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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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

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 126 to 150 out of 529:

  1. Tom Dayton: "Instead they (climate models) are physical models that incorporate knowledge of fundamental processes." I just read this history of climate models: It seems that at least some effects are still not really based upon a fundamental understanding of underlying physics. The effects of clouds are still apparently used as fitting parameters to climate data. The fits to climate data are then used to predict climate over other periods. I don't really have a problem with this in principle, but it does seem that these are not really fully based on fundamental physics and this type of fitting leaves open the possibility of trying to use the fitted parameters outside the region of validity (extrapolation rather than interpolation). Apparently things like clouds are not really understood in enough detail to truly predict climate from fundamental physics. Of course, this is just the impression I got from one source, perhaps it is not really accurate.
  2. Pdt, not to butt in but your remark will be better served and of better service if delivered on the thread Tom suggested. It's dead on topic for that thread and a rare matter of actual significant uncertainty leading to less redundant fat-chewing. Not so much for this one and thus a missed opportunity for better coherency. Models are unreliable
  3. pdt, in accord with Doug's comment I've responded to you on the Models Are Unreliable thread.
  4. "The paucity of observations in the tropical Atlantic and Indian oceans have considerably retarded our understanding, modeling, and prediction of these coupled modes, which are extremely important not only because of their societal consequences but because it is through them that the ocean actually drives the atmosphere. These regions and coupled mechanisms should constitute a priority of observational and theoretical research. " The confidence of CO2 forcing to the levels that climate models currently predict is tenuous, at best. Indeed, the understanding is still retarded. But it is improving all the time. Can you point to a researcher that has not put out predictions that did not turn out to be serious exaggerations of actually measured impacts?
  5. hang on a sec.. they claim that temperature drives CO2 levels, but then the rising C02 drives the temperature even further... then why is it that we aren't all living in 10000 degree temperatures? oh thats right i almost forgot.... the earth has a saturated greenhouse effect... think about it.. the earth has to have a saturation point
  6. qball17, positive feedbacks need not run away, as you can see for yourself in a spreadsheet by following my instructions in my comment on another thread.
  7. If CO2 is such a strong forcing mechanism how is it overcome so easily when the world slips back to cold?
  8. cruzn246 writes: If CO2 is such a strong forcing mechanism how is it overcome so easily when the world slips back to cold? During the glacial/interglacial cycles, CO2 acted as a feedback amplifying the warming or cooling caused by the Milankovich forcing. In other words, an external source of cooling would reduce the global mean temperature. The oceans would respond by absorbing more CO2 from the atmosphere, causing a feedback that would amplify the cooling a bit. Eventually, when the Milankovich cycle shifted towards warming, this process would reverse, and the increasing CO2 in the atmosphere would amplify the initial warming. The situation today is different -- CO2 is not just a feedback, we're now adding it directly to the atmosphere in large quantities. Does that help clarify things?
  9. What about the ever increasing presence of water vapor? Where are the charts showing its increase over the last 500,000 years?
    Response: Here's the appropriate thread for that topic: Water vapor is the most powerful greenhouse gas
  10. The core graphs prompt one question. The temp. rise out of the coldest part of the ice-age is so sudden and so steep, a dramatic feedback mech. must be happening. But it reaches a point, roughly where we are now, when it stops, suddenly and dramatically, and never went any higher, but drops back equally steeply. If temperatures stopped rising, and dropped steeply many times in the past, why should I believe that they can go higher now? You had rapidly rising CO2 in the past, but the temp. rise was unable to continue, and quickly dropped back. Why?
  11. @mistermack: "If temperatures stopped rising, and dropped steeply many times in the past, why should I believe that they can go higher now? You had rapidly rising CO2 in the past, but the temp. rise was unable to continue, and quickly dropped back. Why?" CO2 levels are higher now (by more than 35%) than at any time in the last 600,000 years. The last time they were this high (with similar solar output), temperatures were almost 5C warmer, IIRC. So, in fact, temps *can* go higher if CO2 levels are pushed higher. That's the essence of AGW theory.
  12. Thanks archiesteel, but you're using your conclusion in your argument there. Why did an obvious violent feedback mechanism suddenly stop, and go into equally violent reverse? 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.
  13. mistermack, the past episodes lacked an ingredient that is present now: the rapid and accelerating injection of greenhouse gases by humans. If those same other factors that operated in the past to cap the warming acted now, they would be overwhelmed by the higher and increasing amounts of GHGs from this new source.
