GLOBAL EDITION: Are players responsible for paying costs for assets that may be sited on home base and not being used?

Yes, every turn. Regard the ‘stage 2 costs’ on the Rules card as overheads that must be paid every single turn regardless of whether the player uses them or not. The important exception is that this requirement only applies to the relevant assets to the turn being played. In other words, if you are playing an ‘Air & Sea’ turn, the relevant costs are $2,000 per plane and ship ~ there is no charge for trains and trucks because it is an ‘Air & Sea’ turn. Similarly, during a ‘Rail & Road’ turn, $2,000 must be paid for every train and truck whether used or not ~ there is no charge, however, for planes and ships because it is a ‘Rail & Road’ turn.