All the previous parts of the programme were leading up to “so if it isn’t CO2, what is it?” to which their answer is “solar”. The section was curiously weak, and largely lead by pictures of people on beaches. It was somewhat surprising that they didn’t feature Svensmark at all; other stuff we’ve commented on before. Note that the graph they used as “proof” of the excellent solar-T connection turns out to have some problems: see figure 1c of Damon and Laut.

Along the way the programme ticked off most of the other obligatory skeptic talking points: even down to Medieval English vineyards and that old favourite, volcanoes emitting more CO2 than humans.

It ended with politics, with a segment blaming the lack of African development on the environmental movement. We don’t want to get into the politics, but should point out what the programme didn’t: that Kyoto exempts developing nations.

[Also: other discussion at InTheGreen, Stoat, The Guardian and

Media lens.]

[Update: What Martin Durkin really thinks!]

[Update for our german readers: A german version of the “swindle” film was shown on June 11 on German TV (RTL); here is a german commentary by stefan.]

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558 comments on this post.
  1. John Lang:

    To Dean Morrison #88 and Brian #92, the differences in the charts are pre- and post-adjustment of historical temperatures by GISS and the Hadley Centre.

    Historical temperature records have been adjusted for change of location, the urban heat island effect etc. The total is about 0.5C upward adjustment in the trend.

    The documentary used the unadjusted raw data.

    Here is what the chart looked like in a National Academy of Science report in 1975.


  2. Ray Ladbury:

    Re 96: Hopp, first, based on the most recent AGU study, 98% of recent PhDs in geo and space sciences found employment in the sciences. An AIP study found that 97 of 2003 and 2004 PhDs found employment–those statistics don’t leave much room for desperate job hunters willing to sacrifice their integrity for a job.
    Then there’s the question of motivation: Why would funding agencies want a scientist to falsify their research in favor of anthropogenic climate change. After all, most climate research funding comes from the US and other governments, and having the scientists say humans are changing the environment doesn’t exactly reflect favorably on the governments’ inaction on greenhouse gas emissions.
    It is difficult to respond to the vague accusations you make. As to having canned responses to the arguments made by so-called skeptics…well, is it Gavin’s fault that the skeptics keep using the same tired, discredited arguments? WRT the arguments about galactic cosmic rays, the main problem I see with the argument is that we have direct measurements of GCR fluxes for the past 30 some odd years (where we’ve seen rapid warming) and there is no upward trend. Last I saw, for something to be a cause, it had to be present when the effect was present. Oops! As to the occasional ad hominem attack on persistent skeptics, mea culpa. However, when you see the same tired, discredited arguments being advanced repeatedly by the same contrarians independent of evidence, you have to wonder whether the problem may not be so much with the argument as with the hominid who keeps repeating it. The number of true experts who doubt Earth is warming is pretty darned close to zero. The number who think humans have nothing to do with it can probably be counted on fingers and maybe a couple of toes thrown in. There is NO controversy in the scientific community–just the normal process of consensus with some cranks who cling to dissent for their own contrarian reasons. It is the media and public who manufacture the controversy.

  3. P. Lewis:

    Re # 100
    Sigh! “all the facts” does not necessarily mean “ALL the facts”.

    I could have qualified the quotation, but thought it unnecessary. After all, we are all intelligent people on this site, aren’t we?

    But fine if you want to play semantics, but you’ll be playing solo.

  4. Craig Truglia:

    “You should be able to spot the difference. -gavin”

    Yes, but shouldn’t you be able to source your claims about the troposphere-ground temperature differences properly? You still have not corrected your claim, which is disproved by the link to the article Spencer help write. You really should correct it, because it is a major red herring. This is leaving all over-drawn claims aside.

  5. Dave Rado:

    A lot of “skeptics” like to talk about water vapor but never mention the fact that combustion of a carbon/hydrogen based fuel releases both CO2 and H2O as vapor. In fact, it is the only process of which I can think that can allow an addition to the absolute amount of water on the planet, except for objects coming from space.

    But it’s beside the point, because it doesn’t change the amount of water *vapour* in the atmosphere, for the reasons explained at http://www.realclimate.org/index.php?p=142. But for exactly the same reasons, water vapour has no *forcing* (causative) affect on temperature changes.

  6. Ray Ladbury:

    Re 101: Boy, I’m not even sure whether that does it, unless they did some very serious “smoothing” on the data–and I mean, well beyond a 5-year moving average.
    Re 100: Colin, one thing that separates science from other forms of empirical investigation is that experiment in science is guided by understanding. The climate models and investigations already include every effect that contributes SIGNIFICANTLY to climate that we have found. The fact that they reproduce trends as well as they do (remember this is a chaotic system we’re looking at here–trends are as much as you can hope for) suggests there isn’t a whole lot else to consider that will significantly alter the conclusions arrived at to date. Every once in awhile you get a wildcard–like GCR fluxes–thrown in. But GCR fluxes have stayed the same on average (modula the solar cycle) throughout the time we’ve been able to measure them. This coincides with the significant warming seen 1975 to the present. So, how do I derive an increase from a stimulus that basically isn’t changing? Also, remember, clouds can be a source of warming as well as cooling, and why would we expect differential formation day and night from a driver of galactic origin?
    Let me again recommend Helen Quinn’s Refernece Frame Column from January’s Physics Today (link in post #48). There are things that we as scientists know. We know them in ways a layman simply cannot understand, because we’ve looked at the evidence and understand how it can be wrong and by how much. Despite this deeper level of knowledge, we will still say we “believe”. This isn’t belief; it is knowledge. That is why we are insistent that we need to do something about the threat.

