Amazon's Climatic Role
12/21/98
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RELAYED TEXT STARTS HERE:
Title: Amazon's Climatic Role, Forests a Sink for Greenhouse Gases
- Usually
Source: The Associated Press
Status: Copyright 1999, contact source for permission to reprint
Date: December 21, 1998
Byline: By Joseph Verrengia
Instead of inhaling extra carbon dioxide, Amazon's rain forest does
the opposite in an El Nino year, exhaling hundreds of millions of tons
of the heat-trapping gas and potentially adding to global warming.
Under normal conditions, rain forests act as the "lungs" of the
planet. Plants absorb carbon dioxide as they photosynthesize,
transforming it into leaves and wood, while decaying plants and trees
release the carbon back into the air.
In the dense canopy of tropical forests, the amount of carbon dioxide
absorbed by living plants is a little more than the amount released by
dying ones - a net "sink" of perhaps as much as 700 million tons of
carbon a year.
Plants and Weather
But when El Nino scrambles the global climate, the rain forest becomes
parched. The carbon balance shifts, with the release of carbon dioxide
by decaying plants outpacing the absorption. According to their
computer models an area two-thirds the size of the U.S. plays a
crucial role in global climate.
Woods Hole Researh Laboratory in Massachusetts determined the Amazon
Basin forests may expel as much as 200 million tons of excess carbon
in an El Nino year.
The calculations by Hanqin Tian and others appear in Thursday's
journal Nature.
"It's a nice study," said Inez Fung, director of the Center for
Atmospheric Sciences at University of California, Berkeley. "But all
models by definition are incomplete."
For example, the Woods Hole model did not take into account the
effect of fires.
The study examined three El Nino episodes from 1980 to 1994. It
didn't include measurements of the record-setting El Nino in
1997-98, but the trend is clear, researchers said.
"In El Nino years, which bring hot and dry weather to much of the
Amazon, the ecosystems act as a source of carbon," Tian said.
Scientists say understanding the planet's fluctuating carbon cycle is
a key in accurately predicting - and managing - global warming in the
21st century.
An Uncertain Future
Some studies show global temperatures have been creeping up as
industry, traffic, deforestation and other human activities generate
more carbon dioxide and other greenhouse gases - so called because
they trap heat from the sun.
Each year, the burning of oil, gas and coal around the world sends 7
billion tons of carbon, mostly in the form of carbon dioxide, wafting
into the air. Clearing and burning of tropical rainforests releases
another 1 billion tons. But only half the carbon remains in the air.
Many natural features on the planet act as "carbon sinks" to absorb
excess carbon and help to stabilize the planet's climate. Oceans
absorb about 2 billion tons of the carbon, and scientists suspect
forests absorb most of the remaining 2 billion
tons.
But not always.
During an El Nino, a vast pool of warm water expands in the equatorial
Pacific. It upsets weather patterns around the world. In the Amazon,
it triggers severe droughts.
Under such severe stress, the forest can't adequately photosynthesize
and store carbon dioxide.
Model Misses Details
The Woods Hole results correspond with the results of carbon cycle
simulation developed at the Max Planck Institute in Germany, which
developed a computer model showing the Amazon acting as a carbon
source during three El Nino episodes between 1982-94.
Researchers at Max Planck said the Woods Hole study is based on
limited field measurements in a small sampling area, and failed
to answer the fundamental question of what is canceling the rain
forest's role as a carbon sink.
"Such understanding is crucial for long-term predictions," said Colin
Prentice, who, with Planck colleague Jon Lloyd, reviewed the new
study for Nature.