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Expert Credibility in Climate Change – Responses to Comments

Filed under: — group @ 3 August 2010

Guest commentary by William R. L. Anderegg, Jim Prall, Jacob Harold, Stephen H. Schneider

Note: Before Stephen Schneider’s untimely passing, he and his co-authors were working on a response to the conversation sparked by their recent paper in the Proceedings of the National Academy of Sciences on climate change expertise. One of Dr. Schneider’s final interviews also addresses and discusses many of the issues covered here.

We accept and rely upon the judgment and opinions of experts in many areas of our lives. We seek out lawyers with specific expertise relevant to the situation; we trust the pronouncement of well-trained airplane mechanics that the plane is fit to fly. Indeed, the more technical the subject area, the more we rely on experts. Very few of us have the technical ability or time to read all of the primary literature on each cancer treatment’s biology, outcome probabilities, side-effects, interactions with other treatments, and thus we follow the advice of oncologists. We trust the aggregate knowledge of experts – what do 97% of oncologists think about this cancer treatment – more than that of any single expert. And we recognize the importance of relevant expertise – the opinion of vocal cardiologists matters much less in picking a cancer treatment than does that of oncologists.

Our paper Expert Credibility in Climate Change is predicated on this idea. It presents a broad picture of the landscape of expertise in climate science as a way to synthesize expert opinion for the broader discourse. It is, of course, only a first contribution and, as such, we hope motivates discussion and future research. We encourage follow-up peer-reviewed research, as this is the mark of scientific progress. Nonetheless, some researchers have offered thoughtful critiques about our study and others have grossly mischaracterized the work. Thus, here we provide responses to salient comments raised.

Definition of groups: The first of four broad comments about our study examines the relevancy of our two studied groups – those Convinced of the Evidence that much of the warming of the last half century is due in large part to human emissions of greenhouse gases, as assessed by the IPCC, which we term “CE,” and those who are Unconvinced of the Evidence (“UE”). Some have claimed that such groups do not adequately capture the complexity of expert opinion and therefore lose meaning. To be sure, anthropogenic climate change (ACC) is an immensely multi-faceted and complex area and expert opinion mirrors this complexity. Nonetheless, society uses simplifications of complex opinion landscapes all the time (e.g. Democrat versus Republican for political views) that don’t “lose their meaning” by ignoring the complexity of nuanced differences on specific topics within these broad groups.

The central questions at hand are: are these groups (1) clearly defined, (2) different in views of ACC, (3) reasonably discrete, and (4) in the main mutually exclusive? Our definition of groups, based entirely in the case of the UE group on their self-selected, voluntarily signed statements and petitions expressing various versions of skepticism about ACC, is clearly defined in the published paper. The strongest evidence indicating that our CE and UE groups satisfy the second and third criteria is that only three of 1,372 researchers fell into both groups—and in two of those cases, the researcher unwittingly added themselves to a statement they did not in fact support. Thus, if only one researcher of 1,372, or 0.07%, legitimately falls into both of our groups, this suggests that the two groups both differ starkly and are discrete. Any statistical analysis would be only trivially altered by having three redundant members of the cohort. Furthermore, the CE and UE groups are coherent, as around 35% of signers in each group also signed another statement in that set.

Another researcher suggests that his views have been “misclassified” by our inclusion of older public statements, as he signed a 1992 statement. Using a sweeping set of public statements that cover a broad time period to define the UE group allows us to compile an extensive (e.g. make an effort to be as comprehensive as possible) dataset and to categorize a researcher’s opinion objectively. However, were we to reclassify this researcher, it would only strengthen our results as then none of the top fifty researchers (rather than one researcher, or 2%) would fall in the UE camp.

Others have contended that the only experts we should have analyzed were those researchers involved specifically in detection and attribution of human-caused climate change. Importantly, much of the most convincing evidence for ACC comes from our understanding of the underlying physics of the greenhouse effect, illuminated long before the first detection/attribution studies, and these studies provide only one statistical line of evidence. The study could have been done in this manner but let us follow that logic to its conclusion. Applying this stricter criterion to the CE list does cause it to dwindle substantially…but applying it to the UE list causes it to approach close to zero researchers. To our knowledge, there are virtually no UE researchers by this logic who publish research on detection and attribution. Following this logic one would have to conclude that the UE group has functionally no credibility as experts on ACC. We would, however, argue that even this premise is suspect, as ecologists in IPCC have done detection and attribution studies using plants and animals (e.g. Root et al. 2005). Finally, applying a criterion such as this would require subjective judgments of a researcher’s focus area. Our study quite purposefully avoids making such subjective determinations and uses only objective lists of researchers who are self-defined. They were not chosen by our assessment as to which groups they may or may not belong in.

Some have taken issue with our inclusion of IPCC AR4 WGI authors in with the CE group, in that the IPCC Reports are explicitly policy-neutral while the four other CE policy statements/petitions are policy prescriptive. However, we believe our definition of the CE group is scientifically sound. Do IPCC AR4 WGI authors subscribe to the basic tenets of ACC? We acknowledge that this is an assumption, but we believe it is very reasonable one, given the strength of the ultimate findings of the IPCC AR4 WGI report. We classify the AR4 WGI authors as CE because they authored a report in which they show that the evidence is convincing. Naturally, authors may not agree with everything in the report, but those who disagreed with the most fundamental conclusions of the report would likely have stepped down and not signed their names. The presence of only one of 619 WGI contributors on a UE statement or petition, compared to 117 that signed a CE statement, provides further evidence to support this assumption. Furthermore, repeating our analysis relying only on those who signed at least one of the four CE letters/petitions and not on IPCC authorship yields similar results to those published.

