I... guess? That hypothesis conflicts with our best data and you end up at the same policy results anyway, so I'm not sure why one would prefer that roundabout method instead of simply agreeing with the scientific consensus.
You switched topics. They were talking about contribution (albeit enough contribution to be the main cause), and you tried to make it as though they were saying causation (meaning no other causes).
The common jargon in Liberalese is "anthropogenic climate change", i.e., climate change created by humans. My argument is that they'd have an easier time getting people on board if they went about this without assigning blame.
Saying "there's a problem we need to solve" is going to get a more productive reception than saying "you created this problem and now we need to solve it".
maybe one should instead push something wacky, like that the great spaghetti monster caused global warming... [insert missing logic] ...and that's why we should shut down coal plants.
How would someone go about it, and would you trust them?