It is the way of extinction that what kills the last individual commonly has nothing to do with the underlying factors that doomed the species. Could climate change by itself kill everyone on earth? No. Could it be a significant contributing factor to a downward spiral that ends in extinction? I hope not, but I don't really know. Leaving aside the purely fictional versions of AI and nanotech to which you refer, could real-life versions of those technologies help us develop sustainable energy sources? Yes. Will they do so fast enough? I hope so, but I don't really know.

As for whether there's anything we here can usefully do about it, I don't think it would be useful for us to get bogged down in the sort of bickering about politics that all too often goes with this kind of territory, but LW does have a good track record of avoiding that; and perhaps it would be useful for us to explore potential solutions.