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.
Richard S Courtney says:
August 24, 2010 at 1:45 am
Do you have a reference for your “quasi-equilibrium” statement? I was curious about your example of concrete, and found a lot of literature which doesn’t support your statement. You said:
As an illustration, I point out that this reduction of diffusion rate is why steel can be used as reinforcement in concrete. Iron oxide is about four times larger than the oxidised iron. So, if steel rusts it breaks the concrete. (Many people have seen a concrete fence post that has been destroyed by rusting of its internal steel reinforcement that is close to the post’s surface). But if the concrete’s steel reinforcement is about 10 cm or more from the concrete surface then the steel does not rust. This is because the diffusion rate decreases to almost nothing when the partial pressure gradient at the tip of the diffusing oxygen becomes very small, and the partial pressure gradient reduces with distance from the high partial pressure at the concrete surface.
While that may true, it seems that the diffusion goes on indefinitely, but the migration rate decreases with the distance in the concrete. The chemical reactions of the concrete with CO2 (which also influences rust formation) neutralises the high pH of the cement. The layer thickness with which that occurs is increasing with the square root of the period involved. The speed varies with porosity, temperature and humidity between 0.5 and 15 mm/sqrt(years). Humidity plays a strange role: highest humidity hinders CO2 migration because of the presence of liquid water in the pores (I learn new things every day!). Relative high humidity gives the highest reaction speed, and low humidity prevents the reaction of CO2 with the cement. See:
http://www.nordicinnovation.net/_img/03018_the_co2_balance_of_concrete_in_a_life_cycle_perspective_final_report1.pdf
No, I don’t know more about ice than the next guy other than having a BS Chem degree. But I do know how to Google and I’m a bit disappointed that people don’t do more research when they argue here. It would be really great to have access to the scientific literature for free, but that ain’t happening for me. It looks like the crystalline structure of the most common form of ice, out of 15 known forms, does not have big enough voids to accommodate a CO2 molecule. So if there is any path it would have to be along grain boundaries or outright cracks. Also, it seems CO2, if it could move, might migrate from higher to lower pressure – but do not know this for sure.
Ferdinand Engelbeen : “There is a quite good correlation between (ocean) temperature and increase rate in the atmosphere, far less between temperature and increase of CO2 in the atmosphere. Many, warmers and skeptics alike, agree on that.”
I agree too – see my first post on this thread “I have worked through the figures for both ocean temperature and THC in multiple ways, and am now satisfied that their contribution to atmospheric CO2 is small compared to fossil fuel emisions. I am not satisfied with my own findings, because they do nothing to explain the long term CO2 lag [does anyone have an explanation for it?], but they do lead me to accept that F.E. is correct.” [emphasis added here]
So I was obviously not arguing that temperature was more important than CO2 re increase in CO2 over the last few decades. What I was arguing was that the graphs I posted seemed to indicate that CO2 did mix across the hemispheres.
Ferdinand Engelbeen : “Well, the increase in temperature certainly added more CO2 to the total natural input flows, but it didn’t add to the increase, as the total natural outflows were larger”
You still don’t get it. In the absence of fossil fuel emissions, the increase in temperature would have caused atmospheric CO2 to increase. I don’t think there is any disagreement on that – you accept that increasing temperatures caused CO2 to increase by 8ppm or 16ppm since the LIA. If we call the observed CO2 increase over the last 50 years “100%”, then, if there had been no fossil fuel emissions, we would probably have had (from my calcs) at least a “5%” CO2 increase, possibly “16%” (using your 16ppm figure), and an unspecified amount more or less than that because some of my assumptions (such as linear relationships) might have been invalid. Therefore, even though nature was in fact a net sink of CO2, the contribution of fossil fuel emissions to atmospheric CO2 was actually less than “100%”. It seems counter-intuitive, that a net sink can contribute to the increase, but it is so. The reason is that the CO2 added to the atmosphere from fossil fuels causes the concentration to be greater than that which the temperature increase would have caused, and therefore the oceans absorb some of it. But without the temperature increase the exact same fossil fuel emissions would not have caused the CO2 concentration to increase by as much.
