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Climate Hustle

CO2 has been higher in the past

Posted on 27 October 2009 by John Cook

We've seen empirical evidence that more CO2 causes an enhanced greenhouse effect. However, when we look back over the Earth's history, we see many periods where CO2 is higher than current levels of 384 ppm. Intriguingly, for some of those periods where CO2 was higher than now, the planet experienced widespread regions of glaciation. Does this contradict the warming effect of CO2?

No, it doesn't, for one simple reason. CO2 is not the only driver of climate. To understand past climate, we need to look at other forcings that drive climate. One paper that does this is CO2-forced climate thresholds during the Phanerozoic (Royer 2006). It pieces together 490 proxy records to construct a 540 million year timeline of CO2 levels. This period is known as the Phanerozoic eon.

Figure 1: Atmospheric CO2 through the Phanerozoic. Comparison of the predictions of GEOCARB carbon cycle model (dashed line) with a smoothed representation of the proxy record (solid line). Source: Royer 2006.

CO2 levels reach some spectacular values in the deep past, possibly topping over 5000 ppm in the late Ordovician, around 440 million years ago. However, solar activity also falls as you go further back. In the early Phanerozoic, the solar constant was about 4% less than current levels. Royer 2006 combined the radiative forcing from CO2 and solar variations to find their net effect on climate. The result is shown in Figure 2. Cooler climate is indicated by shaded areas which are periods of geographically widespread ice.

Figure 2: Combined radiative forcing from CO2 and sun through the Phanerozoic. Values are expressed relative to pre-industrial conditions (CO2 = 280 ppm; solar luminosity = 342 W/m2); a reference line of zero is given for clarity. The dark shaded bands correspond to periods with strong evidence for geographically widespread ice.

They find that periods of low CO2 correlate with long-lived, extensive continental glaciations while periods of high CO2 don't overlap with these glaciations. They also explore the concept of the CO2-ice threshold - the CO2 level required to initiate a glaciation. When the sun is less active, the CO2-ice threshold is much higher. For example, if the CO2-ice threshold for present-day Earth is 500 ppm, the equivalent threshold during the Late Ordovician (450 million years ago) would be 3000 ppm.

A follow up paper Climate sensitivity constrained by CO2 concentrations over the past 420 million years (Royer 2007) offers a more quantitative comparison of global temperatures and CO2 levels over the Phanerozoic. They couple the CO2 record to temperature and find a climate sensitivity of 2.8°C. The results "indicate that a weak radiative forcing by carbon dioxide is highly unlikely" and that a "climate sensitivity greater than 1.5°C has probably been a robust feature of the Earth’s climate system over the past 420 million years"

So we see that comparisons of present day climate to periods 500 million years ago need to take into account the fact that the sun was 4% less active than now. What about times closer to home? The most recent period when CO2 levels were as high as today was around 15 million years ago, during the Middle Miocene. CO2 levels were at about 400 ppm. What was the climate like at the time? Global temperatures were 5 to 10 degrees Fahrenheit higher than they are today. Sea level was approximately 75 to 120 feet higher. There was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland. The close coupling between CO2 and climate led the author to conclude that "geological observations that we now have for the last 20 million years lend strong support to the idea that carbon dioxide is an important agent for driving climate change throughout Earth's history."  (Tripati 2009).

To sum up, Dana Royer says it best: "the geologic record contains a treasure trove of 'alternative Earths' that allow scientists to study how the various components of the Earth system respond to a range of climatic forcings." Past periods of higher CO2 do not contradict the notion that CO2 warms global temperatures. On the contrary, they confirm the close coupling between CO2 and climate.

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Comments 1 to 50 out of 61:

  1. One important point:
    Isn't C02 concentration in the atmosphere strongly correlated with ocean temperatures at the time: ie: the oceans absorbs more c02 when the oceans, and the earth is cooler, and the oceans realease c02 as they warms/the earth is warmer? (A simple water temperature-c02 solubility relationship).

    The correlations in earth history between c02 concentration in the atmosphere and earth temperatures given above, therefore, are at least in part simply a reflection of this ocean temperature/c02 concentration relationship. Correlation is not causation.

    Therefore, the important issue is establishing to what effect earth temperature drives ocean temperature which then drives c02, and not the other way around.

    (This is also the reason c02 lags temperature rises at the end of ice ages by several hundred years (something Al Gore forgot to mention) the oceans take longer to warm and then release their c02).
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    Response: You're correct that correlation doesn't necessarily prove causation. Causation comes from our high understanding of the radiative forcing from CO2. Reinforced by observations of the enhanced greenhouse effect. So from this, we determine the radiative forcing from CO2, calculate the radiative forcing from the sun and work out their combined effect on climate.

    Does CO2 drive temperature or the other way around? Both actually. But this is not the question addressed in Royer 2006. The focus is the measured CO2 levels and the radiative forcing they would impose on the climate - is the forcing consistent with temperature records?

    I imagine the GEOCARB carbon cycle model used would examine what drives CO2 so he possibly goes into more detail about the carbon cycle in previous papers (here's a complete list of his research complete with PDF links).
  2. @thingadonta
    "Isn't C02 concentration in the atmosphere strongly correlated with ocean temperatures at the time:"

    That is right under presumption that CO2 levels in the system (biosphere and hydrosphere)are nearly constant.
    You have to understand, that CO2 levels in the atmosphere and in the oceans are in equilibrium. This equilibrium is dependent on the temperature of the system. If you rise temperature more CO2 will find its way into the atmosphere, if temperature falls, the oceans will absorb more CO2.

    But, what will happen if you release large amounts oc CO2 into the atmosphere from sources other than the ocean? A certain fraction of this CO2 will be absorbed in the oceans and the other fraction will stay in the atmosphere, according to equilibrium.
    This is exactly what we see. The amount of CO2 in the atmosphere is rising and the amount of CO2 in the oceans is rising too. This is seen in every measurement in the atmosphere and in the ocean. This is a fact that is not possible to neglect.

