I believe the conceptual problem most people are stuck on is the couple second at most gamma burst by itself is quite harmless to life on the surface. The guys

I believe the conceptual problem most people are stuck on is the couple second at most gamma burst by itself is quite harmless to life on the surface. The guys on the ISS are likely totally screwed. Anyway massive radiation spike in the upper atmosphere has a rather well understood and very unfortunate chemical effect on the ozone layer, where its basically eliminated for about a calendar season. A demonstration can be provided COTS from marine reef tanks, you can buy UV sterilizers which continuously zap flowing water with UV, quite effectively killing all floating algae and pretty much anything else floating in the water. The problem in the ocean is for some months they'll literally be nothing for plankton to eat at all, and the sheer level of rot and rot byproducts would be pretty spectacular making life really difficult. And the recolonization process once UV levels drop enough to make it possible will result in some really weird blooms, and algae blooms lead to busts so the oscillations will likely be pretty exciting after the initial crash. A few million years later they'll be a lovely layer of petrochemicals to mine. On land, the couple month UV hit would be very much like hitting the entire surface of the planet with defoliants. You might survive the lack of food, but no clean water for awhile and no harvest this season and everything green pretty much just died and started washing away in the rain might be a bigger mess. In a way the best place to hang out might be a desert. All the cacti will die, but there won't be many mudslides. A forest might be a good place to chill out too, all the leaves will die and the trees themselves might die but the roots won't rot for a long time, keeping dirt in place. Grassland areas will be pretty much screwed.