In climate skeptics circles, many take the words of Jaworowski about the unreliability of CO2 measurements in ice cores as truth and reject the possibility that ice cores reflect the ancient atmosphere. That, together with the historical measurements of Ernst Beck (see here), should show that pre-Mauna Loa CO2 data were much more variable and that higher values were present in certain periods of time. That effectively refutes that humans are responsible for the current increase of CO2 and thus of global warming.

While the cause of the increase of CO2 and its effect on temperature are two completely separated items, it is very probable that humans indeed are the cause of the CO2 increase (see here) and Beck's historical data lack long data series and most are taken at the wrong places, where there is a proven positive bias (see here). Now what can be made of Jaworowski's take on ice core CO2 data?

I have read several remarks made by Jaworoski about the ice cores. The first point that strikes me is that Jaworowski mainly refers to works written by... Jaworowski. And mostly for the period until begin 90's. Not a very strong sign of reliability of his remarks...
While several of his remarks may influence CO2 levels measured in ice cores, if not taken properly into account, many of these problems would lead to too high measurements, not too low.
Jaworowski has a paper on ice cores at the Warwick Huges web site [1]. Here are step by step reactions on what Jaworowski says. Follow the steps:
  1. Water in the ice.
  2. Clathrates and cracks in the ice.
  3. The deleting of inconvenient data.
  4. The arbitrary shift of air/ice data
  5. Conclusion
  6. References

1. Water in the ice.

This is because the ice cores do not fulfill the essential closed system criteria. One of them is a lack of liquid water in ice, which could dramatically change the chemical composition the air bubbles trapped between the ice crystals. This criterion, is not met, as even the coldest Antarctic ice (down to –73oC) contains liquid water[2].

According to what Jaworowski suggests, CO2 may go into that water, even may be retained there during the measurements, which leads to too  low CO2 measurements. But the article where he refers to is not about water, but about sulfuric acid at the triple joints of ice crystals, away from enclosed air bubbles [3]. Moreover, concentrated sulfuric acid may melt a tiny part of the ice, but it also makes that little CO2 (if in contact at all) can be dissolved in the liquid. Further, CO2 measurements are done by crushing the ice at low temperatures, under high vacuum, over a cold trap (-70°C), which effectively sucks CO2 out of any liquid water...

There is not the slightest evidence that liquids in the ice at the extreme cold temperatures in Antarctica play any role in the CO2 values measured. Moreover, different ice cores of Antarctica with completely different profiles near the coast (high accumulation, more dust/salt inclusions, less cold temperatures), compared to the more inland ice cores, show the same low CO2 values (within 5 ppmv) for overlapping periods of the same gas age.

There is no evidence that liquids in the ice structure lead to underestimated CO2 values for the Antarctic ice cores.

2. Clathrates and cracks in the ice.

After decompression of the ice cores, the solid clathrates decompose into a gas form, exploding in the process as if they were microscopic grenades. In the bubble-free ice the explosions form a new gas cavities and new cracks. Through these cracks, and cracks formed by sheeting, a part of gas escapes first into the drilling liquid which fills the borehole, and then at the surface to the atmospheric air. Particular gases, CO2, O2 and N2 trapped in the deep cold ice start to form clathrates, and leave the air bubbles, at different pressures and depth. At the ice temperature of –15oC dissociation pressure for N2 is about 100 bars, for O2 75 bars, and for CO2 5 bars. Formation of CO2 clathrates starts in the ice sheets at about 200 meter depth, and that of O2 and N2 at 600 to 1000 meters. This leads to depletion of CO2 in the gas trapped in the ice sheets. This is why the records of CO2 concentration in the gas inclusions from deep polar ice show the values lower than in the contemporary atmosphere, even for the epochs when the global surface temperature was higher than now.

Well, these are a lot of allegations. To begin with, indeed clathrates are formed at different depths. But that is a two-way process. Ice cores are extracted from the depth and kept up to a year under cold circumstances (mostly on site under the ice surface, packed in PE foil to prevent contamination). That is the time needed for the ice to expand, including the decomposition of clathrates. Of course when measurements are made, one uses parts of the ice where no clathrates or cracks are found.

But let us suppose that Jaworowski is right and that the scientists don't care about clathrates or cracks...

What will happen with clathrates? Well, N2 and O2 clathrates will decompose first, as that happens at much higher pressure and lower temperatures than for CO2 clathrates. Thus IF that leads to cracks at all, N2 and O2 will escape first ("explosive" if you want), long before CO2 clathrates will decompose. As CO2 is only 0.03% of the other two components together, there is little pressure for CO2 to escape anymore. Thus this will lead to too high levels of CO2 in the measurements, not too low.

Further, cracks in the ice core, caused by drilling, extracting and relaxation can be introduced (but are avoided as much as possible). But the outside world nowadays has a CO2 concentration of 380+ ppmv. If anybody can show me how one can measure 180-280 ppmv CO2 in ice if there may be an exchange of CO2 through the cracks, I am very curious to know the mechanism with which that may occur.

