Climate change may alter the natural cycling of carbon (C) in ecosystems in the Arctic. The Arctic carbon cycle is an important factor in the global climate system. Significant amount of carbon has been accumulated over thousands of years and stored in permafrost soils because of the process of cryoturbation, which moves organic matter into the deeper soil layers. Other processes, such as decomposition, wildfires, and logging, cause release of carbon into the atmosphere and, thus, act as carbon sources. At present the Arctic is a sink for carbon however climate warming - and thawing of the permafrost and accelerating decomposition processes - could disrupt the balance between accumulation of carbon in Arctic soils and emission of CO2 back into the atmosphere.
Furthermore, the report highlights another issue relevant for the understanding of the carbon cycle in the Arctic: "In addition to the usual sources of carbon, primarily from plant matter, the Arctic appears to have huge quantities of methane hydrates. Methane is stable in cold conditions and under high pressure, and thus found in permafrost on land and continental shelves and also beneath the sediments of the Arctic Basin. As hydrates warm or as pressure is reduced, the methane is released. The amount of methane hydrates is not well known, but some global estimates suggest it may rival the amounts of all known sources of gas and oil."
The rate of carbon release from permafrost soils is highly uncertain, but it is crucial for predicting the strength and timing of this carbon-cycle feedback effect, and thus how important permafrost thaw will be for climate change this century. Permafrost's role in isolating carbon from participating in the carbon cycle could be challenged by global warming and an accelerating permafrost thawing - and transform the Arctic into of carbon source where no known mitigation measures exist.
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