[Legate of Amon Lanc]

I think if you ask for the answers of Arda, then it's clear from the Ainulindalë to me, as Elempi said: all the bad things come from Morgoth's marring, for example he was the one who created the unbearable cold and also the... (*interesting, now I had some sort of problem with memory, and could not think of what is the English word for the opposite of cold... but the word that immediately came to my mind, was the Elven word úre. So yup, that's it Interesting, by the way - the Prof would surely be happy if he heard about this, because he'd explain it so that's because I find the word úre suitable for naming that thing *) I imagine it the way that he could misuse any power of Valar, because originally

Originally Posted by Ainulindalë

he had a share in all the gifts of his brethren.

Which is the main point. Or more elaborated

Originally Posted by Valaquenta

Great might was given to him by Ilъvatar, and he was coeval with Manwë. In the powers and knowledge of all the other Valar he had part, but he turned them to evil purposes, and squandered his strength in violence and tyranny.

And we also know Morgoth was expert in twisting things as he wanted, and in making the "illusions" or "tricks", to make something appear differently, to make something look as if it came from Valar but it came from him, for example what I call the "Hunter-trick" to make the Elves be afraid of Oromë and thus disable the possibility of joining him:

Originally Posted by Silmarillion, Chapter 3

And indeed the most ancient songs of the Elves, of which echoes are remembered still in the West, tell of the shadow-shapes that walked in the hills above Cuiviénen, or would pass suddenly over the stars; and of the dark Rider upon his wild horse that pursued those that wandered to take them and devour them. Now Melkor greatly hated and feared the riding of Oromë, and either he sent indeed his dark servants as riders, or he set lying whispers abroad, for the purpose that the Quendi should shun Oromë, if ever they should meet.

So in conclusion, either the catastrophes come from Morgoth himself (when he's present) or are the continuing work of his marring (already "written" in the song).