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CO2 lags temperature - what does it mean?

What the science says...

Select a level... Basic Intermediate

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)

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 trigger the initial warming (starting approximately 19,000 years ago), which is first reflected in the the Arctic.
  • This influx of fresh water then disrupted the Atlantic Ocean 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.
    The warming Southern Ocean then released CO2 into the atmosphere starting around 17,500 years ago, which in turn caused the entire planet to warm via the increased greenhouse effect.

Shakun Fig 2a 

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

Last updated on 15 April 2014 by dana1981. View Archives

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Related Arguments

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).

Climate 411 have a succinct explanation of the Greenhouse Effect.

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

Comments

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Comments 251 to 300 out of 442:

  1. Poptech@253 I agree, E&E *is* a peer reviewed journal; the problem is that the peer viewiew at E&E regularly fails and publishes papers with obvious gross errors (e.g. Beck). As a result, the journal is not very highly regarded, the papers it publishes are not widely cited and it has a low Impact Factor. That doesn't mean papers are wrong just becuase they are published in E&E, they stand and fall on their won merits.
  2. Funny (but unsurprising, going by past form) to read Poptech 'correcting' others (this time Scopus) and telling them the 'truth' as he sees it - just like he did with Pielke Jr when he decided (against Pielke's wishes) to include his papers in his little list of what he believes confirms his own version of AGW 'alarm' - whatever that is.

    No matter. He will believe what he wants to believe and no-one else can tell him otherwise.
    And he does have to do his utmost to defend E&E, because so much of his little list rests on papers from that source, but we can look at some quotes to do with E&E, with links from the same WIKIPEDIA page that Poptech failed to acknowledge :


    "On our Energy and Environment paper from 1999, had we known then how that outlet would evolve beyond 1999 we certainly wouldn't have published there. The journal is not carried in the ISI and thus its papers rarely cited. (Then we thought it soon would be.) We were invited to submit a piece in 1997 or 1998 and we had this in prep and sent it in."
    Roger Pielke Jr again
    (Wait for Poptech to 'correct' Pielke Jr...)


    "Sonja Boehmer-Christiansen[Editor of E&E], a reader in geography at the University of Hull, in England, says she sometimes publishes scientific papers challenging the view that global warming is a problem, because that position is often stifled in other outlets. "I'm following my political agenda -- a bit, anyway," she says. "But isn't that the right of the editor?""
    Chronicle of Higher Education, 4 September 2003


    "Plimer repeatedly veers off to the climate sceptic's journal of choice, the bottom-tier Energy and Environment, to advance all manner of absurd theories: for example, that CO2 concentrations actually have fallen since 1942."
    Michael Ashley, Professor of Astrophysics at the University of NSW
  3. Poptech@256

    My opinion on E&E's reviewing standards has been formed by reading many of the papers published there that have been actively discussed. Many of them are badly flawed. If your opinion differs, that is fine, but if you want to change my mind on this, what is your evidence that the standards are as high as any other journal?

    As to Beck, the fact that refutations were published (with rejounder from Beck) is a confirmation that the peer-review failed. If a paper contains an error bad enough to warrant correspondance it should have been picked up by the reviewers and it shouldn't have been published (in that form) in the first place.

    Impact factor is not subjective in any way, it has an objective mathematical defintion. It may be discredited in the notes on your list, but gven that you have just demonstrated that you don't know what an impact factor actually is, it devalues your critique somewhat.
  4. Well, rather than go round and round in circles once more, all I have to do to kill two birds with one stone (so to speak) is this :

    50 YEARS OF CONTINUOUS MEASUREMENT OF CO2
    ON MAUNA LOA, by Ernst-Georg Beck, ENERGY &
    ENVIRONMENT, VOLUME 19, No. 7 2008

    (I can only find the full paper on ICECAP.US, so I won't link to it)
    (Note also that I have copied the title, etc. straight from the source - I am not shouting !)

    The above paper suggests that CO2 levels were 400ppm in 1942 (i.e. they were higher than they are now), and this paper appears in a certain little list.

    Now, does this mean that CO2 lags temperature, according to this particular paper ? Or has CO2 been falling while temperatures have been rising ? Or temperatures will soon be falling, to follow the so-called fall in CO2 since 1942 ? Or what...?

