Greenland Ice Core CO2 during the past 1,000 years

Guest Post by Renee Hannon

This post compares CO2 ice core measurements from Greenland to those from Antarctica over the last millennium. Paleoclimate studies typically use only Antarctic ice cores to evaluate past CO2 fluctuations. This is because 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. This post will demonstrate that CO2 data from Greenland ice cores have scientific value and respond to key paleoclimate events such as the Little Ice Age and Medieval Warm Period.

Antarctic Ice Core CO2 Trends
Antarctic ice CO2 data is readily available and has been studied extensively (Bauska, 2015, Ahn, 2012, Siegenthaler, 2005 and Rubino, 2019). Most of the focus of recent studies has been on high snow accumulation sites which tend to have higher resolution and less smoothing of the trapped gas age in ice bubbles due to the firn to ice transition. Gas age width and resolution ranges from 10 years in Law Dome ice cores to 65 years in Dronning Maud Land DML. Figure 1 shows CO2 data from Antarctic high-resolution ice cores over the past millennium.

Ahn et al, 2012, compiled CO2 records from the West Antarctic Ice Sheet (WAIS) and compared them to other key datasets such as Dronning Maud Land (DML), and Law Dome. Their study recognizes and discusses elevated CO2 during the Medieval Warm Period (MWP) at 1000 AD, decrease of CO2 around 1600 AD during the Little Ice Age (LIA) and the subsequent rapid increase beginning around 1850 AD.

Figure 1: Antarctic ice core CO2 data during the past 1000 years. Actual data points are plotted with 20-yr trend lines fitted to these data. Law Dome trend is the 20-year spline provided by Rubino, 2019. Siple and Adelie Land D47 57 is a 100-year trendline from Barnola, 1995. Gas width due to firn-ice transition and sample spacing resolution in years (yr) are noted in text box. Data references shown on plots.

More recently, Rubino 2019, presented revised ice core gas records for Law Dome. His robust study evaluates multiple gases such as CO2, CH4, N2O as well as carbon isotopes. He has a good discussion on the LIA where the ice record shows CO2 decreasing as delta 13C increases which favors reduced soil or terrestrial respiration in response to cooling. Rubino also discusses the CO2 decrease of 10 ppm in the Law Dome record around 1610 AD which is not present in any other records. This rapid decrease demonstrates the higher resolution of Law Dome which is the highest Antarctic snow accumulation site.

Figure 2 compares the Antarctic CO2 trends. Surprisingly, there is quite a bit of difference ranging from 0-11 ppm. Ahn, 2012 noted that WAIS is generally 2-4 ppm higher than Law Dome CO2 data. WAIS CO2 is also systematically higher than DML CO2 by up to 6 ppm, with an average of 4 ppm higher. This shift occurs with both CO2 and its carbon isotopes but not with CH4, methane. The reason for the shift is not well understood.

Figure 2: Antarctic ice core CO2 trends during the past 1000 years compiled from Figure 1. Data references in figure 1.

The high-resolution Law Dome data can identify CO2 rises and dips of less than 30 years. WAIS is up to 10 ppm higher during the Law Dome dip at 1610 AD; due to lower resolution as noted by Rubino, 2019. Law Dome also shows modest CO2 rises during the MWP, but not as high as WAIS. Interestingly, Law Dome is 2-4 ppm higher than DML pre-1600 AD except for a few dips.

DML CO2 has the lowest snow accumulation and is the lowest resolution Antarctic dataset shown. The resolution is about 65 years with a more muted representation of atmospheric CO2 history, explaining the systematic lower CO2 readings. DML does show key CO2 events such as a decrease during the LIA, subtle increase during the MWP, and a rapid increase beginning around 1850 AD. DML and Law Dome CO2 trends converge during the LIA and recent rapid rise.

The Siple D47 D57 data shown as the dashed line in Figure 2 was not utilized in either Ahn or Rubino’s studies due to uncertainty in age dating and/or imprecise experimental methods. Clearly it is the odd dataset, particularly pre-1400 AD. There is an 11-ppm difference in CO2 from Law Dome at 1200 AD. The oddities of the D47 D57 measurements are important to note because this is the Antarctic dataset used to compare and discredit Greenland CO2 data (Barnola, 1995).

