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  1. Eric,

    Thanks for this clearly written post. The Antarctic ice core data is presently to the public very loosely, often in the interest of time or print space (I did so myself in a talk with high school students last week). It is important to remind everyone that i) we expect CO2 to lag behind temperature in ice core records, because of feedbacks, and ii)that the Antarctic cores are not a global temperature record.

    Comment by Simon D. — 27 Apr 2007 @ 3:14 PM

  2. Somebody give me a best estimate.

    We can predict a GLOBAL temperature within —– degrees based on 600,000 year old ice core samples.
    And I am —- % confident in the accuracy of those GLOBAL temps.

    [Response: These statements don’t make any sense and so can’t be filled in. -gavin]

    [Further Response: Our estimates of the magnitude of future global warming do not come from ice core data, and do not depend on it in any way. The point of this post is that the ice core data are entirely consistent with what we already knew (and have known since 1896 A.D. when Arrhenius published his climate sensitivity calculations). The ice core data make a nice illustration, and do provide an independent test of climate sensitivity. That the ice core data do not change the answer demonstrates that there is not very likely anything missing in our understanding. One of the things that motivated this post was Congressman Barton’s use of ice core data to try to contradict more than 100 years of well established physics. But the data do no such thing.–eric]

    Comment by tom — 27 Apr 2007 @ 3:14 PM

  3. Tom, is your objection that the ice core is 600000 years old, or do you object to the reconstruction of temperature based on deuterium? The latter technique is established and based on very reasonable physics. The former…? Well, is it your contention that D2O diffuses preferentially relative to H2O?
    Or is it the fact that the ice cores were taken from a small geographic region. I don’t think the intent is to give “global” temperatures, but I trust the data locally to within, say 10-20%, and globally, I think it accurately portrays trends. This is born out by other techniques where we can cross correlate them.
    It can be risky to assume that just because YOU don’t understand something, nobody else does either.

    Comment by Ray Ladbury — 27 Apr 2007 @ 3:56 PM

  4. Tom appears challenged by the idea of building global climate models based on atmospheric physics and doing years of testing those models against actual data. Of course, no one is trying to make a prediction based on global ice core data. The ice core data are used in model validation.

    Comment by FishOutofWater — 27 Apr 2007 @ 4:29 PM

  5. [apologies up front for simplifying some things, but I think it is too easy to go in too much detail and miss the main points – though the devil is often in the details…]

    Historically, before human intervention, changes in CO2 lagged temperature rises – accepted fact. But the CO2 rising does enhance the effect of rising temperature – a positive feedback. The warmer it is, the more CO2 released into the atmosphere, which makes it get warmer still – a basic positive feedback system.

    In itself I dont think the positive feedback can be disputed as it is just based on the effect of CO2 on solar radiation coming in and radiation from the earth going back out. Never mind the historic record – a simple lab experiment can prove the feedback effect.

    What may happen is that other feedbacks balance this out on some timescale or another, but that doesn’t change the fact that atmospheric CO2 and other greenhouses cause a positive feedback effect.

    When we increase CO2 artifically we are simulating that positive feedback, and it has just the same effect – ie it gets warmer. The fact that the climate record shows a strong correlation between temperature and CO2 certainly seems to tell us that the balancing effects don’t add up to enough to prevent the changes, because if they did, then the climate wouldn’t have oscillated like it did.

    I just read the comments on coyoteblog about this and had to reply there becuase such an incomplete picture was presented – but thought I’d add my reply here too, for folks who don’t follow that blog:

    http://www.coyoteblog.com/coyote_blog/2007/04/the_800year_lag.html#comment-67871824

    There seems to be an assumption in that thread that a positive feedback is just that – a positive feedback that keeps on forever being positive.

    There are many examples in nature of positive feedbacks that die out.

    – Set fire to a forest. It starts from a cold forest, then add a small flame, it grows to a huge forest fire, burns out, goes out, goes cold. Few years later the whole thing repeats.

    – Population growth – algae blooms – they start small, they grow almost exponentially, run out of food, die off.

    – Spread of a disease in a population – the more people have it, the more they infect, until it burns itself out.

    The same thing happens with CO2 and temperature. The positive feedback starts up, gets worse, until eventually it hits a stabilisation.

    In the case of our climate it could be as simple as it is only very marginally positive, so our extra help is enough to put it into a growth mode when combined with the increase in solar influx. Take away either and that is enough to kill the positive feedback.

    Or it could be that eventually it gets so hot that we become a shiny ball of cloud which cools down rapidly.

    The whole of the last several million years has been a classic two state climate, oscillating between ice ages and warm periods, with sudden changes between the two. That is undisputed by anyone on any side of the debate. That is exactly the sort of situation that would be caused by having positive feedback to switch from cold to warm, and eventually a negative feedback to switch fom warm to cold.

    In geological time, the balance of the system has changed several times, and just like any system can have a resonance at certain points, the climate can reach a resonant point where it is teetering between two states (our current 100,000 year ice age warm period cycle). Eventually the contintents shift or the sun changes and things settle down into a long warm or cold period.

    If you look at our climate, and compare it to a machine that has a vibration problem, you hear the vibration build up and then die away, build up and die away – the big build up and die away is the hundreds of millions of years climate shift, and the individual vibrations that make up the fine grain are the 100k year switches between ice age and warm spell. Of course, in the climate case, the whole thing is bounded by the creation of the solar system and the sun going poof and is definitely not cyclic in the billions of years timescale. Maybe someone can think of a better analogy?

    What we have right now (in my view) is an opportunity to actually control things and prevent both the positive feedback being enough to lead to rapid temperature growth, and the negative feedback being enough to cause an ice age. At least for the time being, when the continents, orbits and solar situation mean it is so finely balanced. In longer timescales, we will have to adapt, but for the next few million years its finely balanced and we can keep it just where we want it.

    If people would stop bickering about it and misrepresenting the situation in either direction and look at the bigger picture then we might actually start constructively planning the climate for our future.

    Comment by Jeremy Kenyon — 27 Apr 2007 @ 4:44 PM

  6. What if the oceans are being warmed due to another forcing? How is GHG warming the oceans AT THE OBSERVED RATE? How do the models account for this? Do the models predict the rate of ocean warming we are seeing? Do the models use field measurements to verify assumptions regarding heat transfer between air and ocean?

    I noticed that JA Smith, in a comment on this subject on this site said that heating of the oceans by GHG was expected to take decades to centuries, yet it seems to be showing up now. The mechanism of IR radiation heating the ocean through the skin seems very slow, much slower than observed.

    The reason I think that this is important is that if some other mechanism is heating the oceans, then wouldn’t they be expected to outgas CO2?

    I know that Solanki says that he has bounded solar forcings a something like .5 watts/m^2, but how does he do this? Does he extrapolate a couple of decades worth of satelite oberservations over centuries?

    Is cloud formation well understood? Isn’t it possible that even minor variation if solar output could affect cloud formation, would this not greatly amplify any effect, even if the variations were minor?

    How is it known that the cosmic ray theory is untrue?

    [Response: …Sigh… We’ve addressed all of these questions elsewhere on this site. –eric]

    Comment by Moptop — 27 Apr 2007 @ 5:03 PM

  7. An unanswered question is that 55 millon years ago CO2 levels reached 1000ppm. According to many predictions in the media those levels of CO2 should have caused a runaway greenhouse effect. Though the climate then was considerably warmer than today this did not happen, otherwise we would not be here. Can somebody explain this?

    [Response: No one seriously predicts a runaway greenhouse effect: http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/ -gavin]

    Comment by David Price — 27 Apr 2007 @ 6:01 PM

  8. Hello to the respected scientists at RealClimate. Congratulations on your efforts! This site brings good understanding of the current status of climate science in a clear way, understandable by the laymen like me.

    There is still plenty of misunderstanding and confusion about the scientific findings on the climate science, promoted by some people. I am hoping that your research and explanations reach further in the minds of the masses by perhaps writing a book or airing a documentary made by scientists; as the skeptic side has done, but mostly by misleading and inaccurate arguments.

    Continue the good work!

    Comment by ginin — 27 Apr 2007 @ 6:02 PM

  9. A recent published paper states that “phase relationship between CO2 and EDC temperature inferred at the start of the last deglaciation (lag of CO2 by 800±600 yr) is overestimated and that the CO2 increase could well have been in phase or slightly leading the temperature increase at EDC.”

    What do you think about this?

    Yo can find the paper here: http://www.copernicus.org/EGU/cp/cpd/3/435/cpd-3-435.htm

    [Response:I haven’t read that paper yet but it’ll be interesting to look at. I’ll be very surprised if it turns out that CO2 leads global temperature after all, but it could certainly lead Antarctic temperature. Yet the evidence published to date — for the few intervals of time where one can actually do the calculation accurately, show that CO2 does lag Antarctic temperature — refer to the papers cited in the post –eric]

    Comment by Scaramanga — 27 Apr 2007 @ 6:14 PM

  10. Try putting that in the search box for previous mentions.

    Comment by Hank Roberts — 27 Apr 2007 @ 7:28 PM

  11. Eric,

    Ok, so you come up with ONE POSSIBLE explanation for the temp/co2 lag. A much simpler and logical explanation is that temperature controls co2 concentration.

    [Response: Temperature does have an influence on CO2 concentration. Indeed, about 1/5 of the glacial interglacial change in CO2 can be explained by the greater solubility of CO2 in cold ocean water. So what? That doesn’t change the fact that if you burn fossil fuels you put CO2 into the atmosphere, regardless of what temperature does (or would do) on its own. Why do people find this so difficult to comprehend? It is not complicated!–eric]

    Regardless, we are now in a position where co2 levels and temperatures are rising. Using your logic, the following is happening:

    – C02 concentrations have risen from about 290 to 380 ppmv in the last 100 years.
    – Since co2 levels were otherwise constant, the entire 90 ppmv rise is due to man’s burning of fossil fuels. The Mona Loa co2 record shows a smooth constant rise of co2 in the atmosphere, as one would expect from an accumulation resulting from the burning of fossil fuels.
    – For this buildup of c02 in the atmosphere to occur over the 100 year time frame, the residence time of co2 must be between at least 50 and 200 years. Essentially once emitted, co2 in the atmosphere is almost permanent. Even though the relationship between co2 in air and dissolved in fluid is well known, and dozens of independent calculations of residence time center around a 5 to 6 year residence time.
    – Mass balance calculations, however, indicate that co2 concentrations should be twice as high as they are given the known emissions and the long residence time, indicating a missing sink. It is postulated that the ocean is a major carbon sink, absorbing most of the missing 50 percent of the co2. Somehow, at the same time, co2 is both stable in the atmosphere for hundreds of years and 50 percent of the co2 emitted each year is absorbed by the ocean.

