The largest fossil subsidy is the lack of a tax or regulation on greenhouse gas pollution. I used to work in emissions and most other types of air pollution (NO

The largest fossil subsidy is the lack of a tax or regulation on greenhouse gas pollution. I used to work in emissions and most other types of air pollution (NOx, SOx, mercury, etc.) had either a permitting or cap-and-trade process that source emitters had to follow. These regulations were put in place to offset the cost of the externalities of those types of air pollution. For greenhouse gasses, it's only been recently that we even considered greenhouse gasses as pollution, and the EPA was actually starting to implement similar regulations (called Clean Power Plan). However, that is being rolled back by the Trump administration. So it looks like externalities subsidies will continue for the time being, at least on the federal level.