  14. Further to Tom's remarks, look at the ppm levels in the graph in John's post. We're at ~386ppm today, off that chart, in a new mode. "'s surely unjustified to claim that the warming that's happening today won't meet the same "barrier" that warming did in the past. " The present warming's not going to meet the same barrier, that barrier's efficacy won't be the same today because we've created a novel situation. "Past is prologue" arguments always face the fundamental problem that we're not living in the past, we're living in the present, us and our effluent.
  15. Mistermack, The information you are looking for is available on this site. I can't post direct links, since this is being tapped out from my phone. Read up on the Milankovitch cycles and climate sensitivity in regards to CO2 as a feedback agent. Currently, CO2 is the forcing agent rather than a feedback. This is why archiesteel's comment was spot on.
  16. mistermack, another difference between then and now is the time scale. The "sudden," "steep" rises and drops you see in those graphs of olden times are not so sudden or steep when plotted on the timescale of the recent, human-caused temperature rise of the past 150 years.
  17. I'm sorry, Tom, Doug and Biblio, but 1) that was no answer to why warming stopped before, and 2) You're using an assumption that GW is caused by CO2 levels, to argue for it. I think about the four peaks in temp. in the graph above. Just before that peak, temp was rising at an enormous rate, and so was CO2. Something stopped it suddenly, and sent it the other way, EVEN THOUGH CO2 WOULD CONTINUE RISING STEEPLY FOR ANOTHER 800 YEARS !! According to the models, 800 years of steeply rising co2 should cause at least 750 years of more temperature rises, not a steep plunge.
    Response: Please don't use all caps. It's considered yelling. See the Comments Policy.
  18. Ah, sorry about the caps. I wasn't intending it as a yell, just as emphasis, like underlining.
  19. mistermack, On point 1) You were told to read up on Milankovitch cycles. Milankovitch cycles are periodic shifts in the earths orbit. When the orbit moves closer to the sun we get the warming trend, when the orbit moves further from the sun the warming trend is reversed and we get a cooling trend. The orbital cycles drive the direction of temperature change while CO2 only acts as a feedback or amplifier of said changes. Get it? On point 2) You asked how current theory explains the temperature trends. You can't very well expect someone to explain current theory without using the theory itself. Also, Milankovitch cycles on their own have nothing to with CO2, CO2 just acts as a feedback. If your question is what evidence do we have that CO2 levels are causing GW, then that is a separate topic and is covered here.
  20. Hi e, 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. And nothing in any Milankovitch cycle that could suddenly negate 800 years of steeply rising co2 levels, if the models are correct.
  21. Mistermack, you related yesterday's behavior to today's behavior, yourself suggesting that yesterday's behavior is cause to doubt what will happen today. As has been pointed out to you, today is different. Again, look at the CO2 concentration in times you refer to, compared to today. On a side note, it's not an "assumption" that increasing concentrations of CO2 cause the atmosphere to be a more efficient insulator. If you want to argue about that, however, use the search function to find a suitable venue for chasing that topic.
  22. mistermack, Amplifying e's comment about your point 2: The main evidence for CO2's warming effect is not passive observation of its historic relationship to temperature. Rather, it is fundamental physics. CO2's warming effect was postulated in the early 1800s, long before there was evidence of its historic relationship to global temperatures. The exact mechanism by which CO2 does that was discovered in the early 1900s, again before there was much historic evidence. Later the historic relationships were discovered and found to match those predictions. For a good summary of the physics see Ramanathan's paper. For a good history see Weart's The Discovery of Global Warming.
  23. mistermack, Yes, which is why feedbacks are required to account for the degree of temperature swings. The models accurately recreate these temperature swings, so your claim that the models are inconsistent with the models is wrong and nonsensical.
  24. mistermack, Multiple, interrelated, not entirely synchronous factors were responsible for both the onset and offset of ice ages. They are not understood completely, to say the least. But just one example of how those factors can have sudden onsets and offsets is the recently discovered CO2 "burp" from the deep ocean.
  25. Doug and Tom, thanks for your comments. I of course don't dispute co2 acting as a greenhouse gas. But the amount of warming, for a specific increase, is only guesswork at the moment. (otherwise, why is the IPCC only claiming 90% certainty? That leave 10% chance that the current levels are not to blame, does it not?) The problem I'm pointing out with the graphs above, is that at the peak of previous warming, you get an 800 year period, when co2 levels are high, and rising steeply, and yet temperatures are plummeting. This is in stark contrast to todays models. And our point in the cycle now is at or near that historic maximum. I don't see any explanation why the models are so wrong, for so long, for these events. The Milankovitch cycles just don't cut it. The insolation curves are extremely gentle.
    Response: Regarding uncertainty, please read (and comment there) the Argument "The science isn’t settled". Be sure to check out both the Basic and Advanced tabbed pages there.

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