By Don J. Easterbrook, PhD.
In a paper “Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation”, Shakun et al.(Nature 2012) contend that rising temperature at the end of the last Pleistocene glaciation were preceded by increasing atmospheric CO2. In his usual masterful fashion, Willis Eschenbach has dug deeply into the data used in the paper and shredded the conclusions in it (see http://wattsupwiththat.com/2012/04/06/a-reply-shakun-et-al-dr-munchausen-explains-science-by-proxy/
and http://wattsupwiththat.com/2012/04/07/shakun-redux-master-tricksed-us-i-told-you-he-was-tricksy/#more-60932/. So rather than dwell on the things that Willis has already shown so well, I thought I’d take a look at some of the assumptions and misconceptions that paper is built upon.
When reading a paper like this, I always like to ask myself, what are the basic assumptions that underlie the methodology involved? What contentions are simply stated as fact or generated in a computer model, rather than demonstrated with real, physical evidence? I will confess here that I don’t believe computer models really prove anything. Sure, they can suggest many things and point out areas of interest, but I live the real world and prefer real physical evidence upon which to base important conclusions. That doesn’t mean I discount models out of hand—it simply means that I look for physical evidence to confirm or deny what the models are saying. So I asked myself a series of questions about the basic issues in this paper. Here are some of the questions that I came up with (the answers follow).
1. Can the Antarctic ice cores be dated with sufficient accuracy to establish a firm temperature chronology?
2. Are the 80 temperature proxies used in the paper sufficiently accurate to establish a solid global temperature chronology?
3. Can CO2 in the ice cores be measured with validity and accuracy?
4. Can the difference in the age of the trapped air and the age of the enclosing ice be determined and is it constant with age?
5. Are CO2 measurements from air bubbles valid or do diffusion and the uncertainty in the timing of isolation of air in bubbles render them invalid?
6. Is the data from Antarctic ice cores consistent with data from the Greenland ice cores?
7. Is the temperature chronology of the ice cores and global proxies consistent with the well-dated, global glacial record?
8. Is the so-called ‘see-saw’ of climate changes between hemispheres valid, i.e, are climate changes in the Northern Hemisphere out of phase with those in the Southern Hemisphere?
9. Would correlation between CO2 and temperature necessarily prove that CO2 causes climatic warming?
10. Since CO2 is incapable of causing climatic warming by itself (CO2 makes up only 0.038% of the atmosphere and accounts for only a few percent of the greenhouse gas effect), is there evidence of concomitant increase in water vapor (which causes more than 90% of the greenhouse gas effect)?
11. Is the AMOC the only viable causal mechanism? What about the influence of the Pacific Ocean, which covers about half the Earth’s surface
So, what is the main contention of this paper and what does it imply? The authors claim to have “compelling evidence that rising CO2 caused much of the global warming” at the end of the last ice age, roughly 11,000 to 25,000 years ago. According to the authors, “if you reconstruct temperatures on a global scale – and not just examine Antarctic temperatures – it becomes apparent that the CO2 change slightly preceded much of the global warming, and this means the global greenhouse effect had an important role in driving up global temperatures and bringing the planet out of the last Ice Age.” The crux of their contention is illustrated in their Figure 2.
Shakun et al. Figure 2. The Red line is Antarctic temperature curve based on ice cores; the yellow dots are CO2 measurements from ice cores; the blue line is composite global temperature from 80 proxies.
Willis has sliced and diced the data behind these curves so be sure to read his analyses. I’ll refer to some of his graphs and conclusions but look at the Shakun et al. contentions from a somewhat different angle. Because this is such a marked divergence from the widely held view that CO2 lagged rising temperatures at the end of the last ice age, careful scrutiny must be given to evidence and assumptions upon which this contention is based. Right off the bat, a most surprising conclusion in this paper is that the authors claim that correlation proves cause. Simply showing that CO2 correlates with anything surely doesn’t prove that CO2 was the cause. It’s the same kind of mindset involved with the oft-heard claim that if we have had global warming while CO2 was rising that proves the cause was the rise in CO2. Heck, I had hair before CO2 began to rise, but I don’t blame that on CO2.