    An alternative explanation is that temperature controls co2. Using this logic, the following is happening:

    – Temperatures rise naturally, warming the oceans.
    – Warmer oceans release co2 into the atmosphere, raising its concentration in the air.
    – Co2 released to the atmosphere through the burning of fossil fuels is cycled through the oceans based on a five year residence time, so that only about a quarter of the co2 in the atmosphere at any one time is from man.
    – A close review of the Mona Loa data indicate substantial fluctuations in the incremental annual increase in co2. For the 50-year record, annual increases vary from as low as 0.25 to as high as 2.70 ppmv. The co2 levels do not increase on a steady basis, say at a rate corresponding the growth in the world economy.
    http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_mm_mlo.dat

    – There is a strong (qualitative) correlation between ocean surface temperature and the increase in atmospheric co2. After relatively cooler ocean surface years, the increase is small, and after relatively warmer ocean surface years, the increase is large. The relative annual increase in co2 mirrors ocean surface temperatures.
    http://www.ncdc.noaa.gov/oa/climate/research/2007/mar/global.html#Temp

    – Therefore, it appears that temperature (of the ocean) does in fact control co2 concentrations in the atmosphere

    [Response:Much of what you say may sound sensible, but it isn’t. There is *zero* question about the cause of the recent CO2 rise, as we’ve explained multiple occasions (e.g. here). One of the things pointed out in that post is that we know that the rise in atmospheric CO2 is entirely caused by fossil fuel burning and deforestation because many independent observations show that the carbon content has also increased in the ocean. If the oceans had contributed to the rise in atmospheric CO2, it would hold less carbon. There is no surprise that the CO2 in the atmosphere winds up partially in the oceans, nor that the amount of CO2 going into or coming out of the oceans varies in time and space — that’s simple equilibrium chemistry between the liquid (that is, dissolved) and gaseous phases, and does explain part of the variability about the long term rising trend. So what? That doesn’t change anything!–eric]

    Comment by B Buckner — 27 Apr 2007 @ 8:05 PM

  12. If people would stop bickering about it and misrepresenting the situation in either direction and look at the bigger picture then we might actually start constructively planning the climate for our future.

    I agree, we are presented with a golden opportunity for global planetary engineering. If we pin atmospheric carbon dioxide concentration to right about 300 to 320 ppm, we are looking at 20-30 thousand years of stable climate, with huge fresh water reserves, and we are only about half way into a global mass extinction.

    The entire system indeed appears to still be salvageable IF WE START RIGHT NOW!

    Any suggestions? I have a few.

    Comment by Thomas Lee Elifritz — 27 Apr 2007 @ 8:05 PM

  13. You nicely rebutted what Tim Ball had said here:

    http://www.desmogblog.com/tim-ball-deceptions-prevarications-and-arguments-with-no-evidence

    From the article:

    “Q: Is the rising CO2 level the cause of global warming or the result of it?

    Ball: That’s a very good question because in the theory the claim is that if CO2 goes up, temperature will go up. The ice core record of the last 420,000 years shows exactly the opposite. It shows that the temperature changes before the CO2. So the fundamental assumption of the theory is wrong. That means the theory is wrong. … “

    Comment by Stephen Berg — 27 Apr 2007 @ 8:07 PM

  14. B. Buckner
    “Temperatures rise naturally, warming the oceans.”

    You know, as a physicist, I really have trouble letting go of conservation of energy. I mean if temperatures are rising, what is the source of all that energy. It has to come from somewhere, right. We know it’s not the Sun–not enough change there. Let me know when you have a theory that is consistent with at least the basic laws of physics.
    Likewise, if the carbon is coming from the oceans, then why is it depleted in C-14. Are you proposing it stays put in the oceans for tens of thousands of years? There are LOTS of other inconsistencies in your little theory, but I’ll stop there. Come back when you’ve worked those out.

    Comment by Ray Ladbury — 27 Apr 2007 @ 8:19 PM

  15. Post #7 (B Buckner): So, let me get this straight, you are seriously proposing that by pure coincidence the levels of CO2 started rising naturally over the last 100 years or so to levels not nearly seen in at least 650,000 years…and probably for millions of years? And, that just coincidently, the rate of the rise has consistently been (when averaged over a few year period to smooth out variability due to seasonal cycles and other factors) equal to about half of the emissions of CO2 that we are putting into the atmosphere?

    And…this isn’t even mentioning the isotopic evidence.

    [Response: I think he is proposing just that. Not a little bizarre, but I’ve heard it before. It is getting quite boring to hear it over and over again, particularly when we’ve addressed it no less than three times here at RealClimate. To paraphrase someone else, just because you can say something that sounds like science doesn’t make it science (or true). –eric]

    Comment by Joel Shore — 27 Apr 2007 @ 8:53 PM

  16. The more I read Real Climate, the less convinced I am of the underlying hypotheses that form the AGW assumptions. There is a Temp/CO2 lag throughout the entire periodic cycle (even at cooling)? Why is there a methane correlation as well (that isn’t explained by a dependence on temperature)? Is there a delay in the methane concentrations as well? Where can I find a simplified description of the feedback equations that model such a system?

    [Response: The methane correlation is because natural methane emissions are also affected by climate – principally from wetlands. They increase in wet and warm conditions and decrease when it is cold and dry. These changes combined with the shorter residence time for methane in the atmosphere mean that the lag is much less (a few years or so). In fact, methane reacts so quickly and in both hemispheres almost simultaneously that its variations are used to tie the together the ice core records in Greenland and Antarctica. But as with CO2, those lags are related to the climate effect on sources and don’t have anything to do with the GHG effect on climate which is known from lab measurements and direct observations. – gavin]

    Most importantly, why are the tropospheric temperatures not changing at the modeled rate?

    I read your explanations for some of these fundamental questions, and they make sense – but they are only hypotheses – where are your testable predictions and experimentally derived results? Please don’t answer with models! Models can be made to verify any results – but validation is another matter.

    thanks in advance for any help in clearing this up for me

    Comment by Steven — 27 Apr 2007 @ 10:55 PM

  17. Eric,
    Another great post. Like most people who comment on this site I have had arguments about this issue with contrarians.
    But there is one issue that I need clarified: the fraction of warming or cooling caused by CO2.
    In one paragraph you say that it is 1/3 but in the next you say that CO2 and other greenhouse gases amount to about 1/3. Jeff Severinghaus in his letter says that CO2 and other greenhouse gases amount to about 1/2.
    Thanks for this great site.

    [Response:The exact amount depends on the magnitude of other changes, which aren’t certain. In his Sci. Amer. article, Hansen estimates that the radiative forcing from all greenhouse gases together (glacial-interglacial) is -2.6 +/- 0.5 W/m^2, and ice sheet albedo is -3.5 +/-1 W/m^2. So the greenhouse gases together (excluding the water vapor feedback) account for 0.3 to 0.55 of the total. CO2 is roughly half of the total greenhouse gas change, so thats 0.15 to 0.26. Note that part of the uncertainy in all this is the time uncertainty — from the ice core records, we can pick a rather precise time and look at a rather precise number for greenhouse gas concentrations, but pinning down the magnitude albedo change at exactly the same time (since albedo is not globally uniform, obviously) is impossible. –eric]

    Comment by Stephen Spencer — 27 Apr 2007 @ 11:53 PM

  18. Eric says
    Temperature does have an influence on CO2 concentration. Indeed, about 1/5 of the glacial interglacial change in CO2 can be explained by the greater solubility of CO2 in cold ocean water.

    Umm read Drever again!

    Comment by makarov — 28 Apr 2007 @ 2:42 AM

  19. Don’t bother to quibble with Coyote over the cause. The important issue is whether we are going to get the climate under control and survive or not get the climate under control and die attempting to breathe hydrogen sulfide. It seems that hydrogen sulfide from overheated oceans is implicated in the end-permian event and at least one other extinction. The question is what levers do we have to push the climate away from a hydrogen sulfide catastrophe? Regulating carbon dioxide is one of those levers and maybe the only one of those levers within relatively easy reach.

    Comment by Edward Greisch — 28 Apr 2007 @ 2:53 AM

  20. I love realclimate for its deep understanding of climate issues that people like myself cannot get anywhere else. It is like having your own personal scientist at your disposal whenever it is needed.

    For instance I am currently still remonstrating with some people on another forum about the hockey stick data and realclimates insights into it have been invauable.

    I have read all of the arguments about climate change and lets get it clear. Relative to 1750 greenhouse gases are now higher by 150 ppmv and in addition to this the world is warming. What lags what might seem like a good debate to have and one that has to be answered to as the skeptics for good scientists to set up sites like this to argue the cause but come on the evidence is clear, it is not the SUN that has caused the current warming and we have a perfectly robust argument for stating that it is greenhouse gases (all of which has increased).

    Case closed for me, however as we rely on fossil fuels for everything you can understand the reticence for doing anything about it but that is what Governments are for, to make tough choices and to limit our freedoms when necessary.

    I beg the world for R&D of a magnitude not seem since the second world war but the world is slow to respond unfortunately.

    Comment by pete best — 28 Apr 2007 @ 5:00 AM

  21. Thank you both Eric and Jeff for a clear explanation of a difficult issue.

    I’ve only recently stumbled across RealClimate and it’s a breath of fresh air to find climate scientists endeavoring to make the science of climate change accessible to the public. Unfortunately most of the “accessible” (read superficially plausible) material I have encountered to date is from skeptics.

    I was aware of Milankovitch cycles and their role in driving ice ages and so I was somewhat confused by Al Gore’s implicit attribution of global temperature changes to CO2 in An Inconvenient Truth. Another quibble I had was that Gore presents the impact of sea level rise without referring to the long time scales (in human terms) involved. (Although recent data from Greenland and Antarctica suggest that these timescales may not be as long as the IPCC says.)

    However, on reflection I think Gore’s approach is apposite. Scientists are guarded and reticent by nature and training. Carefully qualified statements on the probability that climate change is real and anthropogenic, along with possible potential impacts – also carefully qualified and filled with jargon – are lost on the general public, who would find even the simplified approach of RealClimate overwhelming.

    On the other hand, politicians speak with absolute conviction even when telling the most outlandish lies. In fact, the art of persuasion in the real world (think advertising) is far removed from that in the scientific world. In contrast to most politicians and many sceptics, Gore is reasonably careful with the truth. However, he is aware that leadership requires forceful persuasion and clearly articulated conviction about the correct path. Consider the difference between, “If we don’t reduce our use of fossil fuels we can kiss our way of life goodbye”, and “I think the balance of evidence suggests we reduce CO2 emissions or there is potential for serious consequences.”

    A final point. The fact that CO2 lags temperature during cooling and warming periods in the last 600,000 years means that it does not initiate these changes. This means that the current warming trend is qualitatively different from those we can study through ice cores etc., even if past warming was amplified by a CO2 feedback. Past warmings are not an analogue for our present situation, which to my mind places a greater burden of proof on climate scientists regarding evidence for climate change.

    Thanks again.

    Bruce

    Comment by Bruce Tabor — 28 Apr 2007 @ 7:25 AM

  22. Eric wrote,
    “the ice at any time will always be younger than the gas bubbles it encloses”

    I have read the exact opposite i.e. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=33751

    I kindly thank you If you could clarify this point.

    [Response: Oops, you are right! That was a typo on my part. If you think about the process, it can’t be right the way I wrote it. Thanks for pointing that out.–eric]

    Comment by Ellis — 28 Apr 2007 @ 7:27 AM

  23. Not only does CO2 lag the temperature changes in the ice age, but the CO2 feedback is only capable of explaining 20% to 40% of the total temperature change and, in many timelines, the temperature trends and the CO2 trends are going in the opposite direction.

