To change someones opinion, first change the behaviour of the individual. Research shows that people can grow an attitude originating from their behaviour. An individual that starts to consequently separates waste is most likely to perceive itself as environmental conscious.
The working mechanism behind this is the commitment- or consistency principle. Humans have a deep need to be seen consistent. As soon as we have committed to a thing, we want to stay true to it.
Astrid Groenewegen - De Kunst van Gedrag Ontwerpen