GCMs and Ice Ages

I’ve tried to stay away from discussing GCMs where my knowledge is limited, but everyone seems to want to discuss them, so, against my better judgement, I’m posting up some thoughts. asked some people at AGU about whether GCMs could model getting into and getting out of ice ages. In some treatments, the presence or absence of ice sheets appears as an independent forcing, which seems to be peeking at the hand a little when you’re trying to explain ice ages. CO2 fluctuations are integral to current glacial modeling, but there doesn’t seem to be any agreed explanations for glacial/interglacial CO2 cycles.

Caspar Ammann said that GCMs took about 1 day of machine time to cover 25 years. On this basis, it is obviously impossible to model the Pliocene-Pleistocene transition (say the last 2 million years) using a GCM as this would take about 219 years of computer time. So I think we can safely conclude that any models of this period have not been done using a GCM. Even a “short” period of (say) 40,000 years, about one obliquity cycle, would require about 4 years of computer time and, again, I think that we can assume that this exercise has not been done using a GCM. Presumably models of such time intervals are done with “intermediate-complexity” models or some other method, but I’ve not attempted to canvass the literature.

With respect to ice age models, Peter Huybers said that some models could plausibly get into ice ages, but, once in, couldn’t get out; conversely, other models could plausibly get out of ice ages, but couldn’t get in. If I recollect correctly, he thought that no intermediate-complexity model did both. Also if I recollect correctly, he thought that no intermediate-complexity model accurately modeled the Pliocene-Pleistocene transition. Some models include ice sheets as a “forcing” variable, which seems unreasonable if you’re trying to explain ice ages. Other models include CO2 levels as a “forcing” variable, which again seems unreasonable since it seems to be endogenous to the system being modeled.

I’ve been browsing some of the literature on CO2 cycles. Obviously the covariance in Antarctic cores of CO2 and àƒÅ½à‚ⳏ18 (held to be a temperature proxy) is one of the remarkable aspects of these cores. Changes in CO2 levels are popularly held to be important in explaining the amplitude of major glacial changes, but there is no agreement on what causes the changes in CO2 levels. I’ll discuss this on another occasion, but, for now, I’ll mention that most explanations involve biological feedback. I suspect that the handling of biological feedback issues is not strongly done in GCMs and/or intermediate-complexity models (but haven’t checked this and could be wrong.) There seems to be a general view that lowering CO2 levels is essential to getting SH glaciation.

As to GCMs providing a base case for assessing natural variability: one of my starting points in reflecting about climate change is that one wanted to be confident as to an understanding of big changes in order to assess the significance of “little” changes such as the LIA or MWP. If we do not have GCM models of the entry into and out of ice ages, then I don’t see how GCMs can serve as a benchmark for “natural climate variability. What am I missing?


  1. Posted Dec 18, 2005 at 3:43 PM | Permalink

    I thought it was obvious why there is less CO2 during ice ages.
    1. Cold ocean water stores more CO2 than warm water does.
    2. A lot of dead plants and animals will be stuck under the ice sheets and so will the carbon they contain. Soil with CO2 and CH4 will also be covered by thick ice.
    To summarize it: Cold temperatures shift the carbon balance away from the atmosphere towards the other storages.

  2. JerryB
    Posted Dec 18, 2005 at 5:25 PM | Permalink

    I will venture the guess that a plethora of comments in this thread will have a side effect of reenforcing your better judgement. 🙂

  3. mart
    Posted Dec 18, 2005 at 5:31 PM | Permalink

    ok wot comes first?co2 increases or global warming???

