About the reliability of ice cores…
Guest Post by Ferdinand Engelbeen
There have been hundreds of reactions to part 1 about the mass balance (http://wattsupwiththat.com/2010/08/05/why-the-co2-increase-is-man-made-part-1 ). Many respondents still are not convinced that the mass balance is a firm proof that the observed increase of CO2 in the atmosphere is human made. But there are more indications. Ultimately, any alternative explanation must fit all the observations. If the alternative hypothesis fails even only one of the observations, then the alternative is rejected. But before we start to look at more observations which support an anthropogenic cause, we need to address several misconceptions which fly around on the Internet, mainly on skeptic blogs… This part has a detailed look at the reliability of ice cores, which are quite important for our knowledge of the pre-industrial CO2 levels, but have been subject to a lot of critique.
Note that the ice cores only show CO2 levels back to about 800,000 years, but measurements may in the future be extended to over one million years. What is found in the ice cores is only relevant for the most recent period of our history and not for more distant geological time periods.
About the reliability of ice cores:
Some have objections to the ice core measurements, as these are regarded as the main reason for the “equilibrium” assumption of ancient CO2 levels. The only real problem in this case is the smoothing of CO2 levels. That depends on the snow accumulation rate, as it takes a lot of time to close all air bubbles in between the snow flakes. That happens at a certain depth where the pressure is high enough to transform the snow, then firn (densified snow still with open pores) into ice. The averaging happens partly because at first the firn pores are large enough to let the air in the pores and in the atmosphere exchange with each other, partly because some bubbles close early, others at a lower depth (thus contain air which is different in composition, “age”, than other already closed bubbles). The depth where this happens depends on the pressure from the layers above and the temperature of the ice. The time needed for full closure of all bubbles largely depends on the accumulation rate of snow at the place where the ice core is taken (or upstream if coring at a slope).
That makes that the average smoothing of CO2 levels is about 8 years (Law Dome 2 out of 3 ice cores, 1.2 m ice equivalent/year accumulation), some 21 years (the third Law Dome ice core, 0.6 m ice equivalent, see http://www.agu.org/pubs/crossref/1996/95JD03410.shtml unfortunately behind a pay wall…), some 570 years (Dome C, a few mm/year, see http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html ) and everything in between. The Law Dome closing period of the bubbles was measured, while for Dome C one needed models to estimate the time resolution in the far past.
Thus the smaller the snowfall at a certain place, the longer it takes for the bubbles to fully close and the longer averaging one has. At the other side, the smaller the accumulation rate, the further we can look back in the past, as for the same depth of ice, there are many more years of snowfall.
The fact that the pores still are open over a long period, also means that there are differences in the age of the ice and the age of the enclosed gas. The age of the ice can be counted, as it simply is the result of ice formation from yearly snow accumulation where winter/summer snow density differences gives clearly distinguishable layers if there is sufficient accumulation. If, as depth increases, the pressure and/or flow result in layers that are near invisible, one may use several other methods like electro conduction or X-rays (see http://iopscience.iop.org/1742-6596/41/1/034/pdf/jpconf6_41_034.pdf ) to distinguish the layers/age.
Determining the gas age is not as easy. Over the years of accumulation of the snow/firn, the pressure builds up and the firn becomes more dense with decreasing pore diameter. That reduces the exchange of air in the pores with the air in the atmosphere, until the pores are too small to make any further exchange possible. If there has been considerable accumulation, as in the two fast Law Dome cores, at the depth of the first closing (about 72 meters) the ice is already 40 years old (40 layers), but the air has the average CO2 levels of less than 10 years ago, which makes the average gas age (including the average time for fully closing of all bubbles) about 30 years younger than the ice at the same depth. For the top layers, we have the advantage of direct measurements in the atmosphere for overlapping periods, which makes a comparison possible.
For cores with far less accumulation, the analysis is more problematic, as the difference increases with the reciprocal of the accumulation rate. During ice ages, there was less precipitation, thus increasing the ice age – gas age difference. The ice-gas age difference for the Vostok ice core is over 3,000 years. Be aware that the ice-gas age difference has nothing to do with the resolution of the CO2 levels, as these are in the bubbles themselves, but it makes a chronology of what happens between temperature (measured as dD and d18O proxy in the ice, see further) and CO2 levels (measured in the bubbles) more difficult to establish. But here also different techniques are used: diffusion speed is a matter of pore diameter, directly related to firn/ice density and densification speed is directly related to accumulation speed. This can be used to model the exchanges between air in the pores and the atmosphere.
The calculations to establish the gas age did fit quite well for the Law Dome ice cores, where besides ice age, the average gas age was established by measuring CO2 levels top down in the firn. That showed that the gas age at closing depth was less than 10 years old on average, but more importantly, the CO2 levels in the already fully closed bubbles and the still open pores were the same. For the low accumulation ice cores like Vostok, there is more discussion about the ice-gas age difference and different time scales were established…
The accuracy of the measurements in the three Law Dome ice cores for the same gas age is about 1.2 ppmv (1 sigma). Later works compared different ice cores for CO2 levels at the same average gas age. These show differences of only 5 ppmv, despite huge differences in average temperature (coastal -20°C, inland -40°C), salt inclusions (coastal), accumulation rate and resolution. There are a lot of overlapping periods between the ice cores, the resolution decreases with increasing length of period (from 150 years – for 2 of 3 Law Dome ice cores – to 800,000 years – Dome C), but even so, the measurements (done by different labs of different organizations) show a remarkable correspondence for the same average gas age. This is a nice indication that the CO2 levels of the ice cores indeed represent the ancient levels.
