Natalie Twisleton-Wykeham-Fiennes: don’t you just love her? One of the Black Lives Matter campaigners, our Nat caused chaos by occupying the runway at London City Airport, on the grounds that climate change is racist.
She and eight others, including a former member of the Oxford University Croquet Club, were sentenced by the courts last week. For many, their punishments were derisory: token fines and suspended prison sentences.
Would harsher treatment deter future protests like this and the one which disrupted Heathrow last month? Anecdotal evidence suggests it would.
In the town where I grew up, nestling in the foothills of the Pennines, the police would often drive miscreant youths late at night to remote hamlets up on the moors and make them walk home. It helped if it was raining, which it usually was. The more recalcitrant were likely to discover that the damp made the steps of the local police station unusually slippery. Compared to today, crime was low.
But this is mere causal empiricism, and there is a vast academic literature on whether or not harsher punishments deter crime. As a broad approximation, criminologists themselves tend to be sceptical about the impact of punishment as a deterrent.
A few years ago, I was at a seminar on the topic in which a criminology professor at Middlesex University asserted, without a trace of irony, that crime was caused by capitalism. In contrast, economists, who believe that agents respond to incentives, often claim that deterrence works.
Economists base their conclusions not just on theory, but on statistical analysis of detailed databases. Even so, the results might not be straightforward to interpret. For example, if prison sentences are increased and we see a fall in crime, is this because potential criminals are deterred, or because prolific criminals are in jail and can’t commit crimes?
Francesco Drago and colleagues published an influential paper in the Journal of Political Economy in 2009. They exploited the natural experiment provided by the Collective Clemency Bill passed by the Italian Parliament in July 2006. This provided for an immediate reduction of three years in the sentences of existing inmates, and as a result 22,000 of them were released. But if they re-offended, they had to serve all the suspended time, plus whatever extra they were given.
The study showed decisively that an additional month in expected sentence reduced the propensity to recommit a crime by 1.24 per cent. Steve Levitt, in his bestseller Freakonomics, described similar results obtained by smart analysis of American data.
Perhaps the way forward is to experiment with another fundamental concept in economics, that of externalities. Twisleton-Wykeham-Fiennes believes that flying, while convenient for the individual, imposes costs on others through its negative impact on the climate. Other people bear these costs, which are external to the benefits to the person flying.
The airport protests inconvenienced many others. So the fines should be in proportion to the external costs created by the crime. The assets of the well-heeled protestors would vanish in a trice. Anyone for this natural experiment? Future Twisleton-Wykeham-Fienneses might prefer croquet instead.