Comment by archangel_one

But isn't the point that the externality is in fact not that heavy? That implies that the process is at most 97% efficient, which is actually pretty damn good (of course, there'll be other inefficiencies, but nobody's complaining about those). If the rest were burnt in internal combustion engines to move cars about, it's almost certainly < 30% efficient and very often < 20%, which implies most of the externality comes from people further down the chain.