You're missing a main point - we can't magically undo 150 years of CO2 creation when we decide the effects are noticeable. There will be a time when actions are taken to reduce the effects, but that won't stop the effects from increasing for the foreseeable future. Will it cause our extinction? Doubtful. Will it cause extinctions and much harm? It's already happening. Even with the asteroid 65M years ago, it wasn't a dino free world the next day. The extinctions took several 1000s of years, IIRC, and then another 1.5 million or so before the biosphere started seriously diversifying again. So, to put that in perspective, recorded history only barely covers 5000 years.
If scientists came and told the average couch potato that unless they stopped driving their gas-guzzler today, their great great great grandchildren might be living in an arid desert barely scratching out a living and dying of thirst, I'm sure exactly 0% would stop driving their gas guzzlers. The average couch potato can barely conceive of issues next week, much less several generations away. Look what it took to get chloro-flouro-carbons out of use.