If you've read "The Collapse of Western Civilization: A View from the Future" by Oreskes and Conway, what did you make of it? The collapse they portray (and they're not so much saying "this is how it will happen" as just running with an idea) is driven by climate change and a refusal (political and social inability?) of the West to save themselves, if I recall correctly.

You certainly touch on this in your first section, although Spengler and Toynbee discuss other ways for a civilisation to collapse.