  4. epica
    Posted Dec 18, 2005 at 5:49 PM | Permalink

    Several Points
    1 GCMs exist as coupled ocean/atmosphere models, rarely as fully coupled ocean/atmosphere/biosphere models. Depending on how you run these models you can ask certain questions and certain you cannt. E.g. usually the CO2 concentration is an external forcing to these models because they are not fully coupled with vegetation models.
    2 a reasonable question to a GCM therefore would be the following: lets run the model under LGM conditions, lets see how it fit to observations (continental temperature and precipitation estimates based on pollen, 18O, etc) , how important is the influence of CO2 vs icesheet extension vs solar insulation changes for the model’s glacial climate. And turns out that CO2 is essential to give a satifying agreement with the observations.
    3 transient simulation is another problem alltogether. The melting/forming of an ice sheet depends on many factors, some of them definitely out of what GCMs can describe (such as sliding of the icesheet on the bedrock). A model serves as a playtool to answer certain questions. To start ice sheets at the right location or to melt the ice at fast rates is certainly no pre-condition to tell us about global warming (because of the involved time scales, ice physics, eustatic rebound etc).

  5. Armand MacMurray
    Posted Dec 18, 2005 at 7:45 PM | Permalink


    And turns out that CO2 is essential to give a satifying agreement with the observations.

    But if you’re not modelling the biosphere, isn’t the model really telling you “in the absence of a biosphere, CO2 is essential…”. Although such incomplete models may be necessary steps on the way to constructing a complete model, the result from a model that ignores the biosphere doesn’t seem very relevant. Perhaps I’m missing something?

  6. andre bijkerk
    Posted Dec 19, 2005 at 6:50 AM | Permalink

    I think that the concept of ice ages is a basic mistake when regarding the ever increasing array of mysteries. Have a look at a nice overview of the problems here:


    This mistake could be rectified nowadays if we are willing to revisit all the evidence and discard all the current conclusions.

    Steve, perhaps review my flickering climate discussion with RC part 1 – 5 in the CS group

  7. epica
    Posted Dec 19, 2005 at 10:03 AM | Permalink

    For the atmosphere CO2 is just one forcing factor entering in the radiation code. You need the vegetation only if you want to describe certain feedbacks. E.g. warmer temperature, more water stress (everything else kept constant), less photosythesis etc might lead to an effective CO2 flux into the atmosphere before a new equilibrium is reached. You can imagine many of these feedback becoming more important when the water cycle is involved. Anyhow to describe the mean climate of a several 1000 year period without strong transitions it is ok to run the atmosphere with a constant 180ppm under glacial conditions and with an estimated constant continental surface (albedo, surface roughness, soil water depth etc). If you have doubts that a particular mechanism is more important than thought before you can test this by running the model with the changed forcing.

  8. John A
    Posted Dec 19, 2005 at 10:25 AM | Permalink

    Re #7

    I think you’ve perfectly encapsulated the problems of climate modelling. Well done.

  9. andre bijkerk
    Posted Dec 19, 2005 at 2:16 PM | Permalink

    Re #7

    Of course the ice cores show a rather smooth CO2 graph with no excursions below century scale, but stomata research is booming business and it is showing a quite different picture. Some plants react on CO2 variation with changing the number of leaf stomata. The result shows considerably larger excursions on century scales. The results are reproduceable and correlate with ice cores but not with temperatures.

    The reason for the smoothing of CO2 in ice cores is the open firn phase in the higher layers 80-100 meters of the ice sheets where the air can move in and out freely, acting as a bypass filter

  10. pat
    Posted Dec 19, 2005 at 3:35 PM | Permalink

    Some random notions:


    I used to do econometric models in grad school and shortly thereafter for government agencies. I was always under pressure or direct orders to acheive the desired outcome. Are things different now that the major political parties have staked out positions and billions of dollars are in play?

    Chaotic Uncertainty

    The very concept of sensitivity to initial conditions arose in climate modeling. Edward Lorenz discovered that very, very small errors in the independent variables he put into his climate model yielded huge dependent variable outputs in ways that were not predictable. The plot of the Lorenz function looked like a butterfly which led to the name Butterfly Effect.

    Everyone including Al Gore gives lip service to the Butterfly Effect but consistently seem to miss the point. Climate models are seriously limited by this effect to only very short term predictions. The Butterfly Effect also limits the ability of long range weather forecasts. After billions spent on weather modeling, the best forecasts are still only good for a couple days. The Lorenz effect says that if we double our computer power, double our model complexity, and double the accuracy of our initial measurements we will still be able to only predict weather a few days ahead.

