I don't know if anyone's literally going to say nature awoke Godzilla to come down on them for their crimes against it, I think it's just mainly going to be inference from context or maybe vague implication from Serizawa who seems to be the spiritual/metaphorical aspect of the film. Cranston's character is just terrified of what these creatures mean and he just sees them as a race that could take over the world so I don't see him thinking its nature getting back at us.