Greenland Ice Core CO2 Trend
CO2 measurements from Greenland ice cores are believed to be unreliable due to in situ production of CO2 by carbonate-acid reactions and oxidation of organic compounds (Anklin 1995, Barnola 1995, and Tschumi 2000). This premise was put forward because Greenland CO2 data differed from Antarctic CO2 ice core data. CO2 concentrations in Greenland ranged up to 20 ppm higher than Antarctic CO2 although the records are in good agreement for about the last 300 years. Greenland CO2 had more variability with standard deviations of 6-10 ppm compared to 2-3 ppm in Antarctic ice cores. Also, of note, Greenland CO2 concentrations from ice cores (Summit, GISP2, GRIP, Dye3) agree well with each other and all show similar disagreements from Antarctic. See my previous post for a more thorough discussion of Greenland CO2 data here.

Let’s take a closer look at Greenland ice core CO2 data during the past 1000 years. Barnola, 1995, analyzed ice core samples from Greenland Summit at two different laboratories, Grenoble and University of Bern. Summit has high snow accumulation rates, and the smoothing is only about 15 years. Digital data is not available; however, tables of the data are included in their publication. Sample spacing is erratic and ranges from 5-80 years with an average of 30 years. Carbon isotope data from Greenland ice cores are not publicly available.

Barnola, 1995, states the agreement between the Greenland Summit CO2 measurements from the two laboratories is very good with the mean difference being about 2 ppm. It is common to see 3 ppm discrepancies in CO2 between different laboratories according to Rubino, 2019. Due to the good agreement, Greenland CO2 samples at the same depth were averaged between laboratories. The data was then resampled and smoothed over 60 years. The results are plotted in Figure 3.

Figure 3: Graphs are Grenoble and University of Bern lab CO2 measurements from the Summit Eurocore in Greenland overlain on a low pass filter of 60 years, solid green line. Vertical error bars are 5 ppm deviation. Triangles represent the 2 data points outside error bars in bottom graph.

Greenland ice CO2 decreases to 280 ppm during the LIA and shows a rapid CO2 increase starting about 1850. Greenland CO2 data shows two earlier increases: a better defined Medieval Warm Period and another distinct rise around 1550 AD. CO2 data reaches nearly 300 ppm on individual data points during the MWP.

CO2 Inter-Hemispheric Differences
One of the reasons Greenland CO2 measurements in ice were questioned was due to a large inter-hemispheric difference (IHD) of 20 ppm when compared to Antarctic data. The modern inter-hemispheric gradient of atmospheric CO2 concentrations after being de-seasonalized range from 1-6 ppm measured during the short window of the past 45 years.

The CO2 trends between Greenland and Antarctic data are shown in the top graph in Figure 4. Law Dome is not plotted due to its higher resolution as WAIS and Siple D47 57 mostly bracket the range of Antarctic CO2 data.

Greenland CO2 was originally compared to Antarctic Siple D47 D57 and demonstrated differences up to 20 ppm, which is unreasonable according to Barnola, 1995. Indeed, the bottom graph in Figure 4 shows that the difference between Siple D47 57 and Greenland (gold line) is up to 20 ppm briefly around 1200 AD. For the most part, the IHD is less than 5 ppm from 1300 AD to the LIA, with an exception at 1550 AD. Greenland and Antarctic differences are practically zero during the LIA to present day. The IHD tends to become higher during the MWP and around 1550 AD. As previously mentioned, the Siple D47 D57 ice core is an odd outlier Antarctic CO2 dataset.

Figure 4: Top graph shows Greenland and Antarctic ice core CO2 trends over the past 1000 years. Bottom graph shows interhemispheric difference (IHD) between Greenland and Siple D47 57 in gold and the Greenland and WAIS difference in blue. The light gray shaded band is the acceptable modern IHD range. Error bars represent 2 standard deviations. Modern observatory Barrow (BRW) and South Pole (SPO) IHD data are shown by the gray line.