Data over the past 10,000 years of average gas age in ice cores from:
http://www.ncdc.noaa.gov/paleo/icecore/current.html
As result, for the past 150 years (Law Dome) we have accurate data with a reasonable resolution. The cores average the CO2 levels over 8 years, so any peak of 20 ppmv during one year or 2 ppmv difference sustained over 10 years would be observable. For older periods, the resolution is less and the averaging applies to the full period of resolution (about 570 years for Dome C).
The visual correlation between temperature and CO2 levels in ice cores is well known to everybody, as that was used by Al Gore and many others, although he forgot to tell his audience that the CO2 levels lagged by some 800 years during a deglaciation and many thousands of years at the onset of new glaciations:
Data from the Vostok ice core via:
The temperature is derived from dD and d18O proxies in the ice. dD means the change in the deuterium/hydrogen ratio measured in the water molecules of the ice and d18O is the change in 18O/16O ratio of the water molecules in the ice. Both heavier isotopes of hydrogen resp. oxygen increase in ratio to the lighter ones, when the ocean temperature, from where the precipitation originates, increases. Thus the change in ratio is an indication of the ocean temperature changes. For coastal ice cores, that indicates the temperature changes in the nearby Southern Ocean, while the deep inland cores receive their precipitation from the more widespread SH oceans, thus representing the temperature changes of about the whole SH. The NH ocean temperature changes are more or less represented in the Greenland ice cores, which show similar changes (over the last about 120,000 years), but with some differences in timing and more detailed extreme events (like the Younger Dryas).
There is a remarkable near-linear ratio between ice core CO2 and the temperature proxy record in the same core over 420,000 years of Vostok. Work is under way to confirm this ratio in the 800,000 years of Dome C (for the overlapping period, the CO2 levels are already confirmed similar): about 8 ppmv/°C:
Data of the Vostok ice core from NOAA, temperature proxy indication shows zero at current temperature. From:
http://www.ncdc.noaa.gov/paleo/icecore/current.html
The spread in temperature/ CO2 data, mainly at the high side, is from the long lag of CO2 levels which remain high for thousands of years at the end of a warm period, while the temperature is dropping back to a minimum. The 8 ppmv/°C is not absolutely right, because temperature at best represents a hemispheric ocean temperature, but not far off, as the pCO2 in seawater dependency of temperature shows about 16 ppmv/°C. But besides pCO2 of seawater, other land and (deep) ocean items also play a role.
This all is an indication that temperature is not the cause of the sharp increase of CO2 in the last 150 years, as that wouldn’t give more than 8 ppmv (or 16 ppmv based on ocean solubility) increase with a maximum 1°C temperature increase since the depth of the LIA, while the current increase is over 100 ppmv.
Be aware that, besides some fractionation of the smallest atoms/molecules (not of CO2), and a small fractionation of isotopes, the bubbles still reflect the ancient atmosphere as it was. Ice core CO2 thus is not a proxy but a direct measurement, be it smoothed, of what actually happened in the (far) past.
The objections of Jaworowski:
What about the objections of Jaworowski against the reliability of ice cores (http://www.warwickhughes.com/icecore/ )?
Jaworowski assumes that CO2 “leaks” via cracks in the ice, caused by the drilling and pressure release of the deep core ice. But how can they measure 180-300 ppmv levels of CO2, when the outside world is at 380 ppmv? If cracks (and drilling fluid) are found in the ice, that would show levels which were too high, compared to other neighbouring layers, never too low.
The formation of clathrates (solid forms of O2, N2 and CO2 with water at very cold temperatures and high pressure) depletes CO2 levels, according to Jaworowski. This is well known in the ice core world. Therefore they allow the ice cores to relax up to a year after drilling. Moreover: O2 and N2 clathrates would decompose first, thus escaping as first via microcracks (as Jaworowski alleges). This would lead to too high CO2 levels, not too low.
Jaworowski accuses Neftel of “arbitrary” shifting the Siple data with 83 years to match the ice core CO2 with the Mauna Loa data. But the page from Neftel’s report ( http://www.biokurs.de/treibhaus/180CO2/neftel82-85.pdf ) contains two columns in the table: the counted ice age and the calculated gas age, the latter based on porosity measurements of the firn. Jaworoski used the age of the ice, not of the air bubbles, to base his accusation on, which is quite remarkable for a specialist in these matters. CO2 is in the air, not in the ice and the average age of the gas is (much) younger than the ice where it is enclosed. Neftel even made specific remarks about the gas age, which was compared to the South Pole atmospheric data, to confirm the average age of the gas bubbles at depth:
If the 328 p.p.m. measured at a depth of 68.5 m.b.s. [note: meters below surface] is matched with the atmospheric South Pole record, the mean gas age is 10 yr, corresponding to a difference between mean gas age and ice age of 82 yr, which lies in the above estimated range. The difference is used in calculating the mean gas age for all depths.
