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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. |
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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.
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
tcflood, the Nature paper is important in that the modeling efforts are able to successfully simulate the various ice age cycles, including the 100,000 year cycle, by successfully identifying and accounting for the various knock-on feedbacks. These feedbacks include albedo, CO2 levels, ice sheet configuration (including elevation), air- and ocean-circulation changes.
The paper confirms, via modeling, that the aforementioned effects (combined with Milankovitch orbital forcings) can account for the various iterations of the ice age glacial / interglacial cycles.
Above quotes are from the Phys.org article linked below.
http://phys.org/news/2013-08-ice-ages-feedback.html
The Shakun et al 2012 paper showed that warming was indeed triggered by the Milankovitch cycles, and that small amount of orbital cycle-caused warming eventually triggered the CO2 release, which caused most of the glacial-interglacial warming. So while CO2 did lag behind a small initial temperature change (which mostly occurred in the Southern Hemisphere), it led and was the primary driver behind most of the glacial-interglacial warming.
According to the Shakun data, approximately 7% of the overall glacial-interglacial global temperature increase occurred before the CO2 rise, whereas 93% of the global warming followed the CO2 increase.
http://www.skepticalscience.com/skakun-co2-temp-lag.html
Daniel,
Thanks for your response. An especially interesting feature of their modeling results is that if [CO2} is kept constant at 220 ppm, the model still produces the 100 ky ice age cycle. If [CO2] is kept constant 260 ppm, the ice ages disappear. If [CO2} is kept constant at 160 ppm, the ice age frequency is much higher and interglacials are much colder.
These models point to non-linear coupling of numerous variables that is indeed complex. From my point of view, it is exciting to finaly see a quantitative treatment that actually does reproduce the periodicity, shape, and intensity of the ice age/interglacial cycles. Now perhaps they can begin to really nail down the explicit quantitative role of [CO2] in all of this and finally lay the "lag" BS to rest.
Tzedakis et al 2012 found that the threshold for the current interglacial / glacial transition was about 240 ppm CO2, so that is in-line with other research.
Back at #70, the moderator said:
I'm wondering if there have been any follow-up articles on the topic of what brought our climate back out of Greenhouse Earth periods. I haven't read through the entire comments section yet, so sorry if this has already been addressed.
[JH] You may also want to try using the SkS search engine to identify articles that address your topic of concern.
dvaytw, you would need to be a bit more specific about which events you have in mind. keysersoze's comment at 70 was pretty vague, but I suspect he meant the Paleocene-Eocene Thermal Maximum (PETM), in which case the recovery wasn't nearly as rapid as he suggests, according to Wikipedia (yes, I know) the Earth cooled again over a period of 120,000 years which is not at all brief in relation to the 800 year lag time in the question. A timespan of 120,000 years is a bit brief to be fully explained by weathering, but not by a huge amount.
The other problem with keysersozes question is that the existence of feedback does not necessarily mean that there is runaway feedback. In the case of the carbon cycle, equilibrium temperatures rise only logarithmically with rising CO2 (which is slow), but the rate at which the oceans degass goes up linearly with temperature, so immediately there is a case of diminishing returns. Also the solubility of CO2 in the oceans increases with increasing atmospheric concentrations, which makes it progressively more difficult for CO2 levels to rise substantially naturally (other than due to volcanos or methane releases etc.). The positive and negative feedbacks involved keep the carbon cycle quite well balanced unless perturbed by some external forcing. These positive and negative feedbacks tend to bring the carbon cycle back into line automatically if left alone.
Dikran, thanks... that was exactly what I needed. Can you point me to a good online source to read more about this particular topic?
Also, a couple clarifications, please. When you say "temperature only rises logarithmically with CO2", does that mean that the rate of warming per CO2 concentration actually decreases as concentration increases? (I know this is a dumb question... sorry!)
About ocean solubility increasing with atmospheric concentration, is that also affected by temperature?
Finally, to JH: I apologize if I appear lazy in not using the search engine; however the problem I often find is in properly wording the inquiry and in searching through extraneous links. People are often better at pinpointing what you want and getting you the answer with minimum hassle. I spend a lot of time in these debates, and I try to minimize the time I spend on research as much as possible for obvious reasons (IE, no one's paying me!) That said, I feel I've learned so much about the topic in recent years maybe I should start working towards a degree!
dvaytw, yes the rate of warming per unit CO2 does indeed decrease with increasing CO2 concentration, which is why equilibrium climate sensitivity is usually presented as the temperature rise for a doubling of CO2, rather than for a fixed increment.
