Anyone who has ever pointed out that a scientific consensus exists on a certain matter has probably been meet with laughter and derision. The word consensus has practically become a punchline. It is reminiscent of the famous corollary to Godwin’s Law which states that the first person to mention Nazis has automatically lost the argument; so it frequently goes with the first person to mention consensus. So many highly visible personalities deny and deride scientific consensus that the term has, in popular usage, become synonymous with a fatally weak argument.
A common criticism I hear of scientific consensus is “science should not be decided by a vote”. I agree. People making this argument are probably genuinely unaware that science-specific use of the word consensus differs from its common use. Of course, the scientific community does not ever gather in a secret conference and vote on the official scientific dogma of the day. That would make a cool 1984-style cautionary sci-fi story, but it doesn’t happen in real life. (Who would pay for all those flights, hotel rooms, and bar tabs?)
The way the word use differs is that in common use, a consensus merely means the general agreement of the majority. We all have a consensus that killing people is bad. Non-scientists also have a consensus on certain matters of science: gravity makes a ball drop, the Earth is globe shaped, sunburns are harmful. But for a scientific consensus to exist, it must be based on more than just personal opinions and observations of the majority; it must be based on results.
I found a dramatic example of this when I did my Skeptoid episode on left handedness. I found that the majority of research shows that left handers have shorter life expectancy. Now there are a lot of ways that the data can be analyzed, and a lot of possible explanations for this; and quite a few researchers disagree with that finding. However, I found that the scientific consensus shows left handers do indeed have shorter life expectancy. Not everyone agrees, but a clear majority do. This is based on the conclusions reached by many, many researchers over many, many studies. This consensus excludes Joe Blow like you and I, who have not done any such research. Ideally, it also excludes psychologists who may have strong opinions, but who have not performed or analyzed the research. Even though handedness is an active field of study that includes dissenting viewpoints, we currently have a scientific consensus that left handers have shorter life expectancy.
The obvious application of consensus in today’s political climate is global warming. A scientific consensus exists that shows anthropogenic global warming is a reality. This consensus is far stronger than the one I found pertaining to lefties; it is, in fact, virtually unanimous among professional climate researchers. But quite obviously, there is no common consensus about global warming. If we took a vote among the public, we’d essentially get a near-50/50 division along political party lines. This does not constitute a general agreement among a clear majority. However, the more we focused our study group toward people in scientific fields, the closer the common consensus would morph toward the scientific consensus. The scientific community at large would show a trend toward AGW as a reality, but it would include many dissenting voices, and could not really be called a scientific consensus. If we focus our group further to exclude scientists from non-climate fields, the scientific consensus would strengthen. Finally, if we limit our group to only those professional researchers with advanced degrees in climate science who actively work, publish, and review work specific to global climate, we find that the consensus is (very nearly) unanimous.*
So, simultaneously, there is no consensus on AGW, and there is strong consensus on AGW. It depends on whether you’re using the scientific meaning of the word consensus or not. Scientific consensus does not equate to a vote of the majority. It more closely represents the majority of the current published research.
Consensus does, of course, change as knowledge improves. It must change, or it is useless. Its whole value is that it represents the current state of our knowledge, to the best of our ability to determine it. When the fringe research turns out to be true, the results are repeated by others in the field and the consensus changes to represent it. Cold fusion failed to persuade other researchers who failed to replicate the results; and consensus did not change. The idea that HIV does not cause AIDS has also failed to move the consensus. However, scientific consensus does still actively change. It has recently changed to reflect that a type of bacteria, not stress or diet, is the cause of peptic ulcers; and even the Standard Model has had to have been updated recently to show that neutrinos have mass. Scientific consensus is an extraordinarily powerful tool.
By all rights, it should be the case that the first person to reveal the scientific consensus should win the argument. Because, really, whatever the current consensus is, is the first and last word on a scientific question for us people on the street — until the researchers working hard at changing it manage to do so.
* – The question of whether these authors and researchers are all paid stooges participating in a global conspiracy is an unrelated question. To change the scientific consensus, the brave patriots who turn down the Big Warming paychecks need to get publishing!