This week Policy Exchange launched a report called "Green skies thinking: promoting the development and commercialisation of sustainable bio-jet fuels". The thrust of their argument is that bio-fuels cannot replace oil as the primary energy source for all transport because of production constraints, but road vehicles can be powered by electricity or hydrogen. However, such options are not open for aircraft, so bio-fuels should be used primarily by them.
The logic is fine as far as it goes, although of course it takes it as a given that we will all be going to hell in a handbasket if carbon dioxide emissions are not drastically cut back. And we might well see flights in a generation's time largely powered by economically viable algal bio-fuels. But what has sustainability got to do with it?
The term has become a convenient catch-all for environmentalists' policy prescriptions for pretty much everything we do. But the supply of jet fuel is at present perfectly "sustainable", in that the demand for flights can continue to be met for the forseeable future. When oil prices rise sufficiently high for alternatives to become viable, things will change. Something which can only be sustained by use of high and continuing public subsidy does not deserve to be called sustainable.
The mantra of sustainability assumes that future generations will continue to use resources in the same way as we do. A quick review of the last two centuries would surely be enough to show the fallacy of that argument. And if we do not need to second guess how our grandchildren might choose to live their lives, then there is a strong case for regarding sustainability as just another fashionable but failed concept.