Smoke

Although the Cave Goblins had sucked all the colors out of Nature, their thirst seemed unquenchable
Now they built huge plants in order to produce artificial colors
Smoke poured out of the factory chimneys, and darkened the sky
Sun was no longer able to penetrate the smoke, and it was always dusk
Corrosive vapors lay over the land
The air became stuffy, breathing more difficult

At first the White Goblin had watched the activities of the Cave Goblins with astonishment, but soon with increasing alarm
When he advised moderation they laughed
Then, in their sickness, drove him back to his glacial world