    If you understand this simple connection of CO2 level, equilibrium and temperature, it will be very easy for you to understand, why rise of temperature is able to force CO2 into the atmosphere and why CO2 is increasing in the oceans despite of rising temperature.
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  3. thingadonta, we have quite a good handle on the temperature-dependent partitioning of CO2 between the atmosphere and oceans/terrestrial environment. One rtaher simple way of looking at this is to consider the relationship between atmospheric CO2 levels and earth temperature during the recent ice age cycles, since it's likely that the full increase in atmospheric CO2 levels during glacial to interglacial transitions results from temperature-dependent repartitioning.

    Looking at multiple ice age cycles, there is a generally consistent increase of atmospheric CO2 near 90 ppm (190 ppm glacial to 280 pm interglacial), and this is associated with a globally-averaged increase in earth temperature of 5-6 oC.

    Since these transitions are long (~5000 years), we can assume that the repartitioning has come near to equilibrium. So each degree centigrade of temperature rise "flushes" 15-18 ppm's worth of CO2 into the atmosphere at equilibrium.

    That's a useful "rule of thumb" in considering the likely contribution of temperature-dependent repartitioning to CO2 levels in the past. Since much of the tempeature variation during the Phanerozoic covers around 8-10 oC between coldest and hottest, we don't really expect variation of atmospheric CO2 from temperature-responsive repartitioning of more than around 150-200 ppm.

    Since atmospheric CO2 proxies indicate variations of CO2 levels of up to several thousand ppm of CO2, we can be pretty confident that these arise from factors other than temperature-dependent repartitioning.

    And when one examines the geological record, the causes of many of the large variations of atmospheric CO2 that likely dominate temperature variation, are apparent.
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  4. Commenter #1 misses the point of this blog post -- with a weaker solar forcing, and no CO2 causation of warmer temperatures, how could temperature be warm enough to bubble all that CO2 out of the oceans? Anyone who challenges the role of CO2 in warming the planet should be prepared to provide an alternate explanation of what accounts for warm geologic periods.

    The other point I was going to try making was that CO2 proxies include phytoplankton, such that high CO2 concentrations in the atmosphere are actually inferred from high CO2 in the photic zone of the oceans, contrary to the interpretation in comment 1. However, when I looked at the paper (Royer 2006, figures 1b and 3b) I noticed that there are no phytoplankton proxies for CO2 when CO2 is estimated to be quite high. I haven't read the paper yet (too many things on the go), but I found that interesting.
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  5. I have a question about the Tripati paper I hope somebody can answer.

    If CO2 levels are about the same today as 20 million years ago and I guess from what is said in this article the sun is a little warmer thn 20million years ago as well then where is all the water?

    Why don't we have 3-6oC higher global temperatures and 75 to 120 feet higher sea levels. Thats 2200-3000cm of sea level rise.

    Given an estimate of sea level rise was 3cm for the previous decade that means we'd have to wait 1000 years for that publications prediction to come true. Why aren't sea levels that much higher?

    Maybe not knowing all the conditions 20million years ago might have something to do with it?
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  6. To be able to say the Sun was 4% cooler 540 million years ago assumes linearity associated with a slope of
    0.04 divided by 540 E+6, which equals 7.4 x E-11. Is this based on science or scientology?
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  7. To #5:
    As you mention yourself: If you extrapolate the average sea level rise of the last 40 years, you'll get up into that interval in a few thousand years. Which is not to say that is what will happen, we may have negative feedbacks, like clouds and (possibly) aerosols. On the other hand, there may be positive feedbacks kicking in significantly, too. Like the mentioned CO2/sea water temperature relation.

    Remember, the forcing from radiation imbalance we have now is very small compared to the natural seasonal and cyclical variations, and the effects are to be seen on longer time scales.
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  8. RSVP,
    it looks like you think that scientist are stupid or that you don't trust science at all.
    Comparing what solar physicists know on our sun (on all the stars) to scientology means that you did not even try a wikipedia search for stellar evolution, let alone scientific papers.
    They might of course be wrong, but this is what our scientific knowledge tells us. And one needs scientific arguments to contend.
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  9. John
    The cited reference in the article starts like this...
    "Carbon dioxide (CO2) is an important greenhouse gas,
    and its role in regulating global surface temperatures has been recognized for over a century (Arrhenius, 1896;
    Chamberlin, 1899). It is now generally accepted that the
    36% rise in atmospheric CO2 since 1860 (280–380 ppm) is
    partly responsible for the concomitant rise in global surface temperature"

    If you looked up the Wikipedia reference on Arrhenius, you will find he met resistance for his idea. So to say that his idea was RECOGNIZED is an overstatement, especially with whatever data he had in 1896!

    Also, in terms of establishing this man's credibility, the Wikipedia article includes a little more. It goes on to say that Arrhenius apparently felt that global warming would be a good thing in that it would help world food production. In addition, he apparently supported the following...

    Wikipedia on Arrhenius...
    Racial biology
    "Svante Arrhenius was also actively engaged in the process leading to the creation in 1922 of The State Institute for Racial Biology in Uppsala, Sweden, which had originally been planned as a Nobel Institute. Arrhenius was a member of the institute's board, as he had been in The Swedish Society for Racial Hygiene (Eugenics), founded in 1909. Swedish racial biology was world-leading at this time, and the results formed the scientific basis for the Compulsory sterilization program in Sweden, as well as inspiring the Nazi eugenics in Germany"

    Getting back to Dana Royer's intro...
    A 36% increase in CO2 to a roughly 0.34% (1 degree K/290 degree K = .0034) change in global temperature doesnt seem to indicate strong coupling. In fact, it tends to signal that there is quite a lot margin for continued CO2 polluting.
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  10. Excellent post, as usual. I always learn something new here. Loads of thanks!
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  11. I don't think the political views of a scientist 100-plus years ago has much influence on our perception of his understanding of the physics of processes in the natural world RSVP. That sounds like a very modern concept (attempting to trash science that one doesn't like by reference to peripheral political or character traits in individuals)!

