Scientific Consensus Stronger than Scientists Thought?

An innovative sampling of a small group of climate scientists’ perspectives suggests their views may be more commonly shared among their science colleagues than they had thought.

More than two decades after the Intergovernmental Panel on Climate Change (IPCC) began publishing the latest scientific consensus on the globe’s changing climate, widespread doubts persist in the U.S. over whether there really is widespread agreement among scientists. It’s the primary argument of those who deny basic scientific foundations of warming.

But new and innovative survey results suggest the consensus among scientists might actually be stronger than the scientists themselves had thought.

The battles to define and debunk scientific consensus over climate change science have been fought for years. In 2004, University of California San Diego science historian Naomi Oreskes wrote about a broad consensus she found after studying 928 scientific papers published between 1993 and 2003.

Meanwhile, the blow-up over climate researchers’ hacked e-mails in 2009 fueled speculation among skeptics that “consensus” actually is the closely guarded creation of a small cabal of scientists determined to silence opposing views, accusations now widely dismissed as unsubstantiated. That perspective has been largely debunked, but the beat goes on.

On the heels of a January 26 skeptics letter (“No Need to Panic About Global Warming“) in The Wall Street Journal, there have been several follow-up commentaries. They include a vigorous rebuttal on March 22 in the New York Review of Books by Yale University economist William D. Nordhaus; a follow-up response in the April 26 edition of same journal by climate change skeptics Roger W. Cohen, William Happer and Richard Lindzen; and a second response by Nordhaus.

Now, from Carnegie Mellon University and the University of Minnesota Institute on the Environment, comes a fresh study on the question of scientific consensus. Its findings offer something new: scientists appear actually to underestimate the extent to which they, as a group, agree on key questions related to climate change science.

In sum, the newly released poll results identified surprisingly common points of agreement among climate scientists; and yet for each point, those scientists underestimated the amount of agreement among their colleagues. The results:

  • Human activity has been the primary cause of increases in global average air and ocean temperatures in the last 250 years. (About 90 percent of respondents agreed with this characterization, but those respondents estimated that less than 80 percent of their scientist colleagues held that view.)
  • If governmental policies do not change, the CO2 concentration in the atmosphere will exceed 550 parts per million between 2050 and 2059. (More than 30 percent agreed, but those respondents estimated that just over 20 percent of their peers held that view.)
  • If and when atmospheric CO2 concentrations reach 550 ppm, the increase in global average surface temperature relative to the year 2000 will be 2-3 degrees Celsius, or 3.2-4.8 F. (More than 40 percent agreed, but those respondents estimated that less than 30 percent held that view.)
  • If governmental policies do not change, in the year 2050, the increase in global average surface temperature relative to the year 2000 will be 1.5-2 degrees Celsius, or 2.4-3.2 F). (More than 35 percent agreed, but those respondents estimated that just over 30 percent held that view.)
  • The likelihood that global average sea level will rise more during this century than the highest level given in the 2007 assessment of the IPCC (0.59 meters, 23.2 inches) is more than 90 percent. (More than 30 percent agreed, but those respondents estimated that less than 20 percent held that view.)
  • Since 1851, the U.S. has experienced an average of six major hurricane landfalls (> 111 mph) per decade. The total number of major hurricane landfalls in the U.S. from 2011-2020 will be seven to eight. (Nearly 60 percent agreed, but those respondents estimated that just over 30 percent held that view.)
  • The total number of major hurricane landfalls in the U.S. from 2041 to 2050 will be seven to eight. (About 35 percent agreed, but those respondents estimated that less than 30 percent held that view.)
  • Given increasing levels of human activity, the concentration of CO2 in the atmosphere can be kept below 550 ppm with current technology — but only with changes in government policy. (Nearly 70 percent agreed, but those respondents estimated that just over 50 percent held that view.)

Vision Prize:  What Do You Think Your Colleagues Think?

The specialized poll of scientists earlier this year is a project involving research director Peter Kriss, a doctoral candidate in the Department of Social and Decision Sciences at Carnegie Mellon in Pittsburgh. The poll concluded on March 31.

Dubbed the “Vision Prize,” the method of questioning is designed to poll experts on a range of scientific topics relevant to decisionmakers and financial markets. It asks scientists about their own views on a range of subjects, and asks them to also predict the views of their colleagues on those same subjects.

