I just asked this question elsewhere in the thread. It seems that a lot of people just blindly believe it because it sounds good. But as you say between Asia and Africa we have over half the world's population. They're pretty far back in industrialization and they're bound to pollute way worse per person (divided by wealth on some way I'm sure).

Frankly I'm sick of people using environmentalism as their soap box like this. It doesn't make anything better to ignore reality because they want to condescend to the US and Canada and Europe. It's actively making it worse.