    Can we trust this paper or anyone who uses it to try to claim...whatever they're trying to claim ?
  5. PS The above paper has already been seen-off in the following Skeptical Science thread :

    The Dunning-Kruger effect and the climate debate

    Perhaps that would be the best place for any replies or further discussion, especially comments that would highlight that effect ?
  6. THIS IS the science.
    From the US Government National Academies of Science.
    NOAA Paleoclimatology is a branch of NOAA's National Climatic Data Center
    click here
    Temperature/CO2/Solar chart. And the truth of the ridiculous notion of man caused.
    There are no longer ANY authoritative sources that state that man caused global warming is significant. ALL state it contributes. DUH. As one tree rots it contributes too. Additionally as the oceans warm, significant amounts of CO2 are absorbed starting the glacial cycle.
    click here
    Earth has its equivalent to the human immune system. It has healed itself for billions of years. At some point, the powers that are getting us to beg them to spend trillions to stop the earth's natural inter-glacial cycle, will be getting us to beg them to spend trillions to stop the glacial cycle.
  7. @263 stephenwv

    Do you realize that neither of those links support your claims. In fact they show the opposite of what you are claiming. Must be the Monckton effect.
  8. Stephenwv,

    From your link:

    "As the ice-core data show, the increase in carbon dioxide is unprecedented and well outside the range of natural variations. The recent increase matches the increase calculated from the fossil fuel emissions."

    That would mean the CO2 you believe is due to natural cycles is, in fact, anthropogenic.

    " Additionally as the oceans warm, significant amounts of CO2 are absorbed starting the glacial cycle"

    As oceans warm CO2 is released, not absorbed. Furthermore we're not at the beginning of an interglacial, we're roughly in the middle, so natural forcings are for the most part on the cooling side. But we aren't seeing cooling are we? We're seeing an abrupt spike that just happens to perfectly coincide with the industrial revolution.

    You need to calm down and try to understand the terminology involved. Of course authoritative sources say anthropogenic CO2 contributes (contribute in this context means 50-90% by the way). Land use changes also contribute, and that is also anthropogenic. No scientist is going to say CO2 is entirely at fault without including uncertainty in the mix.

    Science is inherently conservative, not alarmist. This is why data over the last two years indicates climatologists have been understating the problem.
  9. @ stephenwv (262)

    Welcome to Skeptical Science! There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions. That's why we recommend that Newcomers, Start Here and then learn The Big Picture.

    I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history.

    Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (given the plethora of posts [I get paid extra for using big words and alliteration :-) ] odds are, there is). Or you can search by Taxonomy.

    I'm afraid the vast majority of your comment is simply incorrect. The warming of the globe is an accepted fact. That humans are causing a good part of it is accepted at over a 90% scientific certainty level.

    Only the anthropogenic contribution (which did not exist in the paleo record) completes the picture, explaining the warming we can empirically see and measure in the absence of other forcings. Else we would be measuring a decades-long cooling trend. Which we aren't:



    Forcings, except for CO2, have been flat for nearly 40 years. Temperatures continue to climb, and that rate of climb is still increasing (as are CO2 levels).