    Arrhenius was pretty much spot on in his understanding of the relationship between atmospheric CO2 (carbonic acid in his terminology from the manner in which CO2 concentrations were then determined) variation, and the earth temperature response, recognising that the temperature varies according to the logarithm of the CO2 concentration change:


    "if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression" [*]

    The reason that he didn't consider increased CO2 particulalry problematic is that in his time atmospheric CO2 concentrations were rising very slowly indeed. He considered that doubling of atmospheric [CO2] would take about 3000 years. We now know that mankind can very easily achieve this massive amplification in a century and a half.

    In fact the concerns relating to massive enhancement of atmospheric [CO2] only really began to be voiced by scientists in the 1970's, when the scale of man-made CO2 emissions began to bite home:

    e.g. Broecker, W.S. (1975) "Climatic change; are we on the brink of a pronounced global warming?" Science 189, 460-3.

    [*] S. Arrhenius (1986) On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground Philosophical Magazine and Journal of Science 41, 237–275
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  12. This is an odd thing to say RSVP:

    "A 36% increase in CO2 to a roughly 0.34% (1 degree K/290 degree K = .0034) change in global temperature doesnt seem to indicate strong coupling."

    The three fundamental errors in that statement are ones that Arrhenius would have recognised over 100 years ago:

    (i) the relationship between earth temperature and atmospheric CO2 is not linear. The temperature varies according to the logarithm of the CO2 variation as Arrhenius had already deetermined in 1896.

    (ii) The relationship between earth temperature and the logarithm of the change in [CO2] refers to an equilibrium response.

    (iii) The temperature scale is not a linear one with respect to heat content, and it's very easy to produce spurious arguments based on misunderstanding this. The non-linearity of temperature can be illustrated by the observation that the rates of chemical reactions broadly double with each temperature increment of 10 oC. Thus a reaction that has a rate constant of 1 (say) at zero oC, may well have k=2 at 10 oC, 4 at 20 oC, 8 at 30 oC, 16 at 40 oC, 32 at 50 oC and so on...

    Arrhenius knew this too...

    If we're going to use arguments to assess relationships in the natural world, we should base these on physics that is at least at a late 19th century level!
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  13. RSVP,

    When you turn on your heating at home, do you also set your target temperature as a significant percentage change on a kelvin scale? I cannot see any sense in assessing the magnitude of a temperature change as the relative difference from absolute zero, that's an arbitrary point. Why not celsius scale instead (i.e. freezing point of water instead of absolute zero)? What is important is that it shouldn't deviate from the average value in which human civilization has thrived. That's the dangerous boundary.
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  14. Chris,
    Being on the board of an institute specifically created to promote pseudoscience isnt exactly "periperal". Eugenics may be considered politially incorrect now, but at that time he was promoting it as respectable science. My comment is about judgement, not politics.

    Secondly, I never said anything about a linear relationship. I was only giving my opinion that a ratio of 0.0094:1 (i.e., .0034:.36) doesnt seem to reflect considerably tight coupling. Which is a completely separate issue from CO's atmospheric molecular mass percentage of 0.045, and the fact that CO2 absorbs energy from only a fraction of the IR spectrum. And after considering all these small values taken together, whether logarithmic or seismic or however you want to package it, the CO2 greenhouse theory (or smoke and mirrors theory or however you want to call it) is definitely not intuitive to me.
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  15. Peter Pan
    Radiation energy is proportional to absolute temperature.
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  16. That's funny. RSVP is attempting an ad-hom on Arrhenius that is somewhat reminiscent of what we see with creationists. "Establishing this man's credibility"? The rethoric is getting down to the most miserable levels.

    Whether there was resistance to his CO2 ideas and the presence of other non related stuff has no bearing whatsoever on the validity of the physics involved, which can not be disputed. The initial formulation may not have been totally accurate, but the principles were correctly understood. That is an objective fact. Arrhenius could have been a paranoid schizophrenic, he would still have been right on this subject.

    The fact that some things are not intuituve to you is exactly why this site's focus is on science papers published by researchers active in their field.
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  17. RSV #15,
    I may have misunderstood your comment, because I don't see the point of the Stefan–Boltzmann law here. I thought you were doing a (empirical) rule of three, suggesting that a 36% increase of CO2 (empirically) drove a (small) 0.34% change in temperature with reference to the absolute zero (i.e. percentage of change in the kelvin scale). (Leaving aside the fact that the equilibrium temperature is higher) that's why I asked what the point was in assessing the temperature change as a difference from the absolute zero.
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  18. re #14

    O.K., you don't believe in the greenhouse effect RSVP. The arguments you employ to try to support that astonishing position are weak 'though. You seem to be attempting to insinuate that Arrhenius's insight (which we know to be fundamentally correct) can be made to appear incorrect by reference to his views on sociological aspects of human evolutionary genetics.

    Your numerology is suspect, and perhaps that's partly why you don't find the greenhouse effect "intuitive". For example it makes rather more sense to consider the temperature variation throughout the last 500 million years (the Phanerozoic), a variation of the order of 10 oC (minimum to max). It’s variation within that temperature range that is relevant to the role of CO2 variation in modulating the greenhouse effect. After all we know (more 19th century science!) that a “naked” atmosphere-free earth has a temperature of around 255K from its cosy location near the sun. When considered in that light, a temperature increase of 1 oC as a result of a 34% increase in atmospheric CO2 concentration doesn’t seem so puny. It's already around 10% of the entire temperature variation of the last 500 million years, and pretty much what we expect within our (and Arrhenius’s for that matter) understanding of the greenhouse effect…
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  19. Philippe. It only took one man, Isaac Newton, to point the world in the right direction about the basic laws of physics. Later again, only one man, (Einstein), to introduce important caveats. On the other hand, with the smoke and mirrors theory, an international commitee has been invoked to establish its credence, and now you talk about "low blow" creationist tactics? Why a commitee? Why not just one man?
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  20. chris
    "Numerology"! At least I can see you have a sense of humor.
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  21. Chris
    I understand what the implications could be if such a small increase in CO2 could in fact create so much havoc. However, it helps to be optimistic (while taking this possibility into consideration), and make absolutely damn before going nuts about CO2. I think there is still some time.
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  22. RSVP
    Arrhenius is cited exactly once in the introduction of "CO2-forced climate thresholds during the Phanerozoic." The fact that he's a racist is not really a strong rebuttal to a paper that 1) in no way relies on any of Arrhenius' observations or opinions and 2) cites over 100 (non-Arrhenius) references.

