On consensus in science

“Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory.” –Stephen Hawking

“It does not matter who you are, or how smart you are, or what title you have, or how many of you there are, and certainly not how many papers your side has published, if your prediction is wrong then your hypothesis is wrong. Period.” –Richard Feynman

“Who would dare assert that we know all there is to be known?” –Galileo Galilei

On many of my posts about climate change, I get comments from believers in catastrophic anthropogenic global warming that take issue with what I have written.  That’s fine.  But, instead of presenting facts to support their case, many of these commenters resort to invoking the myth alleging that about 98% of climate scientists say human carbon dioxide emissions are the major cause of recent warming. This alleged consensus, they say, must mean it’s true and should end all argument.  Some of these commenters also seem to be confused about cause and effect, and so conflate the perceived incidence of warming or cooling with attribution of cause.

So let’s look first at where these consensus numbers came from and then I will comment more generally on consensus in science.

One source was from a study by Peter Doran and Maggie Zimmerman at the University of Illinois. (See here and here.) They emailed 10,257 scientists and asked two questions:

Question 1: “When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?” I would answer that temperatures have risen because in the 20th Century the planet warmed from the depths of the “Little Ice Age.” The answer to this question is verifiable by observation of physical evidence.

Question 2 (the controversial question): “Do you think human activity is a significant contributing factor in changing mean global temperatures? The researchers didn’t define “significant.” This question solicits an opinion. The basic premise of the question has not been verified by physical evidence.

Of the original 10,257 scientists queried, 3,146 responded. Of those, Doran and Zimmerman whittled the number down to 77 who had been successful in getting more than half of their papers recently accepted by peer-reviewed climate science journals. Of the 77, 75 answered “yes” to question 2,that’s 97.4%. So, in that study the whole 98% claim is based on 75 positive answers out of 3,146 respondents.

The other possible source for the consensus myth is a paper by Anderegg et al, in PNAS. In that study, the researchers didn’t bother to poll scientists, rather they scanned the literature and constructed a “database of 1,372 climate researchers based on authorship of scientific assessment reports and membership on multi-signatory statements about ACC [anthropogenic climate change]” as outlined by the Intergovernmental Panel on Climate Change. The researchers then arbitrarily assigned “expert” status to those who had published at least 20 papers. That cut the number of “experts” to 908. In the supporting material at the end of the paper we find that of the original 1,372 researchers, 619 were contributors to the IPCC’s Fourth Assessment report, and 212 were signatories to the UN’s Bali declaration. After culling duplicate names, the paper’s authors wound up with 472 “experts” out of tens of thousands of practicing researchers.

We see from the two studies, therefore, that this claim of a 98% consensus comes from carefully culled researchers, most of whom worked on the IPCC reports, are said to believe that humans are the principal cause of climate change. The 98% consensus consists of researchers who have a vested interest in continuing the myth of significant global warming caused by human carbon dioxide emissions. Follow the money. The 98% consensus is just another manipulated number pulled out of the air.

Now, let’s turn to a more general discussion of consensus.

Dr. Judith Curry, Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, has a long paper on consensus in climate science. She begins by saying: “The manufactured consensus of the IPCC has had the unintended consequences of distorting the science, elevating the voices of scientists that dispute the consensus, and motivating actions by the consensus scientists and their supporters that have diminished the public’s trust in the IPCC.”

She goes on the write: “With genuinely well-established scientific theories, ‘consensus’ is not discussed and the concept of consensus is arguably irrelevant… While a consensus may arise surrounding a specific scientific hypothesis or theory, the existence of a consensus is not itself the evidence.” And she notes: “If the objective of scientific research is to obtain truth and avoid error, how might a consensus seeking process introduce bias into the science and increase the chances for error? ‘Confirmation bias’ is a well-known psychological principle that connotes the seeking or interpreting of evidence in ways that are partial to existing beliefs, expectations, or an existing hypothesis. Confirmation bias usually refers to unwitting selectivity in the acquisition and interpretation of evidence.”