    These are facts that should be studied and understood versus downplayed or ignored.

    [Response: These are facts that are studied and indeed understanding the details of the glacial-interglacial CO2 changes ranks as one of the great challenges in the field of paleoclimatology. It has not means been entirely solved. Prior to human activities interveneing, the CO2 and temperature have often been going in opposite directions because there is a lot else going on, and that continues to be the case. The well known cooling due to Pinatubo in 1992 is a case in point. But as greenhouse gases increase — at many many times the rate than they have int the past — they become the dominant forcing, and the other causes of temperature change become decreasingly relevant. If you are riding your bicycle, there is a myriad of things that might make you fall over — hitting a rock, wobbling because you’re tires are flat, looking distractedly at a cute member of the opposite sex. If a car runs you over, those minor forcings become pretty irrelevant. The point is that we are essentially (rather literally) running over the climate system with a car.–eric]

    Comment by Chris Shaw — 28 Apr 2007 @ 7:29 AM

  24. Eric,
    Your response to #11 begs the question if the oceans are adding CO2, does that offset the missing 50 percent of CO2 that should be in the atmosphere due to the Mass Balance Calculations for 50-200 year residency of CO2. Also, I would like to know how this fits in with the Modeler’s use of buffers to explain why the oceans do not recycle the CO2 in the atmosphere.
    You state in the response to #10, “…There is no surprise that the CO2 in the atmosphere winds up partially in the oceans, nor that the amount of CO2 going into or coming out of the oceans varies in time and space — that’s simple equilibrium chemistry between the liquid (that is, dissolved) and gaseous phases…”
    Are the buffers a part of simple equilibrium chemistry, and where can I go to read up on this and how it pertains to the Models.

    [Response: You could start with virtually any basic undergraduate textbook on the carbon cycle. For example, The Earth System by Lee R. Kump et al., Prentice Hall, 2nd Edition, 2003, 419 pages. –eric]

    Comment by Ellis — 28 Apr 2007 @ 8:06 AM

  25. I mean if temperatures are rising, what is the source of all that energy. It has to come from somewhere, right. We know it’s not the Sun–not enough change there.

    No, the energy does come from the Sun. Not because the Sun has changed its brightness, but because the ability of the enormous flow of solar energy through the Earth’s surface environment to escape back to space has been impaired.

    Comment by Paul Dietz — 28 Apr 2007 @ 8:43 AM

  26. I’m curious about the use of the Pinatubo eruption in testing the climate models. Their success in modeling the effect of the eruption is brought up quite frequently. What else is used to assess their efficacy? I imagine the modelers are all waiting with baited breath for the next big eruption, but in the meantime, what else is of particular use in this regard. I heard a retired professor on the radio recently going on about how the models are being tweaked so that they agree with each other and so they aren’t independent and aren’t tested like real scientific theories are. That seemed like a totally implausible assertion to me. I would have thought that you were trying to make them agree with reality rather than each other. Given that, what aspects of the climate system in particular are used for testing in the absence of volcanic pyrotechnics.

    [Response: Lots of the things! Response to El Nino events, the 20th century trends, the mid-Holocene (6kyr ago), the 8.2kyr event, the last glacial maximum, ozone depletion, North Atlantic Oscillation, the Sahel drought…etc. These are all (in some sense) a response to forcings and so allow us to test exactly the aspects that will be important in the future. The models are not tuned to these events (most ‘tweaking’ is done to match the climatologies, seasonal cycles and diurnal cycles instead) and so they provide a good validation of the models. – gavin]

    Comment by Craig Allen — 28 Apr 2007 @ 8:49 AM

  27. Eric says “If you are riding your bicycle, there is a myriad of things that might make you fall over — hitting a rock, wobbling because you’re tires are flat, looking distractedly at a cute member of the opposite sex. If a car runs you over, those minor forcings become pretty irrelevant. The point is that we are essentially (rather literally) running over the climate system with a car.”

    Now that sir is a good analogy (even if some will doubtless disagree).

    :o)

    Comment by Hugh — 28 Apr 2007 @ 8:55 AM

  28. Eric: thank you for your thoughtful response. I would be interested in seeing data indicating that ocean levels of carbon are increasing over time. I have been unable to find such a data set, so any help would be appreciated. I am skeptical that such comprehensive data can exist given the size and depth of the ocean. Also, seeing as the oceans contain 50 times the co2 of atmosphere, and the huge exchange that occurs between ocean and atmosphere, I would think such an increase would be trivial and difficult to document.

    [Response:You are right that this is a non-trivial calculation, but there is a huge literature on this. Much of the work is based on carbon isotope studies. You might start with the web site of the Carbon Dioxide Information Analysis Center. –eric]

    Ray Ladbury: Your theory on the co2 temp lag is that temperatures stop falling and then rise for some unknown reason, in an environment of low and falling co2 concentrations. After 5000 years of rising temperatures and 4200 years of rising co2 concentrations, temperatures reverse themselves in an environment of high and rising co2 concentrations and start falling for some unknown reason. It seems you have a few things to work out yourself.

    [Response: You are adding no clarity to this! –eric]]

    Comment by B Buckner — 28 Apr 2007 @ 8:56 AM

  29. Glad this issue is finally put to rest.

    And now we can get on to the more serious implications of CO2 & CH4 lagging warming. Re #7, while permanent venusian-style runaway warming is not possible now (until the sun becomes a lot hotter in billions of years), we could go into (what scientists have told me) is hysteresis, a really great warming for even up to 100,000 or 200,000 years, in which a lot of life dies out, before the world cools back down again.

    We humans could be pulling the trigger on that right now, and who knows when we might reach a point at which even if we cease & desist from our human emissions, the positive feedback chain of “warming causing emissions causing more warming” takes on a life of its own. Maybe in 10 years, maybe in 100 years, maybe in 200 years.

    Maybe we’re in this hysteresis phase already, and in 2058 scientists will be able to definitively say that on April 29th, 2003 at 3:20 pm (well, science does improve over time) the world passed the tipping point into this hysteresis period, and if only people had listened to Earth Day suggestions back in 1990, and put forth all effort to implement them, we could have avoided it.

    This hysteresis may not be a high probability, but it is a possibility, since it happened 55 & 251 mya, so we laypersons need to keep our sights trained on that, and do all we can to prevent it from happening.

    That CO2 lags (& is caused by) warming is no consolation to me whatsoever. It make the whole thing a lot more dangerous.

    Comment by Lynn Vincentnathan — 28 Apr 2007 @ 9:40 AM

  30. Re #28 Data on oceanic acidity:

    The Royal Society (the national academy of science of the UK) produced a very readable report in 2005 titled Ocean acidification due to increasing atmospheric carbon dioxide it includes very clear explanations of the science, both that relating to levels and how they have and are changing, and the likely impact on marine ecosystems. It has informative graphics and references to the most important papers and datasets up to that time. You could take this as your starting point in hunting down the actual raw data.

    Re #26 Testing the models:

    Thanks Gavin. I suspected that the answer was going to be along those lines. This would make for a worthwhile article some time in the future. Especially given the never-ending skepticism about the validity of climate models.

    Comment by Craig Allen — 28 Apr 2007 @ 9:44 AM

  31. Re #30
    I’m puzzled by two points.
    1) Figure 1 in the report you cite states that atmospheric residence times for CO2 are 3 years, which seems at odds with the stated residence times of 50-200 years elsewhere in this blog (and from many other sources).
    2)It has also always puzzled (Figure 1 again) me that the anthropogenic fluxes of CO2 are approx 6Gt/yr or only 5% of the terrestrial biological fluxes to and from the atmosphere and 6% of those to/from the surface ocean. It’s amazing such a tiny perturbation can have such a huge impact of atmospheric CO2 and climate (yes I realise the maths adds up). It makes me wonder whether we can be confident that reducing the burning of fossil fuels will restore the balance, or could it be that large scale anthropogenic land use changes are more important than fossil fuels.

    [Response: Fossil fuels are the main problem but land use changes are a non trival part of it (something like 20%). The residence time calculation is confusing and indeed the concept of residence time is not very useful for a multicomopnent system. The average CO2 molecule does spend only a few years in the atmosphere, giving that 2-3 year residence time you cite. But effective residence time is much longer because of the equlibrium (or near equlibrium) between surface ocean and atmosphere and biosphere and atmosphere. The residence time of a CO2 molecule in the surface ocean is nearly as short as in the atmosphere, so many of the molecules that go in come right back out! So the effectie residence time of the combined system is what is important, and that is more onthe order of hundreds of years — or indeed, thousands, if we are talking about the residence time inthe combined surface ocean/atmophere/biosphere, vs. the deep ocean.–eric]

    Comment by Bruce Tabor — 28 Apr 2007 @ 10:12 AM

  32. Re # 28 (and 30) ocean carbon uptake

    See also:
    Feely, R.A. et al. (2004) Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans. Science Vol. 305. no. 5682, pp. 362 â?? 366 (16 July) http://www.sciencemag.org/cgi/content/abstract/305/5682/362

    McNeil, B.I. (2003) Anthropogenic CO2 Uptake by the Ocean Based on the Global Chlorofluorocarbon Data Set. Science Vol. 299. no. 5604, pp. 235 â?? 239 (10 January) http://www.sciencemag.org/cgi/content/abstract/299/5604/2357

    Sabine, C.L. et al (2004) The Oceanic Sink for Anthropogenic CO2. Science Vol. 305. no. 5682, pp. 367 â?? 371 (16 July)
    http://www.sciencemag.org/cgi/content/abstract/305/5682/367

    Orr, J.C. et al. (2005) Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437, 681-686 (29 September)

    Plus, there is plenty of info at the NOAA Pacific Environmental Laboratory CO2 Program website:

    http://www.pmel.noaa.gov/co2/co2-home.html

    Comment by Chuck Booth — 28 Apr 2007 @ 10:34 AM

  33. I would propose that the lag of CO2 behind temperature is simply an artifact of the measurement technique. Hand waving arguments about dynamics of feedback etc. are unnecessary. Here is an electrical engineer’s take on it.

    The temperature record is inferred from hydrogen/deuterium ratios in the ice itself. The H2 is “trapped” instantaneously as the snow is deposited. Thus the signal instantaneously follows temperature.

    The CO2 is determined from analysis of ice bubbles. Formation of ice bubble is not instantaneous. How long does it take to form a bubble? It depends, since it is controlled by depths and pressures. In the websites from the Siple and Vostok sites you can find that it takes 60-80 meters for the snow (fern) to be compressed to form ice which has bubbles trapped. They alsa say that below 3000m, the pressure is so great that the bubbles are crushed.

    This implies that the resolution of the ice core C02 time series is related to the length of the record. Long records necessarily have low resolution because you need to have a low accumulation rate to get only 3000m in 400,00 to 600,000 yr. The Siple site has a resolution of 22 years because the accumulation rate is high. However the record only goes back 200 years for the same reason. THERE CAN BE NO UNIVERSAL TRAP TIME. It depends onthe particular site ( i.e. on the snowfall rate at that site).

