That Precautionary Principle

October 10, 2018


Long ago, when it was still acceptable to voice doubts about computer projections of the climate apocalypse, people often answered critics who mentioned the uncertainty in the predictions by citing “The Precautionary Principle.”  This self-evident axiom of risk management means that if the consequences of a low-risk, uncertain event are so catastrophically awful, we are prudent to act as though the event will happen.  So, even if the predictions about climate change are not very certain, the impacts on us if they turn out to be true are so horrific, we might as well not argue, and just assume that they are correct.  Case closed.

When I first began to track the issues related to climate change more than twenty-five years ago, that was pretty much my point of view, but after a lot of thought, discussion, and experiences at conferences, I have modified my view to one of rather harsh skepticism.  I’m not going to discuss that process here:  I just want to dispose of this supposedly common sense precautionary principle (PP).

First, a little story:  My sister has an old friend that she has known for many years who suffered significant brain damage a long time ago when he fell and struck his head.  He is severely impaired these days, as though he had been the victim of a stroke.  He was quite robust and healthy when it happened; he just slipped on the ice one winter and banged his skull.  A fluke accident with terrible consequences.  Could happen to anyone, right?

Now, this sad event the befell my sister’s friend was forseeable.  After all, everyone knows that you can slip and fall on the ice, and many of us have done it, although with consequences that ranged more towards embarrassment than disability…but it could happen to us, even if we are not old and frail.  It happened to my sister’s friend!  The chances are not zero.  If you do research on it, you might find that they are not even considered trivial, so this is my question.  Given that the consequences of this accident, with a probability notably above zero, are so life-shattering, why don’t we all walk around wearing football helmets in the winter when there is ice on the ground?  It would seem to be a perfect and unassailable application of the precautionary principle.

The reason that we don’t wear helmets is that we all make our own calculations, knowingly or not, and assume that the risk is so vanishingly small that we need not worry about such a “fluke” happening to us.  We are totally unpersuaded by the logic of the PP.  Some people are so foolish as to never wear seat belts despite the much stronger statistical evidence in their favor.  We might think those people are nuts, but still not don the helmet in icy weather.

In the end, we are left with nothing but data, and our judgment about how powerful a case it makes for taking action.  The PP is simply a way of trying to shut down consideration of the data and the possible courses of action by asserting that only one alternative is possible and logical, but in practice, nobody reasons that way when they actually have to make a choice.