Methane emissions from Alaska in 2012 from CARVE airborne observations

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-11, Vol.111 (47), p.16694-16699
• Main Authors: Chang, Rachel Y.-W., Miller, Charles E., Dinardo, Steven J., Karion, Anna, Sweeney, Colm, Daube, Bruce C., Henderson, John M., Mountain, Marikate E., Eluszkiewicz, Janusz, Miller, John B., Bruhwiler, Lori M. P., Wofsy, Steven C.
• Format: Article
• Language: English
• Subjects: Atmospheric models; Atmospherics; Bootstrap method; Carbon dioxide emissions; Ecosystem models; Emissions; Hydrological modeling; Measurement; Methane; Modeling; Permafrost; Physical Sciences; Pollutant emissions; Stochastic models; Wetlands
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1412953111

We determined methane (CH ₄) emissions from Alaska using airborne measurements from the Carbon Arctic Reservoirs Vulnerability Experiment (CARVE). Atmospheric sampling was conducted between May and September 2012 and analyzed using a customized version of the polar weather research and forecast model linked to a Lagrangian particle dispersion model (stochastic time-inverted Lagrangian transport model). We estimated growing season CH ₄ fluxes of 8 ± 2 mg CH ₄⋅m ⁻²⋅d ⁻¹ averaged over all of Alaska, corresponding to fluxes from wetlands of [Formula] mg CH ₄⋅m ⁻²⋅d ⁻¹ if we assumed that wetlands are the only source from the land surface (all uncertainties are 95% confidence intervals from a bootstrapping analysis). Fluxes roughly doubled from May to July, then decreased gradually in August and September. Integrated emissions totaled 2.1 ± 0.5 Tg CH ₄ for Alaska from May to September 2012, close to the average (2.3; a range of 0.7 to 6 Tg CH ₄) predicted by various land surface models and inversion analyses for the growing season. Methane emissions from boreal Alaska were larger than from the North Slope; the monthly regional flux estimates showed no evidence of enhanced emissions during early spring or late fall, although these bursts may be more localized in time and space than can be detected by our analysis. These results provide an important baseline to which future studies can be compared. Significance Alaska emitted 2.1 ± 0.5 Tg CH ₄ during the 2012 growing season, an unexceptional amount despite widespread permafrost thaw and other evidence of climate change in the region. Our results are based on more than 30 airborne measurement flights conducted by CARVE from May to September 2012 over Alaska. Methane emissions peaked in summer and remained high in to the fall. Emissions from boreal regions were notably larger than from North Slope tundra. To our knowledge, this is the first regional study of methane emissions from Arctic and boreal regions over a growing season. Our estimates reinforce and refine global models, and they provide an important baseline against which to measure future changes associated with climate change.