So let’s look at each of questions posed above.
- How accurate is the dating of Antarctic ice cores? How can you date ice that has nothing in it that can be directly dated? The Shakun et al. paper states that they use the methodology of Lemieux-Dudon et al. (2010), which involves construction of a model using estimates of snow accumulation rates, temperature, firn densification rates, and ice flow rates, all of which vary from glacier to glacier and from glaciation to interglaciation (thus introducing large potential errors). The modeling data is then modified by matching with tephra horizons, sulfate spikes, δ18O, firn densification model results, and orbital tuning. All of the assumptions built into the modeling are cumulative, resulting in large possible age errors. As Lemieux-Dudon point out “One special feature of glaciological models is a large model error due to unresolved physics and errors on the forcing fields, clearly affecting the quality of the inferred dating scenarios.” What this means of course is that the age determinations of the Antarctic cores are, at best, educated guesses with large uncertainties. Because chronology is so critical to the Shakun et al. contention, the ages of the Antarctic cores shown in their Figure 2 cannot be considered accurate.
- Are the 80 temperature proxies used in the paper sufficiently accurate to establish a solid global temperature chronology? Willis Eschenbach has made a detailed analysis of the data used to construct the global temperature curve in Figure 2 of Shakun et al.(see this in his web posting) He plotted individual curves for each of the 80 temperature proxies used to create Figure 2 in the Shakun et al. paper. What he found was large variability in the data, which led him to conclude that “The variety in the shapes of these graphs is quite surprising Yes, they’re all vaguely alike, but that’s about all. The main curiosity about these, other than the wide variety of amounts of warming, is the different timing of the warming.” When he ploted all the individual proxies all together (see below), the scatter is readily apparent, leading him to conclude: “It’s clear that there is warming since the last ice age.” “But if you want to make the claim that CO2 precedes the warming? I fear that this set of proxies is perfectly useless for that. How on earth could you claim anything about the timing of the warming from this group of proxies? It’s all over the map.”
===============================================================
Dr. Easterbrook requested this correction below saying:
As one of your readers pointed out, Willis used ‘Year’ for his time scale (meaning years BC, rather than years BP). I didn’t notice this (geologists always use years BP for events older than a few thousand years), so there really isn’t a discrepancy between the Shakun global curve and Willis’s data points. That graph and the text with it should be replaced with the attached file “dje response to Nature paper x.doc”) or it can just be removed from the posted version. That also means that the YD shown vertical time lines in the previous graph needs to be moved over 2000 yrs so we might as well just Willis’s graph (see attached file).
Sorry for the glitch–my fault–I should have caught it, but the thought never occurred to me that Willis would use 25,000 years BC. It doesn’t change any other of the other material.
Large scatter of individual data points on Willis’s plot from the 80 proxies used in the construction of the Shakun et al. temperature curve. I’ve added lines to show the age of Younger Dryas interval, which doesn’t correspond to the dip in the Shakun et al. temperature data.
Just for fun, I superimposed the curves on Shakun et al. figure 2 over Willis’s data point plot (see below). Because the global temperature curve (the blue curve) was presumably derived from the data in Willis’s plot, it should fit well with it. Interestingly, it doesn’t. I’ve shown with a blue arrow the dip in temperature that corresponds to the Younger Dryas and a black arrow pointing to what should be the same dip in temperature on the plot of individual data points. Other arrows point to similar differences for the end of the Younger Dryas. Now you would think that since the Shakun et al. blue curve was constructed from the individual data points shown on the graph, the two should surely be compatible! I’ve also shown on the graph the well-established age of the Younger Dryas—note that the Shakun et al. global temperature data points show a dip in temperature (presumably the Younger Dryas) that is considerably younger. Makes you wonder!
==============================================================
3. Can CO2 in the ice cores be measured with validity and accuracy?
4. Can the difference in the age of the trapped air and the age of the enclosing ice be determined and is it constant with age?