There are some famous failures of consensus in history. The pre-eminent one was the belief that the Earth was the center of the universe. That was the prevailing consensus 500 years ago. That consensus was shown to be in error, first by Nicolaus Copernicus and later by Galileo, Kepler, and Newton.

In 1912, Alfred Wegener, building on earlier work by Frank Bursley Taylor, proposed that the continents did not have a permanent spacial relationship to each other, i.e., there was continental drift. Wegener could not, however, provide a reasonable mechanism for his hypothesis, therefore the consensus, for 50 years, was that he was wrong. By the 1960s, geological research did provide the mechanism and Wegener’s continental drift became part of the larger theory of plate tectonics.

Those who credulously invoke the “ 98% consensus” as an argument are displaying an ignorance of the facts and of how science works.  I refer you to Michael Crichton who said:

“I regard consensus science as an extremely pernicious development that ought to be stopped cold in its tracks. Historically, the claim of consensus has been the first refuge of scoundrels; it is a way to avoid debate by claiming that the matter is already settled. Whenever you hear the consensus of scientists agrees on something or other, reach for your wallet, because you’re being had.”

“Let’s be clear: The work of science has nothing whatever to do with consensus. Consensus is the business of politics. Science, on the contrary, requires only one investigator who happens to be right, which means that he or she has results that are verifiable by reference to the real world. In science consensus is irrelevant. What is relevant is reproducible results. The greatest scientists in history are great precisely because they broke with the consensus.”


  1. Thanks Jonathan, pretty interesting – just another popularly accepted “fact”. Reminiscent of the many baseless “facts” put forth in “Silent Spring”.

  2. You obviously do a lot of painstaking research in finding material that reinforces your beliefs. Let me put in simple terms what I take from this column and others that you’ve written. There’s no real reason to believe the vast majority of climate scientists, solar energy is not a viable alternative, hybrid cars are not practical.So essentailly, human activity has no effect on climate so there’s no need to change our behavior patterns. It’s Ok to just continue doing things the way we always have. It must be comfortable in your little cocoon of denial. Facts can be ignored but that doesn’t mean they don’t exist.

    1. If the premise is true that current changes in global temperatures require action, then the argument is not about science but about engineering. The notion that exchanging carbon credits or changing modes for surface generation of useful power will change either the levels or trends in global temperature changes is purely speculative, and possibly counter productive. If the requirement is to apply positive and fully reversible control over the distribution, trend and actual levels of global surface temperatures, then a limited set of technical options apply to the problem. None of those options are what the political movement around climate change proposes. If “mandatory” on a global level and required within the current decade, then all nations should be taxed and those nations capable of establishing a constellation of controllable orbital reflective satellites should work together to deploy the constellation. There are other technical options, but no other option has the maturity or rapid time-to-deploy of space reflectors to effect change within a practical program timeline. Certain options such as deployment or change of chemical species in the atmosphere carry significant risk, including loss of control issues.

    2. Alohapuna, Can you provide some specific facts of physical evidence showing that our carbon dioxide emissions are a significant driver of temperature? That is what the whole global warming debate is about. And as I have shown, the contention that “the vast majority of climate scientists” believe X, is a myth.