This is completely refuted by the measurements on ice cores, where indeed problematic parts were found, including cracks, see next item...

As long as Jaworowski doesn't show an adequate mechanism, why cracks should lead to lower measured CO2 levels, that remark is pure speculation, contradicted by real world facts.

3. The deleting of inconvenient data.

In another article (1997) [4], Jaworowski accuses several scientists of fudging data by deleting inconvenient high values.

Jaworowski accuses Neftel e.a. that they deleted inconvenient (high) measured values after they published all data in 1982. Here is the original graph [5]:

Siple Dome Neftel
CO2 measurements of the Siple Dome ice core (WAIS) by Neftel e.a. (1982) [1]

The comment of Neftel e.a. for the dashed lines was that drilling fluid was observed in the large samples. The wide range is from different measurements at the same part of the ice, thus of the same gas age. That all measurements show the real CO2 levels of the time period in question is impossible. Thus one need to look at the probabilities. Inclusion of drilling fluids (a mix of gasoil and a freon), and thus cracks in the ice, may lead to too high values, never too low. Thus it may be appropriate to use the lowest values in such cases, which are anyway far more in line with the other datapoints (where the median is taken, the thick point within the range). In fact to be sure, one should delete the whole datapoint/range, as there are problems with the reliability of the data at parts which are clearly contaminated.

This was done recently with a few datapoints of Epica Dome C, the oldest ice ever brought to the surface, some 800,000 years old [6].

Epica Dome C
CO2 levels 650-800 kyr BP in the Epica Dome C ice core [6].
The black arrow indicates a CO2 value of 339 +/- 56 p.p.m.v. (s.d.), an artefact detected at a depth of 3,178.12 m (age: 783,040 yr bp).

From [6]:

This artefact can be explained by the fact that this ice is from an ice-core section drilled towards the end of the season 2002–2003, when an ethanol–water mixture had to be added at the bottom of the borehole to allow further drilling. This caused partial melting at the outside of the core and subsequent refreezing when hoisting the core through colder sections of the bore hole. This is the only artefact discovered in the ice above 3,190.56 m.

Thus there is a clear cause for the outliers, and these are rightfully discarded...

The exclusion of outliers, when there is a clear mechanical/methodological cause, is a normal method in science of only retaining data where we are interested in: in this case, the atmosphere of the far past.

Jaworowski is wrong about retaining outliers: these have no relevance at all for historical CO2 levels and are rightfully discarded.

4. The arbitrary shift of air/ice data.

One of the most basic accusations by Jaworowski is that for the Siple Dome ice core, CO2 data from Mauna Loa and from the ice core were matched by a completely arbitrarely shift of 83 years in time.

The data from shallow ice cores, such as those from Siple, Antarctica, are widely used as a proof of man-made increase of CO2 content in the global atmosphere, notably by IPCC[7]. These data show a clear inverse correlation between the decreasing CO2 concentrations, and the load-pressure increasing with depth (Figure 1 A). The problem with Siple data (and with other shallow cores) is that the CO2 concentration found in pre-industrial ice from a depth of 68 meters (i.e. above the depth of clathrate formation) was “too high”. This ice was deposited in 1890 AD, and the CO2 concentration was 328 ppmv, not about 290 ppmv, as needed by man-made warming hypothesis. The CO2 atmospheric concentration of about 328 ppmv was measured at Mauna Loa, Hawaii  as later as in 1973[8], i.e. 83 years after the ice was deposited at Siple.

An ad hoc assumption, not supported by any factual evidence, solved the problem: the average age of air was arbitrary decreed to be exactly 83 years younger than the ice in which it was trapped. The “corrected” ice data were then smoothly aligned with the Mauna Loa record (Figure 1 B), and reproduced in countless publications as a famous “Siple curve”. Only thirteen years later, in 1993,  glaciologists attempted to prove experimentally the “age assumption”, but they failed.

Here are the graphs

Siple Dome CO2 pre-Mauna Loa   Siple Dome shifted
The left image is the data with the age of the Siple Dome ice, compared to the Mauna Loa age.
In the right image, according to Jaworowski, the Siple Dome data are arbitrarely shifted 83 years to match the Mauna Loa data.

This is what Jaworowski writes in 2004. Either he hasn't the slightest clue about what happens in the gas phase of compressing snow (firn), or he has not read the literature since 1991.

From the original Neftel paper of 1992 (!) [5]:

Siple Dome data
The Siple Dome data [5] as published by Neftel in 1992.

As everybody can see, there are two columns in the table: the ice age and the enclosed air age. The latter is younger than the ice at the same depth, simply because during the time that the air bubbles still are open, an exchange between the atmosphere and the air in the firn is possible. The exchange speed reduces with depth, and once that a certain ice density is reached, stops completely. Due to these exchanges and the time/depth needed for fully closure of all bubbles, not only the gas age at closing depth is younger than the ice age, but the air composition is an average mixture of several years.

