Begging the question

Longtime reader Jack Strocchi sent me this piece from the Times, reprinted in the Oz, with the headline “Carbon crash hits Europe’s emission trading scheme”. The main point is that, with the economic downturn, the price of carbon permits has fallen. The author concludes that this proves the need for a carbon tax rather than an emissions trading scheme.

This is a fine example of the fallacy of “petitio principii” or, in English, begging the question. This does not (yet) mean what TV commentators seem to think, namely “begging me to raise the question”.* Rather it refers to an argument in support of a proposition which assumes the truth of the proposition in advance. Clearly, if price instability is, in itself, evidence that a program has failed, then you need a program with fixed prices, that is a tax.

The main argument for a carbon tax rather than a trading scheme is that, if there is a lot of uncertainty about the cost of reducing emissions, and not much uncertainty about the damage caused by climate change, a fixed price for emissions (that is, a tax) will get closer to the optimal outcome than a fixed quantity.

But what’s happening here is completely different. The demand for emissions has fallen due to the economic slowdown. The reduction in price offsets the adverse impact of the trading scheme on firms that are already facing hard times. Equally, if the economy booms, the price of permits will rise. This is a clear case when a fixed quantity trading scheme performs better than a tax.

* Of course, meaning is defined by usage, so if a word or phrase is used in a particular way long enough, that becomes the meaning. But “begging the question” in its traditional sense is a useful phrase for which we have no good substitute. For the TV usage, “raising the question” is perfectly adequate.

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