Geochemistry, Mineralogy, Volcanology Research Spotlight

Earth's Carbon-Climate Feedbacks Varied in Past Warming Episodes

Records from drill holes in the eastern equatorial Pacific indicate that Earth's orbital eccentricity played an important role in controlling climate as the planet warmed.

Source: Paleoceanography


Embedded within the Earth’s long-term cooling trend over the past 65 million years are several climate spikes—swift transitions to “hothouse” conditions—that had profound consequences for life. These spikes could serve as analogues for the future of our warming planet.

The cause of these spikes may in part be due to changes in the atmospheric concentration of carbon dioxide, an important greenhouse gas. But the complex feedbacks between the Earth’s climate and the carbon cycle have been hotly debated, and there is little scientific consensus on this issue.

To help unravel the relationship between the carbon cycle and climate during an extended warm period, Kochhann et al. present a data set of stable isotope and carbonate records. These records, indicators of changing temperature and the growth or contraction of ice sheets, are from an Integrated Ocean Drilling Program drill site in the eastern equatorial Pacific Ocean. The authors also correlate these results with data collected from other regional sites.

Their new record spans the Miocene Climatic Optimum (MCO), the hothouse interval between about 17 and 15 million years ago. During the MCO, the average global temperature was up to 4°C warmer than today, and carbon dioxide concentrations hovered at about modern levels (400 parts per million).

The results show that the stable isotope and carbonate records varied over regular cycles of both 100,000 and 400,000 years. Because these time frames correspond to the eccentricity of Earth’s orbit and its corresponding variations in incoming solar radiation, the authors argue that this finding suggests that this orbital parameter played an important role in controlling the climate as the planet warmed during the MCO. The study also provides strong evidence that the lysocline, the depth in the ocean below which carbonates are much more quickly dissolved, was very dynamic during the MCO, repeatedly fluctuating by up to 600 meters.

To see how the authors reached this conclusion, one has to envision how marine sediment cores store carbon as calcium carbonates. When organisms that hold carbon in their calcareous skeletons die, they sink through the water column to the seafloor. If a given drill site is located above the lysocline, these calcareous skeletons will be preserved in the sediments. If a site is located below the lysocline depth, some—or most—of these skeletons will be dissolved. By comparing carbonate records from drill sites located at different ocean paleodepths, it is possible to estimate vertical movements of the lysocline depth through time.

Notably, episodes of peak carbonate dissolution during the MCO coincided with warmer temperatures (as indicated by the oxygen isotope records), as well as a lightening of carbon isotopes. In contrast, during Pleistocene interglacial warming intervals, periods of higher temperatures (as indicated by the oxygen isotope records) corresponded to records of heavier carbon isotopes. This difference caused the team to conclude that the feedbacks between climate and the carbon cycle during the Miocene differed fundamentally from those at play during the more recent Pleistocene glacial-interglacial cycles.

The authors note that correlation between high temperature and light carbon isotopes, as seen during the MCO, was also observed during the Paleogene, an interval noted for its extremely rapid episodes of global warming and probable lack of ice caps. Therefore, they argue that climate and carbon cycle variability during the MCO, when global warming conditions probably limited ice cover at the poles, corresponded more closely to patterns observed during the Paleogene than those seen during more recent Pleistocene times, when Earth hosted two polar ice sheets. (Paleoceanography, doi:10.1002/2016PA002988, 2016)

—Terri Cook, Freelance Writer

Citation: Cook, T. (2016), Earth’s carbon-climate feedbacks varied in past warming episodes, Eos, 97, Published on 29 November 2016.
© 2016. The authors. CC BY-NC-ND 3.0
  • STeamPlayer

    You don’t have to believe the “climate masterminds”. It’s really not a question of belief. When reading a scientific paper it’s always important to be on the lookout for signs of sloppy, tendentious or self-serving research, which you can find on any side of any scientific debate. I didn’t see detect any of that in this particular article. In fact, the article doesn’t really support or refute either side of the climate change issue. It’s just about research on the (obviously) natural causes of climate change millions of years ago.

