Ah, the joys of reading libertarian economics obsessed blogs. I could pretend to be all smart and knowledgable, or I could admit that tim_worstall mentioned this very thing a few weeks back.

Pigouvian Taxes, an attempt to put the external costs back intot he market.

See, me knows stuff. Wot I read elsewhere. But I still knows it. My offer/invite above for contributors, you interested on occasions?