It all began in the atmosphere.where Carbon Dioxide was created.The carbon cycle
Some of the carbons get to ground and was absorbed by plants.
When an animal eats a plant, it also eats the carbon of it. The breathing of animals can return carbon into the air. And if an animal died(either being killed or died of age), its body decomposes and more carbon was sent back to the sky.
Some carbon was trapped forever underground or ocean and turned to be Coal, oil, or natural gas due to extreme heat and pressure. (that is, until we came along)
One by one, factories burned fossil fuels and release Co2 which should be trapped deep underground forever into the air.
'The world is changed; I can feel it in the water, I can feel it in the earth, I can smell it in the air.' in LOTR) If climate change did happen, we can feel water pollution, desert expansion and air pollution. And this is all caused by ourselves, not any dark spirit!