    The US Weather Service confidently predicted that Katrina would hit New Orleans when it was about three days away. In fact it didn’t hit N.O. because of a last minute swerve. Unlike global climate, hurricanes are comparatively simple and well understood. Somebody who believes in GCMs tell me the number, the paths and the land falls for all the hurricanes coming in 2008.

    A Global Climate Model that predicts conditions in a hundred years is about as likely as a perpetual motion machine.

    Milankovitch etc..

    First of all everyone should stop referring to Ice Ages as a thing of the past. We need to be reminded that we live smack in the middles of an Ice Age. The Great Pleistocene Ice Age has gone on now for perhaps three million years (some say two). In the absense of some major change, man-made or otherwise, the current Ice Age will go on for a couple million more years.

    We, meaning all civilization, live in an inter-glacial. As is well known and undisputed, the inter-glacials average about 10K years. Ours is now also about 10K years old. This means that that which has caused the advance and retreat of the ice should shortly come into play again.

    Incredibly while facing a return of mile high ice sheets over the US, the popular press worries about Global Warming. Unlike the Global Warming issue, there is no controversy about the return of the ice (its coming) or the magnitude of its consequences (life is difficult under a mile of ice).

    Also incredibly, we don’t have a very good idea as to what causes Ice Ages or even what causes the advance and retreat of the continental ice sheets. The Milankovitch cycles based on orbital shape and axis precession is the most popular theory. However the advance and retreat of the ice sheets corresponds most closely with one of the minor cycles and not at all well with the perdicted major cycles. The Milankovitch cycles just don’t work very well but they seem intuitively plausible because they predict a change in the earth’s heat budget.

    Other theories include the sun spot cycle. The sun spot cycle is only eleven years but perhaps there is a longer cycle which we haven’t observed yet. The theory is that the solar wind interacts with the earth’s magnetic field which causes changes in the cloud cover. The cloud cover acts like a set of shutters letting light and heat in. Others point to galactic particles from super novae which have a similar effect on cloud cover. Super novae follow a cycle caused by the sun’s orbit around the Milky Way.

    Mueller at Cal Berkeley has a theory based on the earth’s orbit rising and falling through the dusty interstellar medium.

    What good is a GCM of Ice Ages if chooses the wrong theory of solar variance? Or do all the GCMs assume a constant sun?

  11. Armand MacMurray
    Posted Dec 19, 2005 at 4:12 PM | Permalink

    Re: #7:

    Anyhow to describe the mean climate of a several 1000 year period without strong transitions it is ok to run the atmosphere with a constant 180ppm under glacial conditions and with an estimated constant continental surface

    My point in post 5 was *how* do you know it’s OK without doing it? If the biosphere can affect the CO2 concentration and other factors in a complex fashion involving feedbacks, how can you assume constant CO2 concentration, constant land albedo, etc? Is there perhaps some previous science showing you can ignore the biosphere and still get correct results?

  12. Ian Castles
    Posted Dec 19, 2005 at 4:42 PM | Permalink

    Re #10, the first point on “Bias”. It is certain that much of the data fed into the econometric models that the IPCC relies upon for its emissions projections is extremely biased. In evidence to the UK House of Lords Committee inquiry into the economics of climate change on 1 February last, Richard Tol of Hamburg University revealed that he was in at the “very start” of the Special Report on Emissions Scenarios exercise in 1996, and that “it was clear that the SRES team had placed itself under constraints of political correctness, that is to say because it was an IPCC exercise it has to be reviewed by all the governments in the world, and if you come up with scenarios in which the African countries, which are a fairly large bloc (in the UN) – if they do not grow fast enough, they will never approve our scenarios.” Thus the claim that “600 ppm [CO2 concentration] will be reached within this century with very high probability” (epica at #162 on the Burger and Cubasch thread) is spurious: it relies on projections derived from inflated CO2 emissions profiles, which were in turn derived from economic growth projections that were biased upward in order to win acceptance of the SRES from governments. The all-party House of Lords Committee unanimously concluded that “the emissions scenarios are influenced by political considerations”, and that “Sound science cannot emerge from an unsound process” (Report, paras. 171-74).

