In the creation that took place in Ginnungagap we were introduced to the primal ice first, and so it is when the worlds are to be destroyed, at least in a sense. This is the second Fimbulwinter, where the elements themselves begin to turn against the divine order and rip apart the landscapes of our planet and beyond. The first Fimbulwinter took place in the Ancient Time (Ár Alda), when Volund turned against the Gods, Frey and Freya were handed over to the Etins, and Idun, along with her apples, went missing from Asgard. This is likely a mythic rendition of the Ice Age that took place long ago.
Such an Ice Age is foretold to take place again right before the final battle:"Then will come the second Fimbulwinter. Snow will drive in from all directions; the cold will be severe and the winds will be fierce. The sun will be of no use. Three of these winters will come, one after the other, with no summer in between. But before that, there will have to be another three winters with great battles taking place throughout theworld." (LXXXI.3)The moon will either be outright destroyed or permanently hidden, for we are told that it will be eaten by Hati Managarm, and the sun will be spattered by its blood. "Because of this, the sun will lose its brightness, becoming black for summers hereafter" (LXXXI.2). This may refer to an eclipse of some sort, or perhaps even a complete breakdown of our stratosphere, the skies filling with poisonous clouds that will black out the sun and moon indefinitely. We are then told that the wolf "Skoll will capture Sol and offer her to Fenrir. The wolf will swallow the sun and mankind will think it has suffered a terrible disaster"(LXXXII.2).
The wolves are perhaps personifications of these deadly clouds, such as the one's seen during volcano eruptions (when Vesuvius erupted in 79 CE, burying the towns of Herculaneum, Pompeii, and Stabiae in ash and lava, its ash cloud blackened out the sun for several years). The reason we cannot assume that the sun and moon will be completely destroyed here is because the battle is said to continue after this. We know that if the sun and moon are eliminated there will be no battle, because Midgard would be immediately annihilated by such an event. We would lose our orbital direction, our planet would instantly freeze over, all oxygen would vanish, and nothing would be left alive. If the sun exploded we would be engulfed in the flames and reduced to cinders. It is possible that we will lose these celestial bodies in the nearer future, but our vision of the end could be something else altogether.
There are some scientists who predict that we are heading towards another Ice Age, which would be catastrophic for humankind. Whether or not this will be the Fimbulwinter we are here describing is anyone's guess, but we do know that occasionally we will experience polar shifts that can cause severe change in our climate. We accept that such an event is likely, and will face it courageously when it comes, for this is a part of the natural life-cycle of our world. Although we must be wary of those who mislead us for the purposes of a political agenda, we do understand the role that we play when it comes to conserving our natural resources. We are responsible for this planet, for we are its ultimate caretakers, but at the same time we must be able to accept that cataclysmic events will occur, no matter what we do or have ever done.