Without the emissions, CO2 would have gone up.
Without the temperature increase, CO2 would have gone up by less.
No matter how you look at it, there has indeed been a natural contribution to the level of CO2 concentration over the last 50 years.
Correction – for “16%” read “12%”
Mike Jonas
I agree with your comment at 1.43 but would add that the actual observed surface temperature rise and its effects on Co2 concentrations need to be considered with that of ocean variabilty.
It is said that there is a 8ppm outgasing for every 1Degree rise of the ocean temperature.
http://noconsensus.wordpress.com/2010/03/06/historic-variations-in-co2-measurements/
If the LIA was generally a world wide event, with its effects proably greater in higher latitudes than the tropics, it is likely that the LIA ocean temperatures in many parts of the world would, at times, have been very much less than 1 degree cooler than today’s ‘average’ values. Therefore there should have been a notable dip in Co2 in such proxies as ice cores, then a subsequent increase as ocean temperatures subsequently picked up by (presumably) several degrees.
Generally we know that the Arctic and Antarctic SST’s appear to be largely out of sync with each other, thereby to some extent cancelling out some of the effects, but there are times in recorded history -such as the 1930’s- when they were in sync and doubtless this has happened before.
This synchronicity plus the extreme climatic effects of such events as the LIA and MWP should all have had a discernible effect on ocean temperatures and subsequent CO2 concentrations, but the signal appears to be missing.
We are talking pre Keeling here of course, as since the Mauna Loa readings there has been a steady increase without the peaks and troughs that would be expected in more climatically varied times.
Tonyb
Richard S Courtney says:
August 24, 2010 at 1:45 am
In addition, if we may assume that the migration of CO2 through the ice is comparable to the migration rates through concrete, the distance reached over each period of 100,000 years back in time, starting with current CO2 levels would be:
150, 220, 270 and 310 mm if the pores are very small.
4, 6.7, 8.2 and 9.4 meter if the pores are wider.
There are of course differences between concrete and ice: at one side concrete uses CO2 for the chemical reaction, but that also makes that the pressure difference is maintained until the cement in concrete is neutralised, while CO2 in ice has only the partial pressure difference. At the othes side, ice pores are much finer if not (near) absent at -40°C…
Mike Jonas says:
August 25, 2010 at 1:43 am
Sorry, I didn’t look at the context of your graphs…
But without the temperature increase the exact same fossil fuel emissions would not have caused the CO2 concentration to increase by as much.
I did get it, but you are right and wrong: indeed the increase in temperature did increase the input and highly probably caused an extra increase in total CO2, by reducing the sink rate. But at the other side, the extra input is halved, because the outputs increased too (mainly by the human emissions, a small part by the extra input from the temperature increase… E.g. the uptake by vegetation increases with temperature and humidity. Thus if we look at that extra outflow, that increases the total of the outflows and probably reduced the increase rate. Thus without the extra output, CO2 levels would have increased faster…
One can have different opinions, simply because the way you look at it, separate or combined, makes a huge difference.
Further, you look at one (net) input in isolation, only because we have a pretty good idea what CO2 levels in general do with changes in temperature. Other flows and their variations are less known.
But I find it a rather academic discussion if it is 92% or 96% or 100% which is caused by human emissions. Others go much farther as they say that human emissions are only 4% of the total input (which is right), thus only 4% of the increase (which is wrong as we are talking about increase in mass, not what fraction of molecules is coming from human emissions).
tonyb says:
August 25, 2010 at 4:30 am
This synchronicity plus the extreme climatic effects of such events as the LIA and MWP should all have had a discernible effect on ocean temperatures and subsequent CO2 concentrations, but the signal appears to be missing.
We are talking pre Keeling here of course, as since the Mauna Loa readings there has been a steady increase without the peaks and troughs that would be expected in more climatically varied times.
