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CO2 lags temperature - what does it mean?

What the science says...

Select a level... Basic Intermediate Advanced

CO2 didn't initiate warming from past ice ages but it did amplify the warming.  In fact, about 90% of the global warming followed the CO2 increase.

Climate Myth...

CO2 lags temperature

"An article in Science magazine illustrated that a rise in carbon dioxide did not precede a rise in temperatures, but actually lagged behind temperature rises by 200 to 1000 years.  A rise in carbon dioxide levels could not have caused a rise in temperature if it followed the temperature." (Joe Barton, US House of Representatives (Texas) 1985-2019) - Full Statement

Earth’s climate has varied widely over its history, from ice ages characterised by large ice sheets covering many land areas, to warm periods with no ice at the poles. Several factors have affected past climate change, including solar variability, volcanic activity and changes in the composition of the atmosphere. Data from Antarctic ice cores reveals an interesting story for the past 400,000 years. During this period, CO2 and temperatures are closely correlated, which means they rise and fall together. However, based on Antarctic ice core data, changes in CO2 follow changes in temperatures by about 600 to 1000 years, as illustrated in Figure 1 below. This has led some to conclude that CO2 simply cannot be responsible for current global warming.

Figure 1: Vostok ice core records for carbon dioxide concentration and temperature change.

This statement does not tell the whole story. The initial changes in temperature during this period are explained by changes in the Earth’s orbit around the sun, which affects the amount of seasonal sunlight reaching the Earth’s surface. In the case of warming, the lag between temperature and CO2 is explained as follows: as ocean temperatures rise, oceans release CO2 into the atmosphere. In turn, this release amplifies the warming trend, leading to yet more CO2 being released. In other words, increasing CO2 levels become both the cause and effect of further warming. This positive feedback is necessary to trigger the shifts between glacials and interglacials as the effect of orbital changes is too weak to cause such variation. Additional positive feedbacks which play an important role in this process include other greenhouse gases, and changes in ice sheet cover and vegetation patterns.

A 2012 study by Shakun et al. looked at temperature changes 20,000 years ago (the last glacial-interglacial transition) from around the world and added more detail to our understanding of the CO2-temperature change relationship.  They found that:

  • The Earth's orbital cycles triggered warming in the Arctic approximately 19,000 years ago, causing large amounts of ice to melt, flooding the oceans with fresh water. 
  • This influx of fresh water then disrupted ocean current circulation, in turn causing a seesawing of heat between the hemispheres.
  • The Southern Hemisphere and its oceans warmed first, starting about 18,000 years ago.  As the Southern Ocean warms, the solubility of CO2 in water falls.  This causes the oceans to give up more CO2, releasing it into the atmosphere.

While the orbital cycles triggered the initial warming, overall, more than 90% of the glacial-interglacial warming occured after that atmospheric CO2 increase (Figure 2).

Shakun Fig 2a 

Figure 2: Average global temperature (blue), Antarctic temperature (red), and atmospheric CO2 concentration (yellow dots).  Source.

Last updated on 21 April 2021 by eckahle. View Archives

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Further reading

That CO2 lags and amplifies temperature was actually predicted in 1990 in a paper The ice-core record: climate sensitivity and future greenhouse warming by Claude Lorius (co-authored by James Hansen):

"Changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing"

The paper also notes that orbital changes are one initial cause for ice ages. This was published over a decade before ice core records were accurate enough to confirm a CO2 lag (thanks to John Mashey for the tip).

Also, gotta love this quote from Deltoid in answer to the CO2 lag argument: See also my forthcoming paper: "Chickens do not lay eggs, because they have been observed to hatch from them".

Further viewing


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Comments 151 to 200 out of 636:

