Tundra to become source of greenhouse gas: report

Scientists say vast swaths of Arctic tundra could become massive sources of carbon dioxide despite increased plant growth spurred by warmer temperatures in the north.
“It’s going to happen as a slow-motion time bomb,” said Ted Schuur, an ecologist at the University of Florida, and the lead author of a paper that appeared yesterday in the journal “Nature.”

Researchers have long known that permafrost contains huge amounts of frozen carbon trapped in organic material. It’s believes the amount of carbon stored in permafrost around the world is almost double the amount currently in the atmosphere.
But scientists have been unsure of the fate of that carbon as global warming slowly melts the permafrost.
Some have held it would be released into the atmosphere and amplify the effects of climate change. Others suggest it would be absorbed by heavier vegetation.
Schuur’s research in a well-studied area near Denali National Park in Alaska used radio-carbon dating to find out how much old carbon released from permafrost was being absorbed by plants.
His findings suggest the plants would win—for a little while.
“At first, the first couple decades, these areas were net sinks of carbon,” he said. “It seemed good.
“But then, over more decades, we found that plants were still growing faster but they couldn’t offset even more old carbon coming out.
“Finally, that rate overwhelms anything that the plants can do.”
Schuur said the switch would come sometime between 15 and 50 years after the permafrost thawed.
Even if a stretch of previously-frozen tundra sprouted and supported an entire boreal forest, it only would capture and store about five percent of the carbon being released by microbes feasting on the organic material in the newly-thawed permafrost.
There are 13 million square kilometres of permafrost around the world. Thawing along the southern edges already has begun.