Which of These Doomsday Scenarios Is Most Likely to Kill Us All?

The Big One: That's the premise of Bryan Walsh's new book, End Times: A Brief Guide to the End of the World, in stores and on Amazon now. Walsh skips the small stuff and focuses on the things that might be able to end all of humanity.

"The sort of global risks or threats that could plausibly result in actual human extinction or so much disaster that you'd have a permanent downgrading of the future of the human race," Walsh tells Popular Mechanics. "We've never experienced anything like this. World War II, the Black Death ... none of them really come close to what we're talking about here."

It's a fascinating and horrifying premise. During an interview with Walsh, who has been a science reporter for 15 years and is an editor at Time, we worked up a few scenarios and asked Walsh what the chances of survival were for each one. A 1 score means we have a pretty good shot of living in some capacity. A 10 means we're all totally screwed.