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Climate change from 40 million years ago shows climate sensitivity to CO2

Posted on 6 November 2010 by John Cook

Around 40 million years ago, sea surface temperatures rose around 5°C in a period called the Middle Eocene Climatic Optimum (MECO). A new study Transient Middle Eocene Atmospheric CO2 and Temperature Variations (Bijl et al 2010) has found atmospheric CO2 was the primary driver of this global warming event. During this period, CO2 levels rose dramatically to 2 to 3 times previous levels. This study gives us further insight into how climate responds to changing CO2 levels and provides evidence for strong climate sensitivity.

The Eocene is a period spanning 56 to 34 million years ago. Over this time, global temperatures showed a long, gradual cooling as the planet moved from a warmer climate to a cooler one (the end of Eocene was marked by Antarctic glaciation). To determine temperature and CO2 changes during the middle Eocene, sedimentary ocean cores were taken from the east coast of Tasmania. The cores contain fossilised microorganisms that provide several independent proxies for temperature. The proxies, or "paleothermometers" as the authors describe them, indicate a warming of the sea surface of around 5°C.

Carbon isotopes in alkenones (produced by algae) serve as a proxy for CO2 levels. Before the MECO warming, CO2 levels were between 600 to 1600 parts per million (note that at these higher CO2 levels, there were no ice sheets in Antarctica). During MECO warming, atmospheric CO2 increased to between 6,400 to 15,000 ppm. The trends in sea surface temperature follow CO2 trends remarkably well.

 

Figure 1: Sea surface temperatures from two different proxies (red and purple). Atmospheric CO2 levels from algae (light grey band) and phosphate estimates (dark grey band). Yellow shaded area indicates the MECO warming interval.

The advantage of this type of study is it gives us the climate response to changing CO2 levels over long time-scales. This means any temperature changes to rising CO2 will include long-term climate feedbacks like changes in ocean chemistry or changes in vegetation (but in this case, not changes in ice sheets or sea ice as there were no ice sheets during the Middle Eocene). During the Middle Eocene Climatic Optimum, temperatures warmed around 5°C with CO2 increasing by a factor of 2 to 3. This yields a climate sensitivity range of around 2° to 5°C per doubling of atmospheric CO2 (but note that ice feedbacks aren't included). This is broadly consistent with the IPCC climate sensitivity range of 2°C to 4.5°C which is based on a consideration of many estimates of climate sensitivity using instrumental, satellite and proxy data.

One intriguing question remains. Vast amounts of carbon were injected into the atmosphere during the Middle Eocene - where did it all come from? Volcanic outgassing is a possible contributor although it's unlikely it provided all the CO2. It'll be interesting to see what future studies will discover about this distant period.

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Comments 1 to 50 out of 69:

  1. Was that intended to be 2-3 doublings of CO2?
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  2. John, thanks for the interesting summary of the paper. One housekeeping question: the abstract mentions both Peter K. Bijl and Alexander J. P. Houben contributed equally to the paper. In that event, wouldn't it be customary to cite both principal authors in your reference (i,e., Bijl and Houben, et al 2010)?

    Another question: do they give some idea as to how long it took to both raise CO2 concentrations and temps? Just trying to prepare for the inevitable nay-saying.

    Thanks!

    The Yooper
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  3. Earth's climate will have changed many times over its 4.54 billion years http://en.wikipedia.org/wiki/Age_of_the_Earth

    Since the Earth and its atmosphere is a closed system all the CO2 that's here has always been here. Its just moved around a bit :-)

    So what? So what nothing! Its simply my layman observation. Perhaps someone else can add to it.
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  4. #4: "all the CO2 that's here has always been here. Its just moved around a bit"

    Over-generalizing a wee bit? You would do well to read up on what is called the Carbon Cycle and how the climate changed in the past in the past.

