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CO2 lags temperature - what does it mean?

What the science says...

Select a level... Basic Intermediate Advanced

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

Climate Myth...

CO2 lags temperature

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

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

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

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

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

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

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

Shakun Fig 2a 

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

Last updated on 21 April 2021 by eckahle. View Archives

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Further reading

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

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

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

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

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Comments 401 to 450 out of 636:

  1. 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 researchers obtained their results from a comprehensive computer model, where they combined an ice-sheet simulation with an existing climate model, which enabled them to calculate the glaciation of the northern hemisphere for the last 400,000 years. The model not only takes the astronomical parameter values, ground topography and the physical flow properties of glacial ice into account but also especially the climate and feedback effects.

    Using the model, the researchers were also able to explain why ice ages always begin slowly and end relatively quickly. The ice-age ice masses accumulate over tens of thousands of years and recede within the space of a few thousand years. Now we know why: it is not only the surface temperature and precipitation that determine whether an ice sheet grows or shrinks. Due to the aforementioned feedback effects, its fate also depends on its size.

    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 article linked below.

    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.

  2. 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. 

  3. 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.

  4. Back at #70, the moderator said:

    Response: Good question - I considered addressing this in the original article above but opted to keep things simple and address it in a future post. In the case of Milankovitch cycles, just as orbit changes initiate the warming, they also end the warming. Towards the end of the deglaciation, orbit changes cause the amount of June sunlight falling on the northern land masses to change by several tens of percent (not an insignificant change). Gradually over time, northern ice sheets start to grow again.

    For greater time scales (eg - over millions of years), rock weathering is another factor that keeps the climate regulated. Rock weathering is the phenomenon where CO2 is scrubbed out of the atmosphere by chemical reactions with rock surfaces. As temperatures warm, the rate of rock weathering increases - this acts as a natural thermostat to keep CO2 levels from getting too high. However, this process occurs over millions of years so don't expect rock weathering to bail us out of our current situation (although interestingly, there is research into using artificially accelerated weathering as a technique in sequestering CO2).

    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.

  5. 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.

  6. 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!  

  7. 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).

  8. 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? 

  9. 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. 

  10. 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.

  11. 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.

  12. "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."

    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.

  13. 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. "

  14. 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.

  15. 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.

  16. dwm, I replied to you on an appropriate water vapor thread.

  17. 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.

  18. 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.

  19. dwm, for details supporting scaddenp's comment, watch Richard Alley's lecture "The Biggest Control Knob: Carbon Dioxide in Earth's Climate History."

  20. 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.

  21. 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.

  22. 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.

  23. 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.

  24. 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.


  25. To Scaddenp:  (-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.

  26. dwm wrote "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."

    Has anybody suggested otherwise? 

  27. dwm wrote "This chart was used for years to prove the driving effect co2 has on temperature,"

    This is simply incorrect, the data shown in the chart provides evidence that CO2 is a greenhouse gas that can act as a feedback mechansim (amplifying the effects of orbital forcing).  This is very clearly stated in the article above.

    Nobody is claiming that CO2 forcing DRIVES climate change on that particular timescale, so you are just making a straw man argument.

    "Regarding the variability of solar energy reaching the earth and whether it is sufficient to cause the warming patterns shown in this chart, I disagree."

    Fine, care to provide any evidence to support your disagreement with the scientific mainstream on this one, some calculations perhaps?

  28. (-snip-).  "History", (-snip-), is anything for which there exists a record.  Ice cores make history.

    This chart was used for years to prove the driving effect co2 has on temperature, and only after the accuracy of the dating was improved, showing that the co2 increases actually lagged warming, did explainations such as this article begin to evolve.



    [DB] Inflammatory tone snipped (twice); sloganeering snipped.

  29. dwm, I suspect you are using the refresh or back buttons on your browser, which are resulting in reposts of your previous messages.

