Carbon dioxide in the atmosphere. Sure, we breathe it out and it's necessary for plant life. But we are currently at levels beyond what we've had in the last 14

Carbon dioxide in the atmosphere. Sure, we breathe it out and it's necessary for plant life. But we are currently at levels beyond what we've had in the last 14 million years. I don't think people have realised yet we're in a slow-motion car crash. It also ticks all 5 of the criteria dredmorbius stated in this thread.