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 the demonstrate that it considers itself - as all public bodies always do - underfunded.
...the excitable idea that one volcanic belch has reminded us how small we are reveals what lies behind the contemporary green outlook: a misanthropic view of mankind as a cocky and destructive species which needs to be firmly put back in its place. It is striking that even a natural event which cannot in anyway be described as 'manmade' has unleashed so much nature-dominates-man commentary. This shows that, for all contemporary commentators' claims that they are only interested in communicating the 'scientific facts' about what will happen if we continue distorting and warping the natural world with CO2, in fact they are instinctively drawn to any natural occurrence that can be held up as evidence of Mother Nature's power over deluded mankind.