    Hope that helps,

    The Yooper
  10. The second quotation in my previous post is from Stephenwv, not from his link. Sorry I didn't make that clear.
  11. It is undeniable that we have yet to reach the 100,000 year interglacial temperature peaks. CO2 is constantly absorbed and released from the oceans and is the obvious simultaneous prime emitter and absorber of CO2.
    Who would like to address the statement that so far you ignore: "WHAT IS GLOBAL WARMING DOING TO THE OCEANS? It's raising the oceans' temperatures ever so slowly, but also, it's making it easier for the ocean to absorb carbon dioxide (CO2). Large amounts of CO2 are absorbed by the ocean, up to a million tons an hour worldwide." click here
    At some point (as it has been shown else where on this site), the amount of CO2 emitted decreases and the oceans begin to absorb more than is emitted by the oceans and created else where on Earth. Thus the glacial period begins in the natural 100,000 year reoccurring cycle. Hundreds of thousands of years ago, the more prevalent volcanic eruptions emitting vast amounts of global warming gasses appear to have been naturally remedied by the Earth as well. To deny that we will enter into a glacial cycle is ludicrous as I'm sure you would all agree.
    Those that would attempt to prove man caused as a significant problem go to extreme lengths to re-categorize CO2 emissions. As just one example, adding a lack of CO2 absorption due to deforestation while ignoring reduction of CO2 emission of rotting materials as a result of deforestation.
    Then statistically choosing the time frames to allow the data to fit the conclusion.
    The vast majority of the data and statements made here totally disregard recent studies that have shown a much greater correlation between temperature change and sun activity, than exists between temperature and CO2 levels in the short term.
    The isolation of data types, time frames, thus ignoring the over all picture to fit the desired conclusion, are the studies that are being funded and pushed by the special interests.
    The statement that cap and trade costs would not significantly cause any economic problem is the same sort of isolation tactic, ignoring the increased cost of business compliance, costs passed on to the consumer, taxes to fund the grants for alternative energy solutions, the higher costs associated with alternative power generation, the taxes required to support the added bureaucracy required to regulate, enforce, and other wise administer policy, etc.
    For the economic impact, all admit that increased consumer spending is required to drive the economy. The private sector jobs supply that consumer spending. No matter how the consumer is downsized, taxes, or increased costs for goods and services, it hurts the economy. If increased government spending and jobs were real jobs, Greece would be a thriving economy.
    The macro picture tells the real story. The micro spin creates the hysteria to get the masses to beg government and special interests to take our money.
    Response: [Daniel Bailey] Sigh. That's a pretty impressive Gish Gallop. I must remind you of the Comments Policy: your above comment violates it in many ways. On the chance you are just genuinely under-informed, I'll leave this up here for a while. If anyone wants to reply to this, please do so one one of the many more appropriate threads than this one. Thanks in advance!
  12. Are there actually any verifiable facts in stephenwv's post ?
    No doubt it will soon disappear into the ether of denial...
  13. What facts would you like verified?
  14. Stephenwv,
    Another new poster was greeted (by DB)with this:
    "Welcome to Skeptical Science! There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions. That's why we recommend that Newcomers, Start Here and then learn The Big Picture.

    "I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history.

    "Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (given the plethora of posts [I get paid extra for using big words and alliteration] odds are, there is). Or you can search by Taxonomy.

    "I'm afraid the vast majority of your comment is simply incorrect. The warming of the globe is an accepted fact. That humans are causing a good part of it is accepted at over a 90% scientific certainty level."

    Me again:
    Here at Skeptical Science we like to review Scientific Data. If you want to convince anyone that what you have to say is worth listening to you need to cite documented facts and provide links to the data. Your opinion or recollections will not do (mine are no good either). Please read and become informed on the facts here. Post your questions individually in the appropriate locations. A laundry list of objections is not useful. Have fun.

    Did someone post a link to this thread on WUWT?
  15. Stephenwv,
    Sorry, I did not realize that DB was greeting you before with my quoted material. The links are above at 265.
  16. #264
    how can you possibly say "we're not at the beginning of an interglacial, we're roughly in the middle, so natural forcings are for the most part on the cooling side" when both the reference I presented and the chart at the beginning of this blog both clearly show time frames and temperature levels consistent with past end of inter-glacial periods?
    Then your statement "As oceans warm CO2 is released, not absorbed." totally ignores the second referenced statement from another scientific government web site. (see my links at #262) Additionally you state "That would mean the CO2 you believe is due to natural cycles is, in fact, anthropogenic." In no way do I state such a belief! In fact i do not disagrees that it contributes. The government site statement that 1 million tons of CO2 are absorbed an hour, considering the UN Global warming commission (after scrambling to dig up adjustments to their 1990's statement of 8 million tons of man caused) now blames man for contributing 40 million tons of CO2 per year, 40 hours worth of oceanic absorption, which of course, does not include absorption that is land based, hardly an argument for a significant man caused problem, especially considering that government site states that ocean warming is "making it easier for the ocean to absorb carbon dioxide (CO2)."
    Now I admit I have been unable to find the studies that the National Science Academies' web site statements base their statements on. It was difficult enough to find the telling statements of the ignored and hidden information of the hugely significant absorption rates that exist. Obviously there are interests that would prevent this data from being available or it would be easily found. In fact I think someone probably lost a job by including that statement in attempting to pose it as a negative factor in the over all statement about increasing levels of CO2 in some parts of the ocean.
    One must be able to pull information from different studies which have differing data sets and time frames to step back for the overall picture. This site, and many other limited data set/time frame sites and arguments, are seen as, and are being referenced by the average public as proof how significant man caused global warming is. Which of course they are neither intended to do that nor do they do that. But they assist in the spin that creates the public hysteria.
    The primary question of this blog, CO2 lags temperature, in any time frame, some times does some times does not. So the that CO2 lags Temperature is false just as CO2 leads temperature is false. The truth is there is a correlation, but recent studies have shown that sun activity is more highly correlated to short term temperature changes, and even 23,000 year time frames, than CO2 levels.
    Response: You're making multiple, separate claims, that have different "Argument" pages on this site. You need to split your comment up, putting each comment on the appropriate thread. For example, the fact that we are in the cooling phase of the glacial cycle is based not on the current temperature but on the orbital cycles, which is described and needs to be commented on in the Argument page "We’re heading into an ice age." Don't worry about your comments on other threads being missed, because most people watch the Recent Comments page. Also, you should read all the comments responding to your comment, before commenting again. Several folks have pointed out that you have interpreted your linked sources backwards.
  17. stephenwv (#272)
    "One must be able to pull information from different studies which have differing data sets and time frames to step back for the overall picture."

