By Uven Chong SLATE
On a sweltering Tuesday afternoon in June in Washington, D.C., President Obama unveiled “a plan to lead the world in a coordinated assault on a changing climate.”
His speech was complemented by a plethora of visual exclamation points.
Acknowledging the heat, Obama took off his jacket and paused several
times to wipe the sweat off his brow. After a first term in which many
environmental supporters felt neglected, the speech suggested that the Obama administration is finally ready to spend some political capital on climate change.
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| Courtesy of Jason Lawrence/Flickr |
A large tenet of Obama’s energy plan is to promote the use of shale natural gas that has recently become accessible due to advances in drilling technology (that is, fracking). This appears to be working. A recent report by the U.S. Energy Information Administration shows that carbon dioxide emissions in the United States are steadily decreasing in large part to the substitution of coal with natural gas. More recently, the Economist has also enthusiastically embraced the potential of natural gas to replace demand for oil.
However, shale exploitation is not without critics, and rightfully
so. In terms of climate change, there are two main objections to shale
gas. One is in the process of digging up the gas and moving it to fuel
stations through pipelines, and the second is in the use of the gas
itself. The former gets most of the attention, but the latter could also
have significant implications, especially if predictions of increased
natural gas vehicle adoption come to fruition.
The exact quantity of so-called “fugitive methane” continues to be hotly debated,
but the good news is that there seems to be an emerging consensus that
containing the leaks is neither difficult nor expensive. In April 2013,
the EPA lowered its estimates
of methane leakage from natural gas production in part due to voluntary
industry-imposed methane control measures, such as better-sealed
replacement gaskets.
But there’s a second problem here, one that hasn’t received nearly as
much attention as fugitive pipeline methane leaks: methane emissions
from in-use natural gas.
Over the past decade, there has been an increase in the adoption of
natural gas vehicles in bus and truck fleets. Most recently in December
2012, the San Diego Metropolitan Transit System Board of Directors
announced a planned $343 million and 500-bus transformation of its transit bus fleet to compressed natural gas. The New York Times recently reported
that there is momentum in the trucking industry to adopt natural gas
vehicles, as the increase in shale gas supply has made the fuel cheap
and economically attractive. As an added marketing incentive, most
transit agencies trumpet their natural gas vehicle investments to burnish their green credentials.
What those bragging campaigns fail to mention, however, are the methane emissions that have been reported by several studies.
The emissions occur when the natural gas is actually combusted to
create energy (such as in the engine of a natural gas vehicle). Just as
hydrocarbons, for example, are belched out by gasoline and diesel vehicles today,
methane is a pollutant that is emitted by natural gas vehicles. Vehicle
emissions are highest when operating conditions are unsteady or
dynamic, such as when a cool engine is first turned on or when an engine
has to speed up. That’s particularly worrisome if natural gas vehicles
like transit buses or freight trucks are operated in urban environments
and are subject to a lot of stops and starts that could result in
methane emissions. One study
of compressed natural gas buses even suggests that when methane is
considered, the total global warming impact for natural gas vehicles
could be greater than current diesel buses. The methane impact
from smaller vehicles (such as passenger cars) is unclear, as most
studies have been conducted on heavy-duty trucks and buses. However,
since the current interest in natural gas vehicles is predominantly
coming from freight and bus companies, tailpipe methane emissions from
these studies are still relevant. Yet, amid the optimism for natural
gas, it seems that these results have been outshined by the bright
promise of a fuel that can ease the tension between economic cost and
environmental protection.
The threat of methane emissions should not necessarily spell the end
of natural gas vehicles. One clear solution is to develop a catalyst
that is able to reduce methane. Catalysts are devices that cause
chemical reactions in a vehicle’s exhaust to eliminate many of the toxic
air pollutants that result from cars and trucks. Much in the same way
that catalysts are used in diesel or gasoline engines to chemically
convert exhaust gases to meet federal emissions limits, a catalyst could
be designed to break down methane to solve this suffocating issue.
But this is easier said than done because existing catalysts are not
effective at reducing methane, a very stable compound that is resistant
to chemical reaction. Researchers at the University of Trieste, the
University of Pennsylvania, and the University of Cadiz recently
published promising findings
of a new catalyst using palladium and ceria that can reduce methane.
The solution is not yet commercially feasible, but the results are
promising. Methane emissions limits
have also been developed by the U.S. EPA and will be implemented
starting with model year 2014 vehicles. These regulatory actions will
spur on new research programs
to comprehensively measure methane emissions from natural gas fleets
and ensure that natural gas is a truly climate-friendly alternative
fuel.
To be clear, there are political, economic, and environmental
advantages to natural gas use, which make it a potentially important
tool in the fight against climate change. But in the context of urban
transportation fleets, we need to be mindful that natural gas could be a
methane-filled Trojan horse, a deceptively veiled prop that ultimately
proves destructive.