That the CO2 concentration measured on the subsequent samples from 72.5 and 76.5 m.b.s. corresponds with the atmospheric South Pole record justifies this age determination…
This clearly indicates that Neftel based his gas age estimate on firm grounds and there is nothing arbitrary in “shifting” the data, as there was no shifting at all. Thus for the Siple ice core, the ice age – gas age difference is about 82 years (Neftel estimated 80-85 years) for an average gas age resolution of about 22 years in this case.
Many of the objections of Jaworowski were answered by Etheridge (already in 1996) by drilling three cores at Law Dome, with three drilling methods (wet and dry), using different materials for sampling, avoiding cracks and clathrates, allowing a lot of relaxation time and measuring the CO2 levels top down in firn and ice. No difference was found in CO2 levels between firn and ice at closing depth and there is an overlap of some 20 years of the ice core CO2 data with the South Pole data:
Figure from Etheridge e.a.: http://www.agu.org/pubs/crossref/1996/95JD03410.shtml
See more comment and further links about Jaworowski at:
http://www.ferdinand-engelbeen.be/klimaat/jaworowski.html
The “corrections” of J.J. Drake:
JJ Drake (http://homepage.ntlworld.com/jdrake/Questioning_Climate/userfiles/Ice-core_corrections_report_1.pdf ) claimed to have established that the CO2 levels needed a correction for the ice-gas age difference. The result of the “correction” is that the CO2 levels are much higher with little variation and the very good correlation with temperature vanished. This conflicts already with our knowledge of the influence of temperature on CO2 levels in current times…
Even so, the “correction” might be all right, but the reason he provided has no bearing in any physical relationship. He makes the basic mistake of conflating a good correlation with a causation: The error is of the kind:
A causes B and shows a good correlation.
A causes C and shows a good corelation.
Thus B causes C, because there is a good correlation between the two. But that correlation is completely spurious, as there is not the slightest physical connection between B and C.
The explanation for his observation is quite simple:
Temperature (“A”) causes the ice-gas age lag (“B”), as temperature is directly connected with humidity of the atmosphere, thus influences the amount of snowfall, thus the accumulation rate and as reciprocal the speed of closing the bubbles: higher temperature, higher snowfall, smaller ice-gas difference.
Temperature (“A”) influences CO2 levels (“C”) directly: higher temperature means higher CO2 levels.
Because the previous two results have a high correlation with temperature, that gives that the ice-gas age difference and the CO2 levels also show a high correlation, but there is no physical mechanism that shows any direct or indirect action of ice-gas age difference on CO2 levels or vice versa. It is a completely spurious correlation, without any causation involved, but both share the same cause. Any “correction” of CO2 levels found in ice cores based on the correlation with ice-gas age difference is meaningless.
Migration of CO2 in ice cores
Ice shows a thin layer of unstructured (liquid waterlike) water molecules near the surface of the air bubbles. Some CO2 may dissolve in this layer, but that is not a problem at measurement time, as measurements are made at low temperature under vacuum, effectively removing all CO2 from the opened bubbles in the crushed ice, while removing any water vapor as ice over an extra cold trap. Water in-between the ice crystals is very unlikely, as there is still the direct influence of ordered structural ice from both sides.
Migration in even the oldest cores is no real problem. The recent fuss about “migration” speed was deduced from the Siple core, based on layers where remelting occurred, something not seen in any high elevation ice core like Vostok or Dome C. It remains to be seen to what extent the Siple Dome results are applicable to other ice cores.
But if there was even the slightest migration of CO2, that would affect the ppmv/°C ratio of the above Vostok CO2/temperature graph over time: the proxy temperature indication is fixed in the ice, while CO2 is measured in the gas bubbles. If there was any substantial migration of CO2, the ratio between CO2 and temperature over warm and cold periods would fade away over the recurrent 100,000 years of time difference between the warm periods, but that is not observed.
Conclusion
The ice cores are a reliable source of knowledge of ancient atmospheres, if handled with care. The resolution heavily depends of the accumulation rate, with as result that the data measured in enclosed air bubbles are smoothed, ranging from 8 years for the past 150 years to near 600 years for the past 800,000 years.
The graphs are stunning. They show a remarkably cyclical pattern before there could be any anthropogenic effect. How is this not a natural cycle?
Ferdinand Engelbeen says:
August 21, 2010 at 2:23 am
And please, NO discussion of Beck’s data here.
And please, NO dicussion of Engelbeen’s
data diatribedictates regarding CO2. Thank you.Steve Fitzpatrick says:
August 21, 2010 at 6:01 pm
Wish I had half your enthusiasm and energy for arguing with non-sense.
And I wish I had half Engelbeen’s enthusiasm and energy for arguing non-sense.
Quite a few years ago I did a little research of my own, using the NOAA iadv web site I printed out the CO2 v’s time graphs for the 20 longest running stations which represented a good global coverage then I noted the highest CO2 level and the month in which it occurred and the lowest CO2 level and its month.
Plotted these data on a CO2 concentration v’s latitude graph and the results were very interesting. The northern hemisphere shows a very marked concentration cycle but the entire southern hemisphere virtually none, In fact for 5 months of the year the southern hemisphere has a higher concentration than the northern hemisphere.
