Substituting to travel by boat would almost definitely increase carbon output, unless you mean sailboats. Carbon output is the integral of emissions/hour over t

Substituting to travel by boat would almost definitely increase carbon output, unless you mean sailboats. Carbon output is the integral of emissions/hour over time, and a comparable boat trip could take weeks. High speed rail is also not as great as people think - true HSR uses a pretty huge amount of electricity, which has to come from somewhere. Conventional (aka medium-speed) rail on electrified tracks is probably the sweet spot for efficiency, but the travel times aren't going to make most people happy. More realistically, the solution in a world where carbon is "properly" priced would be that people travel a lot less overall.