    The quick answer? It is clear that all that CO2 has not always been in the atmosphere. A lot that spent millions of years as fossil fuels was dumped into the atmosphere in a very short period of time.
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  5. Re 5 & 6
    The correct thread might be here

    Some comments (incurring the wrath of the moderator) though,
    1. Climate change may result in loss of biodiversity and the extent of loss is likely related to the rate of change

    2. Wouldn't a warming world preferentially favour non-homeostatic organisms (e.g. bacteria and viruses over humans) ?

    3. I was under the impression that for the marine ecosystems cold water played a vital role due to its increased O2 content.
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  6. #7: My point exactly. The fossil fuels that was once living organisms had to get their CO2 from the atmosphere, so early on the atmosphere must have been loaded with CO2. Like I said, its a closed system. Re:How do human CO2 emissions compare to natural CO2 emissions?....quote "atmospheric CO2 is at its highest level in 15 to 20 million years."

    What about the other 4,520,000,000 years?
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  7. "Vast amounts of carbon were injected into the atmosphere during the Middle Eocene - where did it all come from?"

    The Eocene was intensely volcanic, including:
    The most powerful single eruption of this series took place 54.0 million years ago (Ma) and ejected ca. 1,200 km3 of ash material which makes it one of the largest eruptions in geological history. --Egger and Bruckl 2006

    Zachos et al 2008 did a nice job of summarizing the climatic impacts.
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  8. #9: "The fossil fuels that was once living organisms had to get their CO2 from the atmosphere,"

    You are not listening. Fossil fuels accumulated over millions of years; fossil fuel burning during the past 150 years (and half of that within the past 60).

    "What about the other 4,520,000,000 years?"

    We live here, now. Comparing the distant past doesn't add to the discussion. Use the SkS Search if you're curious.
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  9. Having read the paper I've got the usual questions.

    1)Where do they get the 2-3 times increase in CO2? In my mind going from 600-1600 to 6400-15000 is an increase by a factor of ~10? Just to clarify #1 and #2 in case they haven't been able to read the paper John has quoted the paper accurately. The authors say a factor of 2-3 but like Mike and KR I'm confused. This seems like such simple maths there must be an easy explanation.

    2) I see no accounting for polar amplification in this work. There presently exists a theory that says temp will increase greater at the poles. I think ATM the arctic is believed to be warming at twice the rate as the global average. The paper actually says a "high latitude climate sensitivity". John are you assuming a global climate sensitivity in your write up here? I imagine if you were to take this papers estimate of "high latitude climate sensitivity" as accurate you would probably have to reduce the number if you were to try to estimate a global climate sensitivity from this work.
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  10. miekol, during much of the pre-Quaternary Era, the planet was subjected to massive levels of long-term (hundreds of millions of years) volcanism-as Pangaea slowly broke up & the continents moved into the positions we recognize today. This volcanism led to a *very* slow build up of CO2-to levels that were about 10 times higher than they are today-& this gave the planet *average* global temperatures of around 22 to 24 degrees Celsius (or around 6 to 8 degrees warmer than at any point in the Holocene). The CO2 was locked up again, over *tens of millions of years*, by the extensive plant-life that existed during the Carboniferous Era (during this time, most complex forms of animal life still spent the bulk of their time in the water). During the Carboniferous Era, temperatures also fell to levels more closely approximating our own. For at least the last 70 million years, though, levels of CO2 have remained locked between around 200ppm & 280ppm, which is testament to how slowly CO2 levels build up in the atmosphere due to volcanic influences. In the last 200 years or so, though, humans have been digging up these ancient reservoirs of prehistoric carbon & burning them-releasing their stored CO2 back into the atmosphere. Do you *really* believe, Miekol, that we can keep doing that without it having *any* negative impacts on our climate?
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  11. Sorry, I meant around 7 million years, not 70 million!
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  12. Just a side note. This paper is associated with a perspectives article written in the same issue by Paul N. Pearson from the School of Earth and Ocean Sciences, Cardiff University. In it he writes

    "Maximum levels in the MECO reached 4000 ppmv or higher—similar, perhaps, to a future anthropogenic greenhouse maximum."

    I've never seen any suggestion that CO2 levels are heading towards this level. Presently were creeping towards 400ppmv. Is this pure alarmism? If so what's it doing in the pages of Science magazine?
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  13. #9 You said, "You are not listening." Yes I am :-)

    You said, " Fossil fuels accumulated over millions of years." I know this.

    You said, "fossil fuel burning during the past 150 years (and half of that within the past 60)."

    I know this.

