- WASHINGTON (AP) -- There may be a bit of good news on the global-warming
front. North America seems to be removing almost 2 billion tons annually
of the excess carbon in the atmosphere.
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- A team of government and university researchers
speculates that the carbon is being soaked up, at least partly, by the
regrowth of plants and vegetation on abandoned farmland and previously
logged forests.
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- But the report, in Friday's edition of
the journal Science, could mean more controversy for the global-warming
debate.
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- In particular, environmentalists worry
that groups opposed to the global climate treaty negotiated last year in
Kyoto, Japan, will use the findings to argue that the United States doesn't
need to reduce emissions of so-called greenhouse gases, as it agreed to
do.
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- "There is a huge concern that this
result will be misinterpreted," ecologist David Schimel of the National
Center for Atmospheric Research in Boulder, Colo., said in a telephone
interview.
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- "I don't believe this result,"
said Schimel, commenting that other research indicates the amount of carbon
taken up by North America can be no more than 700 million tons, rather
than the 1.2 billion to 2.2 billion tons estimated by the new report.
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- Pieter Tans, one of the scientists who
worked on the paper, admitted the "uncertainties are still large."
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- "This is not ironclad. We say in
the paper the evidence is still somewhat tentative," he said.
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- But "we do think that we have used
good models. ... We think we've used data in a proper way. ... We've tried
to look at all the uncertainties, and this is what we get," said Tans,
an atmospheric chemist at the National Oceanic and Atmospheric Administration's
Climate Monitoring and Diagnostics Laboratory in Boulder.
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- Carbon dioxide released by burning fossil
fuels such as coal and oil has been increasing in the atmosphere. That
has led to the conclusion by many scientists that it might cause excessive
warming of the Earth by trapping heat from the sun, somewhat like the glass
of a greenhouse.
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- The measured increase in carbon dioxide
has been less than was expected, leading scientists to wonder where the
excess was going.
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- The Science paper measures carbon dioxide
levels around the world and concludes that whatever is absorbing the gas
is in the temperate region of the northern hemisphere, roughly between
25 degrees and 51 degrees north latitude.
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- Comparing carbon dioxide levels in America,
Europe and Asia led the scientists to believe that the major absorption
is occurring in North America.
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- Regrowth on farmland and previously cut
forests is a strong possibility, since growing plants absorb carbon dioxide,
use the carbon for growth and release oxygen into the air.
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- Tans also speculated that increases in
carbon dioxide have spurred plant growth, which caused them to grow faster
and remove more of the gas from the air. Fertilization by increased nitrogen
in the air might have had the same effect, he said.
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- The analysis looked at carbon dioxide
levels between 1988 and 1992, measured at 63 atmospheric sampling stations.
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- "The current uptake of carbon by
terrestrial ecosystems is helping to slow down the rise of CO2 in the atmosphere,
but we need to know why it is happening. Only then may we be able to project
for how long into the future this process may continue," Tans said.
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- Jerry Mahlman, director of NOAA's Geophysical
Fluid Dynamics Laboratory at Princeton University, a co-author of the paper,
said that while the North American carbon sink may prove important in worldwide
management of atmospheric carbon absorption, its value will come at a global
level, not regional.
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- In addition to Tans and Mahlman, co-authors
of the article in Science are Song-Miao Fan, Emanuel Gloor, Stephen Pacala
and Jorge Sarmiento of Princeton University and Taro Takahaski of Columbia
University's Lamont-Doherty Earth Observatory.
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