The poll was publicized on the listserves of various climate research centers, on the Real Climate blog, and by word of mouth — and 172 scientists participated, said Kriss. More than three-quarters of the participants identified themselves as working in academia, with the remainder working in industry, government and non-governmental organizations. Nearly half of all participants in the poll were academicians working in the earth sciences.

Questions for the poll were developed after consulting the IPCC Summary for Policymakers and various climate change blogs, Kriss said. An exchange between Kriss and Real Climate contributor Eric Steig on how to frame one of the questions led to the re-wording of the question on sea level rise, for example (see post #10 on January 23).

It is evident that some participants on the Real Climate blog had problems with various aspects of the poll — mostly with wording of the questions. Those can be found in the comment section of the January 22 announcement of the poll.

The Vision Prize poll used a new polling method designed to elicit carefully considered answers, particularly in regard to the views of others. MIT psychologist Drazen Prelec in 2004 described the polling method in the journal Science.

The method, as described in Science, assigns high scores not to the most common answers but to the answers that are more common than collectively predicted by the group. The scoring adjustment is designed to remove all bias favoring consensus.

A 2004 story on the polling method in New Scientist, titled “Mathematical ‘truth serum’ promotes honesty,” explained that the method encourages truthful responses by asking people questions in pairs.

The first question, suggests the New Scientist story, might be something like, “Will you vote in the next presidential election?” or “Have you had more than 20 sexual partners in the last year?” Then, the second question asks the respondent to estimate how many other respondents would answer similarly.

“It is this perception of what other people’s answer might be which gives hints as to whether the person is telling the truth — especially when their answer is the unusual or unpopular option,” according to the New Scientist story.

“Prelec says if people truly hold a particular opinion, they tend to give higher estimates that other people share it,” the story continued. “So if someone did have more than 20 recent sexual partners — but lied about it — that person would probably assume a higher rate of such behavior in general than someone who had not had so many partners.”

Scientists Predisposed to Assume Disagreements?

While the poll revealed consensus among scientists on key questions related to climate science, the question remains: Why do they believe — incorrectly — that consensus on those questions is lacking?

“It’s not just that they’re inaccurate,” Kriss said of the respondents’ assumption that there is not broader agreement on climate science. “They’re systematically underestimating the extent to which they agree. That’s the part that I found most surprising.”

Research going back decades shows that people generally overestimate the extent to which people agree with them. So, what’s going on with climate scientists?

The poll didn’t address that question, Kriss said. But he speculated that scientists may simply expect their views to be challenged. After all, science advances through vigorous questioning and debate. Perhaps that ingrained view shapes scientists’ assumptions about how much their colleagues agree — or more to the point, don’t agree — with them.

Kriss said he wanted to examine the views of scientists on climate change not only to test the polling method developed by Prelec, but also to inform a major policy topic.

“Our biggest concern is that people may underestimate the amount of agreement among climate experts … and we think that may hinder effective decisionmaking — that if people perceive disagreement, that would be a reason to not act,” Kriss said. “If that perception is inaccurate, it would be nice to correct it.”

As an academic studying behavioral science, Kriss added that the climate issue is an interesting case study of how groups form collective opinions and act or don’t act based on those views. Research shows that it’s a challenge for people to work together toward better outcomes, and Kriss said he hopes to help organizations improve decisionmaking.

“In some sense, it’s the mother of all collective action problems,” Kriss said of the climate challenge. “There’s uncertainty, there’s a long time scale, and there are all sorts of factors that make resolving it difficult. This seems like the biggest real world problem where I thought I could make some contribution.”

Bruce Lieberman

Bruce Lieberman is a freelance writer covering science and environmental topics. He has more than 20 years experience in the news business. (E-mail:, Twitter: @brucelieberman1)
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19 Responses to Scientific Consensus Stronger than Scientists Thought?

  1. Bruce says:

    Vision Prize polled a paltry 170 people for this exercise, all of whom had chosen to OPT IN to the poll. Is it any wonder it arrived at a consensus! Vision Prize even admits, its poll will be, “biased towards those with interest and expertise in the topic of the survey.” Since many of those who volunteered are university academics whose careers are funded by the CAGW gravy train, it’s no great surprise that they should engage in an exercise in group think, is it?