5. Are CO2 measurements from air bubbles valid or do diffusion and the uncertainty in the timing of isolation of air in bubbles render them invalid?
Because these questions are all inter-related let’s consider them together. The validity of measurement of CO2 from bubbles in ice cores has been challenged in a number of studies. There are several basic problems: (1) air becomes trapped in ice during the conversion of snow to firn to ice. Air in the snow/firn phase remains in contact with surface air until it turns to ice and seals off air bubbles from further mixing with surface air. The depth at which sealing occurs varies considerably, depending on the rate of firn densification, and may extend to more than 100 meters and take a thousand years or more. This means that the age of air in a bubble is not the same as the age of the inclosing ice. Snow densification rates vary considerably between temperate and polar glaciers and between glacial and interglacial climates, making it difficult to measure and date adequately. In any case, rates are not likely to be constant. (2) a second problem results from possible diffusion along the walls of an air bubble, which can upset the CO2 concentration in the bubble. These and other problems mean that measurement of CO2 in ice cores is not straight forward—measurement of CO2 concentrations in ice bubbles and determination of the age of the air are likely to be quite variable. General trends are apparent in CO2 ice core measurements, but variability in CO2 concentrations and age remains problematic.
At this point, answering the remaining questions is quite obviously going to take some time, so they will be considered in Part 2, coming soon.
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DWR54 says:
April 9, 2012 at 1:52 am
Previously on this blog Dr Easterbrook has stated:
OUT OF CONTEXT. Please try again.
Can we conclude anything from the Shakun paper?
jorgekafkazar says:
April 9, 2012 at 12:03 am
“major9985 says: “…CO2 is a greenhouse gas and has been shown as the principal control knob governing the climate of the for the last half billion years….”
False. Your reference shows association, not causation. Perhaps you misread the abstract. Perhaps you aren’t familiar with scientific principles. Or perhaps you didn’t think we’d check the link?”
The phrase “principal control knob” is the title of the paper I referenced, I did not say that CO2 was the causation of any warming. To understand the temperature of the planet, you have to take into consideration the concentration of CO2, which is what the paper I referenced explains. This has been shown over the last half billion years.
P. Solar says:
April 9, 2012 at 12:19 am
“Well, of course we would have more chance if getting it first hand if they did not publish behind a paywall. However, the graph you post , which it appears in Shakun’s 2b tells up quite a lot. It marks “onset of warming” 19ya BP; onset of CO2 rise 17.5ya BP.
QED.
Oddly they then twist this around to conclude the opposite. Remarkable deductive science!”
CO2 is not the instigator of the end or beginning of the glaciations or ice ages. It is the orbit and tilt of the earth that does it. When this earth change happens, it only melts the ice in the Northern Hemisphere which disrupts the ocean flow. This warms the Southern hemisphere. This Southern warming, releases CO2 from the ocean causing global warming. The idea is, the change in the earth’s orbit or tilt will not do as much to the planet as is observed. CO2 is the best explanation for the global warming that is seen, and this paper reaffirms the idea.
P. Solar says:
April 9, 2012 at 12:38 am
“Indeed it does. Which is in complete contradict with the physical evidence, it would seem.
http://i44.tinypic.com/34gncox.jpg 4 and 5 seems to come first.”
It was an increase in sun light hitting the Northern Hemisphere which caused more ice to melt. This disrupted the warm ocean flow of water from the Southern hemisphere to the Northern Hemisphere, which caused the North to cool and the South to warm up. The increased ocean warming in the Southern Hemisphere released more CO2 into the atmosphere which caused global warming. This is why CO2 is the best explanation for the ice ages. So it was a warming in the Northern Hemisphere that started this processes.
Disko Troop says:
April 9, 2012 at 2:40 am
“As there are “many different warming start dates” and ” a mix of proxy temperature records” You are simply showing that there is no correlation let alone causation. Are you telling us that CO2 can choose where and when it starts the warming, if so there is nothing global about it and the whole paper is a pointless sham.”