  1. Tom, thanks for that link about the "burp from the deep". It's interesting, but tantalisingly low on detail. And I can't make out if they are talking about CO or CO2. They write CO, but talk about CO2. I'll try to find more on it. It doesn't apply to the peaks I was talking about, but could be involved in the troughs, the ending of the ice age. I would have thought though, that such an event would show clearly in the Vostok ice-cores.
  2. Mistermack, when you speak of models being wrong, do you mean somebody has attempted to model past glacial episodes and has failed? As to sensitivity being "guesswork," the largest ball of uncertainty remaining in the air and the one most people studying climate agree is most likely to surprise is the role of clouds. Characterizing sensitivity as guesswork is a departure into hyperbole. Specific discussion of uncertainty might better be conducted on the What is our planet's climate sensitivity?" thread.
  3. BTW Mistermack, it would be helpful if you could confirm you have noticed the difference in CO2 concentration between the graph above and today.
  4. @mistermack: "Thanks archiesteel, but you're using your conclusion in your argument there." No, I'm not. I'm basing my argument on established science, i.e. the greenhouse effect. Are you going to argue the greenhouse effect isn't real? I remember another skeptic in another thread who recently said "no one disputes the greenhouse effect..." "Why did an obvious violent feedback mechanism suddenly stop, and go into equally violent reverse?" If you're speaking about Young Dryas specifically, it seems the lingering Laurentide ice sheet played a major impact in it. As far as the glacial/interglacial cycle goes, Milankovitch cycles are primarily responsible for that. BTW, CO2 is not a feedback, it's a forcing (though heating does release some CO2 from the oceans, so I guess it's both, ultimately). "Until you can answer that, it's surely unjustified to claim that the warming that's happening today won't meet the same "barrier" that warming did in the past." It won't meet the same barrier because CO2 concentrations are much higher today than they've been throughout the current Ice Age.
  5. @mistermack: "According to the models, 800 years of steeply rising co2 should cause at least 750 years of more temperature rises, not a steep plunge." Check out CO2 is not the only driver of climate change for more details on how temperatures could have started to decrease even though CO2 concentrations were still near the high "normal" range (again, much lower than current CO2 concentrations).
  6. It's valid to assume a greenhouse effect for CO2, it's not valid to assume how big, or significant that would be, or that it can go past certain limits. Take the example of heating a nail in a flame. It's dead easy to take the chill from the nail. It's harder to get it very hot, and harder still to make it glow red-hot. This is because hot surfaces radiate heat faster. The earth may well have a mechanism that stops it getting hotter, once it reaches the tipping point of the spikes on that graph. You can point to hotter times millions of years ago, but we are now in an ice-age. It's different now. There's no evidence for or against warming with co2 levels as high as they are now, with global temperatures as they are now. You are assuming current levels of co2 can push it higher. There is no previous circumstance to base that model on. Fair enough you can "claim" that the extra co2 we have now will have the power to push it past previous limits. But that's all it is, someone's guesswork.
  7. mistermack> I have read plenty on the Milankovitch cycles, and I can assure you that there is nothing in the calculated insolation rates that could possibly cause such sudden changes. The changes in the insolation curve are plenty sudden in relation to the temperature cycles. Also, here is an example of a model that accurately recreates these temperature trends using insolation as the primary driver.
  8. No, mistermack, it is not "guesswork." It's basic physics plus advanced physics plus sophisticated but perfectly sensible and comprehensible models of how all that works together, validated against observations. Really, you should start reading more, because you are claiming total absence of evidence when there is a lot of evidence.
  9. mistermack, it's not valid to assume how big, or significant that would be, or that it can go past certain limits. Nobody is assuming. Predictions are made by the physical theory and tested via experiment and evidence. Inventing "limits" where the physics predicts none is certainly not valid. You seem to have a profound misconception of how climate science makes its predictions. It is not a guessing game based on historical reconstructions. It is a direct physical prediction given specific explanations of the mechanisms at play in our climate. Historical data only serves as evidence to support these physical theories.
  10. Hi e, thanks for the link. But I immediatly noticed that the graduations are in 100,000 year sections, which makes it look spikey. Also, this is not "whole planet, whole year" insolation, it's one single day, at one single line of latitude.
  11. Tom, to call it physics is stretching it. It's the brand-new science of climate prediction, that has no previous experience to draw on, and a track record of no successful predictions thus far. You are waaaay overstating the solidness of the science. If it was as straight-forward as physics, they could tell us the climate for next year.
    Response: Regarding success of models, you really need to comment on (after reading) the thread "Models are Unreliable." Type that into the Search field at the top left of this page.
