  While several recent works have identified societal-scale and
extinction-level risks to humanity arising from artificial intelligence, few
have attempted an {\em exhaustive taxonomy} of such risks. Many exhaustive
taxonomies are possible, and some are useful -- particularly if they reveal new
risks or practical approaches to safety. This paper explores a taxonomy based
on accountability: whose actions lead to the risk, are the actors unified, and
are they deliberate? We also provide stories to illustrate how the various risk
types could each play out, including risks arising from unanticipated
interactions of many AI systems, as well as risks from deliberate misuse, for
which combined technical and policy solutions are indicated.
