What does coal do to the environment?
Nothing, really. Now, BURNING coal has some effects!
Good questions generate better answers, especially on some topics with limited or opposing data.
Coal as a material has been on the earth for a long time. Whatever it does (if anything) it is in equilibrium. When we extract coal to burn as a fuel we are changing the system (not the coal). Mining operations themselves can cause the destruction of local regional flora and fauna and affect watersheds.
Burning the coal for fuel, of course, generates different products (no longer coal). Significant amounts of carbon dioxide and sulfur dioxide (as well as nitrogen oxides) are released into the atmosphere from coal combustion. This may affect the environment with more acidic components and "greenhouse" gas effects.