    On the other hand, the one sentence you quoted, and your comment about it, seemed to be in support of a specific viewpoint on the climate change issue. I would therefore presume you have some strong ideas of your own on that issue. So you’re not just an “Unbeliever”, you’re also a “Believer”. What do you believe about climate change, and what are the sources of information that have led you to those beliefs?

  • PeterC

    Bart. Compilation of your badgering.
    “Redefining inconvenient words until you like the definitions you imagine better doesn’t really constitute discussion.”
    As I said earlier, that’s exactly what AGW has done.

    “Peter, I’m quite familiar with your body of work. I spent fifteen minutes this morning reading your published papers.”
    You’ve only read ONE chapter (of seven) and its Summary, and as you say, without understanding.
    What do you consider incorrect? Be explicit.

    “Ar plays what role exactly in acidity, do you say?”

    The Romans discovered that their lead pipes dissolved more readily in soft water. It’s been around for a while. (Oh. Regarding Flint, I’m Australian.)

    “Newton and Einstein, or you? Tough call.”
    It’s your understanding of Newton and Einstein I’d challenge.

    • Bart_R


      Are badgers a different animal in Australia?

      I’ve been nothing but warm, cuddly and patient.

      The decline and fall of Rome isn’t the question; why did you dodge the one that affects the health of millions of people anywhere lead pipes, chlorination and CO2 rise meet?

      Are you so inhuman?

      And by all means, challenge my understanding of Newton and Einstein. That’s always a productive exercise.

      • PeterC

        You know where Australia is? No badgers. Badger (v) is in the dictionary.

        I actually answered your question on lead, but you didn’t notice. I used the term “soft water”. You don’t seem to understand.

        Now stop trolling!

        • Bart_R

          I was hoping for an answer to the question, not a pointless handwave.

          But as you feel ‘badgered’, perhaps you have snowflakes in Australia, too.

          So, snowflake, you don’t need to confirm that chlorinated water absorbs two new heavy metal ions for every carbonic acid molecule, thus contributing to lead poisoning in unprotected plumbing.

          Thanks for playing.

          Also, I see no challenge of my understanding of Newton or Einstein; when can we expect that?

          Or for your next mindreading trick, tell me what I thought of your 1978 paper?

          And who is this AGW person who has shown you how to spin words? Is that a pet name for George Orwell, in Australia?

          Pay what you owe for the fossil waste dumping you do.

  • PeterC

    Just to help clarify the position of CO2 in such discussions.
    1. CO2 is supposed to be the cause of global warming because it is a “Greenhouse Gas” – but ALL gases are greenhouse gases, just some are IR gases, ie can absorb heat via IR in addition to conduction and convection that all gases do. (Thought experiment. Put a flask of O2 or N2 into the sun. Will the contents get warmer?)

    2. The Greenhouse Effect is caused by the gases in the atmosphere absorbing heat released by Earth – rather like a blanket. The heat is carried by all gases, approximately in proportion to their percentage. (Variations of this proportionality are due to the Specific Heat of each gas.)

    3. The heat-carying potentional of the IR gases is therefore tiny; about 0.04% for CO2, and even tinier for CH4. Changes to these percentages are even tinier.

    4. Therefore any foreseeable changes in CO2 level are irrelevant.

    • Bart_R

      1. Nope. Not even close. Greenhouse Gas means that the bandwidths of IR are relatively strongly interacted with compared to background. N2, O2 and Argon, the principle components of air, have practically no IR influence as measured by spectroscopy relative to the tiny relative fraction of water vapor, CO2, CH4, CO, ozone, and lesser components. If they did, heat-seeking missiles wouldn’t be able to seek heat. Thought experiment: put a vacuum flask into the sun. Will the vacuum get warmer? Oh, wait, that analogy is nowhere near appropriate as a model of what’s happening in AGW, and neither is yours.) Conduction and convection are not relevant in identifying GHGs. You’ve committed a category error.