  13. epica
    Posted Dec 20, 2005 at 4:05 AM | Permalink

    I am not an expert at all on the economic models and I take your word that the process of estimating was biased. Since I am convinced of the climatic impact of greenhouse gases please believe me that I think that would be very good news if the scenarios have to be corrected to lower values.
    I have some questions to you: There seems general agreement that Kyoto if successfully fulfilled would have only spurious impact on both CO2 and temperatures (which is why I said 600ppm for sure, but I wont do this in the future, promised!). Do you see signs that an effective reduction of emissions could be established say before 2050? What would be your suggestions?
    I have read that in China and India alone carbon power plants are under constructions or planned with a volume of about 800MTG. Economic development there seems very strong. What is the impact of more/less African economic evolution compared to this economic jump of Asia? I also read that there are now estimates of a stabilization of world population at 9 billion instead of my former (poor) knowledge of 12 billion. What are the uncertainities for 2100/2200? If you have no time to answer I am happy also with some references. Thanks.

  14. Armand MacMurray
    Posted Dec 20, 2005 at 4:42 AM | Permalink


    Do you see signs that an effective reduction of emissions could be established say before 2050?

    I think you’re zeroing in on one of the key questions here. One of the big economic obstacles to a rapid reduction in CO2 emissions is the existing capital investment in fossil-fueled power plants. Since such plants’ lifetimes are on the order of 30-40 years, a policy of encouraging replacement at the normal end-of-life of such plants with [nuclear/wind/insert your favorite lower-carbon-emitter here] would have much lower costs than rapid replacement, which would require abandoning working plants and in effect destroying capital.

  15. epica
    Posted Dec 20, 2005 at 4:46 AM | Permalink

    #9 Yes. Good point. Therefore I said let’s take a factor of 2 larger CO2 variations during the last 1000 years to be on the safe side. I would also take a continuous CO2 reconstruction from stomata if available. Until now they have only peacewise reconstructions (it’s really difficult work) such as:
    Vol. 57 Issue 4 Page 351 September 2005
    Atmospheric CO2 during the 13th century AD: reconciliation of data from ice core measurements and stomatal frequency analysis

    For the moement we have only a very flad CO2 curve and so not much space for temperature variations.

  16. epica
    Posted Dec 20, 2005 at 5:21 AM | Permalink

    “My point in post 5 was *how* do you know it’s OK without doing it?”
    Well I did, but I think this is not your question. It’s rather why it is justified to make simplifications of an obviously more complex world. Let’s stick to the CO2 which we have infact from the ice cores. For the atmosphere this an external forcing (though it’s value is produced by the entire system). To get a resaonable climatic mean it is therefore not necessary to know how the corresponding CO2 has been produced (most probably by ocean chemistry/circulation and so many other things). So that is only a question in what you are interested. For the albedo, land surface properties it is more complicate. The PMIP (paleo modelling intercomparison project) recommended to every participant for example to take modern land surface values when running the different GCMs. This was done because the different models use so many different ways of describing these properties that it was not possible to come up with simple recepes such as: put at this point albedo x and so on. Anyhow for global responses this approach was ok, however locally land surface has important impact. See for example the control water recycling has on the extension of the African monsoon. To estimate the impact of the biosphere you can now run built in biosphere models and see what happens (that is comparing the results with the different data sets such as pollen, snowline extensions and so on). Here are some papers you might find interesting on http://www-lsce.cea.fr/pmip/
    in particular:
    Braconnot, P., S. Joussaume, N. de Noblet, and G. Ramstein, Mid-Holocene and last glacial maximum African monsoon changes as simulated within the Paleoclimate Modeling Intercomparison project, Global and Planetary Change, 26, 51-66, 2000.
    Kohfeld, K.E., and S.P. Harrison, How well can we simulate past climates? Evaluating the models using global palaeoenvironmental datasets, Quaternary Science Reviews, 19, 321-346, 2000.

