How the Conventional Wisdom Can be Like a Pile of Oranges.
A cascade is like a chain reaction that starts one place creating havoc all over, along the lines of a row of dominos. Another analogy is a pile of oranges on a table. Remove one orange from the bottom of the pile on the left side and it starts an avalanche of oranges to the left. Do the same on the right and get an avalanche on the right. The same sort of thing can happen with public opinion.
The old saw says two heads are better than one. Meaning people improve their judgment by putting their heads together, and sometimes they do. For instance, at the game show "Who Wants to Be a Millionaire" the studio audience usually votes for the right answer. This is a consensus judgement.
What if, instead of voting silently in unison without consulting anyone else, the audience voted out loud one after another. Now suppose the first person gets it wrong. If the second person isn't sure, they're liable to agree with the first person's guess. Then, even if the third person suspects a different answer is correct, they're liable to go along assuming the first two together know more than they do. This starts an "informational cascade" as one person after another assumes the rest can't all be wrong.
Like the pile of oranges spilling left or right, the consensus can be lead one way or another depending on what answers are given first. Once it begins it's hard to reverse the avalanche or get it to change directions. In this way a wrong answer can build momentum among the group and become an established majority, consensus answer.
Furthermore, just as in politics, it's harder to get someone to switch parties than to get an undecided voter to go one way or the other. Thus we can create a widely believed "fact" that is not true, as well as very hard to correct in the public imagination. Additionally, because it is widely believed leads many to assume it must be true. This is a logical fallacy, namely...
Appeal to numbers (argumentum ad numerum) or majority, or popular belief: asserting that the acceptance of an idea by a majority, or by a large number of people, is reason to believe it. But as somebody-or-other once said, "If a thousand people believe a foolish thing, it is still a foolish thing."
This happens in many areas of knowledge, including science. Consensus should be anathema to science which is supposed to establish truth based on evidence. But scientists are people and subject to bias and human psychology same as anyone else.
Really there is no such thing as consensus science. As Michael Chrichton said, "If it's consensus, it isn't science. If it's science, it isn't consensus." Besides, the track record of scientific consensus is hardly inspiring. Here's one case.
In centuries past, the greatest killer of women was fever following childbirth. In 1795, Alexander Gordon suggested that the fevers were infectious processes, and curable. The consensus said no. In 1843, Oliver Wendell Holmes presented compelling evidence puerperal fever was contagious. The consensus said no. In 1849, Semmelweiss demonstrated that sanitary techniques virtually eliminated puerperal fever in hospitals under his management. The consensus said no.
There was no wide agreement on puerperal fever until the start of the twentieth century. It took over a century to arrive at the right conclusion despite the efforts of the prominent "skeptics" around the world, skeptics who were ignored and often demeaned. The truth didn't change when the consensus changed, it was true all along. When they followed the evidence they found the consensus was wrong.
This does not mean the consensus is necessarily right or wrong, but in science, as in anything concerning objective truth, consensus is irrelevant. As Einstien said when presented with an open letter signed by German scientists in the 1930s denouncing his theories as Jewish and false, "They didn't need a thousand signatures to disprove my theories, only a single fact."
Now, I am not going to enter into the contentious debate about manmade global warming, but you should remember this: If someone mentions the scientific consensus as any type of supporting evidence, it is not scientific or even logical. Furthermore, this consensus might not have come about by examining the evidence, but was an informational cascade resulting from the strongly held opinions of the first people they listened to. And the constant repetition of the hypothesis in the media leading to another form of logical fallacy...
Argumentum ad nauseam: an assertion is considered more likely to be true the more often it is stated.
But of course, something untrue is just as false the 1,000th time it's reported as the first time. Despite how many times you may have run across science factoids, they aren't true. And still won't be when you stumble upon them again.