It's hard to know isn't it. There's a case to be made that the climate crisis is hugely important, of great interest to younger views (which are supposed to be a bit part of Who's target market) and more widely accepted across the political spectrum than many other issues Dr Who might want to engage with - so I can see a good case for wanting it to be a key theme of your era (assuming, of course, this is deliberate and not just chance). The point where "engage with" becomes "harangue and preach" is kind of hard to judge - there were plenty of people who thought the speech at the end of Orphan 55 was precisely the kind of of direct and on the nose delivery that the current crisis requires.