Researchers sample ice to investigate the history of fossil-fuel emissions of methane, based on measurements of another hydrocarbon, ethane, in air trapped in the polar ice sheets in Antarctica. The ancient air resides close to the surface, within the perennial snowpack, and can be used to study changes in the atmosphere that occurred during the twentieth century. Credit: National Science Foundation |
Recent
data from NSF-funded research in both Greenland and Antarctica
demonstrate that fossil-fuel related emissions of both methane and
ethane, two of the most abundant hydrocarbons in the atmosphere,
declined at the end of the twentieth century, according to a paper
published Thursday in the journal Nature.
The
causes of the decline in methane emission rates to the atmosphere have
been puzzling scientists for some time. This new study shows that a
change in human activities may have played a key role in the recent
leveling off of methane, which, being a potent greenhouse gas
contributes to global temperatures.
Murat
Aydin from the University of California, Irvine is the lead author of
the paper. Other researchers include Kristal Verhulst, Eric Saltzman,
Donald Blake, Qi Tang, and Michael Prather from UCI, Mark Battle from
Bowdoin College, and Stephen Montzka from the National Oceanic and
Atmospheric Administration.
The
team investigated the history of fossil-fuel emissions of methane,
based on measurements of another hydrocarbon, ethane, in air trapped in
the polar ice sheets in Greenland and Antarctica. The ancient air
resides close to the surface, within the perennial snowpack, and can be
used to study changes in the atmosphere that occurred during the
twentieth century.
“Fossil
fuels are a common source of both ethane and methane. Methane has many
other sources, but we know most of the ethane in the atmosphere today is
from fossil fuels. If ethane changes, it is easier to figure out the
cause” said Aydin. “After carbon dioxide, methane is the second most
important greenhouse gas. This research was conducted to track ethane
and to see what it could tell us about methane. We found that ethane
emissions declined at the same time as the rise in methane dramatically
slowed, suggesting a common cause.”
At
the end of the 20th century, methane and ethane were deemed valuable
energy resources; collected and consumed as natural gas they are
converted to carbon dioxide. The researchers’ results for this time
frame indicate that the leveling off in atmospheric methane in recent
years is likely linked to this change in energy use.
“This
research helps explain why atmospheric methane levels stabilized at the
end of the twentieth century” said co-author Eric Saltzman. “Methane
levels are important for global climate and understanding how human
activities affect methane is a key part of predicting how much warming
we may expect in the future.”
“We
still have more research to conduct, but this discovery is significant
to our efforts in determining the link between ethane and methane and
what it may tell us about climate change,” said Julie Palais, NSF
program director. “We must work together to continue to find ways to
further our research on this very important subject.”
Recent decreases in fossil-fuel emissions of ethane and methane derived from firn air