  7. Eli Rabett:

    Re#56 there is something funny in the UAH MSU reconstructions at high southern latitudes perhaps driven by inclusion of albedo effects.

    Re #83 the Revolutionary Communist Party seems quite similar the the LaRouchies in the US who have also added climate denialism to their collection of pathologies.

  8. Eli Rabett:

    Hmm…#101 probably points to one of the usual suspects as the source of the odd graph. Anyone see it elsewhere?

  9. William Connolley:

    Below is the text of a letter from Carl Wunsch, reproduced with permission.

    Mr. Steven Green
    Head of Production
    Wag TV
    2D Leroy House
    436 Essex Road
    London N1 3QP
    10 March 2007
    Dear Mr. Green:
    I am writing to record what I told you on the telephone yesterday about
    your Channel 4 film "The Global Warming Swindle." Fundamentally,
    I am the one who was swindled---please read the email below that
    was sent to me (and re-sent by you). Based upon this email and
    subsequent telephone conversations, and discussions with
    the Director, Martin Durkin, I thought I was being asked
    to appear in a film that would discuss in a balanced way
    the complicated elements of understanding of climate change---
    in the best traditions of British television. Is there any indication
    in the email evident to an outsider that the product would be
    so tendentious, so unbalanced?
    I was approached, as explained to me on the telephone, because
    I was known to have been unhappy with some of the more excitable
    climate-change  stories in the
    British media, most conspicuously the notion that the Gulf
    Stream could disappear, among others.
    When a journalist approaches me suggesting a "critical approach" to a
    technical subject, as the email states, my inference is that we
    are to discuss which elements are contentious, why they are contentious,
    and what the arguments are on all sides. To a scientist, "critical" does
    not mean a hatchet job---it means a thorough-going examination of
    the science. The scientific subjects described in the email,
    and in the previous and subsequent telephone conversations, are complicated,
    worthy of exploration, debate, and an educational effort with the
    public. Hence my willingness to participate. Had the words "polemic", or
    "swindle" appeared in these preliminary discussions, I would have
    instantly declined to be involved.
    I spent hours in the interview describing
    many of the problems of understanding the ocean in climate change,
    and the ways in which some of the more dramatic elements get
    exaggerated in the media relative to more realistic, potentially
    truly catastrophic issues, such as
    the implications of the oncoming sea level rise. As I made clear, both in the
    preliminary discussions, and in the interview itself, I believe that
    global warming is a very serious threat that needs equally serious
    discussion and no one seeing this film could possibly deduce that.
    What we now have is an out-and-out propaganda piece, in which
    there is not even a gesture toward balance or explanation of why
    many of the extended inferences drawn in the film are not widely
    accepted by the scientific community. There are so many examples,
    it's hard to know where to begin, so I will cite only one:
    a speaker asserts, as is true, that carbon dioxide is only
    a small fraction of the atmospheric mass. The viewer is left to
    infer that means it couldn't really matter. But even a beginning
    meteorology student could tell you that the relative masses of gases
    are irrelevant to their effects on radiative balance. A director
    not intending to produce pure propaganda would have tried to eliminate that
    piece of disinformation.
    An example where my own discussion was grossly distorted by context:
    I am  shown explaining that a warming ocean could expel more
    carbon dioxide than it absorbs -- thus exacerbating the greenhouse
    gas buildup in the atmosphere and hence worrisome.  It
    was used in the film, through its context, to imply
    that CO2 is all natural, coming from the ocean, and that
    therefore the human element is irrelevant. This use of my remarks, which
    are literally what I said, comes close to fraud.
    I have some experience in dealing with TV and print reporters
    and do understand something of the ways in which one can be
    misquoted, quoted out of context, or otherwise misinterpreted. Some
    of that is inevitable in the press of time or space or in discussions of
    complicated issues. Never before, however, have I had
    an experience like this one. My appearance in the "Global Warming
    Swindle" is deeply embarrasing, and my professional reputation
    has been damaged. I was duped---an uncomfortable position in which to be.
    At a minimum, I ask that the film should never be seen again publicly
    with my participation included. Channel 4 surely owes an apology to
    its viewers, and perhaps WAGTV owes something to Channel 4. I will be
    taking advice as to whether I should proceed to make some more formal protest.
    Carl Wunsch
    Cecil and Ida Green Professor of
       Physical Oceanography
    Massachusetts Institute of Technology
  10. Matthew Wright:


    The right wingers are distributing this around…. they have the $$$ (resources) to get this to every open wire on the planet.