As the Earth warms up at present, the warming is not standard around the globe, it is different. But there is more to it when looking at the last glaciations as the paper does. The Southern Hemisphere warmed much faster than the Northern, so clearly you are going to get proxy’s showing that, which the paper explains http://i44.tinypic.com/34gncox.jpg
The proxy’s are a local temperature record, if the area that the proxy came from was covered in ice and then warmed from the increased CO2, the area would have melted over time and a forest would have grown. This area is going to show a different temperature record to an area that had no ice and a forest was there from the start. But more to the point, if you or Don J. Easterbrook has an issue with a proxy record, they are all referenced in the paper and can be researched. These proxy papers will explain why they had that type of local temperature record. This is how science works, you have to read.
Then CO2 is not a cause but a side effect…. from basic logic.
P. Solar says: April 9, 2012 at 12:38 am
“Mosh says:
>>…
4. A warming in the SH, leading to
5. MORE c02 outgassed from the ocean.
C02 both leads ( enhances) and lags ( as a feedback) the temperature rise.
It doesnt really change our view of things but adds in a few more details about the sequence.
>>
Indeed it does. Which is in complete contradict with the physical evidence , it would seem.
http://i44.tinypic.com/34gncox.jpg
4 and 5 seems to come first.”
____________________________________
The graph shows that the initial spurt of warming began c. 20 kyr in the NH (purple line, 60′-90′ N). The rise in SH only begins ‘after’ 19 kyr. The authors suggest that the initial NH warming was orbital.
This, they suggest, led to a warming N-S ocean pulse that triggered SH ocean warming c.19 kyr, releasing significant CO2. It’s only after this, post c. 17 kyr, that ‘global’ temperatures start to rise, according to the graph.
The authors suggest that the initial global warming, 20-17 kyr, was caused by orbital forcing, but that the global warming post 17 kyr was mostly due to CO2 forcing, i.e. a positive feedback response.
Eye balling Figure 2 (Shakun’s graph), the global temperature seems to lag the Antarctic and CO2 plots by between 1000 and 2000 years.
Surely a rise in CO2 would have an effect within a few decades, not centuries.
major9985
“Because CO2 is a greenhouse gas and has been shown as the principal control knob governing the climate of the for the last half billion years.. (http://tinyurl.com/6ppedy6) (http://droyer.web.wesleyan.edu/PhanCO2%28GCA%29.pdf) It is not a bold claim to attribute this trail of temperature change to the rise in CO2 as the driver of the change.”
The abstract of of Dana Royer’s paper which is referred to states:
“The correspondence between atmospheric CO2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity. Here, I compare 490 published proxy records of CO2 spanning the Ordovician to Neogene with records of global cool events to evaluate the strength of CO2-temperature coupling over the Phanerozoic (last 542 my). For periods with sufficient CO2 coverage, all cool events are associated with CO2 levels below 1000 ppm. A CO2 threshold of below ~500 ppm is suggested for the initiation of widespread, continental glaciations, although this threshold was likely higher during the Paleozoic due to a lower solar luminosity at that time. Also, based on data from the Jurassic and Cretaceous, a CO2 threshold of below ~1000 ppm is proposed for the initiation of cool non-glacial conditions. A pervasive, tight correlation between CO2 and temperature is found both at coarse (10 my timescales) and fine resolutions up to the temporal limits of the data set (million-year timescales), indicating that CO2, operating in combination with many other factors such as solar luminosity and paleogeography, has imparted strong control over global temperatures for much of the Phanerozoic.”
Unless I am mistaken current CO2 levels are around 392 ppm. Does this mean that we are in for “widespread, continental glaciations”?
