This is a straw man. The price difference between a first class ticket and chartering a private flight is massive.
Semantics, but, I'm not sure either of the people you cited is advocating climate change.
What do you mean? Al Gore made an entire movie about climate change and Leo Di Caprio talked about climate change in his Oscar acceptance speech. GP is right about that.
Most people would say they're against climate change. Advocates of climate change would want to encourage climate change.
Well, Leonardo DiCaprio has a long-standing grudge against icebergs.