If you put some time into looking at various situations where a scientific "consensus" has developed, you will be stunned at how often the consensus has later proved to have been dead wrong. The phenomenon is particularly prevalent in fields involving complex and poorly understood systems. The human body is one such system. The climate is another.
Back in my law school days, one of my friends developed a case of severe and debilitating stomach ulcers. In those days (early 1970s) the "scientific consensus" was that ulcers were caused by some combination of stress and harsh and spicy foods. Of course my friend went to doctors, and of course their diagnosis was that stress was mainly to blame. Hey, what could be more stressful than the first year at law school? (This was actually the year that the book The Paper Chase came out.) Next thing you know the poor guy was told that he needed to take a year off from school and go on a diet of bland mush. After a hiatus he came back, but somehow the ulcers had not really improved.
Turned out that the whole idea of stress as a cause of ulcers was plain wrong. Experiments in the mid-80s by Barry Marshall and Robin Warren established the bacterium Helicobacter pylori as the principal cause. In 2005 Marshall and Warren won the Nobel Prize for medicine. Now most ulcers can be cured by a couple of weeks of antibiotics. But before their hypothesis was established, Marshall and Warren underwent a good deal of scorn and ridicule for bucking the "consensus." Here is a summary from Bahar Gholipur of Live Science, citing Dr. Arun Swaminath of Lenox Hill Hospital:
The discovery of H. pylori's role in ulcers led to the Nobel Prize in 2005 for Barry Marshall and Robin Warren, who were ridiculed when they suggested the idea, Swaminath said. It is a myth that peptic ulcers are caused by stress and spicy food.
Meanwhile, as the consensus persisted, people like my law school friend had to suffer for no reason.
Or how about the consensus that the way to reduce the risk of heart disease is the low fat diet. The geniuses in our government, based on consensus science, started recommending to reduce fat in the diet about 40 years ago. Today the campaign against dietary fat remains literally everywhere, and you can't go to the grocery store without getting bombarded with sales pitches for low fat products. The following line continued to appear as recently as the 2010 guidelines that were not superseded until early this year:
A strong body of evidence indicates that higher intake of most dietary saturated fatty acids is associated with higher levels of blood total cholesterol and low-density lipoprotein (LDL) cholesterol. Higher total and LDL cholesterol levels are risk factors for cardiovascular disease.
And what "evidence" was that exactly? I would say the whole thing was based on myth from the get-go, but it gets worse. This was/is one of those myths that was just so intuitively obvious and had such a strong consensus backing it that it became literally impossible to destroy. Study after study completely contradicted the hypothesis that dietary fat increased the risk of heart disease, but the consensus went on undisturbed for decades. To take just one of the largest and most definitive studies among many, in the 90s the government commissioned a gigantic randomized study of 50,000 women called the Women's Health Initiative Diet Modification Trial. After a full eight years of following the women, in 2006 the Harvard School of Public Health came out with a report summarizing the results:
The results . . . showed no benefits for a low-fat diet. Women assigned to this eating strategy did not appear to gain protection against breast cancer, colorectal cancer, or cardiovascular disease. And after eight years, their weights were generally the same as those of women following their usual diets.
But even that devastating conclusion couldn't kill off this one. Four years after that report -- and plenty of others with similar results -- the government reissued its dietary guidelines without change. And those guidelines remained in effect right up until this year. Finally in February of this year the government's Dietary Guidelines Advisory Committee began the slow backdown from the bogus recommendations it has been disseminating for decades. Here is the February 2015 Report, couched in endless bureaucratese. Or try a summary from the Washington Post wonkblog on February 10:
The nation’s top nutrition advisory panel has decided to drop its caution about eating cholesterol-laden food, a move that could undo almost 40 years of government warnings about its consumption. The group’s finding that cholesterol in the diet need no longer be considered a “nutrient of concern” stands in contrast to the committee’s findings five years ago, the last time it convened. During those proceedings, as in previous years, the panel deemed the issue of excess cholesterol in the American diet a public health concern.
And by the way, it's not just that the government's guidelines were dead wrong for 40 years. Many assert that the guidelines in addition were actively harmful to the health of the American people, basically because reducing fat in the diet inevitably leads to increase in consumption of more-harmful carbohydrates. Here is one such assertion (by a heart surgeon named Dwight Lundell). (For myself, I continue to follow the guidance of eating what tastes good.)
The most remarkable thing about the high-fat-diet/heart-disease hypothesis is that the accumulation of decades worth of devastating contrary evidence has still not killed it off completely. Even the latest report from the Advisory Committee is only a partial backdown from the recommendation to reduce fat. Hey, it's consensus! Everybody knows it's true! Same thing, of course, is going on in climate science. Eighteen plus years of contrary evidence? So? The leader of every single country in the world knows that consensus trumps the evidence!