If the Greenland CO2 trend is compared to Antarctic WAIS ice core, then the interhemispheric difference is always less than 10 ppm shown in blue in Figure 4. And it’s less than 5 ppm during 70% of the past 1000 years like the present atmospheric CO2 differences (the heavy gray line). It should be emphasized that Antarctic datasets have up to 10 ppm difference between them alone. Thus, comparing Antarctic and Greenland datasets and discovering a difference of 5-10 ppm appears to be within the range of reasonable values considering their geographic distance.

The highest polar inter-hemispheric difference and the highest difference between the Antarctic CO2 datasets both occur during the MWP. The D47 D57 shows the greatest divergence from the Antarctic datasets but it is not used in recent publications such as Rubino, 2019 or Ahn, 2012. Unfortunately, the Greenland CO2 data was originally compared to this outlier Antarctic D47 D57 dataset and deemed unacceptable.

Interestingly, all Antarctic and Greenland CO2 measurements tend to converge during the colder LIA period and overlie almost perfectly during the subsequent rapid increase.

Greenland Ice CO2 Rises Mimic Methane
Greenland and Antarctic CO2 trends plotted alongside methane from ice cores over the past millennium are shown in Figure 5. Methane from various ice cores overlie nicely. Methane shows a distinct separation between the polar regions with an IHD of 24 to 58 ppb (Rubino, 2019). This is lower than the current atmospheric methane difference of 100 ppb between the South Pole and Barrow observatories.

In general, methane shows similar trends over the past millennium as CO2. Methane decreases during the LIA with a subsequent rapid increase. There is a distinct rise in methane around 1550 AD that is not captured well by Antarctic ice CO2, especially the DML data. Interestingly, the Greenland CO2 does show the 1550 AD increase. Greenland CO2 also shows character during the MWP that mimics the methane trends, again not seen in the Antarctic CO2 data.

Figure 5: Top graph are Greenland and Antarctic ice core CO2 trends over the past 1000 years. References in Figure 1. Bottom graph shows methane data from Greenland (green/grays) and Antarctic (red) ice cores. GISP2 and WAIS methane from Mitchell, 2013 and 2011; NEEM methane is from Rhodes 2014.

Antarctic CO2 shows more scatter than methane in the various ice cores over the past millennium. As discussed above, Antarctic WAIS is 2-4 ppm higher than Law Dome and 3-6 ppm higher than DML. Additionally, the lower resolution Antarctic DML is 2-4 ppm lower than Law Dome during the MWP and 1550 event. CO2 from all datasets tend to converge during the LIA cold period and subsequent rapid rise.

Figure 6 illustrates some of these CO2 differences for three key events: MWP, 1550, and LIA. All datasets recognize these events; however, the magnitude between the events varies. The left graph shows that Greenland and WAIS have higher average CO2 concentrations during all events. Greenland and WAIS were normalized on the LIA which required a shift of 3 ppm shown on the right graph. Greenland shows the largest magnitude, or CO2 amplitude variation, between the cooler LIA and MWP of over 11 ppm. As expected, DML shows the lowest difference of only 2 ppm between the LIA and MWP due to its lower resolution. Law Dome shows a slightly higher difference of 5 ppm compared to WAIS of 4 ppm.

Figure 6: Average CO2 from Greenland and Antarctic trendlines for key events. Left graph is trendline averages and right graph is normalized on the LIA. Age ranges used for MWP from 1000-1200 AD, 1550 event from 1500-1660 AD, and LIA from 1700-1800 AD.

The reasons for the CO2 scatter and different underlying trends are not well understood and chemical reactions within the core are frequently cited. The scatter in both Greenland and Antarctic tends to occur with elevated CO2 during warmer times.

Another potential explanation is the modification of CO2 during the firn to ice transition. Ahn, 2012, states that WAIS CO2 probably experience additional smoothing processes not captured by firn air models. Their enhanced firn air model still underestimates WAIS CO2 smoothing by 37 percent (19 years versus 30 years). Temporal resolution is certainly a factor in the systematically reduced CO2 measurements in the DML ice core.

