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production and the raising of ruminants
(livestock). Natural methane emissions are
primarily from wetlands, but agricultural
sources other than ruminant livestock, e.g.,
rice paddies, also contribute to methane
gas emissions.
During the last glaciation, methane was
found at concentrations of 400 parts per
billion (ppb). After most of the ice left, it
rose to 700 ppb, and now, after the Indus-
trial Revolution, methane has reached con-
centrations of 1,500 ppb.
The cycle of methane emissions is not
as well understood as that of carbon diox-
ide, but climate change itself may soon un-
leash vast natural reserves of methane and
thereby dramatically amplify the green-
house effect. One particular area of con-
cern is the thawing permafrost of the Arc-
tic, especially in the vast tundras of Siberia.
Melting of the ice contained in the soils will
enhance the bacterial degradation of plant
matter long stored in the soils, releasing
not only potentially large volumes of meth-
ane, which is a byproduct of bacterial de-
cay, but also long-dormant carbon dioxide
molecules. The 2008 yearbook of the United
Nations Environment Program warned that
“methane release due to thawing perma-
frost in the Arctic is a global warming wild
card,” meaning that the potential volume
of CH 4 release is very large and very dam-
aging, but when it will be released remains
a myster y.
The second, even larger potential source
for methane gases is the methane hydrates
or methane ice stored in the deep sea. On a
local scale the massive oil spill in the Gulf
of Mexico in 2010 released a lot of meth-
ane ice. In the cold Arctic, methane ice may
be found in ocean waters as shallow as one
hundred meters. Methane hydrates are
huge deposits of methane produced by de-
grading organic matter that are maintained
in a frozen, immobile state by the cold tem-
peratures and high pressures at the bottom
of the deep-water column (usually greater
than one thousand feet). These methane
ice deposits, which hold the potential for
catastrophic global changes, are found on
many continental margins, including those
of eastern North America. They are also an
important exploration frontier for oil com-
panies, which see a huge energy potential
in the deepwater deposits. Smaller but sig-
nificant volumes of methane hydrates exist
on land, beneath permafrost in the Arctic.
As the ocean waters warm or as warm
currents change their trajectory (often a re-
sult of climate change), more and more hy-
drates will be released from the shallower
deposits. Plumes of methane gas bubbles
have been observed coming from the sea
floor on the West Spitsbergen Arctic conti-
nental shelf, and very high concentrations
of methane in seawater have been observed
recently on the East Siberian continental
shelf. According to Natalia Shakhova of the
University of Alaska, eight million tons of
methane escape every year off Siberia, an
amount equal to what was previously as-
sumed to be the total amount of methane
released from all the oceans. In this case
the methane is probably being released
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