WhenIwasakid,thedisasterweworriedaboutmostwasanuclearwar.That’swhywehadabarrellikethisdowninourbasementfilledwithcansoffoodandwater.Whenthenuclearattackcame,weweresupposedtogodownstairs,hunkerdown,andeatoutofthatbarrel.Todaythegreatestriskofglobalcatastrophedoesn’tlooklikethis.Instead,itlookslikethis.Ifanythingkillsover10millionpeopleinthenextfewdecades,it’smostlikelytobeahighlyinfectiousvir...