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
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.
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. 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, i.e. 83 years after the ice was
deposited at Siple.
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
Here are the graphs
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
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.
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
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
compares the ice
(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
the enclosed air bubbles with the Mauna Loa data.
Moreover, Etheridge e.a. (1996) [7
] has done a very
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:
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:
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.
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
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.