No grouping of scientists is perfect. We contend that ours is clear, meaningful, defensible, and scientifically sound. More importantly, it is based on the public behavior of the scientists involved, and not our subjective assignments based on our reading of individuals’ works. We believe it is far more objective for us to use choices by scientists (over which we have no influence) for our data instead of our subjective assessment of their opinions.

Scientists not counted: What about those scientists who have not been involved with the IPCC or signed a public statement? What is their opinion? Would this influence our finding that 97% of the leading researchers we studied endorse the broad consensus regarding ACC expressed in IPCC’s AR4? We openly acknowledge in the paper that this is a “credibility” study and only captures those researchers who have expressed their opinions explicitly by signing letters/petitions or by signing their names as authors of the IPCC AR4 WGI report. Some employers explicitly preclude their employees from signing public statements of this sort, and some individuals may self-limit in the same way on principle apart from employer rules. However, the undeclared are not necessarily undecided. Two recent studies tackle the same question with direct survey methods and arrive at the same conclusion as reached in our study. First, Doran and Kendall-Zimmerman (2009) surveyed 3,146 AGU members and found that 97% of actively publishing climate researchers believe that “human activity is a significant factor in changing mean global temperatures.” A recently published study, Rosenberg et al (2010), finds similar levels of support when surveying authors who have published during 1995-2004 in peer-reviewed journals highlighting climate research. Yes, our study cannot answer for – and does not claim to – those who have not publically expressed their opinions or worked with the IPCC, but other studies have and their results indicate that our findings that an overwhelming percentage of publishing scientists agree with the consensus are robust. Perfection is not possible in such analyses, but we believe that the level of agreement across studies indicates a high degree of robustness.

Publication bias: A frequent response to our paper’s analysis consists of attributing the patterns we found to a systematic, potentially conspiratorial suppression of peer-reviewed research from the UE group. As of yet, this is a totally unsupported assertion backed by no data, and appears untenable given the vast range of journals which publish climate-related studies. Notably, our publication and citation figures were taken from Google Scholar, which is one of the broadest academic databases and includes in its indexing journals openly receptive to papers taking a different view from the mainstream on climate. Furthermore, recently published analysis (Anderegg 2010) examines the PhD and research focus of a subsample of the UE group, compared to data collected by Rosenberg et al. 2010 for a portion of the climate science community publishing in peer-reviewed journals. If the two groups had similar background credentials and expertise (PhD topic and research focus – both non-publishing metrics), it might indicate a suppression of the UE group’s research. They don’t. The background credentials of the UE group differ starkly from that of the “mainstream” community. Thirty percent of the UE group sample either do not have a documented PhD or do not have a PhD in the natural sciences, as compared to an estimated 5% of the sample from Rosenberg et al; and nearly half of the remaining sample have a research focus in geology (see the interview by Schneider as well).

“Blacklist”: The idea that our grouping of researchers comprises some sort of “blacklist” is the most absurd and tragic misframing of our study. Our response is two-fold:

  1. Our study did not create any list. We simply compiled lists that were publicly available and created by people who voluntarily self-identified with the pronouncements on the statements/letters. We did not single out researchers, add researchers, drop researchers; we have only compiled individuals from a number of prominent and public lists and petitions that they themselves signed, and then used standard social science procedure to objectively test their relative credibility in the field of climate science.
  2. No names were used in our study nor listed in any attachments. We were very aware of the pressure that would be on us to provide the raw data used in our study. In fact, many journalists we spoke with beforehand asked for the list of names and for specific names, which we did not provide. We decided to compromise by posting only the links to the source documents – the ‘raw data’ in effect (the broader website is not the paper data), where interested parties can examine the publically available statements and petitions themselves. It is ironic that many of those now complaining about the list of names are generally the same people that have claimed that scientists do not release their data. Implying that our list is comparable to that created by Mark Morano when he worked for Senator Inhofe is decidedly unconvincing and irresponsible, given that he selected individuals based on his subjective reading and misreading of their work. See here for a full discussion of this problematic claim or read Schneider’s interview above.

In sum, the various comments and mischaracterizations discussed above do not in any way undermine the robust findings of our study. Furthermore, the vast majority of comments pertain to how the study could have been done differently. To the authors of such comments, we offer two words – do so! That’s the hallmark of science. We look forward to your scientific contributions – if and when they are peer-reviewed and published – and will be open to any such studies. In our study we were subjected to two rounds of reviews by three social scientists and in addition comments from the PNAS Board, causing us to prepare three drafts in response to those valuable peer comments that greatly improved the paper. We hope that this response further advances the conversation.

Anderegg, W.R.L. (2010) Moving Beyond Scientific Agreement. Climatic Change, 101 (3) 331-337.
Doran PT, Zimmerman MK (2009) Examining the Scientific Consensus on Climate Change. Eos Trans. AGU 90.
Root, T.L. et al. (2005) Human-modified temperatures induce species changes: Joint attribution. PNAS May 24, 2005 vol. 102 no. 21 7465-7469
Rosenberg, S. et al (2010) Climate Change: A Profile of U.S. Climate Scientists’ Perspectives. Climatic Change, 101 (3) 311-329.