  17. Ian Castles
    Posted Dec 20, 2005 at 9:45 PM | Permalink

    Re #13. Thank you for your comments and your pertinent questions. Unfortunately there is no prospect of the IPCC scenarios being corrected to lower values, because the IPCC has declared that “the SRES scenarios provide a credible and sound set of projections, appropriate for use in the AR4.” As the SRES Summary for Policymakers had previously pronounced ex cathedra that the 40 SRES scenarios “are equally valid with no assigned probability of occurrence” (Figure SPM-1, p. 4), it appears that no further questioning of the SRES projections within the IPCC context will be permitted.

    The UK House of Lords Committee expressed its concern that the Panel “had no intention of undertaking any significant reappraisal of the SRES for the IPCC Fourth Assessment Report exercise (AR4) for 2007” and urged “a wholesale reappraisal of the emissions scenarios exercise.” The UK Government has responded with the claim that “IPCC’s emissions scenarios cover a very wide range and the most reasonable expectations about future outcome of global emissions in the absence of further mitigation action are likely to be included within the envelope.”

    The projected level of cumulative emissions between 2000 and 2100 in the IPCC scenarios does indeed “cover a very wide range” – from 690 GtC (B1T MESSAGE) to 2455 GtC (A1C AIM) – but in my presentation to the IPCC Expert Meeting at Amsterdam in January 2003 and a more detailed paper prepared immediately after the meeting I gave eight reasons for believing that lower emissions levels than those in B1 MESSAGE could be projected “on the basis of assumptions that are fully defensible.” The Australian Government apparently agreed with one of my reasons, because in its submission to the IPCC on the scope and structure of the Fourth Assessment Report (March 2003), it argued that the scoping process “will need to … consider whether there are plausible emissions scenarios outside the range indicated in the SRES and if so, manage integration of such scenarios into the AR4 (for example, consider developing a further scenario with lower developing country growth than the B1 scenarios, but without the high population and slower rate of technology growth associated with the A2 and B2 scenarios)”. No such scenario has been produced.

    In response to your question whether I can see signs that an effective reduction in emissions could be established before say 2050, I would answer with a qualified “Yes”. The peak level of emissions in the B1T scenario is reached in 2030. Like all of the SRES projections, this scenario does not include any future policies that address additional climate change initiatives such as implementation of the Kyoto Protocol. As noted in the previous paragraph, there are many reasons why the emissions profile assumed in B1T MESSAGE may be overstated. To take one example, the assumed increase in electricity use in B1T MESSAGE in the developing countries between 2000 and 2030 is about twice as great as is estimated in the Reference Scenario of the International Energy Agency (IEA) as published in World Energy Outlook 2002. The latter projections have been subjected to far more intense scrutiny than the IPCC projections and were used in the development of the estimates of investment requirements in the IEA’s World Energy Investment Outlook 2003. In the light of these considerations, it seems to me to be reasonable to believe that CO2 emissions could decline before 2050 in the absence of further mitigation action.

    You are right that economic development in China and India is proceeding very strongly, but this is fully taken into account in many of the IPCC scenarios.

    The projections of world population used in the A1 and B1 SRES scenarios reach a peak of about 9 billion in the middle of the century and decline to just over 7 billion by the end of the century. The UN Population Division has published high, medium and low projections of the population of the world and its major regions to 2300. These are available on the UNPD’s website.

  18. Ian Castles
    Posted Dec 20, 2005 at 9:54 PM | Permalink

    In #17, I said that “electricity use in B1T MESSAGE in the developing countries between 2000 and 2030 is about twice as great as is estimated in the Reference Scenario of the International Energy Agency (IEA)”. I should have said “between 2020 and 2030”, i.e., the furthest-out decade in the IEA projection. The point of the calculation is to show that the short and medium-term projections of electricity growth by the IEA, which is well informed about national policies and about the programs of electricity supply authorities, are very much lower than the projections of the IPCC modellers (who were not at all well-informed about these matters).

