About exceedingly little.

Locavore, for those of you who missed its Oxford Word of the Year coming out party, refers to an individual attempting to maintain a diet of locally produced food--with local generally assumed to mean within about 100 miles. Many wonderful qualities are (dubiously) ascribed to locavorism, including increased happiness in agricultural communities and rejuvenated local economies, but the primary selling point appears to be a reduction in global carbon emissions. . .

Or so the thinking goes. In fact, emissions per unit of food depend heavily on how the food is shipped. . . Mr Harford [Undercover Economist and recent addition to the economics blogosphere] continues:

Two-thirds of the social costs of the food distribution system have nothing directly to do with the environment at all: They are attributable to accidents and congestion. More than half of those costs are caused by driving to the shops. My socially responsible advice to you, then, is not to worry about from how far away your food came, but to walk--not drive--to the supermarket.

These complicating factors do suggest how vital it is, as Mr Harford acknowledges, to price carbon. Under a carbon pricing regime--tax or cap-and-trade--the difficult choices facing consumers become simple.

However, it won't do anything useful about the purported issue, carbon emissions. Making the choice between ineffective action A and ineffective action B simple is only useful for exceedingly small values of useful. This is merely politics, the things politicians and economists do instead of engaging issues. It serves only to delude the public. In some cases this is OK since the public is riled up about nits, thanks to the rhetoric of politicians. First cause a panic, then provide a non-answer to the non-problem. That's politics.

Update:

If the USA and Europe ceased to emit anything at all that would only delay the catastrophic warming predicted in doom scenarios. It would only do the job half way. It would also delay development of a real solution of course, and so likely be a net loser.

A real solution is to develop affordable energy systems that the whole world can migrate to. Development may be timely, but implementation will almost certainly be late. Adaptation and perhaps engineering measures will be required to bridge the gap.

All of the insignificant emissions reductions proposals that get so much press and so much hype from posers are negated many times over by new coal fired power plants every year. It's a total waste of time and energy that would be far better spent facing the true situation and doing what can be done to develop real solutions.