Scatter in CO2 may be also be attributed to inter-core variability. Rubino notes that it is not uncommon to see inter-core variability of 3-4 ppm in Antarctic core data. Greenland’s present day atmospheric data shows higher standard deviations from 4-5 ppm with 15-20 ppm seasonal swings than Antarctic atmospheric data. It should not be a surprise that inter-core CO2 variability is higher in Greenland ice cores than Antarctic cores.

Scientists have classified Greenland ice core CO2 measurements as contaminated and mostly ignore these data. These data are a high-resolution polar endmember that can provide additional information to complement Antarctic CO2 datasets. Higher CO2 events are expressed better in Greenland than Antarctic cores. For example, Greenland CO2 data captures CO2 increases almost up to 300 ppm in individual data points during the MWP that correlate well with methane rises. Greenland CO2 data show increases during 1550 AD like methane rises. Perhaps, Greenland data is suggesting that CO2 increases during past warm periods are larger than documented by the muted Antarctic CO2 data. Greenland CO2 data is trying to tell scientists the Arctic side of the paleoclimate story. But many scientists have chosen not to listen.

Errors using inadequate data are much less than those using no data at all” – By Charles Babbage, Inventor and Mathematician

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

Download bibliography here.

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July 2, 2021 10:19 am

Talk about keeping people hanging on! Oh per-lease put the temperatures on those CO2 graphs so we can see how good the correlation between temperature and CO2 is, and whether CO2 is leading or lagging temperature? How hard can it be? Why wouldn’t they? Oh, they wanted to get published….?

Reply to  Brian R Catt
July 2, 2021 11:30 am

Working on comparing temperatures and GHGs. After I saw how gases measured in ice age are simply shifted to a gas age, I am skeptical of interpreting lag and lead times. The gas trapped in ice is believed to be younger than the age of the ice when it is eventually trapped within bubbles. This age difference is referred to as the ice-gas age delta. The delta ranges from about 30 years in Law Dome to 835 years in the lower accumulation DML ice core. To compensate for this age difference, peer reviewed studies use a simple method of shifting CO2 measurements from the core ice age to match a younger CO2 gas age.

Reply to  Renee
July 2, 2021 3:11 pm

This is a good analysis of a specific issue – comparison of Greenland and Antarctic. It shows that, while the differences may be interesting, they are small. I doubt if the conclusions of T vs [CO2] would be much illuminated by that differential.

Reply to  Nick Stokes
July 2, 2021 3:42 pm

Thanks for the compliment on the analysis. You are correct that the differences are small on an absolute scale, however, on a relative scale Greenland shows greater than 50% CO2 increase during the MWP compared to Law Dome (10.5 ppm versus 4.5 ppm, figure 6 normalized).

Reply to  Renee
July 3, 2021 1:21 am

Greenland shows large natural variability, so it is OBVIOUSLY wrong, since we “know” that any change in atm CO2 is due to fossil fuel usage.

Any data showing anything else is obviously “unreliable” because it does not fit exceptions. Selection bias in spades.

R Taylor
Reply to  Renee
July 2, 2021 3:56 pm

The lag of CO2 behind deuterium is consistent through every glacial cycle of the Vostok/Dome C cores.

Reply to  Renee
July 3, 2021 1:25 am

After I saw how gases measured in ice age are simply shifted to a gas age, I am skeptical of interpreting lag and lead times.

My first dive into climate data was the Antarctic ice cores. I was initially impressed by the publicly available data and how open and verifiable it all looked.

However, once I started reading I discovered that whole “gas age” thing was NOT AT ALL open and transparent. There was no accounting for the methods used and NOTHING was reproducible or verifiable or falsifiable. You just have to take it on trust.

Michael in Dublin
July 2, 2021 10:28 am

The graphs that range from 270 to 320ppm are in a sense exaggerating the increases from say 1800 to 1900/1950 (because of the scale) and do not give us an indication of the changes from 1900/1950 to 2020. Are these not available or difficult to determine?