This paper, cosignated by Bard as last author, seems to be the paper too much , too much, trop trop trop for him ; it has a smell of pine tree (or coffin) as that of the « scientific » carrier of M.Mann
It looks a bit bizarre to me that it would be revolutionnary that temperatures of Northern Atlantic and tropical environments do not lag that of polar environments and ice, while the sun irradiates more the poles to the detriment of tropical latitudes ; really, as long , as they do not demonstrate that CO2 does not lag temperature in ice cores , there is nothing new ; and if they do, we are waiting for the explanations of vice président Jouzel to find the source of CO2 before the deep polar oceans started to moove
Why don’t you people (Eschenbach and Easterbrook) submit a rebutal to Nature? Obviously it is full of errors and mistakes. What you are doing now is nothing more than brabbling about a misleading paper.
Vince Causey says:
April 9, 2012 at 3:04 am
Science has looked at the way CO2 participates in the climate system over the last half a billion years and comprehensive conclusions show over the long term there is indeed a correlation between CO2 and temperature, as manifested by the atmospheric greenhouse effect.” p.201. (http://earth.geology.yale.edu/~ajs/2001/Feb/qn020100182.pdf).
This was the same conclusion for all the other studies:
CO2 as a primary driver of Phanerozoic climate — D. Royer et al, GSA Today, March 2004 (http://droyer.web.wesleyan.edu/GSA_Today.pdf)
CO2 forced climate thresholds during the phanerozoic, Dana L. Royer 2005 (http://droyer.web.wesleyan.edu/PhanCO2(GCA).pdf)
Atmospheric CO2: Principal Control Knob Governing Earth’s Temperature, Andrew A. Lacis, Gavin A. Schmidt, David Rind and Reto A. Ruedy, 2010 (http://www.sciencemag.org/content/330/6002/356.abstract)
“The bottom line is that these proxies are attempting to determine whether CO2 leads or follows temperatures – a time resolution of only a few centuries for events that took place hundreds of millions of years ago. You see the problem.”
The paper explains its methods and the “event” took place over 10000 years, not a few centuries.
I’m still confused about the merits of temperature proxies taken from predominantly coastal locations. It appears to me that they are truly representative of neither continental nor oceanic environments.
I don’t know but it seems to me that someone is wrong here, either CO2 rose after temperature as shown in earlier ice cores, or CO2 rose before temperature as shown in these ice cores. I don’t think we can have it both ways.
Perhaps the next study will show that CO2 and temperature rose simultaneously. The we’d have all possibilities covered.
This is a very worrying situation.
The obvious questions to ask are:
Who supervised this work?
What happened to “Peer review”?
Who says these “scientists” are qualified to produce such a paper?
But this isn’t science. This is propaganda.
On the basis of the analyses so far performed, I’m not sure a part two is necessary except to demonstrate the extent to which these “scientists” ought to feel extreme shame and find a different line of work.
It is as if they started out with an objective; to show exactly what the conclusion shows, and then selected and misrepresented the data to show exactly that.
Whatever happened to analysing the data to see what the data shows?
Solomon Green says:
April 9, 2012 at 5:04 am
“Unless I am mistaken current CO2 levels are around 392 ppm. Does this mean that we are in for “widespread, continental glaciations”?”
over half a billion yeas ago, the sun was 4% weaker and I think 30-40% dimmer, for the planet to be nice and warm CO2 had to be very high, 8000ppm compared to 390 today. The sun has gradual decreased over this half billion years and science has shown that the concentration of CO2 when compared to the output of the sun equals the temperature of the earth. This graph shows this correlation over the half a billion years of climate data we have http://tinyurl.com/6ppedy6
I notice that R. Gates has now taken to sniping from SkepticalScience.com rather than debating directly here. He managed to post some off-topic speculation about how the “natural negative feedback pathways become overwhelmed when [CO2 is rapidly increased]”. I mention it here only to point out that he would not get away with such rampant speculation here.
I should add that unless the authors of this paper can defend it robustly and credibly, it calls into question not just this work, but all the previous work done by the lead “scientist” Jeremy D Shakum.
It also calls into question the standards at Havard, the supervision and standards of education there and it brings into question the reputation of journals such as Nature.