  11. Nick Riley:

    Colin re your comment #90

    Hendrix was well aware of science; indeed he was fascinated by science fiction. If you follow to the last verse of “up from the skies”, it has the line, “I want to know about the new mother earth, I want to hear and see everything”. So, I think Hendrix was addressing social (poor modern city design) and environmental issues (disturbing the natural balance) in the lyrics. Also, if you listen to “3rd Stone From the Sun”, “Voodoo Chile (slight return)”, “Power of Soul” and “1983 A Merman I Should Be” there are lots of lines that refer to his appreciation of the wonder of the Earth, solar system and how humans are mucking it up (“out of style,out of style” etc).

    In any case, IMHO- it was Silent Spring by Rachel Carson (1962) set the modern environmentalist movement off on its way – of which the hippies were the first popular cultural response.

  12. Ike Solem:

    RE#98, Phillipe consider how much water is in the oceans. The water vapor feedback effect is primarily what determines the short-term (century-scale) climate sensitivity to CO2; see http://www.sciencemag.org/cgi/content/summary/310/5749/795 The undisputed facts on this matter are that the models are treating the water vapor feedback correctly, which is why the contrarians are reduced to unsupported arguments about changes in solar output causing global warming.

    RE#104 ‘forcing’ and ‘causative’ are not at all the same thing; ‘forcings’ apply to models only, as externally set variables; the ‘feedbacks’ (the internal variables that change as the model does calculations, such as upper atmospheric water vapor) are quite causative (the increased water vapor absorbs more infrared, and causes the surface to warm more). You could make a model of the glacial cycles that includes CO2 as a feedback effect to solar orbital forcing, but the CO2 would still play a causative role in the glacial to interglacial transition (this would be risky, since the specific mechanisms that cause CO2 to increase in the glacial – interglacial transition are still not well understood).

  13. Ray Ladbury:

    Professor Wunsch would perhaps be well advised to subpoena the raw footage of his interviews now. Even if he has no intention of filing suit himself, as a matter of self defense, he needs to make sure that the full story is preserved and not “edited” to support a future case–legal or otherwise.

  14. Reid:

    Gavin – could you please clarify this issue for me succinctly and without a lot of hand waving? Prior to the 20th century, does CO2 concentration lag or lead the temperature cycle?

    [Response: During the ice age cycles, it was mostly likely a lag. The degree of that lag is actually quite uncertain and there is recent paper under review that suggests with good reason that it is less than the 800 years seen in the Caillon et al study. At other points in the past, such as the Paleocene-Eocene Thermal Maximum (55 million years ago), it looks like the CO2 (or possibly CH4) lead. Over very long timescales (millions of years) the overall level of CO2 (driven by weathering/geologic balances) probably lead – and is hypothesised to have contributed to the onset of the Quaternary ice age cycle in the first place. – gavin]

  15. FredT34:

    I’m sure Carl Wunsch feels very uncomfortable being swindled. I’m sure other scientist will get fooled in next months and years. However, you scientist have to continue participating in such programs – or denialists will confiscate the whole media field… You are “our” voice – voice of responsible and worrying humans on this planet (it’s our only one, forever).

  16. James:

    Re #111: [Prior to the 20th century, does CO2 concentration lag or lead the temperature cycle?]

    Maybe a simple explanation from a non-climate scientist would help? What seems to be missing is an appreciation of the fact that for millions of years prior to the 20th century, there was essentially a fixed amount of CO2 in the atmosphere+ocean+biosphere system. The fractions in each part changed as temperatures changed – a cold planet meant more would dissolve in the ocean, for instance, and those changes caused various feedbacks. If you look at climate records such as ice cores, you see that the system has atmospheric CO2 cycling between pretty constant high & low values in sync with temperature.

    Humans changed this, by adding substantial amounts of CO2 to the system as a result of burning fossil fuels. (You can determine quite accurately just how much humans have added. Economic data for instance gives you good values for the amounts of coal, oil, and so on that have been extracted: just add it up and do the math.)

    What this means is that the historical CO2 lead/lag question is a red herring. It’s asking about the behavior of climate given a fixed amount of CO2 in the system, while AGW deals with the effects on the system of adding more CO2.

  17. gary:

    I followed you link on volcano vs. human CO2 output….

    Objection: One decent-sized volcanic eruption puts more CO2 in the atmosphere than a decade of human emissions. It’s ridiculous to think reducing human CO2 emissions will have any effect.

    Answer: Not only is this false, it couldn’t possibly be true given the CO2 record from any of the dozens of sampling stations around the globe. If it were true that individual volcanic eruptions dominated human emissions and were causing the rise in CO2 concentrations, then these CO2 records would be full of spikes — one for each eruption. Instead, such records show a smooth and regular trend.

    “Not only is this false” is not an argument. The graph shows the “inventory” of CO2 not “flow” pf CO2. This is not proof.