243 Responses to “Expert Credibility in Climate Change – Responses to Comments”

  1. 1
    John W says:

    The assumption that experts can be relied upon depends largely on the existence of conflicting interests. How many reports have intentionally caused a malfucntion in a vehicle that only requires minor repair work, driven into a garage and the expert (mechanic) comes back with major repair claims? If your doctor suggested that cancer treatment would not be beneficial to you, but then you discovered the doctor had a wealthy patient that needed an organ that you matched, would this conflict of interest change your decision to forgo cancer treatment? Might you want a second opinion?

    The idea that peer-review is the litmus test is flawed. It is critical review that a theory must stand up to in order to gain credibility and climate scientists have avoided this essential step in scientific advancement.

    [Response: You are attacking strawmen. We have often pointed out that peer review is only necessary, not sufficient for the science to be accepted. Additionally, we have often stressed that no individual scientist's opinions should be taken alone - which is why there are assessment bodies like the NRC, IPCC or CCSP. - gavin]

  2. 2
    SecularAnimist says:

    John W wrote: “The assumption that experts can be relied upon depends largely on the existence of conflicting interests.”

    That’s well worth remembering when you evaluate the opinions of “experts” who are funded by fossil fuel corporations that have a powerful “conflicting interest” in perpetuating their one billion dollars per day in profit from continued business-as-usual use of their products.

    John W wrote: “It is critical review that a theory must stand up to in order to gain credibility and climate scientists have avoided this essential step in scientific advancement.”

    Your assertion that climate scientists have “avoided critical review” is absolutely false. Indeed it is laughably false.

    One wonders which “experts” you relied upon when you accepted that blatant and ridiculous falsehood as truth.

  3. 3
    pete best says:

    Re #1 Sounds to me thay you are inventing motives other than good science such as money or power. Its a cheap shot. I like the term wealthy patient or a garage into making easy money as motives that compare with climate science. Hopeless argument.

  4. 4
    Dale Power says:

    If A mechanic says that you need a major (and costly) repair, it may indeed be fueled by self interest.

    If almost all mechanics say it is true, you probably want to have the work done ASAP.

    Especially if they know that their work is going to be reviewed by millions of people, many or whom are also mechanics.

  5. 5
    G Rowatt says:

    “We accept and rely upon judgement an opinions of experts”

    As an opening statement the message stopped there for me. Anyone who offers you “judgement and opinions” will not give you a guarantee!

    [Response: What good would that do? Can't take the planet back to the shop..... - gavin]

  6. 6
    ghost says:

    RE: 1, Well, if you mean that portion of the 3%ers who pedal the denial lies, then yes, they “have avoided this essential step in scientific advancement.” If you mean the serious scientists who are engaged in meaningful climate research every day, then I have some swamp land that might, ahem, interest you.

  7. 7
    Doug Bostrom says:


    How astonishingly oblivious, almost as though the person writing the words was completely unconscious.

    Critical review is mandatory, thus peer review is useless. Care to try again minus the paradox?

  8. 8
    Bob says:

    “We accept and rely upon judgement an opinions of experts”


    So if a range of doctors state that in their opinion a certain operation would save your life, you wouldn’t listen unless they “guaranteed” it.

    Life isn’t so black and white!

  9. 9
    Dappled Water says:


    None?. Figures.

  10. 10
    Titus says:

    “Judgement and opinion” cannot be compared to “airplane mechanics”. You stopped me dead from further reading at that point.

    Aircraft are repaired and maintained to strict rules and standards which get signed off, documented and audited as a matter of process. No room for judgement and opinion here.

  11. 11
    Günter Heß says:

    If I choose an expert I am looking for credibility and knowledge. For me credibility is more than knowledge. In an expert I am looking for both. I do think the paper is logically flawed, since it mixes up both concepts:
    The authosr’s write:
    I think this paragraphed analogy proves my point. It’s about knowledge, not about credibility.
    For me a scientist, who does not live up to his words might not have the credibility to promote his ideas, but in general I would not doubt his knowledge in his area of expertise. This goes for all sides of the argument.
    Best regards

  12. 12
    Frank Grober says:

    I have observed attempts to infer improper motives on the part of the large majority of scientists who say we have a problem with global warming not just from non-scientist critics, but from some scientists who have what seem to me to have reasonable credentials. Obviously an approach like the one done here can be done badly intentionally or otherwise, but it’s not like it would be the first shot fired in this particular war.
    I personally like to look at the variety of different lines of evidence that support the consensus global warming science and the variety of groups that either produced the studies or endorse the general concepts with some expertise in one or more type of evidence. If there had been no work done on computerized climate models for example the evidence about past carbon dioxide levels and global temperatures would be enough to raise great concerns. It’s also interesting to look at polls and statements by various scientific organizations and to try to decide what their financial interests are. In some ways the 47% of petroleum geologists who believed that human activity was warming the planet in a poll published in EOS was more impressive than the 97% of climatologists who felt that way given the financial interests and questions of conscience involved. Similarly the Canadian national science academy members cannot have overlooked the tidal wave of money and scientific jobs that could come from the exploitation of their nation’s tar sands.
    Another approach I find interesting is to look through denier writings for smoking guns indicating really bad scholarship and sloppy thought processes. S. Fred Singer for example was the coauthor of Unstoppable Global warming Every 1,500 years. He wanted to put in the claim that the amount of CO2 in the atmosphere was already enough to hold in as much heat as possible, an assertion that he should have known was false. To support this claim he quotes the State Climatologist Of North Dakota in a paper published in the Bulletin Of The North Dakota State Geological Survey. Obviously this should be on the front page of Nature and the New York Times if it was true, but doing it this way Singer was able to give the appearence of having supporting evidence to those less well versed in science.
    Those of us who have had the experience of arguing science in a highly politicized environment will know that there are those who will say up is down and smear anyone who knows otherwise. Showing their conflicts of interests and the deficiencies in their backgrounds and arguments may not be pleasant for most scientists, but doing so is essential to the preservation of nature and civilization.