CO2 solubility in the oceans is sensitive to both temperature and the difference in partial pressure of CO2 between surface ocean and atmosphere (Henry's law). Fortunately the difference in partial pressure is currently a stronger influence than temperature, which is largely why atmospheric CO2 has only been rising at half the rate of anthropogenic emissions.
David Archer is a top scientist working on the carbon cycle, and has some lectures etc. on his website that are well worth watching. He has also written a nice primer on the carbon cycle (see also his papers via google scholar).
Isn't CO(2) currently leading temperature and doesn't this reversal of temperature leading CO(2) to CO(2) leading temperature a strong indicator that current global warming is human-caused? If this is true, why do we need such complicated explanations of past natural changes to justify current conclusions about AGW? Why isn't this reversal of which initiates the feedback loop a major indicator that the current situation contrasts with natural climate change because it is human-caused?
So...exactly why on all of these previous cycles where according to the author the sun precipitated a feedback loop causing the ocean to release carbon which then increased the warming so that the ocean then released more carbon...did temperatures begin to drop just as the carbon level was peaking? As documented here, the level of carbon lagged, so just as it was reaching record highs on each occasion temperatures began to drop of their own accord (because of some set of not yet understood mechanisms), but there is no reason given by the author as to why that was the case.
Why has the runaway catestropic disaster scenario never unfolded before, where the rise in carbon would trigger warming to the degree that permafrost melts, adding methane, more warming, more carbon release from the oceans, ecetera, until the earth boils itself into a dry wasteland...?
Something, or likely a whole host of things, have been obviously keeping it in check.
dwm, the oceans do not give up their stored energy immediately. As Milankovitch cycling moves toward cooling, the surface layers may cool and increasingly absorb CO2, but warmer (relative to glacial conditions) water will continue to upwell for quite a while and prevent the kind of carbon uptake one might naively expect to see with a significant drop in insolation.
The "runaway catastrophic disaster scenario" hasn't happened before--and is not happening now (and no one but builders of straw men is saying so)--because conditions are not conducive. Yes, there are limiting factors. The logarithmically decreasing ability of additional GHGs to increase global energy storage is one limiting factor. The slightly spheroid shape of the planet we're on is another. Continental positioning is another. The general circulation regime at any given time is another. There's more here.
All the data shows is that as temperature increases, the oceans breath out co2, then as temperatures decrease, they inhale and store it until it heats up again. According to what I've read, the humidity data (NASA's UARS satellite data for instance) doesn't support the basic requirement (constant humidity levels) of the theory of self limiting feedback loops described in the link you provided. This is a large grey area, and without reliable data regarding humidity, theories about the positive feeback loop caused by water vapor are no more likely than any other theory. For now, the apparent decrease in humidity explains the more recent cooling of the past decade, and points to what one would expect to find: the existence of an as yet unexplained mechanism that prevents small changes in atmospheric composition to have large positive feedback (runaway) effects.
Except that we know that the oceans are not the source for the ongoing rise in atmospheric CO2.
Starting with an erroneous premise, as you do here, leads you further into error.
The data on this page shows co2 rising after (lagging, as in the title) temperature rises, and vice versa. That's "all we know." I didn't say "the" source, the data shows that the oceans are a source. The data on this page is a historical record going back thousands of years and has nothing to do with anthropogenic co2 production. Your erroneous reply avoids the point of what I wrote: that "without reliable data regarding humidity, theories about the positive feeback loop caused by water vapor are no more likely than any other theory." The current climate models predicting catestrophic rises in temperature rely on humidity levels to remain constant in order to trigger a positive feedback loop from the water vapor in the atmosphere, however the most recent data suggests humidity levels are falling, or in other words, from NASA's website:
" Since water vapor is the most important heat-trapping greenhouse gas in our atmosphere, some climate forecasts may be overestimating future temperature increases. "
http://www.nasa.gov/vision/earth/lookingatearth/warmer_humidity.html
To make my point completely clear, also from the NASA article:
"Using the UARS data to actually quantify both specific humidity and relative humidity, the researchers found, while water vapor does increase with temperature in the upper troposphere, the feedback effect is not as strong as models have predicted. "The increases in water vapor with warmer temperatures are not large enough to maintain a constant relative humidity"
[TD] An appropriate place to discuss water vapor is What Does the Full Body of Evidence Tell Us About Water Vapor?
