Well, I AM a religious conservative, so . . . Last time I checked, Protestants believe humanity will hang around until God Himself says, "Okay, everyone out of the pool."
I can't argue that there are left-wing environmentalists who caterwaul about "12 years to save the planet!" and whatever. It was always my impression, though, that they thought less that humanity would be utterly wiped out, and more that the Earth itself would be turned into a horrid wasteland our remnants would wander through. Y'know, like "Mad Max", but without the cool leather clothes.
In terms of our technological ability to provide a higher standard of living, you're right. We aren't in a decline. In terms of our character quality? That's a different story. I believe that humans aren't designed to have things too easy and comfortable; we're designed to have hardship and strife, and be honed into better, stronger beings by it.