Bacon Butty piles on to one of the notions I criticised here. Food miles are, if anything, less useful than embodied energy as a policy target - after all, a whacking 22 per cent of CO2 attributed to UK food transport originates from sea and air transport. Obviously, the first place to start, especially as something like 33 per cent is attributed to trucks within the UK and zero to rail transport.
It's also worth remembering that one of the reasons for the supermarket airfreight phenomenon is that the airlines found they had spare capacity on aircraft coming back from various places in Africa. As any trucker could tell you, a backload is pure profit, as the costs are covered on the outward journey. To put it another way, it's no net increase in CO2 emission unless the route would otherwise be uneconomic and - this being the airline business - politically closeable.
Final thought? Forget all the intermediate interventions, and use the tax that gets to the cause of your problem. But it's becoming a major political line of discourse that environment/energy issues are a question of consumerism, or rather, inverted consumerism. (Consider Martin Wight's typology of international relations theories - Revolutionism, Rationalism, Realism, and Inverted Revolutionism. The last was pacifism.) Stop buying stuff! Better - buy expensive stuff that shows your moral character!
But looking at the data, this is ridiculously ineffective. What works is rockwool. That, and lithium-ion batteries, wind turbines, and incremental improvements on a range of other technologies. Not flying, or not buying airfreighted (or perceivedly airfreighted) goods, will do us no good at all. So why is Diddy Dave Cameron so keen?
My chippy reckoning is that it's class. Anything involving changes to infrastructure or buildings will piss in a lot of Tory pools, from Grecian dukes discovering new laws of atmospheric chemistry to oppose wind power to nifty resellers flipping buy-to-lets in the M4 corridor, and make a lot of sparks very happy, and these things do not please Dave from PR. It's the technocracy, stupid.
It's a pity that Gordon Brown insists on taxing the poor into moral enlightenment.