For the last year, I have been trying to fly less. I am still an ECR (Early Career Researcher), but I have to travel quite often (once per month at least) in Italy and around Europe. I find it quite convenient to take the train if possible; in many cases, it is even faster than going to the airport. Another good option is a night train, that can also save you a night in a hotel (this year I have done Milan->Paris and Zurich->Berlin with night trains).

Of course, to reach more distant places (>1000 km) it becomes unfeasible, since there are very few high-speed trains to take. I think that something is changing, but a large number of colleagues still see me as a bit crazy and are not even looking at alternatives to planes when planning a business trip to a conference or a meeting.