One of the things it mentions is that, if climate change continues unabated, the Middle East would become unbearably hot. It suggests the Hajj could become impossible in just a few decades time.
So what if we imagine earlier industrialisation of somewhere like China - perhaps a Meiji-lite, the monarchy collapses sooner, or the nationalists win the Civil War. Presumably this needs a POD pre-1900, which is why I've put it here.
What would be the impact of much higher pollution, and thus climate change if the Middle East just becomes unsustainably hot?