Rainforest Fails to Absorb Excess Carbon During El Nino
12/22/98
OVERVIEW & COMMENTARY by EE
A recently published study by Woods Hole Research Laboratory in the
journal Nature suggests that the Brazilian Amazon actually releases
millions of tons of carbon during El Nino years, the reverse of what
is usually the case--and some 2/7 of what it usually fixes in a year.
This may have tremendous implications for global climate change.
g.b.
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RELAYED TEXT STARTS HERE:
Title: Rain Forest Fails to Absorb Excess Carbon during El Nino
Source: Associated Press
Status: Copyright 1998, contact source for permission to reprint
Date: December 17, 1998
Byline: JOSEPH B. VERRENGIA AP Science Writer
Instead of inhaling extra carbon dioxide, Brazil's rain forest does
the opposite in an El Nino year, exhaling millions of tons of the
heat-trapping gas and potentially adding to global warming, scientists
say.
The rain forest, under normal conditions, acts as the "lungs" of the
planet. Its dense canopy of trees stretches for thousands of miles,
releasing oxygen and absorbing as much as 700 million tons of carbon
dioxide a year.
But when global climate conditions are scrambled by El Nino and the
rain forest becomes parched, scientists from the Woods Hole Research
Laboratory in Massachusetts determined the Amazon Basin produces as
much as 200 million tons of excess carbon dioxide a year.
The calculations by Hanqin Tian and others are in today's journal
Nature. The study examined three El Nino episodes from 1980 to 1994.
It did not 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 step in accurately predicting -- and managing -- global warming
in the 21st century.
Some studies show global temperatures have been creeping up by as much
as one degree 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.
Many natural features on the planet act as "carbon sinks" to absorb
excess carbon and help to stabilize the planet's climate. The oceans
and the rain forests absorb the largest shares, along with tundra and
rangeland.
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, Tian said.
His 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.
Several groups of scientists are trying to understand the world's
carbon cycle.
Last week, researchers launched a three-year study to find the
"missing sink" to account for lower-than-expected carbon dioxide
levels in the Northern Hemisphere. A likely suspect: trees that have
regrown in previously logged forests and farmland.
"Something in the Northern Hemisphere is sucking up the carbon," said
climatologist Kevin Gurney of Colorado State University. "The missing
sink isn't new, but where it is located and how it works are still
unresolved."
Because of the hemisphere's large cities and industrialization, carbon
dioxide levels are expected to be higher. But measured carbon
emissions have been 2 billion tons lower than expected in recent
years.