Tim Harford writes to me:
Polluters in Europe currently have to pay about euros10 per tonne of carbon dioxide as part of Europe’s efforts to meet its obligations under the Kyoto agreement. That is less than one penny per kg of carbon dioxide. Perhaps that price, in a volatile market, is too low. A Government Economic Service paper on the social cost of carbon emissions recommends a cost closer to euros25 a tonne of carbon dioxide. Even that is less than 10p for a kilogram of mange-tout, or a penny for a 100g packet. If consumers were forced to meet those costs – as in principle they should be – the sum would barely register. There are good environmental reasons to tax airline fuel, but such taxes are not likely to make food imports substantially more expensive.
Here is the link, and Tim notes there are typos in the article, the text is correct as above. When it comes to the social cost of food, one estimate is that congestion and accidents account for two-thirds of that sum. So maybe you should walk or bike more, but eat what you want, from where you want. Here is, again, my review of Michael Pollan’s The Omnivore’s Dilemma.
By the way, for a more skeptical view of a carbon tax, here is Robert Samuelson’s piece from today’s WP.
Addendum: The Economist (MMM?) refers me to a new "AntiPigou" and "Anti-Mankiw" blog, which I have yet to read.