Hello Tony,
The MWP-LIA difference is visible in the best resolution ice core (21 years average) from Law Dome, spanning that period:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/law_dome_1000yr.jpg
There was a clear dip of about 6 ppmv around 1600, about 50 years later than the onset of the coldest period of the LIA.
As one expect a maximum 0.8°C temperature dip (depends of what reconstruction you take into account) in that period, the sensitivity of CO2 for temperature changes is about 8 ppmv/°C, about the same found in very long term changes over the ice ages. The current short term sensitivity (over 1-2 years) is about 4 ppmv/°C around the trend…
“There was a clear dip of about 6 ppmv around 1600, about 50 years later than the onset of the coldest period of the LIA.”
In other words: changes in CO2 are the result of temperature changes.
#
Mike Jonas says:
August 25, 2010 at 1:43 am
In the absence of fossil fuel emissions, the increase in temperature would have caused atmospheric CO2 to increase.
—–
Since the increase in temperature over the last 50 years was likely caused by greenhouse gases, then you could argue that fossil fuel etc burning is responsible for 105% of the observed increase.
Ferdinand
There may have been a .8C Average temperature dip on land (although that is highly debatable) but the oceanic temperature would have eventually dipped much more than that in the real world. For example the distribution of fish is a good proxy indicator and during the LIA we switched from Pilchard to Cod thereby assuming a sea temperature change of several degrees, not a fraction of one.
Again, in the real world, during the LIA the waters in many higher latitude countries-such as the UK or Holland-would certainly be many degrees lower than they are at present. It is pouring with rain outside today and the English Channel 100 yards from my house is still only 17C even though this is the ‘hottest year ever’. In the coldest year ever it is unlikely to have been within 5 degrees of this temperature.
The ice cores should present more spikes than appear to be present to reflect the LIA and MWP.
Also, as Smokey observes, surely this demonstrates that CO2 follows temperature changes, but rather quicker than the 800 years commonly cited?
Tonyb
Smokey says:
August 25, 2010 at 6:35 am
“There was a clear dip of about 6 ppmv around 1600, about 50 years later than the onset of the coldest period of the LIA.”
In other words: changes in CO2 are the result of temperature changes.
Agreed, even nowadays: there is an influence of temperature on CO2 trends (about 4 ppmv/°C), but that doesn’t exclude that CO2 has some influence on temperature. In how far, that remains to be seen.
tonyb says:
August 25, 2010 at 7:27 am
Ferdinand
There may have been a .8C Average temperature dip on land (although that is highly debatable) but the oceanic temperature would have eventually dipped much more than that in the real world. For example the distribution of fish is a good proxy indicator and during the LIA we switched from Pilchard to Cod thereby assuming a sea temperature change of several degrees, not a fraction of one.
Mostly, it is that land temperatures change more that sea surface temperatures. And fish indeed reacts on sea surface temperature, but in this case it seems that the Gulf stream changed direction (as Mörner claims) more southwards (around Portugal, later North Africa) leaving the whole North with colder seas.
The ice cores should present more spikes than appear to be present to reflect the LIA and MWP.
Also, as Smokey observes, surely this demonstrates that CO2 follows temperature changes, but rather quicker than the 800 years commonly cited?
The ice cores present spikes that are high enough or sustained long enough for the resolution they have. The short Law Dome ice cores (150 years) can show any one-year spike of 20 ppmv or a 10 years sustained in/decrease of 2 ppmv (accuracy 1.2 ppmv – 1 sigma, resolution 8 years), but Vostok needs a sustained in/decrease of 5 ppmv over 600 years, or 50 ppmv over 60 years. That is no problem to show the large variations between glacials and interglacials, as these cover periods of many thousands of years, but faster, smaller changes are not visible.
The 800 years lag is what is seen following the increase of temperature at a deglaciation. But the lag is many thousands of years when temperatures fall again.