    My point is ALL of the history of the planet must be factored into the discussion otherwise we just might be missing an important element. Its called lateral thinking. :-) You must think outside the square, otherwise you might miss something :-)
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  14. #11 Thank you for your reply and your patience. No, I do not believe "that we can keep doing that without it having *any* negative impacts on our climate? "
    I have not said it would not have negative impacts on our climate.I have not said anything yet. "I'm still … collating, actually" :-)
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  15. #14: Sorry if you found my replies harsh. Your earlier comment So what? So what nothing! didn't give me the impression you were 'still collating'.

    "ALL of the history of the planet must be factored into the discussion" Yes, that's called geology. Please check the prior articles 'CO2 was higher in the late Ordovician' and 'CO2 was higher in the past' for some context for your thinking.

    Be sure to recall that paleogeography is a controling factor in both oceanic circulation and the degree to which the planet can sustain glaciation; plate tectonic activity (or the relative lack thereof) produces both CO2 and aerosols; carbonate deposition in warm shallow water has the capacity to suck huge volumes of CO2 out of the atmosphere. Oh, and did I mention there weren't any flowering plants in the Ordovician?
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  16. Just wondering if there a position amongst those who truely believe CO2 drives climate, as to what would happen to CO2 levels if it simply got warmer for some other reason??? Would CO2 levels remain the same, go up, go down, etc.
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    Moderator Response: Under modern conditions, which are quite well understood, CO2 is considered to be the biggest control knob of global temperatures, but not the only one. The sum balance of all forcings and feedbacks (of which CO2 acts as both) determines global temperatures. In the situation you briefly posit, rising temps would then drive a methane/CO2 release to some degree, driving a further warming response (a self-limiting mechanism, overall). If you wish something more specific in response, please posit a physics-based mechanism for your thought experiment for the group to discuss.
  17. Considering the correlation assumed between CO2 and temperature, it would seem that the less CO2 changed as a function of warming, the greater its effect. This of course rests on the initial assumption that climate change is driven by CO2, and not (for instance) the fire fly population.
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  18. RSVP,
    As you have been told numerous times before, for the climate to change there has to be a reason. Fireflys don't count. If orbital changes cause temperature changes, as has happened many times in the past, then CO2 rises as a feedback. If temperature goes down CO2 goes down. You appear to be deliberately asking stupid questions that you have been told the answer many times before. Read the basics before you post more questions that everyone knows the answer to.
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  19. Re the increase in C02.
    Although this isn't my field I take it that C02 changes were found by measuring carbon isotopes in algae. The carbon isotopes showed a clear change demonstrating a large increase in C02, but the difficulty is in trying to convert this into actual C02 concentrations.

    How much the carbon isotopes change is apparently also dependent on phosphate concentration, so if you know the phosphate concentration you can get a more accurate determination of what the C02 change was. Their attempts to do this are shown in the light and dark grey bands in figure 1 above. By adding in more information they improved their phosphate concentration estimation and were able to get a better estimate of C02 increase (dark grey band which has lower uncertainty). This suggested a "rise in pCO2 by 2000 to 3000 ppmv" which is 2 to 3 times the baseline C02 of 600 and 1600 ppmv.


    @10 HM.
    AFAIK polar amplification is at least partially driven by the ice albedo feedback which didn't exist at this time (it was an ice free world). You are correct in noting that this paper only measures the change in sea temperature at one site, however as noted in the paper these results are consistent with previous measurements of the temperature change at this time from other sites
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  20. #21: "this paper only measures the change in sea temperature at one site"
    The Eocene climate is quite well-researched. For further reading, here is a database of recent papers.
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  21. From the article:
    During MECO warming, atmospheric CO2 increased to between 6,400 to 15,000 ppm.

    This statement misled me too. There is a peak in the algae estimates band in the CO2 graph at about 15000ppmv alright, but the red trend line seems to meander between 2000 - 3000ppmv as The Skeptical Chymist points out. It certainly never goes much above 4000ppmv.
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  22. Miekol:
    "The fossil fuels that was once living organisms had to get their CO2 from the atmosphere, so early on the atmosphere must have been loaded with CO2."

