The graph shows previous events at a few seconds duration, and the Big one at about 1 minute. So immediate effects would be limited to the air and land of half the Earth. Any further effects must be through disrupting Van Allen belt, ozone layer, NO2 in the atmosphere, secondary ionizing radiation products, etc.
IIUC that paregraph says it depends on the distance to the source and how close we are to the center of the "death ray". My (uninformed) guess is that is much more common to get a half sterelization than a complete one, but don't let probabilities ruin a nice linkbait title.
Somewhat related: (fake linkbait title) "Neutrinos can kill everyone!!! Here is how" https://what-if.xkcd.com/73/
