From: Richard A. Kerr, Science
Published March 13, 2009 11:19 AM
Is Peak Oil Almost Here?
To a geologist, gauging how much coal the world has left to burn is a
fairly straightforward, if daunting, business. Millions upon millions of
drill holes have revealed where the coal is. So geologists can just evaluate
each seam's quality and the cost of extraction. Add up all the coal worth
mining and you've got lots and lots--within the United States, a century or
even two of U.S. consumption; globally, 150 years' worth for the world.
But there's another, emerging approach to assessing coal resources that
yields more sobering results. Rather than go into the field, these analysts
go to the record books to see how fast miners have been producing coal of
late. By fitting curves to that production history, they come up with a
number for the total amount of coal that will ever be mined and a date for
the greatest production, the time of "peak coal," after which production
inevitably declines.
Early results from this curve-fitting analysis of production history show
much less coal being mined than geologists ever expected and a peak in coal
production looming as early as a decade from now. Curve fitting "is a worthy
competitor to a geological estimate" of remaining coal, says David Rutledge
of the California Institute of Technology in Pasadena, a nongeologist who
has produced such an estimate himself. Geologists beg to differ. "The whole
notion of applying statistics to time series [of coal production] is fraught
with danger," says energy resource geologist Peter McCabe of the
Commonwealth Scientific and Industrial Research Organisation (CSIRO) in
North Ryde, Australia. "I think what you see in Rutledge's presentation is a
fundamental misunderstanding."
At stake are two central questions: How bad is greenhouse warming likely to
get? And when must alternatives to coal come online? By Rutledge's
calculations, burning all the coal, oil, and gas humans can get their hands
on won't pump enough carbon dioxide into the atmosphere to drive global
warming past 3°C, a far less intimidating ultimate warming than the 8°C or
10°C of some scenarios. But engineers developing energy alternatives would
have only a few decades to get them in place.
Ringing the bell
The growing popularity of curve fitting to fossil fuel production got its
start with geophysicist M. King Hubbert (1903-1989) and his bell-shaped
curves. Hubbert--a prominent researcher at Shell Oil and then the U.S.
Geological Survey--concluded that the rate at which oil was produced would
follow the same bell-shaped curve over time as production from a single
field does (see top figure, attached).
Production in Hubbert's scheme gradually accelerates from the bell's left
side as drillers tap the most accessible, most easily extracted oil pools at
an ever-faster rate. But eventually, no matter how much they drill, it gets
harder and harder to suck out the oil because the remaining pools are fewer,
smaller, deeper, and more difficult to drain. The earlier acceleration now
slows across the crown of the bell until production stops growing, peaking
at the bell's top. It then declines until, at the right side, all the oil
that will ever be produced has been produced.
In 1956, Hubbert published his curve-fitting prediction that U.S. oil
production would peak in the early 1970s. He used the U.S. production
history up to that point to set the shape of the curve and an estimate of
the amount of oil that would ultimately be produced to set the area
encompassed by a complete curve.
U.S. production in fact peaked in 1970, inspiring a generation of oil "peakists"
to apply Hubbert's approach to world oil (Science, 21 August 1998, p. 1128).
As of 1998, they broadly agreed that world oil would reach its peak by now
or at least by the middle of the next decade. In fact, production outside
oil-rich OPEC (Organization of the Petroleum Exporting Countries) has not
risen since 2004, despite years of encouragement by high oil prices. And
total world production has gone nowhere since 2005.
On to coal
In the last couple of years, forecasting coal production by Hubbert's
approach has come into vogue, partly because geologists seemed to be having
trouble assessing how much minable coal was left. For example, "40% of the
world's coal disappeared in 3 years," recalls retired U.S. Geological Survey
coal expert Harold Gluskoter. For the World Energy Council's triennial
survey of coal resources in 1990, China cut its recoverable coal
reserves--the amount of remaining coal geologists believe can be extracted
with today's technology at today's prices--to one-sixth of what it had
reported in 1987. The coal was mostly still there; the Chinese just decided
they could extract only a smaller proportion of it.
Less dramatically, in 2007 a committee of the U.S. National Research Council
that Gluskoter served on could not support the long-standing estimate of
about 267 billion short tons of recoverable reserves in the United States.
Divided by current U.S. production, the old estimate gave the oft-quoted
figure of a 250-year supply for the United States. "We probably have 100
years. We don't know how much after that," says Gluskoter.
