“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.” — Michael Crichton
September 20th, 2019, was the beginning of a week-long global climate strike. Millions of people around the world marched in support of policy action on climate change, even in Indiana University’s own quaint college town. The message from contemporary climate scientists and activists: the time for debate is over, the time for action is now. Critical to their argument is that
the issue of climate change has reached scientific consensus, or wide-spread
agreement among scientists.
Scientific consensus is frequently employed to defend the truth of one claim or another. For instance, the often quoted statistic that 97 percent of climate scientists believe in human-caused climate change is intended to persuade people to believe in climate change. In fact, uncertainty over the precise percentage of consensus has led to a proliferation of papers on the climate change consensus, culminating in the magisterial Consensus on Consensus.
But why should it work like this? Why should we accept something just because a bunch of people agree on it?
Jurassic Park author Michael Crichton, quoted above — despite being a science fiction writer rather than a practicing scientist — paints a common and appealingly hardboiled picture of science: just the facts, ma’am. And there does seem to be something right about it. We want to accept our claims based on evidence, not mere agreement. In fact, there’s a named fallacy, argumentum ad populum, just to identify the logical error of arguing that because a lot of people believe something it must be true. However, Crichton’s perspective ultimately misunderstands science, misunderstands history, and misunderstands scientific consensus.
Scientific facts don’t simply enter the room like the Kool-Aid Man. Instead, scientists have to slowly coax facts out of the world. They must constantly refine their measurements and instruments, scour for alternate explanations, identify and rectify sources of error, and control for confounding variables. (The complex constitution of facts has been discussed previously on this blog). Claims that survive this gauntlet of inquiry then form the foundation for further claims. And this is yet another kind of test, just the way building a second story serves as a (very extreme) test of the foundations of a house.
Many claims — evolution, the safety of eating GMOs, human caused global warming — that are controversial in public discourse…or at least in congress…are in fact at this foundational level. Scientists have long since stopped debating about those claims as such, and are now building upon them.
This is the crucial point. Scientific consensus ultimately isn’t about mere agreement, or “taking someone’s word” for something. Scientific consensus is evidence. Scientific consensus is evidence that a claim has gone through the rigorous process to get to where it is widely agreed upon among scientists. Implicit in scientific consensus is that a claim has survived replication, and been verified by reference to the real world in accordance with the best practices of the community of scientists.
Crichton is correct that we often endow our scientific heroes with a certain rebelliousness, but that’s more a product of myth than of actual history. Newton famously said, “I have seen further only by standing on the shoulders of giants.” These are hardly the words of a maverick.
And while we credit Copernicus with discovering that the sun was the center of the solar system, he himself was tentative about the claim and, at that time, only a romantic would have accepted it at face value. There was no explanation for how humans stayed on a ball floating in space, nor for how the Earth could move around without causing excessive winds, nor for how a huge chunk of rock was flying around in the first place. Moreover, a key observation that would have helped confirm his theory — stellar parallax1 — was looked for and unable to be found.
It is not that dissenters are never right, but it is a poor bet in the face of the considerable evidence provided by scientific consensus. If we look across the history of science from our present moment, the dissenters that stand out are those rare few who disagreed with something major and were vindicated. We do not even remember those innumerable others who said something controversial only to have it ground to dust by the wheels of science.
 Stellar parallax refers to the apparent shift in position of a star with respect to the background sky caused by viewing it from different positions in Earth’s orbit. Turns out the instruments weren’t sensitive enough at this point in time to detect it.