Reply to  Michael in Dublin
July 2, 2021 11:09 am

It is not a straightforward exercise to compare CO2 from ice core data to CO2 measured in the firn and atmosphere which dominate the CO2 record from 1960 to present day. As atmospheric CO2 passes from firn to ice, it is altered and smoothed due to gas mixing processes with depth and time. Gas concentrations measured during firn densification are an average of atmospheric concentrations that range from 10 years at high accumulation sites like DE08-2 to hundreds of years at low accumulation sites such as Dome C and Vostok. The necessary corrections for atmospheric attenuation of CO2 in ice need to be applied in order to compare it to individual ice core datasets.

Kevin A
July 2, 2021 10:47 am

CO2 evil.. Maybe not:comment image
When you have 12,000ppm CO2 at -25C that would be evil – 4 billion year history and he looks at 1,000 years.

Reply to  Kevin A
July 2, 2021 11:38 am

The graph is attributed to Zachos 2001.No such graph or data series exists in this publication. I searched other Zachos publication and nothing like this appears in those either. There is also a label on this graph that says “solar irradiance 3.6% lower at 550 MYA equivalent -2.3C”. But the thing is per Gough 1981 this value should be 4.6%. And solar irradiance at -3.6% is -8.6 W/m2 which combined with the -2.3C is 0.27C per W/m2. Where did the 0.27C per W/m2 come from? Obviously I’m curious where you found this graphic..

Anyway, I’m assuming you feel Zachos is a trustworthy source? You should read some of his publications. The conclusions are undeniable and overwhelming. CO2 has a significant effect on the global mean temperature and climatic change events. That doesn’t mean CO2 is evil. It just means that it is a factor that modulates the climate system.

Reply to  bdgwx
July 2, 2021 12:04 pm

it is a factor that modulates the climate system

I reckon you would get no argument from most AGW skeptics on that statement.

There are numerous factors that determine how all the climates around this planet behave.

Many such factors are still being arrived at by assumptions, not observations or measurements.

The issue for me is the “CO2 as climate control knob” position asserted by activists.

They’ve taken a scintilla of chemical & physical lab experiments & suggestions, added an eye watering load of conjecture, and asserted they have arrived at “the only answer”

Reply to  bdgwx
July 2, 2021 4:36 pm

I’ve seen several different renditions of this graph. They all are about the same.
From the lack of some useful captions and slight differences in arrangement I don’t think is was intended as more than a cartoon rendition.
The measurements the graph shows are all a bit tenuous. The actual values available are really hard to calibrate tightly to the variables graphed – date, values, possible errors, etc.

Reply to  Kevin A
July 2, 2021 12:02 pm

There are temporal resolution issues comparing high-resolution atmospheric data and the past 1000 years to the past millions or billions of years. The sample spacing resolution of marine benthic stable isotopes is 1000 to greater than 4000 years.

Reply to  Kevin A
July 4, 2021 9:05 am

Looks like we’re on the verge of CO2-starvation — the next great extinction event.

July 2, 2021 11:07 am

I am forming the conclusion that ice cores fail to capture the true scale of short term atmospheric CO2 variability.

Reply to  Stephen Wilde
July 2, 2021 5:27 pm

Especially if you’re looking at cores drilled in ice over a crust deposited by volcanic activity, with CO2 leaking out at the bottom of your core.

Reply to  pochas94
July 3, 2021 11:02 am

Good point, but wouldn’t the co2 levels measured be ridiculously high then?

July 2, 2021 11:07 am

“Errors using inadequate data are much less than those using no data at all” – By Charles Babbage, Inventor and Mathematician

And with one candle of truth at least half of all “climate science” goes poof.

July 2, 2021 11:07 am

The methane rise is a key factor in deciding cause and effect, looks to me like it rose with CO2 due to a change in temperature … but that does not rule out a reverse effect, that the initial temperature rise was enhanced by the gases.

July 2, 2021 11:13 am

The inability of the “high resolution” Antarctic cores to resolve the spike c.1500CE suggests to me that their “resolution” is suspect.

July 2, 2021 11:52 am

An explanation for the differences in co2 could be due to a process of Temperature-dependent fractional distillation which fractionated the gases in the firm layer to some value dependent on the temperature of the firm. This would explain the close correlation between the delta 18 temperature proxy and co2 concentration. Such a fractional distillation process is possible because it is known that other gases fractionate.