Reserve estimates around the world were also coming down, and dividing
estimates of minable coal by current production says nothing about when coal
might peak. To get at both forecasts, analysts tried a variation on curve
fitting à la Hubbert. No results have been published in the peer-reviewed
literature, but Rutledge's effort has probably gotten the widest exposure (
http://rutledge.caltech.edu/ ).
Rutledge, an electrical engineer, adapted a technique used by geologist
Kenneth Deffeyes, professor emeritus at Princeton University, to predict a
world oil peak in 2005. (Deffeyes sees his prediction holding up nicely.) In
the technique, an as-yet-to-peak production history (see bottom graph,
above) is replotted in terms of cumulative production and annual production
in such a way as to produce a straight line, at least if production
approximates an ideal bell-shaped curve. The straight line intercepts the
x-axis at the ultimate production--all the coal that will ever be
produced--and the year in which half of the ultimate production will be
achieved is the year of peak production.
Rutledge tested the method on regions long past their coal peaks. The coal
production of the United Kingdom--once the world's premier energy
supplier--peaked in 1913 and is now at about 6% of its peak. A straight line
makes "a beautiful fit" to the replotted history, Rutledge told audience
members at last December's meeting of the American Geophysical Union. The
projected ultimate production in the United Kingdom is about 28 billion
metric tons of coal, Rutledge said, which should be reached in 8 years.
Geologic estimates made in the 19th century had reserves near 200 billion
tons. In fact, the World Energy Council's geologically based reserve
estimates--provided by the United Kingdom--stayed at 19th century levels
until the 1970s, when they collapsed toward Rutledge's number.
Applied to 14 major coal-producing regions, Rutledge's method gives a world
ultimate production of 660 billion metric tons. That's only one-quarter of
geologic estimates of ultimate production, he says. And when combined with
similar estimates of ultimate production of oil and gas, the total emissions
of carbon as the greenhouse gas carbon dioxide till 2100 are smaller than
any of the 40 emissions scenarios that climate scientists have been working
with for the past 10 years.
As to when coal will peak, Rutledge declines to say, citing the way peak
timing varied widely among regions already well past their peak. He will
say, however, that in his projection the world will have produced a whopping
90% of its coal by 2069. Physicist Mikael Höök of Uppsala University in
Sweden and his colleagues are willing to point to a peak. They have taken a
similar approach to Rutledge's but with some reliance on estimated reserves.
Still, they see world coal production topping out by 2020, entering a
30-year-long plateau, and then declining.
Outside influences
Geologists and resource economists aren't ready to give up on coal so soon.
"The bell-shaped curve is nice to look at after the fact," says Gluskoter,
but "I'm not sure how predictive it is." "You can put me in the skeptical
camp" as well, says physicist and energy analyst Klaus Lackner of Columbia
University. Rutledge "puts too much weight on a simple model," he says. "The
world is not a two-parameter curve."
U.K. coal "did not decline because it reached some magic percentage of coal
depletion," argues CSIRO's McCabe. "Gradually, [U.K.] demand disappeared.
Coal was no longer used for power, steamships, railroads, domestic heating,
or iron and steel production. When I was a kid in England many years ago,
gas for the home was produced from coal. There are much cheaper alternatives
in the U.K. for energy." Natural gas from the North Sea replaced coal gas in
the home, he notes. Relatively inexpensive--and cleaner-burning--oil became
available.
Does it matter why coal production behaves as it does? responds Rutledge.
Whether it's a physical lack of resources or a demand shift to cheaper, more
attractive sources, a limit is a limit. Gluskoter and many colleagues are
betting on a demand shift. "I believe in technology," he says. But first,
technology could actually stretch coal resources. "The resource is there,"
he notes, "it's perfectly minable. It's just not economical right now."
Improved technology will let miners get at thinner, less accessible seams,
he says; uneconomic coal might even be turned into gas right in the ground.
Despite any coal added by technology, "we'll stop using coal before we run
out of it," says Gluskoter. Just as cleaner, cheaper fuels displaced British
coal, less-polluting, less-expensive energy sources will replace coal
worldwide, he argues. His bet is on solar energy. Plenty of usable coal will
be left in the ground, he adds, but "we're not going to be burning coal in a
couple hundred years."
2009. Copyright Environmental News Network To
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