Bryan Caplan  

Trust the Experts: A Reasonable, Defeasible Presumption

Me on the BBC... Are Over- and Underestimation ...

Arnold writes:

It is not the scientific consensus that makes me believe that there is a link between smoking and cancer. It is the evidence for such a link that is compelling. It is the weakness of the evidence of the link between man-made carbon dioxide and climate change that makes the scientific consensus less persuasive than the tobacco-cancer link.

Sincere question: Have you personally reviewed the evidence on smoking, Arnold? I haven't. I believe that smoking causes cancer based on scientific consensus. The same goes for virtually all of my beliefs about the hard sciences, with the exceptions of genetics and evolution.

Is there anything epistemically wrong with my approach? I don't think so. The presumption that experts know more about their subject than laymen is eminently reasonable. Of course, it's a defeasible presumption. If you audit the experts, and discover that their objectivity or evidence is weaker than you would expect, then it's reasonable to downgrade them. I do it frequently, and Arnold's impressions from the global warming conference confirms my suspicion that this is one of the issues where expert consensus means less than usual.

Still, Arnold seems to be saying that you should base all your beliefs on direct examination of the evidence, and ignore expert consensus. I just can't buy that - and I wonder if Arnold really buys it either. Arnold?

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COMMENTS (6 to date)
Rob writes:

I think the difference is that there actually is a consensus regarding smoking. At least I seldom hear anyone arguing otherwise.

As for global warming, I hear at least as many people arguing for as against. I conclude that there is no actual consensus.

Adam writes:

I've talked about this before, but here's my two cents in brief:

No, it is neither reasonable, nor defensible.

For what, exactly, is an "expert"? Everyone who devotes their time to anything has to make judgment calls on what sources they trust--no scientist of any sort has tested every theory that they have to rely on before proceeding forward.

We all have limited amounts of knowledge, and therefore when making a decision we have to make a judgment call for ourselves. Making that call based on an imagined "consensus" of "experts" is just circumventing the issue. Who are the experts? How can you distinguish them from the people proporting to be experts?

In the case of Global warming, there are climatologists and statisticians who disagree with the popular theory; so in order to maintain the illusion of a "consensus" the interested parties do things like accuse dissenters of scientific dishonesty. The reason? Well, so that they can narrow the field of people considered "experts" to only those who agree on the chosen "consensus".

You should never argue for something just because of the authority of supposed experts. In my mind, the only ethical argument you can make is on the merits.

If you do not know much about a subject, then you shouldn't pretend to have an opinion of any great weight on it. If you want to make a case for something, put the effort into the research or have the integrity to admit that you know very little, but from what you've heard you believe X, Y, and Z.

Michael Kruse writes:

I am in agreement with Kling's statement. Scientific knowledge is gained through the scientific method, not a consensus votes. Hypotheses are constructed, tested and weighed against observed data. As hypotheses fail to be falsified they are assembled into theoretical models. These theoretical models will have predictive value. We do more hypotheses, tests and review of data to see if they predict correctly. When a theoretical model emerges and holds its own, a paradigm has been established.

With smoking and cancer there is (and has been for years) a solid paradigm for how smoking works and the damage it causes. The paradigm has been tested and challenged from every angle (as it should be) and it has withstood the tests.

There is no empirically tested paradigm for how climate changes. There are computer models that all say that CO2 is the primary cause (partly because many of the researchers started with that assumption) but they vary widely and contradict each other. Plus, what they predict frequently does not match observations (historical and present.) There are other very reasonable explanations that have not been falsified. Therefore, when “consensus” is claimed about human caused CO2 climate change, it is a consensus of scientists’ opinions not the result of rigorous testing resulting in a paradigm that explains what is happening. (Furthermore, on whose authority are we declaring a consensus?)

I read awhile back that Adolf Hitler was lining up 200 scientists to testify and contradict a scientific claim made by Albert Einstein. A reporter asked Einstein what he thought. He said, “It only takes one to show where I was wrong.”

The smoking and cancer link is based in science. The CO2 and climate change link is based in scientists’ opinions. It is a very big difference.

Dr. T writes:

The problem is the label 'expert.' Most scientists opining about global warming have no more expertise than I do. (I am a pathologist.)

We can do autopsies on persons who smoked, we can do toxicologic studies on their lungs, we can perform carcinogenesis studies on chemicals in cigarette smoke, and we can gather epidemiologic data on smoking and diseases such as emphysema, lung cancer, and heart disease. These have proven that smoking causes emphysema, that cigarette smoke contains procarcinogens, and that smoking greatly increases the risk of getting heart disease. The studies have been done over many years, in many institutions located in many nations, and show remarkable consistency.

Global warming proponents cannot autopsy the planet, cannot isolate the effects of carbon dioxide on air and ocean temperatures, cannot perform studies of the effects of increased carbon dioxide on air temperature, cloud formation, or polar ice cap temperatures, etc. We have just over 100 years of temperature data, with most of the early data coming from uncalibrated thermometers. Weather balloon and satellite derived data only exists for a few decades. The same is true for widespread ocean temperature data. The global warming postulate is based almost entirely on models, and today's models are deliberately biased to support global warming. (Models from the 1980s showed no statistically significant global temperature increases.) Today's models are very poor. The International Panel on Climate Change used a meta-model to predict recent mean temperatures, and the meta-model overestimated actual mean temperatures at the poles by 6 degrees Centigrade. Despite that tremendous inaccuracy, the IPCC used the meta-model to predict global warming, ice cap melting, and worldwide coastal flooding.

Skepticism about global warming is the only logical stance.

Brad Hutchings writes:

The smoking example is ridiculously appropriate in a way neither of you seem to have considered. The question is not whether "smoking causes cancer". The question is, "if a person smokes N cigarettes per day for 50 year (age 20 - 70), what is the likelihood that said person will contract smoking related (typically lung) cancer?". I can't tell you the percentage, but it isn't 100%. Emphysema is another smoking related disease that isn't much fun. And radon gas coming from the ground is another "cause" of lung cancer, even among non-smokers. And you know, this whole discussion leaves aside the possibility that people near Brian's and my age might just be able to print another lung when we are of the age that we would likely contract lung cancer after smoking regularly.

At any rate, when the "scientists" come up with a solution that isn't Draconian or hugely expensive, I'll care about global warming. Until then, it really doesn't matter how correct their consensus is, because the solution part is politics. Working and upper-middle class liberals are already p*ssed off about the price of gasoline. Raising it $1 so the screwball enviros can save the planet will simply break apart the Democratic coalition. And even in California, taxing the oil companies failed miserably in the initiative process. It ain't happening, and if in trying, a few sincere scientists need to have their reputations ground into dust (despite whether they are "right"), well, policy and politics are tough games played by tough people.

aaron writes:

I believe they're cancer causing based on social concensus, they were calling them cancer sticks before any of us were even born.

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