    As for Oreskes’s 2004 study, the necessary criteria for being part of the consensus were so non-controversial that a “denier” such as myself would have no problem with being part of it. In essence, I would be agreeing that mankind had altered the composition of the atmosphere and that we were responsible for about 0.2C warming over the previous 50 years. I don’t know of any sceptics – or “deniers” if you must – who would dispute those two points.

    It would be nice if an august body like Yale would at least take the time to accurately represent the views of sceptics. Overwhelmingly, we accept CO2 is a greenhouse gas, that it will cause some warming, that it has already caused warming and that human emissions have contributed to this warming. The only bone of contention is the feedbacks which alarmists – or premature cli-maxers as I like to think of them – believe will be positive but which empirical evidence suggests so far will be neutral or negative.

    I don’t rule out the possibility of positive feedbacks : I just haven’t seen any convincing evidence for them.

    • John says:

      I, for one, would very much like to see the “empirical evidence [that] suggests…neutral or negative” climate impacts from peer-reviewed literature.

      • GoodBusiness says:

        Peer review was blocked for decades as the base data research used to create the many computer model systems – the oldest computer saying was reaffirmed – GARBAGE – IN – GARBAGE – OUT!

        Tainted science is like tainted food it should make you very ill.

      • Bruce says:

        Here’s a couple, John.

        There are now quite a lot of peer reviewed papers suggesting negative feedbacks. I don’t think anyone is able to say yet whether the overall net impact of feedbacks will be positive or negative but I certainly haven’t seen anything that suggests to me that we will have the strong positive feedbacks that would be necessary for warming to enter a dangerous phase.

        • John says:

          Thanks, Bruce. I had a look, and not being a climate specialist, I could only follow the arguments in a general sense. The first paper, however, seems to say that clouds are important, but there is no smoking gun. Lindzen is about the only one promoting the tropical escape hatch, but his work has been severly criticized. I don’t regard his analysis as empirical evidence as much as a hypothetical mechanism in need of verification.

          • Bruce says:

            Thanks for looking John. There are lots of other papers but I don’t keep a file and you can find them easily enough if you want.

    • Richard N says:

      Even this poll in which the sample of scientists have picked themselves is certainly statistically flawed. But what the hell , I can see it being quoted as gospel truth by alarmists for the next few years. Seems everything is in place to continue the big scare , except for that darn lack of significant warming since 1998. More fudgeing of the figures is definitely required there to produce at least some warming. Back to the old computer boys.

      • John says:

        Why 1998? Why not 1996 or 2000? 1998 was an El Nino year; the high average temperature that year was a shorter-term atmosphere-ocean interaction. The global temperature trend is still upward.

    • Joseph Famme says:

      Agree. When in the 13.73 B year history of the Universe, or 3.8B year history of planet Earth have average temperatures and sea levels been more stable than they are now? See NASA article, “Earth’s Fidgeting Climate”, Earth temps routinely swing for a high average / mode of 72F with dips to 54F, where Earth avg temp is now! Earth’s MODE temp over the past 600M years has been 72F, as it was when the dinos roamed, some 16 degrees F below the / mode temp. Yes, Virginia, Earth’s temps will naturally increase back to the mode 72F even if all humans were eliminated. Earth has made this cycle on its own several times without human help. Yale reports that 500M years ago CO2 levels were 7000 PPM, and during dino period CO2 averaged 1200 to 2000 PPM, and to today CO2 level is 390 PPM. Yale graph shows zero correlation between temperature and CO2 levels over 500M Years! Commercial hot houses regularly elevate CO2 levels to 1000 PPM to double plant growth rate and save water, CO2 being the life building block that it is. This why plants survive in the desert! People who take $$ from the gov for “research” ought to stop lying to us … but then they are incompetent to compete in competitive business. Sea Levels ALWAYS RISE in interglacial periods and Earth is in the middle of an IGP now! etc. But the so-called climate scientists know all of this, … but they have to make up stories to keep their paychecks … how sad!!!

  2. Martin Lack says:

    These questions seem remarkably optimistic (i.e. not realistic) but, I guess the organisers of the research wanted to maximise the potential to get broad agreement.