    60m / 3000m * 600kyr = 12000 yrs to trap a bubble! This is an extreme over estimation, however, because the fern is compressed as it is buried. However 500 to 1000 years (the delays seen between the CO2 and temperature) would not be out of the question. This is much longer than the C02 time constant (100 to 200yr).

    The signal from the CO2 is therefore passed through a moving average filter. Think about the response of moving average to a step function. The output is a ramp with a duration of the integration time. Compared to the input, the output looks delayed. You can imagine any input as composed of a series of small steps, so the output would resemble the input, just a little delayed, and with any “spikes” averaged down. The technical method is to convolve the input with a square pulse. As the pulse with goes to zero, we have a delta function, and the output is an exact copy of the input with no delay. This is the case for the hydrogen/deuterium ratio.

    Conclusions:

    1) Ice bubble CO2 must necessarily show some lage behind the temperature from hydrogen/deuterium in the ice itself.

    2) The CO2 signal is also low pass filtered by a MA filter with this same integration time. This integration time appears to beseveral times longer than the residence time of a CO2 perturbation in the atmosphere.

    Dave Dougherty

    [Response: David, this is all quite reasonable, but be careful not to reinvent the wheel. What you’ve said is encapulated in my short statement that there is uncertainty in the lag/lead precisely because of uncertainty in the trapping time, which does (as you say) vary with conditions (notably, temperature and snow accumulation rate). Lots of work has gone into getting this sorted out in detail, and the Monnin and Caillon papers I cited in my post are the examples of such work — and that work shows a lag AFTER correcting for the trapping time. Read those papers, you will like them! –eric]

    Comment by Dave Dougherty — 28 Apr 2007 @ 10:48 AM

  34. # 19 Edward wrote [It seems that hydrogen sulfide [H2S] from overheated oceans is implicated in the end-permian event and at least one other extinction]

    I don’t want to step on anyone’s current unpublished research, so I have to tread very lightly. This is being actively investigated for the current human-caused global warming scenario with models and paleoclimate data. So far, results indicate that H2S extinction is not one of our biggest worries.

    Comment by Richard Ordway — 28 Apr 2007 @ 11:36 AM

  35. So far, results indicate that H2S extinction is not one of our biggest worries.

    Since our current atmospheric carbon dioxide rise is unprecedented in geological history, short of a major asteroid impact, I would suggest otherwise. Clearly we need to stop and reverse the trend before the end of the century. Apollo 13 needed to stop and reverse the trend before the end of the mission.

    Comment by Thomas Lee Elifritz — 28 Apr 2007 @ 12:22 PM

  36. If you want to boil this post down to its bones and get past the (necessary) scientific language…This is an extremely oversimplified (and scientifically and PC incorrect) explanation… but here it is:

    Natural warming is a three step process between temperature and CO2 where everything “causes” everything else.

    1) The Earth’s temperatures increase a little due to Earth’s orbit changes.

    2) This little warming causes the oceans to warm up which releases huge amounts of CO2.

    3) The increased CO2 now causes a huge temperature increase- like adding billions of tiny suns to our solar system(physics).

    Now that you have a basis for understanding, go and read the original post.

    (Fourthly, I duck as every researcher takes a well-deserved strong swing at me for being [correctly] way too inaccurate, muddying the situation and butchering science and reality…but you get a glimmer of understanding for the first time.)

    [Response: No need to duck. That’s really it in a nutshell. Thanks for the clarity! We scientists sometimes lose sight of the essentials because the details are ultimately imporant, and of course are interesting to us. (I do hasten to add that it isn’t as simple as the oceans warming alone resulting in more CO2. There’s also ocean circulation and chemistry changes, both probably more important than the temperature.)–eric]

    Comment by Richard Ordway — 28 Apr 2007 @ 12:27 PM

  37. Pleeeease (esp the hosts here) comment on the following (which was passed onto me from my parish priest, who refuses to say anything about GW); he simply doesn’t believe anything I have to say on the topic:

    VATICAN CITY, APRIL 27, 2007 (Zenit.org).- Scientists might not have human behavior to blame for global warming, according to the president of the World Federation of Scientists.

    Antonio Zichichi, who is also a retired professor of advanced physics at the University of Bologna, made this assertion today in an address delivered to an international congress sponsored by the Pontifical Council for Justice and Peace.

    The conference, which ends today, is examining “Climate Change and
    Development.”

    Zichichi pointed out that human activity has less than a 10% impact on the environment.

    He also cited that models used by the Intergovernmental Panel on Climate
    Change (IPCC) are incoherent and invalid from a scientific point of view. The U.N. commission was founded in 1988 to evaluate the risk of climate change brought on by humans.

    Zichichi, who is also member of the Pontifical Academy of Sciences, showed that the mathematical models used by the IPCC do not correspond to the criteria of the scientific method.

    He said that the IPCC used “the method of ‘forcing’ to arrive at their
    conclusions that human activity produces meteorological variations.”

    The physicist affirmed that on the basis of actual scientific fact “it is not possible to exclude the idea that climate changes can be due to natural causes,” and that it is plausible that “man is not to blame.”

    To that end, Zichichi explained how the motor of meteorology depends on
    natural phenomena. He gave as an example the “energy sent by the sun and
    volcanic activity that spits out lava and enormous quantities of substances in the atmosphere.”

    He also reminded those present that 500,000 years ago the Earth lost the
    North and South Poles four times. The poles disappeared and reformed four times, he said.

    Zichichi said that in the end he is not convinced that global warming is
    caused by the increase of emissions of “greenhouse gases” produced through human activity.

    Climate changes, he said, depend in a significant way on the fluctuation of cosmic rays.

    [Response: I’m afraid I don’t know what to say. Most of what these guys say is incoherent (we lost the N and S pole!??). The few coherent things are wrong. –eric]

    Comment by Lynn Vincentnathan — 28 Apr 2007 @ 1:07 PM

  38. And who it this Antonio Zichichi?

    And what is the World Federation of Scientists? Credible?

    [Response: Wikipedia has a bio on him. I participated in a workshop in Cicily organized by Zichichi (under the auspices of the WFS) several years ago. Needless to say, I was quite disappointed with Zichichi’s penchant for making brazen assertions in areas of science (such as climate modeling) where he is transparently ignorant. Sadly, this is just more of the same old from Zichichi. -mike]

    Comment by Lynn Vincentnathan — 28 Apr 2007 @ 1:10 PM

  39. # 35 Thomas wrote: [Since our current atmospheric carbon dioxide rise is unprecedented in geological history, short of a major asteroid impact, I would suggest otherwise].

    Now, I am niggling. However, have you recently talked to publishing scientists who are actively researching hydrogen sulfide (H2S) poisoning?

    I have- last month..it’s where I work… and this is what they had to say.

    This does *not* mean that hydrogen sulfide poisoning is a dead issue.

    It does not mean that human-caused global warming is not potentially dangerous…just read the published body of research since 1842…or better yet talk to research scientists who are actively publishing in this like I talk to them weekly.

    Bottom line…many I talk to are scared. They (publishing scientists) use words even publicly such as “the evidence is alarming to me” based on the body of published research since 1842.

    This is about the most forceful that they are allowed to be. Some of them privately state to me that they think it might already be too late to stop extreme damage…maybe even to our civilization, but we still have to try.

    But I am not going to back down from the H2S evidence even if the evidence is currently saying something that people disagree with or is not alarming enough for them.

    However, you are right to question me on what I am saying, because it is not published yet in an open matter. I post from two IP adresses…one of them will tell you what you want to know.

    Comment by Richard Ordway — 28 Apr 2007 @ 3:14 PM

  40. He’s no doubt talking about the periodic collapse of the earth’s magnetic field.

    Comment by cce — 28 Apr 2007 @ 3:30 PM

  41. B. Buckner. Gee. You got all that from a post in which I said butkis about the cause of warming or cooling. My “theory” on the current warming epoch is consistent with the scientific consensus and with the evidence. Look, warming won’t just happen. There needs to be an energy source that is increasing. What is yours?
    As to the question of where the CO2 comes from, that is also unambiguous–it is mainly from anthropogenic burning of fossil fuels with significant contributions from other anthropogenic activities.
    As to the oceans, they are indeed large. The question is how much CO2 gets transported to the depths (where it would indeed be difficult to sample it) and how much stays near the surface. Best evidence is that the oceans remain a net carbon sink.

    Comment by Ray Ladbury — 28 Apr 2007 @ 3:39 PM

  42. #37 Eric: [I’m afraid I don’t know what to say].

    I have something to say to people who deny climate change: It has two parts.

    1. First, does Antonio Zichichi currently publish in established peer-reviewed journals on the issue of climate change(CC)?.

    2. Secondly, does Antonio Zichichi’s published work on CC stand up under long-term peer-reviewed scutiny in the journals?

    Answer: …name one climate change denier scientist or argument that does.

    Simplistic…but it is true.

    Comment by Richard Ordway — 28 Apr 2007 @ 3:46 PM

  43. A trivial correction — despite widespread popular misuse, especially among sportscasters, “literally” doesn’t mean “metaphorically or in an analogy.” That would be “figuratively.” “Literally” means the thing physically happens. If we were literally running over the climate system in a car, Detroit would have produced a car thousands of miles long, probably with its own measurable gravitational pull and perhaps its own atmosphere.

    [Response: You are running a risk discussing language with me, son of a professor of English and grandson of a strict grammarian! In any case, I was using “literally” figuratively. So there!–eric]]

    Comment by Barton Paul Levenson — 28 Apr 2007 @ 3:52 PM

  44. The following is in response to Ray�s question: What causes the drop in CO2, as the earth cools, from the interglacial warm period to the glacial coldest period?

    (Ray your thought that the reason for the drop was an increase in biological production appears to be correct.)

    Review article in Nature “Glacial/interglacial variations in atmospheric carbon dioxide” by Sigman and Boyle (2000)
    http://scholar.google.com/url?sa=U&q…man_nat_00.pdf

    The 100ppm drop in CO2 is not, primarily due to colder oceans. The following is an explanation of why colder oceans alone can not account for a 100 ppm drop in CO2. (This as summary from the paper. See paper for details).

    As there is a vast amount of fresh water in the glacial period, in the new ice sheets, the ocean becomes Salter (3%). Salter water can hold less carbon dioxide (6.5 ppm less for a 3% increase in salt content). Colder water can hold more carbon dioxide, however, the deep ocean is already an average of 4C and will freeze (salty or not) at around -1.8C. The estimated maximum drop deep in deep ocean temperature is 2.5 C. The surface subtropical oceans were estimated to have cooled by about 5C. (Note vast areas of the high latitude oceans were covered by ice, during the coldest period and could hence no longer absorb carbon dioxide.)

    The reduction in carbon dioxide, due to colder oceans, is estimated to be max. 30 ppm. Now as vast areas of land which are currently forested, were covered by the glacial period ice sheets, the temperate forest is no longer using carbon dioxide which adds carbon dioxide to the atmosphere. In addition, during the glacial period large sections of tropical rain forest changes to savannah (About a third of the tropical forest changes to savannah. The planet is drier when it is colder), as savannah is less productive that tropical forests that change also adds carbon dioxide to the atmosphere. The Nature article estimates the temperate forest change and the increase in savannah, adds 15 ppm of carbon dioxide to the atmosphere.