  18. David B. Benson:

    Re #93: Bishop Hill and maybe also #111: Reid —

    Q1. The atmospheric carbon dioxide concentration depends upon biological activity. At the last stadial (LGM) there were extensive deserts. As these began to receive moisture once again, biological activity increased. Eventually all the deserts bloomed (well, many did) and no further increase was possible due to rainfall patterns.

    Q2. Briefly, yes. There are a variety of suggested accelerant causes to assist orbital forcing in lifting temperatures (melting ice) in the first few centuries after LGM.

    Disclaimer: I am a newbie amateur at paleoclimatology. Status is 3.5 books and about two dozen papers. RealClimate, of course.

  19. ziff house:

    I’m not sure where to inject this, as it is always a little off topic. Do models predict any years of cooling or is the temperature straight up from here? Will there not be years ahead when there is some cooling, given that nature rarely moves in a straight line.I would think that such an event will be deeply harmful in so much as it will renew the ‘controversy’.

  20. Brian:

    #101 John Lang: Thanks for clearing that up. Any idea where I can get hold of the unadjusted data?

    BTW Another screenshot from the show, this time more fun. Spot the subtle mistake!

  21. John Lang:

    To Brian #115 – I don’t think you can get the unadjusted raw historical temperature dataset anymore. It has been adjusted three or four times now and only a few reseachers in the field kept the old data in between each adjustment.

    A person could try searching around GISS and Hadley Centre websites.

  22. Reid:

    Thank you, David. I found this in regard to the lead/lag character. Apparently, it is argued here that yes, there is a lag in the historical record, but it is suggested that the lagging CO2 is merely a positive feedback that enhances the subsequent warming. But, if this is the case, it begs the question of what is the stabilizing force that cancelled out the positive feedback and prevented a runaway greenhouse?

  23. Michael Strong:

    Up until the last few weeks, I trusted RealClimate as the most reliable climate blog. Ellen Goodman’s rhetoric comparing climate skeptics to Holocaust deniers drove me to investigate the skeptics for myself. I concluded that, whether or not they are right, it was (and is) simply dishonest to discredit them in the manner that is done in the media and at RealClimate. I am now convinced beyond the shadow of a doubt that there are intellectually credible scientists with relevant expertise who, acting from intellectual integrity, do not agree with the IPCC summary statements. The fact that there may be numerically few of them is perfectly irrelevant.

    These individuals may well be wrong on the substantive issues, but the frequently snide tone and ad hominem attacks on those individuals who disagree with the RealClimate perspective has reduced your credibility for me.

    On the assumption that your perspective is the correct one, and that you want to maintain credibility, I would encourage that you take a far more generous perspective with respect to the motives of those who disagree with you, and become far more patient. The magnitude of policy change that is being demanded justifies, in my opinion, a level of “audit” similar to what climateaudit demands. This is, indeed, an unusual expectation in science, but the level of policy influence that you expect should result from your science justifies that level of audit.

    While you are correct to express outrage over the manner in which Wunsch’s perspective was distorted in this documentary, I don’t believe that you expressed similar outrage when Landsea felt that his perspective was being misrepresented by the IPCC, nor did you express similar outrage when Pielke felt that his perspective was being misrepresented by CCSP Committee. Insofar as you care about the issue, and appropriate policy responses to it, your over-riding concern should be that overly-zealous advocates should not undermine the credibility of the scientific community by politicizing key bodies representing scientific consensus. To an outsider, politicized misrepresentations at the IPCC or CCSP are far, far scarier than are misrepresentations in a documentary. The fact that Lindzen predicted that this type of politicization would take place and thereby create a “consenus,” in the early 1990s, adds to his credibility.

    In the end, all you have is your credibility. As someone who once respected RealClimate, I hope that these comments will ultimately result in a more balanced tone here.

    [Response: Fair enough. These kinds of events tend to bring out the more strident of comments and because this is (for us) an old story, we occasionally get a little snarky. This doesn’t necessarily read well to the casual observer and so we probably should avoid it – but in our defense…. well, forget that. We’ll try better in future. Thanks – gavin]

  24. David B. Benson:

    Re #122: Reid — I attempted to answer this in #118. Briefly, there is only a finite amount of carbon dioxide (say, in the ocean) available to go into the atmosphere.
    Thenceforth the actual amount is controlled by the substantially increased biological activity in areas which were deserts during LGM.

  25. Charles Muller:

    #85 Mike comment

    In particular, note that the radiative forcing associated with increased co2 is logarithmic, so the warming impact of a 100 ppm increase from 180 ppm to 280 ppm (the approximate glacial/interglacial difference) is far greater than that a 100 ppm increase from 280ppm to 380 ppm (the approximate pre-industrial/current difference). This has to do with the saturation of absorption bands within the IR window as greenhouse gas concentrations increase). -mike

    If IPCC formula for CO2 radiative forcing is still correct – ln(C/Co)*5,35 – I get 2,36 W/m2 for 180>280 ppm, 1,63 W/m2 for 280>380 ppm. I woulnd’t say the 0,73 W/m2 difference is “far greater”, with a mean climate sensitivity of 0,85 K/W/m2. Or something I miss.

