"In a typical year the world emits over 51 billion tons of greenhouse gases, and as we keep doing that, the consequences for human life will be catastrophic."

So begins the promotional video for Bill Gates's new book, How to Avoid a Climate Disaster. It's a harrowing thought, really, that the world could be on the brink of catastrophe. But Gates is optimistic that we can mitigate the climate crisis if we take the right steps in the coming years.

Those steps may be painful, however. Drastic threats call for drastic measures, Gates seems to reason, and the chief measure he recommends is completely eliminating greenhouse gas emissions.

"The case for zero was, and is, rock solid," Gates writes. "Setting a goal to only reduce our emissions—but not eliminate them—won't do it."