Much of the coal comes from a unique period in earth's history when there were many trees, but enzymes that could deal with lignins hadn't yet evolved. Which le

Much of the coal comes from a unique period in earth's history when there were many trees, but enzymes that could deal with lignins hadn't yet evolved. Which led to a steady and significant accumulation of carbon in that coal. Humans, and much of the life we see around us, evolved in the subsequent periods of higher oxygen and depleted CO2. As we reverse that effect, we return the atmosphere nearer to how it once was - when humans and such weren't around. The planet and its life will be fine. Us and the multiple species on which we depend may well not be. By burning it we are releasing carbon that has been stored for millennia and accumulated over millennia. It's introduced as though it were new into our carbon cycle.