Then I went to the IPCC data and determined where the anthropogenic CO2 was released and 94% is in the north and 6% in the south. Then I went to the NOAA carbon tracker site and in those days they printed a monthly average surface CO2 profile for the world, sure enough it confirmed my graph and it also showed a distinct horizontal stratification so there is no significant mixing between the north and the south but when you calculate the impact of the CO2 released PER HEMISPHERE it is 1.15 GT per ppm so with about 8.5 GT of carbon released in the north and .5 in the south with no significant mixing why is the average northern concentration not considerably higher than the south if human emissions have such a large effect. In fact there is barely 1 ppm difference in the averages.
Barry Moore says:
August 21, 2010 at 8:30 pm
A good point, no mixing north an south, which can also be seen in the animations provided by AIRS
so there is no significant mixing between the north and the south but when you calculate the impact of the CO2 released PER HEMISPHERE it is 1.15 GT per ppm so with about 8.5 GT of carbon released in the north and .5 in the south with no significant mixing why is the average northern concentration not considerably higher than the south if human emissions have such a large effect. In fact there is barely 1 ppm difference in the averages.
The Lysenko effect?
Decide what the data should say and find it?
Ferdinand;
Did you do any measurements if the ice permeability with regard to O2 and CO2?
Did you do any measurements of the O2 and CO2 solubility in ice?
I´m not talking about pores or cracks, but permeability.
If you can not come up with good answers to this, your ice bubbles will be proxies and nothing else.
I find it deeply disturbing not to be able to discuss Herr Beck’s work. Is there any special reason for this?
Barry Moore says:
August 21, 2010 at 6:26 am
Since Ferdinand scored an F in mass balance calculations and his only response to my mathematical proof than the Anthropogenic component of the current atmosphere could not be greater than 18ppm, was that he could take no responsibility for the IPCC fig 7.3 which he agreed was substantially flawed and yet the values in the NASA numbers he quoted bore an eerie resemblance to the IPCC numbers.
I am pretty sure that you were not my examinator some 45 years ago, but as you don’t know the difference between the origin of an increase in mass and the origin of an increase in fraction I wonder who deserves an F.
Ferdinand appears to support the concept that “air” bubbles exist in the deep glaciers , this is total nonsense since the great pressure which exists in the glaciers will drive ALL the gasses below a certain depth into solution.
Read the literature before you write such things: below a certain depth, all air is captured in clathrates. But that is a two-way process, where during the relaxation of ice at normal pressure and less cold temperatures the air enclosures are reformed. These can be seen under an (electron) microscope.
Now if we reduce an “air “bubble to 1/10th its volume by compression the gas components will go into solution in the ratio of their solubilities, bearing in mind as more CO2 enters solution its partial pressure relative to the other gasses will decrease so the absorption rate will be offset somewhat but the ratio of the CO2 to the other gasses will fall rapidly. Thus we no longer have the mythical “100 000” year old “air” trapped in the ice.
Again read the literature: how much liquid water exists at -40 C, the average temperature of the Vostok ice core? Moreover, CO2 measurements are done under vacuum, which removes all CO2 and liquid water as vapour, the latter is trapped in a cold trap as ice at -70 C.
There are other much more reliable proxies than ice cores for determining CO2 content of the atmosphere such as leaf stomata and they disagree substantially with the ice core data.
Stomata data are proxies and have their own substantial problems, far worse than direct measurements in ice cores…
I see J.J.Drake’s paper was mentioned I strongly recommend people read it, his method for determining the age of the ice verses the CO2 taken from the ice was to compare the O18/O16 ratio of both the CO2 and the water, he found up to a 7000 year difference and produced a very sound correction curve for the ice core data which makes sense.
It seems that you can’t recognise a spurious correlation like the one which J.J. Drake connected. A “correction” only based on a good correlation? What physical mechanism do you think links CO2 levels in the gas phase with the gas age – ice age difference? See further the comment of DeWitt Payne…
Isotope fractionation in the ice is a result of seawater temperature at the origin of evaporation and at the place of condensation. Fractionation in the gas phase is mainly a matter of plant life and reflects the ratio ice sheets/vegetation area, both are temperature related, but independent of each other, as ice sheet formation lags temperature changes even more than CO2.
I notice the subject of Calthrates was glossed over. The missing CO2 is trapped in the ice crystals as a Calthrates and cannot be extracted which explains why the CO2 levels are low.
Complete sublimation of the total ice samples under vacuum decomposes all clathrates. No differences with the “cheese grating” technique found.
Archonix says:
August 21, 2010 at 3:48 am
And please, NO discussion of Beck’s data here.
Why not?
I am sure that would start a flame war, good for a record (even for WUWT) of over 1,ooo reactions… Thus one subject at a time…
Richard S Courtney says:
August 21, 2010 at 4:29 am
Perhaps the most important is that you gloss over a significant problem with the ice cores: viz.
liquid water exists on all surfaces of ice – including surfaces of ice crystals – at all temperatures down to -40deg.C.
There is liquid water at the ice crystals – air surface, but there is no liquid water in between crystals, except for dust/acid/salt inclusions. These are minor in the inland ice cores. And these ice cores are at or below -40 deg.C.
Therefore, it is not possible for the ice cores to indicate any high values of CO2 that existed millennia in the past, and it is not possible for bubbles in the gas to act as sealed canisters of the gas they enclose.
