[Aganzir]

Originally Posted by Inziladun

And now, on to the Middle-earth Climate Change debate: natural, or Morgoth made?

From the Silmarillion, it seems very clear Morgoth is responsible for a lot of the climatic unbalance in the First Age and before (as well as a number of natural catastrophies)! While we have to keep in mind the Silmarillion is mostly written from the Noldor's point of view and they are very unreliable narrators, especially when it comes to Morgoth, a few quotes from the pre-Noldor era need to be brought up in this context.

Originally Posted by Ainulindalë

...and the light of the eyes of Melkor was like a flame that withers with heat and pierces with a deadly cold.

The combination of unexpected heat/cold exists from the very start. These seem to be among Melkor's dominant passions.

Originally Posted by Ainulindalë

He hath bethought him of bitter cold immoderate, and yet hath not destroyed the beauty of the fountains, nor of my clear pools. Behold the snow, and the cunning work of frost! Melkor hath devised heats and fire without restraint, and hath not dried up thy desire nor utterly quelled the music of the sea. Behold rather the height and glory of the clouds, and the everchanging mists; and listen to the fall of rain upon the earth!

It seems very much that not only did Melkor create ice and clouds, but the Climate Change was brought into the Music as part of his discord.

Originally Posted by Of the Beginning of Days

And seeing now his time he drew near again to Arda, and looked down upon it, and the beauty of the Earth in its Spring filled him the more with hate.

And so was the Spring of Arda marred - Melkor seemed to hate everything in its natural state. His need to corrupt reached even the nature and, I would argue, the climate.

Originally Posted by Of Tuor and His Coming to Gondolin

Slow was their going by twilight or by night in the pathless wilds, and the fell winter came down swiftly from the realm of Morgoth.

This quote implies Morgoth had indeed some control over the climate. Of course the phrasing could be a result of Thangorodrim's northern location, but given Morgoth's earlier pendant for fine-tuning the weather, we can't rule out the option that the fell winter (and other such occasions) were entirely his doing. After all, we know even Saruman, who is considerably less mighty than Morgoth, could do all sorts of things with the weather.

Also, think about the fires they burned in Angband and Morgoth's other strongholds. Think about the dragons and the balrogs. It's not far-fetched at all to say that a horde of these spirits of fire could have raised the average temperature in Middle-earth by a couple of degrees during their main era of wreaking havoc.

Based on this, I'm led to the conclusion that the Peoples of Middle-earth had very little to do with the changes in the climate, but it was mostly the Enemies' doing. They played a major part in teaching Men and Hobbits the art of pollution, too - mainly Saruman here, what with everything he did at Isengard and in the Shire.