  13. 13
    Interglacial terror says:

    Here is my suggestion: You group the AGW hypothesis with other big ideas and paradigm shifts such as heliocentric system, relativity, big bang etc….

    That way you can get some idea on the probability of scientists being right or wrong. Anyone got a coin?

  14. 14
    Radge Havers says:

    John W @ 1:


    From the article:


    Did you even read the article?

    captcha: between donkeys


  15. 15

    The World Cancer Research Fund’s 2007 report is pretty much the
    equivalent of the IPCC in its field … 150 experts from around the planet reporting on lifestyle and cancer. They report about
    every 10 years. In 1997, they said meat (all meat) probably causes
    bowel cancer (and several others). In 2007, they said, “okay we have narrowed it down, red meat causes bowel cancer, no ifs, no
    buts no caveats”. How many Governments have acted to warn their populations of this risk? How many individuals react
    with “What the f..k do they know, I like my steak!”. My point is that we do not trust experts unless they tell us what we want to hear and already are close to believing.

  16. 16

    5 (G Rowatt)

    As an opening statement the message stopped there for me.

    10 (Titus)

    You stopped me dead from further reading at that point.

    This is a discouragingly common theme among “skeptics”, who are supposedly self styled auditors, ready to ceaselessly educate themselves in order to make up their own minds, rather than rely on the opinions of others.

    And yet so frequently skeptics decide that it’s time to simply stop listening or reading, that they’ve heard enough, that they already know what they think and the moment any inputs contradict their open minded, closely held opinions, it’s time to simply shut down.

    12 (Radge Havers in response to 1, John W),

    Did you even read the article?

    And once again, a skeptic (John W) is ready to come out, guns blazing, only to expose the fact that he didn’t even read (or comprehend) the article in the first place.

    Thank you, Radge, for dissecting that so cleanly.

    I hope and pray for the day that a true, worthy “skeptic” will arrive to debate the issues intelligently, with facts and knowledge… except, of course, that such a person wouldn’t be arguing against AGW.

  17. 17
    Karsten V. Johansen says:


    “Climate skepticists” are trying to appease global warming, or rather the forces behind it. They’re feeding the crocodile – with oil.

    From around the globe we’re mainly getting more and more serious warning signals from nature – consider fx. the now nearly two months of extreme heat (ten degrees C above normal mean for such a long period) in Russia, Ukraine, Central Asia, drought and spreading wildfires, coinciding with also extreme heat and 100-year monsoon flooding in China ad Pakistan, six meters of downright melting from the top of an outlet glacier from the inland ice in West Central Greenland this summer, continuing big melting rates of the polar sea ice this year, unusual warmth also in the USA and Europe etc.

    Of course, taken each for themselves, these warning signals can’t be attributed to shifting climate, since we have defined climate as the thirty year mean etc. But extreme events almost all pointing in the same direction, year after year, taken together with what the vast bulk of the science tells us, is a very strong indication indeed, that time may be running out even faster than the more pessimistic think. onsider the fact that the leading scientists on polar sea ice, who said in 2007 IPCC report: the ice may be gone i the summer by 2080, are now saying it may be gone already by between 2013-2030.

    In the meantime, the “debate” about the socalled
    “climategate” in the mainstream media have already lead to most politicians and media rather conveniently downplaying the whole climate problem – in fact the US congress is still even stronger outright ignoring it completely.

    I think the scientists of course should do their science, but also that they have to realize their responsibility to tell the public very loud and clear:

    that it is a fatal illusion to believe that the uncertainties about climate in science neccesarily will play out to give us positive surprises (meaning we can just relax)

    that the climate history point to the fact that climatic changes can be very fast and sudden indeed, even if they’re only natural

    that mankind is now making an unprecedented experiment in the earth’s history with the atmospheric composition

    that we’ve only been around with our sophisticated but rather untested industrial and agricultural modes of production for an extremely tiny fraction of the earth history

    These points are to be stressed a lot more than they are now. Problem is, we’ll never know the whole truth about the amount of global warming until it’s (far) too late. And we’ve got nothing to loose by being more cautious and listen to the scientific warnings.

    Of course the science should always be done properly, but the proportions have been completely distorted by the media and the oil interests in this debate.

    And where’s the discussion about the medical science which lead to false alarm about flu pandemic this winter? Nowhere. Why exactly is that so? Has it something to do with (misinterpreted? too narrow?)industrial/financial interests and a complete misunderstanding about how we can use science to make our society more sustainable?

  18. 18
    brad says:

    If it is so important to take expert opinion regarding climate science, why can’t a large number of climate scientists acknowledge they are out of their depth when in comes to advanced statistical analysis. There seems to be a hostility to outside expertise when statistical methods are questioned, and it reflects badly on the science as a whole.

