for National Geographic News
Thawing permafrost in the Arctic could play a role in fueling global warming, scientists in Russia and the United States report.
Writing in tomorrow's issue of the journal Science, researchers say that permafrostthe layer of frozen soil in polar regionstraps far more carbon than previously thought.
The scientists warn that if permafrost continues to thaw due to global warming, the process could pump huge amounts of greenhouse gases into the atmosphere, stoking further temperature rises.
"The reservoir is very large and dangerous," Sergey Zimov of the Russian Academy of Sciences in Cherskii said in an email.
Zimov and his U.S. colleagues estimate that frozen soils across a large swath of Siberia and Alaska hold nearly 500 billion tons (454 billion metric tons) of carbonor two-thirds current atmospheric levels.
Much of that carbon is in the form of plant roots and animal bones that accumulated over thousands of years throughout the soil, which is on average 82 feet (25 meters) thick.
"It's about 75 times the annual fossil fuel emissions by all of humankind," said study co-author Edward Schuur, an ecosystems ecologist at the University of Florida in Gainesville.
"It's a big reservoir. Especially big because right now we don't include it in these analyses of vegetation [and] soil" used to model carbon cycles and global warming, he said.
Increasing carbon dioxide and other greenhouse gases in Earth's atmosphere have fueled rising temperatures over the last century.
Scientists say the warming has already had profound effects on many high-latitude ecosystems.
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