      1. Noticeable changes in climate occurred during the Industrial Revolution with two thirds of the effect occurring since 1980. Global warming was first used by a paper called the Charney Report that said “If carbon dioxide continues to increase we find no reason to doubt that climate changes will result and no reason to believe that such changes will be negligible.” That was put out by the National Academy of Sciences. The term became more widely used when NASA climate scientist, James Hansen addressed Congress. He said “Global warming has reached a level such that we can ascribe with a high degree of confidence that a CAUSE AND EFFECT relationship between a greenhouse effect and observed warming.” Scientists are 90% certain that it’s primarily caused by human activity. The findings are recognized by the national science academies of all major industrialized nations. Conservative think tanks mobilized to undermine the legitimacy of global warming. Disputes are more pronounced in the popular media than in scientific literature. Companies like Exxon-Mobil and Deutschebank hired scientist that disagreed with the theory. My own findings show that almost all of the papers and web sites disputing climate change are connected to conservative groups that have a finicancial or political stake in disproving global warming.
        Physicist, Richard Muller, you may remember, hired by Republicans and the Koch brothers to do his own study to debunk gw in reporting his findings to Congress to their chagrin not only determined that it indeed is real but went further than previous reports. More specifics are far too numerous and complex to try to include them in here.
        No scientific body of national or international standing disagree with global warming.
        That said, there are far greater consequences for inaction than in adapting to climate change and finding global warming a myth.

      2. Excellent, alohapuna! You have way more patience than I do to take the time writing a reasoned response. Sadly, the “facts” bubble that JD, minador and others with biased perceptions suffer from is impermeable. I suspect no amount of discussion will alter their belief about climate change. In fact, another reader warned me a couple of weeks ago, that if you don’t flavor your outlook and opinions with Ayn Randism, JD will not consider your position valid.

      3. By the way, Ricardo, there are two books that offer a very good insight into that mindset. “The Republican War on Science,” and “The Republican Brain.” by Chris Mooney.

      4. Alohapuna, You cite opinions but present no physical evidence. You fall into the trap that Crichton expressed.

      5. Yes, Mr. Duhamel, they are opinions of reputable professionals and organizations based on legitimate conslusive studies over many years. Predictions have already occurred with even greater intensity. You are to science what a boll weevil is to cotton. No doubt, you’ll doggedly continue with your beliefs and put out misinformation. So have your fun. As Thomas Paine said. “To argue with a man who renounces the use and authority of reason is like administering medicine to the dead.”

      6. Michael Crichton is also a right wing conservative expressing an opinion. I wouldn’t expect anything different from him.

  3. Thank you Mr. Duhamel for helping shed some light of truth on the issue(Or perhaps non-issue.) of human contribution to climate change. There will always be those who have an agenda and a closed mind to hearing anything that conflicts with their predetermined notion of how the world turns. A few of them seem to follow your column and continue to want to muddy the water. On the issue of climate change, I find myself in agreement with the facts as you have laid them out, Tree Hugger’s and Chicken Little’s protests notwithstanding.

  4. Headlines from Doha COP 18 show that the permafrost bogeyman has been trotted out. Once again alarmists are in massive denial of the facts.

    1) Permafrost has an active layer that can vary between two to three feet in a typical place like Barrow AK. That layer has melting and freezing every year.

    The methane concentration have been flat in Barrow in recent decades.

    2) Permafrost depletion in NH stopped in 2005.

    Except for warming during the 1970s and 80s, northern Eurasian temperatures appear to have remained fairly stable. And of that warming, Frauenfeld and Zhang state that “the strong decrease in seasonal freeze depths during the 1970s to “1990s was likely the result of strong atmospheric forcing from the North Atlantic Oscillation during that time period.” Thus, their work provides little to no evidence for any significant warming of this massive portion of earth’s land mass over the past two decades, and absolutely no evidence for recent CO2-induced warming.” [Oliver W Frauenfeld, Tingjun Zhang 2011: Environmental Research Letters]

    3) Researchers have discovered that when these melted areas are thawed, the explosion of new growth of vegetation becomes a positive CO2 sink that sequesters carbon dioxide in greater quantities than that released from the thaw. So instead of permafrost melting being a positive warming feedback, it actually becomes a negative feedback.

    “northern peatlands can continue to serve as carbon sinks under a warmer and wetter climate, providing a negative feedback to climate warming,” which is the exact polar-opposite of what has historically been claimed by the world’s climate alarmists.” [Shanshan Cai, Zicheng Yu 2011: Quaternary Research]

    4) Earlier warm periods, such as the Medieval and Holocene optimum, did not produce unusual amounts of CH4.