    The net for this calculation is therefore = – 30 ppm + 6.5 ppm + 15 ppm = -8.5 ppm.

    As there is 100 ppm to explain the above are not the solution. The above article explains that increased biological production in the ocean, due iron and phosphate in the dust is hypothesized to cause an increase in the biological production in regions of the earth�s ocean which are currently almost lifeless due to a lack of nutrients.

    Comment by William Astley — 28 Apr 2007 @ 4:37 PM

  45. Re #39 (cce): He must be, because the ice sure didn’t disappear. Ice, magnetism, whatever. Maybe there’s a solar connection! :( Jim Hansen is probably right that guys like this will go to their grave spouting the same nonsense.

    Comment by Steve Bloom — 28 Apr 2007 @ 4:39 PM

  46. Re #33 (Dave D.): Ice core measurement issues aside, remember that there has to be some degree of lag because a) the initial warming is from Milankovitch changes, not CO2, and 2) the delayed turnover of ocean water means that not all the CO2 will outgas in a short period of time.

    Comment by Steve Bloom — 28 Apr 2007 @ 4:52 PM

  47. Richard Ordway wrote #34:

    I don’t want to step on anyone’s current unpublished research, so I have to tread very lightly. This is being actively investigated for the current human-caused global warming scenario with models and paleoclimate data. So far, results indicate that H2S extinction is not one of our biggest worries.

    Has someone found a new, better and more ghastly way of killing off 95% of all life on earth – and perhaps us as well – so that fungus may once again reign supreme – but you can’t tell us what it is as of yet?

    I for one will be waiting breathless with anticipation…

    Comment by Timothy Chase — 28 Apr 2007 @ 4:57 PM

  48. re #37 and 38 Vatican conference

    Perhaps more important than what Zichichi thinks, is what the Catholic church as a whole, and the pope in particular, think on the subject. Advancing that understanding was the purpose of this conference. Please note that in the article you posted there is no reference to any other speaker or the conclusions of the conference. It’s just coverage of a skeptic’s views.

    Have a look at the following article, found on http://www.climateark.org, with coverage of the conference and the Catholic Church’s rapidly increasing attention to climate change and the environment in general.

    http://www.taipeitimes.com/News/front/archives/2007/04/28/2003358539

    quoting from the article: Pope Benedict XVI urged bishops, scientists and politicians to “respect creation” while “focusing on the needs of sustainable development.”

    Comment by Ed Sears — 28 Apr 2007 @ 5:04 PM

  49. Two myths propagated in this thread. First the ice cores do not show a maximum of 300ppm CO2 or anything like that. There are very few data points for the interglacial peaks before the present one and CO2 spikes like the present one would not show up. The second myth is that the extra CO2 is “entirely” manmade. The thread here http://www.realclimate.org/index.php?p=87 that makes that claim does not show that quantitatively (e.g. does not take into account natural variations in carbon isotope ratios). However, there is certainly plenty of qualitative evidence that much of the current CO2 spike is anthropogenic. As for coincidence, modern man spread across the planet about 60k years ago, but didn’t get beyond hunter-gatherer stage until the present interglacial period. The current CO2 spike is likely to be mostly fossil fuel, but could be partly coincidence. The last century is more likely to be natural coincidence rather than CO2 warming and aerosol cooling (another coincidence?).

    [Response:[No, no, and no. We’ve been through this many times before. As I wrote to another “skeptic” that kept harping on this issue: The point is that more is being produced by humans than is winding up in the atmosphere and this is what we expect to happen. Sure, it is possible that not “all atmospheric increases are anthropogenic.” I never claimed otherwise. But to suggest that the natural environment has arbitrarily decided to start increasing the flux of CO2 into the atmosphere, right around the same time we are doing it is bizarre. Let me turn this around: what is the evidence that would suggest this is happening, and why? As for the aerosols and CO2 going up at the same time, umm. THINK man, THINK!–eric]

    Here’s a link showing one way carbon isotope ratios can vary naturally. http://adsabs.harvard.edu/abs/1996GeoRL..23..371K shows vegetation changing its amount of CO2 it holds (Ci/Ca) based on natural climate changes.[

    [Response: This is a nice paper. Yes of course 13C of the atmosphere varies naturally. I never suggested otherwise. One of the things that is clear is that 13C of the trees is now more negative than in the last 400 years. This is just one of the two million, five hundred thousand, one hundred and twenty five bits of evidence is support of the obvious fact that CO2 is going up because humans are putting it there. –eric]

    Comment by Eric (skeptic) — 28 Apr 2007 @ 5:19 PM

  50. What’s worrying is that positive feed-forward carbon cycle effects have the potential to reduce the effects of any attempts to limit fossil fuel CO2 emissions.

    The lack of understanding of these issues shouldn’t be reassuring. One example is the global soil reservoir of organic carbon (which is not a single ‘pool’, but which is made up of many components, some which are very labile (rapid turnover via microbial and root respiration) and some of which are very long-lived (humic material). Estimates are that microbial respiration will speed up as the soil warms, resulting in a net flux of CO2 to the atmosphere.

    Another is the permafrost reservoir, which is smaller than the active soil pool, but which is similar in size to the atmospheric carbon pool. The permafrost has been melting, and soil temperatures from boreholes are on an accelerating upward trend. That’s another source of CO2 that is responding to the warming temperatures.

    Then you have the terrestrial vegetation pool, which is the most active. The claim that CO2 immediately increases plant growth and acts as a fertilizer is a highly oversimplified argument, since plant carbon uptake is dependent on water, temperature, and nitrogen suppy. The amount of carbon stored as vegetation is similar to the amount in the atmosphere as CO2.

    The historical glacial-to-interglacial transition effects can also be seen in what is happening to the Arctic sea ice. As summer sea ice in the Arctic decreases, the snow/ice cover changes to open ocean, the amount of sunlight that is reflected drops from 80-90% to about 20%. Not only that, but the sea ice insulates the atmosphere from the ocean, and without it heat fluxes from the ocean to the atmosphere increase – all of which assists in the melting of the permafrost. Similar effects are certain to occur with Antarctic sea ice as well – it’s just a question of the heat content of the Southern Ocean and the buffering ability of the Antarctic ice sheet.

    The 8.2 kyr Holocene thermal maximum is thought to have been buffered by the presence of the Laurentide ice sheet in the northern hemisphere. However, there wasn’t a massive increase in CO2 at that time. The critical factor is probably the rate of increase in heat content of the Southern Ocean, and the ability of the massive heat sink of Antarctica to absorb this. As for the Arctic, it seems that it’s already over the ‘tipping point’ and the changes there will not be reversible.

    Comment by Ike Solem — 28 Apr 2007 @ 5:25 PM

  51. Something bother me a little : ice cores analysis are the only and unique indicators of CO2 and methane and also nitrous oxide atmosphere concentrations for the last 600,000 years.
    The three curves follow perfectly the same path. Even so perfectly that one can suspect some kind of bias. When I was at work (I am retired now) in my lab, I should have been very very suspicious if somebody of my team had brought to me such set of curves… too perfect means “not perfect at all”
    Suppose that, for any reason an important bias occurs in these measurements (who knows ?) In that case, the entire construction would collapse.
    An other proxy, indicating precisely what were the CO2 or methane or nitrous oxide contents of the atmosphere 100, 200 or 300 years ago should be welcome…

    [Response: The curves do not perfectly correlate. CH4 for instance has a much stronger precessional component than CO2 or Antarctic temperature and has a much faster response time to climate changes – both completely in line with a shorter atmospheric residence time and important tropical wetland sources. The data for CH4 are also highly replicable from Greenland to Antarctica, and in Antarctica itself all the records – from very different depositional environments – show the same results. Where there are obvious signs of contamination (such as for CO2 in the Greenland cores due to too much organic material in the much higher dust levels there), those data have been discarded. – gavin]

    Comment by Pierre Allemand — 28 Apr 2007 @ 5:53 PM

  52. Thanks for taking the time to clarify again this complicated issue. For laymen, I like the way Justice John Paul Stevens laid out the basic point in his recent Supreme Court opinion:

    “A well-documented rise in global temperatures has coincided with a significant increase in the concentration of carbon dioxide in the atmosphere. Respected scientists believe the two trends are related. For when carbon dioxide is released into the atmosphere, it acts like the ceiling of a greenhouse, trapping solar energy and retarding the escape of reflected heat.”

    Read this, and you have to ask yourself: Is it a coincidence? The answer is obvious.

    Comment by Kit Stolz — 28 Apr 2007 @ 5:59 PM

  53. The following would suggest that the Vatican believes there may be a genuine controversy regarding the threat of global warming.

    “The scientific community has been so divided and so bitter” over the climate-change debate that experts who disagree with each other don’t talk to each other, Silecchia told Catholic News Service.

    Mirroring wider debate, Vatican seminar on global warming gets heated
    By Carol Glatz
    4/27/2007
    http://www.catholic.org/international/international_story.php?id=23925

    However, all in all, they would seem to be giving greater weight to the issue, seeing it as something which must one of three essential goals which are to be balanced against one another: those of addressing poverty, economic inequality, and the environment. Thus, for example, when they speak of development, they speak of “sustainable development.”

    Unfortunately, I think they are still a bit behind the times, not simply in terms of their estimation of the division within the scientific community, but of cultural trends as well.

    From the same article:

    Silecchia said in some ways the environmental movement “has become its own new religion,” and this could be offset by a wider recognition of the church’s own tradition of God asking people to be stewards of creation.

    As near as I can tell, New Age environmentalism is next to non-existent and has been so for nearly two decades.

    Incidently, there were other, more professional contrarians there.

    “Not all the scientific world is crying disaster,” Cardinal Renato Martino, who heads the Pontifical Council for Justice and Peace, told Vatican Radio at the start of the two-day conference he hosted.

    “There are a good number of scientists who consistently don’t view these climactic changes in a negative light, and in fact say that these phenomena recur over the course of years and eras and sometimes they can have favorable results for agriculture and development.”

    Vatican Closes Climate Conference, Some Panelists Consider Warming Beneficial
    http://www.beliefnet.com/story/217/story_21728_1.html

    For example, representing the views of those who believe that global warming results in best of all possible worlds, we have Craig Idso from CO2Science. (See article above.)

    My own impression is that the Vatican isn’t necessarily interested in supporting the science or promoting the anti-science so much as in becoming a player, a power to be reconed with and courted. But that may be just my own cynicism.

    Comment by Timothy Chase — 28 Apr 2007 @ 6:38 PM

  54. #36 Richard Ordway wrote:
    “1) The Earth’s temperatures increase a little due to Earth’s orbit changes.

    2) This little warming causes the oceans to warm up which releases huge amounts of CO2.”
    ==== end of quote ===

    Thank you Richard for this eloquent and precise explanation that huge amounts of CO2 could be releleased by oceans and cause global warming without any presence of humans! As you might be rightfully aware, according to Takahashi measurements of global CO2 fluxes from oceans, they outgas about 100GT of carbon per year in tropical areas. Thank you for boiling this post down to its bones. :-) :-)

    Comment by Alexi Tekhasski — 28 Apr 2007 @ 8:27 PM

  55. Re #41: [Detroit would have produced a car thousands of miles long, probably with its own measurable gravitational pull and perhaps its own atmosphere.]