  30. I don't know why this board sometimes double posts my posts, some kind of feedback loop?

    Happy reading:

    Using the oceans as a calorimeter to quantify the solar radiative forcing
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, A11101, doi:10.1029/2007JA012989, 2008

    Empirical evidence for a celestial origin of the climate oscillations and its implications

    Journal of Atmospheric and Solar-Terrestrial Physics (2010)
    Solar activity and Svalbard temperatures

    Advances in Meteorology Volume 2011 (2011)


    [PS] Fixed link (I hope)

  31. dwm - the double posting is caused by your use of the refresh and/or back buttons on your browser.

    None of the papers you mention show that solar forcing is strong enough to explain the variations in temperature over the last 400,000 years, specifically the transitions from glacial to interglacial conditions.  If you disagree, give page numbers and direct quotations from the paper. 

  32. dwm - let's see if I can get a clearer understanding of your issue. I believe that you agree with the mainline science in that:

    1/ Increase of CO2 in atmosphere at the moment is due to our emissions though in the glacial cycle it was outgassing from the ocean as temperature warmed.

    2/ That increased CO2 does cause warming (and presumably the corallary that reducing CO2 cools the planet).

    3/ That a no-feedback warming would be about 1 degree but the effect is amplified by feedback (including water vapour but also albedo).

    Then we have the statement: "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?"

    Since you agreed that increased CO2 increases temperature, this is a strange statement to make. You claim "deglaciation" (by which I assume you mean the glacial cycle) is offtopic. However, the relationship of CO2 during the glacial cycle is the topic of this article so, as one of the moderators of this site, it is ontopic. Trust me on this. (However, argument that current climate change is caused by the sun are off topic and go to the topic that I pointed out above).

    So to answer your question, "why assume anything other than the sun...", implies you think the graph excludes CO2 having anything to do with glaciation cycle. Beyond the difficulties in making the numbers work, there are two other reasons for assuming something beyond the sun that I can think of.

    1/ If the glacial cycle is only about change in solar (plus its water vapour and albedo feedbacks), then why are NH and SH glaciations not anti-phased? The CO2 and to lesser extent CH4 are well mixed GHGs which contribute.

    2/ The Milankovich cycles have been around a long time and yet we dont get the big glacial cycle till the Pleistocene. Easier to explain when look at earlier CO2 levels.

    Finally note the in the PETM, CO2 increase preceded warming so closest analogue to the current situation.

  33. An interesting collection of denialist writing being linked @430 (Shaviv, Scarfetta & Solheim-Stordahl-Humlum). I'm not sure what we are supposed to make of them.
    The different ilk of "It's the sun wot done it" messages are together rather contradictory. Shaviv's the one who tries to demonstrate ocean heating has an 11-year cycle, good ole Scarfetta fits global temperature to pretty-much every pulse-beat in the solar system with the one exception of the 11-year solar cycle, and the not-to-be-outdone Humlum in that linked paper fits Svalbard temperatures to the duration of the previous solar cycle.
    And the other puzzle is - What has this collection of tosh got to do with the subject of CO2 lagging temperature? Anybody any ideas?

  34. I asked @433 "Anybody any ideas?" It appears from the comments @ 434, 435 & 436 that dwm's answer to this question is "No. I have no idea whatever."

    This still may not be the definitive answer to my question (dwm has not shown here much skill in providing such answers, even when well positioned to do so), so if anybody else has any ideas, I would be happy to learn of them.

  35. Another naive question, please.  When I come across contrarian arguments in a policy discussion, I try to check the relevant science; about half the time I come away thinking the situation is even worse than I had before investigating.  Here, I knew gas solubility goes down with temperature and Milankovitch cycles are completely different "drivers" from digging up coal from the Carboniferous.  So the "lag" argument just reminds me of the worrying feedbacks from more CO2 leaving the oceans (and from changes in polar albedo).  I presume the oceanic CO2 feedback is not included in Transient Climate Response figures - but is it generally included in ranges of Equilibrium Climate Sensitivity we find in AR5?  (I know I could read AR5 more thoroughly myself, but thought it might be a question in other people's minds.)

    And possibly related to that: some graphs showing temperature before the Cenozoic (the last 65 million years when temps and CO2 have gradually been falling), suggest global temps are "bistable", with a 25 °C hothouse plateau.  Do you know a reason for that or is it an artefact?  (Price et al (2013) does not show the plateau.)  (And sepculation: If it is a real effect, are we possibly going to tip the world into a situation uninhabiltable by humans but where at least most classes of animals survive?)

