From my book Prescription for the Planet:

Clean coal advocates do their best to convince people that sequestering carbon dioxide is all that needs to be done. Yet greenhouse gases are released during and after the mining process, gases that have no way to be sequestered because they begin to escape into the air as soon as the overburden is stripped away in opencast coal mines. Much of what is uncovered is carbon-rich shale and mudstone, and the methane, carbon dioxide and carbon monoxide that they contain will continue to be released into the atmosphere. Amounts vary depending on the mine, but anyone who tells you that greenhouse gases are no problem if you use clean coal technology and carbon sequestration is not to be trusted. In fact, many coal seams contain so much methane that they are tapped for their methane rather than their coal.  But those coal mines in which the methane is less concentrated simply release their often considerable quantities of methane into the air. Nearly 10 percent of atmospheric methane resulting from human activity is derived from coal mining.

Tom Blees, author of Prescription for the Planet. "Everyone is entitled to their own opinion, but not their own facts."