Reply to  Rob
July 2, 2021 12:32 pm

The CO2 data presented in this post have been corrected for gravitational fractionation by the various authors. The correction for gravitational fraction rate lowers the CO2 concentration by approximately 1.2 to 1.5 ppm. I agree uncertainties in the measurements between the Arctic and Antarctic may account for some of the dataset discrepancies. Although this has not been noted as a reason by any of the authors.

Ulric Lyons
July 2, 2021 12:33 pm

Cool, the CO2 and methane levels rise through the Sporer Minimum, and are then lower in the early 1600’s. There was lots of very hot weather in the 1610’s and 1630’s, positive NAO/AO regimes driving colder ocean phases, big active solar cycles. That’s a bit sneaky labeling the LIA from around 1600, Sporer was deeper and longer than Maunder.

Reply to  Ulric Lyons
July 2, 2021 9:16 pm

Hi Ulric
I simply plotted the public GHG data, not trying to be sneaky. But the peer-reviewed gas curves could use a bit of shifting and stretching. Depth to time conversion is not static.

July 2, 2021 12:44 pm

Great article Renee. The Greenland ice cores and DE08 from Law Dome, Antarctica are of high enough resolution to integrate with instrumental data.

What would be even more interesting would be a proper analysis of Greenland ice core CO2 from the Early to Mid Holocene. It appears that the Greenland ice cores are fairly consistent with Northern Hemisphere plant stomata chronologies, which indicate that >300 ppm was the norm back then.

Reply to  David Middleton
July 2, 2021 1:23 pm


At the very least,
what considered here as considered, kinda of pointing out that LIA was a global event.

Oh, well maybe I should not have commented in this one!

But still, it points out that if any merit here… it will consist with LIA being considered and addressed as a global event… after all!


Reply to  David Middleton
July 2, 2021 1:55 pm


Yes, the gas width resolution of 10-20 years do make DE-08 and Greenland reasonable datasets to integrate with instrumental data. I’m still trying to get a better understanding of the Firn air transport models and diffusion. Diffusion in the Firn is well understood. However, many Firn models do not have continued eddy diffusion within the lock-in-zone. Also, porosity continues to decrease notably below the LIZ in the DE-08 cores. According to Trudinger, the process of upward flow of air and gases due to compression of the pore space as new snow accumulates above is an important process that has not been incorporated into Firn models. My gut feel is that the gas width or smoothing in ice cores is underestimated. Ahn, 2012, states that their enhanced firn air model underestimates WAIS CO2 smoothing by 37 percent (19 years versus 30 years).

The NH plant stomata chronology also agree better with Greenland over the past 1000 years and show CO2 of 25 ppm higher than Antarctic CO2.

Joel O'Bryan
July 2, 2021 1:22 pm

The nadir of LIA was around 1700. The CO2 slope changes (1st derivative wrt to time) lag relevant paleo temperature records by about 100 years.
Conclusion: CO2 in the paleo records are responding to temperatures, not the other way around with an apparent lag of around 100 years. In the longer term reconstructions, stretching back through the Pleistocene, others have shown the CO2 lag to be around 800 years.

Bill Treuren
Reply to  Joel O'Bryan
July 2, 2021 5:21 pm

Historically that is the probable case but we are adding CO2 in this instance so the argument is rather weak.

What is important is the Holocene being 300ppm so the delta to now given temperature similar is 110ppm.
emitted CO2 is disappearing faster than modeled, this is very good news but not pushed around much.
In the 70’s the expectations presented were that with the amount of CO2 pumped out by now we should be closer to 500ppm than the 410ppm we actually have as such BAU will see at a maximum of 550ppm rather than the RCP8.5 1100 plus ppm.
Things are going well for humanity pity we don’t see it that way.

Joel O'Bryan
Reply to  Bill Treuren
July 2, 2021 6:29 pm

I agree that the data being ignored by mainstream CliSci is that CO2 drawdown happens much faster (residence time) than assumed (and modeled).