    [Response: Your impression of this is very wrong. Scientists talk to people working on different aspects and with different expertise (including statisticians, and software engineers, and geochemists, etc.) all the time. There are specific programs to encourage statistical climatology, and there was recently a big meeting specifically on this. Most of this obviously goes on informally, but it has to be said that building useful and long-lasting collaborations is hard. The kinds of things needed in an applied science like climate aren't often the kind of thing that gets one noticed at statistical conferences. I've personally tried to build collaborations with local academic statisticians, but other than with a machine learning group, there hasn't been much progress. Perhaps you are thinking of cases where there is an ill-informed attempt to 'refute AGW' using poorly posed but exciting sounding statistical methods that come up with completely un-physical results. That kind of thing is not usually very conducive to cross-disciplinary networking. - gavin]

  19. 19
    Eli Rabett says:

    One seldom gets an opportunity to show why you should depend on expert opinion and not the guy on the street better than our #1 here:



    In fact

    A handful of medical conditions will rule out organ donation, such as HIV-positive status, actively spreading cancer (except for primary brain tumors that have not spread beyond the brain stem), or certain severe, current infections.

  20. 20
    Ike Solem says:

    Interesting response – but really, this has all been covered in far more detail in two other books:

    Merchants of Doubt – a general review of issues related closely to climate science coverage:

    The book reveals how those pioneering shills evolved into a small group of well funded pseudo-scientists who now hold influence over perception and policy far out of proportion to their numbers or the credibility of their claims. Along the way the authors expertly cut off examples of denial at its roots, including the ridiculous claim that DDT was really safe and banning it killed more people than Hitler, or why ozone depletion and climate change are mere modern day hysteria.

    This book should be a staple for any scientist or those interested in science, especially journalists and others whose work intersects or informs public policy.

    University Inc. The Corporate Corruption of Higher Education – a general review of the corporate control of university research, which more or less explains how and why various science research programs have been closed down or defunded over the past few decades:

    At the same time teaching is being downsized, universities are courting money from private industry and pouring resources into commercial operations far removed from the universities’ primary teaching and academic-research missions. Universities now run their own industrial parks, venture capital funds, and industry-university cooperative research centers. They also operate expensive patenting and licensing offices to market their research to private companies in exchange for royalty revenues.

    You would think that would lead to a boom in renewable energy research, but due to patent restrictions and the lack of desire of fossil fuel corporations to sponsor renewable competition, it’s actually had the opposite effect.

    You might ask why, if this is true, climate science didn’t suffer the same fate. The truth is that much climate-related science DID suffer that same fate in the 1990s, as USGS toxicology programs were roundly shut down, and so on. It’s all recorded in the literature publication record – for example, in 1979 there were a few thousand papers published on ethanol – four years later, there were about five. Toxicology research on oil spills dried up as well, particularly at major universities, and corporate-controlled programs like the University of California – BP arrangement became more and more widespread. Other sectors of climate science are much more insulated from political attack – after all, everyone needs good weather data, and weather data, over time, becomes climate data. This, of course, is not the case with renewable energy research.

    Clearly, these extensive academic-business interests are not going to be happy with independent science that upsets the profit margins of the private partners, who often have university administrators sitting on their corporate boards these days. This is the central problem – the loss of independence, the loss of transparency, and the loss of peer review (all seen in DOE grant methodology, for example). This is why bogus nonsense like “clean coal” has persisted for so long, too – there’s no external peer review process in DOE grants – it’s all in-house cronyism, and with the #2 at the DOE also serving as BP’s Chief Scientist, who expects anything to change there?

    The entire academic system needs serious reform, sad to say.

  21. 21
    Chris Colose says:

    This is somewhat of a response to #13 (Interglacial) and my own thoughts:

    This article is not perfect but is relatively well-defined in what it aims to accomplish, and so it’s a good starting point in terms of contribution. The problem with assessing expert judgment on a subject like AGW (or ‘ACC’ in the article) is that there is no well-defined hypothesis that is being examined. It would be nice to see public discourse move past broad and meaningless statements like “…agreement with the IPCC.” The AR4 itself is a 3-volume work consisting of almost 1,000 pages per volume, with multiple chapters handling different topics.

    AGW is not an independent hypothesis that can be easily separated from the fundamental physics that is equally applicable to natural climate change, the expansion of cooling thermodynamics of air parcels, the saturation vapor curve for condensable substances, or the same principles remote sensing people rely on for satellite data retrieval. This is all stuff relevant to atmospheric physics in general, ranging from modern-day Earth to snowball or Venus-like climates. In all of these cases, adding CO2 to the atmosphere makes the planet darker in the infrared (when viewed from space) and necessarily warms the lower atmosphere. This, in turn, arises from the quantum-scale radiative transfer which doesn’t care about whether humans released that CO2 or not. Similarly, there is no separate hypothesis for a “positive water vapor feedback” which can easily be distinguished from the physics of any other greenhouse gas which might tend to condense in different planetary temperature/pressure regimes, such as methane on Titan, or CO2 on Mars. There is no separate physical law applicable to humans which is distinguishable from the fact that the area coverage of ice/snow will change as a function of temperature, and insofar as the albedo of these surfaces is different than the underlying and surrounding surface, it follows that the surface albedo is also a function of temperature. AGW, such as it is, is a consequence of these many physical laws in the same way. The TES instrument observing the Martian CO2 spectrum has just as much to do with the radiative transfer equations as the necessity to get warming with more greenhouse gases.

    2-3% seems like an awfully high percentage of experts who have published who extensively disagree with these things. If the people verifying these things find discrepancies between what ought to happen and reality, then there is no fundamental rejection of the human influence on climate, but rather the necessity for a paradigm modification to atmospheric physics on a more general level.

