Other than the poisonous impurities that lurk in coal, which contribute substantially to air pollution, the major problem with it is that coal is almost pure carbon, and it oxidizes into almost pure CO2. All the other fossil fuels are hydrocarbons, of the form CxHy. When you burn them you get CO2 and H2O. Coal is cheap and plentiful compared to other fossil fuels, but we should make every effort to avoid burning it. We should think of it as a reserve energy source, saved for the day when we start running out of petroleum and natural gas. Perhaps by then, we will have developed the technology to burn coal in a more clean and responsible manner.

But we shouldn't be burning it now. There is no such thing as "clean coal". That's just another Big Lie.