  26. Iain:

    William – is Professor Wunsch going to mind that letter being reproduced elsewhere on the internet? I appreciate permission is given for here, I’m wanting to be able to post it elsewhere.

  27. John Lang:

    The issue of the timelag of 800 years for warming temperatures and the increase in CO2 is not as important, in my opinion, compared to the absolute level of CO2 rise (100 ppm) versus the temperature increase (6C to 10C).

    There has been the same 100 ppm increase in CO2 over the last century and temperatures have not increased anywhere near the rise that ended the ice ages.

  28. David B. Benson:

    Re #125: John Lang — The so-called greenhouse effect is proportional to only the logarithm of the change, not the absolute level.

    The timelag issue is of interest in understanding the paleoclimate of the ice ages. The immediate, AGW, effects are rather different.

  29. Nick:

    One fault with the program was that it missed the point about C02 and its effectiveness as a Greenhouse gas. Even if its conccentration is small, if C02 is a very effective greenhouse gas, its significance is higher.

    However, on the other hand, the lead lag question is very significant. Why hasn’t it been openly discussed on this board as being a major open question? The obvious conclusion is that those presenting the board have a major bias, and fall into the same category as those earning money from oil companies.

    Just what is the explaination for the temperature leading the C02. There is a clear explaination and that is that C02 is the side effect.

    From the historical record, what is the average global temperature that corresponds to the current C02 levels?

    From the historical record, what is the average global temperature that corresponds to the forecasted C02 levels?

    What is the forecasted C02 levels and does the assumed increase correspond to the figures used in the models? ie. Is the IPCC reports 1% growth rate in C02 production consistent with the historical observations?

    How many of the IPCC committee are scientists out of the total and is their science qualifications relevant?

    The program raises serious questions that need answers.


  30. Reid:

    #123 David: Do you have a reference which quantifies the finite amount of CO2 available for a positive feedback of this sort that I could look up? Once the oceans had been depleted of CO2, what process kicked in to re-sequester the CO2 and bring temperatures back down? And, once this process began, what prevented the newly restored CO2 from once again driving temperatures up resulting in a limit cycle at the maximum, which is what usually happens when you have a bounded positive feedback (e.g., when you have a “hot mike” forming a positive feedback loop with the speakers but the amplifier output is limited by the power source)?

  31. Steve Bloom:

    Re #125: Your point has been addressed multiple times in the comments above. Please read them. Very generally, close examination of climate behavior shows that it does not respond to forcings in a linear manner. If it did, we wouldn’t be here to discuss it. Even if it was the case that a 100 ppm CO2 increase could be expected to result in the same temperature increase regardless of the starting point, note that you assumed in addition that the response to the present rise should be nearly instantaneous. There’s no reason to think that either. That said, it might be useful for you to compare the temp increase since 1850 with the increase of any similar period during the last deglaciation. Things do seem to be moving along quite rapidly.

  32. Eli Rabett:

    #124 is simply wrong. Soils and plants account for about 2000 petagrams of carbon, the atmosphere and upper ocean about 800, the big cahuna is the deep ocean (actually it is carbonates, but they interchange with the others on millenia time scales), with about 40,000 petagrams. Now the interchange between the upper and lower oceans takes hundreds of years, which is fast enough to keep pace with orbital changes (changes associated with ice ages), but not fast enough to keep pace with the pulse of carbon that burning fossil fuels is pushing into the atmosphere. See http://www.grida.no/climate/vital/13.htm for example.

  33. David B. Benson:

    Re #130: Reid — One interesting attempt to model a feedback system for the long period ice ages is

    Barry Saltzman
    Dynamical Paleoclimatology
    Academic Press, 2002.

    There is more discussion on a thread just a few down regarding the question of what triggers ice ages. But briefly, at interstadials and interglacials, orbital forcings then allow new or renewed ice sheets to begin to form.

    But perhaps the most important comment I can make is that the physical-chemical stability of the climate system is not well understood, only (so far) observed. There is at least one journal entirely devoted to paleoclimate (Climate-of-the-Past) and one to the more specialized topic of PALEOCEANOGRAPHY. (That is the title!)

  34. David B. Benson:

    Re #132: Eli Rabett — Thank you for the correction and the link.

  35. Reid:

    David – Thank you again. I hope you see the problem here. If CO2 feedback is unbounded, then we should have observed (or not, as the case would be) a runaway greenhouse. If it is bounded, then there is still no mechanism for it to have restabilized. It would have created a limit cycle of some magnitude and regularity.

    Orbital forcings which are independent of the internal dynamics here, i.e., which do not form a loop between observables and forcings, would not be able to stabilize such an instability. I am no expert on climate systems, but I am an expert on feedback systems in general.

