The Arctic, a significant sink for the carbon dioxide that humans pump into the atmosphere each year, is losing its ability to absorb CO2 as the world warms.

As part of a new study, an international group of scientists has completed a review of data on the Arctic’s capacity as a carbon sink. According to their study, published in the journal, Ecological Monographs, the Arctic is responsible for taking up 10 to 15 percent of the human-generated CO2 that is absorbed by Earth’s land masses and oceans.

Human activity, primarily the burning of fossil fuels, pumps about 7 billion metric tons of CO2 into the atmosphere each year. About 3 billion tons stay in the atmosphere, but about 4 billion tons are taken up by land masses and oceans. Of that 4 billion tons, the Arctic’s share is about 10 to 15 percent.

It can be as high as 25 percent, said David McGuire of the U.S. Geological Survey and the University of Alaska at Fairbanks, who conducted the study with several colleagues.

That incredible storehouse of greenhouse gas is being diminished by continued warming, according to the study. The rapid rate of climate change in the Arctic – about twice that of lower latitudes – could eliminate the sink and possibly make the Arctic a source of carbon dioxide, McGuire and his colleagues wrote.

Largely accumulated in permafrost, carbon becomes trapped in the frozen soil. Low temperatures slow the rate of decomposition of organic matter, allowing the amount of carbon accumulated in the Arctic to exceed what’s released. But warming temperatures in the Arctic could change this balance. Thawing permafrost also could result in a more waterlogged Arctic, which could encourage the activity of methane-producing organisms.

“If the response of the arctic carbon cycle to climate change results in substantial net releases of greenhouse gases, this could compromise mitigation efforts that we have in mind for controlling the carbon cycle,” McGuire said.

The study was sponsored by the Arctic Monitoring and Assessment Program, the Climate in the Cryosphere Program, and the International Arctic Science Committee.

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