Forests in the United States and other northern mid- and upper-latitude regions are playing a smaller role in offsetting global warming than previously thought, according to a study appearing in this week's issue of Science.

The study, which sheds light on the so-called missing carbon sink, concludes that intact tropical forests are removing an unexpectedly high proportion of carbon dioxide from the atmosphere, thereby partially offsetting carbon entering the air through industrial emissions and deforestation.

The Science paper was written by a team of scientists led by Britton Stephens of the National Center for Atmospheric Research (NCAR) in Boulder, Colo. The research was funded by the National Science Foundation (NSF).

"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.'"

Stephens and his colleagues analyzed air samples that had been collected by aircraft across the globe for decades but never before synthesized to study the global carbon cycle. The team found that some 40 percent of the carbon dioxide assumed to be absorbed by northern forests is instead being taken up in the tropics.

"Our study will provide researchers with a much better understanding of how trees and other plants respond to industrial emissions of carbon dioxide, which is a critical problem in global warming," Stephens says. "This will help us better predict climate change and identify possible strategies for mitigating it."

For years, one of the biggest mysteries in climate science has been the question of what ultimately happens to the carbon emitted by motor vehicles, factories, deforestation and other sources.

Of the approximately 8 billion tons of carbon emitted each year, about 40 percent accumulates in the atmosphere an
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Contact: Cheryl Dybas
cdybas@nsf.gov
703-292-7734
National Science Foundation
21-Jun-2007