Ice cores of extremely different circumstances from coastal to far inland, show very little difference in CO2 levels for the same gas age. And as already said, if there was even the slightest migration, the 100 ppmv differences between warm and cold periods would fade away more and more over longer periods of time.
This is supported by the degree of adjustment the IPCC applied to ice core indications of atmospheric CO2 to provide them with agreement with the Mauna Loa data. The IPCC set the ‘ice age/gas age’ difference at 83 years to obtain that agreement.
This is pure nonsense from Jaworowski. The gas age was calculated for the Siple Dome ice core as 10 years older than atmosphere, which gives the 80-85 difference between gas age and ice age for that core. For Law Dome ice cores, the CO2 levels in the firn were measured top down: 7 years old at sealing depth, 30 years gas-ice age difference. One must compare gas composition of the same gas age with the atmospheric measurements, that has nothing to do with the age of the ice layer or the gas-ice age difference. Thus there was no “correction” at all by the IPCC.
However, as you say in your above article, Etheridge finds much shorter ‘ice age/gas age’ differences than 83 years.
And this causes a real problem.
There is no problem at all: the gas age – ice age difference depends of the accumulation rate, the higher the accumulation, the faster the sealing of the air in the layers, thus the shorter the gas-ice age difference (and the shorter the averaging of the gas phase).
If the IPCC adjustment of 83 years is an indication of diffusion (which seems likely) then all the ice core data has been smoothed by diffusion in similar manner to the conduct of an 83-year running mean.
Nothing to do with diffusion, which is in the top layers until sealing depth of the gas phase, as long as the pores are large enough. The number of ice years (thus the gas-ice age difference) plays no role in this.
Mauna Loa data has only been accumulated since 1958 (i.e. a total of 52 years) and, therefore, the 83-year diffusional smoothing in the ice would conceal any change in the atmospheric CO2 concentration similar to that observed at Mauna Loa.
Both for Siple Dome and Law Dome, the gas age is only 7-10 years, that gives an overlap of about 20 years with the South Pole data for the Law Dome data.
And if the 83-year diffusional smoothing has not happened then how do you explain the findings of Etheridge which you report?
Because there was no 83-year smoothing at all.
anna v says:
August 21, 2010 at 5:03 am
Most of mankind, lives and burns fuels at less than 1000 meters over land. Most of the flora is at less than 1000 meters over land.
You consider 70 stations enough , and those far away from sources?
Why then don’t we measure temperatures in 70 locations far away from heat sources, like deep ravines and caves? That would surely give us the energy content of the globe.
Anna, you are comparing apples with oranges. As the WUWT project of temperature stations showed: never measure temperatures above asphalt, near A/C outlets, etc. Even then it is a hell of a job to obtain something that is called a “global” average temperature, from largely varying diurnal and altitude dependent temperature readings.
The base for CO2 readings is quite similar and different:
Never use measurements near huge sources or sinks of CO2 in the atmosphere for “global” CO2 levels, as these show a local/regional bias, highly variable with diurnal variations in the hundreds of ppmv’s.
Even so, some 400 stations today measure CO2 fluxes over land, in forests, agriculture and volcanic vents, which are of interest to obtain a better insight of the carbon cycle. These stations are not used for “global” CO2 levels.
But away from such influences, the diurnal variation is less than the measurement accuracy, so that outliers are easely recognised. And the latitude and altitude differences are very modest, mainly caused by the seasonal changes and the NH-SH lag.
It is incredible that the assumption of going away from the sources of CO2 will give a correct measure of the CO2 volume in the atmosphere is considered so self evident.
Like measuring smoke to estimate the BTUs of a fire.
The CO2 measurements above 1,000 meter over land (from flights and mountains) and everywhere over the oceans show very similar CO2 levels averaged over a year. That is for some 95% of the atmospheric mass.
Should you support a proposal to lump all the temperature measurements over asphalt and near A/C’s together with the rest of the better situated stations?
Bill Illis says:
August 21, 2010 at 7:06 am
Just noting Ferdinand that the “8 ppmv/C” number is calculated using Antarctica’s temperature estimates which vary by twice as much as the global amount in the ice ages and in general. Antarctica has warmed 10C since the height of the ice age while the global value is assumed to be 5C.
The temperature proxy is based on the isotopic fractionation of water molecules when evaporating at the origin of the precipitation and out of the atmospheric water vapour at the place of condensation (I suppose directly to solids in this case). For the high altitude inland ice cores of Antarctica, that are about all SH oceans, while the coastal cores reflect more nearby water temperatures. As fas as I remember, the Greenland ice core shows about the same variation over the transitions. And the Law Dome ice core shows a change of 6 ppmv, where the reconstructions with the largest temperature differences (Esper, Moberg, Huang – bore holes) show about 0.8 C.
The current short term influence of temperature on CO2 fluctuations around the trend is about 4 ppmv/C.
Further literature of interest for Antarctic (and Greenland) ice cores see:
http://www.ipsl.jussieu.fr/GLACIO/hoffmann/Texts/jouzelJGR2003.pdf
So the 16 ppmv/C value is more accurate if one is using global or ocean water temperature changes.
