Of course, like all NIMBY types, their consumption of air and Brazilian hardwoods is just fine.
I am one. I limit my personal carbon footprint. I do not own a car (and hopefully never will). I rarely eat meat. I live in a cheap, inefficient apartment because I'm living on a student income, but I keep the heat low to try to limit my energy consumption.
I probably won't have kids, because it wouldn't be consistent with my concerns about climate change to bring another high-consuming American into the world.
As soon as some nation makes contraceptives economically available, the native population growth goes negative. Do you know many families with three children? Because that seems like a minimal number, no?
Immigrants who (1) come when younger, and further (2) have more children mask this problem a bit, but their supply is limited. (Sorry for my insensitivity, I'm not from The West myself.) The easy contraceptives will get to even poorest countries in a generation or two. There will be a Big Shrink before the narrative of fertility takes hold again.