The analyses on this website ought to have been performed at various stages during the preparation of this work and certainly should have been performed in any critical peer review process.
If the peer review process is so badly flawed then it is a case of “Falsus in unum, falsus in omnibus’ and taints the work of all other scientists published in Nature. Scientists who have some regard for their reputation and credibility must surely need to consider carefully the journals they submit their papers to.
It seems to me that the whole of the scientific process is seriously damaged by the Climate Change Scandal and while it is difficult to gain a reputation, it is very very easy to lose it and then it is extraordinarily difficult to recover.
It may be that some journals are terminally damaged and will eventually disappear to be replaced by new publications which impose a more rigorous set of standards and are free from the political activist traits now so prevalent.
Climate studies is a subject fast approaching the status of astrology and it too may have suffered irreparable damage. It may endure and even appear to gain in importance for a while, simply a reflection of the money poured in, but in the long term?
Thank you for raising some excellent questions. I do not feel that you should be reluctant to state, “I will confess here that I don’t believe computer models really prove anything” It should be a stated principle for scientific research that computer models, like statistics, are valuable tools to guide the researcher. Tools, such as brushes or chisels, enable artists to be creative. But scientists are not artists. A skillfull scientist can create a model that encompasses scientific principles, but the scientist can not be creative with this tool to create science. A model can only identify issues that have potential. The scientist should use the results from a model to develop a hypothesis, the first step in the scientific method. The scientist should then develop a plan to collect data that would proove or disprove the hypothesis. Using a model as the final step in the scientific process is not science, it is more comparable to playing computer games.
major9985 says:
April 8, 2012 at 10:54 pm
“Because CO2 is a greenhouse gas and has been shown as the principal control knob governing the climate of the for the last half billion years.. (http://tinyurl.com/6ppedy6) (http://droyer.web.wesleyan.edu/PhanCO2%28GCA%29.pdf) It is not a bold claim to attribute this trail of temperature change to the rise in CO2 as the driver of the change..”
Except for the fact that cold sea water holds more CO2 in solution than does an equal amount at a warmer tmperature.
Solomon Green says:
April 9, 2012 at 5:04 am
Bear with me here, you’ve brought a paper into discussion and actually had the audacity to read and comprehend it – how dare you!
/sarc
The existence of glaciation during +1000 ppm CO2 concentrations has always been a problem for the Ecofaschisti. As was said by another commentator, they just wave their hands “waiting for more data.”
This all is a massive attempt to rewrite geological history. Historical revisionism has widely been practiced by those who aim to totally control the poletariat/serfs. Now they’re trying to use another form of fear to drive it. It’s not working out so well, and so we see a doubling down on revisions. It’s so interesting to watch. You don’t need to believe in c*racy to see that like puppies wiggling around the alpha male, newly minted scientists are inclined to support their professors and subsequently those who were taught garbage, promptly generate more. I’m strongly in favor of ridding the ecosystem of that particular type of garbage!
Steven Mosher says:
April 8, 2012 at 10:35 pm
Nothing wrong with being a “Lukewarmer”. I strongly believe a warmer earth with abundant CO2 for the biosphere is a win-win situation.
However, the CAGWCF (CF for “Control Freaks”) is another matter entirely–they’d have you believe we must erase 100 years of industrialization from carbon-based fuels and be forced into wind and solar solutions that have no overall economic advantage–they seem to see a cliff that nobody else sees. Oh, and they’ll control your light switch along with just about everything else.
Beware!
Dear Dr. Easterbrook:
a second problem results from possible diffusion along the walls of an air bubble, which can upset the CO2 concentration in the bubble.
The diffusion was studied along the remelt layers in the Siple Dome ice core, a “warm” core (-23°C). See:
http://catalogue.nla.gov.au/Record/3773250
While that is not necessarely the same as for “normal” ice layers, the results give a broadening of the resolution from 20 to 22 years for middle depths (at a few kyr back) to 40 years for the deepest layers (70 kyr back). Hardly a problem. For the much colder (-40°C) Vostok and Dome C ice cores, there is far less migration, as even the thiniest waterlayer at the edge of the ice crystals is gone at -32°C. Moreover, if there was any migration at all, the ratio between CO2 level and temperature (proxy) would fade over time, for each interglacial/glacial 100 kyr further back in time over 420 and 800 kyr. Which is not observed.