Reply to  Bill Treuren
July 3, 2021 11:16 am

Also being ignored is that the c02 ppm measured seems to ignore any big changes in human emissions like what happened during covid lockdowns, yet responds very quickly to the change in seasons. CO2 levels measurements start to level off in April, peaking in May – just 2 months after the start of spring. Human emissions are just a pimple on the ass of an elephant compared to natures emissions and sinks.

July 2, 2021 1:26 pm

The vapour pressures of O2, n2, ch4, Argon, nitrous oxides are much higher than for co2, so their solubilities in the firn are much lower than co2. If there was a distillation process which was dependent on solubilities, e.g. pressure swing absorption, then this could fractionate co2 w.r.t. n2, O2, argon. Pressure swing absorption and adsorption are industrial processes for distilling and separating gases based on big differences in absorption or adsorption and vapour pressure, so it is possible to fractionate the gases in the firn to a temperature dependent concentration. If this was the case, you would expect to see an exponential change from the final fractionated concentration at the bottom of the firn to the surface firn concentration which would be the atmospheric concentration, which is exactly what you do see. The last 120,000 years of Greenland ice core data supports this hypothesis eg camp century, dye3, grip, gisp2 and ngrip, all of which show quite different co2 concentrations to Antarctic ice cores, especially around the dansgard-oeschger cycles. If this was the case, it would mean that the ice cores would not be true records of past atmospheric concentrations of co2, but would be a temperature dependent artifact or proxy for local temp.

Reply to  Rob
July 2, 2021 2:20 pm

Can you provide some references on the fractionation-temperature dependency and it’s impact on firn CO2 in the Greenland ice cores. I have looked at CO2 in the firn from both Antarctic and Greenland and they show similar decreasing slopes from the surface firn concentration to the bottom of the firn. You have a very interesting theory. Authors have discussed chemical reactions as the main cause of increased CO2 concentrations in the Greenland cores. I have not come across any literature discussing CO2 as a temperature dependent artifact in Greenland or Antarctic ice cores. Thanks.

July 2, 2021 1:38 pm

Errors using inadequate data are much less than those using no data at all” – By Charles Babbage, Inventor and Mathematician

I love that one, didn’t know it was from Babbage.
And this means a few reliable data sets are worth more than models as science.

And the modelers don’t see all the important data, and the data people are fudging the records.

Tom Abbott
Reply to  a_scientist
July 3, 2021 4:16 am

“And this means a few reliable data sets are worth more than models as science.”

So, actual temperature readings would be worth more than computer-generated Hockey Stick anamoly charts.

July 2, 2021 1:51 pm

Renee Hannon ==> Very well done, thank you.

As with many other indicators used as proof of the evils of the “Modern Industrial Era”, CO2 and  Methane both visually start to rise beginning in the early or mid-18th century — 1725-1750 or a bit later. Well before worldwide industrialization begins.

Reply to  Kip Hansen
July 2, 2021 3:43 pm

If only the source was known.

Reply to  aussiecol
July 2, 2021 5:35 pm

aussiecol ==> If you mean the source of the CO2 and Methane, yeah — wouldn’t we like to know….

If you mean the source of Hannon’s data, I’ll point out that Hannon, the author, gives short-form cites on the plots themselves, such as “Bauska, 2015”.

Reply to  Kip Hansen
July 2, 2021 5:42 pm

The early rise is due to land clearing, especially in N America and later Australia
comment image

Clyde Spencer
Reply to  Nick Stokes
July 2, 2021 7:29 pm

The early rise is due to land clearing, especially in N America …

The US land clearing started in New England and along the Eastern Seaboard. With the Midwest opening up, such as the Ohio valley, people started to abandon the rocky, shallow soils of New England. One can walk in the forests of New England today and find stone fences that mark the boundaries of the abandoned farms. In much of the western US, the forests are thicker than the primordial forests because of fire suppression.

I would expect to see a decline in the purple line (cumulative land clearance) as CO2 is taken out of the atmosphere by the regrowth of cleared forests. I don’t see it. Therefore, it looks like the purple line represents gross CO2 cumulative contribution and not net. Thus, it would seem to be an overestimate of CO2 from land clearance.

