"Tailpipe" emission is zero, lifecycle emission is around 3 grams CO2 equivalent per passenger*kilometer, significantly less emissions that a _mechanical bike_ ridden by someone with a _fully vegan diet_.
Hypothetical medium range "clean" planes, or plans for highway with hydrogen refill stations, are a foolish distraction from the fact that **sustainable transcontinental long distance mobility is a solved problem, with well defined advantages, limitations and a proven track record**.
More than four decades after this tech was introduced we could have had a Europe-wide dense network, cross-linking all regional centers from Oulu to Seville, Edinburgh to Athens, Brest to Luhansk. Maybe we could have had sleeper high speed trains. Maybe we could have closed many airports, and made flying very unappealing, without antagonizing families and friends that live scattered away.
But we don't have any of that.
Instead of building and operating infrastructure for the common good, we have elected and non-elected moronic bean-counters forcing what should be public utilities to compete with each other in a race to the bottom.