    A more strict hypothesis is that of climate sensitivity, since there is no fundamental theoretical basis for how sensitive the climate ought to be to some forcing. Some people like Lindzen argue that the sensitivity is on the order of about 0.25 degrees C/(W m**-2) or less; this is almost certainly not the case, although I’m not sure whether or not this is the case can be easily molded into ‘disagreement with the IPCC’ or ‘disagreement with AGW’ without more precise terminology on what exactly experts are agreeing or disagreeing with. If it turns out that Arctic sea ice declines more rapidly than models, or Greenland is less sensitive to melt than previously thought, does this also apply to (dis)agreement with the “AGW hypothesis?” There are also many things which depart from physics and require expert judgment, such as whether climate change will be ‘dangerous’ or ‘important’ which are subjective in nature unless there is some universally-accepted threshold (e.g, CO2 concentration, economic loss, # of species that go extinct) for what these words mean.

  22. 22
    Gerry Beauregard says:

    #20 Ike Solem said:
    “…the lack of desire of fossil fuel corporations to sponsor renewable competition…”

    Interestingly the much (and perhaps justly) vilified BP is a founding member of the MIT Energy Initiative ( which seeks to transform the world’s energy systems. Tony Hayward, BP’s gaffe-prone ex-CEO, seems quite eloquent and sincere in this talk at MIT on how to meet the world’s growing energy demands:—facing-the-harsh-realities

    At about 25 minutes in, he talks at some length about the importance of government intervention, especially to set a price on CO2 emissions.

  23. 23
    Bob Koss says:

    You created a list of people showing the number of publications each had containing the word climate.

    The third most prolific name on that list is Michael Collins. You link to his web-page where he indicates less than 70 publications, and none prior to 2000.

    Why does you list show Matthew Collins with 726 publications and Phil Jones only 724?

    You also link to Michael Mann at the Department of Sociology
    University of California, Los Angeles. How did he make the cut?

    What due diligence was performed on your list?

  24. 24
    dhogaza says:


    That’s a list maintained by one of the authors.

    It is independent of the published paper.

    This article is quite clearly about the peer-reviewed paper.

  25. 25
    Titus says:

    Bob (Sphaerica) @16

    If airplane mechanics used “judgment and opinion” I would be very skeptical and never fly again.

    I offered my comment in good faith. I believe any intelligent, open minded person would say the same. They would not read past that comment. Why would they when it sends a nonsensical message? Kind of taints the rest, which if the overall message is good, is rather unfortunate.

    Take it or leave it.

  26. 26
    Bob Koss says:

    Re: my #23

    Both Collins names should read Matthew Collins. Michael was written in error.

  27. 27
    Doug Bostrom says:


    Commercial aircraft pilots on the other hand frequently employ judgment or opinion, informed by expertise. So does my barber when cutting my hair. Thus I can be assured of equal safety if I should choose to be conducted to a Cat III landing by my barber or a properly certified pilot.

    Or something like that.

  28. 28
    Edward Greisch says:

    17 Karsten V. Johansen: “responsibility to tell the public”
    The scientists have gone way beyond their responsibility to tell the public. This web site is NOT a requirement of the job. It is a gift from the scientists. The public has a responsibility to LISTEN and Listen Good. NASA was not funded to overcome propaganda from the fossil fuel industry. Democracy is based on the idea of an intelligent and informed electorate. That is no longer the case because public education has not kept up with the advance of science, and that is also NOT the fault of scientists.
    Karsten V. Johansen, Andy Revkin and others who lay these “Shoulds” on scientists: Where is your money to pay more than the fossil fuel industry is able to pay for public relations? Where is your reformation of society and the educational system to eliminate the efficacy of disinformation and propaganda?

  29. 29

    Titus, @25, said “I believe any intelligent, open minded person would say the same. They would not read past that comment.”

    Well, I guess I’m either not intelligent, or not open-minded. I find it hard to believe that there is zero judgement involved in airplane mechanics, and harder still to believe that even if that’s true the larger point is invalidated–after all, I in fact do trust the plane and the maintainers thereof, even though I don’t know precisely how their work is carried out. And I’d be very concerned, if, for example, I read that airline X had just laid off all their senior mechanics in order to save money.

    It’s great if you can put calipers on a part and objectively measure whether wear has reached spec limits or not. But in a great many areas in life–and I don’t really care if airplane mechanics is one–we never get to make our decisions on such clear information. And we end up back with the necessity of trusting the judgement and expertise of others–whom rationally we judge (or ought to) by credentials, knowledge, skills and experience.

  30. 30
    Martin Vermeer says:

    John W #1:


    Yep, this is indeed an premise to critically assess. For all self-identifying “experts”. Hint: which position, CE or UE, is the one offering scope for easy personal enrichment? You can figure it out.

  31. 31
    William T says:

    #15 Geoff Russell – The difference of course is that if you (or your whole country) keeps eating red meat it has no effect on my my grandchildren’s health. However if the actions of “obstructionists” result in the world not taking effective action against increasing CO2 then there’s likely to be severe impacts on my grandchildren (as well as theirs).

    CAPTCHA dangerous as

  32. 32
    Alan of Oz says:

    I personally agree with the article, “the republic of science” is the only way to go. However I think you over-estimate many people when you say they would choose an oncologist over a quack. There is no shortage of faith healers, phycic healers, homeopaths, and other assorted vermin who prey on a large population of gullible and superstiuos people.

    James Randi’s father died a premature death because one of them convinced him to avoid the medical proffession, there are millions more stories with similar outcomes.

  33. 33
    Anne van der Bom says:

    Titus 3 August 2010 at 11:0 PM,

    I believe any intelligent, open minded person would say the same

    I believe any intelligent person would understand that the example of the airplane mechanic was a metaphor. Metaphors are imperfect by definition.