  12. mistermack, Uh yeah, it comes from the 100,000 year solar eccentricity cycle. What's your point? It's not just any "single day", it is the peak insolation for the year. Again, what's your point? What I was demonstrating to you is that the "spikiness" of the temperature trend can be predicted given insolation as a primary driver, something you suggested was impossible. You're grasping at straws in an attempt to dismiss this information.
  13. Mistermack, it's probably worth pausing at this moment to evaluate whether it's worth your time pursuing an argument here, or more specifically which argument might be fruitful. In fact you might better spend time learning more about this subject before commencing to disagree because that way you could be more selective in your disagreements and be more generally useful. I only say this because your post at #156 is taking on the classic "throwing a cheesecake underwater" profile. Clouds, that's my suggestion...
  14. e, my point is there is lots wrong with your choice of insolation graph. Firstly, the baseline is 420, not zero. This makes it look far more spikey. Secondly, the 100,000 year graduations accentuate the spikyness. Thirdly, it's not insolation of the whole earth, it's just one line of latitude on the globe. Fourthly, it's just one day's insolation. The sun shines 365 days py. Basically, it's worthless in this context.
  15. Doug, it depends what you mean by fruitful. I don't care if the argument is won or lost. I want the answer. The correct answer, and I don't care which it is. If I learned something new from any of the replies, I would call that fruitful. It wouldn't matter where it pointed.
  16. mistermack, So your claim is that "real" insolation will follow a significantly different pattern than in the diagram provided? Care to show your data, or will you continue making unsubstantiated claims? Of course the graduations accentuate the spikiness, the entire point of the model presented is to examine the theory that multiple equilibria in the climate system can accentuate the changes driven by insolation. The model was indeed able to produce an excellent reconstruction of temperature trends with insolation as the primary driver, in direct contrast to your unsubstantiated claims that such a thing is impossible.
  17. Correction, the graduations you're referring to obviously are from the chart I posted not the paper on the model. How exactly do the gridlines "accentuate" the spikiness? The frequency of variation is clearly much higher than the temperature trend. You're really reaching here.
  18. Ah, you've done Weart, you've read all the literature relevant to this topic, you're here as a last resort, not to argue, mistermack. I see. I was misled when you said sensitivity estimates are "only guesswork" because that remark is on its face ill-informed and sounds simply argumentative. You also sound as though you're more prepared to reflexively disagree as opposed to listen to answers you've asked for, but again that must be a misunderstanding. My apologies. There's a certain familiar pattern to interactions here, which often take the form of rhetorical questions followed by endless refusal to acknowledge new information. Clearly this is not one of those cases.
  19. misterack, You are just repeating the same claims over and over without any empirical support or attempt to substantially address the counter claims. There is no point in continuing this conversation.
  20. I think that right Doug. I'm not talking to the right person. I was looking for good answers. Bye.
  21. e, I posed a good question. I got no answer. To be fair, you are the only one who attempted one. I think my comments about the insolation graph were fair. They weren't just debating points. When the insolation at north iceland (67N) is high, it's going to be low at north Atarctica (67S), cancelling each other out. I don't see why they chose that graph at all. It's bound to give a false impression of reality.
  22. @mistermack: "The earth may well have a mechanism that stops it getting hotter, once it reaches the tipping point of the spikes on that graph." So, you want us to forget all we know about climate science in order to entertained the unresearched hypothesis that some "unknown mechanism" is responsible? mistermack, your question has been answered, and I'll you've been able to produce as counter-arguments is that we "don't know for sure." Well, we sure know a lot more about the Greenhouse Effect and other forcings than we do about your mysterious mechanism. Sure, the CO2/temperature graphs don't match perfectly, becaue the Earth is a complex system, but the correlation between the two is striking. All the available evidence points towards CO2 being the main driver of climate, and CO2 concentrations have not been that high in 600,000 years. If you're going to challenge this, you have to bring your own scientific explanations, and they need to be as solid as the ones presented here. You have clearly failed to do this.
  23. Archie, there is so much wrong there, I don't know where to start. If CO2 were the main driver of climate, the "feedback loop" with rising CO2 would never stop. Even the IPCC don't claim CO2 drives climate, they say it amplifies the effect of the Milankovitch cycles, via a feedback loop. If you look at the ice-core graph above, you will see that "some unknown mechanism" did exactly that, stopped runaway warming, at this point in the cycle, four times in a row. It's there for all to see. If co2 was the main driver then, why did temps reverse as co2 continued to rise?
