2) If something bad is happening and we're causing most of it, are the costs of mitigating it less than the costs of enduring it? This one seems poorly explored so far, I have yet to see a really good analysis. I happen to think the tail risks are high enough it's worth it, but not everyone agrees.
Who decides what is bad and what isn't bad?
This is interesting from a nationalistic point-of-view. Consider Siberia. Warm it up, get rid of the permafrost, and there's some nice arable land there that could feed a lot of people. That would be a pretty good thing for Russia. Consider America's wheat belt, where lots of food is grown for people in the US and abroad. If that were to, say, dry up, that would be bad for the United States.
Right now, you're seeing trade routes open up in the arctic ocean. That's not a bad thing for countries like Canada, Russia, and some of the northern European countries. But if China's rice fields suddenly are starved for water, that would be bad for people in China.
So, yeah, climate change could be a boon for Russia. It might not be so good for the US.