I think we've obviously screwed the pooch with this stuff, but I'm not yet willing to go so far as to say we're doomed in some sort of existential sense. We have gone so far down the bad path that there is no longer a way to avoid suffering some pretty heavy consequences, and if we don't start doing some major and meaningful reform, this could easily become a genuine existential issue. For humans (and other species, but not nearly all). Nature will be fine in the long run no matter what.