With so much focus on sea ice and ice shelves, the role of permafrost in the global climate cycle is often not on the public’s radar screen. But according to a new study published last week in the journal Bioscience, permafrost in the Northern Hemisphere contains more than two times the amount of carbon in the atmosphere, and rapid thawing could make it a significant contributor to global climate change.

Permafrost is defined as permanently frozen ground that remains at or below zero degrees Celsius for two years or longer. It contains organic material that typically decomposes slowly. But when permafrost thaws, bacteria and fungi break down the carbon contained in the organic matter much more quickly, releasing it into the atmosphere as carbon dioxide or methane — greenhouse gases.

The research team, led by Ted Schuur of the University of Florida, reported in Bioscience that an estimated 1,672 billion metric tons of carbon is locked up in Northern Hemisphere permafrost, compared to about 780 billion tons of carbon in the atmosphere. Previous studies by Schuur and his colleagues estimated the amount of carbon contained in permafrost in northeast Siberia; the new research expanded the estimate to include the permafrost-covered northern latitudes of Russia, Europe, Greenland, and North America.

According to Schuur, the amount of carbon dioxide that permafrost will add to the atmosphere depends on how fast it thaws, but his research indicates it could rise to as much as 1.1 billion tons per year if current thawing trends continue. Because plants take in carbon dioxide and release oxygen, it might appear they could absorb the carbon released by the thawed permafrost. But Schuur said the amount of carbon stored in the permafrost is far greater than what is found in shrubs or trees. “You can’t grow a big enough forest to offset the carbon release from the permafrost,” he said.

[Via University of Florida]