Catholics have instructions on how to resolve the dilemma where one candidate supports doctrine A, and the other candidate supports doctrine B. In plain terms, it's basically "choose your battles." This came to light when the dilemma of the day was abortion versus capital punishment and the poor.
Owing largely to the culture war, American Catholics have provided decisive support to the party that calls global warming a hoax. This isn't a political statement on my part, but just a statistical one.
My view is that the Church has quietly held a token position on global warming while concentrating its social influence on other matters. I don't have a definitive answer on this, and could of course be wrong, but choosing the wrong battle is a moral failure.