The length of the lag of deglaciations may be connected to (deep) ocean flows, freeing land from ice sheets, increasing land cover by vegetation,… The opposite lag length seems correlated to the duration of the warm period: the longer/hotter, the longer the lag, may have to do with the amount of carbon sequestered by vegetation which is again decayed by soil bacteria.
The LIA was relative short duration, compared to ice ages, thus not much time to deeply change vegetation or deep ocean currents or ice sheets to build up.
Ferdinand
Ferdinand.
You said;
” That is no problem to show the large variations between glacials and interglacials, as these cover periods of many thousands of years, but faster, smaller changes are not visible.”
That’s an interesting comment which surely gets to the heart of our concerns as to the reality of ice cores as proxies of accurate measurements, as opposed to actual atmospheric records taken at the time.
It is the sea surface that is in contact with the atmosphere and the temperature of that medium changes very quickly and will outgas or absorb CO2. Deep ocean is much less susceptible to temperature change on an annual/decadil basis.
The LIA was typifed by short violent changes between very cold weather and temperatures similar to today, and even looking at the modern record we can see periods of cooling e.g the 1970’s in between the general warming.
Surely the logic of what you appear to be saying is that ice cores are unable to pick up these short sharp spikes of temperature, which presumably would result in short sharp spikes of co2? It is in effect ‘smoothed’ to an unrealistic extent, whereas in the real world it would surely be much spikier (just like land temperature records look totally different in their natural and smoothed states)?
I often wonder what was the effect on oceanic currents when the Dogger Bank became part of the North Sea after the last ice age and Britain became an island instead of part of the land mass.
Tonyb
tonyb, F.E., Smokey, richard telford : thanks for your comments. I do not claim to have all the answers, but I did feel it was important to establish that factors other than fossil fuel emissions affect the level of CO2 over all time frames.
tonyb, F.E. – I doubt that the “8ppm outgasing for every 1Degree rise” is a linear relationship. A really interesting feature of the observed data (atmospheric CO2 concentration “A” and temperature “T“) is that there is a closer relationship between dA and T than there is between dA and dT. This suggests to me that it is very possible that the relationship between dA and dT is not linear, and that unconsidered other factors may come into play. An area that could be worth looking at is the behaviour of CO2 in seawater – it does not just dissolve, it is involved in chemical reactions and biological activity which alters the ability of CO2 that has been absorbed in cooling seawater to be available for re-release when the seawater warms up again.
Until we understand the 800-year time lag [and a few other things], surely we don’t know what is really going on.
F.E. : “I find it a rather academic discussion if it is 92% or 96% or 100% which is caused by human emissions”
Yes and no. As I said, we cannot be sure that the real number is not 88% or less. I do think that it is high, probably well over 90%, but I cannot prove it. The important thing is to recognise that this factor exists, and to make proper allowance for it.
richard telford : yes, the extent to which CO2 affects temperature does affect the equation. At an ECS below 1 the impact is minor, at the IPCC’s 3.2 it is much greater. The calculations are not particularly difficult, and I can assure you that no matter what ECS you plug in the effect of emissions is still less than 100%!
tonyb says:
August 25, 2010 at 12:03 pm
Dear Tony,
The fast spikes, if caused by (surface) oceans only, have not so much influence: the solubility curve of CO2 in seawater is about 16 ppmv/°C, if the whole ocean surface layer warms up in that way. At the other side, more CO2 in the atmosphere and higher temperatures increases plant growth, including in the oceans, which reduces the increase. Thus the 8 ppmv/°C are not far off.
Further, if the the change in Gulf Stream was one of the causes (which might have been the result of less driving force by the spotless, inactive sun), that could give cold weather in our countries, but caused warmer weather first in Portugal, later in North Africa. Thus the overall sea surface temperatures need not be much colder.
The reconstructions with the largest difference in temperature MWP-LIA (or LIA-CWP) show some 0.8°C difference, of which one is based on tree rings (Esper), one is boreholes (Huang) and one is mixed (Moberg), the latter used several ocean sediments and the influence of tree rings is reduced. Although all three have their problems and errors, the general impression is that global temperature differences were not much larger than that.