  36. Dave Rado:

    ‘forcing’ and ‘causative’ are not at all the same thing; ‘forcings’ apply to models only, as externally set variables; the ‘feedbacks’ (the internal variables that change as the model does calculations, such as upper atmospheric water vapor) are quite causative

    So what words would you use instead of “forcings” and “feedbacks” when talking to a non-scientifically-literate layman who nevertheless wants to get a very basic understanding of what the climatologists are saying? Mentioning the models simply in order to explain the difference between water vapour and CO2 would turn many of them right off (they’d think if you can’t explain even something that basic about real world climate without having to resort to models, then it must be all smoke and mirrors and nothing to do with the real world. Can you suggest some layman’s language alternative words for “forcing” and “feedback”, or at the least, layman’s definitions for them that don’t involve the models? (Another word I have trouble translating into layman’s English, by the way is “proxy”).


  37. Reid:

    And, Eli, the question is whether increasing temperatures can create an unbounded positive feedback of CO2 production resulting in increasing temperatures and more CO2 production essentially ad infinitum (or at least to the point where the whole planet is fried). If so, then there is no explanation for why we have not experienced a runaway greenhouse in the past.

    But, as I have stated, even a bounded positive feedback should produce a limit cycle but, it hasn’t so, it is apparent to me that there is currently a discrepancy between the historical record and what appears to be the prevailing paradigm.

  38. Ray Ladbury:

    #123, Mike Strong. Hmm, why do we think the situation is different the unfortunate case of Professors Wunsch and Landsea. Well try this on for size. Landsea was part of a group of scientists trying to reach a consensus on what conclusions the evidence would support. In the end, the conclusion was too strong for Landsea to support, and he withdrew his support. That was well within his rights and even his responsibility. It’s even fine that he took his disagreement public. The point is that Landsea had an opportunity to review the final document and opt out when he found he didn’t agree. He was not quoted out of context with no opportunity to correct the misrepresentation(as was Professor Wunsch) with the purpose of lending credence to a position he doesn’t support. I’d consider that a rather significant difference.
    To characterize as reprehensible actions like the frauds committed by this director–which are reprehensible–is not an ad hominem attack. To point out that the arguments advanced by so-called skeptics have already been discredited is not an ad hominem attack. And finally, to insist that the scientific consensus be given due consideration over positions held by a tiny minority is not “unfair or unbalanced”.
    Re 129: Nick, this issue has been flogged to horseburger. Basically, there is no reason why CO2 should have lead temperature in the past, since past warming epochs largely had other causes (orbital changes, etc.). As the planet starts to warm, permafrost melts, releasing CO2, CH4, etc. CO2’s solubility decreases with temperature, so the oceans release CO2. This release of ghg extends and intensifies the warming trend already underway, causing it to last, say 6000 years on average (compare that’s nearly 8x that 800 year lag). RealClimate has dealt with this extensively and you can find posts in the archives.

  39. Charles Muller:


    – Steve, my post mainly deals with radiative forcing comparison for 180/280/380 ppm CO2 increase, not climate response to this radiative forcing (I recall current best estimate of climate sensivity for 2xCO2 as an order of magnitude).

    – I don’t know what you mean exactly by a “non-linear” manner for climate in responding to a forcing. When we compare LGM / mid-Holocene, for example, where are non-linearities and how do they affect the estimate of climate sensitivity to a particular forcing?

    – I “assume” nothing like an instantaneous response – transient climate response to a forcing is not equilibrium climate sensitivity, of course.

    – The temp. increase since 1850 is 0,57-0,95 K (best estimate 0,76 K) according to AR4 SPM. Do we have any 20.000 yrs temp. reconstruction allowing a comparison for similar 155 yrs / T increase?

  40. Hank Roberts:

    >Wunsch letter
    Right-click on the timestamp and “copy link” — it gets you the info you can post as a clickable link that will take people to the posting right here. Better than second- and third-hand copies, which tend to get unreliable.

  41. Hank Roberts:

    Reid, plankton:
    “The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores …..”

    Global change. Plankton cooled a greenhouse.
    Nature. 2000 Sep 14;407(6801):143-4.
    Erratum in:
    Nature 2000 Sep 28;407(6803):467. (length of warm period has a typo, in the article)
    Comment on:
    Nature. 2000 Sep 14;407(6801):171-4.

  42. Ed Sears:

    re 95 ‘Can anyone point me to work done on plant carbon fixing as a result of an extended growing season in northern land masses?’ Unwashed random

    For the broad picture, try:
    Global Carbon Project (2003) Science Framework and Implementation. Earth System Science Partnership (IGBP, IHDP, WCRP, DIVERSITAS) Report No. 1; Global Carbon Project Report No. 1, 66 pp, Canberra.

    UNESCO-SCOPE (2006). The Global Carbon Cycle. UNESCO-SCOPE Policy Briefs October 2006 – No. 2. UNESCO-SCOPE, Paris.

    Hyvonen, R. et al (2007), ‘The likely impact of elevated [CO2], nitrogen deposition, increased temperature and management on carbon sequestration in temperate and boreal forest ecosystems: a literature review’. New Phytologist 173 (3), pp.463â��480.

    Then have a look on google scholar for D.Baldocchi and FLUXNET, P Smith from University of Aberdeen, and Prof Ian Woodward of University of Sheffield.