    Ad hominem attacks are a technique for winning arguments, not for getting any closer to the truth.
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  23. Riccardo,
    You directed the following comment to me...
    "it looks like you think that scientist are stupid or that you don't trust science at all."

    I do not think anyone is stupid, especially scientists. The problem here has nothing to do with "science" if you understand science as a process that is not involved in the production or defense of dogma. There ways of saying things that reflect the limits of our understanding, and ultimately, all science is based on empirical data obtained with instrumentation that is limited in one form or another.
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  24. Playing the Eugenics card is a tried and true tactic of the creationist rethoric. Your argument had nothing to do with the ideas considered for our subject. It is a textbook example of an ad hom. You say, in essence, this: "Arrhenius did Eugenics, so his work on radiative properties of CO2 is questionable." That's a load of dung. The body of empirical results confirming the original ideas is too large to be covered here, although John has given us excellent references, which you seem to be intent on ignoring.

    What's that new argument about "one man"? The Standard Model took Planck, Einstein, Dirac, Schrodinger, Heisenberg, Bohr, Von Neuman, Feynman and a number of other, less known contributors, such as Aspect. And they all had teams working with them. All this in a number of labs and particle accelerators in many different countries. Some, like CERN, are international entities. We're as far as can be from the "one man" thing. That makes the Standard Model invalid? Total nonsense.

    The IPCC was created to address a problem that is of concern to this entire planet's human community. It intends to do (and regularly updates) the most comprehensive review and integration of the existing, relevant science. You think one man would have been enough? I don't even know why I bother responding to this. Enjoy your fantasy world.
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  25. RSVP,
    maybe i misunderstood you comment #6. You wrote "Is this based on science or scientology?".
    My impression was that calling scientology the knowledge we have on solar physics (right or wrong it might be) is a profound discredit of science.
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  26. At the risk of diluting this thread further, here is an interesting educational website (for kids) on CO2 and the ocean.
    I wish there was a portion of it devoted to how the ancient pH was estimated.
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  27. Phillipe Chantreau
    I was NOT the one that started out a dissertation using another individual's reputation and credibility to back my claims! I just happened to research who he was and found he was actively promoting a body of ideas that have been rejected, not only for moral and practical reasons, but more importantly, in terms of this discussion, for technical reasons.

    You make the case that it is unfair for me to be concerned with a person's grounding, while always defending "your" ideas based on the reputation of source material.

    The "one man" thing has to do with the quality of what committees tend to produce vs the individual. A committee is a mindless body that is incapable of integrating information. It can produce great things, (pyramids, space shuttles, etc), but it can never think.
    Oh, we forgot to mention Copernicus, by the way, who had to deal with your way of "reasoning".
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  28. Arrhenius, or any other author will not be invoked because of his credibility as an individual but because of credibility as an author, proven by work that was subsequently confirmed through innumerable other publications and loads of data. Who the author is and what kind of political opinions he has, or what kind of life he lives has no bearing on that.. Only their work on that subject matters.

    You were the one starting the ad-hom against Arrhenius, here is the exact quote from post #9 above: "Also, in terms of establishing this man's credibility," and then it goes on with other stuff and the Eugenics blurb.

    You don't seem to understand what an ad-hom is. If I said that your opinion on matters of atmospheric physics is garbage because you don't understand the basic physics that would not be an ad-hom argument, whether or not it is correct.
    OTOH, if I said that your opinion on atmospheric physics is trash because you engage in morally reprehensible activities, that would be an ad-hom, whether or not the accusation is true, once again. Your engaging in these activities would have no bearing whatsoever on reflections on atmospheric physics, whereas your ignorance of basic physics would.

    The reason why we often insist on reliability of sources is to avoid giving undue weight to stuff produced by people who are not qualified. Researchers who are active in a given field are good sources about that field. Work that has been confirmed throughout a century of subsequent research confers credibility to its author on that subject.

    Last, refrain from half veiled insults comparing me to religious authorities siding with philosophy against data. It is unwarranted. You're also implying that I am ready to jail or silence by force anyone dissenting (without specifying exactly with what) even if based on valid work. There is NOTHING in any of my posts that could even remotely allow to draw such conclusion. If there is, be so kind as to cite the exact quote and explain how you interpret it. You are using once again a poor rethoric tactic that consists of demonizing the opponent.

    I have my opinion about what transpires of your ideology, I will keep it to myself since it adds nothing to a discussion of the existing science on our subject, which is the focus of this blog.

    If I wanted to, I could easily return the favor and compare you to Stalin who ignored the findings of genetics because he was clueless enough to go for Lysenko and what was ideologically more fitting. But I won't do that. It would add nothing.

    Finally explain how a "committee", unable to integrate information, successfully launches remotely operated vehicles to Mars and all that other stuff. I don't get it. Looks to me that some pretty darn good integration of info was done there.
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  29. Great site John. Are there any papers out there that have examined extinctions and CO2 levels throughout the Phanerozoic?
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  30. Philippe Chantreau
    This very circular. The only way out is for me to concede and find things that I can agree on. For instance, you are right that a person's personal life should not be a determining factor in evaluating a person's achievements. As it turns out, this appears to be what happened to Arrhenius' detractor, Knut Angstrom for being politically insignificant. As you imply, image should not be the concern, and that it was unfair that Angstrom's critique of Arrhenius' greenhouse theory should be dismissed based on an issue of status as opposed to considering Arrhenius was a chemist, while Angstrom dedicated his life to investigating solar physics. (But, unfortunately, as we have witnessed, the world operates on politics and the truth sometimes has to wait.)

    To adress you question. I also agree with you that there are many good things that could never be accomplished by an individual.