    “There appear to be no significant CH4-excursions in ice core records of Antarctica or Greenland during these time periods which otherwise might serve as evidence for a massive release of methane into the atmosphere from degrading permafrost terrains.”


  5. In this manner, all scientific “facts” are theories subject to dispute. From this very valid point of view, gravity is only a theory.

    By the same token, the very real human reaction of denial as a primary psychological defense mechanism when faced with new and challenging circumstances is a similar theory. Notably, denial was the common denominator in the defense of several of the common historical theories (e.g., a geocentric universe) that were finally disproved.

    Might we agree that earth’s atmosphere is a finite resource subject to human effect? Or will some insist, as we once thought of the vitality of the ocean fisheries or the refreshment of the Great Lakes, that human use and abuse would have no debilitating outcome?

    You may very well be right. The problem is, we’re placing the bet, but it’s our children and grandchildren who will have to settle up. I’m not much for hugging trees, but I do so cherish hugging my grandchildren. Or is leaving them a more sustainable world somehow a bad idea?

    1. A warmer, more CO2 enriched world will be more sustainable because plants, including our food crops, will grow better with less water.

      1. One thing I learned is that, in any closed system, alterations to one part cause changes in another. I find it difficult to imagine that the suggested benefit would be without less salubrious consequences elsewhere on the planet.

      2. Planet Earth is not a closed system, we get energy from the Sun and cosmic radiation. We also get solid material from all the comets, meteorites and cosmic dust that impinge on Earth every day. Geologic history shows that a warmer world with more carbon dioxide is more robust in all life.

      3. For the purposes under discussion, it is a generally fixed, if not a specifically enclosed system. Not to further pick nits, it is, nonetheless, a working system which we meddle with at our own, or, more realistically, our children’s peril. I envy the certainty you feel in your theories and that you are comfortable with the meddling. I would prefer not to bet the long shot. Another thing history teaches is that humankind, as a general rule, does not respond to overwhelming issues until they become crucial, so I suppose we are under standard operating procedures.

        Thank you for your responses. I will retire from this discussion.

  6. How many people believe something is not evidence of its truth. However, it is not evidence of its falsehood either. Someday scientists will likely laugh at most of what we believe today, but that does not excuse our ignoring the best evidence available to us.

    The relevant question is whether we ought to change our behavior in a significant way. Logic and observation, along with a basic understanding of physics and chemistry, are what we have to work with. Using fossil fuels releases energy that has been stored for a long time. This creates heat. We do not need to look for “greenhouse gas” theories, etc, just the experience of touching a car engine that has been running a while, or seeing the steam and smoke coming from a power plant, to know heat is created and that warms our environment a little bit. It is logical that a lot of car engines burning fossil fuels add up to heat the environment a little bit. Since the whole “climate change debate” started, people have been arguing about just a few degrees or fractions of a degree of average temperature, which is apparently enough warming (or cooling) to drastically change our daily surroundings.

    So, whether or not one believes in greenhouse gases, it is foolish to say that human activity is not warming the atmosphere. Mr. Duhamel’s argument seems to be that (1) over geologic time, earth is cooling, and (2) fluctuations occur in cycles due to planetary distance and alignment with the sun. This is true because (1) the heat inside Earth’s core is stored heat from earth’s birth, is radiated gradually and is not regenerated and (2) basic heat transfer laws say the distance and angle to the sun dictate how fast heat is transferred from the sun to Earth. HOWEVER, it is completely IRRELEVANT to the question of whether human activity is having a net warming effect in the shorter (tens or hundreds of years) term, which is the relevant question from a policy standpoint.

    We cannot get rid of the basic truth that burning fossil fuel releases stored chemical bond energy into the atmosphere as heat. And while that may be “a drop in the bucket,” those drops add up, and the metaphorical bucket does not need to change very much to cause dramatic changes in local and global weather patterns.

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