If I had ten billion dollars to spend on combatting climate change, I'm honestly not sure what I'd do with it, and I rather think that if you are then you haven't really looked into the question.

(For obvious reasons this is not investment advice).

This is also an obvious EA rabbithole I am not diving into today. (To my mind a big EA weakness is it doesn't, as a movement, seem to have much interest in climate change though this is unfair to parts of it).