Anybody who replies to dwm about this topic in future, please do so there, not here.
dwm wrote "All the data shows is that as temperature increases, the oceans breath out co2, then as temperatures decrease, they inhale and store it until it heats up again."
This is basically true, but only if temperature is the only thing that is changing. An important feature of the science that is missing here is that the uptake of CO2 into the oceans is also governed by the difference in partial pressure between the atmosphere and the surface ocean. If the amount of CO2 in the atmosphere increases, the solubility of CO2 in the oceans also increases. Fossil fuel emissions have caused atmospheric CO2 concentrations to rise, which in turn has resulted in a strengthening of the oceanic sink. The fact that atmospheric CO2 levels have only risen at about half the rate of anthropogenic emissions shows that the effect of the change in the difference in partial pressure dominates the effect due to the increase in temperature.
Thus, as Daniel correctly pointed out, we know for sure that the oceans are not the source of the post-industrial rise in CO2 (in fact the oceans have been opposing the rise by taking in more CO2 than it emits).
The water-vapour feedback mechanism seems to be off-topic for this article, so if you want to discuss that, please take the discussion elsewhere on SkS.
dwm, I replied to you on an appropriate water vapor thread.
I didn't bring up water vapor, I was replying to DSL, who first referred to the water vapor feedback loop by referring me to a link.
To Dan & Dikran: As I pionted out, the chart we are discussing here goes back 400,000 years and recent history is basically not visible on this scale, so human activity has no bearing on this chart of the lag of co2 levels relative to the earth's temperature. I don't know why you keep bringing that up. Dan either doesn''t understand that or deliberatly tries to misinterperate what I wrote.
Meanwhile, his patronizing attitude ("Starting with an erroneous premise, as you do here, leads you further into error") is wildly off base.
I'll say it again: The chart above shows clearly that more Co2 is given off by the ocean after temperatures become warmer, and less co2 after temperatures become cooler. As Dikran pointed out, there is absolutely nothing erroneous about that. Since man's injection of co2 into the atmosphere has nothing to do with this chart, the only relationship on display is that as the earth's temperature rises, the oceans give up co2, and as temperatures cool, the ocean responds by absorbing co2. Despite the scientific equivilant of wrangling and wringing of hands, this chart is nothing other than a clear representation that co2 is not driving anything historically. Since you admit to the fact that the amount of solar radiation the earth receives is variable/cyclical, why assume anything other than that (solar) for the changes in temperature, which then cause co2 to go up or down accordingly? Often in science, complex theories are built up to support a set of assumptions that are later shown to be wrong. It seems to me that a lot of effort is going on to retrofit data sets to fit theories about co2 as a primary driver of climate, and that this article is a prime example.
[JH] Please lose the condescending tone.
dwm - your chart is about what happened in the past in response to solar forcing changes. You won't find anything in any IPCC report that contradicts that. While extremely valuable to understanding climate, it is however not so relevant to the present situation.
1/ You cannot explain the glacial cycle by change in solar alone and albedo. For a start, SH and NH cycles would be antiphased. CO2 is operating as both a feedback and a forcing agent in that cycle. First the changes in solar, but this is then amplified and globalized by GHGs.
2/ If current warming was due to milankovich cycle, then we should be slowly cooling and CO2 dropping. If due to change in sun, then why warming when TSI (measured directly) is stable (see the Its the sun argument).
3/ The change in CO2 in the atmosphere is not from the ocean. The isotopic signature among other things tells you that. Actually the oceans are still absorbing nearly half of our emissions. They will continue to absorb for possibly hundreds of years more before temperature rise causes outgassing.
Science theories have to work with all of the data available not just that which works for a simple explanation. The idea that climate change this time is a natural cycle does not fit the data. It also violates the physics of GHG. And to quote a well known analogy, just because forest fires occur naturally doesnt mean arson cannot happen.
dwm, for details supporting scaddenp's comment, watch Richard Alley's lecture "The Biggest Control Knob: Carbon Dioxide in Earth's Climate History."
dwm, please focus on the purpose of this original post. It is to rebut the denier myth that human-caused CO2 rise cannot cause warming, because CO2 rise always only follows temperature rise, as seen in these de-glaciation episodes. This original post successfully rebuts that myth, by showing that CO2 rise was followed by temperature rise. The fact that that CO2 rise was a consequence of a previous temperature rise is irrelevant to rebutting that myth.
By the way, for more details of the mechanism of deglaciations, read the post about Shakun et al.'s 2012 paper.
To scaddenp:
1.this is not the "appropriate place" to debate de-glaciation.
