After the advent of petroleum oil as the leading source of electrical power, coal's importance diminished. However, coal has recently experienced a "comeback," both because of the Middle East oil crisis of the 1970s and because of a new development called "Clean Coal Technology."

Clean Coal Technologies (CCTs for short) are processes of refining coal to create cleaner, more efficient energy. With CCTs, emissions such as sulfur dioxide and nitrogen dioxide are reduced, thus cutting back on pollution from coal combustion.

The implications of CCTs are extensive. Only time will tell how much further countries around the world will choose to exploit the remaining coal supplies here on earth, but it is certain that CCTs will play a role in any future in coal.