Here's Gary Johnson backtracking on his seeming support of a carbon tax or fee, in an interview by Nick Gillespie at Reason:
Me: If Johnson is really open to ideas, he should consider the carbon fee and dividend proposal put forward by the Citizen's Climate Lobby. It is guided by the principle stated by one prominent supporter, George Shultz, that "It's not a tax if the government doesn't keep the money," as the revenues would be sent back to households as checks. It would deal with the international aspect by using border adjustments, which are import fees on products from countries that don't have carbon pricing. It is a proposal that has been around for several years, and it would be nice if people running for president of the United States actually knew something about it.