Professor Karthik Ramanna writes in ProMarket (the publication of the Stigler Center, University of Chicago Booth School of Business) as President Trump pursues his trade agenda, to say that if levelling the playing field for American manufacturers is the goal, tariffs based on greenhouse gas emissions could be the answer. American manufacturers generally use cleaner energy sources and production methods than overseas competitors – so emissions-based tariffs would favour the USA without triggering inflation or a trade war, he argues.