Thus, while the exact timing of the average CO2 age is a real problem, CO2 diffusion is not a problem in the “cold” ice cores.
I have noted this same problem in all papers with the seemingly purposeful exclusion of error bars in reconstructions of ice core and other proxy CO2 and temperature graphs, regardless of which is leading and which is lagging. Both sides overstate the case in my opinion. It was this observation that led me to agree with Nick that it appears that there is data to be had that may show CO2 increase precedes temperature increase. Leading versus lagging CO2 is a fair and questionable focus of research endeavors.
Given the spread of proxies, it would not be hard to find data that appears, at first glance, to agree with one’s pet theory fairly easily. The above reviewed paper has done that. But this is where Nick and I part company. On second glance, and with proper attention to error bars, which the authors failed to do, at the very least it should give us pause to consider that neither side has a lock on this.
There are three basic statements to make when reporting findings. The two gold standard classics are yes, there appears to be a statistical difference, or no there appears not to be a statistical difference. The post modern era AGW scientists seem willing to submit papers that have not completed this essential statistical step and appear very willing to convince us of their eye-ball opinions. Worse, Hansen appears eager to pick the pockets of all based on such a conclusion.
bubbagyro says:
April 8, 2012 at 8:34 pm
It diffuses from areas of high concentration to low concentration. SO high concentration bubbles will diffuse toward the outside, to be in equilibrium ONLY when the concentration in the bubble is equal to concentration outside.
A small problem here: we measure 180-300 ppmv CO2 in the ancient air bubbles, but our present outside air is already near 400 ppmv. Thus if there was any migration, we would see an increasing gradient between older air and current air, but over the full length of the ice core, not only over the past 160 years… And the ratio between CO2 level and temperature (proxy) for the older parts would be different than for the younger parts. In addition, 180 ppmv is already critical for several plant species, thus a substantial migration would mean that the real values were even below 180 ppmv…
ALSO, when the ice core is removed from “down under”, where there exists high pressure at the bottom of the ice column, the pressure is removed, and the ice bubbles, retaining the pressure from below, diffuse faster toward lower pressure at the surface. Diffusion then becomes directly proportionally increased in accordance with the pressure gradient. This is additive to the diffusion gradient.
That implements that the migration speed for CO2 is faster than for O2/N2, or there wouldn’t be a change (I do expect the opposite, as CO2 has a higher affinity to the ice surface than O2 or N2). The deep cores are kept on low temperature for almost a year to expand the ice (“relaxation”). Once the internal and external pressure would be the same, any migration would go from out to in. And again, that would give different results for the deeper parts than for the younger ones.
Uncertainty abounds !!
Steven Mosher says:
April 8, 2012 at 10:35 pm
A couple of points. The proof that C02 causes warming is not from corelation. Its from experiemental evidence and basic engineering.
The question is how much warming.
Is sensitivity 3C as Hansen and the IPCC claim?
This study by Shakun implies a LOWER number actually. It implies 2.5C
Yes. Shakun adds another win for Lukewarmers.
=================================================================
Specific to this study, it does not such thing. It flies in the face of conventional thought which the lukewarmers embrace. But, to the ‘how much’ question, I reckon it would be analogous to trying to warm your house with a laser pen with the windows open. (Unique CO2 absorption spectrum)
Towards this study, though, if the CO2 increased first, and assuming it was well distributed, how is it the Antarctic was lagging behind the rest of the world? If that’s true, it destroys much current climate thought. ….. And then there’s the question of how the CO2 spontaneously emerged to cause any warming.
To me, this is a great victory for the hard skeptic line. It can’t really be both, this paper being science or current climate thought.