From Neftel (1992) [5]:

Based on porosity measurements the time lag between the mean age of the gas and the age of the ice was determined to be 95 yr and the duration of the close-off process to be 22 yr. These values are, of course, evaluated for one particular core representing the present situation (1983), assuming a homogeneous enclosure process and not taking into account the sealing effect of observed impermeable layers.
Because of the layers between 68 and 69 m.b.s., the air below is already completely isolated, about 7 m above the debt obtained assuming a homogeneous enclosure. Consequently, for this core, the difference between ice and mean gas age is only 80-85 yr instead of 95 yr as estimated previously.

While the methods to estimate the difference between ice age and gas age of that time are rather coarse compared to modern methods based on firn densification models, Jaworowski on the other hand compares the ice age (which has nothing to do with the CO2 measurements) with the Mauna Loa data, as one must compare CO2 data of the same gas age of the enclosed air bubbles with the Mauna Loa data.

Moreover, Etheridge e.a. (1996) [7] has done a very detailed research work on three ice cores at Law Dome. His works answers many of the objections that Jaworowski poses.

- They used three different drilling methods (wet and dry) to see what the effect on CO2 measurements was. There was no difference outside the accuracy interval (1.3 ppmv, one sigma).
- Two cores had about the same high accumulation speed (about 1.5 m ice equivalent/yr), the third was somewhat slower accumulating. Despite that difference, all three cores give similar values for the overlapping gas age periods.
- CO2 levels in firn were measured with pumping equipment composed of different materials and sampling in three types of flasks: glass, steel and stainless steel. Steel did give lower values, probably due to the chemical treatment of the inner surface. The pumping equipment with different materials didn't cause differences in measurements.

The results of CO2 measurements in firn are interesting:

Law Dome firn
CO2 measurements in firn and ice, Law Dome, Etheridge e.a. (1996) [7]

As one can see, the above ground CO2 values (localy measured and from the south pole) are equal, while CO2 values slowly decrease, due to closing speed at one side and migration speed at the other side, until the density is high enough at app. 72 m depth to prevent further diffusion. At that depth the gas age of these two cores is about 10 years older than the surface air, and 30 years younger than the age of the ice itself (observed by counting the layers). The closing of the bubbles need some further 8 years for completion. Even more interesting: the firn CO2 (measured by pumping and flask sampling) from not yet fully closed bubbles and the already closed bubbles (measured by cold crushing of ice parts under vacuum and cold traps) at the same closing depth show the same CO2 values. This points to the fact that no redistribution of CO2 takes place at closing depth between ice and still open bubbles.

With this knowledge in mind, one can compare the Law Dome CO2 data with an average gas age with the south pole data of the same age, that gives an overlap of about 20 years of data:

Law Dome SP data overlap
Overlap of Law Dome ice core CO2 data with the same average gas age
as the south pole CO2 data: a near perfect match within 20 years overlap [7].

As everybody can see, there is nothing "arbitrarely" in the shift of data to match the atmospheric measurements. All is based on calculated gas age, that is the average age of the air bubbles wherein CO2 is measured. In the case of Law Dome it is even based on in situ measurements of CO2 in firn, which confirms the calculations of the ice core air bubbles age. Jaworowski is wrong by using ice age as base for his conclusions, since that this has no connection with CO2 measurements, which are in the gas phase.

Jaworowski is not correct about the "arbitrary" shift of data to match ice core data and atmospheric measurements, as he refers to ice phase dating instead of gas phase dating.

5. Conclusion

Too many of the objections made by Jaworowsky are either completely outdated, physically impossible (even the reverse of what he alleges) or based on wrong age data.

6. References

[1] Zbigniew Jaworowski, M.D., Ph.D., D.Sc., March 2007. Climate Change: Incorrect information on pre-industrial CO2: http://www.warwickhughes.com/icecore/

[2] Mulvaney, R., E.W. Wolff, and K. Oates, Sulpfuric acid at grain goundaries in Antarctic ice. Nature, 1988. 331(247-249). Not directly available on the Internet.

[3] Mulvaney et al. on H2SO4 inclusions, on the blog of Jim Easter: http://www.someareboojums.org/blog/?p=17

[4] Zbigniew Jaworowski, M.D., Ph.D., D.Sc., 1997, Ice Core Data Show No Carbon Dioxide Increase http://www.warwickhughes.com/icecore/IceCoreSprg97.pdf

[5] On the main page of Ernst Beck's thesis about the historical CO2 measurements, "180 Years of atmospheric CO2 Gas Analysis by Chemical Methods":  http://www.biokurs.de/treibhaus/180CO2/neftel82-85.pdf

[6] Lüthi e.a., High-resolution carbon dioxide concentration record 650,000–800,000 years before present, Letters to Nature 453, 379-382 (15 May 2008):  http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html

[7] Etheridge e.a., GRL 1996, Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn:  http://www.agu.org/pubs/crossref/1996/95JD03410.shtml

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Last update: 21 January, 2009.

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