    Thanks in advance.

  36. Ceddars @435, in answer to your second question, the graph by Scotese that you link to (which is much loved by deniers) is not generated by any proxies.  Rather, scotese mapped different rocks known to be formed in particular climate conditions onto maps of the continents in their arrangement at the given time.  This provides an approximate measure of the width of various climate zones, which are then equated to a temperature.  Thus, Late Carboniferous is shown as having very extensive cold regions at the poles, and is therefore plotted as being cooler than today.  In contrast, the Early Carboniferous has no cold zones at the poles, but rather cool temperate zones.  Consequently it is mapped as warmer than today, but not very much warmer than today.  The Middle Triassic has warm temperate zones at the poles, and is therefore plotted as being much warmer than today, ie, warmer than the Early Carboniferous.

    This is a crude measure of temperature, and consequently only resolves (effectively) four climate states - Colder than today, about the same as today, warmer than today, and very much warmer than today.  That does not mean temperatures were at precisely 25 C, or 20 C, etc.  It only means this method cannot resolve differences in global temperature finer than about 5 C.

    What is more, because this method requires mapping "thousands of rock types", it is not even capable of the normal million year plus minimum resolution found in geology.  Rather, it resolves in terms of fractions of epochs, ie, 10 to 50 million year intervals.  As such it is far inferior to the various proxie based temperature records produced by Dana Royer, both in resolution of temperature, and temporal resolution.

  37. Thanks, Tom.  I'll think of that temperature plateau as an artefact, and look for other proxies.

    My other question remains.  Does it make sense?  Is effect of degassed CO₂ released from warming oceans (a) measurable; (b) a substantial feedback; (c) already included in models?

  38. Cedders - the feedbacks that work with the Milankovich cycle are slow. With around 1000 year cycle time, the ocean's wont be outgassing anytime soon. At the moment, oceans are mopping up much of our emissions (See the OA is not okay series for detail). CMIP3 models did not include carbon cycle feedbacks. I believe that some of the CMIP5 model are "earth system" models with these feedbacks included, but they have little impact on what happens in the next 100 years.

    As to measurable - Ocean pH and isotopic composition of CO2 in atmosphere would both constrain estimates of outgassing.

  39. Cedders @437, when looking for other proxies, Dana Royer's publication page is a wise place to start.  In particular, his 2004 paper with others, uses a dO18 proxy to reconstruct temperatures over the last 500 million years, which is presented below along with the known forcings over that period:

    (The image is from a slide for a talk, and presented in a non-peer reviewed article in 2009, but the reconstruction is from the peer reviewed Royer et al (2004).)

    That reconstruction has better time resolution than scotese's graph, but the time resolution is still restricted.  Consequently Royer (2006), which looks at CO2 concentrations with reference to glacial states at a much higher time resolution is also of interest. 

  40. Ceddars @435, supplemental to Scaddenp @438, IF global temperatures had risen by 1 C without any anthropogenic of volcanic increase in CO2, ocean outgassing would have raised CO2 levels by about 10-20 ppmv.  The increase in atmospheric concentration from anthropogenic emissions is far greater than that, so CO2 has entered the ocean rather than left it.  However, it would have entered it more readilly without the temperature rise, so that if anthropogenic emissions had been the same, but temperature not risen, there would have been about 10-20 ppmv less CO2 in the atmosphere, and correspondingly more CO2 in the ocean.

    The consequence is that the reduced capacity of the oceans to absorb CO2 as they warm is not included directly in transient or equilibrium climate response estimates, they are included indirectly for that effect is included in historical rises in CO2 concentration, and partially and in estimates of future rises.  There is a slight kicker for simple models that use a linear retained fraction of atmospheric CO2, in that the ability to absorb CO2 will fall with further rises in temperature, but the effect will remain small relative to anthropogenic emissions.  It will only result in increases of about 10-30% in CO2 concentration.  That works out at about 1 W/m^2 of forcing, or the equivalent of about 0.75 C increase in eqilibrium temperature.  So simple models will likely underestimate temperature rises by a small amount.  I do not know to what extent GCMs already include the effect.