    There is a tread on this site (linked on the front page!) named The Big Picture. Breaking the evidence down into discrete chunks allows for far more detail than in a more holistic approach. It also makes those chunks easier to find. Suffice to say that the whole is equal to the sum of the parts.

    Would someone care to clarify the points about ocean warming and CO2 release/absorption? As I understand it Ocean Acidification indicates increased CO2 absorption.
  18. #267: You've scrambled up quite a lot, so I'll try to go point by point.

    "the statement that so far you ignore" See this thread on ocean acidification, which actually one of several. So it is not ignored.

    Ocean acidification is a bad thing, indicating that atmospheric CO2 is being absorbed -- and the atmospheric concentration is still going up. That demonstrates how much of an impact we have on the environment. See also the very detailed thread on Physical Chemistry of CO2.

    "Thus the glacial period begins " You seem to be implying that glacial stages are initiated by CO2 changes; most look to the well-known orbital cycles to start the slip towards cold.

    "Those that would attempt to prove man caused as a significant problem" See the thread Human CO2 is a small % or Its not us for the proofs.

    "disregard recent studies that have shown a much greater correlation between temperature change and sun activity" No one here disregards the sun. See the thread It's the sun.

    I could go on, but you should already see that most of your objections are addressed in specific terms on other threads. All one can ask of you is that you find the appropriate threads, read the post and accumulated comments and then reevaluate your opinions based on what you learn. Comment on the appropriate threads. You'll find it slow-going at first, but you will learn a lot if you make the effort. That will create a more productive discussion than a mere rant.


    #272: "This site, and many other ... sites ... are being referenced by the average public as proof how significant man caused global warming is." I wish that were true.

    "But they assist in the spin that creates the public hysteria." Now that's problematic and indicates you haven't looked around much. SkS deals in science; far more spin originates at denial sites.
  19. stephenwv, I've replied to your comment over on the ocean acidification thread. This is how we move conversations from inappropriate threads to appropriate ones without losing any readers along the way.
  20. stevenwv wrote : "What facts would you like verified?"

    Well, let's start with the first paragraph of that previous post of yours :


    "It is undeniable that we have yet to reach the 100,000 year interglacial temperature peaks."


    What figures/data can you link to, to show those "undeniable...100,000 year interglacial temperature peaks" ?
    You can reply on the following thread : Are we heading into a new ice age ?



    "CO2 is constantly absorbed and released from the oceans and is the obvious simultaneous prime emitter and absorber of CO2."


    What figures/data can you link to, to show the oceans currently being "the obvious simultaneous prime emitter and absorber of CO2" ?
    You can answer on : CO2 is coming from the ocean
    Response: Stephen, when JMurphy wrote "you can answer" on specific other threads, he/she really means you must, or your answer likely will be deleted from this thread, where your answer would be off topic.
  21. Thank you for the references. I have been frustrated in my attempts to find any real answers to my questions. Especially the apparent flattening of temperature for the past few thousand years as opposed to the normally rapid drop off; and the lack of the elimination of the northern ice cap as has occurred in past end of inter-glacial cycles. Hopefully there are answers here somewhere. Any suggestions?
  22. #277: "the apparent flattening of temperature for the past few thousand years"

    This statement has no obvious meaning to me. As I asked on Are we heading into an ice age?, please define what you mean - use that thread and provide some source for this notion.