Ocean temperatures may give the largest contribution for long-term CO2 changes in equilibrium level, but other items also have their contribution (vegetation as largest, opposite for temperature). But even with 16 ppmv/C, that can’t explain the 100+ ppmv increase we see…
Richard S Courtney says:
August 21, 2010 at 4:29 am
Sorry, I misundertood your last question:
And if the 83-year diffusional smoothing has not happened then how do you explain the findings of Etheridge which you report?
Most of the smoothing is in the deepest part of the firn where already closed and still open bubbles are both present. The time needed between first bubble closing and all bubbles closed is what defines the averaging. That depends of the accumulation rate, which depends mainly on ocean temperatures and resulting precipitation at the site of interest.
Barry Moore says:
August 21, 2010 at 8:30 pm
…. so with about 8.5 GT of carbon released in the north and .5 in the south with no significant mixing why is the average northern concentration not considerably higher than the south if human emissions have such a large effect.
anna v says:
August 21, 2010 at 9:45 pm
A good point, no mixing north an south, which can also be seen in the animations provided by AIRS
Dan says:
August 22, 2010 at 1:04 am
I´m not talking about pores or cracks, but permeability.
If you can not come up with good answers to this, your ice bubbles will be proxies and nothing else.
So we have some ice core proxies for CO2… of unknown accuracy / validity… which demonstrate CO2 levels vary over time. End of story.
Using the Vostok ice core proxy to determine CO2 levels world wide is pretty far fetched. It is like using today’s temperature reading from Vostok to determine today’s temperature readings for every place on earth.
There are some points which are overlooked in the discussion on the reliability of ice cores as proxies for CO2.
1. Ice cores are full of living bacteria. These organisms use CO2 as a carbon source.
(Please see here for literature: http://brent.xner.net/publications.htm)
I have discussed the influence of bacteria on the enclosed CO2 with Prof. Buford Price, one leading expert in this topic (http://icecube.berkeley.edu/~bprice/). According to him the metabolic activities of bacteria are small that in ice cores covering 1000 years we cannot see any influence but in ice cores like the Vostoc (450 000 years) the accumulated metabolism should have changed CO2 concentrations.
And what can we see in the Vostoc ice core? Very low CO2 concentrations in former glacials (~190 ppm) and interglacials (~280 ppm). Plants have many problems with such low concentrations (180 ppm), and an extinct of plants has to be found at those times, but we cannot found any. Furthermore the temperatures in the interglacials are mostly higher than today: +2-3 °C. The CO2 was very low (~280 ppm) compared to today.
2. Time lags of CO2
Analysis of modern data reveal a lag of 5 month to surface temperature (Kuo et al. 1990: http://www.nature.com/nature/journal/v343/n6260/abs/343709a0.html) using Mauna Loa data and 1 year behind SST (sea surface temperature) using combined Mauna Loa and my data (www.realCO2.de).
This suggests the CO2 variability is controlled by the oceans as the largest source of CO2.
Vostoc ice cores show about 800 years time lag CO2 behind temperature. That means our modern CO2 rise follows the Medieval optimum warmth.
But this is impossible. So the 800 years must be an artifact (as the 200 ppm in glacials) and shows distorting activities of bacteria.
3. Ice cores covering modern times (Siple, Law Dome)
These cores show partly very high CO2 which was ignored (Siple) and have a gas age/ice age of about 30 years (Etheridge). So they show an uncertainty of 30 years where they cannot resolve actual CO2 at that times.
Etheridge et al. (1996) determined the sealing depth at DE08 to be 72 m where the age of the ice is 40±1 years; so back from 1975 (end of Law Dome ice core) we have firm and diffusion of CO2. So they cannot resolve smaller CO2 variability.
Please look at this paper by Schneider and Steig:
http://www.pnas.org/content/105/34/12154.full.pdf+html
They reported of a significant 1940s Antarctic warmth detected in ice cores showing a large temperature peak in the 40s. But nothing to see in the CO2 ice cores records!
That’s exactly the 1940 CO2 maximum I have found in the direct measured data.
(and they follow temperature)
Stomata data show also much higher CO2 at that times: 330-360 ppm during ~1935-1950.
Kouwenberg at al.: http://www.geocraft.com/WVFossils/Reference_Docs/Kouwenberg_et_al_2005.pdf
4. Spectral analysis of CO2 time series reconstructed from modern ice cores (Siple. Law dome)
Every climate time series show spectral information which can often be returned to solar or lunar influence. (e.g.- H. Yndestad: http://ansatte.hials.no/hy/climate/defaultEng.htm)
Law dome and Siple dome show NO spectral information (Wavelet, MTM, http://www.realCO2.de). This looked much like an artifact!
My Conclusion:
Ice cores are only giving a rough resolution of atmospheric CO2 influenced by diffusion, 30 years uncertainty in modern times and artifacts in older series introduced by bacterial activities and other influences.
Ernst-Georg Beck
http://www.realCO2.de
There are some points which are overlooked in the discussion on the reliability of ice cores as proxies for CO2.
1. Ice cores are full of living bacteria. These organisms use CO2 as a carbon source.
(Please see here for literature: http://brent.xner.net/publications.htm)
I have discussed the influence of bacteria on the enclosed CO2 with Prof. Buford Price, one leading expert in this topic (http://icecube.berkeley.edu/~bprice/). According to him the metabolic activities of bacteria are small that in ice cores covering 1000 years we cannot see any influence but in ice cores like the Vostoc (450 000 years) the accumulated metabolism should have changed CO2 concentrations.