    Is James Hansen really that isolated? I think not. On the contrary, I think he is just about the only one who dares to be honest. In his 2012 TED Talk he made 10 key points, which I have documented on my blog:

    • Bruce says:

      Why would the organisers want to maximise the potential for “broad agreement”, Martin? You seen to be suggesting they asked the questions guaranteed to get the outcome they sought. Heaven forbid!

  3. Mike Bromley says:

    What a shamefully embarrassing exercise for science. Propping up a sagging consensus with a sagging consensus. Do they really think that this will solve their problem? Let’s begin with a slippery slope and grease it with some meaty logical fallacies. As for Hansen daring to be honest, watch the contempt on his face in any videos where he speaks about climate change.

    • Hansen dares to be honestly contemptuous of differing opinions.

      He talks about coal transported by rail as “death trains.”

      He is honest – honestly unhinged…

  4. Peter Kriss says:

    We agree that nonprobability sampled “opt-in” polls like Vision Prize have shortcomings, which we considered when formulating our design. In particular, as Bruce points out, we expect our sample to be biased towards those with interest and expertise in the topic of the survey. For the case of polling expert opinion, however, our view is that our opt-in approach — with screening for relevant expertise — offers a reasonable way forward, especially in a field like climate science where the population of interest transcends multiple domains and affiliations.

    A consequence of this approach is that we are unable at this point to draw conclusions such as “90% of climate scientists believe that human activity has been a primary cause of changes in air and ocean temperatures in the last 250 years.” However, we believe that our self-referential “surprisingly common” metric is less susceptible to the shortcomings of nonprobability sampling. Provided the population of participants is known to the participants themselves (which is a focus of the site), we believe that finding which answers are more common than expected can provide meaningful insight. Another important advantage of our “surprisingly common” approach is that there is no bias against atypical views. It does not give any special weight to the majority (or plurality) opinion.

    As for the questions themselves, we welcome suggestions for questions to ask in the next round of the poll:

    • He he he… 250 years? Seriously? Why not go full-on insane and make humans responsible for the entire Holocene! I mean, if these believers are crazy enough to believe 250 years, then it shouldn’t be too much effort to see how deep their crazy goes…

      Air AND ocean AND the sun AND… God complex much?

  5. Mariss says:

    I think there is a typo in the article. Shouldn’t it be 172% of 90 self-selecting activist-scientists agree man-made global warming is real? The math would then be consistent with the soundness of the science behind anthropomorphic global warming.

  6. Nullius in Verba says:

    With a sample size of 171 and assuming independence, I think the 2-sigma error is on the order of plus or minus 7%. Numbers would have to be more than 10% apart to constitute a significant difference.

    Previous surveys (e.g. Von Storch and Bray) have come out with 85% thinking more than half the 20th century change being anthropogenic, so both 80% and 90% are within the bounds of uncertainty.

    And as others have noted, if you recruit all your experts from the readers of RealClimate and their friends, it’s not a uniform sample of the entire population.

    Incidentally, the statement being tested is not all that far from the position many sceptics would take, too. Most sceptics agree that some warming effect is to be expected, and most think that the observed 20th century rise is below the predictions. If doubling CO2 contributes a 1 C rise, then increasing it 40% would contribute a 0.5 C rise. As CO2 has risen 40% over the 20th century, and temperature has risen around 0.6-0.8 C, would it really be so inconsistent for a sceptic to think more than half of it was due to CO2?

    The issue is whether the future changes will be catastrophic, and whether the models have enough fidelity in detail to reliably predict them. Those are the elements for which a consensus has been claimed to advocate political action, and which need to be tested.

    It would also be nice to ask scientists why they believe, and how confident they are. Is it because they’ve checked the results personally, or because they trust their colleagues and the journal peer-reviewers to have got it right?

    But it’s very good that people are trying to quantify what scientists’ actual views are. I hope to see more of this sort of work.

  7. ramjetrth says:

    I have no opinion on whether there is global warming or cooling. What I do have an opinion about is the faulty logic being used. There seems to be a mistaken impression that consensus of opinion constitutes proof. What constitutes proof is a preponderance of evidence and that is what’s lacking. The models used to prove global warming have so far not shown predictive capability and the information used to construct and support the models appears to be unavailable for the most part to those with dissenting opinions. Until the models and the data have been widely disseminated, appropriately reviewed, and the constructed models show they can be used to predict and not just explain past historical weather patterns global warming is not a science, it is speculation.