Missing carbon is in the tropics, not temperature forests
Carbon mystery solved
June 21, 2007

Temperate forests are doing less than expected to offset climate change, while tropical forests are absorbing an unexpectedly high proportion of carbon dioxide from the atmosphere, reports a study published this week in the journal Science. The findings have implications for offset programs and climate policy.

The research, which analyzed decades of air samples collected by aircraft, found that 40 percent of the carbon dioxide assumed to be absorbed by northern forests is instead sequestered in the tropics. Overall, northern forests appear to absorb about 1.5 billion tons of the 8 billion tons of carbon emitted each year. About 3.2 billion tons of this amount ends up in the atmosphere, while another 2.4 billion is taken up by the oceans.

Tropical forests not a net source of CO2

Previous models suggested that tropical forests were a large net source of carbon (up to 1.8 billion tons per year), due to greenhouse gas emissions released by deforestation and forest fires. However the new study estimates that tropical ecosystems are the net source of only about 100 million tons.

Measurements show that about 40% of the carbon dioxide emitted through fossil fuels and deforestation remains in the atmosphere, while an estimated 30% is absorbed by trees and other plants and another 30% by the oceans. Computer models have indicated that forests in the mid and upper latitudes absorb a high amount of carbon dioxide, while tropical forests emit the gas because of deforestation. But a new study led by NCAR's Britton Stephens shows that the two regions are more balanced than previously thought, with intact tropical forests playing a major role in absorbing carbon dioxide. Illustration by Steve Deyo, ŠUCAR
"Our results indicate that intact tropical forests are taking up a large amount of carbon," said lead author Britton Stephens of the National Center for Atmospheric Research (NCAR). "They are helping to offset industrial carbon emissions and the atmospheric impacts of clearing land more than we realized."

The authors found the earlier models generally produced incorrect estimates because the relied on ground-level measurements which fail to "accurately simulate the movement of carbon dioxide vertically in the atmosphere," according to a statement from the National Science Foundation (NSF), which helped fund the research. "The computer models tended to move too much carbon dioxide down toward ground level in the summer, when growing trees and other plants take in the gas, and not enough carbon dioxide up from ground level in the winter" leading scientists to conclude there was less carbon in the air above mid-latitude and upper-latitude forests.

"This research fills in another piece of the complex puzzle on how the Earth system functions," said Cliff Jacobs of NSF's Division of Atmospheric Sciences. "These findings will be viewed as a milestone in discoveries about our planet's 'metabolism.'"

Related articles

Reducing tropical deforestation will help fight global warming. (05/09/2007) More scientists have joined the growing chorus to support a plan by developing countries to fight global warming by reducing deforestation rates. Tropical deforestation releases more than 1.5 billion metric tons of carbon into the atmosphere every year, though in some years, like the 1997-1998 el Niņo year when fires released some 2 billion tons of carbon from peat swamps alone in Indonesia, emissions are more than twice that. Writing in the journal Science, an international team of scientists argue that the "Reducing Emissions from Deforestation" (RED) initiative, launched in 2005 by the United Nations Framework Convention on Climate Change, is scientifically and technologically sound, and that political and economic challenges facing the plan can be overcome.

Amazon rainforest locks up 11 years of CO2 emissions. (05/08/2007) Using a new method to determine the amount of carbon stored by vegetation, a team of scientists from Caltech, the Woods Hole Institute, and INPE (Brazil's space agency) estimate the total biomass of the Amazon Basin is around 86 petagrams (86 billion metric tons) of carbon--for comparison, 7.9 billion metric tons of carbon dioxide were emitted in 2005. This means that Amazon locks up at least 11 years of recent carbon dioxide emissions, though clearing the Amazon would have a disproportionate impact due to its role in global weather regulation and other ecosystem services.

Temperate forests do not help fight global warming. (12/11/2006) Trees planted in temperate zones could worsen global warming according to research that will be presented on December 15 at the American Geophysical Society annual meeting in San Francisco. The study, which shows that trees planted in tropical regions can help fight climate change, found that global forests actually produce a net warming of the planet.

Temperate forests may worsen global warming, tropical forests fight higher temperatures. (12/5/2005) Growing a forest might sound like a good idea to combat global warming, since trees draw carbon dioxide from the air and release cool water from their leaves. But they also absorb sunlight, warming the air in the process. According to a new study from the Carnegie Institution's Department of Global Ecology and Lawrence Livermore National Laboratory, planting forests at certain latitudes could make the Earth warmer.

Forest fires may cool climate. (11/16/2006) Boreal forest fires may actually cool climate according to research published in tomorrow's issue of the journal Science. Researchers at the Univerisity of California, Irvine (UCI), found that cooling may occur in regions where burned trees -- and reduced canopy cover -- exposes more snow, which reflects the sun's rays back into space. This effect may outweight the climate warming impact of the grenhouse gases released by forest burning.

CITATION: Britton B. Stephens, Kevin R. Gurney, Pieter P. Tans, Colm Sweeney, Wouter Peters, Lori Bruhwiler, Philippe Ciais, Michel Ramonet, Philippe Bousquet, Takakiyo Nakazawa, Shuji Aoki, Toshinobu Machida, Gen Inoue, Nikolay Vinnichenko, Jon Lloyd, Armin Jordan, Martin Heimann, Olga Shibistova, Ray L. Langenfelds, L. Paul Steele, Roger J. Francey, and A. Scott Denning (2007). "Weak northern and strong tropical land carbon uptake from vertical profiles of atmospheric CO2." Science, June 22, 2007


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