We support levies and charges on activities that generate negative externalities, where the producer's costs are borne by society in general. Likewise those activities which generates benefits carried by society in general they can be susidised to that level. The combination encourages socially beneficial activity and reduces socially negative activity. Al Gore, correctly said: "Global warming pollution, indeed all pollution, is now described by economists as an 'externality.' This absurd label means, in essence: we don't need to keep track of this stuff so let's pretend it doesn't exist... But what we're pretending doesn't exist is the stuff that is destroying the habitability of the planet."