Actually, that was not what I was thinking. Mostly I was thinking that the entire point of this tax is that it should eliminate itself - The income base beneath it disappears as utilities stop using coal and gas, and if it is part of general revenue that creates incentives for government to keep coal and gas in use- if it is being used to build the replacement infrastructure for the coal and gas plants this is not a concern - the need for the income disappears along with the income stream.