Rising gasoline prices brings usually bring bouts of worry about "peak oil," the idea that petroleum supplies will peak and then inexorably decline, leading to price shocks.
Recent studies have stirred up similar concerns about peak coal. Stop right there. Peak coal? Why would anyone worry about peak coal? Haven't we been told that the U.S. is the Saudi Arabia of coal, with a domestic supply exceeding 200 years?
Maybe not, if new information from the U.S. Geological Survey (USGS) is on the mark. In December, USGS reported the results of its detailed look at the mammoth Gillette field in Wyoming's Powder River Basin, the most productive coal region in the country.
Total coal in place is an estimated 201 billion tons, USGS estimated. That's enough to supply 182 years of domestic use, at current consumption rates.
The news goes downhill from there. Much of the Gillette coal is unavailable, because it's physically inaccessible or because people's stuff is in the way - inconvenient highways, railroads, and cities, for example.
Recoverable coal, then, totals 77 billion tons. That's still enough for 70 years at present burn rates.
The 77 billion tons could be recovered if money were no object. But for coal companies, and any other energy business for that matter, money is the object. They will extract coal to the extent that sales will yield an acceptable rate of return.
USGS plugged the economic factor into the equation. For companies to earn an 8 percent return, only 10.1 billion Gillette tons would be profitable to mine at prices of $10.50 per ton. That was the prevailing price a few years ago. Today, the price for Powder River Basin coal is around $8.75 per ton.
Sure, the price of coal could rise and move more coal into the economical reserves category. But rising coal prices are good news for coal's competitors for generating power - renewables, gas, and nukes.
In 2007, the National Academy of Sciences published a report that also throws cold water on the notion that the U.S. has sufficient coal to last for more than 200 years.
"It is not possible to confirm the often-quoted assertion that there is a sufficient supply of coal for the next 250 years. A combination of increased rates of production with more detailed reserve analyses that take into account location, quality, recoverability, and transportation issues may substantially reduce the number of years of supply," the academy's report noted.
Instead of 250 years, the scientists who wrote the report suggested that the U.S. has enough coal to meet present consumption rates for at least 100 years. Beyond that, nobody knows.
Also in 2007, a group of German scientists calling themselves the Energy Watch Group looked at global coal resources and reserves data. The quality of information that's available isn't particularly good, they concluded, but their analysis suggests that the size of reserves tends to be overestimated.
For the U.S., rising production of Wyoming's sub-bituminous coal has made up for declining production of Appalachian coal. Expressed as energy content, however, the Germans said U.S. coal production has already peaked, since sub-bituminous coal doesn't yield as much energy as the better quality stuff east of the Mississippi River.
Three reports do not a coal supply crisis make. Nevertheless, the federal government ought to follow up its Gillette research with a hard look at how much mineable coal is available nationwide, and consider the implications for climate policy.
If there is a lot of usable coal left, then spending a lot of money on carbon sequestration technology is worth doing. If there isn't, then low-carbon energy sources ought to get the lion's share of the R&D pot.
There's another angle to keep in mind. Estimates on how long a finite resource is expected to last include a critically important caveat that often is overlooked - the resource will last a given number of years at present rates of consumption. If the rates of consumption rise, the resource won't last as long.
Even modest rates of growth will shave a resource's lifetime considerably. If, for example, we have enough coal to last 300 years at current rates of consumption, it will last less than half that long if consumption grows 1 percent per year. Double the growth rate to 2 percent and it lasts less than a century.
As Al Bartlett, the guru of exponential math and resource economics, is fond of noting: "The greatest shortcoming of the human race is our inability to understand the exponential function."
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