    Even at a basic level that is incorrect.
    You are confusing carbon with CO2.
    A lot of CO2 would have been sequestrated by life at the time and held as carbon. As a poster pointed out you need to understand the carbon cycle. Apart from that, the faint young Sun and the CO2 thermostat would have taken care of long term CO2 effects and levels over hundreds of thousands of years.
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  23. Very interesting paper! Perhaps you could add a few clarifying words about the CO2 increase.

    The fact that there was not a strong signal in carbon isotopes is stunning. The source of carbon must be an different as in PETM (probably methanhydrates).
    PS Does anyone know why reasearch focuses so much on PETM? I havent heard of MECO until a few minutes ,while PETM is discussed for a long time in journals?
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  24. As it seems this CO2 increase was even lager than PETM (about 700 ppm), and no knows source (but lower temperature increase)? Seems to be an interesting research topic ;-)
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  25. moderator #18
    Thanks for your answer.

    michael sweet #20
    Thanks for listening so keenly. Again, the stronger one assumes the coupling between CO2 and climate, the less change in CO2 level needed to affect climate (i.e., CO2 has great leverage)..., or the inverse; the weaker the coupling between CO2 and climate change, the more change in CO2 level needed to affect climate (i.e., CO2 has little leverage). This paradox makes it difficult to know with certainty that CO2 has any effect, because in the first case any correlation may be completely false, and in the second, if true, the coupling is weak and might as well be ignored. If, as has been stated, CO2 is released with higher temperature, it is clear that cart is in front of the horse, and neither are going anywhere.
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  26. RSVP: The CO2 feedback (you increase the temperature 1°C, how much does CO2 rise?) is about 15 ppm/K. In MECO temperature increase was according to Bijl et al 2010 6°C or less, thus an increase of 2000 ppm or more is difficult to explain with CO2 outgassing as an feedback.

    Another point is that there are many different ways to estimate climate sensitivity, they ALL come up with about 3°C, read for example Knutti 2008
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  27. #25: "I havent heard of MECO "

    MECO shows up in literature as early as Bohaty and Zachos 2003

    This isotopic event is designated as the middle Eocene climatic optimum, and is interpreted to represent a significant climatic reversal in the midst of middle to late Eocene deep-sea cooling. The lack of a significant negative carbon isotope excursion, as observed during the Paleocene–Eocene thermal maximum, and the gradual rate of high-latitude warming suggest that this event was not triggered by methane hydrate dissociation. Rather, a transient rise in pCO2 levels is suspected, possibly as a result of metamorphic decarbonation in the Himalayan orogen or increased ridge/arc volcanism during the late middle Eocene.
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  28. #28, I am curious where you came up with the figure of 15 ppm CO2 caused by 1 C temperature increase. Consider that only the upper 10% or so of the ocean has time to respond to a 1 C temperature change in just 100 or so years. In a few thousand years, all of the ocean would be affected, so about 10 times the CO2 would be released. Actually, since the deep ocean is far colder than the surface, and since the solubility of CO2 is far higher in cold water, I expect even more than 10 times the CO2 would be released for a 1 C increase.

    You are welcome to try to refute this.
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  29. @Iweinstein: For example the interglacial/glacial cycles, there you have enough time (5000 years ca.) and the feedback is about 15 ppm/K. Furthermore oceans were ventilated during that time, biological pump was more efficent during the glacials.

    Check also the Frank et al 2010 Nature paper. They state that there is only a limited time dependece of the co2 feedback.
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  30. #31, Bodo, I agree with your comment. 15 ppm per 1 C it is.

    Going back to the post by John Cook:
    John, I look at figure 1 and ask where you get 5 C as the temperature change. It appears the temperature and CO2 were going in opposite directions up to the beginning of MECO. Explain that. Also the 5 C assumes the red proxy case is the correct one, and the value was used at the low at the beginning of MECO and the high within it. However, if you start at the earlier time on the graph, the maximum increase in MECO is only about 2.5 C for the red and near zero for the purple proxy (based on the earlier maximum than MECO). In addition, there is a slow peak after MECO in CO2 but a dropping temperature. It clearly appears something happened, but the deduction shown is not a strong one.
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  31. Another comment to John Cook:
    You take one location and say it is a reasonable representation of global effects. I won't dispute that, but it is weak. Now let us look at the Greenland ice core going back the last 10,000 years, and even back it up with an ocean floor core in the Sargasso sea. These (and other sources) show that the temperature was warmer several times and cooler several times by up to 2 C or more. The present temperature at these sites, which appears to be a natural recovery from a cool period called the little ice age, is actually slightly below the average peak for the last several thousand years. The speed of change was as high or higher for many of these variations. Yet the CO2 is indicated as constant to a narrow level. What do you propose as the cause of the variations, which make the present 150 year variation seem as typical? I would be glad to input the curves, but I am sure you have seen them.
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  32. 32:"where you get 5 C as the temperature change."