    I think up to here, that is about all I can agree on, so I will not go on, lest this discussion never end.
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  31. I'm sure I'd want to respond to what appears to be some sort of insinuation if I had any idea what the heck you're trying to talk about. I don't and don't feel curious enough to go through the hassle of deciphering it.
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  32. Not only is the above attack on Arrhenius an ad hominem, and no reflection on his CO2 science, it's also inaccurate. Eugenics in Arrhenius' time was the study of racial genetics and health. It's absurd to call him a racist- he would have been interested in the genetics of Scandinavian peoples. It's also dubious that he had anything to do with the Swedish voluntary sterilisation program, since it was introduced in 1934, and he died in 1927.

    A modern doctor giving advice to members of ethic groups on specific genetic disease risks would be doing what Arrhenius would have regarded as eugenics. Of course that doctor wouldn't use that term because of it's association with policies of compulsory sterilisation, genocide and racism from the Nazi period; perhaps Arrhenius wouldn't want to use the term either today. As he's dead, we can't ask him, and it's unfair to smear him with the abuses eugenics came to be associated with after his death.
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  33. re #33 It’s likely a matter of time scales and the direction of the evolution of the climate in response to long lived changes in radiative forcing. You can think about it from both cooling (then) and warming (now) directions:

    (i) The Miocene, moving forward in time: 25 million years ago (MYA), the Earth was warm and there were no major ice sheets. Atmospheric CO2 levels were 600 ppm and higher, a level that was incompatible with the formation of major stable ice sheets. CO2 levels dropped slowly (thought to be the result of enhanced weathering [1] due possibly to movement of India and the Deccan Trapps into the equatorial humid belt with a resulting slow excess in the rate of CO2 removal from the atmosphere over many millions of years, relative to atmospheric influx [2]).

    (ii) The threshold for ice sheet growth seems to be around 500 ppm during this period, likely simlar to the current threshold. From around 15 MYA to 10 MYA CO2 levels fluctuated below and above this threshold with Antarctic ice forming somewhat and waning [3]. Going from warm, ice-free world to a CO2 level dropping to 500 ppm and a bit below, ice formation and extensive build up would be slow, a situation supported by a negligible ice albedo going in the cooling direction from an ice-free world. Simply due to the fact that ice sheet growth was very slow under these conditions, sea levels remained much higher then than now even as CO2 levels were dropping below the threshold for ice sheet formation. It was really only as a result of the further drop in CO2 levels around 13 MYA and again around 11 MYA, that extensive ice sheet formation occurred and sea levels dropped towards present day levels.

    (iii) Now consider the situation in reverse. The CO2 levels are rising and the threshold is being crossed in a warming direction. We’ve raised CO2 levels towards the 500 ppm threshold for a ridiculously short period of time (a few decades!) in the geological context, and the ice sheet response is (we hope!) slow. A world with extensive ice sheets takes (we hope) an awful long time to come to a new equilibrium with respect to a new enhanced forcing. The albedo effect from land ice probably results in significant hysteresis in the system, such that it’s more difficult to lose ice in a warming scenario, and more difficult to form ice in a cooling scenario.

    [1] Wan SM et al. (2009) Extreme weathering/erosion during the Miocene Climatic Optimum: Evidence from sediment record in the South China Sea Geophys. Res. Lett. 36 Art. # L19706

    [2] D. V. Kent and G. Muttoni Equatorial convergence of India and early Cenozoic climate trends PNAS 2008 105:16065-16070

    [3] W. M. Kürschner et al. (2008) The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems. PNAS 105, 449-454

    Those are all likely to be considerations relevant to the relationships between CO2 levels, temperatures, and climate, ice sheet and sea level responses over very long periods.
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  34. Actually, my scenario isn't quite right, since there was significant Antarctic ice already by around 33 MYA and I think that the threshold for a fully-ice-free world is considered to be more like 700-750 ppm. Otherwise, the main points apply - it took an awful long time for extensive ice to form and major ice sheet expansion including Greenland ice only occurred later in the Miocene when CO2 levels dropped to Holocene levels. Even though we're approaching (or may have passed in the case of Greenland) thresholds for major ice sheet melt and sea level rise, we have only just done so, and the melt response is (hopefully) slow...
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  35. In case anyone is wondering why I launched into a description of my understanding of the relationships between CO2 levels and ice sheet dynamics/sea levels in the Miocene and now, it was in response to a question posed by Mizimi in what was then post #33, asking why if CO2 levels are approaching levels observed 15 million years ago, why aren't sea levels much higher now (as then).

    However Mizimi's post disappeared shortly after I posted mine!
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  36. re #29; Disclaimed

    There's a decent amount of recent research/reviews on the subject of CO2 levels and extinctions. Here's a selection of papers/reviews that address this. It might be about a year out of date, and I wrote this in a slightly different context elsewhere....I had a quick look at the literature earlier, and didn't find anything that substantially adds to this.

    The major extinction events of the past 300 million years are generally associated with rapid onset and long term warming events, and tectonic processes are considered the most likely causes of the rise in greenhouse gases and warming associated with these (especially massive flood basalt events; e.g. the Serbian Traps at the end-Permian extinction; the Deccan Traps at the end-Cretaceous extinction; the tectonic events resulting in plate boundary separation and opening up of the N Atlantic at the Paleo-Eocene Thermal Maximum)

    Major extinctions are associated with long lived perturbation of the climate system and the atmosphere. For example the early Jurassic extinction is associated with events (greenhouse gas induced warming) lasting 200,000 years

    Svensen H et al (2007) Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming Earth Planetary Sci Lett 256 554-566

    Abstract: The climate change in the Toarcian (Early Jurassic) was characterized by a major perturbation of the global carbon cycle. The event lasted for approximately 200,000 years and was manifested by a global warming of similar to 6 degrees C, anoxic conditions in the oceans, and extinction of marine species. The triggering mechanisms for the perturbation and environmental change are however strongly debated. Here, we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the Karoo Basin, South Africa.......