  24. @mistermack: "If CO2 were the main driver of climate, the "feedback loop" with rising CO2 would never stop." False. Check this article here on why positive feedback doesn't necessarily lead to runaway warming. "If you look at the ice-core graph above, you will see that "some unknown mechanism" did exactly that, stopped runaway warming" No. There's no "unknown mechanism" stopping the warming. The warming stopped because the system reached an equilibrium, i.e. the sum of all forcings and feedbacks was matched by the amount of energy lost to space. "If co2 was the main driver then, why did temps reverse as co2 continued to rise?" That's because CO2 isn't the only driver. "Main" vs. "only" you understand the difference? We can assume that, in those cases, some other forcing (such as aerosols, or lower TSI, etc.) caused temperatures to decrease even though CO2 levels were still high. There's lot of good information on this site. You should start reading the articles before trying to challenge the current theory.
  25. mistermack, It occurred to me that the general thrust of your question is similar to the claim addressed in: are we heading into an ice age. From that post: "How do ice ages begin? Changes in the earth's orbit cause less sunlight (insolation) to fall on the northern hemisphere during summer. Northern ice sheets melt less during summer and gradually grow over thousands of years. This increases the Earth's albedo which amplifies the cooling, spreading the ice sheets farther. This process lasts around 10,000 to 20,000 years, bringing the planet into an ice age." Does that answer your question better? In summary: the leading theory is that Milankovitch cycles are accelerated by changes in albedo due to a reversal of ice melt trends. This combination of forcing and feedback is enough to overcome the effect of CO2 and reverse the temperature trend. The reason we don't expect this process to prevent warming in the next century is elaborated in that post.
  26. Archie, if you click your own link, you will see that a feedback loop doesn't stop abruptly and dive back the other way. It would stop gradually, as the available co2 in the oceans dropped in concentration. There is nothing in that graph that explains the sharp peaks in the ice-core graphs. Conditions most certainly did not reach equilibrium.
  27. Before waffling on with various ignorant remarks about insolation and on the off-chance you actually care about this, mistermack, you might check into these papers: On the structure and origin of major glaciation cycles 1. Linear responses to Milankovitch forcing On the structure and origin of major glaciation cycles 2. The 100,000-year cycle Then, you ought to look at papers in turn cited by these two papers as well as citations of the pair. Once you've done that, you might be better able to simulate being a dilettante. If you don't have access to Paleoceanography your next comment here should be "where do I get a reprint?" If you don't ask that question, there should be a long (days long, at least) delay while you lift a finger on your own behalf, rather than twittering here about "guesses" and the like while rebuffing help you've asked for; between the two of them the papers are cited 748 times. (Don't bother asking me for pdf copies or the like, I could get them but you've got a poor attitude, so tough)
  28. e, the process of heading into the next ice-age seems to be almost continuous, it seems to be the naural condition, with the exception of the dramatic rise out of it. Ive illustrated that here, where I've just tried to show the underlying trends, seperated from the spikes. Time is running from right to left. Temp is blue, co2 is green. It shows rather graphically what should be happening very soon, if manmade co2 doesn't have enough effect.
    Response: Further comments by anyone about the onset of the ice age must be on the appropriate thread, which is not this one.
  29. Oops. Turns out the past is prologue, sometimes (warning: suggestive carrot). Turns out that employing the word "covariance" is evidence of "a deliberately false impression being left, and a false claim being made." So we're looking at argumentation underpinned by a conspiracy fantasy. I'd suggest not providing further entertainment.
  30. @mistermack: "Archie, if you click your own link, you will see that a feedback loop doesn't stop abruptly and dive back the other way." So, you admit that feedback loops don't lead to runaway warming, then? That was the (erroneous) claim you made which I responded to with that link. Try to pay attention. "It would stop gradually, as the available co2 in the oceans dropped in concentration. There is nothing in that graph that explains the sharp peaks in the ice-core graphs." What you call "sharp peaks" are actually gradual changes. They seem like sharp peaks to you because the time scale is compressed. Stretch it out and you'll see that not only are the changes not that quick (thousands of years), especially not when compared to the current warming trend. In short, you should stop eyeballing graphs and make the difference between long-term milankovitch-related cycles (where CO2 acts as a feedback, to get back on topic) and the current CO2-driven warming (where CO2 acts as a forcing. "Conditions most certainly did not reach equilibrium." Here you're half-right. Conditions never reach a total equilibrium, however, the changes are slow enough that they give that impression. This has nothing to do with the rapid rate of change we are experiencing, which is caused by increased CO2 levels.