And what can we see in the Vostoc ice core? Very low CO2 concentrations in former glacials (~190 ppm) and interglacials (~280 ppm). Plants have many problems with such low concentrations (180 ppm), and an extinct of plants has to be found at those times, but we cannot found any. Furthermore the temperatures in the interglacials are mostly higher than today: +2-3 °C. The CO2 was very low (~280 ppm) compared to today.
2. Time lags of CO2
Analysis of modern data reveal a lag of 5 month to surface temperature (Kuo et al. 1990: http://www.nature.com/nature/journal/v343/n6260/abs/343709a0.html) using Mauna Loa data and 1 year behind SST (sea surface temperature) using combined Mauna Loa and my data (www.realCO2.de).
This suggests the CO2 variability is controlled by the oceans as the largest source of CO2.
Vostoc ice cores show about 800 years time lag CO2 behind temperature. That means our modern CO2 rise follows the Medieval optimum warmth.
But this is impossible. So the 800 years must be an artifact (as the 200 ppm in glacials) and shows distorting activities of bacteria.
3. Ice cores covering modern times (Siple, Law Dome)
These cores show partly very high CO2 which was ignored (Siple) and have a gas age/ice age of about 30 years (Etheridge). So they show an uncertainty of 30 years where they cannot resolve actual CO2 at that times.
Etheridge et al. (1996) determined the sealing depth at DE08 to be 72 m where the age of the ice is 40±1 years; so back from 1975 (end of Law Dome ice core) we have firm and diffusion of CO2. So they cannot resolve smaller CO2 variability.
Please look at this paper by Schneider and Steig:
http://www.pnas.org/content/105/34/12154.full.pdf+html
They reported of a significant 1940s Antarctic warmth detected in ice cores showing a large temperature peak in the 40s. But nothing to see in the CO2 ice cores records! That’s exactly the 1940 CO2 maximum I have found in the direct measured data.
Stomata data show also much higher CO2 at that times: 330-360 ppm during ~1935-1950.
Kouwenberg at al.: http://www.geocraft.com/WVFossils/Reference_Docs/Kouwenberg_et_al_2005.pdf
4. Spectral Analysis of CO2 time series reconstructed from ice cores
Every climate time series show some spectral information often returned to solar or lunar influence ( e.g.
http://ansatte.hials.no/hy/climate/defaultEng.htm) But Law dome and Siple dome show NO spectral information (Wavelet, MTM, http://www.realCO2.de). Looks like an artefact!
My Conclusion:
Ice cores are only giving a rough resolution of atmospheric CO2 influenced by diffusion, 30 years uncertainty in modern times and artifacts in older series introduced by bacterial activities and other influences.
Ernst-Georg Beck
http://www.realCO2.de
Alexander Pope (1688 – 1744) in An Essay on Criticism, 1709.
“A little learning is a dangerous thing; drink deep, or taste not the Pierian spring: there shallow draughts intoxicate the brain, and drinking largely sobers us again.”
Malaga View says:
August 22, 2010 at 6:04 am
So we have some ice core proxies for CO2… of unknown accuracy / validity… which demonstrate CO2 levels vary over time. End of story.
Using the Vostok ice core proxy to determine CO2 levels world wide is pretty far fetched. It is like using today’s temperature reading from Vostok to determine today’s temperature readings for every place on earth.
This does seem to be a trait in climate ‘science’ – after all they also claimed to know the climate of the world from the tree rings of a few trees in a small peninsula in Siberia.
Ferdinand Engelbeen says:
August 22, 2010 at 3:32 am
Should you support a proposal to lump all the temperature measurements over asphalt and near A/C’s together with the rest of the better situated stations?
In the ideal case, yes. Satellite temperature readings should read everything, asphalt included. It is the ground skin temperature that is radiating away the energy, not the atmosphere at 2 meters, which is a tiny part of the effect.
The problem that the surface station project is highlighting is not the asphalt per se, but the bad statistical sampling of the temperatures as global representative readings, and the time bias introduced by the UHI changes.
To get the energy leaving the globe one has to integrate over every radiating surface. Station measurements should be representative of the statistical representation of the type of surfaces the globe is composed of, an the surface station project has shown how badly this requirement is fulfilled. ( not to forget the Nyquist requirement about the sampling necessary when there are so many different types of surfaces).
The objective is to measure the energy radiated, not to sit watching it and saying: it is rising it is rising, it is falling it is falling.
Similarly, for CO2 the objective is to measure the amount of CO2 circulating in the atmosphere, from 0 meters to the stratosphere. To say that sitting far away from sources and sampling the air in 70 locations justifies the estimate of the tons of CO2 circulating is as ridiculous as saying that sampling the energy in 70 remote locations away from heat sources can estimate the energy radiated by the globe.
It is simple physics after all.
At least 99.9% of scientists agree with Ferdinand, including those who are skeptical of the notion that humans are responsible for most of the recent warming. I have looked at the data and agree that humans, mainly through burning fossil fuels, are responsible for the steady increase of atomospheric CO2 over the last 60 years or so since we have had good measurements. In my view, the scientific evidence is nearly as good as the evidence that the planets of our solar system orbit around the sun. This is smply a well-supported fact.