    Sshh! Don’t start giving them ideas!

    Comment by James — 28 Apr 2007 @ 9:18 PM

  56. Following on from Richard Ordway�s excellent 1-2-3 post (#36), we can take it then that 1 and 2 are already done.

    So in regard to our response to todays climate conditions cant we just ignore the arguments about the past, and simply start from today and say:

    a)The present temperatures are not in equilibrium with present-day CO2 levels.
    b)The climate will adjust the temperature to reach the correct equilibrium temperature. At 390ppmCO2 that temperature is about (say) 1K to 2K above today�s mean and the global effects identified in IPCC AR4 will prevail.
    c)If we keep adding CO2 (and with the third worlds fossil fuel power stations in the pipeline and unabated growth among *developed* nations, we will) then the equilibrium temperature will increase further.

    In essence the only equation that matters is the equilibrium equation, and the only variable input to that which matters (in the range we are interested in) is the concentration of GW gasses (CO2 among them). Put it on the front page of every newspaper, and let folk work it out for themselves!!!

    With all these discussions; Its as if our house is on fire; I have the impression that the head-in-the-sand folk are trying to identify and incarcerate the arsonist BEFORE they call the fire brigade! I feel you guys n gals at RC have done all you need to � the physics is simple. The hard question is What will humanity do about it?

    Comment by Nigel Williams — 28 Apr 2007 @ 9:47 PM

  57. Hi Eric,

    Re – your response to my post about residence time:
    “The residence time calculation is confusing and indeed the concept of residence time is not very useful for a multicomopnent system. The average CO2 molecule does spend only a few years in the atmosphere, giving that 2-3 year residence time you cite. But effective residence time is much longer because of the equlibrium (or near equlibrium) between surface ocean and atmosphere and biosphere and atmosphere. The residence time of a CO2 molecule in the surface ocean is nearly as short as in the atmosphere, so many of the molecules that go in come right back out! So the effectie residence time of the combined system is what is important, and that is more onthe order of hundreds of years — or indeed, thousands, if we are talking about the residence time inthe combined surface ocean/atmophere/biosphere, vs. the deep ocean.–eric”

    I can see that “The residence time of a CO2 molecule in the surface ocean is nearly as short as in the atmosphere.” makes sense given the surface ocean (600Gt – 6 year residence), atmosphere (700 Gt – 3 year residence) and indeed the dead biomass (1100 Gt – 20 year residence) have similar carbon masses, and fluxes. What puzzles me is that a CO2 molecule released from the fossil fuel reservoir becomes indistinguishable from a CO2 molecule in the atmosphere and hence should be subject to the same residence time (3 years). In compartmental model terms, surely the atmosphere is ONE compartment WRT CO2 (I’m assuming it is well mixed). The equilibrium exchange rates with the surfact ocean and terrestrial biosphere sum to about 220 Gt/yr, which is consistent with an e-folding or half-life of CO2 of about 3 years (I’m not going to do the detailed sums but 220 is about a third of 700).

    The crux of the issue is this. If we completely stopped anthropogenic CO2 emissions, how long would it take to get CO2 down to say 330 ppm (half the anthropogenic addition). It might be helpful if you could refer me to a good paper on the topic. Since I’ve studied compartmental models I could handle a paper written in those terms.

    I’ve had a thought on this – the excess uptake over the equilibrium exchange rate for both the ocean and terrestrial biosphere are both about 2 Gt/yr, giving a total of 4 Gt/yr. Of the 700 Gt CO2 in the atmosphere we’ve added 100 ppm of the 380 pmm (26%), which is about 182 Gt (current net addition is about 2-3 Gt/yr). Relying on the excess capacity of the biosphere to take this up would take about 184 divided by 4 equals 46 years – sat 50 years. If I took into account the exponential decay, the half-time of anthropogenic CO2 would be about 50 years. Is this the correct track?

    Thanks.

    Comment by Bruce Tabor — 28 Apr 2007 @ 11:11 PM

  58. Re Richard Ordway #39, –

    With regard to the possible role of hydrogen sulfide in mass extinctions, this pop article might be of interest to those who aren’t familiar with it…

    Impact from the Deep
    Strangling heat and gases emanating from the earth and sea, not asteroids, most likely caused several ancient mass extinctions. Could the same killer-greenhouse conditions build once again?
    By Peter D. Ward
    Scienctific American October 2006 issue
    http://www.sciam.com/article.cfm?chanID=sa006&articleID=00037A5D-A938-150E-A93883414B7F0000&pageNumber=1&catID=2

    Fortunately, we are still a fairly good distance from that sort of scenario – at least in terms of the current levels of CO2 are concerned: less than 400 ppm CO2 compared to the 1000 ppm they are talking about, and it has been rising recently somewhere around 2 ppm per year. However, I would be interested in seeing what role the methane which might be released by thawing Russian tundra or shallow arctic methane hydrate deposits might play in getting us closer to it to that limit.

    In any case, I don’t like games of chance, either. But if this is the right explanation for the extinctions, I think the scientific community will come to realize it sooner rather than later. The evidence will have a way convincing them at least.

    Comment by Timothy Chase — 28 Apr 2007 @ 11:20 PM

  59. c)If we keep adding CO2 (and with the third worlds fossil fuel power stations in the pipeline and unabated growth among *developed* nations, we will) then the equilibrium temperature will increase further.

    My personal feelings are that the 3rd World will never be able to be a big enough player in adding CO2 to the environment because it simply lacks the wealth to do so.

    The real risk, in my mind, isn’t the 3rd World, it’s countries such as India and China trying to modernize in a hurry, and depending very heavily on fossil fuels for doing so. China has plans to dramatically increase nuclear power production. India has six plants under construction, but will need to dramatically increase that number. If the developed world is already being forced to move from fossil fuels due to cost, I don’t see how the 3rd world is going to grow its fossil fuel consumption to any appreciable level.

    Comment by FurryCatHerder — 29 Apr 2007 @ 1:37 AM

  60. I finally got around to watching “An Inconvenient Truth.”

    I was impressed, particularly with how Gore managed to weave together the personal and the global – and to illustrate that the issue is ultimately a moral one. At a personal level, I think that all issues are moral issues, and that the deepest of all is our commitment to acknowledge reality for what it is – which we face at every moment of our lives – but that I suppose is a different issue.

    In any case, I believe it is a highly effective film, and I can understand why it resonates with people. However, there were at least three factual issues where Gore was somewhat off mark.

    One was in overplaying ice melt in Greenland and Antarctica. One would get the strong impression that ice in both these places is being lost on the whole. However, depending upon the year of the survey, the net amount of ice in either landmass may in fact be increasing. A warmer ocean means greater evaporation, more evaporation means greater precipatation, and greater precipatation in a land that is well enough below freezing and which is still below freezing throughout the year even after having its temperature raised by several degrees will in fact accumulate more ice.

    However, this is not something which will seem entirely straightforward when a “contrarian” first denies the existence of a general trend of global warming – and cites surveys showing increasing accumulation of ice in some parts of either landmass or in one of the landmasses as a whole. Nevertheless, I have to wonder whether given the complexity of ice dynamics (some of which he speaks of in terms of the “moulins”) might conceivably make possible the sort of collapse which he warns the audience against with regard to Greenland.

    The other was with regard to the sea level. The documentary is written as if the only factor affecting sea level is the melt of ice and glaciers. However, they are not even so much as the dominant factor at this point. Instead, it is the thermal expansion of sea water itself which is currently causing the greatest increase in sea level.

    So if so much of the emphasis of the film is upon how the rising sea levels will affect hundreds of millions of people within the next few decades, its case is unnecessarily weakened when it fosters the view that ice melt is “the cause” of sea level rise.

    Then of course this piece dealt with another one of the weaknesses of “An Inconvenient Truth” – the issue having to do with the fact that, in deep time, temperature rises have often lead carbon dioxide rises, which makes it easier for “contrarians” to deny that raising the level of carbon dioxide will raise the temperature. One has to recognise the existence of positive feedback, such that a rise in either quantity will lead to a rise in the other.

    In any case, such weaknesses, while small, should be acknowledged – as they are weaknesses which will be made use of by those who seek to deny the science. Likewise, uncertainties should be acknowledged where they exist – to the extent that they exist. For the most part, I believe Gore’s “An Inconvenient Truth” did quite well in this regard.

    I think things are shifting, partly as the result people becoming increasingly informed and partly given the increasingly dramatic developments. But for the time being, there will no doubt be contrarians, and we certainly don’t need to make their goals any easier for them to achieve. We can make things especially difficult for them if we keep things simple without oversimplifying.

    Comment by Timothy Chase — 29 Apr 2007 @ 3:45 AM

  61. I have a question about the earth reaching temperature equilibrium with different forcings and the speed of climatic changes that maybe someone here would be kind enough to answer.

    From reading here and elsewhere I know that earth takes some time to reach equilibrium temperature in response to the increase in CO2. Is this time lag similar for other kinds of forcings (solar, aerosol etc)?

    Volcanos seem to have very rapid effects which suggest there is variation in how long things take to unfold. Is this quick-acting nature purely because of the size of the forcing or is there more to it? On the face of it if it was just a matter of reaching thermal equilibrium one would imagine the time involved should be the same for a given size of forcing regardless of the forcing type.

    Here’s hoping someone is prepared to satisfy my curiosity :-)

    [Response: The response time has to do mostly with the thermal intertia of the ocean mixed layer, and ultimately the mixing time of the deep ocean. The reason that one tends to think that volanos have “rapid” effects is that the volcanoes themselves are rapid events. The initial response is the only response you get, because just a couple of years later the volcanic aerosol has been cleansed out of the atmosphere. If you could keep Pinatubo going to hundreds of years, at the same rate, then the cooling would continue towards an equilibrium that was a greater response than the initial cooling actually seen for the real Pinatubo. So in general yes, your intuition is correct. The response time is the same for the same magnitude of radiative forcing, regardless of cause. Indeed, that is why the Pinatubo event is a good validation of climate models’ ability to accurately simulate other forcings. –eric]

    Comment by SCM — 29 Apr 2007 @ 6:57 AM

  62. Sorry for the out of place post – but I just watched ‘ The Gulf Stream and the Next Ice Age’ on Australian (SBS) TV, featuring RC’s Stefan Rahmstorf. The programme was rather alarmist for my tastes, giving the impression that an ice age was just around the corner. Some words of wisdom from the RC team wouldn’t go amiss (I wasn’t able to locate any previous forums dedicated to the likelyhood and consequences of a THC shutdown).

    Comment by Alex Sen Gupta — 29 Apr 2007 @ 7:52 AM

  63. Slightly of topic but similar, Although I think I understand and can explain what’s mistaken with most of the beliefs of Alex Cockburn in his article From Papal Indulgences to Carbon Credits
    Is Global Warming a Sin?
    By ALEXANDER COCKBURN
    http://www.counterpunch.org/cockburn04282007.html
    I have not been able to find an explanation of this depite searching Real Climate.

