You hardly need to go anywhere near "the globe becoming uninhabitable for humanity" before you run into pretty devastating consequences for significant percenta

You hardly need to go anywhere near "the globe becoming uninhabitable for humanity" before you run into pretty devastating consequences for significant percentages of the world's population. And even if we encouraged poorer countries to burn as much cheap fossil fuel as they possibly could to improve their standards of living, I very much doubt it would even come close to enabling them to mitigate against some of the worst sorts of natural disasters and weather extremes that are expected to be more severe and frequent as the planet continues to warm. Though realistically it won't be lack of cheap energy that continues to hold back economic development for much of the world anyway.