    As it happens :) I am going in a couple of weeks to a conference held by the NERC Quantifying and Understanding the Earth System programme. The agenda is:
    1: How important are biotic feedbacks for 21st century?
    2: How are climate and atmospheric composition regulated on timescales up to a million years?
    3: How much climate (change) is dangerous?
    4: How much can be avoided by managing the biosphere?
    5: Observing the Earth System (and Earth System Atlas)

    A last point on GGW Swindle: one of the closing remarks referred to Britain’s chief scientist and breeding pairs of humans in Antarctica. The scientist in question is James Lovelock and he talks about the Arctic (rather than Sir David King, the official British Govt Chief Scientific Advisor).

  43. Ike Solem:

    Dave, what I would say is that climate is naturally variable and responds to a wide variety of influences, but that burning fossil fuels has increased the atmospheric CO2 levels to levels not seen in millions of years; this additional CO2 acts as an extra blanket that causes the Earth to warm, on top of any natural variability in climate and weather. The mechanism responsible is absorption and re-radiation of infrared radiation (heat) by atmospheric CO2 and also by methane and other gases including water vapor.

    This warming causes all kinds of secondary effects, like the evaporation of more water into the atmosphere, the melting of ice sheets and permafrost, the drying of continental interiors, changes in precipitation patterns and the warming of the the oceans. More water in the atmosphere means a thicker blanket; melting the ice sheets means that less sunlight is reflected back to space, and so you end up with a significant effect. Based on the physics involved, it seems that the ‘blanket effect’ may have been a better term than the ‘greenhouse effect’.

    There are long-term consequences to doing this – rise in sea level is one, and it may happen faster than we think due to rapid melting of Greenland and Antarctic ice sheets, and there may be significant effects on the circulation of the oceans as well, with all kinds of attendant problems related to ecosystems, agriculture, extreme weather events, and so on. The current scientific debate is not over whether this is happening or not, but rather over how fast will it happen and how far will it go? The largest uncertainty in this seems to be what future human behavior will be over the next century, however – but at the higher end of possibilities, there may be unpleasant surprises, like release of vast amounts of methane to the atmosphere.

    Unfortunately, we can’t do experiments such as doubling the CO2 on one Earth while leaving it at the pre-industrial level on another Earth, so we have to rely on (1) detailed observations of the land, ocean, ice sheets and atmosphere and (2) computer models that attempt to calculate how the climate will change over time due to changes in the atmosphere’s composition. The terms ‘feedbacks’ and ‘forcings’ are scientific model jargon with very specific meanings (internal variables and external variables for a specific model), rather like ‘critical analysis’ which doesn’t mean doing a hatchet job on the subject, but rather carefully looking at all the variables involved (after Carl Wunsch). Water vapor is treated as an internal variable because of the effect of warming the surface on evaporation rates. Does warming the surface also affect the CO2 fluxes? Probably yes.. but that hasn’t been included in the models… and if it was, then you could say that CO2 was a feedback as well as a forcing.

    There’s just no way to put all that into a thirty second soundbite, without talking too fast to be understood.

    As far as a proxy goes, that’s a paleoclimate term that is best translated as indirect evidence. Paleoclimatology is like what a forensics expert does at the scene of a crime – collecting fibers, hairs, mud, etc. in the hope of reconstructing the events that took place. For example, ice cream that’s been frozen and thawed repeatedly looks a lot different from ice cream that’s never thawed, so that serves as a rough proxy for the past temperature of the freezer (big ice crystals are a bad sign). Hope that helps, any corrections or suggestions appreciated.

  44. Mark A. York:

    RE #135 “Forcing” is what CO2 as a molecule does. We add it to the atmosphere by burning carbon based fuels, and it becomes a driving force for greenhouse warming. It doesn’t leave, nor would it be there at this level were we not adding it. Water vapor is just recycled. That’s as basic as it can be.

  45. Reid:

    OK, Hank, so I guess you are saying plankton processes basically form a negative feedback which is more puissant than the positive feedback of CO2 release due to warming. So, what keeps the plankton feedback from working similarly now?

  46. Eli Rabett:

    137 No. Two answers. First, the practical the original earth atmosphere (~4.5 billion years ago) was about 30% CO2 and there was no runaway. Second, the theoretical, an an argument in Atmospheric Chemistry by Richard Wayne pp 58 points out that if the water vapor pressure becomes saturated with respect to ice or liquid any runaway would stop (the water vapor would precipitate cooling everything). This happens at the orbit of the earth a a few mbar water vapor pressure. OTOH, Venus is that much closer to the sun so that the P(T) vapor pressure curve (Clausius Clapyron) never hits the liquid/solid boundary, so it can grow without limit and go into runaway. Venus basically cooked out most of the water early on. Very interesting stuff.

  47. Reid:

    Thank you, Gavin, for responding to #114. But, as you may have seen if you have read my posts, this is a problem that needs careful explication. If there is a positive CO2 feedback that did not lead to instability, and it aparently did not, either of a runaway or limit cycle, then there must be some counterbalance, a negative feedback which is stronger than the positive feedback of the CO2 release. And, this leads to a problem because a negative feedback is inherently stabilizing. As a result, whatever exogenous forcing humankind contributes in the form of production of greenhouse gases is going to be degained by the one plus the feedback gain of this negative feedback, whatever it is, what we feedback engineers refer to as the “Sensitivity Function.”

