Itwasactuallypartof a regularcycleinEarth's climateandiceage, specificallyanextracoldpartofaniceagewhereicesheetscreepdownfromthepolls.
It's possiblycausedwhentheupperpartoftheNorthernHemispherereceiveslesssunlightdueto a bunchoffactorslikehowmuchtheplanetwobblesonitsaxisandhowitsorbitaroundthesunchangesshape.
Afterall, theyhave a magicbondwiththeStarksandcandetectzombiesthatbeingsaid, Direwolves, spelledlikethisreallydidroamtheearthprowlingtheAmericasbetween 125,000 and 10,000 yearsago.
Huntinginpacks, theytookdownpreyaslargeas a 300 kgmoose.
Soundfamiliar?
NoMontylinesinthesewoods, butunliketheStarksmascot, thesedoggoesnevergrewtothesizeof a smallhorse.