    “”Now imagine two lines on a piece of graph paper. The first rises to a crest, then slopes sharply down, then levels off and rises slowly once more. The other has no undulations. It rises in a smooth, slowly increasing arc. The first, wavy line is the worldwide CO2 tonnage produced by humans burning coal, oil and natural gas. On this graph it starts in 1928, at 1.1 gigatons (i.e. 1.1 billion metric tons). It peaks in 1929 at 1.17 gigatons. The world, led by its mightiest power, the USA, plummets into the Great Depression, and by 1932 human CO2 production has fallen to 0.88 gigatons a year, a 30 per cent drop. Hard times drove a tougher bargain than all the counsels of Al Gore or the jeremiads of the IPCC (Inter-Governmental Panel on Climate Change). Then, in 1933 it began to climb slowly again, up to 0.9 gigatons.

    And the other line, the one ascending so evenly? That’s the concentration of CO2 in the atmosphere, parts per million (ppm) by volume, moving in 1928 from just under 306, hitting 306 in 1929, to 307 in 1932 and on up. Boom and bust, the line heads up steadily. These days it’s at 380.There are, to be sure, seasonal variations in CO2, as measured since 1958 by the instruments on Mauna Loa, Hawai’i. (Pre-1958 measurements are of air bubbles trapped in glacial ice.) Summer and winter vary steadily by about 5 ppm, reflecting photosynthesis cycles. The two lines on that graph proclaim that a whopping 30 per cent cut in man-made CO2 emissions didn’t even cause a 1 ppm drop in the atmosphere’s CO2. Thus it is impossible to assert that the increase in atmospheric CO2 stems from human burning of fossil fuels.””

    Could someone explain this or point me to a previous explanation thanks Rob

    Comment by Rob Brookes — 29 Apr 2007 @ 9:08 AM

  64. Re: #61 (Rob Brookes)

    The whole story by Alexander Cockburn is, to quote Macbeth, “a tale told by an idiot, full of sound and fury, signifying nothing.”

    1st: CO2 increase lasts a long time. So even if we completely stop emitting CO2 now, it’ll take hundreds of years for what we’ve already put there to be removed.

    2nd: He’s can’t even get the numbers right. Today, the CO2 emissions from the U.S. alone in only one year, is about 7 gigatonnes.

    Comment by tamino — 29 Apr 2007 @ 9:27 AM

  65. Re: Cockburn’s analysis.

    I don’t know the answer to your question, and I hope one of the RC experts will address it. One relevant fact is that accurate measurments of atmospheric CO_2 concentration weren’t done until Keeling’s work in the 50s. But the important thing to remember is that people who study atmospheric CO_2 are not idiots. They are not likely to have missed something like this, were it an issue. The link between the rise in atmospheric CO_2 concentration and human activities has been established beyond any doubt, by a variety of arguments. If Cockburn had been seriously concerned about the issue, he would have checked the IPCC publications to find a few Carbon budget experts and posed the question to them before trying to make a scientific argument about a subject he doesn’t have the qualifications to understand.

    [Response: Watch this space! We are working on a letter to the Nation regarding Cockburn’s rantings. It ought to please some of our readers that we’re no more tolerent of idiocy on the left than we are on the right. It does happen that the idiocy on cliamte issues has generally been fairly partisan, with the Right generally getting it more wrong! Perhaps Cockburn’s intent was restoring some balance…. –eric]

    Comment by Leonard Evens — 29 Apr 2007 @ 9:38 AM

  66. Re #33 and #46

    Eric, I should have read those papers. They are the best I’ve seen on this topic, which has been bothering me. And they were free!

    I have some disagreement with the Monnin paper. They seem to focus ont he intitiation of the ramps at 17000 yrs, but ignore other breaks, which don’t show a lag. The second paper with the Argon ratio gets a temp from gases in the bubble itself, and is pretty convincing. Having more examples than this one transistion would be nice. Wow, they can measure isotope ratios very accurately.

    Still, the two papers quote ice – air age differences for Vostok of 2200 to 5000 and 4100 years. Muuuch longer than the CO2 lifetime (or trap time numbers that I have seen thrown around.) There should be a qualifier when people say that ice cores prove that CO2 is higher now than any time in last 420000yrs. You got to take that 4000 year (20 time constant) averaging into account. It may be true from other arguments, but you just can’t take the CO2 ice core data by itself.

    Thanks for the great post. I always learn a lot here.

    Dave

    [Response: There are no records as long as Vostok and Dome C, which as you point out are low resolution. But there are shorter but still quite long (>20,000 years) records that are high enough resolution to rule out completely CO2 values as high as today for periods of more than about 40 years. So yes, strictly speaking one cannot prove that there wasn’t a year, or a day, when CO2 levels were higher. But the mechanism for accomplishing this would have to be rather strange, and is currently unknown. I would devote my own research career trying to find such an event, because the chances that it occurred are vanishingly small.–eric]

    Comment by Dave Dougherty — 29 Apr 2007 @ 9:44 AM

  67. I continue to be amazed at the informative contributions here. I am light years ahead of where I was just a few weeks ago in terms of understanding the science of climatology as it relates to the climate change debate. So thank you, again.

    A few more questions:

    What was the trend of global temperature in the 250 years prior to the beginning of the Industrial Revolution (1750)? Has this been quantified with a high degree of confidence?

    What was the trend in CO2 levels during the same 250 year period?

    What was the trend in sea level rise in this period?

    What external solar forces are at work currently (orbit, wobbling, etc.)? Were the same forces largely at work in the 250 years prior to the Industrial Revolution?

    Comment by Tim — 29 Apr 2007 @ 10:11 AM

  68. George Will is still on the case. Drive a Hummer!

    http://www.washingtonpost.com/wp-dyn/content/article/2007/04/11/AR2007041102109.html

    Comment by Mark A. York — 29 Apr 2007 @ 10:18 AM

  69. On the matter of ice core sample timing, it is clearly part of the debate and should not now be dismissed as irrelevant.

    My problem is that what I see in the data is not what is being discussed. I down loaded Vostok CO2, Me, and O18, dusted off my 3.5 in. disk of ACM algorithms, and got the following, generally the same for either parameteric or nonparametric analysis:

    1) CO2 and methane are highly correlated, 0.75 at the peak.

    2) Both CO2 and methane cross correlate with O18, such that a
    decline in O18 leads a rise in either methane or CO2 with a
    broad peak at around 3000 years, led by O18. Methane is much stronger (-0.6) than CO2 (-0.43). (+/- 0.1 would be “highly significant”).
    In any event the time is more than a few hundred years, more like a
    few thousand.

    3) The autocorrelation is quickest for O18, then methane, both around 500 y to half max, but much slower for CO2 at around three times as long.

    My understanding is that higher O18 is higher temperature proxy, is it not? Any explanation (except that I mucked up the numbers)?

    Comment by Allan Ames — 29 Apr 2007 @ 10:23 AM

  70. Indeed, CO2 lags temperature increase if one of the most frequently used arguments by skeptics. One of my favorite skeptic, Lubos Motl says, that if the amplyfying effect of CO2 was to be true, then this positive feedback would end in the hot-house, i.e. there would be no other mechanism, which could stop the onset of this positive feedback. Obviously, this was not the case. I opposed to him, that at some stage, some (unknown?) mechanism will inhibit this positive feedback and will trigger the onset of cooling. For instance, take an example of THC, of which shut-down (and subsequent cooling) was triggered (in the past) by warming. Did I got it right? ;-)

    Comment by Alexander Ac — 29 Apr 2007 @ 10:23 AM

  71. Eric wrote: “While we don’t know precisely why the CO2 changes occur on long timescales, (the mechanisms are well understood; the details are not), we do know that explaining the magnitude of global temperature change requires including CO2.”

    Do you have any references that discuss the mechanisms that are associated with the positive feedback effect of CO2? I understand the long-term chemical weathering negative feedback but I’m still a little unclear on the positive feedback. Thanks a lot.

    Comment by egbooth — 29 Apr 2007 @ 10:34 AM

  72. Scratch that last comment.

    Here are the positive feedbacks for CO2 that I have found:

    soil respiration, permafrost, and fire.

    Those all make sense. I would imagine that the tough part is to figure out the magnitudes of each. Am I missing any others?

    Thanks

    Comment by egbooth — 29 Apr 2007 @ 10:51 AM

  73. Re: 66

    George Will’s point is very clear to the reasonable reader. To what part of his column do you object and why? How does this relate to the science of climate change discussed in this forum?

    Comment by Tim — 29 Apr 2007 @ 11:14 AM

  74. Alexander Ac #67 wrote:

    One of my favorite skeptic, Lubos Motl says, that if the amplyfying effect of CO2 was to be true, then this positive feedback would end in the hot-house, i.e. there would be no other mechanism, which could stop the onset of this positive feedback. Obviously, this was not the case.

    Agreed. The problem lies with the assumption that positive feedback necessitates runaway effects. This is a fallacy Gavin deal with in some detail a while ago. However, as he points out, there is no need for a special mechanism to bring positive feedback to an end in many cases:

    People often conclude that the existence of positive feedbacks must imply ‘runaway’ effects i.e. the system spiralling out of control. However, while positive feedbacks are obviously necessary for such an effect, they do not by any means force that to happen. Even in simple systems, small positive feedbacks can lead to stable situations as long as the ‘gain’ factor is less than one (i.e. for every initial change in the quantity, the feedback change is less than the original one). A simple example leads to a geometric series for instance; i.e. if an initial change to a parameter is D, and the feedback results in an additional rD then the final change will be the sum of D+rD+r2D…etc. ). This series converges if |r|<1, and diverges (‘runs away’) otherwise. You can think of the Earth’s climate (unlike Venus’) as having an ‘r’ less than one, i.e. no ‘runaway’ effects, but plenty of positive feedbacks.

    5 Jul 2006
    Runaway tipping points of no return
    Gavin Schmidt
    Climate modeller at the NASA Goddard Institute for Space Studies in New York
    http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/

    But obviously once the system reaches equilibrium, in order to push it away from that equilibrium will require a change in one of the parameters maintaining that equilibrium – assuming it is a stable equilibrium, such as that which we have been blessed with for 10,000 years of recorded history prior to the twentieth century.

    Comment by Timothy Chase — 29 Apr 2007 @ 12:17 PM

  75. Re: #70 (Tim)

    Where shall I begin? How about with this:

    … the media-entertainment-environmental complex is warning about global warming.

    Will is implying — but doesn’t have the courage to say outright — that global warming science is trumped up by the “media-entertainment-environmental complex.” Detestable.

    Then there’s this:

    … require significant reduction of greenhouse gas emissions in America and some other developed nations but that would involve no “specific scheduled commitments” for 129 “developing” countries, including the second-, fourth-, 10th-, 11th-, 13th- and 15th-largest economies (China, India, Brazil, South Korea, Mexico and Indonesia).

    Now Will wants to fall back on the “why should we do anything when others won’t” argument. This is as morally bankrupt as claiming that I shouldn’t have to refrain from mass murder, because Ted Bundy didn’t.

