The revelation that the decision to close Europe’s skies following last week’s eruption of an unpronounceable Icelandic volcano, and the spewing of ash into the sky, was triggered by advice from the Volcanic Ash Advisory Centre of the UK Met Office, based not on all relevant empirical evidence but on their computer model, has led to no small controversy. IATA, representing the airlines, has condemned the advice as absurd and unnecessarily alarmist, while others have noticed the parallel with the drastic decarbonisation policies promoted by the climate change lobby, similarly based largely on alarmist interpretations of the projections generated by Met Office computer models.
However, the folly of everyone relying on Met Office computer modelling is only half the story. An even more important read-across concerns our old friend the precautionary principle.
What the Met Office/Volcanic Ash Advisory Centre model does is essentially to provide short-term predictions of the extent and location of the clouds of ash. It may well do this (not a very difficult task, after all) pretty accurately. It is clearly a very much simpler and hugely less uncertain task than predicting the likely temperature of the planet a hundred years from now. It is, however, a very limited model, which does not even pretend to predict the intensity of the ash within the cloud, or in different areas of the cloud. Nor, of course, does the VAAC have any knowledge at all of what level of ash intensity is a serious hazard to jet aircraft and what level is not a serious hazard. When tackled about the intensity issue by the BBC, the Met Office spokesman claimed that this was irrelevant, since the policy in force was one of 'zero tolerance'. This, of course, is complete idiocy (and is conspicuously not the policy in the US, whose air safety record is as good as Europe's). It is, however, the so-called precautionary principle again – and indeed only a few days ago the Eurocontrol spokeswoman was explicitly justifying the original blanket flying ban on the grounds of the precautionary principle.