  31. Archie, "never stop" was not meant to be taken literally. (why do I have to explain that?) If CO2 is the main driver, the feedback loop would have to continue as long as there was dissolved CO2 available to come out of the oceans. Which would heat the planet way past the point where it "did" stop. Is that any easier? If you look at the graph I posted above, where I averaged out the peaks and troughs, you can see that the trend is a continuous fall into an ice age, until some drastic event causes a spectacular temperature rise to a one-off peak, with this repeated over and over. It doesn't reflect the patterns of the Milankovitch cycles at all. Find out what drives that huge rise, and you will know what drives the climate. That's why the widely accepted 800 year lag is important. A tiny CO2 rise, following 800 years after a miniscule rise in insolation due to the Milankovitch cycle, just doesn't fit the bill. At the depth of the ice-age, a high proportion of the sun's energy is being reflected back into space anyway. I can't see a slow, tiny, gradual increase in insolation causing such a sudden and violent rise. And as I said earlier, what is the sudden stopping mechanism?
  32. mistermack #181: "Archie, "never stop" was not meant to be taken literally. (why do I have to explain that?)" Because it's the opposite of what you said? "If CO2 is the main driver, the feedback loop would have to continue as long as there was dissolved CO2 available to come out of the oceans." Why? If we take humans digging up and burning fossil fuels out of the equation then rising CO2 levels are a FEEDBACK. Once the forcing, in this case increased insolation of the northern latitudes, stops the feedback will eventually stop as well. Look at the ice-albedo feedback for example. Even if we stopped increasing atmospheric CO2 levels today ice would continue to melt for decades to centuries. It should not be at all surprising that there is a lag time between the point that a forcing peaks and the point that all of the feedbacks caused by that forcing peak. "And as I said earlier, what is the sudden stopping mechanism?" So long as the feedback factor is less than 1 it is simple mathematics that once the forcing ends the feedback must eventually do so as well. Ergo, the 'stopping mechanism' is quite obviously the end of the forcing. When you move your foot from the accelerator to the brakes of your car does the vehicle stop instantly? If not, why would you think that the entire planet can shift directions on a dime?
  33. CB, you clearly don't rate CO2 as having much of a greenhouse effect, if you think that a slight drop in insolation could halt temperature rises, at a point of extremely high and rising CO2 levels. A factor of 1 could hardly suddenly drag the world out of the depths of an ice-age, all the way to the hottest point in the cycle.
  34. @mistermack: you clearly didn't understand what CBDunkerson explained. During those times, CO2 was a feedback. When the main forcing stopped, the feedback diminished. Today the situation is different. We don't have an insolation-based forcing. However, CO2 levels are 35% higher than at the highest point during the past 600,000 years. It *is* the forcing, not the feedback. If you disagree, please provide scientific evidence supporting your point of view. Anything else will be ignored as more noise from the contrarian side.
  35. #181: "A tiny CO2 rise, following 800 years after a miniscule rise in insolation due to the Milankovitch cycle, just doesn't fit the bill. At the depth of the ice-age, a high proportion of the sun's energy is being reflected back into space anyway." Your remarks convey a very one-sided sense of scale. A tiny CO2 rise? Look at the CO2 graph you posted in #178: 180ppm at LGM, 280 at the graph's t=0 and 390 now. Those are not tiny changes. A high proportion of solar energy reflected back to space? This requires that you understand how the LGM changed the total albedo of both the sum total land area and the oceans basins. From Broccoli and Manabe 1987: ... both the ice sheet and CO2 effects are found to be required in order to produce sufficient cooling on a global basis. ... the loss of heat energy due to the reflection of solar radiation by Northern Hemisphere continental ice is almost entirely compensated by a reduction in the upward terrestrial radiation from that hemisphere.
  36. You know, in science, there was once this thing we called the Theory of Multiple Working Hypotheses. Anathema (a formal ecclesiastical curse accompanied by excommunication) in modern climate science. So, in juxtaposition to the hypothesis of future global climate disruption from CO2, a scientist might well consider an antithesis or two in order to maintain ones objectivity. One such antithesis, which happens to be a long running debate in climate science, concerns the end Holocene. Or just how long the present interglacial will last. Looking at orbital mechanics and model results, Loutre and Berger (2003) in a landmark paper (meaning a widely quoted and discussed paper) for the time predicted that the current interglacial, the Holocene, might very well last another 50,000 years, particularly if CO2 were factored in. This would make the Holocene the longest lived interglacial since the onset of the Northern Hemisphere Glaciations some 2.8 million years ago. Five of the last 6 interglacials have each lasted about half of a precession cycle. The precession cycle varies from 19-23k years, and we are at the 23kyr part now, making 11,500 years half, which is also the present age of the Holocene. Which is why this discussion has relevance. But what about that 6th interglacial, the one that wasn’t on the half-precessional “clock”. That would be MIS-11 (or the Holsteinian) which according to the most recently published estimate may have lasted on the order of 20-22kyrs, with the longest estimate ranging up to 32kyrs. Loutre and Berger’s 2003 paper was soon followed by another landmark paper by Lisieki and Raymo (Oceanography, 2004), an exhaustive look at 57 globally distributed deep Ocean Drilling Project (and other) cores, which stated: “Recent research has focused on MIS 11 as a possible analog for the present interglacial [e.g., Loutre and Berger, 2003; EPICA community members, 2004] because both occur during times of low eccentricity. The LR04 age model establishes that MIS 11 spans