    Off topic comments have a way of disappearing, especially after several attempts at re-direction.
  23. Muon,

    I believe he's referring Figure 1, where the peak of the current interglacial appears more extended along the x-axis than the previous interglacials, which look more like a sudden increase, and an equally sudden decrease.

    I assumed this was due to greater resolution the closer we got to the present.
  24. Re: Interglacials

    Just because the ice core records show an apparent periodicity and rhythm to the interglacials, it would be a mistake to assume that they are created equally. Milankovitch forcings do vary, as does solar output and a plethora of other variables. The most recent interglacial could also have been affected by mankind to some degree as well (Google Ruddiman's Hypothesis).

    Key takeaway: interglacials happen during a glacial epoch for known reasons, but each differ from the others as they are but a sum total of forcings and feedbacks that can individually differ over time.

    The Yooper
  25. The key reference for length of current interglacial is Berger and Loutre 2002. In a nutshell, it the result of the particular orbital configuration at present.
  26. Tell me if I have this right...

    The 100,000 Milankovitch Cycles are the result of eccentricity of the Earth's orbit.

    So, interglacial periods, like the present, occur when the planet is closer to the sun.
  27. The 100,000 cycle is problematic. See here for some more discussion. I'd say the jury is till out.
  28. Responding from here

    The newtonian gravity situation is an n-body body, so quite definitely deterministic chaos. However, the milankovitch cycles are predictable, regular cycles at the time scales we are talking about (whether you could extend 100my back is entirely different).

    However, what you think of a chaotic signal is not - the spectral analysis gives that away. Set up a spreadsheet with
    =R*sin(a*A1]) + S*sin(b*A1) + T*sin(c*A1)

    where R,S,T are within an order of magnitude and
    a,b and c are not multiples of each other, and you get an utterly non-chaotic,predictably cycle but no repeats.
  29. scaddenp,

    Perhaps I'm doing it wrong. I tried (1.1*sin(2*x) + 2.2*sin(3*x) + 3.3*sin(5*x)) but what I get seems to repeat at intervals of 2*pi (minus a precision error on the order of 1e-15 or so).

    The reason I asked about these things is that if the clockwork Milankovitch cycle were the only driving force behind the ice ages, then I would have expected each ice age to be identical. As mentioned in the other thread and here, I guess it's not that simple -- there's continental drift, plants, asteroid strikes, volcanic activity.

    As far as I can tell from what people are saying here, these extraneous forces that give the jagginess to the above temp/CO2 plots are considered to be random, not chaotic. I can buy into their reasoning, though I doubt I'll ever do so wholesale.

    Thank you for the info!

    - Shawn
  30. Well a,b,c is no. of cycle repeats in 2*pi! Try
    say =(0.3*SIN(0.00006283*B1) + 5*SIN(0.000299199*B1) + 2*SIN(0.000153248*B1)) (which has frequencies around the milkanovich). Note no phase terms either. Now you have peaks of different size and magnitude but a very long time before they repeat (I graphed say from angle 0.01 to
    710000).
    However, I agree though that the cycles are the major driver, a lot of other factors play as well, and yes, random, not chaotic.
  31. Since we have accepted the fact that atmospheric CO2 concentration is a primary driver of the earth's climate and also the fact the the earth has been much warmer in the past this presents a dilemma.

    The oceans contain about 50 times more carbon dioxide than does the atmosphere. It has been well noted that warming oceans release more of their absorbed carbon dioxide than they at the same time sink from the atmosphere.

    So remembering that atmospheric carbon dioxide concentrations are the primary driver of our climate any previous warming in excess of what we see in modern times should have driven a runaway warming cycle, driven by massive releases of oceanic carbon dioxide in a positive feedback loop.

    But somehow this didn't happen. I wonder why?
  32. A positive feedback does not necessarily mean runaway feedback. See run away warming
  33. 287: Bruce,

    A couple of misconceptions in your comment: CO2 is not the only driver of climate. It happens to be a strong positive forcing now; that does not mean it always was.

    Oceans are acidifying, meaning they are absorbing CO2 from the atmosphere. At some point (or perhaps at some locations) they will warm sufficiently to release dissolved CO2.

    As always, the picture is more complicated than one can sum up in a sentence or two.

    There is a wealth of information here at SkS designed to inform and dispel some of the myths, half-truths and outright distortions that kick around the internet. Use the Search function to browse the most commonly heard 'skeptic arguments.'
  34. This is continuation of argument in another thread.

