Last week, the prestigious journal, the Proceedings of the National Academy of Sciences, published an article that tried to assess the relative credibility of climate scientists who "support the tenets of anthropogenic climate change" versus those who do not. One goal of the study is to "provide an independent assessment of level of scientific consensus concerning anthropogenic climate change." The researchers found that 97–98 percent of the climate researchers most actively publishing in the field are convinced of man-made climate change. In addition, using publication and citation data, the study found that the few climate change dissenters are far less scientifically prominent than convinced researchers. The article concludes, "This extensive analysis of the mainstream versus skeptical/contrarian researchers suggests a strong role for considering expert credibility in the relative weight of and attention to these groups of researchers in future discussions in media, policy, and public forums regarding anthropogenic climate change." Translation: reporters, politicians, and citizens should stop listening to climate change skeptics.

Naturally, there has been some pushback against the article. For example, Georgia Institute of Technology climatologist Judith Curry who was not pigeonholed in the study told ScienceInsider, "This is a completely unconvincing analysis." One of the chief objections to the findings is that peer review is stacked in favor of the consensus view, locking skeptics out of publishing in major scientific journals. John Christy, a prominent climate change researcher at the University of Alabama in Huntsville who is skeptical of catastrophic claims, asserted that because of "the tight interdependency between funding, reviewers, popularity. … We [skeptical researchers] are being 'black?listed,' as best I can tell, by our colleagues."

This fight over credibility prompted me to wonder about the role that the concept of a "scientific consensus" has played out in earlier policy debates. We all surely want our decisions to be guided by the best possible information. Consider the overwhelming consensus among researchers that biotech crops are safe for humans and the environment—a conclusion that is rejected by the very environmentalist organizations that loudly insist on the policy relevance of the scientific consensus on global warming. But I digress.

Taking a lead from the PNAS researchers I decided to mine the "literature" on the history of uses of the phrase "scientific consensus." I restricted my research to Nexis searches of major world publications, figuring that's where mainstream views would be best represented. So how has the phrase "scientific consensus" been used in past policy debates?

My Nexis search found that 36 articles using that phrase appeared in major world publications prior to my arbitrary June 1985 search cutoff. One of the first instances of the uses of the phrase appears in the July 1, 1979 issue of The Washington Post on the safety of the artificial sweetener saccharin. "The real issue raised by saccharin is not whether it causes cancer (there is now a broad scientific consensus that it does)" (parenthetical in original) reported the Post. The sweetener was listed in 1981 in the U.S. National Toxicology Program's Report on Carcinogens as a substance reasonably anticipated to be a human carcinogen. Interesting. Thirty years later, the National Cancer Institute reports that "there is no clear evidence that saccharin causes cancer in humans." In light of this new scientific consensus, the sweetener was delisted as a probable carcinogen in 2000.

Similarly, the Post reported later that same year (October 6, 1979) a "profound shift" in the prevailing scientific consensus about the causes of cancer. According to the Post, researchers in the 1960s believed that most cancers were caused by viruses, but now diet was considered the far more important factor. One of the more important findings was that increased dietary fiber appeared to reduce significantly the incidence of colon cancer. Twenty years later, a major prospective study of nearly 90,000 women reported, "No significant association between fiber intake and the risk of colorectal adenoma was found." In 2005, another big study confirmed that "high dietary fiber intake was not associated with a reduced risk of colorectal cancer." While dietary fiber may not prevent colon cancer, it is associated with lower cardiovascular risk.

In its June 1, 1984 issue, The Washington Post reported the issuance of a massive new report by the White House science office supporting the scientific consensus that "agents found to cause cancer in animals should be considered 'suspect human carcinogens,'" and that "giving animals high doses of an agent is a proper way to test its carcinogenicity." Although such studies remain a regulatory benchmark, at least some researchers question the usefulness of such tests today.

The December 17, 1979 issue of Newsweek reported that the Department of Energy was boosting research spending on fusion energy reactors based on a scientific consensus that the break-even point—that a fusion reactor would produce more energy than it consumes—could be passed within five years. That hasn't happened yet and the latest effort to spark a fusion energy revolution, the International Thermonuclear Experimental Reactor, will not be ready for full-scale testing until 2026.

