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CO2 lags temperature - what does it mean?

What the science says...

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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

At a glance

Antarctic ice-core data today provide a continuous record on temperature and atmospheric composition that goes back for some 800,000 years. The data track the last few glacial periods and their abrupt endings, with rapid transitions into mild interglacials. But in some of the ice-cores, temperature rises first and is followed, a few hundred years later, by rising carbon dioxide (CO2) levels.

Certain purveyors of climate-myths seized on this observation, claiming it to be “proof” that carbon dioxide doesn't cause climate change. Wrong, wrong, wrong. But how? The answer lies in a beer-can.

In fact, you can do this one yourself. You need two cans of any fizzy beer. On a nice summer's day, take one out of the fridge and place it outside in direct sunshine for a few hours. Leave the other where it is. Then open the two at the same time. The warm one will froth like mad, half-emptying the can and making a mess. What is left in the can will be horrible and flat. Conversely, the one straight from the fridge will just give a “pfft” noise and will be pleasant to drink, being cool and fizzy.

What's that got to do with this myth? Well, you have just demonstrated an important point about the solubility of CO2 in water. CO2 gives fizzy drinks their fizz and it is far more soluble in colder water. As the water warms, it cannot hold onto as much CO2 and it starts to degas. Hence that flat lager.

Exactly the same principle applies to the oceans. When global warming is initiated, both land and the oceans start to warm up. On land, permafrost starts to thaw out, over vast areas. Carbon dioxide (and methane) are released, having been trapped in that permafrost deep-freeze for thousands of years. At sea, that “warm beer effect” kicks in. Thanks to both processes, atmospheric CO2 levels rise in earnest, amplifying and maintaining the warmth. That rise in CO2 thereby caused more of the gas to be released, warming things up yet more in a vicious cycle, known as a positive feedback. Other feedbacks kick in too: for example as the ice-sheets shrink, their ability to reflect Solar energy back out to space likewise decreases, so that heat is instead absorbed by Earth’s surface.

The trigger for the initial warming at the end of an ice-age is a favourable combination of cyclic patterns in Earth's orbit around the Sun, leading to a significant increase in the solar energy received by Earth's Northern Hemisphere. That's no secret. Glacial-interglacial transitions are caused by several factors working in combination – triggers and feedbacks. We've understood that for a long time.

And when you think about it, saying CO2 lagged temperature during glacial-interglacial transitions so cannot possibly be causing modern warming is a bit like saying, “chickens do not lay eggs, because they have been observed to hatch from them".

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

That CO2 can lag behind but amplify temperature during a glacial-interglacial transition was in fact predicted as long ago as 1990. In the paper The Ice-Core Record: Climate Sensitivity and Future Greenhouse Warming by Claude Lorius and colleagues published in the journal Nature in 1990, a key passage reads:

"The discovery of significant changes in climate forcing linked with the composition of the atmosphere has led to the idea that 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 and by constituting a link between the Northern and Southern Hemisphere climates."

This was published over a decade before ice core records were accurate enough to confirm a CO2 lag. We now know that CO2 did not initiate the warming from past ice ages but it did amplify the warming. In fact, about 90% of the global warming followed the CO2 increase.

Antarctic ice cores reveal an interesting story, now going back for around 800,000 years. During this period, changes in CO2 levels tend to follow changes in temperatures by about 600 to 1000 years, as illustrated in Figure 1 below. This has led some to disingenuously claim that CO2 simply cannot be responsible for the current global warming. Unsurprisingly, such a claim does not tell the whole story.

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

The initial change in temperature as an ice-age comes to an end is triggered by cyclic changes in Earth’s orbit around the sun, affecting the amount of seasonal sunlight reaching Earth’s surface in the Northern Hemisphere. The cycles are lengthy: all of them take tens of thousands of years to complete.As both land and oceans start to warm up, they both release large amounts of CO2 into the atmosphere, from melting permafrost and from warming ocean water, since CO2 solubility in water is greater in cold conditions. That release enhances the greenhouse effect, amplifying the warming trend and leading to yet more CO2 being degassed. In other words, increasing CO2 levels become both the cause and effect of further warming. Once started, it’s a vicious, self-reinforcing cycle - an excellent example of what science refers to as a positive climate feedback.

Indeed, such positive feedbacks are necessary to complete the shifts from glacial to interglacial conditions, since the effect of orbital changes alone are too weak to fully drive such variations. Additional positive feedbacks which play an important role in this process include other greenhouse gases like methane - you may have seen videos of that gas bubbling up through icy lakes in permafrost country and being ignited. Changes in ice sheet cover and vegetation patterns determine the amount of Solar energy getting absorbed by Earth’s surface or being reflected back out to space: decrease an ice-sheet’s area and warming will thereby increase.

The detailed mechanisms for the above general pattern have of course been investigated. In a 2012 study, published in the journal Nature (Shakun et al. 2012), Jeremy Shakun and colleagues looked at global temperature changes at the commencement of the last glacial-interglacial transition. This work added a lot of vital detail to our understanding of the CO2-temperature change relationship. They found that:

1) 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.

2) This influx of fresh water then disrupted ocean current circulation, in turn causing a seesawing of heat between the hemispheres.

3) 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.

4) Finally, CO2 levels may lag temperature in some ice-core records from Antarctica, but in some other parts of the world the reverse was the case: temperature and CO2 either rose in pace or temperature lagged CO2. Figure 2 demonstrates this graphically and shows how things are never as simplistic as purveyors of misinformation would wish.

Shakun Fig 2a 

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

Last updated on 14 February 2023 by John Mason. 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

Denial101x video

Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Lag

Please check the related blog post for background information about this graphics resource.


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Comments 151 to 175 out of 451:

  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.

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