    Is this negative feedback of plankton sequestration mentioned by Hank accepted by the mainstream of climate scientists? Or, is there some other process which accounts for the fact that the Earth has not already suffered the Venusian fate? Is there a reference which addresses this which I may consult?

    BTW, in this post:

    “”Even in simple systems, small positive feedbacks can lead to stable situations as long as the ‘gain’ factor is less than one”

    This is otherwise known as a negative feedback. In a discretized system, if the feedback gain is g, the discretized feedback gain is exp{g*T} where T is the sample period. This maps the “s-plane” of positive and negative feedbacks to the “z-plane” in which negative feedbacks are mapped to the interior of the unit circle in the complex plane.

    [Response: Please read the linked post again. You can think of negative feedback as a series where each perturbation has an opposing effect i.e. 1-r+r2-r3… and positive feedback where each perturbation is additive 1+r+r2+r3… Negative feedback is always stable (the series converges to 1/(1+r) which is always less than 1), while positive feedback will only converge to 1/(1-r) (> 1) if r is smaller than one. The point is that positive feedbacks are often bounded – which is a good thing. – gavin]

  48. Reid:

    Note, I am focusing on the ice age era in which the lag appears to be confirmed. It only takes one counterexample to invalidate a theory. The idea that a positive feedback of CO2, which is the focus of all the brouhaha, did not lead to an instability of either the bounded or unbounded type, is a circumstance which must be explained.

  49. Steve Bloom:

    Re #139: Charles, the comment numbers shifted afterwards. My comment was in response to what is now #127 by John Lang. I need to remember to add a name on my responses for when this happens.

  50. Ike Solem:

    Regarding the issue of the temperature lag in the glacial-to-interglacial transition, this issue has indeed been discussed at RC. For an overview of the topic see http://geoweb.princeton.edu/people/faculty/sigman/paperpdfs/Sigman00Nature.pdf “Glacial/interglacial variations in atmospheric carbon dioxide, Sigman & Boyle Nature 2000” (this covers the hypothetical role of the phytoplankton in detail) – the issue addressed is this:

    However, the regularity of the CO2 variations and the consistency of the upper and lower limits of atmospheric CO2 through multiple 100-kyr cycles (Fig. 1) are suggestive of a well ordered set of dominant mechanisms, the `holy grail’ of glacial/interglacial CO2 research.

    An alternative but similar hypothesis (more terrestrial) is that as the interglacial-to-glacial transition sets in, you start getting cold autumns – and microbial respiration of plant matter is generally controlled by temperature. The seesaw pattern in the 20th century Northern hemisphere CO2 record is a result of this seasonal imbalance between spring photosynthesis and fall respiration of dead plant matter. Cold autumns would limit one side of the seesaw, but photosynthesis would still occur in the summer – and over thousands of years, this imbalance would slowly draw down atmospheric CO2. The change in the orbital forcing would help this out – so you would get a buildup of organic carbon in soils and bogs in the latter half of the interglacial.

    At the height of the glacial period, this carbon would remain frozen in the ground an inaccessible. As the orbital solar forcing starts warming things up, this carbon becomes exposed – except now the situation is reversed, and there is suddenly a lot of edible carbon around for microbes to devour, resulting in a net excess of respiration over photosynthesis – thus the relatively rapid rise in CO2. More interesting in terms of this notion is the co-rise of atmospheric methane coming out of the glacial period; where does that methane come from? Wetlands are one possibility (vast herds of ruminants might be another?).

    In any case, we can come up with different hypothesis on this, but they are a lot harder to test. However, rates of photosyntheis and respiration on a yearly basis are on the order of 100 GT carbon/year, compared to the ~6 GT of fossil carbon that humans inject into the atmosphere. Small imbalances in the P/R ratio over thousands of years can easily change the atmospheric CO2 levels. Our use of fossil fuels represents a large imbalance of respiration (of ancient carbon) over photosynthesis.

    In any case, the argument that since CO2 lags behind temperature, CO2 can’t be responsible for temperature changes is not logical. Falling pebbles can trigger an avalanche, but that doesn’t mean that the boulders are not responsible for the net force of the avalanche. One hypothesis for why the avalanche doesn’t run on forever is that photosynthesis comes into balance with respiration at the height of the interglacial. Others are possible – but we know from the ice core record that CO2 peaks at the temperature maximum of the interglacials, and doesn’t continue increasing.

    The current situation is very different from the glacial to interglacial transition. Rates of atmospheric CO2 increase from the burning of fossil fuels are some 30X greater than anything seen in the glacial to interglacial transition – and the climate background is fundamentally different. A slowing of the Atlantic thermohaline circulation due to a less saline North Atlantic should not be expected to cool Europe, for example. Rather, we seem to be rapidly heading into a climate regime similar to those of over 3 million years ago.