In how far ice cores pick up real spikes is mainly a matter of accumulation rate: The more snowfall, the faster the air in between is sealed and the less spread in years you have in averaging the CO2 levels. The backdraw is that more accumulation means thicker layers and a shorter duration of the full period, as one reaches the rock bottom. Thus for the fastest accumulating Law Dome ice cores, one can only look back some 150 years. The third core, which was taken more downslope goes back some 1,000 years and the longest, Dome C, goes back some 800,000 years.
Thus fast changes like El Niño/La Niña periods will not be noticed in even the fastest ice cores, neither the Pinatubo eruption. But you may be sure that if there was any increase and decrease of 80 ppmv between 1935-1950, that would be visible in the fast Law Dome ice cores (and even in the slower one), as a Gaussian peak value of at least 60 ppmv spread over a period of some 20 years.
Further, averaging doesn’t change the average: a peak must be followed by an equal level of low values to give the average as found in the ice core…
As far as we see in the Mauna Loa and other stations data of the past 50 years, the mainly temperature controlled variability around the trend, as well as from the seasons as from spikes like an El Niño is some 4 ppmv/°C, not really huge… One need very huge worldwide temperature changes like a glacial-interglacial transition, to give a natural change of 100 ppmv.
I am sure that the fact that England now is an island has a huge effect on the psychology of the people living there, not sure if that makes much difference in climate, as in general we receive the same bad weather, be it somewhat later (it just starts raining here…).
Mike Jonas says:
August 25, 2010 at 12:57 pm
I doubt that the “8ppm outgasing for every 1Degree rise” is a linear relationship. A really interesting feature of the observed data (atmospheric CO2 concentration “A” and temperature “T“) is that there is a closer relationship between dA and T than there is between dA and dT. This suggests to me that it is very possible that the relationship between dA and dT is not linear, and that unconsidered other factors may come into play.
The solubility coefficient of CO2 in seawater indeed is not linear, but that doesn’t stop there. There is some factor 4 increase in pCO2 pressure of seawater between the poles near 0°C and the equator near 30°C. On the other hand, biological activity reduces the pCO2 from the poles to the equator. Thus these two factors are opposite. And we have more vegetation growth and thus carbon sequestering with higher temperatures. That all makes that we see a remarkably linear response of CO2 levels to temperature over the ice ages.
The current T/A rate around the trend is more related with the vegetation response to temperature and precipitation than by the oceans (these may be the cause of the temperature changes, but CO2 responds faster on vegetation – see the seasonal changes). See
http://esrl.noaa.gov/gmd/co2conference/pdfs/tans.pdf from page 11 on.
And while the pCO2 of ocean surface and atmosphere seek an equilibrium, a doubling of CO2 in the atmosphere only increases the CO2-bi-carbonate content of the oceans surface with 10%, due to the change in pH.
I still disagree with the less than 100%… If we may assume that the current natural sink rate is directly related to the difference in pCO2 between the current levels and the “equilibrium” level, dictated by temperature changes, then the increase in temperature since the LIA indeed has changed the equilibrium level somewhat, decreasing the sink rate, but that still is no contribution to the increase itself. Stop the emissions, and there is a quite certain drop in CO2 levels in the next years, despite an increased temperature, until we are back to equilibrium…
F.E. : I find it hard to accept that “we see a remarkably linear response of CO2 levels to temperature over the ice ages” and “I still disagree with the less than 100%” are compatible.
I have no difficulty agreeing with “Stop the emissions, and there is a quite certain drop in CO2 levels in the next years, despite an increased temperature” [provided that the temperature does not increase by too much, of course]. But in making that statement I must point out two things: (1) We have always implicitly agreed on that. The dispute concerns by how much since, as you say, it would be “dictated by temperature changes” – which is the basis of my case. (2) My statement is made in a scientific context, not a political context; in a political context, I would argue that there are far far better things to do than stop the emissions.
