When the wealth of the ruling class is under threat?

I don't think it'll be a single point. The calamity has been happening, but we aren't super directly threatened yet. However, my more pessimistic view is that as the climate changes, those with more resources will be more insulated to the effects, and we'll likely see climate refugees first, then wars because of the climate refugees and a loss of natural resources (like water).

Something, something, interesting times...

That breaking point has already arrived for many under developed countries, and for the industrial first world, the breaking point will arrive for them far after the point where something could have been done to change it. Since those effects haven't arrived yet for the first world, there's no interest in doing anything to change it.