    likewise comprehensive analyses of the coincidence of major tectonic events, and resulting elevation of greenhouse gas levels, are associated with several of the major extinctions of the last 300 million years. Note that CO2 isn't the only player. Methane is implicated in several of these events (see especially the PETM below) and sulphurous oxides and their effects on ocean acidity and oxygen content are also implicated:

    Wignall P (2005) The link between large igneous province eruptions and mass extinctions Elements 1, 293-297

    Abstract: In the past 300 million years, there has been a near-perfect association between extinction events and the eruption of large igneous provinces, but proving the nature of the causal links is far from resolved. The associated environmental changes often include global warming and the development of widespread oxygen-poor conditions in the oceans. This implicates a role for volcanic CO2 emissions, but other perturbations of the global carbon cycle, such as release of methane from gas hydrate reservoirs or shut-down of photosynthesis in the oceans, are probably required to achieve severe green-house warming. The best links between extinction and eruption are seen in the interval from 300 to 150 Ma. With the exception of the Deccan Trap eruptions (65 Ma), the emplacement of younger volcanic provinces has been generally associated with significant environmental changes but little or no increase in extinction rates above background levels.

    R. J. Twitchett (2006) The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events
    Palaeogeog., Palaeoclimatol., Palaeoecol. 232, 190-213

    concluding paragraph: "Mass extinction studies have enjoyed a surge in scientific interest of the past 30 years that shows no sign of abating. Recent areas of particular interest include the palaeoecological study of biotic crises, and analyses of patterns of post-extinction recovery. There is good evidence of rapid climate change affecting all of the major extinction events, while the ability of extraterrestrial impact to cause extinction remains debatable. There is growing evidence that food shortage and suppression of primary productivity, lasting several hundred thousand years, may be a proximate cause of many past extinction events. Selective extinction of suspension feeders and the prevalence of dwarfed organisms in the aftermath are palaeoecological consequences of these changes. The association with rapid global warming shows that study of mass extinction events is not just an esoteric intellectual exercise, but may have implications for the present day."

    Notice that greenhouse environments are associated with the very delayed (millions of years) recovery of biota following thse extinctions;

    Fraiser ML et al. (2007) Elevated atmospheric CO2 and the delayed biotic recovery from the end-Permian mass extinction Palaeogeog. Palaeoclim. Paleoecol. 252, 164-175

    Abstract: Excessive CO2 in the Earth ocean-atmosphere system may have been a significant factor in causing the end-Permian mass extinction. CO2 injected into the atmosphere by the Siberian Traps has been postulated as a major factor leading to the end-Permian mass extinction by facilitating global warming, widespread ocean stratification, and development of anoxic, euxinic and CO2-rich deep waters. A broad incursion of this toxic deep water into the surface ocean may have caused this mass extinction. Although previous studies of the role of excessive CO2 have focused on these "bottom-up" effects emanating from the deep ocean, "top-down" effects of increasing atmosphere CO2 concentrations on ocean-surface waters and biota have not previously been explored. Passive diffusion of atmospheric CO2 into ocean-surface waters decreases the pH and CaCO3 saturation state of seawater, causing a physiological and biocalcification crisis for many marine invertebrates. While both "bottom-up" and "top-down" mechanisms may have contributed to the relatively short-term biotic devastation of the end-Permian mass extinction, such a "top-down" physiological and biocalcification crisis would have had long-term effects and might have contributed to the protracted 5- to 6-million-year-long delay in biotic recovery following this mass extinction. Earth's Modern marine biota may experience similar "top-down" CO2 stresses if anthropogenic input of atmosphere/ocean CO2 continues to rise.

    The lesser extinction associated with the Paleo-Eocene-Thermal Maximum (PETM) 55 MYA is probably the best characterised (not surprisingly since it's the most recent!) example of massive tectonic processes (the opening up of the N. Atlantic as the plates seperated) associated with enhanced atmospheric greenhouse gases, ocean acidification etc.:

    M. Storey et al. (2007)Paleocene-Eocene Thermal Maximum and the Opening of the Northeast Atlantic Science 316, 587 - 589

    abstract: The Paleocene-Eocene thermal maximum (PETM) has been attributed to a sudden release of carbon dioxide and/or methane. 40Ar/39Ar age determinations show that the Danish Ash-17 deposit, which overlies the PETM by about 450,000 years in the Atlantic, and the Skraenterne Formation Tuff, representing the end of 1 ± 0.5 million years of massive volcanism in East Greenland, are coeval. The relative age of Danish Ash-17 thus places the PETM onset after the beginning of massive flood basalt volcanism at 56.1 ± 0.4 million years ago but within error of the estimated continental breakup time of 55.5 ± 0.3 million years ago, marked by the eruption of mid-ocean ridge basalt–like flows. These correlations support the view that the PETM was triggered by greenhouse gas release during magma interaction with basin-filling carbon-rich sedimentary rocks proximal to the embryonic plate boundary between Greenland and Europe.

    And even the end-Cretaceous extinction (that did for the dinosaurs) seems to have had at least a significant component from massive flood basalt events (that resulted in the Deccan Traps in what is now India). In fact there is increasing evidence that the impact that resulted in the Chicxulub crater in the Yucatan post-dates the onset of the extinction by several 100,000's of years, and the extinction is associated with global warming (including a sudden contribution from the impact into limestone-rich deposits that vapourized massive amounts of carbonate (limestone) back into CO2):

    Keller G (2005) Impacts, volcanism and mass extinction: random coincidence or cause and effect? Austral. J. Earth Sci 52 725-757.

