The upshot of a much-publicised Twitter altercation between climate activist Greta Thunberg and Germany's state-owned rail operator, Deutsche Bahn: Train companies aren't really ready for an increasing number of passengers who want to fly less to minimise their carbon footprint.

Last Saturday, Greta tweeted a picture of herself sitting on the floor in a train vestibule, next to a pile of luggage. "Travelling on overcrowded trains through Germany," she wrote. "And I'm finally on my way home!"