Averting Catastrophe is a book by Cass Sunstein that NYU Press published in April 2021. I'm surprised that nobody has mentioned it on the EA Forum before (AFAICT). Quoting from the NYU Press page:

Averting Catastrophe explores how governments ought to make decisions in times of imminent disaster. Cass R. Sunstein argues that using the “maximin rule,” which calls for choosing the approach that eliminates the worst of the worst-case scenarios, may be necessary when public officials lack important information, and when the worst-case scenario is too disastrous to contemplate. He underscores this argument by emphasizing the reality of “Knightian uncertainty,” found in circumstances in which it is not possible to assign probabilities to various outcomes.

The Google Books page includes a table of contents:

• Introduction
• What We Don't Know
• With and Without Numbers
• The Maximin Principle
• The Precautionary Principle
• Uncertainty
• Objections
• Irreversibility
• Departments and Agencies

I found this book while researching the precautionary principle. Sunstein has written multiple papers on this topic, including two that seem particularly relevant to x-risk:

• "Irreversible and Catastrophic"
• "The Catastrophic Harm Precautionary Principle"

Sunstein also wrote Laws of Fear: Beyond the Precautionary Principle, which Cambridge University Press published in 2005.

See Sunstein's Wikipedia page for a (somewhat) comprehensive list of his books. Also note that he appeared on the 80,000 Hours Podcast in 2019.