    Abstract: Large impacts are credited with the most devastating mass extinctions in Earth's history and the Cretaceous - Tertiary (K/T) boundary impact is the strongest and sole direct support for this view. A review of the five largest Phanerozoic mass extinctions provides no support that impacts with craters up to 180 km in diameter caused significant species extinctions. This includes the 170 km-diameter Chicxulub impact crater regarded as 0.3 million years older than the K/T mass extinction. A second, larger impact event may have been the ultimate cause of this mass extinction, as suggested by a global iridium anomaly at the K/T boundary, but no crater has been found to date. The current crater database suggests that multiple impacts, for example comet showers, were the norm, rather than the exception, during the Late Eocene, K/T transition, latest Triassic and the Devonian-Carboniferous transition, but did not cause significant species extinctions. Whether multiple impacts substantially contributed to greenhouse worming and associated environmental stresses is yet to be demonstrated. From the current database, it must be concluded that no known Phanerozoic impacts, including the Chicxulub impact (but excluding the K/T impact) caused mass extinctions or even significant. species extinctions. The K/T mass extinction may have been caused by the coincidence of a very large impact ( > 250 km) upon a highly stressed biotic environment as a result of volcanism. The consistent association of large magmatic provinces (large igneous provinces and continental flood-basalt provinces) with all but one (end-Ordovician) of the five major Phanerozoic mass extinctions suggests that volcanism played a major role. Faunal and geochemical evidence from the end-Permian, end-Devonian, end-Cretaceous and Triassic/Jurassic transition suggests that the biotic stress was due to a lethal combination of tectonically induced hydrothermal and volcanic processes, leading to eutrophication in the oceans, global warming, sea-level transgression and ocean anoxia. It must be concluded that major magmatic events and their long-term environmental consequences are major contributors, though not the sole causes of mass extinctions. Sudden mass extinctions, such as at the K/T boundary, may require the coincidence of major volcanism and a very large Impact.

    Beerling DJ et al. (2002) An atmospheric pCO(2) reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils Proc. Natl. Acad. Sci. USA 99 (12): 7836-7840

    Abstract: The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO2 concentration (pCO(2)) levels with special emphasis on providing a pCO(2) estimate directly above the KTB. Our record shows stable Late Cretaceous/ Early Tertiary background pCO(2) levels of 350-500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO(2) increase. Instead, we calculate that the postboundary pCO(2) rise is most consistent with the instantaneous transfer of approximate to 4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W(.)m(-2) would have been sufficient to warm the Earth's surface by approximate to7.5degreesC, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB.

    Note that there may be some question over the absolute concentrations of atmospheric CO2 calculated using the plant stomatal frequency index.

    Note also that since these processes all occurred in the deep past, we obviously don't know exactly all the contributions to all the extinctions. However the associations between tectonic/mantle plume breaching/flood basalt eruptions/global warming and extinctions are increasingly supported by the evidence.
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  37. Re #35: Don't worry Chris, pretty much all of your contributions are appreciated (at least by me) regardless of what baited you into the work.

    Re #36: Here is an excellent example of a very worthwhile comment that I just about missed. In fact, I was trying to stimulate something similar on another thread in which I noted that "Global Warming is Good" is an argument not often tackled here, and where I suggested that skeptics should ask how fast CO2 concentrations have changed in the past and what was the result. Thanks.
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  38. Chris thank you for that excellent response. It seems apparent that past CO2 levels were driven by tectonism. Might be a little premature to assume the sole driver of extinction was climate response, but it's certainly plausible.

    I hear a lot about what makes CO2 go up. But isn't an understanding of what forces lower CO2 equally important? What are the mechanisms that make the CO2 drop? If it's falling temperature, what is causing the drop in temperature, and I'm speaking about over the Phanerozoic, not recent glaciation cycles?
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    Response: This is an excellent question. A process that removes CO2 from the atmosphere is rock weathering - where chemical process convert CO2 in the air into other chemicals. This process takes thousands of years. However, rock weathering activity increases in higher temperatures (Walker 1981). This acts as a natural thermostat on climate. As the earth gets hotter, CO2 is scrubbed out of the atmosphere by the accelerated rock weathering and CO2 levels drop.

    On the downside, this process happens over geological scales so natural rock weathering isn't a short term solution. On the up-side, there is research into using artificially accelerated rock weathering to sequester carbon dioxide from coal plants (Kelemen 2008).
  39. Jay Cadbury... (Continued from the Preventing Misinformation thread.)

    Models tell us very little about whether we can survive if we heat the planet back up to the levels of 65 mya. Models only tell us about the climate. Survival is going to have to do with the ability of species other than ourselves to adapt to such a dramatic and rapid change in climate.

    Paleoclimate records tell us far more about how species deal with rapid climate change. And there you don't find such pretty pictures of how well living things adapt to change.

    Yes, we are a very adaptable species. We are probably the most adaptable mammalian species there is, though probably less adaptable than many species of insects. So, is that the world you want to bequeath to your grandchildren and great-grandchildren? Us and the insects? Again, not a pretty picture.

    But don't worry. There's nothing we can do that nature won't fix in, say, another 20 million years. A mere blink of the eye, as they say.
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  40. In what way does "technology will save us" (what "we are adaptable" means) differ from "God will save us"? Both are entirely faith based and neither has a shred of evidence to support it.
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  41. "technology will save us"? Only if we choose, actively choose, to apply our skills appropriately.

    This article is just one example of approaches that some people are considering. A lot of this work, of course, is focused on how it might be applied for 'clean coal' technology.

    While we sit and wait for 'clean coal', there's no reason why we couldn't set up a few trial projects to quarry, mill and distribute by wind and water some of the minerals that would normally do the job on geological time scales. No matter how slow or inefficient some of those techniques are, all of them would be much, much faster than geological weathering.

    And when coral reefs start collapsing badly under acidification, scattering dust and gravel from such rocks into the rivers feeding into the waters around reefs might be the least worst thing we could do to hold back the speed of the damaging effects. I'm sure there will be other geo-engineering ideas (forget the sulphur) and some of them will have to be implemented when we spectacularly fail to deal with the carbon side of the geological equation.
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  42. Jay Cadbury (in response to your comment from Preventing Misinformation thread)

    Seeing that the current fauna is very different from what you would find all those years ago, I am not sure how comparing the projected temperature and CO2 to their respective values in a such a distant past relevant.

    What strikes me the most is the fact that even during the wild prolonged swings seen in the Volstok ice-core data, the warming was 10 degrees per 10,000 years, or maybe about 0.05 degrees per century (assuming arctic is warming twice the rate of the global average as it currently is); this pales in comparison to the projected warming (2 degrees per century even on the low end), which is a factor of 40 difference!