      2. Nope. Not even close. It’s not that the gases absorb heat released by Earth. It’s that gases slow the progress of that heat out of the troposphere, changing the distribution of heat as it passes through air, a little like a mylar space blanket. Also, you appear to need a primer on Ideal Gas Law and mixed gasses, in particular referencing fugacity. A published scholar in the field ought be familiar with sophomore level information.

      3. Irrelevant; see #1 & 2.

      4. False.

      For a PhD in Physical Chemistry, your claims are remarkably naive. This is remarkable, given that as recently as 1978 your published work in the field was competent, and a few collaborations in the last quarter century seem to reflect excellent choice of co-authors.

      GHE is not about heat absorption by GHGs. Have you believed this to be how it is thought to work all along? That’s sad.

      Pay what you owe for the fossil waste dumping you do.

      • PeterC

        Perhaps you can explain why Mars has such a small GE relative to Earth’s yet its CO2 concentration is 14X that of Earth’s?
        My site’s Chapter 2A shows how my proposition works out exactly.
        BTW. Your understanding of “Greenhouse Gas” comes from a recognised incorrect definition: IR does not have to be involved.

        • Bart_R

          Because it’s Mars; fugacity factors there are very different, and most notably there’s no significant water vapor to provide feedback.

          Really not interested in emeritus projects, sorry; won’t be visiting your site, and I mean this with utmost respect.

          As for who recognizes definitions, I tend to be utilitarian. A GHG definition that is so broad as to be useless isn’t a working definition.

          • PeterC

            You – and AGW – can’t explain it!
            Additionally, fugacity varies maybe 20% from Earth’s – way too small to be quantitatively accurate. And what’s water got to do with it? You are clutching at straws.
            The real greenhouse definition holds for the rocky planets, Venus, Earth and Mars – despite the fugacity! (Mercury is consistent but has no atmosphere and so no greenhouse.)
            The real definition works perfectly well. AGW’s does not.
            This AGW wrong version virtually defines that CO2 will have a pronounced effect. Too bad it doesn’t match facts.

            • Bart_R

              Redefining inconvenient words until you like the definitions you imagine better doesn’t really constitute discussion.

              Are you really unfamiliar with the role of water vapor in the terrestrial GHE?

              Again, I recommend David Archer’s work as a great place to start.

  • STeamPlayer

    What’s your point, Unbeliever? Is it news to you that natural factors have contributed to climate variations during earth’s history? Every climate scientist knows that. Obviously during the Tertiary times discussed in this article, there was no anthropogenic contribution, because there were no people. This article is about using the geologic record to better understand some of those natural factors. That understanding can then be applied to today’s situation to distinguish between natural and anthropogenic changes. That’s the kind of thing objective scientists do. What denialists do is comb scientific literature for sound bites that they think support their point of view. The fact that there are natural variations in climate doesn’t conflict at all with the strong scientific consensus that climate change observed in the last 50 years or so is predominantly anthropogenic. I think if you read the article again carefully you’ll see what I mean.

    • Bart_R

      Unbeliever used the word “now”.

      Goodwill reading equates “now” with “currently”, so could and ought be construed as applying to current climates, ie 30-year periods on the instrumental record.

      During the Tertiary times discussed in the article, time spans of millions of years would be incommensurable to current 30 year climates. Natural factors that apply to those time scales as dominant are easily shown to be mere noise or background on 30-year scales.

      I think we all agree the study is well worth pursuing and of use to today’s science. Were it not for the anthropogenic signal so completely overwhelming the orbital signal, even the Hale Cycle signal, in the global temperature record and that of other essential climate variables, we might even see other important conclusions that now are lost in the noise.

      I believe that’s part of Unbeliever’s point, so both your conclusions bear equally respectable reasoning.

    • Unbeliever

      You just have to believe that the climate masterminds can distinguish between natural (good) warming versus (bad) anthropenic warming in order to come up with a consensus for what the earh’s temperature is supposed to be.
      I don’t.