two precession cycles, with 18O values below 3.6o/oo for 20 kyr, from 398-418 ka. In comparison, stages 9 and 5 remained below 3.6o/oo for 13 and 12 kyr, respectively, and the Holocene interglacial has lasted 11 kyr so far. In the LR04 age model, the average LSR of 29 sites is the same from 398-418 ka as from 250-650 ka; consequently, stage 11 is unlikely to be artificially stretched. However, the June 21 insolation minimum at 65N during MIS 11 is only 489 W/m2, much less pronounced than the present minimum of 474 W/m2. In addition, current insolation values are not predicted to return to the high values of late MIS 11 for another 65 kyr. We propose that this effectively precludes a ‘double precession-cycle’ interglacial [e.g., Raymo, 1997] in the Holocene without human influence.” To bring this discussion up to date, Tzedakis, in perhaps the most open peer review process currently being practised in the world today (The European Geosciences Union website Climate of the Past Discussions) published a quite thorough examination of the state of the science related to the two most recent interglacials, which like the present one, the Holocene (or MIS-1) is compared to MIS-19 and MIS-11. The other two interglacials which have occurred since the Mid Pleistocene Transition (MPT) also occurred at eccentricity minimums. Since its initial publication in 2009, and its republication after the open online peer review process again in march of this year, this paper is now also considered a landmark review of the state of paleoclimate science. In it he also considers Ruddiman’s Early Anthropogenic Hypothesis, with Rudddiman a part of the online review. Tzedakis’ concluding remarks are enlightening: “On balance, what emerges is that projections on the natural duration of the current interglacial depend on the choice of analogue, while corroboration or refutation of the “early anthropogenic hypothesis” on the basis of comparisons with earlier interglacials remains irritatingly inconclusive.” As we move further towards the construction of the antithetic argument, we will take a closer look at the post-MPT end interglacials and the last glacial for some clues. An astute reader might have gleaned that even on things which have happened, the science is not that particularly well settled. Which makes consideration of the science being settled on things which have not yet happened dubious at best. Higher resolution proxy studies from many parts of the planet suggest that the end interglacials may be quite the wild climate ride from the perspective of global climate disruption. Boettger, et al (Quaternary International 207 [2009] 137–144) abstract it: “In terrestrial records from Central and Eastern Europe the end of the Last Interglacial seems to be characterized by evident climatic and environmental instabilities recorded by geochemical and vegetation indicators. The transition (MIS 5e/5d) from the Last Interglacial (Eemian, Mikulino) to the Early Last Glacial (Early Weichselian, Early Valdai) is marked by at least two warming events as observed in geochemical data on the lake sediment profiles of Central (Gro¨bern, Neumark–Nord, Klinge) and of Eastern Europe (Ples). Results of palynological studies of all these sequences indicate simultaneously a strong increase of environmental oscillations during the very end of the Last Interglacial and the beginning of the Last Glaciation. This paper discusses possible correlations of these events between regions in Central and Eastern Europe. The pronounced climate and environment instability during the interglacial/glacial transition could be consistent with the assumption that it is about a natural phenomenon, characteristic for transitional stages. Taking into consideration that currently observed ‘‘human-induced’’ global warming coincides with the natural trend to cooling, the study of such transitional stages is important for understanding the underlying processes of the climate changes.” Hearty and Neumann (Quaternary Science Reviews 20 [2001] 1881–1895) abstracting their work in the Bahamas state: “The geology ofthe Last Interglaciation (sensu stricto, marine isotope substage (MIS) 5e) in the Bahamas records the nature of sea level and climate change. After a period of quasi-stability for most of the interglaciation, during which reefs grew to +2.5 m, sea level rose rapidly at the end ofthe period, incising notches in older limestone. After briefstillstands at +6 and perhaps +8.5 m, sea level fell with apparent speed to the MIS 5d lowstand and much cooler climatic conditions. It was during this regression from the MIS 5e highstand that the North Atlantic suffered an oceanographic ‘‘reorganization’’ about 11873 ka ago. During this same interval, massive dune-building greatly enlarged the Bahama Islands. Giant waves reshaped exposed lowlands into chevron-shaped beach ridges, ran up on older coastal ridges, and also broke off and threw megaboulders onto and over 20 m-high cliffs. The oolitic rocks recording these features yield concordant whole-rock amino acid ratios across the archipelago. Whether or not the Last Interglaciation serves as an appropriate analog for our ‘‘greenhouse’’ world, it nonetheless reveals the intricate details ofclimatic transitions between warm interglaciations and near glacial conditions.” The picture which emerges is that the post-MPT end interglacials appear to be populated with dramatic, abrupt global climate disruptions which appear to have occurred on decadal to centennial time scales. Given that the Holocene, one of at least 3 post-MPT “extreme” interglacials, may not be immune to this repetitive phenomena, and as it is half a precession cycle old now, and perhaps unlikely to grow that much older, this could very well be the natural climate “noise” from which we must discern our anthropogenic “signal” from. If we take a stroll between this interglacial and the last one back, the Eemian, we find in the Greenland ice cores that there were 24 Dansgaard-Oeschger oscillations, or abrupt warmings that occurred from just a few years to mere decades that average between 8-10C rises (D-O 19 scored 16C). The nominal difference between earth’s cold (glacial) and warm (interglacial) states being on the order of 20C. D-O events average 1470 years, the range being 1-4kyrs. Sole, Turiel and Llebot writing in Physics Letters A (366 [2007] 184–189) identified three classes of D-O oscillations in the Greenland GISP2 ice cores A (brief), B (medium) and C (long), reflecting the speed at which the warming relaxes back to the cold glacial state: “In this work ice-core CO2 time evolution in the period going from 20 to 60 kyr BP [15] has been qualitatively compared to our temperature cycles, according to the class they belong to. It can be observed in Fig. 6 that class A cycles are completely unrelated to changes in CO2 concentration. We have observed some correlation between B and C cycles and CO2 concentration, but of the opposite sign to the one expected: maxima in atmospheric CO2 concentration tend to correspond to the middle part or the end the cooling period. The role of CO2 in the oscillation phenomena seems to be more related to extend the duration of the cooling phase than to trigger warming. This could explain why cycles not coincident in time with maxima of CO2 (A cycles) rapidly decay back to the cold state. ” “Nor CO2 concentration either the astronomical cycle change the way in which the warming phase takes place. The coincidence in this phase is strong among all the characterised cycles; also, we have been able to recognise the presence of a similar warming phase in the early stages of the transition from glacial to interglacial age. Our analysis of the warming phase seems to indicate a universal triggering mechanism, what has been related with the possible existence of stochastic resonance [1,13, 21]. It has also been argued that a possible cause for the repetitive sequence of D/O events could be found in the change in the thermohaline Atlantic circulation [2,8,22,25]. However, a cause for this regular arrangement of cycles, together with a justification on the abruptness of the warming phase, is still absent in the scientific literature.” In their work, at least 13 of the 24 D-O oscillations (indeed other workers suggest the same for them all), CO2 was not the agent provocateur of the warmings but served to ameliorate the relaxation back to the cold glacial state, something which might have import whenever we finally do reach the end Holocene. Instead of triggering the abrupt warmings it appears to function as somewhat of a climate “security blanket”, if you will. Therefore in constructing the antithesis, and taking into consideration the precautionary principle, we are left to ponder if reducing CO2’s concentration in the late Holocene atmosphere might actually be the wrong thing to do.
    Response: Your comment likely will spark discussion that belongs on the thread We’re heading into an ice age. So will you please copy it into a comment on that thread? Then post a new comment on this thread, simply pointing to your comment's new home. When you have done that, I'll delete this original comment from this thread. Thanks.
  37. Sentient, can you provide a link or citation for Tzedakis' paper? Can't find it, would like to take a look. BTW, mistermack might want to read sentient's post so as to get a better understanding of how tracking insolation for a single day is actually employed. Reevaluate what's "worthless," your remark versus the science.
  38. There seems to be very poor understanding of feedback among posters, so I'll try to give a simplified description. Imagine you have a football, (soccer), and a golfball. Chop the football in half, and lay it on the ground as a bowl. Put the golfball inside. That's negative feedback. If anything disturbs the golfball, it will roll back to the middle. Turn the football over, and put the golf ball on top. A very slight forcing factor ( a breath of wind ) causes it to roll. Once it's on the down slope, gravity, the feedback mechanism, takes over, and the ball runs away. It no longer needs the wind that started it, and wind in the other direction can't blow it back up the football. So those who claim that a reverse in the level of insolation would stop a feedback mechanism are really not understanding what's happening at all. For that to happen, the feedback would have to be incredibly weak, nowhere near what could pull a planet out of an ice-age. In reality, it's removing the feedback power source that stops positive feedback loops, like turning down the volume knob on your guitar amplifier. In climate terms, that would require the CO2 to run out, or the process of outgassing from the ocean to suddenly stop.
  39. @mistermack: you don't seem to understand that climate feedbacks don't necessarily lead to runaway warming. Did you read the article I linked to earlier? "In climate terms, that would require the CO2 to run out, or the process of outgassing from the ocean to suddenly stop." There is a finite amount of CO2 sequestered in the oceans, so it is possible that the rate of CO2 release from oceans would slow down as that amount decreases. Your analogy is inadequate, and your conclusions are thus erroneous. I suggest reading more from this site before attempting to take down current AGW theory.
  40. Archie, that's totally illogical. If you consider the peaks of the graphs, you have a huge steep rise, coming to a sudden stop, followed by a huge steep fall. How on earth does that happen in response to CO2 feedback? Does the ocean suddenly stop outgassing, and suddenly start sucking in CO2? In huge quantities? How would that happen?
