Tracking Methane Emissions from Arctic Tundra
The Arctic tundra is a cold, desert-like biome, with a layer of permanently frozen soil and organic matter below the surface containing vast stocks of carbon. As Arctic tundra soils warm in response to climate change, methane emissions from decomposing organic material could increase dramatically, representing a potentially significant positive feedback on climate warming. However, seasonal and climatic influences on methane emissions from these systems are not well understood outside of the summer months, representing a major uncertainty for the Arctic methane budget. To help address a critical knowledge gap in cold-season methane emissions, a coordinated international, multiagency field study sponsored by NASA, NSF, and DOE made year-round measurements of methane emissions from Alaskan Arctic tundra eddy covariance towers and regional flux estimates from aircraft data. Recent findings report that emissions during the cold season account for approximately 50% of the annual methane flux, with the highest emissions from dry upland tundra. Scaled to the global Arctic, cold-season fluxes from tundra represent about 25% of global emissions from wetlands outside of the tropics, or about 6% of total global wetland methane emissions.
Emissions of methane in the cold season are linked to the extended “zero curtain” period, when subsurface soil temperatures are poised near 0°Celsius, indicating that total emissions are very sensitive to soil conditions and related factors, such as snow depth. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionately impacts the cold season, results suggest that higher cold-season methane emissions will result from observed and predicted increases in snow thickness, active-layer depth, and soil temperature, representing important positive feedbacks on climate warming.