    RW1 - Yes, I'm arguing the evidence doesn't support that GHGs (i.e. CO2 levels) are a significant factor in the glacial/interglacial cycle.

    Firstly, Timothy Chase (and the intermediate version here) challenges the idea evidence doesnt support it. Solar + albedo doesnt produce the same curve shape. Likewise how does NH change alter the SH as well?

    Second, this is an idea that only works without the maths. Like the idea that sealevel rise is due to more people and that they are obese. The change in DLR for the change in GHG can be calculated and the change in albedo can also be estimated. See the IPCC WG1 Chpt6 for the values of these forcing and source papers. Are you suggesting the albedo forcing is greater or DLR less? What papers support this? Actually the convincing evidence would be a physics-honouring model that can do it without GHGs but noone's been able to do that to date and they have been trying since Milankovitch.
  35. SOMETHING has buffered global warming at the apex of every interglacial warm period for the last 2 million years. Otherwise we would have reverted to the so called greenhouse climates that have dominated earth history.It would be really nice to know what that SOMETHING is.The apparent lag of CO2 behind temperature for the last 800000 years may provide a clue. Temperature has led on both the rapid recoveries where CO2 positive feedback is likely and on the slower declines to ice ages where CO2 may have acted as a brake. Whatever the SOMETHING is, it prevented CO2 from taking control of climate until possibly the last few years.
  36. trunkmonkey, I am not sure I follow. The ice-age is driven by orbital forcings. When the forcing changing to negative, then feedbacks work the other way pulling CO2 out of atmosphere. There is no "run-away" to pre-Pleistocene atmosphere (see here for more on run away feedback). It seems to me that you are postulating an unknown in ice-age model that doesnt exist.
  37. scaddenp, the orbital variations have probably been constant as long as there has been life on earth, yet glacial periods are exceptional in earth history.We're just lucky I guess? The orbital insolation variation is miniscule, on the order of a tenth of a Watt per square meter, and its 100000yr signal matches only rather crudely the glacial-interglacial periodicity.I sense were working a puzzle with missing pieces.
  38. Under "recent" times, CO2 levels have been much higher. Geological processes gradually remove CO2. When CO2 is above a certain level, you dont get a glacial cycle because its always warm enough to prevent ice build up and the feedbacks that amplify the glacial cycle. While the global forcing is very weak, the forcing at 65 is rather stronger. Land and altitude allow ice sheet build up in the NH. The 100,000 cycle IS a puzzle, but the problem (as with a lot of problems in paleoclimate) is not finding a solution but that there are more solutions than the data can constrain. Yes, there are missing pieces but the overall mechanism is understood.
  39. scaddenp: ...the orbital variations have probably been constant as long as there has been life on earth, yet glacial periods are exceptional in earth history.We're just lucky I guess?

    If you are going back pre-Quaternary you need to account for paleo-geography, i.e., continental drift. If you don't have a continental mass at the poles or at least enclosed around a pole as is present day, it is not likely an open ocean is going to freeze. Further consideration would be different ocean circulation and a dimmer sun.
  40. Rick G -
    if you are going back pre-Quaternary you need to account for paleo-geography


    And orography (mountain-building), and the rise of angiosperms (flowering plants). The climate models show some pretty marked cooling when these are accounted for.
  41. 294.

    "the problem (as with a lot of problems in paleoclimate) is not finding a solution but that there are more solutions than the data can constrain."

    Sad but true. The only data that can really constrain anything come from the last sixty years and everything pre satellite is sketchy.

    Paleoclimate is really a logic excercise where you are lucky when the disparate signals from proxies give you a correlation.

    What is unique about the Antarctic ice core data (although the "down under" data point is less than ideal) is that they give us independent signals for both temperature and CO2 at the same time and in the same medium.

    I believe that the clear signal that temperature lead CO2 in these data is an extremely important clue that is not adequately explained by Milankovitch.

    Invoking Occam, we should probably suppose that temperature has lead CO2 for all of earth history, or at the very least in prior glacial episodes.
  42. trunkmonkey @ 297,

    I see a lot of hand waving but not a bit of supporting evidence to back up anything you said.
  43. trunkmonkey - "Paleoclimate is really a logic excercise where you are lucky when the disparate signals from proxies give you a correlation."

    This simply not true. Uncertainty bands gets larger but you will find that alternative theories have to work with quite strong constraints. Suggest you read up on this.