    Response: Again, you seem to be assuming that putting the label "positive feedback" on any phenomenon necessitates the runaway version of positive feedback. See the Argument "Positive Feedback Means Runaway Warming", and read all three versions--Basic, Intermediate, and Advanced.
  41. In any case, Archie, for that to happen, the CO2 graph would have to get ahead of the temperature graph.
  42. mistermack, your incorrect analogy with a moving ball makes me suspect that you are incorrectly thinking of temperature as having inertia.
  43. mistermack, lots of factors influence temperature. Although CO2 is a really important one, it is not the only one. The interplay of those factors is complicated. Our knowledge of that interplay is summarized in causal models. Those models do a good job of hindcasting the changes in temperature in response to changes in those factors.
  44. @mistermack: you seems to assume a lot of things wrong. What you says happens "suddenly" in reality takes hundreds, even thousands of years. You also seem to believe only CO2 affects temperature. You've been provided with links explaining why these ain't so. Why not try to study these various mechanisms a bit more instead of taking such an adversarial approach? Did you come here to learn, or to make a point?
  45. mistermack, since you seem frustrated at the answers you are getting here, why don't you post your question about the rapidity of cooling over on this particular post on ice ages at RealClimate?
  46. MrResponse, I have read that article about runaway warming, someone already linked it on this thread. But you can't have it both ways. If there is a built-in mechanism that stopped runaway warming, (as seems perfectly clear anyway from the graphs), then there should be little to worry about. And also, what is the mechanism that happens so suddenly (suddenly in climate terms Archie), and sends the whole process into reverse? There is nothing similar to that in the page you linked. If it was the CO2 supply dwindling in the ocean, wouldn't it happen incredibly slowly? How do you think that could happen quickly, and go straight into steep reverse, as I asked? People seem to be dodging the difficult question here.
  47. mistermack, you are incorrect that runaway warming was happening but something else stopped it. Positive feedbacks that are not of the runaway variety never can run away. They are self-limiting. Each little bout of positive feedback is just that--a little, short-lived bout that inherently, by its fundamental nature, will die out. They do not strain toward running away. They are introspective. Belly button "innies" rather than "outies." In our current era, there is a lot for us to worry about despite the lack of the runaway variety of positive feedback, because we keep adding greenhouse gases; our addition of greenhouse gases is a forcing. The non-runaway positive feedback amplifies the effects of those additions. If we suddenly stopped adding greenhouse gases and all other emissions, temperature would continue to rise for several years due to the Earth working toward equilibrium, but then the temperatures would fall. If we continued to emit but at a constant rate instead of an increasing rate, temperature would continue to rise for longer but then would asymptote. Tying all that back into the topic of this post: Those past CO2 positive feedbacks also were not of the runaway variety. So they, too, inherently would peter out. Unlike the human-caused addition of CO2, there was no forcing by independent addition of CO2. CO2 was instead acting as a non-runaway feedback. Other, forcing and feedback, factors needed to keep stimulating the system and thereby prompting more (non-runaway) positive feedback from CO2. Most prominent among those factors was orbital cycles, but there also were effects of changes in vegetation, dust, snow and ice cover,.... So your question "what made the temperature rise stop" is ill posed. The better question is "what made the temperature continue to rise as long as it did?"
  48. Tom, if the graphs remotely resembled a process "petering out", I would have to agree. However, as I've pointed out so many times, they don't. Draw your own graph, of a feedback loop "petering out". What does it look like? Does it resemble the ice core records? And why don't the CO2 graphs jump in front of the temperature graphs when that happens? If a drop in CO2 is pulling down temperatures?
  49. @mistermack: again, you are misled by the time scale used in the graphs. The changes seem sudden to you because the scale is in hundreds of thousands of years. If you were to see these changes happen on a much smaller scale, they wouldn't look so sudden, and would be consistent with the feedback loops ending. Also, Tom has not claimed that a drop in CO2 is what drove the climate down. Instead, CO2 is a *feedback* mechanism in those cases. You won't learn much (and you clearly have much to learn still) by refusing to listen to rebuttals to your erroneous claims.
  50. mistermack, you continue to refuse to acknowledge the importance of the time scales of the graphs. Try mentally zooming in on Figure 1 at the top of this post until its x axis had the same time scale as the graph of temperature response to cessation of human emissions. The "sudden" drops would not seem so sudden. Or zoom out of the the graph of temperature response to cessation of human emissions until its timescale matches that of Figure 1. Then the "gradual" drop would seem just as sudden as Figure 1's drops. What seems to you personally to be unrealistic and unreasonable rates of decrease when you look at a graph zoomed out so far, in fact are completely reasonable when the actual times involved are recognized.

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