Year-to-year changes in concentration of carbon dioxide
and methane, two important greenhouse gases in the atmosphere,
can be linked to fire activity associated with the El Nino-La
Nina cycle, according to a study conducted by a team of NASA
scientists and other researchers.
Study results appear in an article in the Jan. 2, 2004, issue
of Science. “Many scientists have attributed this atmospheric
variability to changes in the balance between plant growth and
microbial respiration,” said James Randerson of the University
of California-Irvine, one of the study’s authors. “Our work
indicates, however, that the sum of these two processes has a
smaller impact on atmospheric carbon dioxide levels than
previously believed.”
The scientists also determined almost all the increased levels
of carbon dioxide and methane measured during 1997 and 1998
could be attributed to the worldwide fires at the time,
underscoring the impact El Nino has on greenhouse gas
emissions. Carbon is stored in vegetation, and when the
vegetation burns, the carbon returns to the atmosphere.
y combining satellite data and measurements of atmospheric
gases, researchers from NASA, the University of California-
Irvine and other institutions have for the first time
quantified the amount of greenhouse gases, like carbon dioxide
and methane, emitted by these fires on global and interannual
scales.
The researchers found that fire emissions of greenhouse gases
increased across multiple continental regions in 1997-98,
including Southeast Asia (60 percent of the global increase),
Central and South America (30 percent), and boreal forests of
North America and Eurasia (10 percent).
“The rate of accumulation of these gases in the atmosphere is
highly variable,” Randerson said. “Vast areas of the tropics
dry out and become vulnerable to fire during El Nino events. It
appears that El Nino events accelerate carbon loss from
terrestrial ecosystems because they enable humans to use fire
more effectively as a tool for clearing land in the tropics.”
Scientists today are trying to understand the relationship
between the carbon cycle and the climate system. The carbon
cycle is the movement of carbon, in its many forms, among the
biosphere, atmosphere, oceans and the geosphere. The cycling of
carbon affects the amount of carbon-based greenhouse gases in
the atmosphere and thus the Earth’s climate. This study shows
carbon loss in the biosphere over the next several centuries
may be sensitive to the intensity and variability of El Nino-
induced droughts.
“An important next step is to identify the processes that
contributed to the high fire emissions, including
deforestation, pasture maintenance, agricultural waste burning
and savanna fires,” Randerson said. “This will help us
understand how quickly greenhouse gases like carbon dioxide and
methane will accumulate in the atmosphere due to burning.”
Satellite measurements of many Earth system properties were
input into fire models. “The work involves data products from
instruments aboard NASA’s Terra, Aqua, Tropical Rainfall
Measuring Mission and Active Cavity Radiometer Irradiance
Monitor satellites,” said Guido R. van der Werf of NASA’s
Goddard Space Flight Center, Greenbelt, Md., one of the study’s
authors. NASA also processed data on vegetation, precipitation,
surface air temperatures and changes in Earth’s radiation, all
used in the fire modeling. Data from the European Space
Agency’s Along Track Scanning Radiometer was used as well.
The study authors, in addition to Randerson and van der Werf,
include G. James Collatz and Louis Giglio of NASA’s Goddard
Space Flight Center; Prasad S. Kasibhatla and Avelino F.
Arellano Jr. of Duke University, Durham, N.C.; Seth Olsen of
the California Institute of Technology, Pasadena; and Eric S.
Kasischke of the University of Maryland, College Park.
The research was funded by NASA’s Earth Science Enterprise,
which is dedicated to understanding the Earth as an integrated
system. The Enterprise applies Earth System Science to improve
prediction of climate, weather and natural hazards using the
unique vantage point of space.
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