    I believe any open minded person would continue reading, because open minded persons like to be challenged in their beliefs.

  34. 34

    It is jolly useful to have a handy guide to how involved various writers and bloggers have been with the science of climate change – and a list like this does give a rough idea. So if I am reading a newspaper article that quotes some “expert” I can quickly see just how expert that expert actually is.

    However, I am still at sea as to why the list was divided into those convinced of AGW and those not convinced. I fail to see the purpose of that.

  35. 35
    willard says:

    Even if airplane mechanics does not use opinion, there are still opinions involved in the quality of soldering, the general inspection and the commanding of the airplane, and many more areas that may be cause of concern.

  36. 36
    M says:

    “If airplane mechanics used “judgment and opinion” I would be very skeptical and never fly again.”

    Really? I suggest you stop flying then. _Everyone_ uses judgment and opinion. Usually that’s matched with tests, checklists, and all sorts of other tools… but when it comes down to it, the reason you have trained airplane mechanics rather than Joe Schmoe following an instruction manual is _because_ the airplane mechanics have judgments and opinions: “this looks fishy. The standard check says its fine, but I think I’m going to look at it again”.

  37. 37
    Ray Ladbury says:

    Titus, your comment illustrates a lack of understanding not just of the role of experts, but of how mechanics work. Mechanics are not machines. I expect them to use judgment in their work. I’m left wondering not only whether you’ve ever talked to a scientist, but whether you’ve ever even talked to a mechanic!

  38. 38
    Ray Ladbury says:

    Bob Koss, I think you are misinterpreting the table you cite. It list citations of the author’s publications, not the number of publications. Number of publications gives a measure of productivity. Citations also measures how influential the output has been.

  39. 39
    Mitch Lyle says:

    The fundamental issue in this argument is whether the few scientists that have argued against a large anthropogenic effect represent the leading edge of new science or some kind of last gasp.

    Having lived through the plate tectonics revolution, I can clearly see the differences between that scientific revolution and this one. In the case of plate tectonics, there were initially few convinced but they kept coming up with exciting new data. When others tried to falsify the idea, they found more interesting observations that got them excited. It really didn’t take long to convince almost everybody, except a few diehards, that the science was right. Meanwhile these diehards (e.g., the Meyerhoffs) continued to publish for decades about ‘problems with plate tectonics’.For all I know, they are still publishing.

    In the scientific (vs media) discussion of global warming, all the interesting new data points to warming changes in the system, or to new but interesting complexities that make scientists stretch their models. People like Lindzen are not bringing new, exciting, or even interesting data to the table. It is no wonder why the Lindzen idea of strong negative feedback is not well regarded in the scientific community–it doesn’t lead anywhere and doesn’t match with the other data available. Nevertheless he will probably keep publishing.

  40. 40

    25 (Titus),

    Let’s see… You didn’t read the article, and then your defense for not bothering to read and inform yourself is that you knew that what you didn’t read held a “nonsensical message” (which you would know how, seeing as you didn’t read it?).

    As far as airplane mechanics, you are completely (purposely?) misunderstanding the statement, by misinterpreting (being overly literal with) two words. Obviously, the point of the statement is that the passengers themselves, as well as the owners of the airline, are not capable of determining whether or not the plane is capable of flying. The mechanics are capable. The clear point is that we rely on experts in everything, every day. Our modern world is far too complex to do otherwise.

    Your singular and unnecessary focus on the words “judgment and opinion” is the problem, and a typical denial debate tactic (nit pick by purposely misinterpreting a detail to the point of distraction). There is nothing wrong with the statement itself.

    If you prefer, wordsmith the article to use the words “knowledge and expertise” in place of “judgment and opinion.” It reads the same, it says the same thing, but it won’t be so offensive to someone who is fooling themselves into thinking that they know better than everyone else, particularly the experts, in one of the most important issues of our day.

    And that last part is, in fact, the crux of the article which you didn’t even bother to read.

  41. 41
    Silk says:


    So how do they make planes fly? Magic?

    What processes do these mechanics use that don’t rely on their judgement, and their opinion?

  42. 42

    Why would they

    Because they were “intelligent and open-minded.” Such a person would read on to see if they might have misinterpreted the passage and determine whether “the overall message is good.” Open-minded people tend to not draw snap conclusions that conveniently align with their preconceived notions, nor use terms like “take it or leave it” when discussing ideas.

    An ideologue, on the other hand, would exclaim “gotcha!” and not read past that comment. Why would they if they had already gotten what they had come for?

    re-captcha: “c’est Trenholm

  43. 43
    Donna says:

    To Titus – “If airplane mechanics used “judgment and opinion” I would be very skeptical and never fly again.”

    Then you had better stop flying. Airplane mechanics use judgement (which one of several different issues that could cause the same problem are most likely to have caused a problem this time and so should be checked first) and opinion (which tool do they like to use for a fix when several different tools would work) all the time.
    When judgement/opinioon is based on the evidence then its use reflects well on the expertise of the person. Judgement or opinion that goes against the evidence is problematic.

  44. 44
    vboring says:

    Except that we don’t actually rely upon the judgment or opinions of experts when we don’t want to.

    There is a strong consensus in the medical community that eating less animal products will greatly reduce the risk of heart disease. Even after having a heart attack, most patients ignore the advice of experts.

    There is a strong consensus among the experts that low level exposure to electro-magnetic fields is harmless, yet every time a transmission line goes in the NIMBY crowd wails about EM.

