Well, there is a problem becoming evident with any further "we'll take action once the situation proves itself so bad that action is unambiguously necessary".

Well, there is a problem becoming evident with any further "we'll take action once the situation proves itself so bad that action is unambiguously necessary". That problem is that human civilization is becoming less rational in response to the stresses of the situation. The degree to which a country or the entire world has ever able to act "selflessly" or broadly altruistically has always been limited but some things have happened - banning Ozone destroying chemicals was an action. Wars have shown change (negative change but change) can happen quickly if a society needs it. I don't think there's a fundamental technological barrier to forcing a lessening of green house gas production. Rather, it's a loss of capital investment barrier. The forces arrayed to prevent oil assets from losing value are huge. Maybe a fund could just buy these assets and let them wind-down or maybe we're all doomed or maybe there's another escape. I'm not sure but I think pushing for quick, not slow action, is appropriate, whatever one think is realist (the end of the human race looks realistic, certainly but I don't see a reason to simply accept it).