  • davidlaing

    Interesting how different people looking at the same evidence can come to vastly different conclusions. I studied these same eastern equatorial Pacific carbonate lenses twenty years ago, and concluded that they were not affected by cyclic nondeposition due to intermittent rising of the lysocline but by corrosion due to emanations of acidic water from the nearby East Pacific rise, indicating periods of increased sea floor spreading. I also noticed the Milankovitch periodicity in these corrosional episodes, and I also attributed that to orbital eccentricities, but I noticed as well a 41,000 year periodicity, which is associated with Earth’s axial tilt.

    Instead of the usual invocation of insolation variability as a result of these motions, I suggested a gravitational effect, in which such orbital eccentricities and axial tilt stimulate motion and attendant volcanism on Earth’s delicately balanced plate tectonic system. Basaltic volcanic emanations are acidic, and their diffusion above the carbonate lenses would have produced corrosion of the carbonate.

    I submit that this is a simpler and more direct explanation of the data than that given in this paper, and that it requires fewer ancillary mechanisms to make it all work.

    • Vince Pellerito

      DavidLaing, I don’t see how the mechanisms that you proposed would account for changes in the oxygen isotopes. Did you consider dO18 in your work?

      • davidlaing

        I did, but it was a long time ago (1990), and I’ll have to dig through my files in my very messy barn to recapture what I actually concluded. Stay tuned!

        Given that sea floor spreading should cause warming of the ocean, and since warming oceans release carbon dioxide, it seems to me that my conclusions are consistent with those of the above study.

    • Bart_R

      The first order influence of gravity changes relative to the orbital plane (presuming this is the gravitational effect you intend, given it would be the largest of the effects) on plate tectonics must be many orders of magnitude below the direct effects of temperature on ocean chemistry, no?

      • davidlaing

        I don’t really know, actually. Comparisons of quantifications of the two mechanisms would be quite difficult, as would the quantification of the gravitational influence on plate tectonics itself. I’ve read that eruptions at Mt. Saint Helens and Etna tend to be more frequent during full Moons, and that’s where I got the idea that gravitational influence of orbital motions might have an effect on the plate tectonic system.

        • Bart_R

          Full moons are determined by the relative angle of the Sun and Earth to the moon, and not particularly related to Earth-Moon distance, which would be a much stronger influence.
          Is it possible you were reading a horoscope?

          Check out Tidal Triggering of Earthquakes and Volcanic Events, Emter (2005) for a survey of literature up to that date.

          Sorry, the literature seems to indicate there to be zero or near-zero observational support for your claim, and the reasoning appears to visit attribution of false cause.

          • davidlaing

            The second sentence in your first paragraph is snarky, and not particularly helpful.

            During New Moon and Full Moon, with the line-up of Earth, Moon, and Sun, the gravitational effect on Earth is much stronger than during half Moon, in which Moon’s gravitation is at a right angle to Sun’s.

            Thanks for the reference.

            My suggestion was not a claim. It was simply a suggestion that this possible mechanism might be looked at.

            Milankovitch rhythms are present in many non-glacial deposits throughout Phanerozoic time and perhaps before. This mechanism would explain these much better than insolation would, as there is no credible mechanism for insolation being responsible for the cyclic deposition of different varieties of sediment other than glacial.

        • Bart_R

          I openly admit that my snark is unhelpful, and certainly apologize

          Milankovitch cycles include more than just orbital obliquity and axial tilt, but also orbital eccentricity at ~100,000 years, which ought have the most particularly marked of the gravity influences, barring Moon-Earth interactions.

          As these influences vary with the fourth power of distance, while many suppose conjunctions to matter most, the simple mathematical fact is that the Moon’s orbital eccentricity ought be the stronger gravity marker than phase of the Moon.

          If you see 41,000 year intervals in your data, you’re observing the least gravitationally influenced of the Milankovitch components.

          No one needs to point out that this is of course a hairy topic of much discussion and controversy, often in the gray literature polluted with superstitious hype and astrology dressed up pseudoscientifically, so care is always warranted.