    There is a strong consensus among the experts that vaccines help humanity, yet the most educated populations in the world have a widespread fear of them.

    So, why should we expect people to react any differently to the consensus of experts in climate science?

  45. 45

    43 (Donna),

    Titus, I’m sure, will disagree with your position. My guess is that he’s an engineer. Engineer’s live in a world of black and white, and so they tend to have difficulty with generalizations and nuance. They deal with problems with a very limited scope, always well defined with well defined parameters and boundary conditions, and often armed with a tool set limited by their specific field and position. As such, judgment and opinion can often be dismissed with cold, hard facts (or rather, they don’t realize how much their judgment and opinion come into play to help them avoid wasting time pursuing fruitless avenues).

    There are very few professions in the world like that, however, and cutting edge engineering (think NASA space program) certainly does involve a lot of judgment and opinion (i.e. “talent”).

    I don’t mean to entirely disparage engineers (I am one myself), but in my mind engineers and scientists are both faced with and good at word problems. The main difference is that the problems presented to engineers include the question. The scientist must not only answer the question, but must also figure out what the question is (or rather, what the right/best question to ask would be).

    The secondary difference is that engineers are usually handed all of the necessary data as part of the word problem, while the scientist is left with the need to determine what he hasn’t been given but needs, and to somehow tease it out of the situation.

    The typical engineer’s failure to grasp these differences, along with an intelligence and self-confident arrogance that are necessary to being successful in the field (I will admit to being both myself) are, I think, prime ingredients for succumbing to Climate Change Denial Syndrome.

  46. 46
    Gordon says:

    Another aspect which I think you are neglecting: whether to fly on that airplane, or to take the advice of your oncologist, are personal matters which will affect (almost entirely) you alone. Whether to act on the advice of climate scientists is a political decision, one that will affect your neighbors, friends and enemies just as much as it will affect yourself. If you decide not to fly on that airplane, you won’t die if it crashes. If you reject the advice of your oncologist, it will be you who dies (or doesn’t die) of cancer. Rejecting (or accepting, and taking appropriate action) the advice of climate scientists will affect every damn person on the planet. And all the credibility in the world will get you exactly nothing if there is no money in it for the bankers.

  47. 47

    To get away from the whole airplane mechanics distraction (and that’s what it is, a huge distraction, although it is a wonderful example of extreme denial-in-action)…

    The Denial Team has somehow succeeded in making “expert” a dirty word. They’ve done it using a variety of attacks.

    1) They’ve misrepresented the “appeal to authority” fallacious argument to imply that any reference to an authority (i.e. expert) is simply wrong (a trick they use when they need it, but not when referencing their own chosen “experts”).

    2) They’ve undermined the perceived intentions of the experts by saying that they’re in it for the money (as if they wouldn’t get any money to study climate without GHG, or as if the money they’re given to study the subject goes straight into their own pockets, or as if that amount of money is really comparable to the intake of, oh, say, the Koch family, and so provides any noticeable incentive to fudge the results).

    3) They’ve undermined the definition of an expert by characterizing certain rank amateurs as experts (e.g., M&M), while also misinterpreting and attacking the actual work of true experts (e.g., the real MM), and so by proxy attacking the validity of the work and so expertise of all climate scientists. Sadly, some scientists are buying into this portrayal, giving it further weight.

    4) They’ve very commonly gone on the offensive with their own weaknesses by projecting them onto those that understand climate change, in this particular case by casting recognition of the facts and conclusions behind the science as a “belief” or “religion,” hence allowing them to dismiss even consideration of the evidence or the position of experts (since they are no longer then “scientists,” but rather “priests of a heretical religion”).

    5) They’ve recently taken to inaccurately casting all of climate science as an immature field, and so by extension the definition of expertise within the subject matter as relatively untrustworthy.

    So while the work behind this post do help people to focus on exactly how much effort it takes to qualify as an expert, and which side of the debate expert opinion predominantly falls, it does little to affect those (like Titus) who have fallen for the Denial Team bag of “tricks” (there’s that word again!) by twisting “expert” into a dirty word.

  48. 48
    Witgren says:

    Bob, good summary of points on what’s happened re: the term expert. You did forget one item – basically a variant of the Galileo Gambit, essentially asserting that since the commonly held view of “the experts” was wrong in that instance, that therefore the experts are wrong now. Never mind that science and the scientific method has progressed a wee bit since the 1600′s, or that they are completely unrelated subjects in any way – the mere fact that “experts” were wrong on a completely different subject four hundred years ago calls the competence of other experts into question today.

  49. 49
    Hank Roberts says:

    Bob Koss did catch an error in Jim Prall’s list — the wrong school for climatologist Michael E. Mann, who is at Penn State

    Sociologist Michael E. Mann, at UCLA, is worth reading in his own right, on policy and politics:

  50. 50
    Tom Fuller says:

    Real Climate has published a letter in defense of an indefensible paper. I have attempted to respond on Real Climate’s website, but they have decided not to publish my response.

    [Response: Most of this comment and the previous one was simply a list of accusations and insults, and not appropriate in this forum. The one possibly substantive issue we have left in for people to respond to. - gavin]


    They used Google Scholar instead of any one of several academic databases. They searched only in English, despite the fact that many climate scientists publish in other languages (and have many more who are skeptical of the English and American mania for histrionic claims of disaster due to CO2).

    They got names, job titles and specializations wrong–they obviously did zero quality control checking.

    As for the publications they were counting, they got them incredibly wrong. They hugely inflated the publication counts for their ‘side’ and reduced the publication counts for the opposition.


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