Bad sign for global warming: Thawing permafrost holds vast c...( GAINESVILLE Fla. --- Permafrost blan...)

GAINESVILLE, Fla. --- Permafrost blanketing the northern hemisphere contains more than twice the amount of carbon in the atmosphere, making it a potentially mammoth contributor to global climate change depending on how quickly it thaws.

So concludes a group of nearly two dozen scientists in a paper appearing this week in the journal Bioscience. The lead author is Ted Schuur, an associate professor of ecology at the University of Florida.

Previous studies by Schuur and his colleagues elsewhere have estimated the carbon contained in permafrost in northeast Siberia. The new research expands that estimate to the rest of the permafrost-covered northern latitudes of Russia, Europe, Greenland and North America. The estimated 1,672 billion metric tons of carbon locked up in the permafrost is more than double the 780 billion tons in the atmosphere today.

"It's bigger than we thought," Schuur said.

Permafrost is frozen ground that contains roots and other soil organic matter that decompose extremely slowly. When it thaws, bacteria and fungi break down carbon contained in this organic matter much more quickly, releasing it to the atmosphere as carbon dioxide or methane, both greenhouse gases.

Scientists have become increasingly concerned about this natural process as temperatures in the world's most northern latitudes have warmed. Just last week, it was announced that the amount of sea ice covering the Arctic may reach a new low this summer. Meanwhile, there is widespread consensus that the highest latitudes will warm the fastest, a process already visible in the accelerated thawing of glaciers worldwide.

Two years ago, Schuur and two colleagues authored a paper in the journal Science estimating that 400,000 square miles of northeast Siberian permafrost contained 500 billion metric tons of carbon. For this new paper, scientists combined an extensive database of measurements of carbon content in different types
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