Background/Question/Methods The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales, and have the potential to cause rapid changes in the earth system. While the response of the carbon cycle in the Arctic to changes in climate is a major issue of global concern, there has not been a comprehensive evaluation of the status of the contemporary carbon cycle of the Arctic and its response to climate change.  This study provides an evaluation that is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle in the Arctic to ongoing climatic change.

Results/Conclusions While it is clear that there are substantial stocks of carbon in the Arctic, there are substantial uncertainties in the magnitude of storage associated with the storage of organic matter in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic.  The Arctic plays an important role in the global dynamics of both CO₂ and CH₄.  In recent decades the Arctic has recently been a sink for atmospheric CO₂ of between 0 and 0.8 Pg C yr^-1, which is between 0 and 25% of the global net land/ocean flux during the 1990s.  The Arctic is substantial source of CH₄ to the atmosphere (between 32 and 112 Tg CH₄ yr^-1, respectively), primarily because of the large area of wetlands throughout the region.  Analyses to date indicate that the sensitivity of the carbon cycle in the Arctic during the remainder of the 21^st Century is highly uncertain.  To improve the capability to assess the sensitivity of the carbon cycle in the Arctic to projected climate change, (1) integrated studies of regional carbon dynamics should be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from integrated studies should be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts.