November 20, 2006
LEVEL
OF IMPORTANT GREENHOUSE GAS HAS STOPPED GROWING
Scientists at UC
Irvine have
determined that levels of atmospheric methane – an
influential greenhouse gas –
have stayed nearly flat for the past seven years, which follows a rise
that
spanned at least two decades.
This
finding indicates that
methane may no longer be as large a global warming threat as previously
thought, and it provides evidence that methane levels can be
controlled.
Scientists also found that pulses of increased methane were paralleled
by
increases of ethane, a gas known to be emitted during fires. This is
further
indication that methane is formed during biomass burning, and that
large-scale
fires can be a big source of atmospheric methane.
Professors
F. Sherwood Rowland
and Donald R. Blake, along with researchers Isobel J. Simpson and
Simone
Meinardi, believe one reason for the slowdown in methane concentration
growth
may be leak-preventing repairs made to oil and gas lines and storage
facilities, which can release methane into the atmosphere. Other
reasons may
include a slower growth or decrease in methane emissions from coal
mining, rice
paddies and natural gas production.
“If
one really tightens
emissions, the amount of methane in the atmosphere 10 years from now
could be
less than it is today. We will gain some ground on global warming if
methane is
not as large a contributor in the future as it has been in the past
century,”
said Rowland, Donald Bren Research Professor of Chemistry and Earth
System
Science, and co-recipient of the 1995 Nobel Prize for discovering that
chlorofluorocarbons in products such as aerosol sprays and coolants
were
damaging the Earth’s protective ozone layer.
The
methane research will be
published in the November 23 online edition of Geophysical
Research Letters.
Methane,
the major ingredient in
natural gas, warms the atmosphere through the greenhouse effect and
helps form
ozone, an ingredient in smog. Since the Industrial Revolution in the
late
1700s, atmospheric methane has more than doubled. About two-thirds of
methane
emissions can be traced to human activities such as fossil-fuel
extraction,
rice paddies, landfills and cattle. Methane also is produced by
termites and
wetlands.
Scientists
in the Rowland-Blake
lab use canisters to collect sea-level air in locations from northern Alaska to southern New
Zealand. Then, they
measure the
amount of methane in each canister and calculate a global average.
From
December 1998 to December
2005, the samples showed a near-zero growth of methane, ranging from a
0.2
percent decrease per year to a 0.3 percent gain. From 1978 to 1987, the
amount
of methane in the global troposphere increased by 11 percent
– a more than 1
percent increase each year. In the late 1980s, the growth rate slowed
to
between 0.3 percent and 0.6 percent per year. It continued to decline
into the
1990s, but with a few sharp upward fluctuations, which scientists have
linked
to non-cyclical events such as the eruption of Mt. Pinatubo
in 1991 and the Indonesian and boreal wildfires in 1997 and 1998.
Along
with methane, the UCI
scientists also measured levels of other gases, including ethane, a
by-product
of petroleum refining that also is formed during biomass burning, and
perchloroethylene, a chlorinated solvent often used in the dry cleaning
process. Ethane levels followed the peaks and valleys of methane over
time, but
perchloroethylene had a different pattern. This finding provides
evidence that
biomass burning on occasion, as in Indonesia
in 1997 and Russia
in 1998, can be a large source of atmospheric methane.
The
researchers say there is no
reason to believe that methane levels will remain stable in the future,
but the
fact that leveling off is occurring now indicates that society can do
something
about global warming. Methane has an atmospheric lifetime of about
eight years.
Carbon dioxide – the main greenhouse gas that is produced by
burning fossil
fuels for power generation and transportation – can last a
century and has been
accumulating steadily in the atmosphere.
“If
carbon dioxide levels were
the same today as they were in 2000, the global warming discussion
would leave
the front page. But to stabilize this greenhouse gas, we would have to
cut way
back on emissions,” Rowland said. “Methane is not
as significant a greenhouse
gas as carbon dioxide, but its effects are important. The world needs
to work
hard to reduce emissions of all greenhouse gases.”
NASA
and the Gary Comer Abrupt
Climate Change Fellowship supported this research.
##
Contact:
Jennifer
Fitzenberger
University of
California-Irvine
949-824-3969
jfitzen@uci.edu
This text derived from:
http://today.uci.edu/news/release_detail.asp?key=1549
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