    Since this figure is a stratigraphic record, time advances towards the present from bottom up. Below the MECO (yellow), the red is at 23C, during the MECO red is in excess of 28C.

    "if you start at the earlier time on the graph, the maximum increase in MECO is only about 2.5 C for the red "

    By the definition in this paper, the MECO is a short duration 'transient' event.

    Bohaty et al 2009 provide additional context:
    The identification of the δ18O excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive. The total duration of the MECO event is estimated at ∼500 ka, with peak warming lasting <100 ka. Assuming minimal glaciation in the late middle Eocene, ∼4°–6°C total warming of both surface and deep waters is estimated during the MECO at the study sites. ... The synchroneity of deep-water acidification and globally extensive warming makes a persuasive argument that the MECO event was linked to a transient increase in atmospheric pCO2.
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  33. Re: RSVP (27), Bodo (28, 25)

    To augment Bodo's excellent response to you, RSVP, at 28 above, remember that temps are a sum of forcings and feedbacks, of which CO2 is one (but the principal one). If CO2 levels spike, say due a methane clathrate/hydrate release as is theorized occurred during the PETM, then it would be reasonable to expect a temperature response of about 3 degrees per doubling of CO2 from baseline.

    But if that CO2 spike were accompanied by a lowering of TSI (as occurred during the Ordovician) and also some large volcanic aerosol releases in the tropics (where volcanoes have their greatest impact), than the global temperature response to CO2 will be more muted

    We know with certainty that CO2 is a greenhouse gas, that a certain increase in concentration will, other forcing and feedbacks remaining constant, drive a certain global temperature increase. Slow changes in Milankovich orbital cycles drive slow changes in temperatures, which can then change CO2 levels in response (an example of CO2 acting as a feedback to drive a limited secondary temperature increase). In this case, CO2 lags temps.

    How the modern era differs from past comps is this: we have injected an immense bolus of formerly sequestered (i.e., removed from the carbon cycle's closed budget) fossil-fuel derived CO2 back into circulation in the carbon cycle. So, despite a quiet sun with a flat TSI, despite some of the strongest La Nina's on record, global temps are up, Arctic ice area (and extant and volume) are down, Greenland, the WAIS and the EAIS are losing mass and sea levels are rising - all within ranges of predictions based upon the physics of greenhouse gases...CO2 in specific. In this case, CO2 is acting as a forcing to drive temperature increases, which then drive secondary CO2 releases which act as feedbacks; temps lag CO2 increases.

    As a result, the nearest analogue to the current spike in atmospheric CO2 levels is probably the PETM (which will be a worst-case scenario for us). If we continue BAU for long enough and spike temps high enough, the probability of a methane hydrate/clathrate release goes from a remote possibility to a probability. Hence the need to further study the PETM (per Bodo's question). The more we know about the PETM, the better able we may be to gauge how near the cliff's edge we actually are in this fog of lack of knowledge about climate response we are in.

    Given that, to say
    "it is clear that cart is in front of the horse, and neither are going anywhere"
    as RSVP says is specious and anything but helpful.

    The Yooper
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  34. #34: "You take one location and say it is a reasonable representation of global effects."

