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America's Leaky Natural Gas System Needs a Fix
updated: Feb 13, 2014, 12:30 PM
Source: University of California Santa Barbara
The first thorough comparison of evidence for natural gas system leaks confirms that organizations,
including the Environmental Protection Agency (EPA), have underestimated methane emissions in the
United States, as well as those from the natural gas industry. The review, published in the Feb. 14 issue of
the journal Science, synthesizes diverse findings from more than 200 studies ranging in scope from local
gas processing plants to total emissions from the United States and Canada.
Natural gas consists predominantly of methane. Even small leaks from the natural gas system are important
because methane is a potent greenhouse gas - about 30 times more potent than carbon dioxide.
"People who go out and actually measure methane pretty consistently find more emissions than we
expect," said lead author Adam Brandt, an assistant professor of energy resources engineering at Stanford
University. "Atmospheric tests covering the entire country indicate emissions around 50 percent more than
EPA estimates - and that's a moderate estimate."
One possible reason leaks in the gas industry have been underestimated is that emission rates for wells and
processing plants were based on operators participating voluntarily. One EPA study asked 30 gas
companies to cooperate, but only six allowed the EPA on site.
"This study very clearly validates that there is much higher emission than what has been predicted," says
co-author Galen Stucky, a professor in the Department of Chemistry at UC Santa Barbara. "In the end, I'm
not too surprised that the inventory did not match actual emissions. The black holes are primarily what are
called high emitters, and the big question is exactly where those emissions are coming from?"
The standard approach to estimating total methane emissions is to multiply the amount of methane
thought to be emitted by a particular kind of source, such as leaks at natural gas processing plants or
belching cattle, by the number of that source type in a region or country. The products are then totaled to
estimate all emissions. The EPA does not include natural methane sources such as wetlands and geologic
The national natural gas infrastructure has a combination of intentional leaks, often for safety purposes,
and unintentional emissions, such as faulty valves and cracks in pipelines. Emission rates of particular U.S.
gas industry components - from wells to burner tips - were established by the EPA in the 1990s.
Since then, many studies have tested gas industry components to determine whether the EPA's emission
rates are accurate, and a majority of these have found the EPA's rates too low. The new analysis does not
try to attribute percentages of the excess emissions to natural gas, oil, coal, agriculture, landfills, etc.,
because emission rates for most sources are so uncertain.
Several other studies have used airplanes and towers to measure actual methane in the air in order to test
total estimated emissions. The new analysis found these atmospheric studies, which cover very large areas
consistently, indicate total U.S. methane emissions are between 25 and 75 percent higher than the EPA
Some of the difference is accounted for by the EPA's focus on emissions caused by human activity.
However, in addition to excluding natural methane sources, the EPA also omits some emissions caused by
human activity, such as abandoned oil and gas wells, because the amounts of associated methane are
Natural gas as a replacement fuel
Authored by researchers from seven universities, several national laboratories and federal government
bodies and other organizations, the new analysis shows that even though the gas system is almost certainly
leakier than previously thought, generating electricity by burning natural gas rather than coal still reduces
the total greenhouse effect over 100 years. Not only does burning coal release an enormous amount of
carbon dioxide, but mining it releases methane.
Perhaps surprisingly, the analysis finds that powering trucks and buses with natural gas instead of diesel
fuel probably makes the globe warmer, because diesel engines are relatively clean. For natural gas to beat
diesel, the gas industry would have to be less leaky than the EPA's current estimate, which the new study
determines is improbable.
"Fueling trucks and buses with natural gas may help local air quality and reduce oil imports, but it is not
likely to reduce greenhouse gas emissions," Brandt said. "Even running passenger cars on natural gas
instead of gasoline is probably borderline in terms of climate."
According to the authors' analysis, the natural gas industry must clean up its leaks to really deliver on its
promise of less harm. Fortunately for gas companies, a few leaks in the gas system probably account for
much of the problem and could be repaired. One earlier study examined about 75,000 components at
processing plants. It found some 1,600 unintentional leaks, but just 50 faulty components, were behind 60
percent of the leaked gas.
"If you look at how energy is used, there is a huge amount of it that's wasted," Stucky said. "What needs to
be done is to better identify the discrepancies between our invoices and what we actually observe in the
atmosphere. Our analysis identifies the problem and that is an important first step."
Other co-authors are Garvin Heath, a senior scientist at the National Renewable Energy Laboratory; Eric
Kort, an atmospheric science professor at the University of Michigan; Francis O'Sullivan of the MIT Energy
Initiative; Gabrielle Pétron of the National Oceanic and Atmospheric Administration (NOAA) and the
University of Colorado; Sarah M. Jordaan of the University of Calgary; Pieter Tans of NOAA; Jennifer Wilcox
of Stanford University; Avi Gopstein of the U.S. Department of State; Doug Arent of the National Renewable
Energy Laboratory and the Joint Institute for Strategic Energy Analysis; Steven Wofsy of Harvard University;
Nancy Brown of the Lawrence Berkeley National Laboratory; independent consultant Richard Bradley;
Douglas Eardley of the University of California-Santa Barbara; and Robert Harriss, a methane researcher at
the Environmental Defense Fund.
The research was funded by the nonprofit organization Novim through a grant from the Cynthia and
George Mitchell Foundation.
View the full story at News.UCSB.edu
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