    Whereas in the past longer living mammals have 100s of generation to adapt, now it becomes two generations or so. How can this not be significant to the entire biosphere?

    While humans as a whole are adaptive, I think there are two caveats
    1) Adaptability comes at a price. Most studies on the economic impacts of GW concludes that it is cheaper to cut back on GHG now rather than to adapt.
    2) Adaptability depends on the wealth of the country. While people in developed countries are better at adapting (we can buy food from chile if crops from mexico fails), but what will an African family do when crops fail? What will a village in indonesia do when fish stock crashes?
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  43. Well I have to say I am shocked. The reason I am shocked is because these are pretty good answers and I couldn't get them on realclimate or ( -snip- ). This website sets a great example and I think above mentioned sites could take a lesson.


    What do you mean when you say "the artic is warming at twice the rate of the GAT"? I've been under the impression that parts of the arctic are warming but there are also parts growing?
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    Moderator Response: [DB] Inflammatory portion deleted.

    [Not DB] Normally we don't snip out offending portions of comments; we just delete the entire comments. Snipping is done as a courtesy to the commenter, to help them understand exactly what violates the comments policy. DB is being more forgiving than I am, given the aggressive and insulting language in your first several comments here.
  44. Jay Cadbury, see info on Arctic amplification.

    About the only things I can think of which you might have heard of 'growing' in the Arctic (as supposed contradictions to global warming) would be claims that Arctic sea ice is 'recovering' because the extent does not hit a new record minimum each year (which is simply false since the trend lines are sharply negative) or that ice mass in central Greenland is increasing due to increasing precipitation, which is true but vastly offset by the decreasing ice mass along the coasts due to melt and export.
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  45. Jay Cadbury... To put the bigger picture in context, RealClimate is a group of scientists who are real working climate scientists. They are discussing real climate science. They frequently delete posts that are long debunked or blatantly wrong. They have to in order to have a reasonable high level discussion. Personally, I don't post much there. I mostly just read and learn.

    Skeptical Science is established to specifically look at "skeptic" claims and address them by looking at the published literature.

    If you ask an easily debunked question at RC it will, appropriately, get deleted. If you ask the same question here we address it. You just need to watch the inflammatory language that is allowed at many other climate related sites. It's not allowed here from either side of the issue. (My posts get deleted as well when I get all worked up on a topic.)
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  46. Well this is a topic where 32 years of data just doesn't do it for me.


    Let me give you another example of a comment realclimate won't touch.

    I have often asked them why Al Gore fired Dr. Happer and they will not comment on it.
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    Moderator Response: [Dikran Marsupial] Probably because contravenes the comments policy at RealClimate, just as it contravenes the comments policy here. Politics is off-topic here, this is a forum for discussion of the science. Likewise accusations of dishonesty or deceptions or ad-hominems are not acceptable, which is where the discussions seems likely to be headed. So no further please.
  47. Regarding the moderators comment "Snipping is done as a courtesy to the commenter, to help them understand exactly what violates the comments policy." at Dr. Jay Cadbury, phd. at 01:21 AM.

    I think snipping is perhaps an even greater courtesy to all other readers as it provides a transparency that is otherwise missing and allows all to develop a better sense of the flow of the argument.
    Above all else, I believe it is transparency that determines how much faith readers will have in the moderation process, and snipping brings such transparency that I would like to see it become standard practice.
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    Moderator Response: It takes more time, though. And patience. We all are volunteers here.
  48. What topic are you talking about only 32 years of data for? That would seem to be the satellite record only, but CO2, Arctic warming, and all other topics I might guess you were referring to have records going back further than that.

    As to your question about Happer... note that you assume Gore did fire Happer. Which is Happer's story. No 'skepticism'? Just accepting it as fact?

    Consider that while Happer now claims he was fired because he disagreed with Gore on global warming... back at the time his claim was that he was fired because he disagreed with Gore staffers on the ozone hole.

    Why would expect people at realclimate (or here) to know whether either of Happer's claims were true or why he was actually fired?

    That said, please do note that Happer was one of those who claimed that ozone depletion wasn't happening, that it wouldn't have harmful effects if it were, and that legislation being pushed to address it would bankrupt the economy. The scientific community overwhelmingly said otherwise even at the time. Now history has conclusively showed that it was nonsense. Fast forward 20 years and we find Happer singing the same song about global warming... right down to the claim that he was 'fired over the issue'.
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    Moderator Response: [Dikran Marsupial] Please, no more discussion of the reason for Happers firing, it is off-topic. Further discussion will be deleted.
  49. Yes, "technology will save us" is a slightly higher level of speculation than "God will save us". There is still no evidence that geo engineering will save us even if it is implemented. The implementation will require funding mostly from people who have demonstrated that they would rather see civilization destroyed than suffer the slightest diminution of their wealth and power.
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  50. Don@49, you're pretty right. But .....

    The devastating consequences we foresee relate to our experience of the world. Our grandchildren''s grandchildren will have a different - horrifying to us - experience of the world. They will have more knowledge than we do and, unfortunately, direct evidence of the wrongs that must be righted.

    They won't be able to recreate our congenial world. Certainly not in their own lifetimes. But they will be able to gain satisfaction from doing things that they know will benefit their own grandchildren's grandchildren.

    Staring into this abyss can make us weep. It can also galvanise us into determination that we should, must, will do whatever we can to speed our own societies onto a better path. Fatalism and depression are not good options.

    Geo engineering is, in fact, the thing that must be done some time or other to extract, absorb, sequester the accumulated geological release of carbon. Tree planting and similar bio-engineering of the carbon cycle in the surface and atmosphere won't be enough - but they must also be done thoroughly, extensively, permanently.

    Me? I'm pretty sure that the greedy will find a way to make some cash out of both bio and geo-engineering once they realise societies want it done and are willing to pay for it. The greedy, like the poor, are always with us. But their activities don't =always= have to be damaging.
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