    Then there’s this:

    … higher than the cost of providing the entire world with clean drinking water and sanitation, which would prevent 2 million deaths …

    For the simple-minded, this is the most persuasive argument. It’s not only wrong, it’s just plain unethical to imply that action on global warming will deprive the world of clean drinking water. The reason we don’t spend the money to do so now has nothing to do with diverting funds to fight global warming, it has everything to do with the developed world lacking the moral fortitude to do so.

    Comment by tamino — 29 Apr 2007 @ 12:59 PM

  76. eggbooth (#69) wrote:

    Here are the positive feedbacks for CO2 that I have found:

    soil respiration, permafrost, and fire.

    Those all make sense. I would imagine that the tough part is to figure out the magnitudes of each. Am I missing any others?

    What I would be interested in are the causal sequences myself, although in the process one is likely to see some double-counting.

    However, in a certain sense, there is already some double-counting. But lets do it anyway so that we can track the lines of causation…

    1. With permafrost melting, the soil which makes up the permafrost is finally having a chance to respire, with the organic material being metabolized by bacteria, releasing carbon dioxide and methane which eventually decays to carbon dioxide.

    2. Raising the carbon dioxide level raises the temperature. This causes ice to melt, exposing the permafrost and raising its temperature to the point at which organic decay sets in, raising the level of methane and carbon dioxide.

    3. However, the melting of ice decreases the albedo near the artic, resulting in less light being reflected into space and more light being absorbed by the ocean, further raising the temperature of the ocean which will feed back into the release of methane and carbon dioxide.

    4. Raising the temperature of the ocean will also result in more melting of ice, at least if the ice is in contact with the ocean.

    5. The formation of dark pools (moulins) on the surfaces of glaciers speeds up the absorbtion of light by those glaciers and likewise results in runoffs which lubricate their descent into the ocean and their melting – further diminishing the albedo, raising the global temperature and thus the release of carbon dioxide.

    6. Higher temperatures result in increased evaporation of moisture from the soil, making increasing the likelihood of forest fires which will add to the carbon dioxide in the atmosphere.

    7. Higher temperatures make more violent storms more likely, and with them the discharge of atmospheric electricity, lightening and thus triggers for such forest fires.

    8. Increased evaporation makes soil more dry, resulting in decreased plant growth, and thus results in the diminished sequestration of carbon by plants.

    9. Decreased foliage increases the rate of evaporation at the edges of such foliage, further decreasing plant growth and increasing the likelihood of forest fires.

    10. Increased atmospheric carbon dioxide raises the temperature of the ocean, reducing the amount of oxygen and carbon dioxide which it can absorb, thus reducing the amount of carbon dioxide which it has the capacity to sequester.

    11. Increasing atmospheric carbon dioxide raises the level of carbon dioxide absorbed by the ocean, increasing its acidity and further diminishing its capacity to sustain life through the destruction of coral.

    12. The warming of the ocean, particularly in the upper layers, raises the temperature of methane hydrate deposits in shallow waters, resulting in more methane being released to the atmosphere.

    13. An increased rate of evaporation makes it more likely that precipitation will occur nearer the source of the evaporation – over the ocean – making droughts more likely over land.

    14. An increased rate of evaporation means that when precipitation occurs over land, it is more likely to be infrequent, running off of impoverished soil rather than being absorbed by soil which is rich in nutrients, further reducing plant growth.

    *

    There are multiple feedbacks, but there are also multiple feedbacks to the feedbacks. Incidently, while I focused on the positive feedbacks, there are also clearly some negative feedbacks, too. For example, exposed polar water is capable of radiating more heat back into space than polar water which is insulated by ice. I suspect that this effect is relatively small in comparison to other effects, such as the absorbtion of light by the very same waters, but it is an effect which we would want to take into account nevertheless. Likewise, the greater the amount of a given green house gas in the earth’s atmosphere, the less effective the gas is as a green house gas. This is largely why methane is twenty times more effective than carbon dioxide as a green house gas, and nitrous oxide (a product of biodiesel fuel) is twenty times more effective than methane.

    Comment by Timothy Chase — 29 Apr 2007 @ 1:16 PM

  77. [[Thank you Richard for this eloquent and precise explanation that huge amounts of CO2 could be releleased by oceans and cause global warming without any presence of humans! As you might be rightfully aware, according to Takahashi measurements of global CO2 fluxes from oceans, they outgas about 100GT of carbon per year in tropical areas. Thank you for boiling this post down to its bones. ]]

    The oceans give off about 90 gigatons of carbon altogether per year, and absorb 92 gigatons. They are presently a sink for carbon dioxide, not a source. The recent increase in carbon dioxide has come about from fossil fuel burning and land-use changes.

    Comment by Barton Paul Levenson — 29 Apr 2007 @ 1:55 PM

  78. [[The two lines on that graph proclaim that a whopping 30 per cent cut in man-made CO2 emissions didn’t even cause a 1 ppm drop in the atmosphere’s CO2. Thus it is impossible to assert that the increase in atmospheric CO2 stems from human burning of fossil fuels.””
    Could someone explain this or point me to a previous explanation thanks Rob
    ]]

    Sure. Cockburn is assuming the amount in the air is directly proportional to the input from the US. It isn’t. His 0.9 gigaton burn in 1933 was half absorbed by the ocean, and has to be compared to the 600 GT or so then in the air. To expect a 33% drop or increase is asinine. The man doesn’t understand the difference between total ambient CO2 and added CO2. Like saying if there’s 15 gallons in your car’s fuel tank, and you put in 2 extra gallons, then only one, the amount of gas in your car should suddenly be cut in half.

    Comment by Barton Paul Levenson — 29 Apr 2007 @ 2:06 PM

  79. [[Do you have any references that discuss the mechanisms that are associated with the positive feedback effect of CO2? I understand the long-term chemical weathering negative feedback but I’m still a little unclear on the positive feedback. Thanks a lot. ]]

    In the long run, the amount lost to weathering — about 330 million tons a year — is balanced by the amount added by volcanism and rock metamorphism. In the short run, these don’t always match and the amount in the atmosphere can go up or down.

    When it gets colder, ice covers the ground, so there’s less weathering from that cause, and weathering goes down with temperature anyway. So the atmosphere is losing less, but volcanoes and metamorphism are still pumping CO2 into the atmosphere.

    Comment by Barton Paul Levenson — 29 Apr 2007 @ 2:09 PM

  80. Re #77, I have read that the Oceans are currently absorbing 45% of human carbon emissions but by 2030 it will be down to around 30% and in effect become a source?

    [Response: RealClimate contributor David Archer can give a better answer to this than I can, but in a nutshell yes. This is because as CO2 enters the ocean, the ocean becomes more acidic, and this shift the dissolved-CO2 / biocarbonate / carbonate ion balance in favor of CO2, which drives up the atmospheric CO2. –eric]

    Comment by pete best — 29 Apr 2007 @ 2:38 PM

  81. Tim (#67) wrote:

    A few more questions:

    What was the trend of global temperature in the 250 years prior to the beginning of the Industrial Revolution (1750)? Has this been quantified with a high degree of confidence?

    What was the trend in CO2 levels during the same 250 year period?

    What was the trend in sea level rise in this period?

    I found the following for temperature between 1850 and 2000:

    Figure 1. Global warming revealed . Air temperature measured at weather stations on continents and sea temperature measured along ship tracks on the oceans are combined to produce a global mean temperature each year. This 150-year time series constitutes the direct, instrumental record of global warming..
    http://www.lib.utah.edu/services/prog/gould/1998/Figure_1.gif

    … from :

    Global Warming – Just Hot Air?
    David S. Chapman
    http://www.lib.utah.edu/services/prog/gould/1998/index.html

    The same article contains the following for sea levels from 1800-2000:

    http://www.lib.utah.edu/services/prog/gould/1998/Figure_2.gif
    Figure 2. Sea level is changing. Observing stations from around the world report year-to-year changes in sea level. The reports are combined to produce a global average time series. The year 1976 is arbitrarily chosen as zero for display purpose.

    Then it includes the famous deep-time diagram for CO2:

    http://www.lib.utah.edu/services/prog/gould/1998/Figure_6.gif
    Figure 6. Rise in atmospheric carbon dioxide. The concentration of carbon dioxide in Earth’s atmosphere has increased steadily from 270 to 370 ppm since 1700. Early data come from gas bubbles trapped in ice. Since 1959, carbon dioxide concentration has been measured at observatories in Hawaii and elsewhere. Recent measurements show uptake and release of carbon dioxide with seasons (inset) superimposed on the steady global increase.

    As for current orbit, wobbling and solar output, I don’t have the figures right off hand, but from what I understand, minus the increased carbon dioxide due to manmade emissions, we should actually be in a cooling period right now. Additionally, some of the global warming which would have taken place in past decades due to increased carbon dioxide levels has been masked through aerosols increasing the albedo of the earth, resulting in global dimming (e.g., jet entrails seeding the formation of clouds).

    Incidently, there is a great deal of information on all of this available on the web – so if you are really interested and people are a little busy you be able to find some of the stuff for yourself.

    Comment by Timothy Chase — 29 Apr 2007 @ 3:00 PM

  82. Re #61: SCM — The brief answer is no. A good book with regard to the various time scales is

    W.F. Ruddiman
    Earth’s Climate: Past and Future
    W.H. Freeman & Co, 2001.

    Comment by David B. Benson — 29 Apr 2007 @ 4:56 PM

  83. RE#80, there’s a simple experiment that shows how warming a liquid reduces the capacity to hold dissolved CO2 – take two beers, open them, and warm one up, in a water bath perhaps, while placing the other in a freezer. After ten minutes, return both open bottles to the fridge and wait for them to cool. One will be flat, one will still have plenty of CO2. For demonstration purposes, it’d be best to get your hands on “Global Warming Beer”, produced from the melting Greenland icecap (Natl Geo)

    Comment by Ike Solem — 29 Apr 2007 @ 6:00 PM

  84. I saw the film.

    The most dramatic part of the film was when Gore showed the temperature and CO2 graphs together, and then rose up on the mechanical lift to show that currently increasing CO2 concentrations are likely to lead to significant temperature increases. There is no question that his aim was for the audience to believe that CO2 rise drives temperature rise in both the past and present day. This was deliberate deception.

    [Response: There is nothing deceptive about this. Once a greenhouse gas, always a greenhouse gas. -gavin]

    To attempt to [inappropriate and inflamatory language edited]

    Comment by PHE — 29 Apr 2007 @ 6:03 PM

  85. #76. About methane hydrates. I read that massive release of oceanic methane hydrates was suspected to have played a significant role in the P/t extinction. Any take on that?

    Comment by Philippe Chantreau — 29 Apr 2007 @ 6:03 PM

  86. Re #61: Just to add that you can search this site for more detailed answers. Briefly, solar, volcanic and CO2 forcings of the same initial size will behave quite differently over time. Solar variations are to all intents and purposes instantaneous, volcanic dust has a short lag time since such emissions fall/rain out of the atmosphere within a few years, but CO2 tails off over centuries.

    [Response: This is right but doesn’t quite answer the quesiton posed. See my comments after #61 above.–eric]

    Comment by Steve Bloom — 29 Apr 2007 @ 6:13 PM

  87. Comments are now off on this post. Thanks to all who commented in a constructive manner.

    Comment by eric — 29 Apr 2007 @ 6:42 PM

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