Co2 has had spikes up to > 5000 ppm in the atmosphere in the past. Is anything possible? Sure. Is anything currently proposed as possible likely to sterilize

Co2 has had spikes up to > 5000 ppm in the atmosphere in the past. Is anything possible? Sure. Is anything currently proposed as possible likely to sterilize the planet? No. We could get hit by a mini-moon sized asteroid tomorrow though that liquifies the crust, of course.