    No, this is a global event. See Bohaty, cited in #35, who used OSDP cores; see Luciani et al 2010, who studied samples of Tethyan oceanic sediments now exposed in northeastern Italy.
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  35. Daniel Bailey #36
    "...an immense bolus of formerly sequestered (i.e., removed from the carbon cycle's closed budget) fossil-fuel derived CO2 back into circulation in the carbon cycle"

    In order for hydrocarbons to have accumulated over the eons, there must have been a steady stream of CO2 being liberated from somewhere and for some reason (lets assume the ocean). But in order for plants to thrive, and for CO2 to be released, temperatures need to go up. How could this have happened if the plants where continually sequestering the CO2? What''s good for goose, must also be good for the gander.
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  36. #38: "there must have been a steady stream of CO2 being liberated from somewhere and for some reason"

    Yes, its called the Carbon Cycle. There are numerous discussions of it here, which you can no doubt find on your own.

    "(lets assume the ocean)." Why?

    "But in order for plants to thrive, and for CO2 to be released, temperatures need to go up." Again, why? There is always some CO2 in the atmosphere; the amount moved around the photosynthetic cycle doesn't necessarily cause temperature increase -- that's why today's climate change is called Anthropogenic.

    A large percentage of the fossil fuels we've burned recently was formed at times in the geologic past when CO2 was much higher than it is today: That's why this is a bad thing. We've put back into the atmosphere the stuff that was put away long ago.

    "How could this have happened if the plants where continually sequestering the CO2?" Perhaps read up on how fossil fuels are formed and then come back to the Carbon Cycle.
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  37. muoncounter #39
    "this is a bad thing"

    From what you say, the energy stored in fossil fuels is apparently from the Sun which constitutes a source of biological solar energy. The biproduct of this process that favors plant growth, and yet it is "a bad thing". I am sure I can think of worse things.
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  38. #40: "and yet it is "a bad thing"."

    The bad thing in question is: we released the carbon that was stored in fossil fuels back into the atmosphere in the form of CO2. But I'm sure you knew that already. If not, you really should do some more reading.
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  39. And does correlation prove causation, or in this case climate sensitivity? No. When climate warms, more CO2 is released from the oceans, CO2 lags temp and thats all we know (well yes it can amplify the change but self-evidently its not _the_ control knob).

    If some warming event coincidences with a volcanic eruption which huge releases of CO2, that does not prove CO2 was the main cause either. The geologic history is SOOOO long it is actually evident such coinsidences occur.

    Response to #18 was also a bit silly imho. The paper linked just proves how fatally flawed the climate models are, and thats it. They claim there would be almost no greenhouse effect without CO2, thats an outrageous misinterpretation. Which one of you really believes that we would lose nearly all water wapor and have over 70% cloudiness without CO2? omg...

    Determining climate sensitivity or anything as complex as that from inaccurate paleo-reconstructions is just pop-science. When all of the forcings (including the multi-decaedal and multi-cencennial oscillations) are not known the climate sensitivity can not be determined.
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  40. RSVP Ya know, heroin is also biological solar energy ... just kind of processed...like petroleum.

    And if the point isn't clear...You judge whether something is "bad" based on it does, not where it comes from.

    Surely you're just taking the mickey, right?
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  41. Re: protestant (42)
    "Response to #18 was also a bit silly imho. The paper linked just proves how fatally flawed the climate models are, and thats it."
    Um, are you referring to the linked video in the response to #18? If so, then you should really watch it and try and learn something about CO2.

    And the specifics about GHG's are that, without their effect, the average temp of the Earth would be 33 degrees C less than it is now (about 59 degrees F less). Since that puts the Earth well below the freezing point of water on a global basis, there would likely be no life, as the Earth would be a global iceball, pole to pole. This is well-understood and has been for over a hundred years.

    The majority of your posts here thus far are fraught with a lack of understanding of, well, just about anything to do with climate science, actually. And I see by the responses that many commenters have stepped in to help you gain understanding on a post-by-post basis. Have you actually read any of their references they cite? Did you have any questions or reservations on what you read?

    Quite frankly, I don't think you're trying. I'm not sure anyone here can help you if you're not willing to let anyone actually help you.

    The Yooper
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  42. #42: "When climate warms, more CO2 is released from the oceans, "

    For starters, when atmospheric CO2 increases, climate warms and oceans become more acidic.

    "If some warming event coincidences with a volcanic eruption which huge releases of CO2"

    Sorry, no soap. CO2 volumes from most eruptions are comparatively small. Large eruptions (such as Pinatubo) cause cooling due to their aerosol volume - that's well-documented. Along with that particular early 90's cooling event came a temporary drop in the rate of global CO2 increase -- also well-documented.