And I still want to know the mechanisms behind the 800-year lag.
Mike Jonas says:
August 26, 2010 at 5:31 pm
F.E. : I find it hard to accept that “we see a remarkably linear response of CO2 levels to temperature over the ice ages” and “I still disagree with the less than 100%” are compatible.
The endpoint (equilibrium) shifts somewhat with temperature, but we are already 100 ppmv above equilibrium. No matter of that in reality is 90 or 110 ppmv, there is no real contribution of temperature to the increase, only a contribution to the sink rate.
For your own bussiness, it doesn’t matter that others also have contributed to the gain of the bank (even if their contribution was higher than yours), if the gain at the end of the year is less than what your own contributions during the year where: better look for another bank…
(2) My statement is made in a scientific context, not a political context; in a political context, I would argue that there are far far better things to do than stop the emissions.
Ditto.
And I still want to know the mechanisms behind the 800-year lag.
Probably caused by the app. 800 years mixing time with the deep oceans, see:
http://icebubbles.ucsd.edu/Publications/CaillonTermIII.pdf
F.E. : Thanks for the link on the lag. I will read.
About your unprofitable bank : We are talking about a rather unusual bank. This bank has two divisions, and the more profit that division A makes (emissions into the atmosphere), the more difficult it makes it for the division B (emissions from warming oceans) to make a profit. So profitable has division A become, that it has forced division B into making big losses. So, as you correctly state, all the profit comes from division A. But now there is a threat to division A and the bank may be forced to close it down (stop emissions). Investors shorting the bank are thrilled “all their profits come from division A, if division A closes down the bank will make no profit at all”. But of course, they are wrong – if division A closes, then the bank will make a profit again from division B.
Mike Jonas says:
August 27, 2010 at 2:46 pm
if division A closes, then the bank will make a profit again from division B.
But not immediately, only after many years, when the buildup of capital from division A is (near) completely gone…
RE: Ferdinand Engelbeen: (August 21, 2010 at 7:07 am) “Hardly any, as what animals respire has been captured some months/years before. Some carbon is temporarely stored in fat tissues, but that is very small, compared to what is stored in vegetation in general.
As I understand it, you are saying that even if a massive decline of the primary CO2 emitting biota (animals) relative to oxygen emitting biota (plants) did happen during a cold period, that would not cause the CO2 levels to fall because of the continuing release of CO2 from decaying vegetation. Is it possible that the colder temperatures would slow down those decay rates? Perhaps the issue is moot because no such plant/animal imbalance ever happens.
Ferdinand Engelbeen says: August 24, 2010 at 2:27 am
“The refresh rate of 150 GtC doesn’t change the total mass in the atmosphere, it only governs how much red CO2 resides there, it is only the imbalance which adds or removes CO2 from the total mass in the atmosphere.”
Sorry to come back to the material balance again, because I think that your reasoning still contains a flaw.
It is obvious that if the refreshment rate 150 GtC/y is constant, it will not change the total mass in the atmosphere. But the basis for the assumption that a natural source is contributing to the increase of the total mass in the atmosphere, is that the refreshment rate is not constant. It is at least not over a short time interval of years. The increase of CO2 in the atmosphere Fa (GtC/y) fluctuates from 1.5 to 5.5 GtC/y. Fluctuations are the result of the difference of the flow Fin at the source and the Fout at the sinks. Both are independently influenced by other forces than the actual CO2 concentration in the atmosphere alone. Let’s assume an ‘average’ flow in, which equals the flow out, and add to both a variability dFin and dFout, the addition to the atmosphere Fa = (150 + dFin) – (150+dFout) = dFin – dFout.
Next we add to the atmosphere an extra anthropogenic flow Fem, then Fa reads:
[1] Fa = Fem+dFin – dFout
Fem consists of aC, dFin of CO2 from the natural source nC.
In your way of reasoning, you say Fa= 0.5 times the value of Fem, thus dFin-dFout = – 0.5 times of the value of Fem. If we introduce for Fem = 7 GtC/y (near year 2000).
