You kind of set off an eternal winter... everywhere.
Anna to Elsa, Frozen
Oh my sweet summer child, what do you know about fear? Fear is for the winter, when the snows fall a hundred feet deep. Fear is for the Long Night, when the sun hides for years and children are born and live and die, all in darkness. That is the time for fear, my little lord, when the White Walkers move through the woods. Thousands of years ago there came a night that lasted a generation. Kings froze to death in their castles, same as the shepherds in their huts, and women smothered their babies rather than see them starve, and wept and felt the tears freeze on their cheeks. So, is this the sort of story you like?
—Old Nan, Game of Thrones
Once upon a time, there was spring, summer, fall and winter. Now there is only winter.
All we know for certain is that Pakistan was fenced in when her two hundred nukes came home. And the wall somehow processed all the radiation. But it was a wall, not a box, and those millions of tons of pulverised dirt and building and human and animal and plant all funnelled straight up, into the atmosphere: nuclear winter. Krishna didn't especially care. The planet could stand to cool down, and he had other work to be getting on with - the re-engineering of India. But for everyone else... well, you know what it was like, Tommy. And our eventual audience will have access to better records about Fimbulwinter. I was the one who attached that term to the long winter, did you know? That position paper that got leaked, I wrote it. Fimbulwinter. Three winters without a summer. The immediate presage to Ragnarok, the final destiny of the gods. Hence, it all kicked off...
The Legendary Realm as a whole is gripped in winter, the great Fimbulwinter of the Last Days. The Winter is less strong in the tropics, strongest in the polar lands, but it reaches everywhere, sapping the strength of the realm's inhabitants. Astrologers of the Realm, noting that the winter began with the coming of the star Anthelios in the heavens, commune with the spirits of the Aetherial Realm for answers, but no answers are forthcoming. The Fimbulwinter is more than a chill of the body; it is a chill of the soul. Entire kingdoms in the north lie gripped in icy shackles, frozen solid and imprisoned in great glaciers that grind down from the ice floes.
—Werewolf: The Apocalypse - Umbra: The Velvet Shadows
Atylwith is a realm locked in the icy embrace of winter; is boughs are ever covered in a thick rime of frost, its glades always heavy with snow. Pale statues line every path, and mark the entrance to every hall. Some of these works are exquisite ice sculptures, shaped by an artisan's patient touch. Others are frost-caged mischievous naiads or spiteful kelpies, imprisoned by Elven magics in punishment for past misdeeds or to prevent future ones. These statues flow and reform when the eye does no rest upon them, the creatures inside ever seeking to escape.
Few forest spirits awaken in this land, for the biting chill lulls them and keeps them slumbering. Most sleep willingly through the centuries, waiting for the arrival of a glorious dawn that will never come.
—Warhammer: Wood Elves Army Book (8th edition)
A ceaseless night brings with it, of course, the cold. With the suns disappearance, temperatures around the world plummet drastically, and continue to drop, while the moons absence results in the loss of tides. The results of the celestial changes have profound repercussions, as air temperatures change abruptly and currents dissipate. Massive thunderstorms split the sky, earthquakes wrack the globe, and titanic hurricanes churn the seas. To most observers, it seems clear that the world is ending.
Soon, as the temperature plummets and the seas calm, storms and quakes give way to silence and stillness or they would, were it not for the ceaseless warfare between the armies of humanity and otherworldly forces. Around the globe, snowfall blankets the ground, lakes freeze, and all of the Earth has become a frozen battleground.
—"Ragnarok - Apocalypse," The End of the World: Wrath Of The Gods