Corrections to Estimates of Fossil Fuel Lifetimes Albert A. Bartlett Department of Physics, Box 390, University of Colorado at Boulder, Boulder, CO 80309 The largest estimate in ( 5 )would do the same for
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the J. CHEM.EDUC.staFP (1)for the Chem I ~upplement column. This article contained statements on fossil fuel lifetimes which the JOURNAL later identified ( 2 ) as being "erroneous" or "misleadine." The second note, offered as a "correction" to the first one, contained further statements that are erroneous and misleading. The present article offers corrections to these estimates of fossil fuel lifetimes based on the latest accepted data as well as explanations of the method of estimation. Referring to the U.S., the first of the articles under discussion stated that our supplies of petroleum in oil shale are extremely large, enough to last 7000 years at present rates of crude oil consumption. Our proved coal reserves are enormous (at least 120 billion recoverable tons):these could satisfy present US. energy needs for nearly a thousand years. The statement ahove is reasonably in accord with the following, which is quoted from the principal source ( 3 )cited in (I). US. resources of petroleum in oil shale are extremely large-possibly enough to last 7000 years at present rates of consumption of crude oil and 3000 vears at oresent rates of consum~tionof hvdrocarbons. Our proved coal reserves are enormous a"d could satisfy present US. energy needs for about a millenium. Let us look first a t the data on known oil shale reserves in the
U.S. Dr. M. Kine Huhbert, the eminent world authority on fossil fuel resources, writes, (4) In the higher grade (oil) shale averaging 30-35 gallons per ton in units of more than 25 feet thick and lying less than 1000 feet below the surface, Duncan and Swanson estimated (U.S. reserves oO 160 X 109barrels. Of this they considered about 80 X loy barrels to be recoverable under conditions prevailing in 1965.
One of the large estimates of the recoverable U S . shale oil is 7.6 X 10" barrels ( 5 ) .These estimates of the reserves of oil shale should be compared with "present rates of crude oil consumption." Landsberg reports ( 6 ) "US. petroleum demand" in 1973 was 1.7 X lo7 barrelslday or 6.3 X lo9 barrels/ yr. Thus the estimate of the recoverable oil from shale cited by Hubbert would supply the 1973 rate of crude oil consumption for go -- log- 13 years 6.3 x lo9
The results of these two simple calculations should be compared with the estimate of 7000 years which the JOURNAL staff passed on to its readers (1). Let us now examine the statement from the JOURNAL that says that our coal reserves of 120 billion recoverable tons would satisfv present U S . enerm needs for nearlva thousand years. Coal was mined jn the U ~ Sa. t a rate of 0.6 X lo9 tons/ year in 1973 (7). By 1980 the rate is probably closer to 0.7 X lo9 tonslyear. We can see how long 120 X loytons would allow the estimated present rate of coal mining to continue,
satisfy present U.S. energy needs," wemust multiply the denominator of the above fraction by 5.
This should he compared with the estimate of "nearly a thousand vears" given in the JOURNAL article (1 ). The J o i r ~ ~ ~ L > u b l i s ha e"Correction d to Energy Reserve Estimates" ( 2 ) which said that "Portions o f ' the statement in April 1978 issue "are erroneous or are misleading." The "correction" then cites an estimate of U S . oil shale reserves that is approximately 337 times as large ax the estimate cited by Dr. M. Kine Hubbert and that is approximately 36 times as large as the-largest estimate that &given in the Annual then uses its large Review of Energy, Vol. 1. The JOURNAL estimate of the size of U.S. shale oil reserves to "correct" its earlier estimate by saying that U S . oil shale is sufficient, for about 5400 (not 7000) years," which must be compared with the estimates of 13 to 121 years calculated above. The "correction" goes on to say that The total remaining coal reserves of the U.S. to a depth of 3000 ft are estimated at 1.58 X I0l5 tons.
The JOURNAL attributes this statement to the U.S. Bureau of Mines (8).Compare the ahove statement with the following statement in the Annual Review of Energy (9)
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The total remaining coal resources of the United States to a depth of 3000 ft, determined by mapping and exploration are about 1580 billion tons.
Comparison of these two statements shows that the figure the JOURNALused in its "correction" is larger than the estimate given by the Annual Reuiew of ~ n e r g y k ya factor of exactly 1000! The estimate in the Annual Reuiew is in accord with that given in the authoritative report by Averitt, (10). T h e JOURNAL then concludes its "correction" by saying that if technology is developed to recover as much as one percent of the total U.S. coal reserves or 1.6 X loL3tons, this could satisfy present U.S. energy needs for 4000 years. This author has shown elsewhere (11) that if one uses Averitt's "Reserve Base" of I ' S . roal reimrces, thv mining cot' roal in rht. l1.S. could continue at tht. prment t i l t ? 1~1632years and th,n coal could suoolv "oresent US. enerev needs" ior onlv 126 vears. 'l'he &cle then shows the dramatic drop in theseulifeexpectancies which occur if one nostulates steadv. growth " in the orodnction of US.coal. For example, our present national goal is to try to achieve a growth rate of coal production of 5%per year. If this growth rate could he sustained until the "Reserve Base" was used up, the 632 years (at zero growth) is reduced to 70 years! As science teachers we have an enormous responsibility in regard to the growing shortages of energy. We nked to be well informed, we need to be skeptical, and above all we should never hesitate to do the simple hrithmetic that is necessary to check the predictions of life expectancies of non-renewable resources even when these predictions are made by experts. As a general rule, the more optimistic the prediction, the
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Journal of Chemical Education
greater is the need that it he checked. We must then share with our students our recognition of the urgency of doing this simple arithmetic. We must encourage our students not to accept statements because they come from authoritative sour~es.We must give our students the confidence they need to recognize that only minimal mathematical skills are needed to evakate authoritative statements and to verify them or to prove them wrong. A comprehensive survey is available (11) which sets forth the arithmetic that is needed to understand the energy crisis. It also disolavs . . a collection of authoritative statements that can he proven wrong by arithmetic, and it points out how the uncritical acceptance of these authoritative statements contributes to the widespread national misunderstanding of the energy crisis. Literature Cited Review"1nChern I Supplernml J. CHEM E ~ ~ c . 5 5 . 2 6(April 3 1978). (2) "CorreetiunfoEnoqyResorveEstimates"J. CHEM.EOUC..56. IBBIMarch 1979). (1) ''Energy
(61 Landaberg. H. H..Seionce, 186.247 (April 1974).Tahle 1. (71 Refennce 16).p. 38. Fig. 1. (8) '4frippable R p s e m o f Biturninmu Cml and Lignite in the United States," U.S. Bunau of Mines information Circular, 8531, 148 pp. I1 am unahle to find in this report anything that could be the barla for the statementattributed to it1 (91 Refexnee (3).p. 40. (10) Av8rilt. P.,"Cosl Renource. ofthe United States,January 1. 1974"U.S.Gaolwieal Survey Bulletin 1112,131m..1975. Ill1 Rartlett, A. A., Jour Cool. Ed., 2% 4 (1980):See also Am. Jour. Phyr, 46, 876 (197R1.
