In the US, laws that are enacted at the federal level have to be implemented by individual states. In general, although a single market for the environmental externality is ideal, only separate markets may be feasible.
The difficulty of establishing a single market raises the question to what extent separate markets are good enough substitutes for a single market. This study empirically examines this question in the context of the Clean power Plan. The goal is to compare electricity market outcomes under regional and state-by-state implementations of the CPP, and to identify the important economic mechanisms that drive their relative efficiencies.
Read the working paper: http://assets.wharton.upenn.edu/~abito/COAL_LIVE_ST.pdf