  19. Willis Eschenbach
    Posted Dec 21, 2005 at 2:08 AM | Permalink

    Re 17 & 18, oh, man, Ian, that’s bad, bad news. I assume that also means they’re going to use the discredited MER projections rather than the correct PPP projections?

    Bummer …


  20. Ian Castles
    Posted Dec 21, 2005 at 3:40 AM | Permalink

    Yes Willis, I’ve been told that the Contributions of Working Groups II and III are unbelievably poor. As recently as 1999 the World Bank advised the UN Statistical Commission that “It must be clearly stated that … there is unanimous agreement among researchers and theoreticians; proper cross-country comparisons can only be made once values have been adjusted to eliminate differences in price levels using purchasing power parities.” To the best of my knowledge this is still the unanimous expert view, but this counts for little in the eyes of the IPCC milieu, including the Bank’s Chief Scientist, Robert Watson, the former Chair of the IPCC (he ceased to hold that position in April 2002, but his personal page on the World Bank’s website still says that he’s Chair). Dr. Watson hasn’t replied to my letter to him of 17 June in which I asked that he arrange for the Bank to present the scenarios of the IPCC, the Bank itself and the Millennium Ecosystem Assessment on a standardised basis. The IPCC milieu is determined to avoid having the SRES projections expressed in a way that would expose the fact that they are way out of line with the more professional work of bodies such as the US Energy Information Administration and the Paris-based International Energy Agency.

  21. Willis Eschenbach
    Posted Dec 21, 2005 at 4:28 AM | Permalink

    Ian, is there anyone we can write to in order to protest this economic travesty?


  22. epica
    Posted Dec 21, 2005 at 4:30 AM | Permalink

    #17 and 18
    thank you for your detailed answer. Sorry to bother you with more questions/precisions
    1) You say stabilization is reached without any mitigation or Kyoto like actions. What is then the 2100 level for your scenario, when is (if ever) the 2*CO2 level reached?
    2) If for example the next 20 years would be marked by a slow cooling trend to temperature levels of the 1940s that would be a clear indication that GW is not working like we (vast majority of climatologist) think. This is a rough statement without statistics. When would you say can your scenario be distinguished from the IPCC scenarios in observed CO2 fluxes and concentrations?
    3) How would you characterize your position within the comunity of economist? Would you describe it as as marginal as a “there is no climate change due to greenhouse gas concentration” position among climate researchers or do you have the impression that your position is though only supported by a minority but at least a strong minority (in number and/or reputation)? Very subjective question, sorry.
    Thanks again. I’ll check on the UN webside for population growth. In the article (not scientific but from a good journal) I have read that a fertility of 2.1 leads to the 9 billion stabilzation scenario, whereas 2.2 leads to 36 billion in 2300 and 2.0 to 2billion in 2300. Funny thing these exponential laws.

  23. Ian Castles
    Posted Dec 21, 2005 at 5:31 AM | Permalink

    Re #22. In response to your question (1), it has been my understanding that the IPCC B1 marker scenario (B1 IMAGE) stabilises atmospheric concentrations of CO2 at about twice the pre-industrial level (i.e., at around 550 ppm.) by around 2100, without any mitigation or Kyoto like actions. This is my lay interpretation of the fact that the modelled increases in CO2 burdens in the last four decades of the century are, successively, 16, 12, 8 and 4 ppm (see the relevant table in Appendix II of Climate Change 2001: The Scientific Basis). This apparent stabilisation in CO2 burdens is achieved notwithstanding projected increases in annual CO2 emissions of about 70 per cent in the first half of the century (see SRES, p. 506). The lowest IPCC emission scenario, in terms of the forcing pattern in 2100, is the B1T MESSAGE scenario. whioh according to Dr. Tom Wigley (speaking at the Expert Meeting I attended at the IPCC’s invitation in January 2003) yielded a burden of 475 ppm in 2100. I am subject to correction, but again it was my interpretation that under this scenario the CO2 burden would stanilise or fall below 475 ppm in the early 2100s. The Australian proposal was that the IPCC should examine a scenario in which growth in developing regions was less rapid than under the B1 scenarios (but still rapid by comparison with past experience). This isn’t “my” scenario, but in my view it’s a scenario that the IPCC should have explored.