2. the continuous re-referencing of this one website for all of the answers is suspect. I would suggest finding a few other sources in order to seem credible.
3. According to the article above (to quote this website) - "as ocean temperatures rise, oceans release CO2 into the atmosphere"
Just because there is a fire doesn't mean it's arson.
[JH] Please lose the condescending tone.
Tom - the repeated use of the phrase "denier myth" shows complete bias not conducive to scientific discussion, so I would suggest that you refrain from such inflammatory rhetoric.
By the way, this is not the "appropriate place" to debate de-glaciation.
[JH] Please lose the condescending tone.
dwm. This site exists to point readers to what the science actually says about "denier myths" - ie stories being told by people who are in denial about the science is actually saying. I do not think it encourages good debate by labelling people as "deniers" or "warmists" but the myths are what they are.
As such, it is especially appropriate when talking about myths to reference this site because considerable efforts goes into the articles to collect the appropriate science papers about a subject. The whole point is that you dont have to rely on the site - from an article you can go and read the referenced material. Having found the papers, you can put them into Google Scholar to see cites and other discussion.
1/ I did not talk about deglaciation - I talked about the entire aspect of relations between glacial cycle and CO2 which is necessary if you want understand the CO2/temperature relationship in past climate. If you do not understand that then you are not equipped to understand modern relationships.
2/ Read the references there instead. I dont know a better collection of reference material so naturally I point to that.
3/ Absolutely - and as the lag shows, it takes a long time to warm an ocean to the point where that happens and its not some mystery - you pump the numbers into Henry's law plus ocean-mixing rates. Fortunately, we dont have to worry about outgassing this century. The isotopic ratios cannot be ignored however. We are responsible for the extra CO2 in the atmosphere.
And no, fire doesnt mean arson - you instead weigh all the evidence and see which fits the observed data. The sun isnt causing it. The CO2 is not from the ocean. The energy imbalance matches the GHG calculations. There is more backradiation heating the earths surface. The data fits what is more obvious - the tons of fossil fuel we burn is trapping more of the sun's heat at the surface.
dwm, I'll ignore your attempts to irritate by use of phrases such as "Despite the scientific equivilant of wrangling and wringing of hands,", which strongly suggest you are not really interested in the answers to your questions and answer them anyway:
"this chart is nothing other than a clear representation that co2 is not driving anything historically."
For the last 400,000 years, excluding the post-industrial rise in CO2, this is essentially true, because CO2 has acted as a feedback mechanism, rather than a forcing, which is what the article actually says, if you bothered to read it. Note the first line is "CO2 didn't initiate warming from past ice ages but it did amplify the warming.".
However, "history" (I use inverted commas because history doesn't go back 40,000 years, never mind 400,000) goes back rather further than 400,000. This paper for instance discusses the possibility of climate change in part induced by a reduction in atmospheric CO2 as a result of increased chemical weathering following the uplift of the Tibettan platueau in the Cenozoic era. There is also the example of the Paleocene-Eocene Thermal Maximum, where rapid climate change ocurred most plausibly as a result of increases in greenhouse gasses. So your conclusion is incorrect, CO2 has "historically" acted as both a feedback and a forcing, although over the interval covered by the chart it is only acting as a feedback.
"Since you admit to the fact that the amount of solar radiation the earth receives is variable/cyclical, why assume anything other than that (solar) for the changes in temperature, which then cause co2 to go up or down accordingly?"
Because the changes in solar forcing due to Milankovic cycles are far too small to explain the observed changes in temperature. You would know this, had you actually read the article above. "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. "
"Often in science, complex theories are built up to support a set of assumptions that are later shown to be wrong. It seems to me that a lot of effort is going on to retrofit data sets to fit theories about co2 as a primary driver of climate, and that this article is a prime example."
This is deeply ironic, given that you obviously didn't read the article, but drew a stong conclusion which is at odds with that of the scientists who have actually studied this topic in detail.
To Scaddenp: (-snip-).
(-snip-)?
1. de-glaciation is no more relevant to this thread than the water vapor feedback loop, for which I was scolded for answering someone else about after they brought it up.
2. (-snip-).
3. In no way did I ever imply that co2 contributed by man does not contribute to warming. We should all know, however, that it would not contribute to much more than 1 degree celcius of warming this century by itself without any feedback loop from water vapor, so to suggest otherwise would be disingenious.
[DB] Inflammatory tone snipped (twice), link to fossil fuel shill site snipped.