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To Counter Global Warming, Focus
Far More on Methane, a New Study Recommends
Scientists at Stanford have concluded that the EPA has radically
undervalued the climate impact of methane, a “short-lived climate
pollutant,” by focusing on a 100-year metric for quantifying global
warming.
By
Phil McKenna
![](images/images_02_10_2022/methane_orjan-f-ellingvag-corbis-getty-2048x1365.jpg)
Flames from a flaring pit near a
well in the Bakken Oil Field. Credit: Orjan F. Ellingvag/Corbis via
Getty Images
The Environmental Protection
Agency is drastically undervaluing the potency of methane as a
greenhouse gas when the agency compares methane’s climate impact to
that of carbon dioxide, a new study concludes.
The EPA’s climate accounting
for methane is “arbitrary and unjustified” and three times too low to
meet the goals set in the Paris climate agreement, the research
report, published Wednesday in the journal
Environmental Research Letters, found.
The report proposes a new
method of accounting that places greater emphasis on the potential for
cuts in methane and other short-lived greenhouse gasses to help limit
warming to 1.5 degrees Celsius above pre-industrial levels.
“If you want to keep the
world from passing the 1.5 degrees C threshold, you’ll want to pay
more attention to methane than we have so far,” said Rob Jackson, an
earth system science professor at Stanford University and a co-author
of the study.
Methane is the
second-leading contributor to climate change after carbon dioxide but
is a far more potent greenhouse gas.Unlike carbon dioxide, which can
remain in the atmosphere for centuries, methane is a “short-lived
climate pollutant” that stays in the atmosphere for approximately 12
years.
The vastly different
atmospheric lifetimes of methane and carbon dioxide make comparing the
climate impact of the two gasses difficult.
The EPA, following guidance
by the United Nations Framework Convention on Climate Change (UNFCCC),
quantifies how equal amounts of different climate pollutants like
carbon dioxide, methane, and nitrous oxide contribute to warming the
planet over a 100-year period.
The comparison allows
government agencies and the private sector to weigh the relative
impacts of different greenhouse gasses and then determine how much
emphasis to place on reducing their emissions. However, the use of the
100-year yardstick results in a greater emphasis on pollutants like
carbon dioxide that remain in the atmosphere for a relatively long
time and downplays the contribution of short-lived pollutants like
methane, even though they do far more, on a metric ton-for-metric ton
basis, to warm the atmosphere in the short-term.
Sam Abernethy, a Stanford
doctoral student and the lead author of the study, said he became
interested in the “global warming potential” of methane after looking
into why the United States and other countries use the 100-year time
frame.
Abernethy found that the
period of 100 years was an “arbitrary and unjustified” choice adopted
by the Kyoto Protocol, the first binding international climate
agreement, in the 1990s, and used in international reporting and
agreements ever since.
The 100-year measure was
selected for the Kyoto agreement because it was the middle ground
between two other possible time frames—20 years and 500 years—provided
in early reports by the Intergovernmental Panel on Climate Change (IPCC).
“I was confused at how
something so arbitrary could be underpinning so much of climate policy
and how we think about different greenhouse gasses,” Abernethy said.
Over a 100-year period,
methane is 28 times more potent than carbon dioxide as a greenhouse
gas. However, over a 20-year period, a yardstick that climate
scientists have previously suggested would be a more appropriate
timeframe, methane is 81 times more potent than carbon dioxide.
“It’s a huge swing in how
much we value methane, and therefore how many of our resources go
towards mitigating it,” Abernethy said.
However, the use of either
time frame remains largely arbitrary.
To determine a “justified”
time frame, the Stanford researchers took the Paris climate goal of
limiting warming to 1.5 degrees Celsius as a starting point, and then
calculated the most appropriate time frame to meet that goal.
Based on climate models
using scenarios where global warming is limited to 1.5 degrees, they
determined the planet would reach 1.5 degrees of warming above
pre-industrial levels in approximately 24 years.
“If that’s the case, and
you’re using a 100-year frame for methane, then you’re not going to
put enough value on reducing methane emissions compared to other
greenhouse gasses,” Jackson said..
Over a 24 year time period
methane is 75 times more potent than carbon dioxide as a greenhouse
gas. This is three times higher than 25, the current value that the
EPA uses for methane.
“It’s not inherently wrong,”
Abernethy said of the 100-year time frame. “It’s just not aligned with
our current [climate] goal.”
Jackson said that carbon
dioxide remains the most important greenhouse gas. But he added that
additional attention must be paid to methane if the world is to limit
warming to 1.5 degrees Celsius.
Taylor Gillespie, a
spokeswoman for the EPA, defended the agency’s use of a 100-year time
frame and said the relative values they give to different greenhouse
gasses “is separate from the choice of temperature targets.”
The agency’s use of a
100-year time frame is based on international guidelines set by the
UNFCCC, which seeks to ensure uniformity between countries so that
national greenhouse gas inventories reported by all nations are
comparable, Gillespie said.
The UNFCCC did not respond
to a request for comment about the time frame it uses for comparing
the relative climate impacts of greenhouse gasses.
The UNFCCC and international
agreements like the Paris climate agreement, have historically placed
greater emphasis on reducing carbon dioxide to meet climate goals.
However, efforts to reduce methane emissions
played a leading role in the UNFCCC’s international climate
conference in Glasgow in November.
In the runup to Glasgow,
many environmentalists and officials in the Biden administration
argued that a focus on reducing methane emissions would have a much
greater impact in the short-term than the focus on carbon, given how
much more potent methane is, and how much longer carbon stays in the
atmosphere. Focusing on methane, they said, would give governments the
ability to slow global warming in the near-term, while buying
additional time to tackle long-term warming driven by carbon
dioxide..
Steven Hamburg, chief
scientist for the Environmental Defense Fund, said he sees a growing
realization within the UNFCCC of the need to place greater emphasis on
tackling methane emissions alongside carbon dioxide. What’s lacking,
however, is an effort to revise the metrics used to measure the gas’s
relative climate impact, he said.
A 2017 study co-authored by Hamburg and published in the journal
Science called for the adoption of a dual 100-year and 20-year “Global
Warming Potential” or time frame for reporting the impacts of
different greenhouse gasses.
“I think there is no perfect
metric,” Hamburg said of the current study and its call for a 24-year
timeframe synched to limiting warming to 1.5 C. “But they’re trying
to continue to draw attention to the bias that’s inherent to GWP 100.
And that is very real, and very problematic.”
The EPA’s current
global warming potential figure for methane is too low not only
because it uses a 100-year time frame but also because the figure
relies on outdated science, Hamburg said.
IPCC reports released in
2014 and 2021 placed the 100-year climate impact of methane at 28,
while the EPA still relies on a 2007 IPCC report which calculated a
slightly lower value of 25.
“At a minimum, they should
update the numbers,” Hamburg said.
Gillespie, the EPA
spokeswoman, said the agency will begin using a value of 28 for
methane, a 12 percent increase in methane’s climate impact, in 2024,
in line with the UNFCCC international guidelines.
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