What’s a scientific consensus?

It’s challenged by some and denied by others. But scientific consensus remains the collective rampart to counter disinformation and respond to skeptics and conspiracy theorists. Talk about it is in the air due to COVID-19 and the litany of opinions relayed through the media. Some deplore the absence of this consensus, while others invoke it to explain the situation. The Rumour Detector proposes to set the record straight.  
Consensus isn’t unanimity 

Scientists don’t work in a vacuum. They publish their research in peer-reviewed scientific journals. That means their work is read, commented on and sometimes refuted. Scientific consensuses are established from the cumulative scientific studies published on a given subject. When the majority points in one direction, a consensus is formed. That’s why, even if we can’t reach the absolute truth, scientific consensus is the best indicator of the truth we have

Because unanimity isn’t mandatory to proclaim a scientific consensus exists around an issue, what proportion of scientists must share the same opinion to merit the label? 

The controversy surrounding the human role in climate warming offered us a partial answer to this question. 

In 2004, Naomi Oreskes, a science historian at Harvard University, examined the publications of climate specialists published between 1993 and 2003 in 928 scientific journals. She concluded that 97% of the authors confirmed the impact of human activity on climate warming. By showing the magnitude of the consensus (97%) around this question, she affirmed the precedence of the results of the scientific community’s work over results from other sources (industry, various organizations). 

However, we should note that this 97% threshold was calculated only for climate research. 

Scientific experts 

The legitimacy of the people who take a position on the issue is also an indicator of scientific consensus. Thus, Naomi Oreskes, like others who subsequently engaged in a similar exercise, only retained the research done by climate experts for their compilations.  

“Scientists from the targeted field, recognized by their peers, must be presented. The media also have an important role to play, but they don’t always play it,” deplores Yves Gingras, historian, science sociologist and Scientific Director of UQAM’s Observatoire des sciences et des technologies.  

As evidence, there was the media visibility obtained a few years ago by French Minister Claude Allègre, presented as a CNRS scientist, who denied the very existence of climate warming. The hitch is that he’s a geologist, not a physicist or climatologist.  

Similarly, climate skeptics like to brandish “letters” signed by multiple scientists who deny climate warming. Every time, they include signatories who do not belong to the targeted field. Furthermore, an opinion letter will never have the same value as a series of studies.  

The consensuses on COVID-19 

There is consensuses around COVID-19: scientists all say that it is an adenovirus and that some of its properties have been duly identified. It has a specific shape, and it is contagious and lethal. That’s what science tells us today. But some questions currently remain unanswered. For example, how does this infection trigger so much damage in certain patients? What is the exact risk level in a poorly ventilated place compared to a well-ventilated location? What is the exact percentage of people without symptoms? How effective would an eventual vaccine be?  

“Human beings abhor a vacuum, so they want answers. And they find them, no matter what and no matter where,” Yves Gingras points out. That’s the origin of the demonstrations by certain anti-mask and anti-vaccination groups, and the proliferation of various conspiracy theories around the pandemic.  

That’s without counting those who reject science for ideological reasons and who brandish the fact that some scientists may have issued a hypothesis in the spring and then rejected it in the fall. “Yet it’s up to science to rerun experiments, measure in another way based on another model, with better performing tools and other approaches, and arrive at new results,” Yves Gingras reminds us. By betting on this scientific approach, other consensuses will form on COVID-19 in the months ahead. 

This article was originally published on the website of L'Agence Science-Presse (French only).


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