Landfills, such as this one in Arizona, are sources of human-caused methane emissions. (photo: Alan Levine/flickr)
Oil,
Gas and Cows Culprits in Methane Spike, Study Says
By Bobby Magill, Climate Central
09 October 16
When
trying to figure out why atmospheric concentrations of methane — a potent
greenhouse gas driving climate change — have been rising continuously since
2007, fingers often point to North America’s shale oil and gas boom over the last
decade.
But a National Oceanic and Atmospheric
Administration study published Thursday in
the journal Nature paints a different picture of the role oil and gas have
played in the global methane spike.
The study shows that even though fossil fuels
development has polluted the atmosphere with up to 60 percent more methane than
scientists previously thought, the main culprits behind the rise in global
methane levels are wetlands, landfills, rice fields and belching cows.
Methane is about 34 times as potent as carbon
dioxide in warming the climate over the span of a century. Global methane
emissions have risen and fallen since the 1980s, but have been rising steadily
for the last nine years.
Using an emissions database 100 times larger
than those used before, the scientists set out to update estimates of global
methane emissions. They used the differences in methane isotopes to determine
their sources — fossil fuels, biomass burning, microbes, agriculture and
others.
They found that biological sources such as
cattle, landfills and agriculture account for up to 67 percent of total
human-caused methane emissions.
Study lead author Stefan Schwietzke, a research scientist at NOAA’s
Earth System Research Laboratory in Boulder, Colo., said the team hasn’t been
able to determine which of those biological sources are primarily driving the
methane spike. More research is needed, he said.
The team found that while fossil fuel
development is responsible for more methane pollution than previously thought,
it accounts for just 20 to 25 percent of all the world’s methane emissions.
“We recognize the findings might seem
counterintuitive — methane emissions from fossil fuel development have
been dramatically underestimated — but they’re not responsible for the
increase in total methane emissions observed since 2007,” Schwietzke said.
Over the last decade, the oil and gas industry
has clamped down on methane leaks from wells and pipelines, cutting methane
emissions by up to 8 percent. But a huge boom in oil and gas production during
the same time has balanced those cuts, keeping the industry’s methane emissions
roughly constant, the study says.
“Our study shows that leaks from oil and gas
activities around the world are responsible for a lot more methane than we
thought,” said study co-author Lori Bruhwiler, a NOAA
research scientist. “The good news is that fixing leaking oil and gas
infrastructure is a very effective short-term way to reduce emissions of this
important greenhouse gas.”
Schwietzke said it will be difficult to cut
methane emissions from biological sources until more research is conducted that
pinpoints their specific sources, he said.
“If the microbial methane increase is mainly
coming from cows or agriculture, then we could potentially do something about
it,” he said, adding that if wetlands are the source, global warming itself
could be driving those emissions.
For example, research has shown that thawing
Arctic permafrost is a major source of
methane emissions.
Robert Howarth, a Cornell
University biogeochemist who studies methane emissions and is unaffiliated with
the research, said the NOAA study is an improvement over previous studies
because it uses a much larger set of emissions data than previous studies.
He said the study is one of several recent
papers that have tried to explain the cause of the global methane spike, but
their conclusions have all been different.
For example, a research team led by scientists
in New Zealand published a study in March
suggesting that agriculture is the primary cause of the rise in global methane
emissions. A Harvard study published in
February used satellite data to suggest that the U.S. alone could be
responsible for up to 60 percent of the global increase in methane possibly
because of U.S. oil, gas and cattle operations.
Eric Kort, an assistant professor of climate and
space sciences at the University of Michigan, said the NOAA study is valuable
because of the large size of the database the research team used and their use
of methane isotopes to determine the emissions sources.
The study adds clarity to the conflicting
results of other research, and it shows that because fossil fuels are a large
source of methane emissions, there is a major opportunity to reduce humans’
impact on climate change by cutting oil and gas emissions, he said.
“Fossil fuel emissions are much larger than
previously thought, and thus there is larger mitigation potential than
previously appreciated,” Kort said.
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