Reply to  Clyde Spencer
July 2, 2021 9:09 pm

The early part was N America. But then came Australia, and then parts of S America. And there was continual erosion of forests in Europe. Plus just harvesting forest timber.

Reply to  Nick Stokes
July 3, 2021 8:13 am

The greening of the planet is shown by satellite photos…more CO2 = more plant matter which uses CO2.

Reply to  Nick Stokes
July 3, 2021 4:42 pm

Except your land clearing theory has a floor.
The forests were replaced by grass, crops, plantations, shelterbelts, etc, etc. They all use CO2 the same as the forests, which by the way are carbon nuetral.

Reply to  aussiecol
July 3, 2021 9:27 pm

They use CO2. But they don’t store C. What counts is the tonnage of C/area, which is obviously less for crops and pastures than for forests.

Reply to  Nick Stokes
July 3, 2021 11:21 am

Your graph shows emissions noticeably increasing from 1850, but the ice core data shows 1700-1800.

Reply to  PCman999
July 3, 2021 9:28 pm

Land clearance data starts from 1850 (Vaughan et al). But land clearance was happening earlier.

Tom Abbott
Reply to  Kip Hansen
July 3, 2021 4:17 am

“Renee Hannon ==> Very well done, thank you.”

I agree, and the comments from all involved added a lot to the conversation, too.

Jackie Pratt
July 2, 2021 3:14 pm

Pardon my density. The convention that the Greenland cores are ‘no good’; is that because they do not match multiple other sources? The other sources being comparable? Thanks

Reply to  Jackie Pratt
July 2, 2021 5:38 pm

No, the Greenland issue is that there are carbonates present which could (but probably didn’t) exchange with gas CO2. This whole article is about matching with Antarctic cores; there are some differences, but overall the match is good.

Reply to  Nick Stokes
July 3, 2021 11:08 am

There is another issue with the Greenland icecore gas records. During the last interglacial the Dansgaard-Oeschger events have a completely different signature in Greenland CO2 and in Antarctic CO2. Since CO2 is quite a global gas this difference strongly supports the contamination issue. By looking only at the Holocene part of the record, we avoid the biggest disparity between records.

July 3, 2021 1:17 am

So clearly Greenland CO2 gets ignored because it does not provide the required hockstick. Any data which does not fit “expectations” is summarily rejected with some hand-waving reasoning about “contamination”.

overlain on a low pass filter of 60 years, solid green line.

Perhaps Renee Hannon could describe exactly what filter he used, and how he padded the data to run it up the both ends of the data.

Reply to  Greg
July 3, 2021 10:48 am

The filter was loess. She extrapolated the ends to fit the last data points.

July 3, 2021 8:48 am

I have to say that this new article has convinced me of the value of Greenland CO2 records.

Now when we compare your figure with the Summer Northern Hemisphere temperature record from Anchukaitis et al. 2017 and Solar TSI record from Vieira et al. 2011, we can put a name to those CO2 bumps in Greenland (Oort, Wolf, Sporer, and Maunder+Dalton). They support that solar activity is one of the main centennial to millenial climate determinants. It is not the only one, as volcanic activity and multidecadal oceanic variability also play a role. That´s why the 1550s increase is not explained only by increasing solar activity.

Reply to  Javier
July 3, 2021 8:31 pm

Hi Javier,
Glad you are able to correlate these reactions to a climate determinant(s). I always appreciate your feedback.

July 3, 2021 9:49 am

I’m wondering why the author keeps saying that co2 started increasing about 1850 when all the graphs show the increases started easily at 1800, even 1700 in one graph. Looks like they have the idea that emissions are solely dependent on the industrial revolution that it’s affecting their eyesight.

Reply to  PCman999
July 3, 2021 10:45 am

The steepness of the slope increases around 1850 in CO2 data compared to 1800-1850 AD or older (figure 5, top graph). Many of the authors in the reference list also note this age as the beginning of rapid CO2 increase. It’s certainly not a precise age. I agree methane gases appear to increase sooner as we exit the LIA. Whether that is true or whether that’s a function of a different ice-gas shift applied to methane, not sure.

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