Matt Ridley notes that the recent shutdown of air travel near Iceland was a huge buearucratic over-reaction to a theoretical model and based on a zero-tolerance approach to ash that makes no sense:
No coincidence that the models were built for radioactivity. Ash, chemicals, fallout and heat are things which are not linear in their risk. That is to say, a very low dose is not slightly more dangerous than no dose. It’s no more dangerous. This is not true of burglars and smallpox viruses.
He continues at John Brockman’s Edge site:
The ash cloud reminds us of the risks of risk aversion. Shutting down Europe’s airspace removed the risk of an ash-caused crash, but it also increased all sorts of other risks: the risk of death to a patient because an urgent medical operation might have to be postponed for lack of supplies, the risk of poverty to a Kenyan farm worker because roses could not be flown to European markets, the risk of a collision between ferries on extra night-time sailings in the English Channel. And so on. Risk decisions cannot be taken in isolation. The precautionary principle makes too little allowance for the risks that are run by avoiding risks — the innovations not made, the existing suffering not alleviated. The ash cloud, by reminding us of the risks of not being able to fly planes, is a timely reminder that the risks of global warming must be weighed against the risks of high energy costs — the risks of poverty (cheap energy creates jobs), of hunger (fertiliser costs depend on energy costs), of rainforest destruction and indoor air pollution (expensive electricity makes firewood seem cheaper), of orangutan extinction in subsidised biofuel palm oil plantations.
Oh, and remember the lessons of public choice theory: if you set up a body called the Volcanic Ash Advisory Centre, don’t be surprised if it over-reacts the first time it gets a chance [to] demonstrate that it considers itself — as all public bodies always do — underfunded.