@Jose Fly & I disagree about the possibility of
changing the mind of global warming deniers.
He says it can't be done. He's wrong of course.
But this set me a'wondering about the titular question.
It could be about GW, religion, politics, guns, etc.
What effected the change?
I was a wildfowler.
If I could have done so I would have lived out on the creeks and saltmarshes for ever. I lived for it. I loved it. I would never ever want to give up.
And then during one dawn I shot a curlew, it was legal to shoot curlew back then, and they tasted quite like steak. It fell in to the creek just out of my reach, and I have left my fowling punt a long way further up the creek.
It was cold. Freezing. The curlew lay in the water, injured, with its wings outstretched. It began to shiver, and this caused circles of ripples to radiate away from its freezing body. I shot it again to end its torment and the close range shot disintegrated it to pieces, inedible.
It was like a mind-punch that happened to me, as I realised I was a total moron to have taken that shot, and to have wasted the life of such a beautiful creature.
I walked back to my punt, rowed home, and never went out again. I sold my punt to a Maldon wildfowler who later became famous. . I hung my gun over the fireplace and years later I sold it to an antiques dealer who came around doorknocking in the hope of bargains.
That was the biggest change I ever made in my life, I think.
I don't knock wildfowlers and never have, but I'm sure that if they ever did something as stupid as that that it might change them too.