    If you would like references for any of the above, start with SkS search. I'm with Yooper on this, you need to do some research to support your ideas. And please, try harder than the old correlation-causation canard.
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  43. #24 The Ville

    You post "Apart from that, the faint young Sun and the CO2 thermostat would have taken care of long term CO2 effects and levels over hundreds of thousands of years"

    I still question the "faint young Sun" hypothesis. It is based upon some solar models but are they correct? If our sun was faint in the past (when CO2 levels were in the 6000 PPM range) then how did Mars have flowing water on its surface? These two conclusions are mutually incompatible. Either the Sun was not cooler and could warm Mars or Mars could never had liquid water with a fainter Sun.

    From studies on downwelling IR radiation, the contribution given by current levels of CO2 is about 10%. That's it.

    Here is what CO2 will give you: http://www.google.com/imgres?imgurl=http://www.real-debt-elimination.com/images/lynchi2.jpg&imgrefurl=http://www.real-debt-elimination.com/real_freedom/Propaganda/Global_Warming_Myth/lynching_of_carbon_dioxide.htm&h=818&w=870&sz=73&tbnid=mooueGrTNRbqNM:&tbnh=136&tbnw=145&prev=/images%3Fq%3Dcarbon%2Bdioxide%2Babsorption%2Bspectrum&zoom=1&q=carbon+dioxide+absorption+spectrum&usg=__pSKV5BxhGfhn4yRlb1D39C9_ZWw=&sa=X&ei=ITzXTISaNM-cnwfq_fzhCQ&ved=0CB8Q9QEwAw
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  44. Did not put up the link I will use Hyperlink. This chart shows the amount of IR CO2 will absorb from the IR spectrum.

    Chart of CO2 absorption ability.
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  45. Norman #46, as it happens there is more than one star in the universe. Thus, astronomers have been able to study the life cycle of stars in considerable depth. The idea that stars get hotter as they grow older is not, as you seem to imply, some vague hypothesis based on nebulous computer models... it is observed reality.

    As to Mars... the belief that it once had surface water goes hand in hand with the belief that it once had an Earth-like atmosphere. Just as the greenhouse effect keeps Earth habitable it could have once allowed liquid water on Mars. Now that Mars has lost most of that atmosphere it has very little greenhouse warming... and thus is too cold for liquid water. In short, the Sun is not the only thing which could have made Mars warmer in the past. Odd that you would assume that.
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  46. @protestant #42
    "Which one of you really believes that we would lose nearly all water wapor and have over 70% cloudiness without CO2? omg..."

    Actually, I do...and it doesn't take a complex climate model to believe it. Let's try...

    If you remove all the CO2, the climate will cool as 1/5th of IR absorption by the atmosphere is due to CO2 (that is well measured). You will rightly point out that there is still water vapor present that accounts for at least 75% of the greenhouse effect including clouds (also well measured). But I also know it's raining outside my house right now. That tells me water vapor condenses when the air temperature falls below a critical threshold, and that temperatures on earth often fall below this threshold...we have water in our atmosphere precisely because that atmosphere is warm enough to allow water vapor to keep from precipitating out faster than it evaporates.

    What happens when we weaken the greenhouse effect by removing CO2? It would lead to a colder atmosphere, which causes evaporation to decrease and precipitation to increase, which leads to a lower greenhouse effect, which cools the earth some more, which causes more water to precipitate, which lowers the greenhouse effect....and on and on until you reach a new much colder and drier equilibrium that depends on the other control knob -- the incoming solar radiation and the earths ability to absorb it and redistribute the remaining heat.

    You only need the model to estimate that stabilization point and the time frame over which it is reached. You don't need it to tell you that earth would be a lot colder than now in the absence of CO2, and that water would be less abundant. All you need to know that is that it rains, that water vapor absorbs IR radiation and that earth would be a lot colder if there was no greenhouse effect. Those facts are not in dispute.