          First order effects of temperature change due GHE are orders of magnitude stronger than gravity, and the evidence well fits direct thermochemical explanation above a more convoluted tectonic supposition. So while your ideas certainly will have their fans, they are unparsimonious and do not match the evidence on their face.

          • davidlaing

            Tx! I meant orbital eccentricity. I don’t know how obliquity got in there. It is, indeed, a hairy topic, involving a large number of variables. I tend to look for a particular hypothesis that addresses many variables at once rather than on exactly quantifying any one particular variable, i.e., a synthetic rather than the more typical analytic approach. If an idea solves a large number of problems all at once and contradicts none of them, the likelihood of its being right is greatly increased.

            • Bart_R

              Sadly, short cuts around logic are seldom by mere coincidence the same as actual logic.

              More to the point, depending how you frame your narrative one idea of climate change is more encompassing and universally solves more problems than one idea of eccentricity does. It’s like the difference between comedy and tragedy: it only depends on where the storyteller stops.

              Gravity is a cool thing, don’t get me wrong. In the end, gravity wins the war. But it loses every battle along the way.

              ~41,000 rather than ~100,000 in your observations contradicts eccentricity. Observations trump (excuse the unintended use of what once was a more useful word) ideas. The ~5 degrees interstitial global warming is far more directly powerful than gravity, and we’re missing a ~41,000 year stratigraphy confirming cyclic volcanism. That’s three strikes.

              However, you have brought up rather excellent points in your argument confirming climate change due Milankovitch forcings, positive CO2 feedbacks, and the profound effects of carbonic acid on the oceans. That’s laudable in and of itself.

              • davidlaing

                What you say makes tentative sense, but before we continue this, please Google “Interesting Climate Sensitivity Analysis,” select the first hyperlink, and see what you think of the hard-data study presented there. This could bear heavily on the interpretations we’re talking about.

                • Bart_R

                  Ah, WUWT. The scientific equivalent of being Rick Rolled.

                  Sorry, I long ago shook the dust of that den of virulent nonsense and malice from my sandals.

                  What I say makes scientific sense on its own merits from all observation. What you say does not.

                  That’s the end of a scientific discussion.

                  Leg-pulling and Rick-Rolling? No thanks.

                • davidlaing

                  Don’t be a snob. Shallow-mindedness leads people to dismiss others on the basis of associations. WUWT picked it up because it looked interesting. Read it. You’ll find it interesting, as the title suggests. I would have called it “The First Hard-Data Test of Greenhouse Warming Theory in 115 Years.” Anyway, it feeds into what we were talking about, as you’ll see.

                • PeterC

                  I agree with davidlaing; don’t be snob Bart!

                • davidlaing

                  Tx, PeterC!

                • Bart_R

                  Have you read Peter C’s papers?

                  Do you understand them?

                  Gone to his website and reviewed his emeritus project?

                  And you agree with it?


                • PeterC

                  Blind as a badger Bart.
                  You said you wouldn’t read my site – and you haven’t read much. No wonder you can’t understand it!
                  I haven’t read DavidLaing’s treatise; where is it located?
                  (This Eos site seems not to like referring directly to sites. My direct reference to mine was not shown.)

                  Anyway, you may have difficulty as it’s quantitative – and accurate.

                • Bart_R

                  Newton held accurate the fit inferred from all observation given least assumptions or exceptions and broadest scope possible, (Einstein added “but no more than possible”), until new observation yields amended or new fit.

                  You hold accurate what yields the consequences that make you feel good.

                  Newton and Einstein, or you? Tough call.

                  I know which one you made.

                • davidlaing

                  PeterC, please Google “Interesting Climate Sensitivity Analysis” and select the first link. Comments welcome, of course.

                • Bart_R

                  Also interesting, Google “Bart R appears to have had enough nonsense for one day.” 😀

                • PeterC

                  Quid pro quo.

                • Bart_R

                  Have you read his treatise?

                  This unpublishable paper you’re agreeing with?

                  Do you know what it says?

