North America Forests Provide New Clue to World's Carbon Cycle
11/16/98
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Title: North America Forests Provide New Clue to World's Carbon Cycle
Source: U.S. News
Status: Copyrighted, contact source to reprint
Date: 11/16/98
Byline: Laura Tangley
As officials from 170 nations wrangle this week in Buenos Aires over
details of implementing last year's climate-change treaty, their efforts
are hampered by the fact that predicting the impact of global
warming is an imprecise science at best. One unsolved mystery is where
all the carbon dioxide (COy) pumped into the atmosphere ends up. A
controversial new study suggests that North American forests, through the
process of photosynthesis, soak up 1.7 billion metric tons of COy a
year-roughly the same amount the region discharges by burning fossil
fuels.
Scientific uncertainty has plagued the global-warming debate from the
start. Still, a broad consensus has emerged on a few key facts:
Atmospheric gases such as water vapor and COy can trap the sun's infrared
radiation and warm the Earth's surface. Since the Industrial
Revolution, when factories began spewing out the gas, COy in the
atmosphere has increased by 30 percent. Since the late 1800s, global
surface temperatures also have increased, between 0.5 and 1 degree
Fahrenheit, most likely as a result of fossil-fuel burning. But it is
much less certain what will happen next-how much higher temperatures
will rise and how global warming will affect sea levels, rainfall, and
other variables critical to human welfare.
Globally, about 7.1 billion metric tons of COy are released annually by
factories, power plants, and cars, and through deforestation. Of that
total, about 3 billion metric tons end up in the atmosphere and 2
billion tons are thought to be absorbed by oceans. Researchers from
Princeton University's Climate Modeling Consortium may have found
where much of the remaining 2 billion tons end up. In a study published
last month in Science, they fed COy data from dozens of sampling stations
into mathematical models that identified North America as an enormous
carbon "sink."
The study has drawn a chorus of criticism. Environmentalists worry
that opponents of COy controls will use it to argue that the United
States already does its share. Some scientists, meanwhile, question the
models' precision and note that the results conflict with other measures
of COy uptake. Richard Houghton, senior scientist at Woods Hole
Research Center in Massachusetts, says that forest-growth surveys, for
example, show that North American forests soak up only 0.1 billion to
0.2 billion metric tons of COy annually.
But Stanford University climatologist Stephen Schneider is not surprised
by the new results. Because a third of U.S. forests were cleared between
1630 and 1920, it makes sense that trees growing back on abandoned farms
are sopping up huge amounts of COy-at least in the short term. Once these
woodlands mature and COy absorbed through photosynthesis equals that
released through respiration and decomposition, Schneider predicts
that North America again will become a net producer of this greenhouse
gas.