This site likes to debate the cost effectiveness of clean energy vs. conventional fossil fuels. Most environmentalists argue that fossil fuels wouldn't look so good if "external" costs - i.e., costs due to environmental damage - were factored in. Often the debate is over global climate change which is a complicated issue and certainly hard to prove. Other impacts, such as air and water pollution may be noted. Here in NC we are getting a display of one of those hidden costs - coal ash ponds. An ash pond has sprung a leak and is poisoning a major river. http://abcnews.go.com/US/wireStory/coal-ash-spill-nc-river-contained-22384415 "Since the leak was first discovered by a security guard Sunday afternoon, Duke estimates up to 82,000 tons of ash mixed with 27 million gallons of contaminated water has spilled into the river. Officials at the nation's largest electricity provider say they cannot provide a timetable for when the leak will be fully contained, though the flow has lessened significantly as the pond has emptied."