 336 ppmv; δ13C -7.50 per mil
Average δ13C of incremental CO2:
(336*-7.50 – 280*-6.4) / (336 – 280) = -13.0 per mil
1980: CO2 336 ppmv; δ13C -7.50 per mil
2019: CO2 406 ppmv; δ13C -8.44 per mil
Average δ13C of incremental CO2:
(406*-8.44 – 336*-7.50) / (406 – 336) = -13.0 per mil
So, in summary, I have two major problems with the published δ13C models:
1.    They fail to acknowledge the longer term ‘constancy’ of the δ13C content of all incremental atmospheric CO2 since 1750 (or thereabouts); and,
2.    They fail to provide an explanation for the short term fluctuations in δ13C behavior.
I see these two points as a starting position for discussion of possible models/hypotheses, unless either one or both can be shown to be incorrect.

Last edited 1 year ago by Jim Ross
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