A group of top climate scientists say the world needs to think about the ultimate climate catastrophe — human extinction — and how possible it is. They are calling on the world’s main climate science body to look at the ultimate climate catastrophes, no matter how remotely unlikely they are. They say the worst of the worst case scenarios are being ignored. The scientists say they aren’t likely to happen, but need to be studied so we can be sure. It’s smart risk management to know how remotely possible the very worst is, they say, so the world can better avoid it.