    "I believe that the clear signal that temperature lead CO2 in these data is an extremely important clue that is not adequately explained by Milankovitch."

    And what is the basis of your belief? Certainly not published science. How come models using known physics have little problem with such data?

    As to whether CO2 has always led temperature, possibly but PETM is closer to what we had. Temperature increases will certainly lead to CO2 increases to amplify the effect but if another mechanism (eg burning fossil fuel) will increase CO2, then you still get the temperature rise.
  44. 299.

    "I believe that the clear signal that temperature lead CO2 in these data is an extremely important clue that is not adequately explained by Milankovitch."

    And what is the basis of your belief? Certainly not published science. How come models using known physics have little problem with such data?

    I have read most of the threads on this website and I have not seen many citations. I presume the models you refer to are GEOCARB and GEOCARBSULF (see Berner@"I believe that the clear signal that temperature lead CO2 in these data is an extremely important clue that is not adequately explained by Milankovitch."

    And what is the basis of your belief? Certainly not published science. How come models using known physics have little problem with such data?

    I have read most of the threads on this website and I have not seen many citations. I presume the models you refer to are GEOCARB and GEOCARBSULF. A good synopsis can be found at Breeker et al 2010. If I may be permitted to incorporate herein by reference all of his citations, it will save me a lot of trouble.

    A philosophical question: can a computer model with postulated imputs that successfully match a known phenomenon, but which has never successfully predicted anything, ever be considered to be more than a correlation, or indeed a logic exercise?
    Response: See the Argument "Models are unreliable." And post further comments about that topic over there, not here, please.
  45. 299. PS.

    Sorry, everything went wanky when I tried to paste the Berner citation. I think it is in Breeker anyway.

    I wanted to cite a specific example. Berner, in the failed citation, makes the grand arm waving statement " A large Devonian drop in CO2 was brought about primarily by the acceleration of silicate rock weathering by the development of deeply rooteds plants in well drained upland soils."
  46. Your Honor, I swear I was going to pull this back to temperature precedence, but at your guidance I will move my post script to "models", even though they may be non sequitur there
  47. I'm unfamiliar with paper you are trying to cite. Thanks to colleague who are interested in PETM and want to use my hydrocarbon maturation model to examine sedimentary basin feedback, I have suddenly had to come to speed on PETM. The models I was referring to are GCM-type models used in PMIP. See Ch 6 of WG1 for access to the enormous literature on this. I would readily agree that the relative contributions of various carbon sources and sinks are still uncertain. However, the climatic response response is well captured.

    The main takeaways though are:
    1/ carbon-cycle feedbacks in the SHORT term (1000's of years) amplify the effects (positive and negative) of other climate forcings.
    2/ The CO2/CH4-feedback in the glacial cycle is from ordinary organic carbon.
    3/ The CO2 in the atmosphere today is from fossil fuel sources.
    2 and 3 are evidenced from carbon isotope data.

    Carbon-cycle feedbacks are slow. Most AR4 models ignored them as irrelevant for next 100 years. If this is incorrect, then warming would be worse.
  48. 299.PPS.
    Berner is alledging here that he has some knowledge that there was a lot of silicate (read rhyolitic and granitic)well drained upland rock for the giant Gymnosperms (tree ferns) to sink their roots into 370 Ma. He goes on to alledge that he has somehow tested this in modern soils.
    Assuming for the moment he is correct, this might explain the decent into a glacial epoch, but not the climb out.
  49. Without reading the papers and associated evidence, I cant comment on the reliability of the data. However, as a general rule, anything "paleo" in investigation has to necessarily form an hypothesis based on what we do know and then project back into the past to see if it fits paleo data. A fit gives us confidence that our ideas are not grossly wrong but cant of course "prove" that we are right.

    Since this is a climate blog concerned with the more immediate future of planet, you also need to recognize the significance (and insignificance) of this work. The geological processes at work here are largely irrelevant to climate of next 100 years. However, the predictions for the next 100 year ARE dependent of a model of drawn from physics (not paleoclimate). If this model of climate is correct, then it must also work (within the uncertainities) for paleoclimate.
  50. Also, if you think paleoclimate is more or less unconstrained, invent anything, have a look at Zeebe et al 2009 on difficulties with PETM. (Doesnt begin to address the cause of carbon release but deals with other issues). Needless to say my colleagues think they have a possible solution to the conundrum posed...

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