Methane has attracted a lot of
misplaced attention from the global warming crowd and this continues the
tradition. It is sort of amusing to see
the arguments marshaled in the face of a major reversal.
I have argued before that methane
simply does not matter. It is produced
everywhere by the soil in particular and then migrates directly upward out of
harm’s way. In time it is consumed in
the troposphere.
It has always been irrelevant
with no evidence of real accumulation anywhere.
That has not stopped debate however.
UCI studies find different reasons for global methane riddle
by Staff Writers
Two new UC Irvine papers reach markedly different conclusions about why
methane, a highly potent greenhouse gas, unexpectedly leveled off near the end
of the 20th century. They appear in the journal Nature.
Both note that after decades of increases due to worldwide industry and
agriculture, the tapering off of the hazardous hydrocarbon in the atmosphere -
which began in the 1980s - was remarkable.
"It was an amazing mystery as to why this occurred,"
said earth system
science professor Eric Saltzman, a co-author of one paper, which suggests that
reduced use of petroleum and increased capture and commercial use of natural
gas were the driving factors. Huh? What reduction?
A second UCI paper found that water efficiency and heavier commercial
fertilizer use in the booming Asian farming sector provided less fertile ground
for soil microbes that create methane, while at the same time increasing nitrous oxide,
another greenhouse gas.
Associate researcher Murat Aydin, lead author on the first paper,
drilled into South Pole and Greenland glaciers
to extract trapped air as much as a century old. The samples were analyzed for
ethane, a chemical that has some of the same sources as methane but
is easier to track.
"Levels rose from early in the century until the 1980s, when the
trend reverses, with a period of decline over 20 years," Aydin wrote.
"We find this variability is primarily driven by changes in emissions from
fossil fuels."
The authors posit that replacement of oil with lower-priced natural gas
could be key.
The second team measured and analyzed the chemical composition of
methane in the atmosphere from the late 1980s to 2005. They found no evidence
of fewer methane atoms linked to fossil fuel.
Instead, the sharpest trend by far was changes in the Northern
Hemisphere linked to new farm practices, mainly the use of inorganic
fertilizers instead of traditional manure and drainage of fields mid-season.
"Approximately half of the decrease in methane can be explained by
reduced emissions from rice agriculture in Asia over the past three decades,
associated with increases in fertilizer application and reductions in water
use," said lead author Fuu Ming Kai, who wrote his UCI doctoral thesis on
the work and is now with the Singapore-MIT Alliance for Research and
Technology.
Martin Heimann, director of Germany's Max Planck Institute for
Biogeochemistry, was asked by Nature editors to write a commentary on both
papers.
"It is indeed very remarkably rare that two differing studies
about the same subject come out from the same department - I can't think of a
similar case. But I think both analyses are scientifically sound and in
themselves consistent," said Heimann, lead author on the Nobel
Prize-winning Intergovernmental Panel on Climate Change reports.
"At this time I would not favor one over the other."
Heimann has invited members of both teams to a September symposium at
which, he said, "we will discuss the two studies from all angles."
Identifying methane sources is urgent. Research has shown that the
fast-acting greenhouse gas is the second-largest contributor to climate change.
Scientists around the world were heartened by the stabilizing levels, but there
are now signs the hydrocarbon may be on the upswing again.
"We will need to reconcile the differences," said earth
system science professor James Randerson, a co-author on the second paper.
"The important thing is that we must figure out - as scientists and a
society - ways to reduce methane emissions."
Other co-authors on the ethane paper are UCI's Kristal Verhulst, Qi
Tang, Michael Prather and Donald Blake; Mark Battle, from Maine's Bowdoin
College; and Stephen Montzka, from the National Oceanic and Atmospheric
Administration. Additional contributors on the microbial paper are Blake and
retired UCI researcher Stanley Tyler
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