Worrying New El Nino Effect Seen in Amazon Rainforests
12/16/98
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Title: Worrying New El Nino Effect Seen in Amazon Rainforests
Source: Inter Press Service
Status: Copyright 1999, contact source for permission to reprint
Date: December 16, 1998
WASHINGTON, (Dec. 16) IPS - The El Nino weather phenomenon
may be causing rainforests in the Amazon Basin to emit the
heat-trapping gas carbon dioxide, rather than absorbing it,
say scientists.
Normally the world's largest tropical rainforests act as a
natural sponge or "sink" -- soaking up carbon dioxide which
most scientists believe is one of the "greenhouse" gases
that causes global warming.
But during the years of El Nino -- the warm tropical current
that appears in the Pacific -- the drier and warmer weather
in the Amazon caused the tropical rainforest to emit, rather
than absorb, large amounts of carbon, according to a new
study published today in the scientific journal Nature.
"When soil becomes dry during the El Nino phenomenon plants
seem to respire less and absorb less carbon," says Hanqin
Tian, a researcher at the Marine Biological Laboratory, in
Woods Hole, Massachusetts. "Soil also stores less carbon
when it is dry."
Such new observations on the flow of carbon are being
closely watched by scientists worldwide as governments
debate how they can get credit for preserving forests as
natural 'sinkholes' for greenhouse gases -- part of an
international strategy to reduce the threat of global
warming.
Most scientists believe that these gases, mainly resulting
from the burning of oil, coal and gas, are responsible for
heating the earth's surface.
If current trends continue, average global temperatures
could rise between one and 3.5 degrees centigrade by the
year 2050. The increase in temperatures could have major
climatological and environmental effects, ranging from an
increasing intensity of storms to flooding and
desertification, scientists say.
In Kyoto, Japan last December, industrialized nations agreed
to reduce the emissions of six greenhouse gases -- including
carbon -- by an average of six percent from 1990 levels, and
to complete
the reductions between 2008 and 2012.
The Kyoto Protocol, as the basic framework of the treaty is
known, provides industrial countries the option to offset
their greenhouse emissions by counting the carbon absorbed
by their forests and other ecosystems that absorb carbon
dioxide, termed "carbon sinks."
Yet, at these negotiations many scientists argued that they
did not understand the carbon cycle in its entirety well
enough to predict how much carbon forests absorb or if the
carbon absorbed by forests would remain there, notes Ashley
Mattoon, a researcher at the Washington-based Worldwatch
Institute.
"In their view, carbon sinks shouldn't have been entered
into the treaty until more solid data on them had been
collected." According to the latest report in Nature
magazine, researchers found that, overall, the Amazon was a
carbon sink from 1980 to 1994. But, year to year the amount
of carbon the lush tropical vegetation mops up varied
greatly, depending largely on how dry and hot the region
becomes during the periodic appearance of El Nino.
Using data on vegetation, soil, temperature, and
precipitation, the study reveals that the three strongest El
Nino events (in 1982-83, 1986-87, and 1991-92) corresponded
with when the region acted as a weak sink or as an actual
source of carbon.
In 1987 and 1992 -- when El Nino made the region much drier
and warmer -- the region actually added 0.2 petagrams of
carbon to the atmosphere. One petagram of carbon equals one
billion metric tons of carbon.
In the non-El Nino years of 1981 and 1993, however, the
region stored away 0.7 petagrams of carbon. In comparison,
researchers said the deforestation in the Amazon in the
early 1990s added 0.3 petagrams of carbon per year to the
atmosphere.
Soil moisture, which is affected by both precipitation and
temperature, and which affects both plant and soil
processes, seemed to be an important factor concerning
carbon storage, according to the study.
"Increased temperature from El Nino is not as important as
the impact of dryness," says Hanqin Tian, who designed the
scientific model for which the study was based. "The real
problem is the lack of moisture."
Drier soil is believed to decrease the rate at which plants
respire and take in carbon. Lack of moisture in the soil
also increased the rate at which the soil emits carbon, he
says.
The increasing amount of carbon concentration in the
atmosphere also was believed to impact whether carbon was
absorbed or emitted, he added. Such concentrations affect
the ability of plants to photosynthesize but "the impact of
carbon dioxide concentration needs to be studied more," says
Tian.
Despite the year-to-year fluctuations caused by weather
changes, overall these areas absorb carbon from the
atmosphere and therefore need to be protected.
"It is really important to protect tropical forests because
when we cut them down they cannot function as a sink," he
says.