Government agencies have estimated that there is about 850 billion to 998 billion tons of coal in the ground that can be economically recoverable.
Not so, says David Rutledge, the Kiyo and Eiko Tomiyasu Professor of Engineering at Caltech, who has done his own estimates and showed them off this week at the American Geophysical Union in San Francisco.
Rutledge estimates that the Earth had only 662 billion tons of recoverable coal in the first place and around 59 percent of the total remains. Thus, the real estimate of existing reserves is closer to 400 billion tons. (The earth, he added, contained the equivalent of 1 trillion tons of oil before the industrial age began.) He came to the conclusion by analyzing production data, similar to how M. King Hubbert in 1956 predicted U.S. oil production would peak in 1970. It peaked in 1971.
That number, to some degree, is good news for the renewable power industry. Nearly 400 tons of coal would be enough to provide electricity for decades. It would also add huge amounts of pollution to the atmosphere. Still, it makes a peak for coal more tangible and realistic and thus can prompt policy makers and investors to take even more interest in things like solar thermal power or nuclear.
How come his estimates differ so much from the officially sanctioned ones from government? Secrecy and national pride play a huge part. Russia analyzes its own coal estimates but the real number is treated as a state secret.