There was a time when I was angry with climate deniers. I was convinced that most were stupid, or that those who clearly weren't stupid simply lacked any understanding of chemistry or physics. The anger was certainly warranted, though perhaps not so constructive. It's like being stuck in a lifeboat with another shipwreck survivor who insists on rowing further out to sea when land is already in sight. If only it were so simple! We could just clock them over the head with an oar and be done with their nonsense until we were safely back on shore.
I'm increasingly convinced that the people making such arguments do not in fact believe them, but are instead displaying a complete inability to handle the horrific implications of climate change (you know, like the death of *everyone*, for instance). For all practical purposes, excessive (and well warranted) fear has tripped their mind's "circuit breaker", making them not only unhelpful but actively pushing us towards the very thing they fear. It's no coincidence that most of the climate deniers have conservative personalities, whom a psychological study has shown have a much stronger fear response than those with liberal personalities. Acknowledging the truth also means they'd have to make significant changes... which isn't easy with a conservative mindset.
The logic I'd long adhered to was that increasing evidence would eventually break through to them, and they would fall into line and begin to help. I'm now convinced that this will never happen. They will fight us at every turn, because they cannot handle the truth, and anyone who acknowledges the truth only makes their fear worse and their denial more adamant.
History is loaded with similar examples. Author Elie Wiesel, who survived the Holocaust to tell his story, made mention of a man who had escaped from a concentration camp and came back to warn the people in his village (most of whom later ended up in a similar camp). His story was so horrific that nobody believed him. He was ostracized and ignored. Could he have told it in a way that people would've listened to him?
I wish I knew of a good way to motivate such people without driving their circuit breaker even further into the off position. The only thing which comes to mind is the possibility of showing them the good world that could be had if we do the things necessary to save ourselves. The longer we wait, the harder it will be to paint the picture of that world in a convincing manner. The hour is late, and the task likely to fail, but I'd suggest we start rowing.