Fa= 3.5 and dFin-dFout = -.3.5. Thus dFin must be smaller than dFout and I read from your figure 3 in part one you even indicated that dFin is lower than 0. But I suppose that this has not been measured and that you reach this conclusion by calculation to balance the equation [1] to make dFout less than 3.5 . That is the problem with the solution of one equation with two unknowns (dFin and dFout).
Solutions for -3.5 = dFin-dFout can be
[a] dFin = -3 dFout = 0.5
[b] dFin= 0 dFout = 3.5
[c] dFin = + 3 dFout = 6.5
The difference between [a] and [c] is in words, that in [a] the Fa was reduced below the value of Fem by a required small increase of dFout, and that in [c] the contribution of dFin requires a considerable increase of dFout to keep the value Fa below the value of Fem. Your way of reasoning to favor [a] (or [b] ) over [c], with the argument that dFin-dFout must be negative to reduce the value of Fa below Fem, I still fail to understand because in all three assumptions this is the case.
I am not excluding either [a] beforehand. The change of dFout depends on what distance the system is operating from its assumed equilibrium state Fin=Fout.
Previously I have rewritten in the equation [1] the dFout as containing a fraction x of what is coming in as Fem and dFin
[2] dFout = x*(Fem+dFin)
because the sink will not discriminate between aC and nC
Then [1] reads
[3] Fa= (Fem+dFin) – x(Fem+dFin) = (Fem+dFin)*(1-x)
In [2]
Case 1: with dFin =0, x becomes 0.5 .
But if I have interpreted your view correctly,
Case 2. dFin should be negative and it requires that x is lower than 0.5. It means that less of the in flow than half of it, can be removed. Thus there is a strong constraint on the absorption of extra in flows. The system operates near a saturation level for removal of CO2 from the atmosphere. .
Case 3. If dFin is positive, than x is greater then 0.5. It means that more than half of the inflow can be removed. Thus there is no strong constraint on the extra in flows. The system operates away from its saturation level.
In summary,
Case 1 is a rather arbitrary assumption
Case 2 needs proof that there is a strong constraint on the extra inflows and that dFin is negative
Case 3 needs proof that there is little constraint and that dFin is positive.
At least we can say that the system is not already at a specific (natural) saturation level, otherwise all of the Fem would be accumulating in the atmosphere.
Arthur Rörsch
Arthur Rörsch says:
August 29, 2010 at 7:25 am
Dear Arthur,
You wrote:
Your way of reasoning to favor [a] (or [b] ) over [c], with the argument that dFin-dFout must be negative to reduce the value of Fa below Fem, I still fail to understand because in all three assumptions this is the case.
I have not the slightest preference for [a] or [b] or [c]. Even have I no problems if
dFin = +10, dFout = +13.5
thus dFin in that case is larger than Fem. As in all cases, dFout is 3.5 GtC larger than dFin for the year 2000, because that is what is calculated as the difference between increase in the atmosphere and emissions.
That indeed doesn’t change the mass balance: dFin increased, but dFout (need to be) increased with the same amount, thus while the input flows increased with dFin, the total mass in the atmosphere, Fa, didn’t change by one gram of CO2, despite the increase of total inflow Fin.
The only effect of the increase of total input caused by dFin is that the throughput, the refresh rate, increased from some 150 GtC to 160 GtC. Thus the replacement of “red” aCO2 by nCO2 is accellerated and a larger fraction (than 0.5) of aCO2 is removed from the atmosphere. But still the emissions are fully responsible for the increase, as that is the only real addition to the total mass. How much of the original aCO2 remains as fraction, even if all aCO2 was completely replaced by nCO2 within a year, that has not the slightest interest for the total mass of CO2 present in the atmosphere…
In the past 50 years there was always a net sink of all natural flows and these only show a moderate variability of Fin and Fout combined: +/- 2 GtC from year to year around the trend of nowadays +4 GtC/year, halve the emissions of +8 GtC/year.