    Without an IR absorbing gas(or gasses) that does not condense out when it gets colder, you cannot have a stable climate on earth that is anything like ours. Of course that also means when that non-condensing gas varies in concentration, for whatever reason, climate will follow it. That can happen for natural reasons, as it has in the past, or due to human impacts, as it does now.
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  47. Protestant - trying the "correlation prove causation" again. Did you read responses from the last time? No, the paper attempts to show that a modelled prediction is in accordance with observation. That is how science is done.

    "They claim there would be almost no greenhouse effect without CO2, thats an outrageous misinterpretation."

    No, what you are saying is an outrageous misinterpretation. I defy you to find any scientific paper that makes such a claim. From both observations and models, water vapour is temperature-controlled. Sure, water vapour feedbacks amplifies any change in any forcing but to investigate the cause of a trend requires looking at the forcings.
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  48. First off the comment Antarctic being ice free because CO2 levels being above 600 ppm is misleading as when Antarctica started to freeze 34 million years ago CO2 levels were 760ppm. The opening of the Drake passage is likely the key factor that caused the initiation of ice sheets in Antarctica.

    Cause and Effect are very confused as a cooling Antarctic would have reduced global CO2 levels as the oceans would have absorbed it from the atmosphere.

    This leads to what is always the biggest problem with paleo records with CO2 and temperature. Changes in ocean temperature CAUSE a change in solubility that leads to the observed EFFECT of changing CO2 levels.

    Determining the climate sensitivity from a CO2 change that is the EFFECT of changing ocean temperatures is meaningless.

    For example... The LGM to Holocene experienced a 80 ppm change in CO2 levels. The polar regions experienced an ~12 °C change in temperature. The change in solubility of CO2 in water for only a few meters deep of the polar oceans is more than enough to explain the change in CO2. No forcing required. Did the warming cause the CO2 levels to change? Yes.

    Much like this case. The polar oceans warmed, even if they were ice free, any water below 18 °C experiences significant changes in CO2 solubility with temperature. How can the climate sensitivity be determined from the FEEDBACK of warming oceans releasing CO2? It can't.

    Much like the cooling Antarctic region would have reduced global CO2 levels. Saying that lower CO2 levels CAUSED the cooling is not accurate. It is fully accurate to say that cooling oceans CAUSE lower CO2 levels. Much like warming oceans CAUSE higher CO2 levels.

    Fortunately the solubility of water is not open to debate.

    John Kehr
    The Inconvenient Skeptic
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  49. #46 CBDunkerson,

    Thanks for your response, but from what I have been able to find, Mars currently has more CO2 in its atmopshere than Earth does. Oxygen and Nitrogen are IR inert so if Mars had a thick atmosphere these gases wouldn't help it.

    "Q) Why is Mars so cold?
    A) Mars is cold because it is much farther from the Sun than Earth. Because of this, Mars receives about 2.5 times less solar energy than Earth."

    From Solar Energy reaching Mars.

    If the Sun was significantly colder eaons ago the amount of radiation reaching Mars would be even less. How would that support liquid water?

    Not sure what information source you are using for you statement: "Thus, astronomers have been able to study the life cycle of stars in considerable depth. The idea that stars get hotter as they grow older is not, as you seem to imply, some vague hypothesis based on nebulous computer models... it is observed reality."

    My source makes the claim it is a model..."Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at the various points in their life, and by simulating stellar structure with computer models."

    Source of above quote.

    A model can imply a generalization of patterns and perform fairly well, it cannot determine a specific case. I am sure astronomers will see various exceptions to predictions and rules.
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  50. Re: HumanityRules (13)

    Missed your question earlier, sorry.

    The referenced quote "similar, perhaps, to a future anthropogenic greenhouse maximum" of about 4,000 PPM CO2 is a bit odd. It is caveated, however.

    My interpretation is that the 4,000 PPM CO2 level referenced as a future anthropogenic maximum is if mankind continues its Business As Usual without change (if we "burn it all"), and if the oceans lose ability to sequester CO2 as they have been doing, and if we trigger a methane hydrate/clathrate release as is thought to have occurred during the PETM, than a 4,000 PPM CO2 level is about the maximum achievable.

    A lot of uncertainly there. But I would not consider it alarmism, but only a reference to an upper limit, caveated appropriately for the intended audience of the magazine. But without seeing the quote in its context, that's as far as I will go.

    Hope that's clear,

    The Yooper
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