An article in the June 8, 1981 issue of The Washington Post cited a spokesman for the American Medical Association opposing proposed federal legislation that would make abortion murder as saying, "The legislation is founded on the idea that a scientific consensus exists that life begins at the time of conception. We will go up there to say that no such consensus exists." It still doesn't.

In the years prior to 1985, several publications reported the scientific consensus that acid rain emitted by coal-fired electricity generation plants belching sulfur dioxide was destroying vast swathes of forests and lakes in the eastern United States. For example, the March 10, 1985 New York Times cited environmental lawyer Richard Ottinger, who asserted that there is a "broad scientific consensus" that acid rain is destroying lakes and forests and "is a threat to our health." In 1991, after 10 years and $500 million, the National Acid Precipitation Assessment Program study (as far as I can tell that report is oddly missing from the web) actually reported, according to a 1992 article in Reason: "The assessment concluded that acid rain was not damaging forests, did not hurt crops, and caused no measurable health problems. The report also concluded that acid rain helped acidify only a fraction of Northeastern lakes and that the number of acid lakes had not increased since 1980." Nevertheless, Congress passed the 1990 Clean Air Act Amendments that regulate sulfur dioxide emissions through a cap-and-trade scheme. Acid rain was clearly causing some problems, but was not the wide-scale environmental disaster that had been feared.

Interestingly, the only mention of a scientific consensus with regard to stratospheric ozone depletion by ubiquitous chlorofluorocarbon (CFCs) refrigerants was an article in the October 6, 1982 issue of the industry journal Chemical Week. That article noted that the National Research Council had just issued a report that had cut estimates of ozone depletion in half from a 1979 NRC report. The 1982 NRC report noted, "Current scientific understanding…indicates that if the production of two CFCs …were to continue into the future at the rate prevalent in 1977 the steady state reduction in total global ozone…could be between 5 and 9 percent." Such a reduction might have been marginally harmful, but not catastrophic. It was not until 1986 that the mainstream press reported the discovery of the "ozone hole" over Antarctica. This discovery quickly led to the adoption of an international treaty aiming to drastically reduce the global production of CFCs in 1987. (For what it is worth, I supported the international ban of CFCs in my 1993 book Eco-Scam.)

With regard to anthropogenic climate change, my Nexis search of major world publications finds before 1985 just a single 1981 New York Times article. "There has been a growing scientific consensus that the buildup of carbon dioxide in the atmosphere is creating a 'greenhouse effect' by trapping some of the earth's heat and warming the atmosphere," reported the Times in its January 14, 1981 issue.

What a difference the passage of 25 years makes. My Nexis search turned up 457 articles in major publications that in the last year cited or used the phrase "scientific consensus." Checking to see how many combined that phrase with "climate change," Nexis reported that the number comes to 342 articles. Briefly scanning through a selection of the articles it is clear that some of them involved the controversy over whether or not there is a "scientific consensus" on climate change. The majority appear to cite various experts and policymakers asserting the existence of a scientific consensus that anthropogenic climate change is dangerous to humanity.

So what to make of this increase in the use of the concept of "scientific consensus?" After all, several scientific consensuses before 1985 turned out to be wrong or exaggerated, e.g., saccharin, dietary fiber, fusion reactors, stratospheric ozone depletion, and even arguably acid rain and high-dose animal testing for carcinogenicity. One reasonable response might be that anthropogenic climate change is different from the cited examples because much more research has been done. And yet. One should always keep in mind that a scientific consensus crucially determines and limits the questions researchers ask. And one should always worry about to what degree supporters of any given scientific consensus risk succumbing to confirmation bias. In any case, the credibility of scientific research is not ultimately determined by how many researchers agree with it or how often it is cited by like-minded colleagues, but whether or not it conforms to reality.

Ronald Bailey is Reason's science correspondent. His book Liberation Biology: The Scientific and Moral Case for the Biotech Revolution is now available from Prometheus Books.

Disclosure: For what it is worth I generally accept the current "consensus" that anthropogenic climate change could be a big problem. I do worry that what governments are likely to do about global warming may be worse than climate change.

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