Burning coal produces large quantities of air pollution, including mercury, carbon monoxide, sulfur dioxide and nitrogen oxides. And that's not even counting the carbon dioxide, methane and other greenhouse gases that contribute to climate change. That isn't conjecture, it's scientific fact. The only way electricity created by burning coal can be regarded as "cheap" is to ignore these human costs — to effectively subsidize the grid by ignoring premature death, asthma attacks and billions in medical expenses. And even then, coal-fired power is a dubious pursuit given the rise of natural gas and increasingly affordable renewable energy alternatives.