Thanks for that link - very interesting. First real discussion I've seen comparing the two mechanisms.

However I'm really not sure I agree on your second point. Like anything ocurring naturally on the planet I think it is economically land" in the Georgist sense. Man can improve it by artificially cleaning it or change it for the worse by polluting it, and of course nature does a major part of regulating it which we are learning we tinker with at our peril, but as a planet we can only hold onto so much atmosphere. And of course individually we are located in a particular part of that atmosphere which gives it a locational value and so an economic rent."