    I think that that answers your question (2). I don’t have a scenario that can be distinguished from the IPCC’s in observed CO2 fluxes and concentrations, other than that I believe it would be interesting to know what the B1T scenario would look like, if it were to be ajusted for more realistic levels of economic growth and power station construction in the early decades of the century.

    Re your question (3), I don’t think economists, as economists, are equipped to answer the question whether there is climate change due to greenhouse concentration. I read the postings on this blog with interest, but the physics are beyond my ken. My expertise is in economic statistics. In that field, my position is mainstream: in fact, I’ve yet to meet a national accounts statistician or index number theorist who disagrees with the views that I’ve been putting on this matter for the past three years.

  24. Steve McIntyre
    Posted Aug 25, 2006 at 9:43 AM | Permalink

    Transferred from Glacier Bay, Alaska

    Re #46,

    Muirgeo (and DanàƒÆ’à‚ⶩ, the question of lead/lags in temperature/CO2 is an interesting one. In the pre-industrial period, it is quite clear that temperature leads the dance, and that CO2 follows temperature changes with some 600 years lag at the end of an ice age, and with several thousands of years at the start of a new ice age. The trend is 8-10 ppmv CO2 for each 1 C change. As there is a huge overlap (the transitions take many thousands of years), this allows climate modellers to include a huge feedback from CO2 on temperature, thus helping to increase (decrease) temperatures during transitions.

    But there is one interesting exception in the Vostok ice core: the end of the previous interglacial, the Eemian. The temperature (and CH4 – methane) levels were already near their lowest, before CO2 levels started to decline. And the result of the ~40 ppmv reduction is not measurable in the temperature record. That points to a low influence of CO2 levels on temperature. See the graphs here.

    Thus, while there is a quite good correlation between temperature and CO2 as cause and effect in the pre-industrial period (even during the Holocene: some 10 ppmv lower CO2 level during the LIA, thus caused by ~1 C difference, or 5 times more than MBH98/99 shows), it remains to be seen what the real influence of CO2 is on temperature…

    Comment by Ferdinand Engelbeen “¢’‚¬? 25 August 2006 @ 3:34 am | Edit This

    If you want to find a relevant thread to muse about CO2 lead/lag times, find it. Otherwise no more in connection with Glacier BAy.

    Comment by Steve McIntyre “¢’‚¬? 25 August 2006 @ 4:13 am | Edit This


    The concern here is for inappropriate irrelevent posts…..my post have made every post on the Mann issue irrelevent and that’s what the support group is whining about.

    Willis just asked me an incredibly good question on CO2 and temperature trends through the holocene…which I’ve been waiting for….. but I guess it’s inappropriate for me to give a response? If this is the new law then fine I’ll impose my own self ban…..There is nothing more to say until the MWP forest start showing from underneath receding glaciers. If you figure out a way for trolls like me to contribute I’ll see you then. Otherwise, the support group can carry on with statistical machinations on Mann’s paper and other “relevant issues”.

    Willis….look at graph C for your answer. oops sorry..couldn’t help myself…. BYE BYE…gbalella/muirgeo troll signing off.

    Comment by muirgeo “¢’‚¬? 25 August 2006 @ 9:12 am | Edit This

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  25. Steve Sadlov
    Posted Aug 25, 2006 at 10:06 AM | Permalink

    It would appear that one unique thing about the Holocene is indeed the success of Man as an organism capable of modifying the environment. On the one hand, we’ve mastered multiple processes for liberating carbon, and increasingly, managing, the carbon cycle. Some of it is via energy production and some of it is via cultivation and industrial processes. Balancing the liberation and management of carbon, however, are a number of other forcings, both intended and unintended, which also would need to be fully understood and accounted for in order to fully understand just what are the unique characteristics of the Holocene.

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