“In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual.” – Galileo Galilei
Recently, I've seen the phrase "scientific consensus" popping up in common discourse more often. For example, here's a recent Google blog post announcing that they are no longer going to allow digital ads bought on its platform to appear next to content that denies climate change.
[W]e’re announcing a new monetization policy for Google advertisers, publishers and YouTube creators that will prohibit ads for, and monetization of, content that contradicts well-established scientific consensus around the existence and causes of climate change. This includes content referring to climate change as a hoax or a scam, claims denying that long-term trends show the global climate is warming, and claims denying that greenhouse gas emissions or human activity contribute to climate change. – 'Updating our ads and monetization policies on climate change'
Maybe scientific consensus is true. Maybe it's not. That's the point. Science is a process of bettering our understanding of the natural world around us. We use tools to help develop a model which then gives us the ability to make falsifiable predictions. If the predictions hold, that's more evidence that the theory has purchase on the real world. If the predictions do not hold, then there's probably some tweak that needs to happen to your model.
The notion of scientific consensus is facially silly since the process of science (in contradistinction to "The Science") depends on individuals staking their reputation on things that most believe to be false.
Consider the canonical case of Galileo. I often wonder how Galileo would have been perceived if he was proposing the Heliocentric model in an age that had social networking as well as similarly incentivized media ecosystem as the one we have today.
My guess is that we'd be treated to an article which highlighted how he broke with the scientific consensus of the time:
(Florence, Italy) 1633 – Earlier this week Galileo Galilei was sentenced to house arrest for dissemination of false information related to the inner workings of the cosmos. Contra scientific consensus about the geocentric nature of the universe, Galilei proposed that the universe was instead heliocentric and orbited around the sun. We spoke to several experts in the field of astronomy all of whom denounced this theory as unfounded, and simply false. Said Enzo Boticelli, a professor of cosmology at the University of Bologna, "The Ptolemaic geocentric model has been a bedrock of our understanding of the universe since its introduction back in the 2nd century. Galilei's suggestion runs counter to what is taught in universities across the continent and to general scientific consensus."
A few years back, the author Michael Crichton gave an excellent talk at Caltech which touched on the idea of scientific consensus and how that relates to scientific understanding.
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.
In other words, scientific understanding is an epistemological approach which serves to develop best guesses (hypotheses) about how things work and rigorously test those hypotheses through predictions. That there is consensus on a topic is in no way dispositive. In fact, as Crichton points out, it's more of a political designation (e.g. plurality of scientists, majority of scientists, vast majority of scientists...).
So when someone uses the phrase "well established scientific consensus" that should be an immediate tell that they are operating in the political – rather than the scientific – realm. Tread carefully and hold onto your wallet!