Hello! First of all, you've chosen a very unique career path! I like it. Secondly, both of the subjects you're thinking of taking are equally respected, a language may be better since universities are becoming more and more keen on languages, but since you're doing environmental stuff, Geography is a good shout as well. So Geography could potentially help you in the career path you want whereas Spanish could help you get into the University you want. Either is good, it just comes down to which one you enjoy more. Good luck!