Thank you for your post. I’ve never really questioned that the recent rise in CO2 was anthropogenic in origin. I do question whether you can use CO2 from ice cores to measure paleo-levels of ambient CO2.
I’m with R Shearer: Ice-cores are an interesting concept, but if they are to be used to compare present day gas-phase CO2 levels with paleoclimatic levels, there is a considerable burden of proof still required. Compare the field of ice core air analysis for example to the sophistication (and profusion) of lab experiments that mineralogists perform to elucidate mineralisation pathways. Perhaps I am being too harsh and somewhere there is an accessible primer in ice-core methodology – if so, please post directions to it, I would be interested to read it.
But I want to see proof that these measurements are robust before I’d treat them as better than a proxy for ambient CO2. Is ice core CO2 really a direct measurement? I.e. are detected CO2 concentrations from samples at different depths directly comparable, or is some ‘adjustment’ required?
Also why are there so few ‘overlap’ points between ice core and ambient air? Surely by now we could get great temporal resolution for the overlap? This is a vital validation of air measurements from ice cores.
You said: “This is a nice indication that the CO2 levels of the ice cores indeed represent the ancient levels.”
It doesn’t really tell you about the ancient levels of CO2 – you’d need a measurement by a different technique that agreed with this one to do that. It does tell you that whatever processes affect CO2 in ice cores probably occur at all these sites.
I can’t avoid coming back to the fact that if ice core data is to be believed, in seeking to maintain a stable gas standard of CO2, one would use ice coated containers – yet in my limited experience of physical chemistry ice is a highly reactive surface and able to catalyse chemical pathways that are impossible based on simplistic application of gas-phase reaction pathways and thermodynamic considerations. I say again, more proof now that the data is being used by others in such a high stakes game.
Barry Moore and Anna v :
You might be interested in these graphs, which might indicate that changes in CO2 concentration are driven by tropical temperatures, with quite rapid mixing across the hemispheres.
http://members.westnet.com.au/jonas1/CO2NorthAndSouth.pdf
(167k)
And a vote from me for Fred Hynie’s work to be a post!
BillD says:
August 22, 2010 at 7:31 am
At least 99.9% of scientists agree with Ferdinand, including those who are skeptical of the notion that humans are responsible for most of the recent warming.
It is trite to say that science is not done by polling, trite but true.
A link to the poll you are quoting anyway is necessary, otherwise you should start your comment with “In my opinion at least 99.9%”, so one could give it the appropriate weight.
Mike Jonas :
August 22, 2010 at 8:06 am ,
Twelve month running averages hide the different breathing of the two hemispheres:
http://airs.jpl.nasa.gov/story_archive/AIRS-CO2-Movie-2002-2009/
Ferdinand Engelbeen,
I find very interesting this entry of yours in WUWT’s ongoing series of posts on the fundamentals of AGW theory. Thank you. You have obviously done a lot of work and thinking on this.
Before I comment on your current post, I would like to pause to reflect on the entries to date in WUWT’s recent series of posts.
NOTE: If you think I am off with my Single Bullet Descriptors please advise. I particularly had trouble bulleting Jeff Id’s post.
Ferdinand,
Note regarding context: In my view we are only discussing this topic here today because of an a priori concept/idea that a net significant AGW (compared to natural GW) is caused by anthropogenic (compared to natural source) CO2. I always need to keep that context in mind.
Your review of CO2 proxy by ice cores is unconnected yet to anthropogenic CO2 or AGW. Also, it doesn’t bring new info to the significant critical reviews of issues with ice core proxies. It can be expected that critical focus on CO2 proxies will only increase significantly in the future as tree ring temp proxies problems are currently being exposed and publicized. You seem to imply that your ice core discussion is relevant to anthropogenic CO2 or AGW. But, actually in your discussion you do not show that it is.
Shall I anticipate an eventual argument that current atmospheric CO2 increase is predominantly or completely anthropogenic? Imagine Person Z, using the context given in above note, who wants to show that current atmospheric CO2 increase is anthropogenic. Person Z shows his facts that in the modern industrial period we know that man has emitted CO2 into the atmosphere at rate of ~X and atmospheric CO2 concentration has increased at the rate of ~Y. He says that X is greater than Y. X he says is the cause of Y. The reason he says so is that it is obvious (see contextual note above) and any skeptic doubting that really reduces both the credibility of the blogs where it discussed and reduces credibility of other more responsible skeptics who are looked on more favorably by some third party. I would find this argument, by itself, unconvincing. It seems like polite blackmail.
Ancillary discussion possibly related to Person Z’s argument: Person Z might seem to say that X is the cause of Y no matter what the value of Y as long as Y is increasing. He might seem to say X the cause of Y even if the variability of X is much less that the naturally observed variability of Y. He might seem to say X the cause of Y even if prior to modern periods X is negligible or zero but changes in Y occur ( likely higher than current ones) and during those periods CO2 concentrations significantly lagged atmospheric temps. He might seem to say X the cause of Y while having a lack of referencing to the earth system total carbon cycle dynamics thus implying it is non-relevant to his argument. A total carbon cycle dynamic discussion would seem to be needed to analyze isotopic differences in CO2 from natural sources versus anthropogenic sources.
John