Arctic Permafrost and Carbon Climate Feedbacks (Invited)

Vast stores of organic carbon are thought to be frozen in Arctic soils; as much as 1,700 PgC, several times the amount emitted by fossil fuel use to date and about equal to known coal reserves. If mobilized to the atmosphere, this carbon would have significant impacts on global climate, especially if emitted as CH4, a gas that is about 25 times more potent a greenhouse gas per mass than CO2 over a century timescale. Arctic temperatures have been increasing rapidly over the last several decades, with melting of ice both on sea and land, sometimes at surprisingly fast rates. Human activities in the Arctic are sure to expand as the climate moderates, and one of the challenges confronting our ability to predict the future global climate is understanding the potential evolution of trace gas budgets in the Arctic. Bottom-up estimates from flux towers and chamber studies over the past several decades imply that the Arctic is taking up more CO2 and emitting more CH4. Atmospheric network observations do not currently support long-term increases in CH4 emissions, although inter-annual variability due to year-to-year temperature changes is seen in the atmospheric data. Small changes in CO2 uptake are difficult to detect given the overwhelming dominance of the fossil fuel emissions in the CO2 budget. A commitment to long-term monitoring of greenhouse gases using both regionally representative bottom-up measurements and top-down atmospheric network observations in the Arctic is fundamental to our ability to detect early changes in carbon emissions, as well as to evaluate and test models that predict future carbon cycle climate feedbacks.