                • PeterC

                  I agree with him that you are showing yourself to be a snob.

                • Bart_R

                  You seem to be very agreeable. You should take fifteen minutes and find out who you’re agreeing with.

                  Lie down with dogs. Wake up with fleas.

                • Bart_R


                  I also don’t cite Mad Magazine, Breitbart or News of the World. Selective reading is not snobbery. And I like Mad Magazine.

                  It appears you’ve been peddling your pet theory for a while. To be blunt, it’s bunk. Get over it and move onto something productive.

                • davidlaing

                  I’m quite disappointed by your intolerant and unscientific attitude, Mister Bart_R, but so be it. I don’t really see it as my fault, or the fault of my study, that you and the contemporary climate science community finds it politically incorrect, and hence unpublishable.

                  As a hard-data-based study, however, the results, that carbon dioxide can’t possibly cause warming, but that ozone depletion very well could, are essentially unarguable.

                  I’d appreciate it if you’d go to the trouble of reading my “bunk” just to familiarize yourself with it because as the actual behavior of the Earth system fails to conform to the predictions of the climate models, you’ll understand why.


                • Bart_R

                  It’s not Mister Bart_R, actually. It’s Bayesian Additive Regression Trees in R.

                  There’s no Mister here. No Mr. No Ms. No Miss, or Mrs.

                  When it comes to hard data, BART in R is very much more trusted than you.

                  If you could in future be so kind as to point out how you hold exact the fit inferred from all observation with least assumption or exception on greatest scope possible (but no farther than possible), until new observation allow amended or new fit, it may save you time trying to attract people to reading your claims.

                  Because my attitude is exactly that of science as set out by Regulae Philosophandi, and does not tolerate more assumptions or more exceptions than needed, nor use on non-inferential methods, nor exclusion of observations, nor limiting of scope to special cases.

                  That’s the discipline of science. All else that pretends otherwise is bunk.

                  Speaking of, how’s your perusal of Dr. PeterC’s website going?

              • PeterC

                The “carbonic acid” problem is also of no importance.
                If one assumes the pre-industrial levels of 280ppm are natural (and pH=8.25), and the current 400ppm (pH=8.12) results from Man adding a further 120ppm, then doubling Man’s contribution to 400+120 = 520ppm gives a pH of only 8.02 – which is less than current variations around the globe. (The variations are due not to CO2 – which is also uniform in the atmosphere – but to undersea volcanically derived sulphuric acid; check where it’s happening.)

                • Bart_R


                  Reasoning from analogy, the variation of temperature on the human body may be more than ten degrees between core and the external surface of extremities. I am assured that if the entire human body were visited with this much variability, it would be unhealthy.

                  Your reasoning violates causality, and is thus false.

                • PeterC


                • Bart_R

                  A fever of 10 degrees is bad for you.

                  Not to worry, a lot of specialists in Physics have zero clue about how biology works.

                • PeterC

                  But I do have knowledge in the properties of gases, CO2 H2O CH4 O2 N2 Ar in this case, and it’s these properties that determine Greenhouse and acidity. (PhD Physical Chemistry.)

                  None so blind as those that will not see.

                • Bart_R

                  Peter, I’m quite familiar with your body of work. I spent fifteen minutes this morning reading your published papers.

                  Ar plays what role exactly in acidity, do you say?

                  And while we’re speaking of things that can cause blindness, chlorinated water dissolves more heavy metals as carbonic acid level increases; do you happen to recall the stoichiometry of that reaction?

                  I ask because you’re bound to be aware that Flint Michigan had a problem where over the last five decades its lead pipes went from being innocuous to a health risk, and it’d be good to hear from a PhD Physical Chemistry about how that happens.

  • Unbeliever

    ” Earth’s orbital eccentricity played an important role in controlling climate as the planet warmed.” Not anymore….it’s all man made now.

    • Rick firestone

      Has volcanism
      ceased?Or wildfires?.. It’s not all man made.

      • Unbeliever

        Which part of the climate is not man made?