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According to M. King Hubbert's Hubbert peak theory, Peak coal is the point in time at which the maximum global coal production rate is reached, after which, according to the theory, the rate of production will enter a terminal decline. Coal is a fossil fuel formed from plant matter over the course of millions of years. It is a finite resource and thus considered to be a non-renewable energy source. There are two different possible peaks: one measured by mass (i.e. metric tons) and another by energy output (i.e. petajoules). The world average heat content per mass of mined coal rose from 8,020 BTU/lb. in 1989 to 9,060 BTU/lb. in 1999. Since 1999, the world average heat content of mined coal has been fairly steady, and was 9,030 BTU/lb. in 2011.〔US EIA, (International Energy Statistics ), accessed 16 May 2015.〕 The estimates for global peak coal extraction vary wildly. Many coal associations suggest the peak could occur in 200 years or more, while scholarly estimates predict the peak to occur as soon as the immediate future. Research in 2009 by the University of Newcastle in Australia concluded that global coal extraction could peak sometime between the present and 2048.〔(【引用サイトリンク】 publisher=The University of Newcastle, Australia )〕 A 2007 study by the German Energy Watch Group predicted that global peak coal extraction may occur sometime around 2025 at 30 percent above the 2005 rate. == Hubbert's theory == The contemporary concept of peak coal follows from Hubbert peak theory, which is most commonly associated with Peak oil. Hubbert concluded that each oil region and nation has a Bell-shaped depletion curve. However, this question was originally raised by William Stanley Jevons in his book The Coal Question back in 1865. Hubbert noted that United States coal extraction grew exponentially at a steady 6.6% per year from 1850 to 1910. Then the growth leveled off. He concluded that no finite resource could sustain exponential growth. At some point, the rate of extraction will have to peak and then decline until the resource is exhausted. He theorized that extraction rate plotted versus time would show a bell-shaped curve, declining as rapidly as it had risen. Hubbert used his observation of the US coal extraction to predict the behavior of peak oil. The Hubbert Linearization using yearly production rates has weaknesses for peak coal calculation, as the signal-to-noise ratio is inferior with coal mining data compared to oil extraction. As a consequence, Rutledge〔 〕 uses cumulative production for linearization. By this method the estimated ultimate recovery results in a stable fit for active coal regions. The ultimate production for world coal is estimated to be 680 Gt, of which 309 Gt have already been produced. However, in 2013 the World Coal Association reported that two different estimates of coal reserves remaining were 1038 and 861 Gt.〔http://www.worldcoal.org/resources/coal-statistics/〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Peak coal」の詳細全文を読む スポンサード リンク
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