“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 20^th 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.”