  41. Thanks, both.  I've downloaded the Ocean Acidification booklet and will work my way through it.  I'm not a scientist, but to me it looks like the temperature effect (evident from the ice cores) is big enough to consider when looking at saturation of ocean carbon sinks; possibly also to investigate in reducing carbon budgets to fit a concentration pathway.  If ECS is defined as equilibrium when holding pCO2 steady, then I presume it's not included there.

  42. Cedders @441, by coincidence, Real Climate has a related thread on past temperatures today, which provides a number of usefull references (if nothing else).  Unfotunately the graphic they show for phanerozoic temperatures is that by Robert Rohdes, and is based on Viezer (2000)'s adjusted dO18 without pH adjustment.  Ocean pH levels do make a substantial difference, that being the difference between Viezer (2000) and Royer et al (2004).

    Also of interest is this temperature reconstruction over the last 3.5 billion years:


    Again, this is without pH adjustment, so temperatures in some periods should be higher.  In particular, temperatures would be appreciably higher in the Archean (up to 2.5 billion years ago), and Proterozoic (2.5 - 0.55 billion years ago).  Of course, this has an even lower temporal resolution than does Royer et al (2004), and there are at least two instances of near complete glaciation ("snow ball earth") in the immediate lead up to the phanerozoic, which the resolution is inadequate to capture.

  43. The earth is 600M years old.  Do you show CO2 levels for earlier periods than 400K (when the levels were far higher and the earth was far warmer) anywhere on this site?


    [PS] your comment tone is bordering on sloganeering. Ie posting long-debunked myths in disguise. If you are genuinely interested in the science, then certainly this is a site to help for instance see "Climate changed before" and "CO2 was higher in the past". Even a cursory read of the appropriate chapters in the IPCC WG1 report will tell you what the science is really saying as opposed to what misinformation sites might claim.

  44. Sorry edgberht, but the Earth is 4.6 billion years old, not 600M years old. 

  45. Link to "Lorius 1990" seems broken:

    Is this the one that is intended?

  46. I'm arguing with a couple guys in the comments under George Marshall's excellent video presentation, How to Talk to a Climate Change Denier

    One fellow there keeps pointing at this one graph as irrefutable smoking, gun proof that CO2 lags temperature: 


    I speculate that this is pretty short-term and in any case we know the source of atmospheric CO2, but can anyone suggest anything more to say about this?


    [RH] Shortened url that was breaking formatting.

  47. I'm suspicious of the 'detrend' term written into the CO2 time series, and the fact that your interlocutor is using the HadCRUT3 unadjusted southern hemisphere temps, instead of global.

  48. Pure misinformation. Go to that link and take off the detrend on the CO2 and look at the picture. When you detrend, all you have left is the short-term seasonal wiggle in CO2 caused by the change in winter/summer vegetation primarily in the Northern hemisphere. Southern hemisphere doesnt have same effect (way less land vegetation) so his plot looks like lag. Try it with Northern hemisphere instead. How much effort do you suppose went in constructing such a story and do you think that some could find that accidentally? If the guy created this himself, then I think you are dealing someone who is delibratedly intending to misled with the full knowledge of what they are doing.

  49. Looks like one of the heavily massaged graphs that Smokey/dbs/dbstealey, WUWT moderator and sock puppet extraordinare keeps posting. Congratulate your guy, he's (re) discovered that atmospheric CO2 varies with the growth and die-off of global seasonal vegetation. Which we already knew. 

    The short term and the use of 'isolate' are the give-aways; removing the long term rise in CO2 and ignoring mass-balance, isotope, oxygen level, and all the other evidence demonstrating an anthropogenic cause for rising CO2.

    It's simply amazing how much deliberate effort goes into these denial graphs. At best (!) confirmation bias, searching for a combination that confirms what they believe despite the evidence, or at worst, flatly attempting to lie with a misrepresentation of the data. Really no way to tell which, unless the person presenting this junk is a known lobbyist...

  50. As usual, fellas, your help is much appreciated!

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